Article

Lithostratigraphy of the Paleogene Deccan Intra-, Intertrappeans of the Saurashtra, Western India and their Prevalence in Large Igneous Provinces

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Abstract

The periphery of the Deccan Volcanic Province (DVP) of India comprises sedimentary succession deposited during the waning phase of volcanism across the Cretaceous-Paleogene boundary which preserves the continental biota. The Saurashtra Peninsula, a part of the Saurashtra-Kachchh sub-province, exposes thick intertrappean sedimentary successions, systematically described to understand the stratigraphic framework with respect to the lava flows and their geographic distinctness. The thickness of the exposed sections is measured, and contact and continuities are marked, revealing two different, small geographically isolated but adjacent, coeval basins, named the Ninama Basin and Chotila Basin, initially comprising fine grain sediment, followed by thick conspicuous limestone and chert deposits respectively. Formal lithostratigraphic unit names are proposed for both basins: Ninama Basin comprises lithic arenite, fossiliferous limestone, bedded siltstone, mudstone and claystone, and is divided into Sukhbhadar Formation and Ninama Limestone. Chotila Basin comprises calcareous sandstone, bedded siltstone, silty shale and mudstone, claystone and chert divided into Rangpar Formation, Chotila Chert, and Bamanbor Formation. Lithology and palynofossil evidence suggest restricted continental environments with varying salinities during the Paleogene.

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... Moreover, the presence of palynofloras such as Longapertites retipilatus (Mandal & Kumar, 1997), Matanomadhiasulcites maximus, Rhombipollis geniculatus, Yeguapollis sp and Lakiapollis ovatus from the Ninama intertrappeans suggest an Early Eocene age (Plate 1, Figures 1-5). Bivalve-bearing shaly sandstone of the Bamanbor Formation ( Figure 1) (Patel & Shah, 2023) consists of a variety of palynofossils, including pollens like Florschuetzia rajpardiensis, Monocolpopollenites plicatus, Meliapollis ramanujamii and Rhoipites kutchensis, and fungal spores like Polycellaesporonites psilatus and P. saxenae (Plate 1, Figures 6-11). Based on the presence of marker pollen M. ramanujamii (Khanolkar & Sharma, 2019;Saxena & Tripathi, 2012) and F. rajpardiensis (Samant & Phadtare, 1997) an Early Eocene age is assigned. ...
... The intertrappean rocks are exposed on the Chotila-Rajkot Highway (15 km west towards the Rajkot) near Bamanbor village, Gujarat State, India (Figure 1a). The Bamanbor Road section (22° 25' 38" N, 71° 03' 23" E) of Chotila Basin has yielded relatively well-preserved fossils of bivalve shells (Figure 1a) (Patel & Shah, 2023). The fossiliferous stratum is dark grey to rusty brown-coloured shaly sandstone and comprises thinly bedded, alternating silty shale and/or clay shale layers, capped by Deccan Trap ( Figure 1b). ...
... In total, 30 cm thick fine-grained sandy layers (with overall bed thickness of 3-4 m) are common which contain >50% of fine-grained sand-sized particles (Figure 1c-e), dominated by quartz and lithic fragments of chert, approximated based on petrographic analysis (Figure 1f-g). This layer contains moderately abundant bivalve shells along with gastropods ( Figure 1c-e) (Patel & Shah, 2023). ...
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The Cretaceous-Palaeogene intertrappean deposits of the Deccan Volcanic Province of India comprise vertebrate, invertebrate and plant fossils of the dominantly continental realm. A 3–4 m thick shaly-sandstone lacustrine intertrappean sequence of Early Palaeogene (Palaeocene-Early Eocene) Bamanbor Formation, Chotila Basin (Saurashtra province, Gujarat State, western India) has yielded a collection of molluscans (bivalve and few gastropods) fauna. High-resolution digital photography and radiography of the recovered bivalves allowed us to gain detailed inferences on shell morphology. In a taxonomical context, we herein propose a new unionid molluscan superfamily Deccanoidea nov. represented by a single new family Deccanoidae nov. that includes two new subfamilies, that is, Deccanoinae nov. (represented by two new genera Deccanoida gen. nov. [including four new species: D. conrugis sp. nov., D. aleta sp. nov., and D. costaria sp. nov.] and Bamanboria gen. nov. [including one new species Bamanboria oblongis gen. et sp. nov.] and Chotiloinae nov. [represented by one new genus Chotilia gen. nov. and three new species: Chotilia trappeansis sp. nov., C. tuberculata sp. nov. and C. deccanensis sp. nov.]). Inorganic geochemistry of host (unionid-yielding) lithologies reveals oxic-freshwater conditions, humid-climate and moderate rainfall. The data on historical biogeography reveals that the Indian subcontinent hosted unionids during the late Cretaceous; however, the presence of new (at family/generic level) unionid fauna during the Early Palaeogene (Palaeocene-Early Eocene) in India indicates changes in the geographic position and ecologic condition linked to northward drift and lava outpouring, respectively. A disjunct distribution of unionid fauna in the erstwhile Gondwanan continents and insular India during the Cretaceous-Palaeogene interval can be explained in terms of both vicariance and dispersal.
... The Saurashtra-Kachchh sub-province of the Deccan Volcanic Province (Mittal et al. 2021) exposes exemplary intra-and intertrappean sediments in Anjar (Khadkikar et al. 1999;Bajpai and Prasad 2000;Parthasarathy et al. 2008;Srivastava et al. 2017), Lakshmipur (Samant and Bajpai 2005;Bajpai et al. 2013), Ninama (Borkar 1973(Borkar , 1986Chiplonkar and Badve 1976;Samant et al. 2014;Patel and Shah 2023), Chotila-Bamanbor (Borkar 1973(Borkar , 1975(Borkar , 1984Arratia et al. 2004;Samant et al. 2014;Patel and Shah 2023), spanning from Maastrichtian to Eocene (Shukla et al. 2001;Bajpai et al. 2013;Samant et al. 2014;Srivastava et al. 2017). ...
... The Saurashtra-Kachchh sub-province of the Deccan Volcanic Province (Mittal et al. 2021) exposes exemplary intra-and intertrappean sediments in Anjar (Khadkikar et al. 1999;Bajpai and Prasad 2000;Parthasarathy et al. 2008;Srivastava et al. 2017), Lakshmipur (Samant and Bajpai 2005;Bajpai et al. 2013), Ninama (Borkar 1973(Borkar , 1986Chiplonkar and Badve 1976;Samant et al. 2014;Patel and Shah 2023), Chotila-Bamanbor (Borkar 1973(Borkar , 1975(Borkar , 1984Arratia et al. 2004;Samant et al. 2014;Patel and Shah 2023), spanning from Maastrichtian to Eocene (Shukla et al. 2001;Bajpai et al. 2013;Samant et al. 2014;Srivastava et al. 2017). ...
... Samant et al. (2014) studied the palynology and clay mineralogy of Ninama intertrappean, assigned Paleocene age based on the palynoassemblage, and suggested an arid climate for the deposition. Patel and Shah (2023) have made a sole attempt to describe the Saurashtra intertrappeans. They have identiBed two different basins, Ninama and Chotila, further divided into several lithostratigraphic units: Sukhbhadar Formation and Ninama Limestone; Rangpar Formation, Chotila Chert and Bamanbor Formation, respectively. ...
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Palynological studies of Deccan volcanic associated sediments of the Sahyadri Group of Nand-Dongargaon basin of Maharashtra, Amarkantak Group of Chhindwara and unclassified Deccan Trap sequences of Saurashtra show the presence of Aquilapollenites pollen. The overall data on this genus from the Indian Late Cretaceous-Early Paleocene indicates that the genus was widely distributed during the Late Cretaceous. A notable decline in abundance in the Early Paleocene may be related to the climatic and environmental changes brought about by the Deccan volcanism.
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We describe here the ornithoid eggshell fragments from the Deccan intertrappean beds (Late Cretaceous) near Anjar, district Kachchh, Gujarat. The find assumes palaeobiogeographic significance as morphologically similar eggshells are known from the Late Cretaceous Nemegt Formation of Mongolia. Taxonomic affinities (dinosaurian/avian) of these eggshells cannot be established at present.