Chapter 19 - Palaeoclimatic imprint on fluvial sediments: examples from Indian Phanerozoic successions

Abstract

Fluvial systems are highly sensitive to changes in climatic conditions. Hence, fluvial sedimentary records provide important hints on palaeoclimatic ambit. Some commonly practiced potential climatic resources in connection to fluvial realm, such as paleosols, floodplain sediments, climate-sensitive lithologies (coal, evaporite, eolianite), and palaeoecological components (fossil plants and trace fossils) have been put forward for discussion; along with their methods of application, both qualitative and quantitative, off-target in a brief way. Four Phanerozoic sedimentary intervals from India have been chosen to exemplify how to decode palaeoclimatic signals from fluviatile deposits: Early Cretaceous (1) Bhuj Formation, Kutch Basin in western India and (2) Basal Siliciclastic Formation, Cauvery Basin in southern India, (3) Mio–Pliocene Siwalik Group, Darjeeling, Sub-Himalaya in north-eastern India, and (4) Late Permian Raniganj Formation with Early Triassic Panchet Formation in Raniganj Basin, eastern India. Palaeoclimatic investigation on riverine palaeosols of Bhuj Formation (Kutch Basin) estimates mean annual precipitation (MAP) and mean annual temperature (MAT) yielding values of 417-1381 mm/year and average 12°C, respectively, with moderate to high soil maturity. Comparable results obtained from Basal Siliclastic Formation (Cauvery Basin) showing 844-1060 mm/year (MAP) and average 12.5°C (MAT) with moderate degree of weathering. Floodplain sediments of both the formations bear flora besides coal stringers, petrified wood fragments, rhizoconcretions, rootlets, and trace fossils within estuarine mudflat of the Bhuj Formation. An overall apparently warm temperate humid palaeoclimate is implied in the case of both. The present study also strives to concentrate over the monsoonal intensification and transformation from C3 to C4 vegetation along the entire 2000 km-long exposure belt of the Mio–Pliocene of Siwalik basin. The geochemical characteristics from foreland molasse deposits taken into cognizance to check the spatial trends in climate change has largely been meted out through the Darjeeling Sub-Himalaya, West Bengal. The spatial variation in precipitation rate and temperature along with 13C enrichment from west to east attests the modern trend and also elicit the present Himalayan Mountain Belt configuration. Predominantly fluvial Raniganj Formation (with abundance of coal) and Panchet Formation (devoid of coal) encompassing the Permo-Triassic transition in Raniganj Basin, West Bengal, indicate significant variations in palaeoclimate reflected in their lithology and bio assemblages.