Early Palaeogene Climate Variability Based on n-alkane and Stable Carbon Isotopic Composition Evidenced from the Barsingsar Lignite-bearing Sequence of Rajasthan

Abstract

The assessment of variations and the reconstruction of palaeoclimate, based on the distribution of n-alkanes and stable carbon isotope data, during early Palaeogene have been made on the Barsingsar lignite-bearing sequence associated with Palana Formation (Bikaner-Nagaur basin). The distribution pattern of various n-alkanes and the derived indices/ratios have widely been used as palaeoclimate indicators in several depositional realms. The distribution of n-alkanes in the studied sequence varies from C13 to C34. The values of calculated n-alkane parameters range from 26.20–28.39 (aliphatic chain length (ACL) index); 0.32–7.21 (low-to-higher molecular weight (L/H) ratio); 0.42–0.85 (Proxy wax (Pwax)); 0.20–0.67 (Proxy aqueous (Paq)); 0.28–5.22 (terrigenous/aquatic ratio (TAR)); 0.16–0.79 (C23/C29 ratio); 1.14–6.31 (C27/C31 ratio) and 1.47–7.02 (C29/C31 ratio). The δ13C varies from −24.8 to −26.1‰ and the TOC varies from 9.6 to 69.5 wt.%. All these variations indicate the changes in palaeoclimate from dry and warm to cool and wet conditions during the deposition of this lignite-bearing sequence. Further, it is also suggested that the climatic condition was cooler than that of the Palaeocene-Eocene thermal maximum (PETM) event.