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 palaeo-climate 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.

Evaluation of Neoproterozoic source rock potential in SE Pakistan and adjacent Bikaner–Nagaur Basin India

“…The n-alkanes distribution profile shows a higher abundance of even-carbon number n-alkanes than odd-carbon number n-alkanes. This suggests a reducing environment of organic matter deposition where even-carbon number n-alkanes were preferably preserved compared to odd-carbon number n-alkanes 46 . An exclusive abundance of lower carbon range alkanes ~ C 16 -C 20 in the WEGC suggests that marine organic matter dominates in the sediments 37,47 .…”

Paleoenvironmental Settings of the Soma Coal Basin (Turkey): Insights from Maceral Data, Biomarker, and Carbon Isotopic Composition

“…Nowadays, it has become important to reassess the vegetation community and paleoenvironmental–paleoclimatic conditions in peatlands through extensive research with biomarker analysis from extractable organic matter (EOM) extracted from coals. − Since the coal formation process can be influenced by many natural factors, it should be supported by other data in addition to organic geochemical parameters. Reconstruction of paleoclimate based on n -alkane distributions has been widely applied in peat deposits. , However, these studies were limited to lignite deposits. , Mathews et al determined the paleoclimatic characteristics of the Early Paleogene Barsingsar lignite-bearing Sequence of Rajasthan based on stable carbon isotope data along with biomarker distributions. This study aims to evaluate and compare the organic matter sources and depositional environment characteristics of the upper, middle, and lower coal seams in the Soma-Manisa coal basin in detail and to estimate the hydrocarbon potential in these three seams.…”

“… 26 , 27 However, these studies were limited to lignite deposits. 21 , 28 Mathews et al 21 determined the paleoclimatic characteristics of the Early Paleogene Barsingsar lignite-bearing Sequence of Rajasthan based on stable carbon isotope data along with biomarker distributions. This study aims to evaluate and compare the organic matter sources and depositional environment characteristics of the upper, middle, and lower coal seams in the Soma-Manisa coal basin in detail and to estimate the hydrocarbon potential in these three seams.…”

Paleoenvironmental, paleovegetational, and paleoclimatic changes during Paleogene lignite formation in Rajasthan, India

“…Previously, numerous techniques, including organic petrology, FT-IR, XRF, XRD, palynology, and organic geochemistry, have been used to study the chemical and structural characteristics of Indian lignite deposits to know the paleodepositional conditions and source rock characteristics (Kumar et al 2020;Singh and Kumar 2020;Mathews et al 2018Mathews et al , 2019Kumar 2017, 2018;Singh et al 2010Singh et al , 2012bSingh et al , 2015Singh et al , 2016aSingh et al , b, c, d, e, 2017aSingh et al , b, c, d, e, f, g, 2018Singh et al , 2019. Carbon isotope and NMR technique have less (Mathews et al 2020) been used to study the chemical and structural characteristics of Indian lignite deposits. This work utilizes the macroscopic, petrographic, geochemical characteristics, 13C NMR, and δ 13 C values to study the chemical and structural characteristics of lignite and reconstruct paleodepositional conditions palaeovegetation, and paleoclimatic changes during peat formation.…”