Reconstruction of Late Quaternary climate, vegetation, fire and sediment provenance of Indo-Gangetic floodplains and its implication for the Paleolithic to Neolithic phases of the Indian subcontinent

Jha, Deepak Kumar (2021) Reconstruction of Late Quaternary climate, vegetation, fire and sediment provenance of Indo-Gangetic floodplains and its implication for the Paleolithic to Neolithic phases of the Indian subcontinent. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Deepak Kumar Jha (13IP028)) 13IP028.pdf - Submitted Version Restricted to Repository staff only Download (8MB)

Abstract

The ‘Quaternary Period’ is the fourth and the latest geological period that commenced at about 2.6 Ma. The Quaternary period is thought to be a crucial Geological period on the Earth because it has witnessed not only extraordinary changes in global climate but also recorded the appearance of genus Homo in the sedimentary record. During the Homo evolution, the emergence of diverse species and adaptation skills have eventually accumulated which includes upright walking, enlargement of the brain, the ability to craft stone tools, the inception of social behaviour, and reliance on stone and fire technology to alter the environment. The comprehensive evolution of genus Homo coincides with environmental change, such as arid, humid, and fluctuating climate over time. The questions that remain a topic of debates are 1. How did the environment shape the evolution of genus Homo? 2. How did changing environmental conditions helped in new adaptations? 3. How climate change controlled the origin and extinction of Homo species? 4. What was the role of climate in the emergence and domination of Homo sapiens over another genus Homo? These questions are still valid, and hence more comprehensive research is required to unravel the mysterious role of climate on the evolution of Homo species. Therefore, it is necessary to reconstruct the climate conditions during the Late Quaternary Period. In the Indian subcontinent, the dominant feature of the climate is monsoon which is a seasonal reversal of the winds. The moisture-laden winds from the Ocean flow towards land during summer and cause rainfall in most of the Indian subcontinent driven by the seasonal migration of the Intertropical Convergence Zone (ITCZ). The variability of monsoon severely affects the ecological balance and gross agricultural productivity in the Indian subcontinent. The understanding of monsoon variability requires a long-term assessment of rainfall records. The instrumental records of the Indian summer monsoon (ISM) are very much limited and hence, hindered our understanding of variability in rainfall over the Indian subcontinent. Given this, the paleoclimate reconstructions can provide a long-term database to understand the variability and its causal relationship with vegetation and landscape evolution during the Quaternary period. The thick sequence of Quaternary sediments deposited in the Indo-Gangetic plain after the formation of Himalaya. The Indo-Gangetic plain also plays a vital role in the archaeology of Indian subcontinent. A variety of stone tools found in the sedimentary deposits of the Quaternary period suggests that the tool-making prehistoric humans were living in the Indian subcontinent. The archaeological records suggest that the prehistoric humans lived mostly alongside lakes and river channels. The discovery of artefacts, stone tools, rock art paintings etc. made by prehistoric humans were recovered from deposits of the Late Quaternary period. Based on the study of excavated artefacts and their morphology, it has been suggested that the prehistoric humans of the Indian subcontinent were rich in cultures phase starting from the Lower Paleolithic to Neolithic. Those archaeological discoveries of artefacts suggest that the Late Quaternary as an age of the human cradle in the Indian subcontinent. Therefore, in this period, climatic conditions, vegetation compositions and landscape structure are the most critical factors in determining where prehistoric humans have made his settlement, performed hunting and how much time they have spent at a single location to understand the linkage between prehistoric humans and its environment. In the present study, the Late Quaternary sedimentary deposits from archaeological sites of Indo-Gangetic plain have been used to reconstruct the past climate, vegetation, fire-use and provenance of sediments. The study has been carried out in the Belan valley archaeological sites named Deoghat, Koldihwa, Mahagara, Chopani-Mando, Chillahia and Main Belan, which correspond to the Paleolithic to Neolithic phase. In addition, two sedimentary cores from Betwa (~25 ka) and Jhusi (~50 ka) were collected, which represented Peninsular and Himalayan dominated sediment source, respectively, in the modern landscape to decode the role of climate in the provenance of Quaternary deposits of Indo-Gangetic plain. For the first time, we have analysed oxygen and carbon isotopes in soil carbonates (SC; δ¹⁸Osc and δ¹³Csc) and hydrogen and carbon isotopes in n-alkane of paleosol (δDc₂₉ and δ¹³Cc₂₉) from chronologically well-constrained six archaeological sites to understand the climate-cultural relationship. Comparison among climatic data, prehistoric phase and the temporal variation in the number of archaeological sites suggest climate-driven shifts in population density during the Middle Paleolithic to Early Neolithic phase. The local factors such as a change in river course in the past and availability of resources in Belan valley are found to be responsible for the local scale migration of population during Upper Paleolithic to Neolithic phase. Further investigation from the Belan valley archaeological sites revealed macroscopic charcoal particles preserved in paleosol units collected from cultural layers corresponding to the Paleolithic to Neolithic phase of the Indian subcontinent. This offered a unique opportunity to understand the linkage between the prehistoric human environment and fire events. This is the first study to analyse macroscopic charcoal particles from 64 paleosols collected from six archaeological sites in the Belan valley to reconstruct fire activity. The result of this study suggests that the ⁸⁷Sr/⁸⁶Sr ratio and εNd values from both sedimentary cores represent the alternate amalgamation of sediments from the Himalayan and Peninsular region. The coupling of results with climate and vegetation data obtained from the same core suggests that the area dominated by ephemeral rivers received sediments from Peninsular region. In contrast, the area dominated by the Himalayan river sourced their sediment from Lesser Himalaya during the beginning of LGM. The primary reason for Lesser Himalaya sediment dominating at the beginning of LGM was a great extent of glacial cover over the Higher Himalaya. Further, as monsoon intensified during the Holocene epoch, the provenance change observed which suggests that the sediments were transported from the Peninsular area at the Betwa region. Conversely, Higher Himalayan rocks contributed a significant amount of sediments at the Jhusi during the Holocene. The high rainfall increased the sediment flux during the Holocene from the Higher Himalaya. A comparison with the available records of provenance change from different parts of the Indo-Gangetic plain demonstrates the role of a river system, climate and glaciation in the provenance of sediment deposits. Therefore, this study has a broader implication for understanding the evolution of Indo-Gangetic plain during the Late Quaternary. The present thesis work from the six archaeological sites and two sediment cores from the Indo-Gangetic plain form a foundation of multi-disciplinary research in the fields of archaeology, geology and biogeochemistry. This study provides a platform for future research on the climate-culture relationship, controlled use of fire by prehistoric humans and the evolution of Quaternary deposits from the Indian subcontinent.

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