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Carbon isotopic composition of fossil leaves from the early cretaceous sediments of Western India

Chakraborty, S and Jana, BN and Bhattacharya, SK and Robertson, I (2011) Carbon isotopic composition of fossil leaves from the early cretaceous sediments of Western India. Journal of Earth System Science, 120 (4). pp. 703-711.

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Abstract

Stable carbon isotope analysis of fossil leaves from the Bhuj Formation, western India was carried out to infer the prevailing environmental conditions. Compression fossil leaves such as Pachypteris indica, Otozamite kachchhensis, Brachyphyllum royii and Dictyozamites sp. were recovered from three sedimentary successions of the Bhuj Formation, Early Cretaceous in age. A chronology was established based on faunal assemblage and palyno-stratigraphy and further constrained by carbon isotope stratigraphy. The three sampling sites were the Karawadi river bank near Dharesi; the Chawad river bank near Mathal; and the Pur river section near Trambau village in Gujarat. The Dharesi sample was also analyzed to investigate intra-leaf δ13C variability. The mean δ13C of the leaf was 24.6 ± 0.4 which implied negligible systematic change along the leaf axis. The Mathal sample was fragmented in nature and showed considerable variation in carbon isotopic composition. The Trambau sample considered to be the oldest, dating to the middle of Aptian (ca. 116 Ma), shows the most depleted value in δ13C among all of them. The overall δ13C trend ranging from mid Aptian (ca. 116 Ma) to early Albian (ca. 110 Ma) shows a progressive increase in δ13C from 26.8 to 20.5. Based on these measurements the carbon isotopic composition of atmospheric carbon dioxide of the Aptian-Albian period is estimated to be between 7.4 and 1.7. The ratio of the partial pressure of carbon dioxide in leaf to that of the ambient atmosphere calculated based on a model is estimated to be similar to that of the modern plants. This indicates that the Early-Cretaceous plants adapted to the prevailing high carbon dioxide regime by increasing their photosynthetic uptake.

Item Type: Article
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Uncontrolled Keywords: Albian; Aptian; atmospheric chemistry; biostratigraphy; carbon dioxide; carbon isotope; chemostratigraphy; Cretaceous; fossil; isotopic analysis; isotopic composition; leaf; paleoatmosphere; paleoecology; paleoenvironment; palynology; partial pressure; photosynthesis; sedimentary sequence; stable isotope, Gujarat; India; Kutch, Brachyphyllum; Pachypteris
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 08 Aug 2014 10:37
Last Modified: 08 Aug 2014 10:37
URI: http://moeseprints.incois.gov.in/id/eprint/697

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