Petrographical and geochemical constraints on carbonate diagenesis in an epeiric platform deposit: Late Cretaceous Bagh
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ORIGINAL ARTICLE
Petrographical and geochemical constraints on carbonate diagenesis in an epeiric platform deposit: Late Cretaceous Bagh Group in central India Dhiren K. Ruidas1 · Fotini A. Pomoni‑Papaioannou2 · Santanu Banerjee1 · Tapas Kumar Gangopadhyay3 Accepted: 10 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A combined facies, petrography and isotope geochemistry reveal an extensive pedogenic alteration of platform carbonate deposits of the Upper Cretaceous Bagh Group in the western Narmada basin in central India. The highly fossiliferous carbonate sequence of the Bagh Group consists of two formations, the Nodular Limestone at the base, and the Bryozoan Limestone Formation at top. The Nodular Limestone Formation comprises primarily of mudstone and wackestone, with relics of bioclasts such as gastropods, echinoderms, molluscs, forams and calcispheres, reflecting a low-energy supratidal to upper intertidal environment of deposition. Prolonged pedogenesis leads to pervasive micritization, brecciation, desiccation and recrystallization. The overlying Bryozoan Limestone, dominated by packstone and planar laminated rudstone with bryozoans, gastropods, echinoderms/echinoid spines, and molluscs, indicates deposition within the lower intertidal environment with moderately high-energy conditions. Abundant meniscus cement and biomolds suggest meteoric vadose diagenetic modification, whereas, intense secondary micritization of sediments indicates prolonged calichification. The δ 13C and δ18O ratios of both Nodular Limestone and Bryozoan Limestone formations are depleted than the normal marine values, indicating an extensive diagenetic resetting of the carbonates. While the meteoric cement is depleted in both δ13C and δ18O ratio, the burial cement shows a decrease of δ18O at constant δ13C. The pedogenetic horizons within the Bagh carbonates bear subtle evidence of subaerial exposures within the overall transgressive Bagh Group. A glauconite bed at the upper part of the Bryozoan Limestone Formation marks the top part of the transgressive deposit. Keywords Bagh group · Pedogenesis · Stable isotopes · Meteoric diagenesis · Cathodoluminescence · Late Cretaceous · Epeiric platform Abbreviation VPDB Vienna-Pee Dee Belemnite
* Santanu Banerjee [email protected] 1
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
2
Faculty of Geology and Geoenvironment, School of Science, National and Kapodistrian University of Athens (NKUA), Athens University Campus, 157 84 Athens, Greece
3
Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India
Introduction A significant interval of the Cretaceous Period corresponds to expansive epeiric seas that formed vast carbonate platforms (Tucker and Wright 1990; Sanders 1998; Gómez-Gras and Alonso-Zarza 2003; Coimbra et al. 2016, 2017; Wilmsen et al. 2018). Shallow water condition with apparently restricted water circulation is characteristic of epeiric seas. The epeiri
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