• Manoj K Pandit

      Articles written in Journal of Earth System Science

    • Paleosol at the Archean–Proterozoic contact in NW India revisited – Evidence for oxidizing conditions during paleo-weathering?

      Manoj K Pandit Helga de Wall Narendra K Chauhan

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      A number of fine-grained sericite bearing pelitic,schistose lithologies occur along the Archean (Banded Gneiss Complex)–Proterozoic (Aravalli Supergroup)contact (APC)in the Udaipur valley in NW Indian craton.These Al-rich lithologies (subsequently metamorphosed)have been described as ‘paleosols ’,developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleopro- terozoic Aravalli quartzite.The paleosol was developed between 2.5 and 2.1,coincident with the globally recognized Great Oxidation Event (GOE).In previous studies these paleosol sections were interpreted to have developed under reducing environment,however,the finding of a ‘ferricrete ’ zone in the upper part of Tulsi Namla section (east of Udaipur)during the present study (in addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development.The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other Archean cratons.The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile while chloritoid and Fe-oxides typify the Fe-rich upper part.Alumina has remained immobile during the weathering process while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part,in the ferricrete zone.The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions.

    • In situ gamma radiation measurements in the Neoproterozoic rocks of Sirohi region, NW India

      Lars Scharfenberg Helga De Wall Stefan Schöbel Alexander Minor Marcel Maurer Manoj K Pandit Kamal K Sharma

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      Natural gamma ray measurements using a portable device were performed at 157 sites in the area around Sirohi town and Sindreth village in Rajasthan (NW India). This region comprises sedimentary rocks, metasediments, granites and gneisses that bear characteristic GR dose values and U/Th ratios corresponding with their specific geological history. A-type Malani granites and rhyolitic derivates, also referred as high heat production granites, show distinct differences as compared to the S-type Erinpura and Balda granites, most prominent in a high Th content of the former (up to 90 ppm). Sedimentary rocks in the Sirohi and Sindreth area are variable in their signatures reflecting their variable source rocks. In the area between the Balda and Paladi villages, northeast of Sirohi, measurements in vicinity of a N–S running shear zone, have shown U enrichment up to 8 ppm. This shear zone has been synkinematically mineralized with quartz and shows evidence of fluid infiltration into the host rocks in the vicinity of the shear zone. Erinpura granites have been altered due to fluid activity and show a light depletion of K (3.96%) and Th (20.11 ppm) as compared to the unaltered rocks (K, 4.06; Th 24.46 ppm). Enrichment of U (with a mean value of 13 ppm) has also been recorded in the lower clastic unit of the Sindreth Basin, especially within gritty conglomerates wherein migration and precipitation along fault planes is proposed.

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