--> Deciphering Tectonic Controls on Fluvial Sedimentation Within the Barmer Basin, India: The Lower Cretaceous Ghaggar-Hakra Formation

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Deciphering Tectonic Controls on Fluvial Sedimentation Within the Barmer Basin, India: The Lower Cretaceous Ghaggar-Hakra Formation

Abstract

The Cretaceous sedimentary succession of NW India is not well documented due to limited exposure in the desert region of Rajasthan. Here, we describe the stratigraphy and sedimentology of outcrops of the Ghaggar-Hakra Formation of probable Lower Cretaceous age from the Sarnoo Hills, which is used to constrain their correlatives from subsurface core data in the Barmer Basin. At outcrop, the Ghaggar-Hakra Formation comprises three fluvial sandstone sequences of varying depositional type, interbedded with coeval floodplain deposits. At the base the Darjaniyon-ki Dhani Sandstone is composed of granule-grade quartzitic conglomerates that form braid bars deposited in a low sinuosity, gravel bedload fluvial system. The overlying Sarnoo Sandstone contains medium- to very coarse-grained, cross-bedded sandstones that pass upwards into fine-grained rippled sandstones, deposited as in-channel bars and point bars, of a high sinuosity, mixed load fluvial system. Lastly, the Nosar Sandstone is composed of very coarse- to medium-grained, planar and trough cross-bedded quartz-arenites, representing in-channel dunes displaying evidence of a low sinuosity bedload dominant fluvial system. The interbedded mudstones are pedogenic in nature, with rhizoliths, slickensides and soil mottle textures that formed in a vegetated floodplain. In the subsurface, two separate palaeoenvironments are identified: 1) a low sinuosity system with associated floodplain deposits and; 2) a lacustrine system. The low sinuosity river facies comprises very coarse- to fine-grained, cross-bedded and rippled sandstones. Associated floodplain deposits are mottled, rooted and fractured. The detrital composition of these sandstones at outcrop and in the subsurface comprises of quartz, lithics, heavy minerals and clays. However, the authigenic minerals vary. Within the subsurface with kaolinite, quartz overgrowths, siderite and pyrite cements. At outcrop there are quartz overgrowths, calcite, dolomite and haematite cements with kaolinite clays. The Ghaggar-Hakra Formation was deposited within a maturing upwards fluvial system. The current view of the regional tectonic framework is one of an actively extending terrane, possibly related to transtension between the Greater Indian and Madagascan continents during Gondwana fragmentation. Ultimately, this work helps the understanding of the regional tectonics and depositional systems of Rajasthan during the Lower Cretaceous.