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Singh, A.
- Barrier Inlet and Associated Facies of Shore Zone: An Example from Khardeola Formation of Lower Vindhyan Sequence in Chittaurgarh, Rajasthan
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 2 (2001), Pagination: 97-111Abstract
Khardeola Formation (∼200 m), representing the lowermost clastic assemblage of Vindhyan Supergroup in southeast Rajasthan, consists of a fine clastic sequence in the lower part and a gritty, coarse to medium grained sandstone in the upper part. The formation crops out as discontinuous linear patches close to the western boundary of the basin. The Khardeola assemblage is investigated in this study for sedimentary facies, palaeocurrents, depositional environments and palaeogeography at the onset of Vindhyan sedimentation.
The lower fine clastic sequence (15-60 m thick) consists of interlaminated shale and siltstone, thinly bedded sandstone and mudstone,and red sandstone in a coarsening upward sequence, showing parallel to wavy lamination, ripple marks, desiccation cracks, bidirectional cross lamination, and gently inclined lamination. The facies assemblage, their characteristics, and occurrence alongside linear bodies of Khardeola sandstone, call for a protected depositional environment (back barrier lagoonal to tidal flat). The succeeding Khardeola sandstone, forming the upper part of the assemblage, represents 40-150 m thick sequence of moderately well sorted quartzarenite, subarkose and sublitharenite, and crops out as narrow linear ridges trending north-South. These sandstone units are divisible into four facies on the basis of fining upward texture, bedding types, and scale of sedimentary structures. Conglomeratic facies occurs in the basal part of sandstone with well defined scour base. The succeeding facies of lenticular sandstone with scour base comprises upward thinning sets of large, medium and small scale planar and trough cross bedding. The paleocurrent pattern reflects bipolar, bimodal to trimodal dispersal from the base of the sequence upward, directed broadly towards east and west, and occasionally towards north or south. Inasmuch as the source area providing quartzo feldspathic sediments was located mainly to the west of study area, the easterly paleocurrents were directed basinward (seaward). These deposits are interpreted as originating within laterally migrating tidal inlets (barrier inlets), in which easterly oriented ebb currents were dominant, with intermittent influx of flood oriented and north or south directed longshore currents. Plane bedded to gently inclined units of quartzarenite are interpreted as beach foreshore (spit) deposits that occur in places, capping the barrier inlet sequence. A combination of barrier inlet migration and shoreline transgression resulted in a truncated and modified barrier island sequence, dominated by inlet fill sandstone that merges with or oversteps westward (landward) the interlayered, fine grained clastic lagoonal/Tidal flat facies.
The Khardeola sedimentation was terminated with the decline in sediment supply, rise in sea level and landward migration of shoreline, followed by deposition of the overlying algae dominated Bhagwanpura Limestone in a quiet,open shelf of transgressive phase.
