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<p>An integrated sedimentological and ichnological analysis of the mixed siliciclastic-carbonate sediments of the Middle Jurassic Bada Bag Member of the Jaisalmer Formation indicates deposition in a subtidal to intertidal paleoenvironment. Four distinct facies were identified – (i) fossiliferous silty limestone, (ii) tidally influenced sandstone–mudstone heteroliths, (iii) lensoidal conglomerate, and (iv) cross-stratified silty limestone. The vertical repetition of the facies types reflect systematic change in hydrodynamic conditions. The succession contains diverse ichnoassemblages, including <i>Asteriacites stelliformis</i>, <i>Cochlichnus</i> isp<i>.</i>, <i>Palaeophycus tubularis</i>, <i>Taenidium</i> isp<i>.</i>, and <i>Thalassinoides</i> isp., representing varied ethological behaviours of invertebrate trace-makers. The ichnogenus <i>Asteriacites</i> von Schlotheim, 1820 is identified within the silty limestone facies and, based on morphological and morphometric parameters, is assigned to ichnospecies <i>Asteriacites stelliformis</i> (Miller and Dyer 1878; Osgood 1970). Varied ecological parameters controlled the ethological responses of the organisms, influencing the trace fossil distribution and assemblages, resulting in the development of <i>Cruziana ichnofacies</i>. A gradual increase in tidal influence and a decline in detrital sediment input toward the upper part of the succession corresponds with the dominance of deposit-feeding ichnotaxa in fine-grained sediments. Overall, the sedimentary architecture and ichnological record reflect alternating low to moderate-energy subtidal and high-energy intertidal conditions during the deposition of the Middle Jurassic Bada Bag Member.</p>

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Sedimentological and ichnological controls on mixed siliciclastic-carbonate sediments of the Middle Jurassic Bada Bag Member, Jaisalmer Formation, Rajasthan, India

  • 期刊论文

  • 发表日期：

    2025年8月22日

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  • Abhirup Saha,
  • Prantik Mondal

摘要

An integrated sedimentological and ichnological analysis of the mixed siliciclastic-carbonate sediments of the Middle Jurassic Bada Bag Member of the Jaisalmer Formation indicates deposition in a subtidal to intertidal paleoenvironment. Four distinct facies were identified – (i) fossiliferous silty limestone, (ii) tidally influenced sandstone–mudstone heteroliths, (iii) lensoidal conglomerate, and (iv) cross-stratified silty limestone. The vertical repetition of the facies types reflect systematic change in hydrodynamic conditions. The succession contains diverse ichnoassemblages, including Asteriacites stelliformis, Cochlichnus isp., Palaeophycus tubularis, Taenidium isp., and Thalassinoides isp., representing varied ethological behaviours of invertebrate trace-makers. The ichnogenus Asteriacites von Schlotheim, 1820 is identified within the silty limestone facies and, based on morphological and morphometric parameters, is assigned to ichnospecies Asteriacites stelliformis (Miller and Dyer 1878; Osgood 1970). Varied ecological parameters controlled the ethological responses of the organisms, influencing the trace fossil distribution and assemblages, resulting in the development of Cruziana ichnofacies. A gradual increase in tidal influence and a decline in detrital sediment input toward the upper part of the succession corresponds with the dominance of deposit-feeding ichnotaxa in fine-grained sediments. Overall, the sedimentary architecture and ichnological record reflect alternating low to moderate-energy subtidal and high-energy intertidal conditions during the deposition of the Middle Jurassic Bada Bag Member.