Tectonics and Sedimentation of Proterozoic Basins of Peninsular India (original) (raw)
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Geological Magazine, 2020
The Vindhyan Supergroup represents the largest Proterozoic sedimentary basin fill in the Indian shield. In addition to some significant palaeobiological discoveries, the sedimentary sequence of the Vindhyan, particularly its argillaceous intervals, holds crucial information for our understanding of sedimentation dynamics in Proterozoic clastic shelves. Here we attempt an extensive, although not exhaustive, review of the physical characteristics of six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from the Son valley sector, Vindhyan Basin, augmented with new observations to unravel the status of current understanding in terms of palaeo-flow dynamics, shelf sedimentation processes and dispersal pattern, depositional cyclicity and basinal tectonics. The sedimentary attributes of Vindhyan shales reveal their deposition largely in relative bathymetry fluctuating from distal shoreface or inner shelf (near to fair-weather wave base) to distal sh...
Geological Journal, 2020
Two major facies associations are identified in the Upper Kaimur Group of the Son Valley, namely, tidally influenced fluvial channel facies association and tidal sand flat association. Lithofacies supports the Dhandraul Sandstone as the product of a tidally‐influenced fluvial channel and the underlying Scarp Sandstone as a tidal sand flat, which endorse a tide‐dominated estuarine setting. Grain size analysis shows that most of the sandstone samples are medium‐ to coarse‐grained and only small fractions are of fine‐ and very fine‐grained categories. In general, sediments are moderately well sorted, near‐symmetrical to fine‐skewed and leptokurtic to mesokurtic in nature, suggesting deposition under fluctuating energy conditions in different geomorphic domains from a tidally‐influenced fluvial channel to beach settings. Bivariant plots combining the textural parameters imply that marine processes dominate over fluvial processes in the Upper Kaimur Group sediments. Cumulative curves and...
A number of studies have been made on stratigraphy of the Upper Assam Basin. A comparison of these studies show various irregularities in nomenclature and assignment of stratigraphic positions to the different lithostratigraphic units. In the Paleogene Stratigraphy of the basin such irregularities are very well identified in the lithostratigraphic classification of Disang Group (≡ Jaintia Group) of sediments. These irregularities occur due to lateral facies variations during deposition in any depositional environment and time transgressive nature of the lithostratigraphic units. The irregularities in lithostratigraphy pose a serious problem in correlation unless a time based stratigraphic surface and process based classification is brought out for these shelf sediments. In the present work the approach of Sequence Stratigraphy using Depositional Sequence Model II is used for Late Paleocene - Early Eocene shelf sediments of the area from electrofacies of thee well logs and a seismic section. The sequence stratigraphic approach helps to identify three 3rd order sequences of Late Paleocene - Early Eocene bounded by unconformity surfaces E1, E2, E3 and E4. By study of stratal geometry and correlating the seismic section with the well log data, three 2nd order sequences bounded by Paleogene Unconformities P1, P2, P3 and P4 are identified in the seismic section. The three 3rd order sequences form the basal part of the seismic 2nd order sequence 1. These sequences are bounded by the erosional surface and therefore are not time transgressive units. The geometry of the facies indicating a sedimentation process occurring in the basin in relation to change in base level is considered for correlation rather than only the lithological characters. So the temporal variations in sedimentation processes related to base level changes can be well understood from the study of these sequences.
Spl Publication National seminar on "Vindhyan Supergroup: Recent Advances, Challenges, and Opportunities (VISACOP),, 2023
The study aims to present a detailed facies analysis and depositional environment of the rocks of the Kaimur Group of the Vindhyan Supergroup. Exposed outcrops and cliffs were examined in detail by section measurement and sedimentary logs were created. The logs are categorized bed by bed into several facies according to lithology and sedimentary structures. The focus was to identify the facies succession and to analyze the depositional environment of Dhandraul and Scarp Sandstone formations. The Scarp Formation comprises six sub-facies namely sandstone with tidal bundles sub-facies, planar cross-bedded facies, herringbone cross-bedded facies, ripples with mud crack, parallel laminated sandstone and trough cross-bed facies. Trough cross bed facies sandstone is thin to medium bedded, fine-grained immature quartzo-felspathic sandstone having erosional surfaces at the top. Trough beds with ripple at the top are characteristic of unidirectional flow and indicate a shallow marine condition, these sub facies are found in association with sandstone having tidal bundle sub-facies, which is thin to medium bedded, fine-grained sandstone. These sub-facies are characteristics feature of the tidal-influenced shallow marine environment which is formed by the periodic activity of flood flow and ebb flow during spring and neap tide. The presence of scour surfaces at the top of the sandstone having tidal bundles indicates features of high energy condition, which causes the flute casts under flood flow during the deposition above the fair weather base. Overall, the Scarp Formation suggests a subtidal to intertidal environment of deposition. The Dhandraul Sandstone Formation comprises five sub-facies namely, planar cross-bedded sub-facies, trough cross bed facies, sandstone having tidal bundle facies, and herringbone sandstone sub-facies. The presence of sandstone having tidal bundle facies with herringbone sub-facies is typical of the intertidal zone, where neap and spring tide dominates. These sub-facies association is overlain by sub-facies of medium to coarse-grained planar cross-bed and trough cross-bedded sub- facies. The grain size of the sediment coarsening sequence, as well as the bed thickening sequence, suggests shallowing of the basin with a repetitive cycle of bed thickening and thinning. Overall, this unit shows intertidal to supratidal zone of deposition. Granulometric analysis of samples from the Dhandraul Sandstone Formation shows that interbeds of the formation have size < (Φ) 3.75 (Very fine sand) to (Φ) -0.2 (Pebbly sand). The analysis results show that a very less amount of sediments is also present which is less than < (Φ) 3.75. The presence of the pebbly nature of grains at the top of the bed either indicates high energy conditions during the sedimentation to drag out coarser sediments or there should be a break in sedimentation. 17 On the other hand, Scarp Sandstone Formation have sizes from < (Φ) 3.75 (Very fine sand) to (Φ) 0.75 (Coarse sand). The average value of skewness of the sediment shows positive nature indicating moderate sorting. The paleocurrent data collected from planar cross beds (28 azimuths) show a mean azimuth of 230o -355 o whereas trough beds (180 azimuths) range between 250 o -355 o . The ripple shows azimuth between 35o -340o whereas 17 nos. of parting lineations shows the trend between 260o -355 o . It is inferred that the granite, granodiorite, gneiss, and metasedimentary rocks of the Mahakoshal Group and Chotanagpur granite–gneiss present in the eastern and southeastern direction may be the possible source rocks for the Kaimur Group.