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Searching for the Age of the Upper Vindhyan: A view from Paleomagnetism and Detrital Zircon Geochronology

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records (Posters)

Presenting Author:

Samuel Kwafo

Authors:

Kwafo, Samuel¹, Meert, Joseph G.², Yasar, I. Dogancan³, Kamenov, George D.⁴, Verma, Nirmal K.⁵, Pandit, Manoj K⁶

(1) Department of Geological Sciences, University of Florida, Gainesville, FL, USA, (2) Department of Geological Sciences, University of Florida, Gainesville, FL, USA; Department of Geology, University of Rajasthan, Jaipur, Rajasthan, India, (3) University of Florida, Gainesville, FL, USA, (4) University of Florida, Gainesville, FL, USA, (5) University of Rajasthan, Jaipur, Rajasthan, India, (6) University of Rajasthan, Jaipur, Rajasthan, India,

Abstract:

The upper Vindhyan basin of north-central India, with a stratigraphic thickness of approximately 5,000 meters, represents a remarkably well-preserved, largely undeformed, and unmetamorphosed sedimentary sequence. Separated from the lower Vindhyan Semri Group by a pronounced unconformity representing a hiatus of approximately 400 million years, the upper Vindhyan Kaimur, Rewa, and Bhander Groups hold the key to determining the age of basin closure. However, the closure age of the upper Vindhyan is contentious due to discrepancies among geochronologic, paleomagnetic, and isotopic datasets. Recent composite detrital zircon (DZ) U-Pb geochronology analyses from the combined Bhander-Rewa formations yielded a maximum depositional age (MDA) of 945 ± 7 Ma, consistent with an early Tonian closure age of ~950 Ma. This interpretation aligns with paleomagnetic data. The Bhander-Rewa paleomagnetic pole (42.1°N, 213.3°E, A95 = 4.3) differs significantly from younger poles, including the 0.74 Ga Bundelkhand dykes pole, the ~0.77 Ga Malani Igneous Suite, and the 0.82 Ga Harohalli alkaline dykes. The pole is very similar to the VGP’s from the ~1.07 Ga Majhgawan kimberlite and the ~1.1 Ga Great Mahoba dyke. However, recently reported Pb-Pb ages and stable isotope stratigraphy from the Bhander and Balwan limestones argue for much younger closure ages (750 Ma – 820 Ma). This age discrepancy (~250 Ma) between Pb-Pb ages, stable isotopic data and detrital zircon/paleomagnetic data remains unresolved. We report new data from the youngest Maihar sandstone from the Bhopal inlier. Contrary to previous studies showing isolated younger Tonian ages, our survey lacks detrital zircon grains younger than ~960 Ma across multiple sampling locations. While our findings do not categorically exclude the late Tonian age, the correlation between the MDA and paleomagnetic studies supports our contention for an early Tonian closure.