Sunday, November 19, 2017

Geology And Homo Sapiens Habitats Pleistocene Indian Subcontinent

Came across an interesting passage from this review paper:

Environments and Cultural Change in the Indian Subcontinent: Implications for the Dispersal of Homo sapiens in the Late Pleistocene - by James Blinkhorn and Michael D. Petraglia

Yet beyond relief, the geological structure of the Indian subcontinent plays another important role in patterns of habitability in the region. The analysis of the structure of geological basins within the Indian subcontinent led Korisettar (2007) to the conclusion that the Purana basins exerted a strong influence on hominin dispersals and occupation history. Although direct precipitation within the Purana basins is lower than other regions of the subcontinent, perennial supplies of freshwater are available because of spring activity from aquifers that deliver water resources from regions that receivemuch higher monsoonal precipitation.As a result of reliable water resources and abundant raw materials for stone tool manufacture, these geological basins are thought to have acted as refugia not only for hominin populations but also for varied flora and fauna (Korisettar 2007).

The importance of such Purana basins for providing refugia is well exemplified by the recent study of fauna from the Billasurgum caves, located within the Cuddapah Basin. Here, excavations revealed the first stratified sequence to document patterns of faunal occupation spanning the late Middle Pleistocene to Late Pleistocene (Roberts et al. 2014). This study illustrated the long-term continuity of large-bodied fauna within South Asia with only a single taxon of twenty-four identified as having gone extinct across the subcontinent (Roberts et al. 2014).

The "Purana" basins are Proterozoic in age. They are scattered all over Peninsular India. A common lithology is silica cemented sandstone or quartzite which forms prominent hill ranges, ridges and escarpments with ledges, overhangs and caves. These hard quartzites would have been one source of raw material for stone tools.  The rocks are also fractured and networks of pervasive cracks allow the storage and movement of groundwater.

The map (from a different paper) below shows the distribution of Middle Paleolithic sites (red dots) in India, Arabia and Eastern Africa. I have outlined in black (very approximate!) the location of three Purana basins. V stands for Vindhyan, C for Cuddapah and B&K for Bhima and Kaladgi.

 Modified from Huw S. Groucutt 2015

This paper have lots of information about climate change, ecology and stone tool record found in India. The authors discuss the Late Acheulean (130k - 100 K) ,  Middle  Paleolithic (94k - 34 K) and the Late Paleolithic ( < 45 K). These terms refer to particular styles of stone tool manufacture.

The India skeletal fossil record is very poor. However, based on comparisons with Middle Paleolithic of Africa and Homo sapiens fossils and tool associations in SE Asia and Australia, the authors are in favor of a wave of  Homo sapiens migrating into India as early or perhaps a little earlier than 100 k ago. This was followed by a later wave around 50 k years ago.  Do changes in cultural style and tool use point to changing populations.. with an intrusive population replacing an earlier one?.. that is an intriguing question. Some recent genetic work suggests that people from these earlier migrations died out without leaving a genetic legacy in us. All non African humans have descended from migrants who left Africa between 50K-80K years ago.  I had summarized these results in an earlier post on human population continuity in India.

See also other papers from this special volume of Current Anthropology on Human Colonization of Asia In the Late Pleistocene

Open Access.

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