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<p>The Jaisalmer Basin serves as a natural laboratory for investigating mid-Jurassic sedimentation patterns and sea-level fluctuations on the Rajasthan shelf (western India). A detailed investigation has been conducted on the representative Middle Jurassic strata exposed at the Khuri Road Outcrop in the Jaisalmer Basin. These lithosections comprise Bajocian carbonates of the Joyan Member, providing an opportunity for in-depth petrographic, microfacies, and depositional sequence analyses to infer depositional environment. The succession is mainly composed of poorly to well-cemented, low-angle cross-bedded, occasionally bioturbated, and ferruginous to calcareous siltstones to medium-grained sandstones, overlain by carbonate beds with reworked coral heads of <i>Isastraea bernardiana</i>. Biotic assemblages include shell pavements, crinoids, brachiopods, echinoids, gastropods, bivalves, oysters, and colonial corals. Twelve microfacies are identified and grouped into two distinct microfacies associations, inner ramp (lagoon and shoal) and mid-ramp (open marine) settings. The shoal deposits comprise four microfacies: (a) bivalve packstone microfacies (b) aggregate-grain grainstone, (c) coated bioclastic packstone, and (d) lithoclastic packstone. The lagoonal deposits include four microfacies: (a) green algal grainstone, (b) peloidal wackestone, (c) non-laminated homogeneous microspar without fossil, and (d) phylloid algal floatstone. The open marine consists of four microfacies: (a) bioclastic-lithoclastic packstone, (b) whole fossil packstone, (c) worn and abraded skeletal grain wackestone, (d) burrowed bioclastic wackestone. The study reveals multiple alternating deepening and shallowing trends, associated with transgressive and regressive phases, respectively, that controlled the overall depositional regime. These transgressive and regressive phases correspond to global eustatic changes, characterized by a major sea-level rise that triggered widespread transgressive events. These transgressions facilitated the development of shallow marine environments and the deposition of marine sediments across diverse settings.</p>

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Microfacies analysis and depositional environments of the Bajocian carbonates of the Joyan Member, Jaisalmer Basin, Western Rajasthan, India

  • 期刊论文

  • 发表日期：

    2026年2月26日

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  • Aashna Javed,
  • M. A. Quasim,
  • K. F. Khan,
  • Sreepat Jain,
  • S. Asjad

摘要

The Jaisalmer Basin serves as a natural laboratory for investigating mid-Jurassic sedimentation patterns and sea-level fluctuations on the Rajasthan shelf (western India). A detailed investigation has been conducted on the representative Middle Jurassic strata exposed at the Khuri Road Outcrop in the Jaisalmer Basin. These lithosections comprise Bajocian carbonates of the Joyan Member, providing an opportunity for in-depth petrographic, microfacies, and depositional sequence analyses to infer depositional environment. The succession is mainly composed of poorly to well-cemented, low-angle cross-bedded, occasionally bioturbated, and ferruginous to calcareous siltstones to medium-grained sandstones, overlain by carbonate beds with reworked coral heads of Isastraea bernardiana. Biotic assemblages include shell pavements, crinoids, brachiopods, echinoids, gastropods, bivalves, oysters, and colonial corals. Twelve microfacies are identified and grouped into two distinct microfacies associations, inner ramp (lagoon and shoal) and mid-ramp (open marine) settings. The shoal deposits comprise four microfacies: (a) bivalve packstone microfacies (b) aggregate-grain grainstone, (c) coated bioclastic packstone, and (d) lithoclastic packstone. The lagoonal deposits include four microfacies: (a) green algal grainstone, (b) peloidal wackestone, (c) non-laminated homogeneous microspar without fossil, and (d) phylloid algal floatstone. The open marine consists of four microfacies: (a) bioclastic-lithoclastic packstone, (b) whole fossil packstone, (c) worn and abraded skeletal grain wackestone, (d) burrowed bioclastic wackestone. The study reveals multiple alternating deepening and shallowing trends, associated with transgressive and regressive phases, respectively, that controlled the overall depositional regime. These transgressive and regressive phases correspond to global eustatic changes, characterized by a major sea-level rise that triggered widespread transgressive events. These transgressions facilitated the development of shallow marine environments and the deposition of marine sediments across diverse settings.