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Sequence stratigraphy of the Oxfordian to Tithonian sediments (Baisakhi Formation) in the Jaisalmer Basin

Pandey D. K., Pooniya D.

Volumina Jurassica

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2015

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Vol. 13, no. 1

65--76

EN

The Oxfordian to Tithonian sediments deposited along the southern Tethyan margin exhibit very diverse sedimentary facies. The Jaisalmer Basin, situated along the northwestern margin of the Indian peninsula, is a good example of those preserving these sediments (Baisakhi Formation). The scattered nature of the outcrops, due to peneplanation and desert sand cover, and the diversity in sedimentary facies, have led earlier workers to employ a confusing lithostratigraphy and lithostratigraphic correlations. New records of ammonites, more detailed facies description and the application of the sequence stratigraphic method helped to sort out the stratigraphical problems of these isolated outcrops. The complexity of the Oxfordian-Kimmeridgian-Tithonian sediments present in the Jaisalmer Basin, as evidenced by ammonite finds can be traced along an onshore – offshore transect. Within the Oxfordian-Tithonian strata of the Baisakhi Formation, Jaisalmer Basin, 35 parasequences grouped into three depositional sequences (TST-HST/FSST) have been recognized. In at least two cases, the maximum flooding surfaces (MFS) are superimposed on the transgressive surfaces within very condensed sections. The parasequences belong to a continuous succession representing shoreface (deepest part of the basin) to foreshore (shallowest part of the basin). During deposition of the Tithonian succession the southern part of the basin witnessed shallow, nearshore, or foreshore to fluvial depositional environments and, consequently, contains several depositional gaps and less distinct parasequences. The chronological order of the parasequences has been established on the basis of ammonites: Oxfordian – Perisphinctes (Dichotomosphinctes) sp. and P. (Dichotomoceras) sp.; Kimmeridgian – Torquatisphinctes alterniplicatus (Waagen) and Pachysphinctes aff. major Spath; Tithonian – Aulacosphinctoides sp., Virgatosphinctinae and other zonal ammonites recorded by earlier workers. The most logical facies correlation in conformity with Walther’s law was also used. Unfortunately, no marker beds have been recognized; however, the record of at least two brackish-water phases helped in the understanding of depositional settings along the onshore-offshore transects during these time intervals. In general, the Kimmeridgian-Tithonian part of Baisakhi Formation exhibits a general coarsening-upward trend and a change from lower shoreface zone to fluvial environments. The three sequence cycles interpreted within the Oxfordian-Tithonian sediments in the Jaisalmer Basin correspond to second-order sequence cycles.

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Integrated biostratigraphy of the Jurassic strata of the Wagad Uplift, Kachchh, western India

Rai J., Garg S., Gupta M., Singh A., Pandey D. K., Fürsich F. T., Alberti M., Garg R.

Volumina Jurassica

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2015

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Vol. 13, no. 2

55--80

EN

An integrated study based on calcareous nannofossils, organic-walled dinoflagellate cysts, and ammonites from the Washtawa and Kanthkot formations of the Wagad Uplift have allowed a detailed documentation of the stratigraphic position of these formations within the Oxfordian and Kimmeridgian sediments of the Kachchh Basin, western India. The nannofossil assemblages from the lower part of the Nara Shale Member exposed in the Nara and Washtawa domes, the Kanthkot Ammonite Beds along the Trambau River section, and the Patasar Shale Member exposed along the Trambau River section and the Patasar Tank section in the eastern part of the Wagad Uplift belong to the NJ 14 Cyclagelosphaera margerelli Zone of the Early Oxfordian, the NJ 15a Lotharingius sigillatus Zone of the Middle Oxfordian, and the NJ 15b Cretarhabdus conicus of Early Kimmeridgian age, respectively. Zonation schemes, based on calcareous nannofossils, dinoflagellate cysts, and ammonites were calibrated highlighting their biostratigraphic potential. These studies may represent a reference biochronology for Oxfordian–Kimmeridgian age strata applicable to the Tethyan realm of which India was a part during Late Jurassic times.

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Dinosaur footprints from the Thaiat ridge and their palaeoenvironmental background, Jaisalmer Basin, Rajastan, India

Pieńkowski G., Brański P., Pandey D. K., Schlögl J., Alberti M., Fürsich F. T.

Volumina Jurassica

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2015

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Vol. 13, no. 1

17--26

EN

Two dinosaur footprints: Eubrontes cf. giganteus and Grallator tenuis, both attributed to theropods, have been found in the Lower Jurassic Thaiat Member of the Lathi Formation at the Thaiat ridge, near Jaisalmer in western Rajasthan, India. The footprints were left in sediments of a tidal origin, located in profile a few meters above a marked transgressive/flooding surface. They show different states of preservation – the smaller Grallator tenuis represents a well-preserved concave epirelief footprint on the upper surface of a sandstone containing nerineid gastropod shells, while the bigger Eubrontes cf. giganteus footprint shows a rare state of preservation as a positive epirelief on the top of a calcareous sandstone bed, where recent erosion exposed the footprint cast by removing the mud above and around the footprint. The Thaiat ridge section has been amended in its lower part, to indicate the marked transgressive surface. Geochemical analyses and calculated weathering indices (such as CIA) show that the hinterland climate was seasonal to semi-arid during deposition of that part of the succession.