An insight to the initiation of Cretaceous sedimentation in Northeast Indian Craton
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ORIGINAL ARTICLE
An insight to the initiation of Cretaceous sedimentation in Northeast Indian Craton Rohini Das1 · Apoorve Bhardwaj2 · Sampita Das Mitra3 · Tapan Pal1 · Bashab N. Mahanta1 Received: 8 July 2020 / Revised: 1 September 2020 / Accepted: 2 September 2020 © Springer Nature Switzerland AG 2020
Abstract The time transgressive Cretaceous sedimentation in northeast Indian craton is represented by the deposition of the Upper Cretaceous Mahadek sediments in Meghalaya. The Lower unit of these sediments is comprised of alternate sandstone and conglomerate horizons, and the Upper unit is composed of arkosic to sub-arkosic sandstones. These sediments are overlain by the calcareous litho-units of Langpar Formation of Cretaceous–Paleocene age. Lithofacies identified from various exposures and studied lithologs reflect a variation from marginal marine to marine depositional set-up in the Mahadek sediments. The Lower Mahadek facies is dominated by large-scale trough beds of medium to coarse-grained sediments which initiates with a conglomerate horizon succeeded by thin beds of shale and fine-grained sandstone with parallel laminations, which are followed by successive deposition of gritty sand and pebbly beds with coarsening upward sequence, suggesting product of delta plain in a marginal marine setting. Moreover, the bioturbated coaly fine-grained sandstone is further representative of tidal flat-tidal channel swamp formed in reducing condition and the trace fossil assemblages depict the channel fills. The Upper Mahadek facies is dominated by glauconitic-gritty fossiliferous sandstone showing fining upward sequence and hummocks, typical of marine environment. This fining upward sequence along with the vertical and lateral facies variation implies superimposition of retrograding shorelines on an earlier progradational alluvial fan sand complex. These differentscale cycles are interpreted as the sedimentary response to movements of the basin margin faults at variable frequencies, related to the contemporary faults. This depositional model of the Cretaceous sediments may further help in paleogeographic reconstruction of the northeast Indian craton during the Cretaceous period. Keywords Marginal marine · Lower Mahadek facies · NE Indian craton · Cretaceous · Sedimentary environment
1 Introduction The Cretaceous paleogeography (Fig. 1) of the Indian subcontinent can be attributed to the break-up of the Greater Indian continent. A large number of linear fluvial to shallow marine basins opened up during the Aptian time followed by basaltic eruption near some basins in east and northeast Communicated by M. V. Alves Martins. * Rohini Das [email protected]; [email protected] 1
North Eastern Region, Geological Survey of India, Shillong‑3, Meghalaya, India
2
Northern Region, Geological Survey of India, Lucknow‑24, Uttar Pradesh, India
3
Southern Region, Geological Survey of India, Hyderabad‑68, Telangana, India
India (Acharyya and Lahiri 1991). The Cretaceous period also marked significant changes on
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