Rapid Uplift

Deccan Volcanism And Mass Extinction

noreply@blogger.com (Suvrat Kher) — Thu, 12 Mar 2026 03:45:00 +0000

What role did Deccan Volcanism play in the end Cretaceous mass extinction?

There is widespread agreement that an asteroid struck what is now the Yucatan Peninsula region of Mexico 66.05 million years ago. The resulting environmental catastrophe precipitated an abrupt mass extinction, wiping out 70% of all species. In the rock record, a thin clay layer preserves evidence of the extraterrestrial origin of this impact event. It is referred to as the K-Pg boundary layer, K being Cretaceous and Pg referring to the Paleogene. The biota below the boundary layer is very different from fossil assemblages above it.

The earth at that time was also experiencing a major episode of basalt volcanism. This Large Igneous Province (LIP) is known as the Deccan Volcanic Province or the Deccan Traps. Volcanism occurred both before and after the impact event. Geologists have been divided on whether most the lava erupted after the asteroid hit or before it with different implications for the role of volcanism in the mass extinction. There was also an uncertain and incomplete assessment of the volumes of lava involved.

A new paper by Vivek S. Kale and coworkers titled “Spatio-temporal volume recalibration shows Deccan volcanism caused Terminal Cretaceous Mass Extinction” leaves no room for doubt about which side of the divide this group stands. The researchers examine over 80 lava sections across the Deccan Volcanic Province and recalculate the lava volume, assigning packages of lava a time bracket based of absolute dating, magnetic signatures, and fossils. They find that around 70% of the Deccan lava erupted in a time span of 300,000 years before the mass extinction.

Their results are summarized in this infographic. Source: Vivek S. Kale and coworkers, GSA Bulletin, November 2025.

The volume estimates of previous workers and their study is shown to the left. Also presented are marine paleo-environmental indicators represented by a paleo-temperature curve and carbon isotope curves spanning the mass extinction.

A short explanation of these curves will be useful.

For estimating temperature, geologists use the ratio of Oxygen 18/Oxygen 16 preserved in the shell (CaCO3) of planktonic organisms like foraminifera or calcareous nanoplankton. During warm phases, vigorous evaporation results in more of O18 escaping into the atmosphere, enriching the ocean slightly in the lighter O16. Calcium carbonate shell growth incorporate O18 and O16 without preference, maintaining the same O18/O16 ratio of sea water .

Warmer seas will result in shells having a lower O18/O16 ratio, than shells that grow in cooler water. The temperature is estimated from these measured oxygen isotope ratios.

The increase in sea surface temperature observed here, known as the Late Masstrichtian Warming Event (LMWE), has been linked to increased CO2 emissions during Deccan Volcanism.

Carbon isotope trends through time are presented by measuring the C13/C12 ratio of the target sample. ‘Bulk’ carbon means any carbon from hard parts as against carbon from organic material. It might mean just ground up limestone made up of a mixture of shells and lime mud. Jurassic onward, the proliferation of planktonic foraminifera has allowed geologists to select shells of just one or two species for their measurements. This makes it easier to screen for post depositional alteration which could reset the original oceanic C13/C12 ratio due to reaction with fluids of a different composition. It is more difficult to recognize these effects in a mixed sample, especially one with fine calcium carbonate mud.

Variation in C13/C12 ratio through time is generally regarded as an indicator of primary productivity. Photosynthesizing organisms have a strong preference for the lighter C12 to build organic tissue. The C13/C12 ratio of organic matter is strongly depleted compared to the sea water C13/C12 ratio. Similar to oxygen intake, growing shells preserve the C13/C12 ratio of the ocean. During environmental crises, reduced primary productivity enriches the ocean in the lighter isotope, also depressing the C13/C12 ratio of shells growing under these conditions.

The modest (relative to earlier Phanerozoic mass extinctions) carbon isotope excursion coincident with the K-Pg boundary suggests a decrease in primary productivity due to the extinction of some photosynthesizing groups. In contrast, the amplitude range of the isotope excursions seen during the Late Maastrichtian Warming Event can also be explained by a non-biological driver.

Carbon dioxide of volcanic origin is isotopically lighter than sea water. Pulses of volcanism may result in a large enough pool of lighter C12 dissolving in the ocean and shifting sea water C13/C12 ratio to the depleted values measured in Late Cretaceous shells.

Kale and coworkers argue that increased volume of lava eruption and emissions of CO2 and other gases in the Late Maastrichtian caused global warming and destabilized the biosphere. Ecosystems were already tottering when the asteroid delivered the knockout punch.

Just how stressed was the ecosystem? The most visible indicator of environmental changes impacting an ancient biosphere is the fossil record of that time period. Their paper however does not present any analysis of the Late Maastrichtian biota.

The several studies (Ref. 1, 2, 3) where from Kale and coworkers source the paleo-temperature and isotope record all unambiguously conclude that the LMWE had a limited impact on marine life. Species diversity did not change much. Fossil community structure remained stable, or where it did change, it reflected migration and range shifts. An example of this is L. Woelders and coworkers study of a Late Cretaceous section from the South Atlantic where they find fluctuating abundances of benthic foraminifera and dinoflagellates tracking climate and sea level cycles.

That is not to say that organisms were unaffected by this warming event. Other studies across the marine realm have documented biotic stress. Vincente Gilabert and coworkers find fragmentation of shells, abundance of low oxygen tolerant taxa, and dwarfing of some species, in their study of planktonic foraminifera of the Caravaca section in Spain. Similarly, Gerta Keller and coworkers study on planktonic foraminifera also reveals species dwarfism and abundance of high stress opportunistic species in the late Maastrichtian of the Indian Ocean and South Atlantic.

Nicholas Thibault and Dorothee Husson in a survey of the Late Cretaceous ocean point out that nanoplankton species numbers dropped during the LMWE, but diversity rebounded and increased with no significant extinction in the last 140,000 years of the Cretaceous. Michael Henehan and coworkers infer an increase in ocean acidity coinciding with the LTME based on reduced preservation of calcium carbonate shells on the sea floor. Shell preservation and sea water carbonate saturation return to pre event values in the last 200,000 years before the K-Pg impact event.

Do these observations on plankton species signal some sort of a beginning of the end of ecosystems across the entire marine biosphere? Since Deccan Volcanism spanned several hundred thousand years, could there have been a mass extinction if there had been no asteroid hit? It is conceivable that the prolonged volcanism could have resulted in a ratcheting of environment stress, eventually crossing tolerance thresholds.

This proposition has been hard to test because the asteroid crashed the Cretaceous party denying us an extended view of a volcanism only unfolding of history.

Still, we do have a good 300,000 year record before the impact of sedimentary deposition that coincided with the most voluminous phase of Deccan volcanism. Finer scale resolution of marine sections in the past few years allow us to examine global biotic trends from this time span.

As mentioned above, the impact of ocean warming seems to be quite limited to changes in shell size, temporary species abundance shifts, and adjustments by migration to favorable locales. Importantly, there is no signal of elevated extinction in diverse groups such as planktonic foraminifera, radiolarians, nanoplankton, ammonoids, bivalves, and gastropods in the final few hundred thousand years of the Cretaceous, when volcanism was at its peak (Ref 1,2,3,4).

A closer look at the environmental proxy data is revealing. After a warming phase, the paleo-temperature curve shows a 150 thousand year cooling trend in the terminal Maastrichtian until the K-Pg boundary. Mirroring this cooling trend is a distinct shift towards heavier carbon isotope values. This may be due to increasing primary productivity signaling a general amelioration of ocean conditions.

What could cause such a cooling despite ongoing voluminous volcanism and CO2 emissions? The answer may be enhanced weathering of all that fresh basalt which kept sequestering carbon dioxide during silicate weathering reactions.

There are two lines of observation that support increased weathering during end Cretaceous times.

The first observation is the recovery of calcium carbonate saturation level of the ocean. Weathering releases divalent cations like calcium and magnesium in to the ocean resulting in an excess positive charge (alkalinity) in sea water. The charge imbalance promotes dissociation of the poorly soluble CO2 gas (represented in equations as carbonic acid -H2CO3) and the formation of more stable negatively charged bicarbonate (HCO3) or carbonate (CO3) anions, raising carbonate saturation state. A decrease in dissolved gas leads to a draw down of atmospheric CO2 in to the ocean by air-sea gas exchange. Alkalinity can also be described as the buffering capacity of the ocean against excessive CO2 buildup.

Today, rapid atmospheric CO2 increase is a major concern for ecosystem and societal health. Research and small scale demonstrations to enhance ocean alkalinity are gaining importance as we try to replicate on human time scales what nature does over much longer time spans.

The other independent support for enhanced weathering comes from another isotope system, the osmium 187/osmium188 ratio. Continental crust is enriched in Rhenium187 which decays to Osmium187. Rocks like basalt derived directly from partial melting of the mantle have much lower Rhenium187 and consequently Osmium187. There is a progressive decrease in the Osmium187/Osmium188 ratio in Late Maastrichtian ocean sediments. This is consistent with weathering and increased supply of non-radiogenic Os188 from a fresh basalt source. Some of the decline can also be explained by a reduced supply of Os187 as large areas of radiogenic continental crust were blanketed by lava.

Late Cretaceous marine ecosystem health can also be assessed by looking at the difference in the C13/C12 ratio between surface dwelling planktonic and bottom dwelling benthic foraminifera shells. This isotope gradient is maintained by the biological pump, a transfer of organic carbon and nutrients from the sea surface to depths. Organic carbon is enriched in the lighter isotope compared to planktonic shells (as explained earlier). This organic matter sinks to the ocean depths and oxidizes, enriching the Dissolved Organic Carbon (DIC) pool in C12. Shells of benthic foraminifera (bottom dwelling) have a lower C13/12 ratio than planktonic calcifiers.

A noticeable C13/C12 gradient is present (Ref. 1, 2) in the latest Cretaceous ocean. It converges immediately above the K-Pg boundary, indicating a disruption of the marine carbon cycle only after the asteroid impact.

Environmental perturbations need not precipitate a terminal decline of ecosystems. My reading of the fossil record and the different proxies is that the effects of the LMWE were transient. Key biogeochemical cycles remained intact through the Late Maastrichtian implying that volcanism did not greatly diminish pelagic ecosystem function. The end Cretaceous marine biosphere shows recovery and resilience and not signs of a ‘critically damaged’ system.

David E. Fastovsky and Antoine Bercovici perceptively ask in their review of the terrestrial record of the K-Pg extinction- “how does one weaken an ecosystem in terms of its ability to withstand catastrophic, that is to say, very short-term events? In other words, this is not a ‘straw that broke the camel’s back’ situation, where preceding events play a big role in the eventual failure. Since large swaths were simply obliterated in the asteroid’s wake, and more distant regions experienced acute shock, it wouldn’t have mattered if ecosystems were weakened or hale and hearty.

I expressed a similar sentiment earlier in the post. To attribute a causal role to Deccan volcanism, there have to be signs that significant global extinction events occurred prior to the asteroid strike. The data just doesn’t point in that direction.

Earlier in earth history, the end Permian (251.9 million years ago) and the end Triassic (201.4 million years ago) mass extinctions have been more convincingly linked to massive environmental damage triggered by sustained igneous activity. The impact on the environment due to Deccan volcanism appears muted in comparison.

One reason could be that during the Permian and Triassic igneous episodes, magma intruded through thick sedimentary basins filled with limestone, organic rich shale, and sulfur bearing evaporites. Interestingly, the mass extinction coincided with the emplacement of thick sills, tabular bodies of magma injected parallel to the strata. As a result, a surge of volatiles emanating from baking sediment amplified volcanic emissions, overwhelming the earth’s natural buffering capacity. Both these mass extinctions are estimated to have unraveled in just tens of thousands of years.

In central Peninsular India, Deccan volcanism intersected older sedimentary basins only at the northern and southern fringes. Slow cooling shallow subsurface sills facilitating effective heat transfer to surrounding crust are absent. Instead, eruptions were fed by magma ascending rapidly along thin conduits (dikes) aligned in swarms. More relevant is that only sterile granitic rocks underlie the regions where the most voluminous eruptions took place.

Volatile bearing sedimentary rocks did play a role in the end Cretaceous mass extinction. But by a quirk of fate, it was the asteroid that found them. The Yucatan region of Mexico where the asteroid hit is underlain by hydrocarbon rich sediments, and sulfur rich salt. The impact released soot and sulfate aerosols in the atmosphere resulting in global cooling and reducing photosynthesis for weeks to months. Eventually, the dust settled upon a world utterly transformed. It was the beginning of a new world, one where flowering plants, song birds, and mammals diversified and flourished. From time to time, chance events have opened up entirely new avenues for evolution to explore.

It is pertinent to stress again the paramount importance of rates of processes in the context of our developing climate crises. Although in absolute terms humans may not emit more than past large volcanic events like the Cretaceous Deccan Volcanism or the Siberian Volcanism of late Permian times, we are emitting CO2 at a rate many times faster than these natural events. Carbon dioxide is building up in the atmosphere too quickly for weathering and ocean ecosystems to offset over the next few hundred years.

Lastly, Jurassic onward, the proliferation and evolution of plankton shell building organisms such as foraminifera and coccolithophores have played an important role in regulating ocean chemistry and as a buffer against atmosphere CO2 changes. This occurs by various processes. For one, the heavy shells act as ballast, exporting attached organic matter to depths before their degradation consumes oxygen in the uppermost oceanic layer. Much of this carbon gets buried, becoming a long term carbon sink.

The other important function is sustaining the ocean alkalinity balance. Precipitation of calcite and aragonite (CaCO3) removes positive charge from the ocean, in the form of divalent Ca cations, reducing alkalinity (see previous section on weathering). This alkalinity is recovered when calcareous skeletons, falling through the water column like an ocean snow, start dissolving when they sink below a threshold depth, releasing divalent Ca ions. This process known as carbonate compensation maintains the ocean’s capacity to absorb atmospheric CO2.

The cooling trend observed in the final 150,000 years of the Cretaceous suggests that the rates of emissions during Deccan volcanism likely remained relatively low. Silicate weathering on land and enhanced ocean alkalinity coupled to weathering runoff and carbonate compensation would have substantially offset Deccan CO2 emissions, moderating their environmental impact.

In the pre-Jurassic ocean, most carbonate skeleton producing organisms lived in the water column or on the sea bed of shallow continental shelves where the sea water was saturated with calcium carbonate. Skeletons did not dissolve in this environment and the biological contribution to ocean alkalinity was limited. This changed when the more geographically widespread plankton evolved biomineralization and their skeletons began settling down to depths where the ocean water is undersaturated with calcium carbonate. The calcareous plankton ecosystem has made post Jurassic oceans more resistant to external shocks, albeit over times scales of thousands of years.

By now readers may be wanting to ask- What about the dinosaurs? Did they persist right until the asteroid hit, or did they go extinct earlier? The avian branch of dinosaurs did survive. The following section is about the non-avian groups and the terrestrial fossil record.

There would have been an extirpation of local populations of dinosaurs and other fauna and flora living in areas directly affected by Deccan Volcanism. But what about the global record?

Terrestrial environments such as lakes and rivers which can preserve dinosaur fossils are patchily distributed. Frequent erosion also removes sediment, making the reconstruction of organic diversity and evolutionary trends much more difficult than for biota living in deep sea environments.

Despite these limitations, we do have some sedimentary sections which inform us about dinosaur life and the terrestrial biosphere of the Late Maastrichtian.

In their work on peat deposits from the Western Interior, U.S., Lauren O’Conner and coworkers estimate end Cretaceous paleo-temperatures based on configuration of preserved organic compounds. Besides the LMWE, they identify shorter warming and cooling phases in the final 100,000 years before the K-Pg boundary, likely driven by Deccan volcanism. However, the impact on the biota seems limited, with no decline in angiosperm diversity until the mass extinction.

Andrew J Flynn and coworkers study in New Mexico on the Naashoibito Member, a dinosaur rich sedimentary deposit, shows that dinosaurs were diverse and formed regionally distinct assemblages during the final few hundred thousand years before the asteroid strike.

The Hell’s Creek Formation spread over the States of North Dakota and Montana also offers insights in to the terrestrial ecosystems (Ref. 1, 2, 3) . Pollen and leaf assemblages attest to a healthy end Cretaceous flora. Both show a substantial and abrupt extinction at the K-Pg boundary. Vertebrate diversity also shows no decline throughout the Late Maastrichtian.

Mammals appear to the exception here. Gregory P Wilson and coworkers detailed survey of the Hell’s Creek Formation reveals two sequential changes in mammalian fauna 650,000 years and 200,000 years before the K-Pg boundary. Apart from changes in mammal assemblages, there is a decline in the abundance of metatherians. The authors link this decline to regional environmental changes, but don’t rule out the effect of Deccan volcanism.

Dinosaur fossils at the Hell Creek section have been found to within a few tens of cm of the K-Pg boundary, representing the last few hundred to a few thousand years of the Cretaceous. Their presence in numbers comparable to lower levels of the sedimentary section negates arguments that dinosaurs were either declining or had gone extinct well before the K-Pg impact event.

The icing on the cake is some recent work by Robert DePalma and coworkers on a debris layer in the Hell’s Creek section. These chaotic beds made up of boulders and fossils was deposited by a tsunami triggered by the asteroid hit. Among other organic remains, the researchers have found a fossil hind limb of an ornithiscian dinosaur. Their work was presented at the EGU 22 General Assembly 2022 in Vienna, Austria. The peer reviewed paper is yet to be published and some scientists have expressed skepticism and called for a more detailed examination of the fossils. But this initial announcement, along with other documented dinosaur fossil finds from North America, does strongly suggest that dinosaurs were well and alive until the very day the world changed 66.05 million years ago.

Geology Books

noreply@blogger.com (Suvrat Kher) — Sat, 28 Feb 2026 15:47:00 +0000

These come highly recommended from the experts I follow-

All released within the past year.

The Whispers of Rocks - Anjana Khatwa: Blending indigenous stories and modern understanding of our world.

Strata: Stories From Deep Time- Laura Poppick: Review by Edward Valauskas.

A Little History of the Earth- Jamie Woodward- Kirkus Review.

I hope to read them soon. Happy reading :)

Mars Geology, Ancient Art, Lake Sediments

noreply@blogger.com (Suvrat Kher) — Fri, 30 Jan 2026 04:01:00 +0000

Another bunch of readings for you :

1) Perseverance Can Continue To Operate On Mars Until At Least 2031- The gallant rover continues its exploration. How do NASA engineers plan a route and how do team geologists decide what to sample? Terrain consideration and rock outcrops are key and so far Perseverance has aced the challenges of topography and geology. Some beautiful maps too in this article.

2) Rock art from at least 67,800 years ago in Sulawesi- How do you date rock art? The material used, mineral pigments mostly, cannot be dated directly. Often, ancient cave walls are covered with layers of calcite precipitated from water seeping along the walls. This calcite can be dated as it contains radiogenic Uranium, giving us a minimum age for the underlying art.

Rock art from Sulawesi, Indonesia, have yielded minimum dates of around 67 thousand years ago. This makes it among the earliest rock art known anywhere. Also, the location of Sulawesi, separated from Bornea by wide deep water channels, suggests that the initial peopling of Sahul around 65k involved maritime journey from Borneo to Papua. Modern Homo sapiens first reached this region sometime after 60,000 years ago.

Who then made this art? Denisovans, or some other branch of humans? The Indonesia- Papua region with an improving fossil and material record of being populated by a variety of humans is proving to be a very important area to understand human migrations and evolution.

3) Sediments reveal 2,600-year-old story of human persistence in central India- Desilting of lakes is going on in many parts of India. I say, before the JCB’s move in , send in the climate scientists. Sahana Ghosh writes about some fascinating work from the wetlands of Bandhavgarh forests in Central India. Scientists have reconstructed a climate and ecologic history going back 2600 years from lake sediment and then matched that with human cultural and political changes. Even as climate changed, humans adapted and modified landscapes. This is one of the few paleoclimate archives from Central India.

Harappan Technology, Homo Floresiensis, Foraminifera

noreply@blogger.com (Suvrat Kher) — Mon, 15 Dec 2025 03:11:00 +0000

Some exciting readings for you-

1) Manufacture of synthetic stone in the Bronze Age Harappan Civilization.

Stone beads were important in Harappan culture and trade. They were made out of agate, an amorphous or cryptocrystalline form of silica. The Kutch region was the primary source of these agates. Stone and bead processing Harappan age workshops abound in this region. The tradition continues today. Some of the best ornamental agate is still being sourced from Kutch. The agates precipitate as secondary silica in cavities of the Deccan Basalts and associated silica rich lava.

To perforate these agates, the Harappans needed tools such as drill bits which were harder than the agate. For this, they manufactured a synthetic stone, now called Ernestite, by high temperature sintering of sand and laterite raw materials. Reaction temperature needed to fuse these materials into a cohesive rock would have reached 1100 deg C! Mesozoic sandstone, found all over Kutch, provided the sand, and the laterite came from iron rich weathered layers capping the Deccan Basalt.

A terrific study by M.K. Mahala and coworkers that details the provenance and fabrication of this interesting artificial stone has just been published in Nature Heritage Science. There is a lot of mineralogy and geochemistry described in the paper, but the conclusions are clearly laid out for all to understand.

2) Climate change and the decline of the Hobbit.

Why are small isolated populations of animals vulnerable to extinction?

Inbreeding, small geographic range, limited access to resources, reliance on one or few food sources, a chance catastrophic event, all may be factors making them susceptible to extirpation.

A case in point is the Hobbit or Homo floresiensis, the diminutive hominin discovered on Flores Island, Indonesia, in 2003. The archaeologic record shows it lived on the island for at least one million years. Homo floresiensis is thought to be a descendant from an early Homo species which dispersed from Africa 2 million years ago. The other famous inhabitant of the island that coexisted with the Hobbit and was its main food source is the dwarf elephant Stegodon.

A careful analysis by Michael Gagan and coworkers, published in Nature Communications Earth and Environment, using geochemistry of calcite from cave deposits show how climate change and decrease in water availability may have increased competition for resources and made life challenging for the inhabitants.

Summer rainfall began declining around 76,000 years ago with record low rainfall between 61,000 to 55,000 years ago. Both the Hobbit and Stegodon fossils become rarer during this interval and disappear by 50,000 years ago. Modern humans entered Flores Island around 46,000 years ago, and whether the Hobbit interacted with them on Flores Island is uncertain.

3) The history of the ocean, as told by tiny beautiful fossils.

The tiny fossils are planktonic foraminifera living suspended in the upper sunlit portion of the ocean. Their shells are made of calcium carbonate. They occur in huge numbers and have short lives. Their shells drop down and carpet the ocean floor, making them valuable archives for understanding evolution. Scientists make use of them for studying climate change too. Certain changes in the chemical composition of their shell are a function of water temperature. Tim Vernimmen has written a short piece on how foraminifera inform us about past environmental crisis and ocean conditions.

Landscapes: PIndari Glacier Trail

noreply@blogger.com (Suvrat Kher) — Sat, 29 Nov 2025 03:04:00 +0000

Every time I am dragging myself back on the last day of a tiring trek in the Himalaya, I curse and swear that I’ll never do this again. And yet, here I am, exploring the Pindari Glacier area in the Kumaon. What a beauty!!

The trail begins at village Khati. This is also the starting point for the trek to Sunderdunga Glacier which I managed to do last year. A third trail to Kafni Glacier also starts here. Landslides has made a section of that trail inaccessible for the time being. Pindari Glacier was a favorite recreation site for colonial administrators during the Raj. As a result, two comfortable guest houses were built along the trail. The first one is at Dwali, a 12 km walk from Khati. The next hut is a further 7 km walk at Phurkiya. A cot and a warm meal is available at both places. The caretaker lives there from April to late November.

My preference has been to go to these Uttarakhand trails in early mid November. I love that season with its cold weather, clear views, and the occasional snow flurry. And the last day walk from Phurkiya camp to the glacier is breathtaking (it was 6 below zero when we started!!).

Here are some pics of the landscapes along the trail.

A walk through the forest with a peek of the snow ridges.

Splashes of yellow in a steep valley.

River terraces.

T0 is the old river bed. It is now colonized by vegetation. The river then incised or cut down into the sediment creating a bench or a terrace clinging to the valley side. There was a second phase of sediment accumulating on the new river bed followed by another incision, creating the T1 terrace at a lower level. I love to observe these changing behavior of rivers as I walk along.

Organic red pigments have colored these boulders in the Pindari river bed.

Dwali campsite which you get to by crossing this rickety wooden bridge over a fast flowing river.

Ahead of Phurkiya camp, walking towards the glacier, the valley widens, opening up some great views.

Pindari Glacier, still about 3 km walk away.

At "Zero Point", standing on a narrow lateral moraine!

Listen to an afternoon rain shower in a High Himalaya valley, near Phurkiya campsite.

Above the tree line. These glacial valleys are harsh, desolate, and beautiful.

Until next time...

Deccan Traps: Thickness And Elevation

noreply@blogger.com (Suvrat Kher) — Fri, 31 Oct 2025 11:49:00 +0000

I recently read Peter Brannen’s excellent book “The Ends of the World: Volcanic Apocalypses, Lethal Oceans And Our Quest To Understand Earth's Past Mass Extinctions”. He has packed quite a few details on the geologic triggers and ecologic upheavals the earth has witnessed from time to time, resulting in the episodic reorganization of the earth’s biosphere.

In the chapter on the Late Cretaceous mass extinction he writes, referring to the Deccan Basalts, .. “today in Western India, 11,500 -foot-tall bar-coded mountains, like the jagged banded peaks of Mahabaleshwar have been carved from this surfeit of molten rock”. He presents a lively discussion on what impact such a prolonged phase of volcanism could have had on environmental health and biodiversity.

The view below of a section of the Deccan Basalts at Warandha Ghat, SW of Pune city, illustrates nicely the 'bar coded mountains" that Brannen mentions.

Repeated effusion of lava which spread rapidly away from eruptive vents has produced the distinct layered architecture. Differential weathering of softer and hard layers produces intermittent rubbly vegetated slopes alternating with scarps resulting in a "bar coded" edifice.

But what about the 11,500 foot tall reference? "Tall" will be read by most as elevation. That is a curious number since the "jagged banded peaks" of the popular hill station of Mahabaleshwar are around 4700 feet high. The highest region in the Deccan Volcanic Province is Kalsubai near Nasik, standing at 5400 feet.

Why such a large discrepancy between Brannen and the measured elevation in the Deccan Volcanic Province? I suspect what Brannen is referring to is a composite stratigraphic thickness of the lava in Western Maharashtra. Refer to the table below. It presents two different approaches to organizing the lava pile into discrete units.

Source: Vivek S Kale and coworkers 2017- Geological Society of London, Special Publications.

"Lithostratigraphy" relies on systematic physical differences in lava packages to classify them into formal units. The "Chemostratigraphy" classification uses chemical differences in successive phases of eruption to subdivided the lava pile.

Add up the thickness of the individual units and you end up with a 3400 meters or 11,150 feet thick section of lava. Branner may have used a slightly different estimate of lava thickness to arrive at a 11,500 foot thickness for the Deccan Basalts.

If, as seen in the section at Warandha Ghat, the lava is nearly horizontally disposed, why then is the stack of lava "only" 4700 feet at Mahabaleshwar and caps out at 5400 feet at Kalsubai?

The answer is in the way the different subunits of the lava are exposed all across the volcanic province. The map below shows sections of the Deccan Traps at different locations.

Source: L Vanderklyusen and coworkers 2011- Journal of Petrology.

In this map, the chemostratigraphic subdivisions are shown. What is important is that all the subunits never stack up in any one place. The reason is in the regional structure of the volcanic pile. It is in the form of a gently waveform with younger packages of lava offlapping towards the south.

Source: M. Widdowson and K.G. Cox 1996: Earth and Planetary Science Letters.

This north to south cross section of the Deccan Traps along the Western region shows how different subgroups are exposed along the profile. You can see how at any one place the lava thickness and altitude is between 1000 to 1500 meters ASL.

It is important to mention that this is a regional view of the lava section across a distance of around 650 km depicted with a 40x vertical exaggeration. The inclination of the lava layers is very subtle and has been deduced from careful measurements of the altitude of the subunit boundaries at different locations along the profile.

The section below shows a close up of the lava stratigraphy along two north to south profiles in mid Western Maharashtra in the well known Harishchandragarh - Bhimashankar area. Notice again how only a few of the units stack in any one location.

Source: Vivek S Kale and coworkers 2017- Geological Society of London, Special Publications.

Why did such an arrangement of the lava units emerge? Is the waveform a regional volcanic dome with lava radiating from one central eruptive center? Or is it due to post-eruption arching of the crust? Have younger lava sections been removed by erosion from the northerly locales, or has there been a southerly migration of eruptive centers over time, resulting in the offlapping arrangement? Anne E. Jay and Mike Widdowson in a study published in the Geological Society of London estimate that as much as 1.5 km of lava section has been removed by erosion from the Nasik area. That region would have stood much taller tens of millions of years ago. We will leave these questions lingering for another time.

What I do wish is that Mahabaleshwar really stood 11,500 feet tall. I could have ice skated on Lake Venna.

Dinosaur Engineers, Laterite Plateau, Social Insects

noreply@blogger.com (Suvrat Kher) — Tue, 30 Sep 2025 03:05:00 +0000

The latest batch of readings and a video for you readers.

1) How the death of the dinosaurs reengineered Earth. Here is an interesting linkage between dinosaurs, sedimentary rock type distribution and river geometry. Fluvial sedimentary environments are different before (Cretaceous) and just after (Paleocene) dinosaur extinction.

In the latest Cretaceous, large bodied dinosaurs destroyed riverside vegetation, destabilizing banks and preventing stable meanders. Natural levees were breached causing sand to spill onto the floodplains, resulting in an open riverine environment. Post dinosaur extinction, vegetation growth stabilized banks, forming stable channels and meander belts, promoting a sharper division between the constrained channel sands and surrounding floodplain fine mud and organic rich swamps.

Ecosystem engineering by dinosaurs!

2) The Rocky Life: Plateaus of the Monsoon. South of the town of Satara in Maharashtra, the crest of the Western Ghats is mantled by a thick hard iron rich soil known as laterite. This red crust is a deep weathering profile that developed by chemical breakdown of the Deccan basalts (in Maharashtra) and of Precambrian metamorphic rocks (Goa and southern Western Ghats) around 50 million years ago in the Eocene during a warm and wet climate phase. For long, these high regions were treated as "wastelands", devoid of vegetation and wildlife.

But as biologist Varad Giri explains in this excellent video, there is a hidden world that a careful observer will notice.

And conservation biologist Neha Sinha writes about (under paywall) the plant life on these rocky plateaus- Why India's "wastelands"are biodiversity hotspots in disguise. As she evocatively wrote about the Kaas Plateau near Satara on her X timeline- "Lakhs of flowers - carnivorous, parasitic, wild, mesmerising, ephemeral, resilient".

3) One mother for two species via obligate cross-species cloning in ants. Social insects must rank as some of the most amazing creatures.

In one species of ants, the mother gives birth to offspring of two different species! This happens because the mother uses sperm from another species male to produce the worker caste.

Yes, they have caste too!

I’ll reproduce the abstract here and leave you to roll your eyes in wonder-

“Living organisms are assumed to produce same-species offspring. Here, we report a shift from this norm in Messor ibericus, an ant that lays individuals from two distinct species. In this life cycle, females must clone males of another species because they require their sperm to produce the worker caste. As a result, males from the same mother exhibit distinct genomes and morphologies, as they belong to species that diverged over 5 million years ago. The evolutionary history of this system appears as sexual parasitism that evolved into a natural case of cross-species cloning, resulting in the maintenance of a male-only lineage cloned through distinct species’ ova. We term females exhibiting this reproductive mode as xenoparous, meaning they give birth to other species as part of their life cycle”.

I love the first line- Living organisms are assumed to produce same-species offspring. After all, we never tried too hard to prove it!

Will Earth Become Venus?

noreply@blogger.com (Suvrat Kher) — Mon, 15 Sep 2025 03:27:00 +0000

I came across an article written by economist Sanjeev Sabhlok on the long term climate future of the earth titled - Limestone proves the impossibility of a runaway greenhouse effect on Earth. Mr Sabhlok has been reading some geology and has found out that the earth can naturally regulate the earth's carbon dioxide levels over geologic time.

The process operates like so: During times of increased volcanism, CO2 levels in the atmosphere increase to a point where the earth starts warming. This in turn enhances rock weathering reactions which pull back CO2 and washes it down into the ocean where it is sequestered as a bicarbonate or carbonate molecule. A fraction of this carbonate gets locked up in limestone precipitating on the sea floor.

Besides this mechanism, photosynthesis also pulls out CO2 from the atmosphere. This CO2 goes into building organic molecules. Some of that organic matter sinks to the ocean floor and is buried, creating another long term carbon sink.

All these natural adjustments to atmospheric CO2 means that a runaway increase where CO2 levels keep rising thousand fold unabated is unlikely to occur. Earth will not turn into a Venus. Mr Sabhlok says that most climate scientists ignore this natural regulator in their panic over a runaway greenhouse effect.

Mr Sabhlok has written quite a nice summary of the geological evolution of the earth's atmosphere. But he entirely misses the point about why scientists ignore geologic sequestration of CO2 in their climate change projections. They do so because it works too slowly to matter to us. Our concern is not a distant future where surface temperatures may or may not reach a Venus like 450 deg C, but one where there is a spike of 3-4 deg C in the next few decades to centuries which nevertheless will result in extreme damage to human society and the ecosystems we depend on.

The geologic thermostat that Mr Sabhlok describes can't prevent these smaller shorter time scale perturbations in atmospheric conditions. Some numbers he shares demonstrates the inadequacy of weathering to neutralize CO2 at short time scales. He quotes from a video put up by a Dr. Johnson Haas; " Typically on an annual basis … about 0.03 gigatonnes of carbon is extracted from the atmosphere and goes into limestone which goes into long-term geologic storage. … [E]ven at that slow rate the drawdown of CO2 from our atmosphere by shell building organisms … would completely exhaust the atmosphere of CO2 in less than a million years”.

What he doesn't add is the impact of human emissions. Our activity is emitting an eye popping 40 billion tons of CO2 to the atmosphere every year. This is 2 orders of magnitude more than what limestone can suck in. About half of this CO2 gets absorbed by the ocean, the vast majority getting locked as a stable bicarbonate molecule (HCO3). The rest remains in the atmosphere, cumulatively increasing its CO2 levels. Over the past 250 odd years, human activity has increased the amount of CO2 in the atmosphere by about 1.5 trillion tons.

When emissions eventually go to zero, absorption by oceans will quickly start reducing atmospheric CO2, putting the brakes on warming. And in the long run, several hundred to a few thousand years after we achieve a net-zero emission scenario, CO2 levels will come down to pre-Industrial amounts. But as long as emissions continue, the earth will keep warming and become a very unpleasant place. The geologic past informs us of the havoc wrecked by increased CO2 levels and a warmer earth. The Late Devonian (372 million years ago), the Late Permian (252 million years ago), and the late Triassic (201 million years ago) mass extinctions were all triggered by increased CO2 levels and warming from sustained volcanism.

The Inter Governmental Panel on Climate Change Synthesis Report outlines many scenarios that might unfold towards the year 2100. No contributing climate scientist on that report is panicking about a runaway greenhouse effect. Instead, they highlight that incremental increases in temperature over the next few decades will place a debilitating burden on our society through myriad impacts on our health, water security, agriculture, and biodiversity. While fixating on an implausible runaway effect, Mr. Sabhlok stays silent on the real impending danger that we are facing.

His sanguine advice that "We should sleep soundly, knowing that no matter how much CO2 mankind emits by burning fossil fuels, our amazing living planet will never go the way of Venus" is utterly irresponsible.

Earth may never go the way of Venus, but if we don't stop burning fossil fuels our amazing planet will turn into a living hell for us and our immediate descendants.

____________________________________________________________

Fun Facts: I didn't want to quibble about some of the specifics in my post, but I want to share this with you.

1) Biocalcification (limestone formation) results in the emission of CO2! Since most of the carbonate in the ocean is in the form of HCO3, we can write the precipitation equation as-

Ca + 2HCO3 -----> CaCO3 + H2O + CO2 --------- Eq.1.

For every molecule of CO2 that gets locked up in limestone, one molecule is released in the ocean and eventually into the atmosphere. Limestones over time do constitute a CO2 sink, but precipitation of carbonate sediment is not that effective an offset of atmospheric CO2 in the here and now.

2) On the other hand, dissolution of CaCO3 in the deep ocean adds alkalinity, neutralizing the increase in ocean acidity due to CO2 released by the oxidation of organic matter. It is Eq.1. in reverse.

CaCO3 + H2O + CO2 ------> Ca + 2 HCO3 ----- Eq.2.

Carbonate equilibria can be counterintuitive and complex!

3) Mr Sabhlok says that "we are currently close to the lowest levels of CO2 in the Earth’s history". It is true that CO2 levels have steadily decreased over geologic time. But they have sharply increased in the past 150 years from 280 ppm in the late 1800's to more than 400 ppm today and will continue to increase as long as we keep burning fossil fuels. The last time earth saw such CO2 levels was 14 million years ago.

Easterly Tilt Of The Deccan Plateau - Update

noreply@blogger.com (Suvrat Kher) — Fri, 22 Aug 2025 03:27:00 +0000

I first wrote about this topic in 2011 in response to a question by a reader. I thought I would update my post with some new maps and explanations. Why is there such a pronounced pattern of easterly flow of the rivers in the Indian Peninsula. I keep getting asked this question. It was time for an update on this interesting topic on geology and landscapes.

The region south of the Tapi river covering the Deccan basalts and the southern Indian peninsula exhibits an easterly drainage with the rivers flowing into the Bay of Bengal. The map below shows the Indian peninsular region with easterly drainage. The Deccan Plateau is mostly but not entirely covered by the Deccan basalts. South of this region is the Karnataka Plateau with a Precambrian geology. Along the east coast there are Permian-Triassic and Cretaceous basins.

Source: Hetu C. Sheth: Deccan Beyond the Plume Hypothesis

The question posed to me was - What is the relationship between the Deccan volcanics and the easterly tilt of the Indian plateau (i.e. the plateau covering the Deccan volcanics and the southern Indian peninsular region)?

The easier more intuitive answer would have been that the western ghats provide the topography and Deccan volcanism created a lava pile that is thicker to the west and which thins to the east, thus generating an east sloping surface. Rivers follow the slope to the Bay of Bengal.

There are some geologic age inconsistency in this answer and this also does also not fully explain why the region south of the Deccan Volcanics too has an easterly drainage. Clearly, something more is going on.

To understand the evolution of the Peninsular drainage patterns let us look back to the time when the Peninsula didn't exist. In early Mesozoic, India was part of Gondwanaland and was joined to Antarctica and Australia to the east, and Africa to the west. The triangular shape of south India with characteristic eastern and western coastlines had not formed yet.

How can we find out the direction rivers were flowing back then? Geologists look to clues in the sedimentary basins of that age. The composition of sand in sandstone is matched to the most likely source terrain. And current directions can be inferred from studying ripples preserved on the surface of ancient sand.

The paleo geographic maps below shows Gondwanaland and the location of the Pranhita Godavari basin in the Mesozoic.

Source: Sankar Kumar Nahak and Coworkers 2024.

West North West flowing rivers originating in the highlands of the future Antarctica and in the Eastern Ghats were funneling sediment to the basin. Much of the interior of the region that would become the southern Peninsular India was a peneplain. There wasn't much topography towards the west for an easterly drainage network to develop.

India broke away from Antarctica beginning about 140 million years ago. A distinct eastern continental margin formed. Several NE- SW oriented basins developed along the edge of the Indian continent. Since by this time an expanding Indian Ocean lay to the east, the orientation of a natural drainage system would have been from the west towards the east.

We can say with some confidence that by 90 to 80 million years ago, east flowing rivers originating in the interior of the Indian continent were depositing sediment along the eastern Indian margin. See this map of sediment distribution along the Indian east coast.

Source: K.S. Krishna and Coworkers 2016.

It shows the thickness of Mid- Late Cretaceous sediment, ranging in age from about 100 million years ago to 65 million years ago. The sediment lobes coincide with the mouths of the Godavari, Krishna rivers and other southern rivers, indicating that the paleo Godavari and the paleo Krishna system had begun building deltas from that time. Since there were no Western Ghats then, these rivers may have been shorter, with their source somewhere in the Archean and Proterozoic terrain of Peninsular India.

Further to the south, geologists find a similar story with the ancient Cauvery. The Cauvery basin formed when Sri Lanka detached from the Indian continent. Its delta and marine deposits too contains sediment from the Late Cretaceous.

The easterly drainage pattern of Peninsular India developed before Deccan Volcanism and the formation of the Western Ghats.

India broke away from Madagascar about 88 million years ago and subsequently from the Seychelles about 66-64 million year ago. The latter separation coincided with Deccan Volcanism and the eventual formation of the western Indian continental margin. Block faulting that accompanies continental breakup would have created a north south oriented high area, which would eventually evolve into the present day Western Ghats. The thinning of the lava pile to the east also would have created an easterly slope. Rivers originating in the western highland now would flow across the length of the Peninsula.

New streams would have incised the fresh volcanic surface as lava buried the older etched landscape. But the regional pattern of easterly flow persisted.

Some geologists maintain that there has been some fairly recent Cenozoic age (past 15-20 million years) uplift of the Western Ghats which has accentuated relief and produced the youthful looking topography of scarps, waterfalls, and deep canyons. These earth movements would have certainly given new energy to the drainage system, but there is some geologic evidence to suggest that the streams originating in the western ghat region are antecedent to the uplift of the ranges.

For example, in the Mahabaleshwar area easterly drainage cuts across the axis of a north south oriented gentle anticlinal structure, implying that the drainage predates the uplift and warping of lava flows. Evidence from sedimentation patterns of the eastern river deltas also show that the easterly drainage originated much earlier than the formation of the Western Ghats.

What then created that initial slope to the east that imprinted the drainage network that continues today?

One reason is that the eastern margin formed first. Basin formation along the eastern edge of the continent would have created a relief difference between the western interior and the eastern depressions, resulting in stream networks flowing eastwards. Secondly, the new oceanic crust made of lava that formed when India and Antarctica separated in the Late Jurassic and Early Cretaceous would have cooled by Late Cretaceous times. Becoming colder and denser it has been sinking and dragging the Peninsular region with it.

Earlier eastern basin formation and a tug from the floor of the Bay of Bengal may have been enough to impress an east flowing drainage. Later, the east sloping lava surface and the rise of the Western Ghats reinforced this distinction between the west and the east perpetuating the direction of river flow initiated since Cretaceous times.

How Old Is Himalaya Topography?

noreply@blogger.com (Suvrat Kher) — Thu, 31 Jul 2025 03:05:00 +0000

Is this true?

The answer is no. To be fair, aside from the click bait, the article itself does not make any such claim. It covers a new study on some igneous rocks from Arunachal Pradesh that formed during an earlier pre-Himalaya stage of the India Asia plate convergence.

By mid late Cretaceous times, between 100 to 66 million years ago, the dense ocean lithosphere that was the front edge of the Indian plate was sinking underneath the Ladakh terrain, a splinter of Asian continental plate disconnected from the mainland. The subduction of the Indian plate triggered extensive melting in the deep subsurface, building over time a magmatic arc. The schematic below shows the plate tectonic scenario.

Source: Sankar Chatterjee and coworkers: Gondwana Research.

This arc has been well studied in the Kohistan and Ladakh areas. The new work found that a body of granitic rock known as the Lohit pluton is also an eastern extension of the Kohistan Ladakh arc complex.

Eventually, the oceanic crust of the Indian plate was consumed and the Indian continental crust collided with the Ladakh terrain, which by this time had sutured with the Asian mainland. Himalayan mountain building begins from this point on, roughly sometime after 50 million years ago.

How do geologists know when topography began to form in the Himalayan region? Various dating methods tell us when a particular rock or mineral crystallized or cooled below a particular temperature. But how do we date the formation of topography? Sedimentary geology, my field of specialization, has played a big role in giving us insights into the tectonic and topographic evolution of the Himalaya. I'll summarize how the story of the formation of the different Himalaya ranges came to be written by these geologists.

Due to inherited geologic history and subsequent conditions during continental collision, the entire region between Ladakh and the Himalaya front can be subdivided into six geologic terrains running along the length of the mountain arc. These are, from north to south, the Gangdese magmatic arc, the Indus-Tsangpo suture zone, the Tethys Himalaya, the Greater Himalaya, the Lesser Himalaya, and the sub Himalaya (Siwalik). Each is made up of distinctive rock associations.

The earliest topography began to from in the north, at the zone of contact between the two continental plates. Over time, there was a step wise progression of southwards topography formation. As each of the geologic terrains rose up, newly developed stream networks started eroding the rocks and delivered distinctive sediment mixtures to two types of sedimentary basins which had developed adjacent to the mountains. The Indus and Bengal basins at the two extremities of the Himalaya received sediments from the Indus and the Yarlung-Tsangpo/Brahmaputra. A second type of basin, known as a foreland basin formed to the south of the orogen. This moat like depression which runs parallel to the Himalaya, and is fed by streams running transverse to the ranges, also became an archive of material removed from the mountains.

By carefully identifying the sedimentary grain types deposited in these basins and how their proportions change through the oldest to the youngest layers, geologists have been able to piece together the evolution of new topography and geologic provenance through time.

I am presenting this reconstruction through a series of time slices which show topography formation in each of the geologic terrains and the resulting stream networks transporting the derived sediment from source to sink. The representation only shows the central foreland basin from Himachal Pradesh to Nepal. I have not shown the sedimentary history of the western and eastern basins. The trends at the Himalaya extremities are similar with some difference due to variations in the dominant geology of the contributing catchments.

I have also not covered a short phase of basin formation in the Indus Tsangpo suture zone between 30 to 20 million years ago. This basin received sediments from both the Gangdese Arc and the Indian plate and was then uplifted to form the Indus Group ranges which include the famous Kailash mountain. For more details of this episode of Himalaya mountain building do refer to my post - Is Mount Kailash the Oldest Mountain in the Himalaya?

In the diagrams, the legend "foreland sandstone diagnostic grains" refers to the arrival of a suite of distinct grain types in the foreland basin. This signals the uplift and erosion of new rock types in the growing mountain range. Earlier formed ranges will in most cases continue to contribute sand, but it is the first appearance of a new grain type in successive strata that is the indicator of tectonic and topographic changes.

The inspiration for these diagrams is from P.G. DeCelles and coworkers paper on the timing of the India Asia collision, published in the May 2014 issue of Tectonics.

A) Initial Continental Collision- 58-54 million years ago: What was the timing of the collision?

As long as Indian oceanic lithosphere was subducting under Asia, a deep trench and forearc basin separated the two continents. Sediments eroded from Asia were trapped in these depressions and could not travel on to the Indian continent. This situation changed on continental impact. By then the intervening basins were shallower, the Tethyan Ocean had started retreating and rivers originating on the Asian tectonic plate could now flow across the zone of collision and deposit sediments on the Indian continent. These Asia derived delta sediments rich in volcanic rock fragments eroded from the Gangdese Arc began to be deposited on the Indian continental shelf between 58-54 million years ago. TH, GH, and LH are the future Tethys Himalaya, Greater Himalaya, and Lesser Himalaya.

B) Proto Himalaya Stage- 45-30 million years ago.

Preceding and during collision, slices of the Indian oceanic plate were thrust up and sandwiched between the two continental plates. Igneous rocks of this "suture zone" are made up of magnesium rich silicate minerals (olivine, pyroxene) and magnesium aluminum oxides (spinel). Only a remnant arm of the Tethys persists, but rivers can now flow across the Indian continent and deliver sediments to the foreland basin. This basin is located roughly over what is now the southern Lesser Himalaya and the Siwalik ranges. Gangdese Arc and suture zone derived sediments first appear in the foreland by 45 million years ago.

C) Early Himalaya Stage- 35-20 million years ago.

A pulse of low grade metamorphic rock fragments start appearing in the early Oligocene to Miocene age foreland basin sediments. These are derived from the newly forming Tethyan fold and thrust belt. Volcanic rock fragments are now absent in the central foreland, suggesting that the growing Tethyan ranges are a barrier to rivers originating in the Gangdese Arc. The Indus and the Yarlung Tsangpo, initiated in the furrow of the suture zone and flowing parallel to the northern ranges before cutting across the rising mountain chain, continue to transport arc derived sediment to the basins at the western and eastern extremities.

D) Main Himalaya Stage- From 20 million years ago.

Three pulses of mountain building are recognized during the Main Himalaya Stage. The early phase from 20 -11 million years ago records the uplift of the Greater Himalaya which are made up of high grade metamorphic rocks containing minerals like mica, feldspar, and garnet. Deformation continued southwards between 11-5 million years ago resulting in the formation of the Lesser Himalaya ranges. These shed low grade metamorphic and dolostone (magnesium calcium carbonate) detritus.

Eventually the foreland basin got caught up in the progressing orogeny. New faults propagated southwards. Slices of the oldest foreland basin deposits were broken and accreted to the mountain front. These freshly exhumed rocks became the major source of sediments feeding the youngest depositional phase in the foreland. Pliocene-Pleistocene (5 -0.5 million years ago) layers of the Siwalik hills are made up of rock fragments cannibalized from Eocene and Oligocene foreland strata.

How is the age of the foreland basin sediments determined? The entire exercise of unraveling the topographic history of the Himalaya depends on that!

These sediments have been dated using a variety of methods. Fossils provide age ranges for packages of sediment. Magnetic signals preserved in iron rich mineral grains are measured and pegged to an absolute date by comparing the magnetic pattern to a global magnetic chronology. Techniques such as fission track dating of zirconium silicate sand (zircon) tells geologists when that zircon in its source was being uplifted and cooled thus giving a fair idea of the time of its erosion, transport, and deposition as a sedimentary particle.

Gathering all this age information on the sediments, the timing of the arrival of distinctive rock fragments and minerals in the foreland agrees well with the exhumation history of their provenance as deduced from bedrock geochronology.

The growth of mountain chains is a long and complex process. The word "collision" may invoke ideas of near instant crustal response, but deformation and surface uplift moves rather slowly across strong and rigid plates. Surface and deep crustal process are linked. For example, the formation of the Tethyan fold and thrust belt resulted in crustal thickening and the deep burial and metamorphism of rocks that eventually became the Greater Himalaya. There was a long time lag between the initiation of collision and the main Himalaya pulse of uplift. The rise of the Greater Himalaya took place a good 35 million years after the India Asia impact.

Foreland basins give us valuable insights into the relationship between sedimentation and tectonics, but they too need careful evaluation. They are not static entities. Compare the proto Himalaya stage with the main Himalaya stage and you will notice that as mountain building moved southwards the location of the foreland shifted too in response to the migrating load of the thickened crust. This process continues to this day. If the region of the Siwalik hills was the foreland a few million years ago, today it is the Ganga alluvial plains.

Orogeny and drainage impact the sedimentation patterns in the foreland. Different rivers breaking through along the mountain front may not be bringing uniform sediment mixtures at the same time. Hinterland differences in geology of the catchment results in variable sand composition along the length of the foreland. Take the example of river Ravi. It drains mostly the Lesser Himalaya and hence its brings with it low grade metamorphic sand grains. On the other hand, the Sutlej flows through a significant portion of the Greater Himalaya. High grade metamorphic grains make up a large proportion of its sand.

Further, chemical reactions taking place in the subsurface may dissolve some types of minerals. This may create an apparent trend in sand composition through time, which may not accurately reflect the actual history of the provenance.

Researchers need to be cognizant of these issues when they construct their answers.

Understanding the timing of Himalaya uplift provides valuable insights into the geodynamic forces at play during continental collisions. But the interest in this question goes beyond geology. Climate scientists want to know more about the linkage between Himalaya evolution and the advent and shifts in the Asian monsoon. And the value of studying the Himalaya spills into many other areas. Orogeny exposed enormous volumes of fresh rock to chemical weathering, mobilizing nutrients and organic carbon which would then be sequestered in fluvial and marine environments. These elemental cycling and budgets are keenly studied by surface systems specialists.

Visit the picturesque Kangra region in Himachal Pradesh. Climb the thick sandstone layers leading up to the historic Kangra fort. Go to nearby Jwalamukhi, where natural gas emanating from the deep keeps alight an eternal flame. Ascend the hills towards the famous town of Dharamshala. You will be traveling through the Miocene foreland basin. Sedimentary petrologists for decades have worked on these and other sites along the Himalaya frontal ranges amassing data on sandstone composition. Even as million dollar instrumentation keep revealing new facets of the earth, their main tool has remained the humble petrologic microscope mounted with a grain counting stage. From this labor of love has emerged the story of how and when the Himalaya came to be.

Joshimath Landslide, Human Evolution, Early Animals

noreply@blogger.com (Suvrat Kher) — Wed, 16 Jul 2025 03:08:00 +0000

Sharing some of my readings over the past couple of weeks-

1) Movement of Joshimath Landslide in India: The town of Joshimath in Gharwal Himalaya is built on an ancient landslide. Geological reports going as far back as the 1970’s had warned that excessive modification of the slope due to urbanization may result in slope movement and eventual failure. These warnings proved correct as slope movement since 2018 has caused major damage to houses and livelihoods. Landslide expert Dave Petley reports on a new study of the region that uses radar technology to track earth movements.

It concludes that removal of vegetation, mismanaged groundwater seepage and blocked drainage paths contributed to accelerated movements of the Joshimath landslide system. There is unplanned and unregulated construction happening in other Himalayan towns. Authorities must take geological advice seriously and plan their growth accordingly.

2) The Olduvai Effect- New questions about meat eating in human origins: How about some food for thought?… I mean literally. Was meat eating connected to the evolution of larger brains in our human ancestors beginning around 2 million years ago? Paleoanthropologist John Hawks writes about recent work on East African sites across the period from 2.6 to 1.2 million years ago that throws doubt on the “meat made us human” hypothesis.

The study he discusses finds no evidence for a systematic increase in meat eating across the studied period. The evidence also points to different hominin groups having flexible strategies for obtaining meat. But can we tie increased meat eating to one particular branch of the hominin tree? This is a very interesting article on how anthropologists retrieve and analyze evidence from sites and how the geography and time depth of sampling influence the conclusions that are drawn.

3) Complex animals living millions of years before the Cambrian Explosion revealed by seabed tracks: What do we know about early animal life before the evolution of shells made their preservation more likely starting around 530 million years ago? That animals were present much before they acquired shells is inferred from molecular data that places their origin and diversification a good 50-100 million years before the Cambrian. But there is another way to understand animal evolution before body fossils appeared. It is through studying their movement on the sea bed. Tracks and burrows made by mobile animals start appearing in the rock record by 550 million years ago.

James Ashworth describes some recent fascinating work that has decoded the morphology of these fossil trails and compared their shape with those made by some common modern sea floor animals. The researchers then propose that the changing shapes of trails across a 10 million year period is indicative of increasing complexity in animal locomotion. Early trails were made by simpler animals with short round bodies and limited sensory capabilities. Later in time, sinuous tracks made by worm like animals characterized by a slender anterior-posterior body profiles appear. A very clever way of understanding morphological changes during early animal evolution.

Fellow- Geological Society of India

noreply@blogger.com (Suvrat Kher) — Thu, 26 Jun 2025 03:05:00 +0000

I'm happy to announce that earlier this month I was elected a Fellow of the Geological Society of India in recognition of my efforts to introduce and popularize geology among the general public.

As I came to know, some senior office bearers have been reading my blog and recommended my induction into the Society. I feel honored to be a part of this distinguished body.

I want to thank you readers for your support and encouragement over the years. It has kept me seeking new topics to learn and write about. I started writing many years ago because I felt that there was a lack of popular style writings on the beauty of geology as a science and its relevance to society. Dramatic events such as earthquakes made news. But the field with its many sub specializations, and as a mode of inquiry into the history of the earth remained invisible to the lay audience. I aimed my writings to fill this lacunae.

Interestingly, biologists were the first to start interacting with me. They were researchers interested in how landscapes impacted biodiversity and evolution. I have had many a fruitful exchange with them. Since then, my readership has expanded and I hear from people from diverse backgrounds. There is a sense of satisfaction that my collection of writings is being used as a resource by many science enthusiasts. A 17 year archive of my posts on varied geoscience topics is available on this blog for your perusal.

Let me share an email I recently received from a student.

These are the moments when you think it has all been worth it.

Be sure to hum "He's A Jolly Good Fellow" when you are reading my posts. And get your friends to subscribe to this blog. Pronto!

Enigmatic Sedimentary Rock Darma Valley

noreply@blogger.com (Suvrat Kher) — Thu, 19 Jun 2025 03:20:00 +0000

A late Neoproterozoic to early Paleozoic section (~600-500 million years old) of the Tethyan Sedimentary Sequence is exposed around the villages of Dantu, Boun, and Philum, in the vicinity of the famous Panchachuli Glacier in Kumaon. The lower part, made up of low grade metamorphic rocks is accessible along the many local trails. The higher summits are made up of sandstone and conglomerate. These are harder to reach, but blocks eroded from the summit can be found in streams near Boun and Philum.

Two years ago I had posted a picture of a sandstone block showing convoluted folded layers and asked whether this folding was tectonic in origin or due to synsedimentary deformation of semi lithified sediment. In the latter case, shaking of the sea floor and mass movement of sediment due to an earthquake or a severe storm results in the sediment layers contorting and deforming in various ways.

Sandstone in stream bed near Boun village.

I could not decide between these alternatives although I favored a synsedimentary origin of these features. My reasoning was that such deformation appears local, since there were also examples of undeformed sandstone with delicately preserved primary bedding. The short wavelength folding observed in my example also is very different from the longer wavelength folds present in the lower part of the exposed Tethyan sequence.

Last month on a trip to Boun village I came across another block from those high ridges which I think lends additional weight to the synsedimentary deformation scenario.

You will notice that the block is made up of a conglomerate (pebbly layer) in the lower part, overlain by a beautifully cross bedded sandstone towards the top. The ten rupee coin gives a sense of scale. The lower half of the block is a classic flat pebble conglomerate. You will realize the meaning of the term as you read along. A more detailed examination of the conglomerate hints at an unusual mode of formation. The clues lie in the four boxes I have drawn. I will focus on them one by one to make my case. This is the cross section of the pebbly layer. The bedding plane view is not exposed in the boulder.

Before that, let me put up this picture of another conglomerate. This sample too has rolled down from the high ridges near Dantu village.

Sedimentologists will be confident in interpreting this as deposition in a gravelly stream or in the surf zone of a beach. The smooth and rounded shape of the cobbles is due to long transport from the source to the site of deposition, followed by the particles rubbing against each other in a high energy current and wave environment.

Now take a look at the pebbles in Box 1.

They have straight and jagged sides and pointed edges. This indicates very little transport and attrition before burial. The source rock of these pebbles must have been near by.

In fact, the source can be observed in Box 2.

The dark grey elongated pebbles were derived by the breakage of the bed in the lower part of the block. The dark grey layer has a fragmented fabric. I have outlined in yellow some larger blocks of the remnant bed. They are surrounded by smaller broken pieces. It looks like a layer which hardened quickly on the sea floor broke due to a disturbance and yielded these flat pebbles. These pebbles are called intraclasts, since they are derived from a source from within the depositional environment. The slab like shape of the pebbles suggests breakage along parallel planes of weakness. The breakage is not due to tectonic overprinting since the overlying cross bedded sandstone is not affected.

Complete disarticulation of an early cemented layer will ultimately yield individual centimeter scale pebbles which make up the pebbly layer highlighted in Box 3.

Notice the mostly horizontal disposition of the pebbles suggesting transport in a viscous laminar flow and quick burial. The sandy matrix has prevented pebbles from bumping into each other, thus preserving their sharp faces and edges. In contrast, constant exposure to waves and currents would have resulted in the sand being winnowed out and caused these platy pebbles to be rounded, imbricated and stacked at an angle.

Fine quartz and lime mud sediment was cemented by calcium carbonate on the sea floor within a few tens of centimeters of burial. This semi lithified layer then broke during an earthquake or when the sea floor was pounded during a severe storm.

Box 4 captures this transition from an in-place unbroken layer which show signs of breakage towards the top.

Slope failure and mass movement of such a layer eventually resulted in complete breakage of the rigid bed and the formation of discrete flat chips which then were deposited as a flat pebble conglomerate. Box 1 to Box 4 represent different stages of the deformation and sedimentation process. The sharp contact of the layer in Box 3 with the underlying layer (see pic of the entire block) suggests that it may be material transported from an adjacent area where an equivalent bed was completely disarticulated.

Occurrence of slope failure induced flat pebble conglomerates have been previously observed and reported from the Cambrian age Snowy Range Formation in northern Wyoming and southern Montanan, U.S.A.

I have observed only one example of this during my recent visit and I have proposed only a tentative answer. Without observing and understanding the stratigraphic and sedimentologic context in an outcrop I cannot be certain that it is correct.

The association of undeformed and deformed blocks does suggest that intermittent disturbances resulting in brittle and ductile deformation of semi hardened sediment masses alternated with quieter periods of sedimentation. The overlying cross bedded sandstone is an example of deposition during quieter phases.

Flat pebble conglomerates mostly form in sedimentary carbonate environments. This make sense since rapid cementation of the sea floor by calcium carbonate saturated sea water is common. This example though is from a predominantly siliciclastic setting where quartz rich silt lithified fairly rapidly.

These conglomerates also show a peculiar temporal range. They are common in Proterozoic and Cambrian age sequences, but become exceedingly rare in younger rocks. Paleoecologists suggest that this is due to the diversification of burrowing animals that took place during the Great Ordovician Biodiversification Event about 485 to 460 million years ago.

The churning of sediment by bioturbation kept the sediment loose and granular and prevented frequent cementation of the sea floor and shallow buried layers. Carbonate intraclasts became rarer, forming only in more geographically restricted harsh hypersaline settings. Flat pebble conglomerates give us a glimpse in to the ecology and physical properties of the sea floor before the evolutionary radiation of burrowing macrofauna.

Geological processes and evolution interact and feed off each other. Through earth history, the formation of diverse topography and chemical environments by geological circumstance have been triggers for evolutionary innovation. In this example, the evolution of animals making deep vertical burrows resulted in the disappearance from the geologic record of a distinctive sedimentary rock type. Yet, the churning and resulting oxygenation of the sedimentary profile opened up new ecologic spaces for the colonization and diversification of a more complex web of marine communities.

My quest for a more complete answer to the origin of these deformed sandstone continues.

Stream near Baun village

On my next trip to Boun I will try to find more of these blocks to gather evidence in support of my theory. Or, who knows, try to find an easier route towards those high ridges! Stay tuned.

Shrinking Panchachuli Glacier

noreply@blogger.com (Suvrat Kher) — Fri, 30 May 2025 02:54:00 +0000

Over the past few years I have been regularly visiting the Panchachuli Glacier in the Kumaon Himalaya. Accompanying me are a group of geology enthusiasts from all walks of life. This is an outreach effort I have undertaken in collaboration with Deep Dive India.

Every time I make it a point to walk to the glacier snout where the river Dhauliganga emerges from an ice cave. Every time my experience of approaching the glacial terminus is different. The Panchachuli Glacier is a shape shifter. I have to walk a little longer each time to reach the snout, negotiating the changing configuration of rubble mounds and streams.

I thought I would document the retreat of the snout over time using field photos from my visits beginning year 2017 and supplemented by Google Earth imagery going back to the year 2000. I won't keep you in suspense. The glacier snout has retreated by about 1 kilometer in the last 25 years. That is by 40 meters per year. But the rate has varied, with an acceleration in the past 8 years.

Let's begin with a synoptic view of the glacial valley.

The walk begins at village Dantu. It is about 6 kilometers to the present position of the snout. The red lines are edges of old lateral moraines. They are stable features and are easily recognizable in the satellite images. They are my fixed marker posts against which I will track the changing position of the snout. Distance to the snout in all images is estimated from marker post A.

Year 2000- Google Earth Imagery.

Notice the curvilinear cracks (white arrow) near the snout. The glacier retreats by slices of ices cleaving off these cracks. Between the two marker posts is a smaller glacial valley. Semicircular depressions and ponds have formed on the glacier surface due to thawing of the ice. The distance to the snout from A is about 1.3 kilometers.

Year 2012- Google Earth Imagery.

Distance to the snout from marker post A is 840 meters indicating a retreat of 460 meters in 12 years, averaging about 38 meters per year. The smaller valley still has a fair amount of ice accumulation.

Year 2017- Field Photo.

This was taken during my first visit from a high vantage point along the trail to "Zero Point", a popular trekking spot along an old lateral moraine.

Year 2017- Google Earth Imagery.

Between 2012 and 2017, the snout has retreated a further 120 meters, an average retreat of about 26 meters per year. The frontal part of the smaller side glacier is now showing signs of collapse. Pronounced curvilinear cracks have appeared and glacier retreat has left behind rubble mounds producing an uneven topography at the front.

Year 2023- Field Photo.

Taken from close to the 2017 vantage point.

Year 2023- Google Earth Imagery.

The snout is now just 280 meters from marker post A. This implies a retreat of about 430 meters between the years 2017 to 2023. The average rate of retreat is an astonishing 71 meters per year. There are signs of significant changes around the glacial terminus. The snout is now up-valley of marker post B. The smaller valley between the marker posts is almost completely ice free. A surface drainage has developed along this side valley and joins the main Dauliganga stream just downstream of the snout. The multiple small streams in the area is due to drainage finding its way around fresh mounds of rubble.

My most recent visit was earlier this month in May. Google Earth does not have imagery from 2025. But I will share a field photo taken from the high slopes looking down towards the snout.

The snout has retreated by tens of meters and is almost in line with marker post A, strongly suggestive of high rates of retreat persisting over the last couple of years. The area around the terminus is a degraded landscape with rubble heaps everywhere. We could not get very close to the ice cave this time due to time constraints but I assessed it would have been a more difficult passage negotiating the multiple streams and boulders.

The rates of retreat that I have estimated are a little higher than those made by geologists from other parts of the Himalaya. A Ministry of Earth Sciences press release from 2023 has shared some data on Himalaya glaciers. The average retreat rate for Ganga Basin glaciers is about 15 meters per year, while that for Brahmaputra Basin is about 20 meters per year.

A more detailed study of Gangotri, India's most famous glacier, shows a retreat rate of 20 meters per year. Significantly, the retreat accelerated in the past few years to about 33 meters per year, a pattern I too have observed for the Panchachuli Glacier.

Himalayan rivers provide water security for hundreds of millions of people in the Indian subcontinent. Glacial runoff contributes a timely and significant amount of water to these rivers. The Indian government is building and planning scores of dams in the Indus, Ganga, and Brahmaputra basins with elaborate arrangements of water use and water sharing with different stakeholders. Given the massive ice loss and changing climatic patterns, it is imperative that detailed feasibility studies of these projects in terms of both safety, and near, mid, and long term projections of water availability are carried out.

I'm putting up this final image taken in May 2025 from near the Dhauliganga stream looking towards the terminus.

It captures nicely the long term changes that have taken place. The blue line marks the top of the glacier. Fresh collapse has exposed shiny ice walls. The brown line above is the crest of an old lateral moraine, several hundred feet higher than the present day glacier surface.

Is there a better landscape to contemplate and appreciate climate change and the dynamic glaciers which have shaped our planet over past centuries?

Deep Sea Mining, Early Indus Farmers, Indus Basin Dams

noreply@blogger.com (Suvrat Kher) — Mon, 12 May 2025 02:55:00 +0000

Some readings over the past couple of weeks-

1) The Promise and Risks of Deep-Sea Mining: In late 1988 I visited the National Institute of Oceanography in Goa for a job interview. The buzz in the marine geology labs was about the discovery of manganese nodules on the deep sea bed of the Indian continental shelf. At that time, exploration had just started and the technology was not advanced enough to mine these lumps which contained, besides manganese, other metals like cobalt, nickel, and copper. The nodule deposits were being looked at as a future resource.

That day is upon us. Many countries have expressed an interest in mining the deep-sea bed for metals required for the transition away from fossil fuels. Metals concentration of Mn, Co, Ni, and Cu also occurs around hydrothermal vents. Not much is known about the ecology and biodiversity of these remote sites. Most experts feel that mining will result in extensive damage to the sea floor ecosystems and to life in the surrounding water column.

Daisy Chung, Ernest Scheyder, and Clare Trainor describe what is at stake in this beautifully illustrated article published by Reuters.

2) Indus Valley farming started later than thought, radiocarbon study shows: Mehrgarh, in Balochistan, Pakistan, was thought to be South Asia's oldest farming settlement going back to around 8000 B.C. New carbon dating of grains using a more robust dating method called Accelerator Mass Spectrometry has revised the date of earliest occupation to around 5200 B.C. Subhra Priyadarshini writes about the implications of this new date with regards to the origins and spread of farming in South Asia and cultural linkages of Mehrgarh to the Indus Civilization.

3) Water Towers of the Indus Basin: Last month's heinous terrorist attack in Pahalgam, Jammu and Kashmir, India, has refocused attention on the Indus Water Treaty between India and Pakistan and the many hydropower projects that India is planning on the Indus and the Chenab rivers. These rivers provide water security to vast areas of India and Pakistan.

Despite the importance of these rivers to local livelihoods, hydropower projects are being built without due consideration being given to the impact dam construction and climate change will have on the Himalaya ecosystem..

Parineeta Dandekar (story), Abhay Kanvinde (photos), and Michelle Hooper (story map) meticulously document the completed and planned hydropower projects along the Chenab river and point to the lapses in science and environmental governance that have taken place during the project planning process.

Oldest Himalaya Rocks

noreply@blogger.com (Suvrat Kher) — Mon, 28 Apr 2025 03:25:00 +0000

In Peninsular India, the most significant change in rock type occur across what is known as the Archean Proterozoic boundary.

Archean rocks, older than 2.5 billion years, are typically varieties of granite and granite gneiss. They formed when the earth was much hotter and silica rich continental crust was growing by injections of magma from the uppermost mantle and by partial melting of older mafic (silica poor) crust. At places the crust subsided by vertical movements, and lava and sediment filled the narrow depressions. These volcano-sedimentary rocks were deformed and metamorphosed to form linear schist enclaves within the granitic crust. The term granite greenstone terrain describes this rock association.

This phase of continental crust building petered out by around 2. 5 billion years ago. The thick crustal blocks or cratons became the nuclei for future continent growth. By 2 billion years ago or so in the Paleoproterozoic (the Proterozoic Eon spans from 2.5 billion years ago to 538 million years ago) , the Archean crust became the floor for several sedimentary basins. Erosion of the Archean rocks provided sediments that accumulated in these basins over the next 1 billion years, with long hiatuses punctuating pulses of sediment deposition. The names of these sites of deposition will be familiar to many readers and travelers. Aravallis, Vindhyans, and Cuddapah, to name a few, represent this younger Proterozoic phase of crustal recycling.

There was limited development in Peninsular India of younger sedimentary basins and as a result Archean and Proterozoic crustal sections are widely exposed all across the country.

The satellite imagery posted below shows one classic locality of the Archean Proterozoic boundary. This is from the Cuddapah Basin of South India.

The Archean granitic terrain has a rough texture due to the bouldery nature of the landscape formed by weathering of fractured granite. Towards the east north east, the layering of sedimentary strata of the Cuddapah Basin is prominent and unmistakable. The following graphic is a geologic log prepared to describe the succession of rock types from the Cuddapah Basin.

Source: Vivek S Kale and coworkers; Proc. Indian. Nat. Sci. Academy 2020.

Archean 'basement' and Proterozoic 'cover sequence' is a common stratigraphic motif of the Precambrian geology of India.

A few weeks ago I found an old paper from the 1970's on the sedimentology and stratigraphy of Tethyan sequences from the Kali valley area, near the Kumaon Nepal border. These are, as the name suggests, sediments deposited in the Tethyan Ocean along the northern margin of the Indian continent. They range in age from the Proterozoic to the Mesozoic.

Here is the stratigraphic column from the paper. I have shown only the Precambrian (Archean and Proterozoic collectively make up the Precambrian) section of the column. The Central Crystallines are assigned an Archean age, while the Tethyan Sequence Martoli Formation is Early Precambrian. The name Proterozoic was not in use in the 1970's when this paper was written.

Source: S. Kumar and coworkers; Journal of Paleontological Society of India 1977.

'Crystalline' in this context refers to the rock texture made up of large interlocking minerals formed during slow cooling of a magma or during high temperature metamorphism of a sedimentary rock.

The geologic sequence I described earlier took place along the northern margin of India too where the future Himalaya would form. At first glance the Himalaya sequence seems a replica of the geology of Precambrian Peninsular India. It records an Archean 'crystalline' basement, succeeded by variably deformed and metamorphosed Precambrian (Proterozoic) sediments.

Except that it is wrong. There are no Archean age rocks exposed anywhere in the Himalaya. And the rock units immediately in contact with the Archean are not Early Precambrian.

When this paper was published there was precious little geochronology work done in the Himalaya. Geologists knew from sporadic absolute dating of Peninsular rocks that the granite and granite gneiss terrains are older than 2.5 billion years (Archean). The thick sedimentary sequences overlying the granite basement also were Precambrian as ascertained by dating intrusive granites and interbedded lava layers. The lack of any shelly fossils in them was another indicator of the Precambrian age of the cover sedimentary sequences.

Given this familiarity with Peninsular geology, it would have been natural to assign the same chronology to a Himalaya rock sequence of high grade gneiss in contact with unfossiliferous sedimentary rocks.

The Central Crystallines are now known as the Greater Himalaya Sequence and they are not Archean but Neoproterozoic (Late Precambrian) in age. Detailed work has shown that they represent sediments deposited roughly between 1 billion and 600 million years ago along the northern continental shelf of India. A paleogeographic reconstruction of the Himachal Himalaya by Alexander Webb and coworkers shows the original disposition of the different Himalaya rock divisions. Observe (A) that the Greater Himalaya (GHC) and the lower part of the Tethyan Himalaya (Haimanta/Martoli Formation) were deposited synchronously in adjacent areas of the continental shelf.

Source: Alexander Webb and coworkers; Geosphere 2011.

They look very different from each other today because they experienced different conditions during Himalaya mountain building. The Central Crystallines which began their life as marine sediments became crystalline gneisses and schists during high grade Cenozoic metamorphism 35 to 20 million years ago, while the Tethyan Sequence escaped being buried deep in the crust and retained much of their original sedimentary character.

What about the oldest Himalaya rocks? These are Paleoproterozoic in age, dated to be about 1.9 to 1. 8 billion years old. The units Damtha, Berinag, Wangtu, Jeori and Baragaon in the Himachal Himalaya cross section are the Paleoproterozoic age rocks. They are remnants of a magmatic arc and associated basins which formed along the northern margin of India when continental blocks were colliding and suturing into an early supercontinent named Colombia.

Underneath these Paleoproterozoic rocks would have been the Archean 'basement'. But where is it now?

We can take a step back and understand how the Himalaya are constructed. As the Indian continental crust collided and pressed into Asia, a crack or a fault initiated in the collision zone started propagating southwards, slowly splitting the Indian crust. As India kept getting pushed under Asia along this master fault, slices of Indian crust get scraped off and thrust upwards along subsidiary faults to form a growing mountain range. This tectonic evolution is depicted as stages B, C, D, E, F. You can also read my post Himalaya: A Critical Wedge for more details on the mechanisms of mountain building.

If as shown in the cross section, the faults that break and transport crustal sheets are located entirely within the Proterozoic and younger layers then the Archean rocks won't get incorporated into the Himalayan orogen. They lie below the basal detachment/master fault. Alternatively, this model may not be applicable everywhere in the Himalaya and there may be slivers of Archean rocks buried deep under the thrust pile, but erosion hasn't exposed them yet.

In the geologic future, the plate tectonic engine that made the Himalaya will change track. The mountain ranges will stop growing. Erosion will wear down the Himalaya and eventually lay bare its roots. The Archean 'crystalline basement' so familiar all over Peninsular India will also be visible at the base of the gentle rolling hills that were once the mighty Himalaya.

Geology Infographics

noreply@blogger.com (Suvrat Kher) — Wed, 09 Apr 2025 03:03:00 +0000

I read a lot of technical literature on various geology topics. The papers are usually long and written in jargon filled language. It can be tough to hold your concentration and read through the paper in one sitting. What can help is a well complied figure which summarizes the ideas and the results of the study. By figure, I don't mean a graph or tabular display of data, but a graphic that presents the data with a combination of symbology, line art, text, and even images. Such infographics help in grasping the gist of the study and make reading the elaborate explanations easier (you still have to read them).

In this post I will showcase three infographics that I liked from my readings. I won't write long explanations about them, since the idea is to see if you can understand the broad findings by looking at a picture. Read the abstract of the paper to assess how effective the figure is.

1) Ediacaran Extinction and Cambrian Explosion.

The distribution through time and the changes in diversity of early complex multicellular life is depicted in this infographic. The evolutionary history of two distinct 'biotas' are tracked. The Ediacaran 'biota' is a catchall phrase that includes a diverse range of extinct large fossil organisms which may include some early animals as well. Metazoans ancestral to living animal groups are the second category. The carbon isotope curve shows two prominent deflections towards negative values, termed the 'Shuram' and "BACE" (Basal Cambrian Carbon Isotope Excursion) excursions. They are thought to indicate global environmental crises. Bookending this graphic are two diversity measures. On the left is the diversity of body fossils. On the right is the diversity of trace fossils, such as imprints, tracks, and burrows.

Take home point. The Cambrian 'Explosion' is not about the origin of animals but their geologically rapid diversification whose roots lie a good 20 to 30 million years preceding the Cambrian events. Pulses of diversity expansion and collapse took place during that time period.

2) Dating Cave Art.

Humans have left some breathtaking artwork on the walls of caves all over the world. But how do we know when they were created? The pigments used in the drawings cannot be directly dated. One can use associated cultural artifacts to narrow down the time period. Or if lucky, mineral layers that entomb the artwork can be dated directly. This method still brackets the maximum and minimum age of the artwork. This infographic explains how artwork in a Spanish cave was dated using uranium and thorium isotopes.

3) Angiosperm and Insect Coevolution.

I had written about this topic is detail in a previous post, but thought I'll share this infographic again. The Cretaceous was a time of great environmental shifts and changes in terrestrial biodiversity. Gymnosperms gave way to a dominance of angiosperms. The diversification of flowering plants had a large collateral impact on earth. The history of angiosperms and insect groups through the Cretaceous and Cenozoic is explained in this beautifully compiled infographic.

If you have come across a science infographic that you particularly like, do share the link in the comments section.

Early Animals, Hominin Diets, Groundwater Governance

noreply@blogger.com (Suvrat Kher) — Fri, 14 Mar 2025 03:00:00 +0000

A few links to interesting listening and reading.

1) Tracking the first animals on earth: Unequivocal evidence of animals is preserved in soft sediments from about 570 million years ago. The fossil record of the Ediacaran to early Cambrian times (570 to 500 million years ago) has yielded rich information about the patterns of animal evolution. Apart from fossils, comparative genetic studies have given insights into how different animal groups are related to each other and the order of branching of these groups. Amazingly, organic molecules recovered from enigmatic fossilized taxa have been used to differentiate between animal and non-animal remains. Zoologist Matthew Cobb explains all this and much more about early animal evolution in about 30 minutes. Give it a listen!

2) Plant-eating and meat-eating in Australopithecus: What did our ancient relatives eat? By ancient, I mean going back a million years or more. We can use isotopes of nitrogen to tease out information about diets. Carnivores have more nitrogen-15 enriched tissue than plant eaters. Carbon isotopes (C13 and C12) also yield information about the diet of herbivores. Grazers munching on grass take in more of the heavier isotope of carbon than browsers eating leaves and stems. Paleoanthropologist John Hawks discusses some recent work on nitrogen and carbon isotopes of Australopithecines and how the patterns of isotopic variation extracted from tooth enamel can be interpreted in terms of diets and life history. Fascinating stuff.

3) Addressing Depletion in Alluvial Aquifers: Why Context Matters in Participatory Groundwater Management: India relies a lot on groundwater for agriculture. There are signs from many parts of the country of acute groundwater distress. Participatory Groundwater Management initiatives have had some success in addressing this distress. Pratik Kumar and Veena Srinivasan point out that these cooperative movements have been more successful in hard rock aquifers from different parts of the country than alluvial aquifers of northwest India. Geology matters. Aquifer properties matter. Hard rock aquifers are more sensitive to abstraction and are rapidly de-watered and recharged seasonally. Alluvial aquifers are spread over vast areas and water levels are less sensitive to abstraction. The amount you can extract doesn't vary with lowering of water level.

People depending on hard rock aquifers experience the limitation of the resource yearly and are more willing to join cooperative initiatives to manage the resource.

I have just given a gist of the more elaborate arguments in the paper. The graphic below very neatly compares hard rock and alluvial aquifers.

Source: Pratik Kumar and Veena Srinivasan 2025

The paper is open access.

Lithospheric Dehumidifier

noreply@blogger.com (Suvrat Kher) — Fri, 07 Mar 2025 03:23:00 +0000

A few years ago a friend decided to demolish his old house due to extensive and expensive water damage to the ground floor.

Could this be the explanation for the damage?

xkcd comics

A spanking new apartment building now stands at the spot of the old bungalow. There are no signs of any water damage so far. A giant lithospheric dehumidifier may have been used during construction.

There is no end to the add on and perks developers promise these days.

Oil Hunters Of India

noreply@blogger.com (Suvrat Kher) — Wed, 26 Feb 2025 03:16:00 +0000

At Independence in 1947, India had just a few operational oil wells situated in the northeastern region of the country. Most of the subcontinent's sedimentary basins remained unexplored for their hydrocarbon potential. The Oil Hunter: Journey of a Geologist for India's Oil Exploration by Dr. Shreekrishna Deshpande is a personal recollection of the immense effort undertaken by Indian geologists to re imagine these basins as hydrocarbon source and reservoir rocks. It is the story of the development of India's oil industry told with unconcealed pride.

Russia, France, and the U.S. offered personnel and technical help along the way, but the lion's share of the credit goes to geologists of the Oil and Natural Gas Corporation for their perseverance and resilience in the face of immense challenges.

Dr. Deshpande joined the ONGC in its early days in 1961 and describes vividly his field experience in remote locales all across the country, from scorching Kutch, to steep Himalaya terrain, to facing personal danger during an insurgency in Assam. There were inevitable career challenges along the way due to changing institutional structure and unrealistic political expectations. Their impact on company work culture and productivity is described in honest and direct language.

One of my favorite passages comes towards the end of the book where he explains the divergence between geologists and management in their basic understanding of exploration and discovery.

"Subsurface discoveries of oil reserves cannot be projected with certainty. The inputs to the discoveries are always deterministic, but the result is never so, and there is a strong factor of probability. Exploration efforts are to reduce the risk factor and increase the probability of discovery. Methods for direct detection of hydrocarbons from the surface, are yet to be evolved. This contrasts with any other industry, where the output is more predictable and proportionate to the input.

.... As a simplistic approach the management decides the cost of discovery of one tonne of oil by dividing the amount of discovered oil by the expenditure met. It is expected by them that similar expenditure should proportionately result in additional discoveries.

When a sedimentary basin turns old and mature, the addition to the existing stock of subsurface oil becomes increasingly difficult. Non-geoscientists then blame geologists for such uncertainty. Only the high profitability in the oil industry is visible; its probabilistic nature and the risks involved are not so obvious. The stochastic nature of oil discoveries is not appreciated by non-explorationists".

My one complaint about this book is that there is very little geology in it! Dr. Deshpande describes the geology work he and others undertook in very broad strokes. I felt that a few examples of how specific types of geologic data is useful for petroleum exploration would be illuminating for the non specialist reader.

Let me give an example. Early in his career he is sent to Osmania University, Hyderabad, to analyze some sedimentary rock samples using Differential Thermal Analysis. He simply mentions that the results were used by ONGC in their exploration efforts, but how so? DTA is a way to understand whether the sedimentary rock was baked during burial to temperatures that are conducive for hydrocarbon formation.

Another example, and one that involves his specialization, could have been a brief passage describing his work on limestones. What is a carbonate sedimentologist looking for in these rocks? The main reservoir of Mumbai High, India's biggest oilfield, are Miocene age limestone beds which were deposited repeatedly during phases of oscillating sea level. Among other things, exploration geologists want to know how open spaces or porosity in these rocks has evolved over time and whether its occurrence can be predicted throughout the sedimentary section. There was a geological detective story waiting to be told there.

But these are mere quibbles. Overall, this is a very readable account of the productive and remarkable career of a pioneer exploration geologist of India. Popular accounts of Indian geology and industry are rare. Recently, Himalaya geology expert Dr. Om N. Bhargava released his memoir, Travails and Ecstasy of a Geologist Addicted to the Himalaya, on his experiences of working in the Himalaya. Indian earth scientists are beginning to share the good work they have done with a more general audience, bringing a much needed familiarity with a lesser appreciated but critical field of study.

20,000 Days In The Life Of A Clam

noreply@blogger.com (Suvrat Kher) — Mon, 17 Feb 2025 03:04:00 +0000

My Whatsapp profile description says, "what's a million years here and there".

It is a tongue in cheek acknowledgment of the vast spans of time geologists often have to contend with. If I am studying a rock that formed more than a billion years ago, a 5 to 10 million year uncertainty in nailing down its exact time of formation is acceptable. Uncertainty in estimating the time of formation may occur due to our as yet not so perfect understanding of the decay rate of various radioactive isotopes being used for dating, or due to limits of sensitivity of the instruments measuring the radioactive isotopes in the mineral. We are making great strides in measurement techniques with a 0.1 % accuracy now achievable.

Sedimentary rocks are harder to date than igneous rocks since minerals with radioactive elements rarely form in them at the time of their deposition (some limestones and black shales are exceptions). Often, using some indirect methods we can bracket their maximum and minimum age. Take the example of the Alwar Group sedimentary rocks which occur in the northern Aravalli mountains in Rajasthan. They are estimated to have been deposited sometime between 2.1 billion years ago and 1.8 billion years ago, an uncertainty of 300 million years! We know from our understanding of sediment accumulation processes that deposition was not uniformly spread out over the 300 million years. Rather, the sequence of sediments would have been deposited in discrete pulses lasting 10 to 20 million years, separated by long phases of non-deposition.

Amazingly, even though we don't know exactly when during the 300 million year interval these sediments came to be deposited, we can track fairly accurately what was happening then on a daily basis. Some strata of the Alwar Group are of shallow marine origin. As the daily tide flooded in and ebbed, a thin layer of sand was deposited during each of these high energy phases. During the slack phase in between, a thin layer of mud was deposited. Stacks of these tidal bundles made of a sand and mud couplet record the passage of daily tides. Observing the stacking pattern closely reveals even more details. Sets of bundles of thicker sand-mud couplets alternate with sets of thinner bundles. Each set formed during alternating spring (thick layers) and neep tide (thin layers) cycles.

We can interpret the ancient record by comparing the patterns with those forming today in different settings. The principle "present is the key to the past" is used with some caution, but it works well in this case.

Such tidal rhythmites are fairly common in the geologic record. The pictures to the left is a section of a core from Cretaceous age sediments laid down in an estuary. The sedimentary section is made up of sets of thicker silt layers capped by a darker mud layer, overlain by a set of thinner silt and mud couplets. Each silt layer represents deposition during the flood or ebb tide. During the slack period, stirred up organic rich mud settled down. Again, we don't know the exact age of the rock to a certainty of few hundred thousand years, but we can track daily events. Image source: G. Shanmugan; AAPG Bulletin v. 84, 2000.

Speaking of tides, the earth's rotation is slowing down due to tidal friction. Marine organisms like corals, brachiopods, and clams build a calcium carbonate skeleton to house their soft tissues. Their shell grows by a daily addition of a thin mineral layer. Geologists have studied the pattern of skeleton growth of Paleozoic corals. Besides daily growth bands, they can identify seasons too, as corals lay down thicker bands during the dry season and thinner bands during the wet phase. The number of days in the year are estimated by counting the number of daily bands in each season. It turns out that there were about 420 days in a year during the early and middle Silurian (between 443 million to 419 million years ago). By middle Devonian (roughly 370 million years ago), some 50 million years later, the number of days had reduced to about 410. Using bivalve shells, scientists estimate that there were 370 days in a year by Late Cretaceous times (about 80 to 70 million years ago).

There are other examples closer to our own existence on earth of natural rhythms being preserved in rock. Geologists and climate experts routinely use mineral bands in cave stalagmites to understand variations in rainfall. A recent study by Gayatri Kathayat and colleagues from Uttarakhand, North India, reveals details of the course of Indian monsoons over thousands of years, mapping dry and wet phases lasting few centuries each. Despite an uncertainty of a few decades in the absolute age of each layer, it gives us a broad picture of climate change through the Holocene.

We accept the fuzziness of our estimates of the age of an event while being able to sharply resolve the changes taking place in that cloud of uncertainty.

I could have named this post "Ode to Laminae", an appreciation of thin layers that form in tune with earth cycles and which preserve in their layering valuable information on ancient tides, earth moon dynamics, changing of seasons, and longer term climate change. I just thought the title of the post and the paper it refers to is better click bait.

Sometime in the Late Miocene (about 10 million years ago, what's a few tens of thousands of years here and there) a giant clam living on the western margin of the Makassar Strait (Indonesia) built a shell with daily growth increments. I will post the entire abstract of the paper below so you can get an idea of the details of ocean conditions scientists can tease out today with sophisticated instrumentation.

Iris Arndt et.al., 20,000 days in the life of a giant clam reveal late Miocene tropical climate variability.

Giant clams (Tridacna) are well-suited archives for studying past climates at (sub-)seasonal timescales, even in ‘deep-time’ due to their high preservation potential. They are fast growing (mm-cm/year), live several decades and build large aragonitic shells with seasonal to daily growth increments. Here we present a multi-proxy record of a late Miocene Tridacna that grew on the western margin of the Makassar Strait (Indonesia). By analysing daily elemental cycle lengths using our recently developed Python script Daydacna, we build an internal age model, which indicates that our record spans 20,916 ± 1220 days (2 SD), i.e. ∼57 ± 3 years. Our temporally resolved dataset of elemental ratios (El/Ca at sub-daily resolution) and stable oxygen and carbon isotopes (δ18O and δ13C at seasonal to weekly resolution) was complemented by dual clumped isotope measurements, which reveal that the shell grew in isotopic equilibrium with seawater. The corresponding Δ47 value yields a temperature of 27.9 ± 2.4 °C (2 SE) from which we calculate a mean oxygen isotopic composition of late Miocene tropical seawater of −0.43 ± 0.50 ‰. In our multi-decadal high temporal resolution records, we found multi-annual, seasonal and daily cycles as well as multi-day extreme weather events. We hypothesise that the multi-annual cycles (slightly above three years) might reflect global climate phenomena like ENSO, with the more clearly preserved yearly cycles indicating regional changes of water inflow into the reef, which together impact the local isotopic composition of water, temperature and nutrient availability. In addition, our chronology indicates that twice a year a rainy and cloudy season, presumably related to the passing of the ITCZ, affected light availability and primary productivity in the reef, reflected in decreased shell growth rates. Finally, we find irregularly occurring extreme weather events likely connected to heavy precipitation events that led to increased runoff, high turbidity, and possibly reduced temperatures in the reef.

Tell me geology isn't the coolest field of study.

Plastic In Sediment, Antarctica Ice Core, Alfred Wallace

noreply@blogger.com (Suvrat Kher) — Thu, 23 Jan 2025 16:28:00 +0000

A few interesting readings:

1) Sedimentation Shifted - How rivers move sediment along their course to the sea is an important aspect of sedimentology research. Grain size, shape, and density, all affect how currents move sediment, and where and in what proportions sand, silt, and mud particles come to be deposited. Now there is a new kid on the block: plastic. Catherine Russell has written a fascinating article diving deep into experimental work on how plastic impacts sediment transport. The work she describes has important implications for our understanding of plastic pollution in rivers, and the role plastic particles plays in enhancing erosion rates and sediment redistribution in riverbeds.

2) Antarctica: 1.2-Million-Year-Old Ice- Scientists use gases trapped in old ice to measure ancient atmospheric composition and estimate past climatic conditions. A long running drilling program in Antarctica had so far recovered 800,000 year old ice. That record has been recently broken. Scientists have reached the very bedrock of the Antarctica continent. The oldest ice at the very bottom is 1.2 million years old. This is the longest continuous record of our climate that we have so far. It hold much valuable information on climate fluctuations through the Pleistocene and Holocene. This article is a press release of the University of Bern.

3) Beyond Evolution: Alfred Russel Wallace’s critique of the 19th century world- Alfred Russel Wallace is the co-discover of evolution through natural selection along with Charles Darwin. He was a brilliant naturalist and made foundational contributions to natural history. But he also was very sympathetic to the plight of local people suffering under colonialism and the environmental degradation the race to strip the land of resources was causing. Marshall A. summarizes nicely Wallace's observations on the impact of environmental damage, both in his native Wales and also during his travels in the far away Malay archipelago.

Let me take this opportunity to share again this lovingly crafted documentary on the life and work of Alfred Wallace. It is made as a paper-puppet animation, produced by Flora Litchman and Sharon Shattuck and narrated by George Beccaloni of the Natural History Museum London and Andrew Berry of Harvard University.

What a fine example of science outreach.

Shear Luck Near Sunderdunga River

noreply@blogger.com (Suvrat Kher) — Sat, 11 Jan 2025 03:33:00 +0000

As I settled down for lunch by the Sunderdunga riverside during my recent Kumaon trek, I noticed a polished boulder nearby. It had a striking appearance dominated by a large crystal of feldspar set in a much finer grained material. This finer matrix had a pronounced streaky fabric, as if made up of very fine layers. Upon closer examination, these layers or foliation was due to the planar arrangement of minerals like amphiboles, mica, quartz, and feldspar. The larger eye catching feldspar grain in the center of the boulder seems a little flattened along one axis and elongated along the orthogonal, giving it a crude sigmoid shape.

I had chanced upon a rock caught up in a shear zone. These are fault zones where movement of the crust causes intense rock deformation. The type of deformation I observed typically occurs at a deeper level where high temperatures make rocks soft and ductile. Rocks caught up in fault zones at shallower levels undergo brittle deformation. They have a broken appearance, made up of sharp edged fragments set in a crushed finer matrix. The rock is fractured, and these cracks get filled with minerals like calcite and quartz.

This typical brittle like deformation was absent in this rock. There was no sign of any fracturing and breakage of the rock. Instead, the finer grained minerals seemed to flow around the larger feldspar crystal. Grain size reduction occurs by plastic rearrangement of atomic layers and recrystallization of softer minerals during deformation. The stronger resistant minerals which remain as large crystals are called porphyroclasts. Since rocks are sliding past, there is a rotational component to deformation also. Larger grains often show signs of being rotated, while finer groundmass wraps around.

The end stage of such ductile deformation are rocks known as mylonites. These have a flinty or glassy appearance due to the extreme grain size reduction.

I suspect this particular rock has not quite reached the mylonite stage. Let us call it a protomylonite. It does show a clear contrast between the finer matrix made up of stretched and elongated minerals and a large porphyroclast.

The asymmetry of the porphyroclast gives geologists an idea of the sense of motion along faults. The annotated photo below shows the relative sense of shear or motion.

Hundreds of such measurements have been made in the Greater Himalaya. When measured in-situ, the direction of relative motion is 'top to the south', indicating the general direction of movement of Himalaya thrust faults. Deformation is not uniformly distributed throughout the Greater Himalaya but appears restricted to narrow zones. These zones of intense shearing containing deformed rocks including mylonites have allowed the recognition of major thrust fault zones such as the Main Central Thrust which emplaces the Greater Himalaya slab on top of the Lesser Himalaya.

There are minor shear zones too. I think this rock was eroded from one such shear zone in the Sunderdunga valley.

Coming back to the brittle versus ductile deformation regimes. Almost all the deformation you observe in the Greater Himalaya took place in the ductile regime. Here are a few examples from the Greater Himalaya of ductile deformation seen in schists and gneisess. These are my observations from various treks in the Kumaon.

A cross section of the Himalaya is presented here to showcase the metamorphic gradients along the Greater Himalaya slab (green). For this reading, you can ignore the rest of the Himalaya orogen shown in the figure. Temperature gradient increases towards the core of the slab with kyanite (k) and sillimanite (sill) as the prime high grade metamorphism indicators. This example is from the Nepal Himalaya, but the arrangement of the different Himalaya divisions is identical in adjacent Kumaon.

Source: Mike Searle et.al. Tectonophysics 2017

Notice the localization of mylonites along the Main Central Thrust zone. Metamorphism of rocks above around 600 degree centigrade during the Eocene (~35 million years ago) and in the Miocene (~25-16 million years ago) has resulted in the ubiquity of ductile deformation observed in the Greater Himalaya. In hotter pockets in the core, metamorphic rocks partially melted and the resulting granitic magma was injected along penetrative weak planes, forming dikes, sills, and small plutons.

Channeled between two great fault zones, the Main Central Thrust at the base and the South Tibetan Detachment as roof, this hot mushy crustal material was then tectonically extruded to shallower levels, its ductile fabrics frozen and preserved as the rocks cooled. Subsequent tectonism has superimposed brittle deformation on the Greater Himalaya ductile structures.

Finally, another beautiful example of a gneiss showing ductile shearing. Fish shaped white feldspar are set in a biotite mica and quartz matrix which flows around the porphyroclasts. Can you guess the sense of relative motion?

Observing features that you have seen only in a textbook - that is the great joy of going out in the field.

Darwin- Patagonian Christmas

noreply@blogger.com (Suvrat Kher) — Sun, 29 Dec 2024 15:46:00 +0000

A friend recently returned from a trip to Patagonia, Argentina. I mentioned to her that Charles Darwin had spent some time exploring the Patagonian coastline and had made some interesting observations about the local fauna and the native people.

Being a bit vague on the details I dug into one of the most reliable source on Darwin's life and work, the Darwin Online archive. I accessed his Beagle Diary, scrolling down to the time the Beagle docked at Port Desire on December 8, 1833. Below is his entry from December 24, 1833:

24th Took a long walk on the North side: after ascending some rocks there is a great level plain, which extends in every direction but is divided by vallies. — I thought I had seen some desart looking country near B. Blanca; but the land in this neighbourhead so far exceeds it in sterility, that this alone deserves the name of a desart. — The plain is composed of gravel with very little vegetation & not a drop of water. In the vallies there is some little, but it is very brackish. — It is remarkable that on the surface of this plain there are shells of the same sort which now exist. — & the muscles even with their usual blue colour. — It is therefore certain, that within no great number of centuries all this country has been beneath the sea. —1 Wretched looking as the country is, it supports very many Guanacoes. — By great good luck I shot one; it weighed without its entrails &c 170 pounds: so that we shall have fresh meat for all hands on Christmas day.

John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online- Beagle Diary.

As always his keen geology eye had spotted shells which were similar to living shelly creatures, leading him to the conclusion that this region must have been under the sea in the past. All along the South American coastline he noticed oyster and shell beds a meter or two above the current sea level. He concluded that there must have been vertical movement of the crust.

He was a good hunter too. Apart from the Guanacoe, one of this shipmates shot a rhea. The crew ate that too. Darwin realized only too late that he wanted the entire bird to compare its form to rhea elsewhere in S.America. Eating valuable zoological samples became a common occurrence all through the voyage of the Beagle.

The Beagle then sailed south to Port Julian. On his walks there Darwin came across bits of spine and hind legs of a largish creature, later identified as a Megatherium or ground sloth. That led him to muse about what could have killed off this variety, as nothing like it existed today. The sedimentary layers entombing the fossil did not indicate any kind of flood. How could an entire species die off? Taking inspiration from cuttings of apple trees which were clearly part of the parent, Darwin wondered if all individuals of animal species too shared some life force. If so, could a common disturbance or event kill all of them off?

In February 1834 the Beagle sailed into the Straits of Magellan and Tierra del Fuego. He immediately formed a low opinion of the natives whom he though of as uncivilized savages, living naked and unkempt in an utterly desolate landscape:

Their country is a broken mass of wild rocks, lofty hills & useless forests, & these are viewed through mists & endless storms. In search of food they move from spot to spot, & so steep is the coast, this must be done in wretched canoes. — They cannot know the feeling of having a home — & still less that of domestic affection; without, indeed, that of a master to an abject laborious slave can be called so. — How little can the higher powers of the mind come into play: what is there for imagination to paint, for reason to compare, for judgement to decide upon. — to knock a limpet from the rock does not even require cunning, that lowest power of the mind. Their skill, like the instinct of animals is not improved by experience; the canoe, their most ingenious work, poor as it may be, we know has remained the same for the last 300 years. Although essentially the same creature, how little must the mind of one of these beings resemble that of an educated man. What a scale of improvement is comprehended between the faculties of a Fuegian savage & a Sir Isaac Newton — Whence have these people come?

John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online- Beagle Diary.

Darwin compared the Fuegian natives with natives he had met further north along the Patagonian coast. Those tribes appeared better dressed, with some European contact spoke a smattering of English and Spanish, and had learned to eat with a fork and knife.

Could the savage Fuegian change their life habits too? Darwin was doubtful. He thought that hundreds of years of living in this habitat had formed an instinct that could not change, a view reinforced when Jemmy a Fuegian native who had lived with Europeans was seen to have gone back to his native state. Perhaps, Darwin thought, differences between human populations were more deep than realized.

Much more of South America remained to be explored. At this time his interest lay primarily in geology, but questions about species extinction and fixity, and the nature of human differences in life habits and intellect, lingered on in his mind.

If you would like to read more about Darwin I will recommend Adrian Desmond and James Moore's fine biography, Darwin: The Life Of A Tormented Evolutionist.

Landscapes: Sunderdunga Valley Kumaon Himalaya

noreply@blogger.com (Suvrat Kher) — Tue, 26 Nov 2024 02:59:00 +0000

In mid November, I explored the Sunderdunga valley in the Kumaon region of Uttarakhand. It was a good rigorous walk through some extraordinarily beautiful landscapes. This area is better known for the famous Pindari Glacier trek. Kafni Glacier is another option for trekkers. All three routes begin at village Khati. The picture taken of the high ranges from nearby Dhakori shows the three glacial valleys.

And here are some more photos of the route with a brief commentary.

The entrance to Sunderdunga valley with the vigorous Sunderdunga river flowing through.

The first day walk to Jatoli village was through golden and green forests.

Village Jatoli in the mid November sun. We stayed there overnight at the Kumaon Mandal tourist guesthouse. They provide excellent clean accommodation.

About 4 km walk upstream from Jatoli the next day and the land cover changes abruptly. The forest is gone. There is no marked trail from here on and a walk over a rugged boulder strewn region begins.

We navigate our way over steeply dipping metamorphic rocks and scree cones.

Numerous rock falls make for tricky passages. You can spot my companions climbing their way up the steep slope.

After slogging for about 8 km through this terrain we arrive at Kathaliya, situated at about 10,500 feet ASL. We have climbed about 2500 feet from Jatoli to Kathaliya. A small trekkers shed has been constructed here. We stayed there for the next couple of days.

Next morning, ahead of Kathaliya camp, we encountered the full glory of Sunderdunga valley. Here, it is a occupied by a wide boulder strewn river bed with several small active channels. The earthy colors of rock and grass were in stunning contrast to the blue sky. A solitary shepherd's hut can been seen in the lower right.

Another view of the valley.

Boulder bed! The surrounding Greater Himalaya are made up of high grade metamorphic rocks. You can spot quartzo- feldspathic gneiss, amphibolite gneiss, mica schist and gneiss, and mica, garnet, and kyanite bearing schist and gneiss in the river bed. Quite a treat to walk along this metamorphic treasure!

Crossing the wider channels on rickety wooden bridges was fun!

Here we are near Maiktoli Top, a high vantage point. Jagdish Bisht, me, Ratan Singh Danu, Lucky, and Kapil. They made my trip safe, comfortable, and memorable.

Why I go to these places. A clear view of the bands of metamorphic rocks exposed along the spectacular cliff face of the Sunderdunga ridge!

Village Khati is such a pretty place.

The high bare peaks in the background speak of a worrying trend. Everyone I talked to told me that this trek would have been impossible a few years ago in mid November. The upper part of the valley and the rocky ridges would have been blanketed in a thick snow pack. This area still had not received a single snowfall when I left on 22nd November. The two or three big snowfalls of the year now occur mostly in January and February. The pastoral and agriculture economy depends on a healthy winter snow cover to rejuvenate the high meadows, and to replenish springs and streams.

My guide tells me that Sunderdunga valley is the tougher route amongst the three treks to the nearby glaciers. I am so glad I walked this valley!