Wednesday, March 25, 2015

Volcanism And The Demise Of Neanderthals

In addition to the many proposed reasons, something more to think about:

From Geology (early edition)-

Campanian Ignimbrite volcanism, climate, and the final decline of the Neanderthals - Benjamin A. Black, Ryan R. Neely, and Michael Manga

The eruption of the Campanian Ignimbrite at ca. 40 ka coincided with the final decline of Neanderthals in Europe. Environmental stress associated with the eruption of the Campanian Ignimbrite has been invoked as a potential driver for this extinction as well as broader upheaval in Paleolithic societies. To test the climatic importance of the Campanian eruption, we used a three-dimensional sectional aerosol model to simulate the global aerosol cloud after release of 50 Tg and 200 Tg SO2. We coupled aerosol properties to a comprehensive earth system model under last glacial conditions. We find that peak cooling and acid deposition lasted one to two years and that the most intense cooling sidestepped hominin population centers in Western Europe. We conclude that the environmental effects of the Campanian Ignimbrite eruption alone were insufficient to explain the ultimate demise of Neanderthals in Europe. Nonetheless, significant volcanic cooling during the years immediately following the eruption could have impacted the viability of already precarious populations and influenced many aspects of daily life for Neanderthals and anatomically modern humans.

Widely varying climatic conditions and resource availability may have hit Neanderthals more than "modern" humans. A number of reasons are given including the ability of "modern" humans to set up long distance networks facilitating exchange of technology and ideas.... Off course some would argue that the Neanderthals  never really became extinct. Their genetic legacy lives on in us. There is no doubt that interbreeding between the two human populations means that Neanderthal genes are with us today, but certainly a way of life, a particular morphology, social mores and perhaps a unique language (s) did disappear.

Tuesday, March 24, 2015

Field Photo: A Bend In A Himalayan River

I took this picture of a meander and a point bar deposit on the road from Munsiyari to Bageshwar along a section of the Sarayu river traversing a section of the Lesser Himalayas. It shows the classic meander landform of cut erosion along the outer bank  and deposition along the inner bank. Land pressure is high in the Himalayas too and the point bar deposit has been cultivated.


Another view of the meander and the point bar deposit.


The cultivated portion of the point bar seems at a slightly higher elevation than the present river channel and I think it indicates that the river has incised a little leaving an older point bar stranded. A younger point bar is developing in front of the cultivated portion made up of gravelly sediments.

Thursday, March 19, 2015

Field Photos: Landscapes And People Goriganga Valley Kumaon Himalayas

Staggering!... is the word that comes to mind with view of sheer rock faces like this one.


The northerly dipping rocks are not sedimentary, but are amphibolite and higher grade metamorphic rocks of the Greater Himalayan Crystalline series (some workers call it the High Himalayan Crystalline series) which make up the hanging wall of the Main Central  Thrust. I hiked through the lower portions of the thrust sheet a couple of weeks ago. The main rock types I encountered were augen gniess, mylonites, biotite schists, quarto-feldspathic gneisses. There is more to the mineralogy and petrology of the GHC. Minerals appear not randomly but in a sequence. I will be writing about that in later post after I've got my head wrapped around some difficult concepts  in metamorphic petrology and Himalayan thrust sheet evolution.

This post is a ramble through the beautiful countryside I hiked through. .. Landscapes and the people of the Goriganga river valley north of Munisyari-

A view from Munisyari looking east- It rained and snowed the first couple of days delaying our trek.


Crossing a Himalayan stream


A house in Lilam village. This village is one of the resting post on the hike towards Milam glacier

 

The children of Lilam village


Hiking uphill from the Goriganga river


Hot chai with two Kumaoni mountain folks- the cheerful crackle of wood fire and the hot sugary tea is just very refreshing


Conversations with an elderly shepherd


The picture postcard Bui Village


The colorful people of Bui Village celebrating Holi, a spring festival. Local booze flowed freely as did our spirits!


It took us four days to reach this weekend getaway at Paton village

 
A view from the Paton village temple
 

 Village Ucchaiti where we spent one night


Hikers break- much needed fluids and trail mix!


A house in the beautiful lush village of Bagankhot


Goriganga!  millennia after millennia.. all those boulders.. all those cobbles, pebbles, gravel... all that sand, mud and clay.. that you wash away... has made Bangladesh


I wish we could have stayed longer. Leaving the Himalayas is always depressing, but next year I am planning another trek, hopefully one that will take me higher up in the Main Central Thrust. Keeping my fingers crossed...

Below: Interactive Google Map of the Goriganga river valley north of Munsiyari-



Wednesday, February 25, 2015

Gone Hiking! Main Central Thrust Goriganga Valley Kumaon Himalayas

At last!

I've been waiting for this for almost 2 years. Friday, I will  be departing for the little town of Munsiyari in the Kumaon Himalayas of Uttarakhand to begin an eight day trek northwards towards the Milam and Rilam glaciers.

Just take a look!


Geology?

The Munsiyari Thrust named after the town of Munsiyari is the lower bounding fault  of the Main Central Thrust Zone along which the High Himalayan Crystalline (HHC) rock sequences have been extruded over the Lesser Himalayan Metamorphic Sequence. The HHC is considered to be the Proterozoic leading edge of the Indian plate which on collision with Asia was broken up into south directed thrust sheets. The HHC is overlain by the Tethyan Sedimentary Series (TSS), a sequence of Paleozoic to Eocene marine sediments. This cover sequence has been detached during Miocene orogeny from the HHC along the Southern Tibetan Detachment Zone. The initial sense of motion along this zone may be a north directed normal sense motion, but sections have been reactivated and thrust southwards or sideways. Its crazy out there!

I hope to see as I  walk northwards from Munsiyari a mostly medium  to high grade metamorphic terrain of the HHC with the grade of metamorphism increasing northwards. Intruding this sequence are Miocene granitic bodies. I hope to see a few of those too. And at the northern limits of the trek in the Milam and Rilam glacier area maybe I will be close enough to glimpse the TSS.

That's all for  now. I am so excited! I'll be posting pictures when I get back and hopefully fill the above images with some geology too.. See you in mid March.

Monday, February 23, 2015

Human Evolution- Multiple Opportunities For Migrating "Out Of Africa"

There really seems to be a connection between orbital mechanics and human behavior, though not in a way astrologers think it to be!

From the early online February issue of Geology-

The dispersal of human populations out of Africa into Arabia was most likely linked to episodes of climatic amelioration, when increased monsoon rainfall led to the activation of drainage systems, improved freshwater availability, and the development of regional vegetation. Here we present the first dated terrestrial record from southeast Arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and interglacial periods. Findings from extensive alluvial fan deposits indicate that drainage system activation occurred during Marine Isotope Stage (MIS) 6 (ca. 160–150 ka), MIS 5 (ca. 130–75 ka), and during early MIS 3 (ca. 55 ka). The development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima, suggesting that humid periods in Arabia were not confined to eccentricity-paced deglaciations, and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of Africa during the late Pleistocene.

One popular compact version of the dispersal of Homo sapiens from Africa was that ecological opportunities and evolution of behavioral sophistication likely coincided beginning around 60,000 years ago or so. Human dispersal from that point on colonized the continents, replacing older human populations (descendants of Homo erectus).

This work provides evidence that it would have been possible during earlier times for modern humans to exploit opportunities in Arabia. Indeed there are tool assemblages in Arabia which are more than 100,000 years old and are very similar to the Nubian Middle Stone Age style found in Sudan suggesting a link between those peoples.

Take a look at the opportune time periods. They occur at around 20,000 year intervals. That aligns with climatic changes associated with the precessional  orbital cycles of 23,000 years frequency. And what are Marine Isotope Stages? The oxygen isotope ratio (O18/O16)  in sea water fluctuates in response to glacial buildup at the poles and to glacial melting and influx of more fresh water into the oceans. During glacial buildup more of the lighter isotope gets trapped in ice (since the lighter isotopes preferentially evaporates and falls as snow in the polar regions) and sea water becomes correspondingly "heavier". During glacial melting, influx of fresh water contributes O16 and sea water becomes "lighter". When  marine organisms like foraminifera  build their calcium carbonate (CaCO3) skeletons, they incorporate differing amounts of the oxygen isotopes in different climatic regimes (glacial versus non glacial). So, their skeletal isotope composition, which geologists measure, becomes a proxy for sea water composition.

If Arabia was colonized much earlier then did Homo sapiens enter India earlier (with a coastal route from Arabia onwards to India) than the unequivocal evidence around 45,000 years or so? Or China and other parts of Asia?  There is quite a controversy about this question. A team led by Michael Petraglia at the University of Oxford, UK think they have evidence of modern human presence in India much before 75,000 years ago based on tool assemblages found below a datable volcanic ash layer attributable to the Toba eruption. One problem has been that the skeletal record of hominins in India is very poor. Scientists have had to rely almost exclusively on the tool record and comparing particular tool assemblages across continents and assigning them as a handiwork of specific human species can be problematic.