Assessment of plant derived alkanes and GDGTs as a paleoclimate proxy in the floodplain settings

Thakur, Subhash (2023) Assessment of plant derived alkanes and GDGTs as a paleoclimate proxy in the floodplain settings. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Subhash Thakur (18MS161)) Thesis_18MS161.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

The long chain n alkanes (n 33) and brGDGTs (n 26) are measured in a coring site near Sahibganj located on the Ganga River Basin floodplain. The analysis of long chain n alkanes shows an odd over even predominance, but we also found a loss of odd over even predominance that may be because of microbial activity in the floodplain settings. We have analyzed the avera ge chain length (carbon preference index (and concentration of n alkanes for soil samples. The relative abundance of long chain n alkanes is higher at C₍₂₇₋₃₅₎ and most of the average chain length is ranging from 27-31 along with the CPI values being more than 1. This suggests that odd over even predominance of long chain n alkanes the source of long chain n alkanes is mainly derived from terrestrial land plants. Furthermore, we have analyzed different indices (CBT, CBT₅Me, MBT', MBT'₅Me etc.) of brGDGTs to establish past climatic conditions using CBT and CBT 5Me indices we have calculated the soil pH and using MBT and MBT₅Me we have calculated the mean annual temperature MAT). The calculated pH values for soil samples are ranging from 7.13 7.71 and the measured pH value is ranging from 7.4 8.4 which indicates that the soil was slightly basic. The mean annual air temperature is ranging from 15 20°C which means the environment was relatively warmer.

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