page_title: Paleogeography of the India–Asia collision system
section_title: Climatic proxies
hierarchical_section_title: Paleogeography of the India–Asia collision system / Paleogeography and paleoclimate / Directions for future studies / Climatic proxies
caption_attribution_description: English: Cross section of a C4 plant. Specifically of a maize leaf. Vascular bundles shown. Drawing based on microscopic images courtesy of Cambridge University Plant Sciences Department.
context_page_description: The paleogeography of the India–Asia collision system is the reconstructed geological and geomorphological evolution within the collision zone of the Himalayan orogenic belt. The continental collision between the Indian and Eurasian plate is one of the world's most renowned and most studied convergent systems. However, many mechanisms remain controversial. Some of the highly debated issues include the onset timing of continental collision, the time at which the Tibetan plateau reached its present elevation and how tectonic processes interacted with other geological mechanisms. These mechanisms are crucial for the understanding of Mesozoic and Cenezoic tectonic evolution, paleoclimate and paleontology, such as the interaction between the Himalayas orogenic growth and the Asian monsoon system, as well as the dispersal and speciation of fauna. Various hypotheses have been put forward to explain how the paleogeography of the collision system could have developed. Important ideas include the synchronous collision hypothesis, the Lhasa-plano hypothesis and the southward draining of major river systems.
context_section_description: Quaternary climatic reconstructions of the Tibetan Plateau area are mostly based on pollen analysis, while Mesozoic climatic reconstructions are done by analyzing benthic foraminifera from paleo-oceanic basins. Little study has focused on the Tertiary period, at which the South Asian monsoon is thought to have initiated. Further studies on Tertiary carbon isotope composition of paleosols could be carried out to examine the shift in C3/ C4 vegetation ratio. C3 and C4 plants practice different carbon fixation mechanism. C4 fixation is more water-efficient and therefore favours plant adaptation to extreme climatic conditions. Therefore, C4 plants are generally more abundant in cold and arid-temperate regions. Carbon isotopes in paleosols are remains of dead plants and therefore accurately reflects climatic regime shifts. Phylogenetic reconstructions of animal taxa is also useful as climate change may promote speciation or trigger extinction.
caption: Cross section of a maize leaf, a C4 plant. Kranz anatomy (rings of cells) shown. Drawing based on microscopic images courtesy of Cambridge University Plant Sciences Department.
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