Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. M. Casshyap ¹, R. K. Jain ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh, IN

Abstract

The Barakar sandstone of Chirimiri (Kurasia) coalfield includes complete or truncated sedimentary cycles, some of which commence with pebbly gritty coarse sandstone and, fining upwards through coarse cross bedded sandstone, end up with carbonaceous siltstone or coal seam. Among the primary depositional structures, ripple drift, trough and tabular cross bedded sets and cosets are common. These structures have been described from the genetic and hydrodynamic viewpoints. Erosional structures occurring in the sandstone include channels, scour-and-fill, potholes and flute casts.

A paleocurrent analysis based on 88 cross bedding azimuths reveals the preponderance of two depositional current systems - the main current system which flowed from southeast, and a tributary system flowing from east-northeast. An increase in cross bedding variability at higher sampling levels reflects the meandering behaviour of depositing currents.

A sedimentary analysis of the sandstone sequence suggests that the Barakar sedimentation in this coalfield was controlled, perhaps right from the beginning, by periodic tectonic uplifts of the granitoid landmass located to the east and southeast. It is suggested each tectonic uplift resulted in the deposition of a fining-upwards fluvial cycle.

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R. C. Tewari ¹, S. M. Casshyap ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh 202001, IN

Abstract

The Late Paleozoic Gondwana rocks underlying the Giridih, Jainty and Saharjuri basins, and Dhakoi outlier of south Bihar comprise Talchir, Karharbari and Barakar Formations. The Talchir strata exhibit a facies change from conglomeratic in the Dhakoi outlier in the south to dominantly sandy, shaly to silty in the Giridih and other basins towards north. The Karharbari abounds in pebbly, very coarse, coarse to medium sandstone (~85% by volume) with thin interbeds of shale (~7%) and coal (~8%). In contrast, the succeeding Barakar is characterised by more of shale (~36%) and coal (~21 %) than sandstone (~43%) which is largely medium to coarse grained. Paleoflow analysis based on cross bedding and other directional attributes reveals a gradual shift with time in paleodrainage in that it was directed towards west-northwest (297 ±46°) during Talchir, northwest (343 ±42°) in Karharbari and towards north (359 ±: 50°) in Barakar. The uniformity of northerly paleoflow during Karharbari and Barakar times in the given area and in the adjoining Gondwana basins to the south is suggestive of a unified Gondwana basin in this part of peninsular India. It is inferred that the outlet of Gondwana streams in this part was dominantly northward.

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V. K. Srivastava ¹, S. M. Casshyap ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh 202001, IN

Abstract

The Subathu, Dagshai and Kasauli rocks of Himachal sub Himalaya have been classically interpreted as of marine brackish or lagoonal origin. In this study, the pre-Siwalik Tertiary rocks of southern Himachal Pradesh are grouped into five distinct lithofacies, which collectively represent a consanguineous association of sediments deposited in related geomorphic environments: 1. Fossiliferous green shale, locally red, with lenses of limestone interpreted as tidally influenced shelf deposits; 2. Clean white sandstone interpreted as coastal barrier bars; 3. Red mudstone locally green, and lenses of grey sandstone with channel lag interpreted as lagoonal and tidal flat deposits; 4. Grey sandstone with channel lag and red mudstone and siltstone inferred to have accumulated in distributary channel and inter-distributary plains of fluvio-delta complex; 5. Grey, white sandstone and mudstone interpreted as a mixed assemblage of fluvio-delta and coastal barrier facies.

Two systems of currents operated during the deposition of these rocks: one, across the delta plain complex was directed towards south and southwest following the prevailing regional paleoslope; and the other representing longshore currents in adjacent coastal areas operating parallel to shoreline, was directed towards west-northwest.

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S. M. Casshyap ¹, M. Aslam ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202002, IN

Abstract

An earthy brown, cross-bedded, channel sandstone body overlying a thinly bedded sequence of white sandstone and red shale of the Surajdeval Formation (Iower-Cretaceous) stands out as a low-lying flat-topped escarpment, about 3-4 m high and 30-60 m wide, alongside the village Dhaduka near Chotila on the Surendranagar-Rajkot highway. Plane ta ble survey brings out a sinuous pattern of the channel sandstone body longitudinally in the north-south direction all along the escarpment.

Integrated evidence from geometry, lithofacies and paleocurrents suggest that the Dhaduka sequence is an example of exhumed channel bar of delta distributary, in association with thinly-bedded coastal plain (1ongshore/tidal current) deposits.

Keywords

Sedimentology, Surajdeval Fm., Gujarat, River delta.

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S. M. Casshyap ¹, R. C. Tewari ², Abdullah Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, IN
2 Department of Geology, D. S. College, Aligarh, IN

Abstract

The Bagra Formation of the Mesozoic Gondwana sequence of Satpura basin has been considered as a facies equivalent of the underlying Denwa, and assigned a late Triassic age. The present study reviews the above contention, prompted by distinctive lithofacies assemblage, depositional setting and tectonic framework of the Bagra Formation, and its variable relationship with the underlying strata.

The Bagra Formation as a whole comprises conglomerate assemblage in the lower and middle parts and sandstones with intercalated lenses of shale in the upper part. The lower conglomerate facies occurring northward is clast - to matrix supported and poorly sorted; it is finergrained, better sorted, including thin lenses of cross-bedded sandstone southward in middle part of the formation. The overlying cross-bedded sandstone and shale facies is the most important assemblage in the distal south. The coarse grained nature of the sediments, the upward- fining distribution and lateral changes in gross lithofacies and stratification types, and paleocurrent data suggest that the Bagra conglomeratic sequence was deposited as an alluvial fan system that prograded southward from a highland source located immediately to the north. In sharp contrast, the fluvial system was directed dominantly northward and source area located southward for the underlying Permo-Triassic Gondwana sediments, including Denwa.

It is argued that a late Triassic age of the Bagra Formation is questionable, in as much as a substantial stratigraphic break in sedimentation is called for after the deposition of Middle Triassic Denwa. The Bagra may well be late Jurassic-early Cretaceous in age based on its relationship with the overlying JabaIpur Formation.

Keywords

Upper Gondwana, Alluvial Fan, Mesozoic, Bagra Formation, Stratigrapghy.

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M. Raza ¹, S. M. Casshyap ¹, A. Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202002, IN

Abstract

Well-preserved accretionary lapilli of different types are reported from the basal volcanic sequence (Khairmalia basalts) of Lower Vindhyan occurring to the south of Chittaurgarh. Four types of lapilli are identified on the basis of the nature of their core, surrounding rim zone and physical appearance. The first two types comprise cores of volcanic glass and welded tuff surrounded by rims similar to the coated accretionary lapilli or type-B of Reimer. The third type is a typical armoured lapilli, and the fourth type is a core type lapilli or type - A of Reimer. The internal structure and characteristics of the lapilli suggest their formation from ash-charged volcanic cloud produced by repeated volcanic explosions. Their excellent preservation, lack of fragmentation, presence of large size vesicles and absence of sedimentary structures in the matrix suggest little post-depositional transport. The initial explosive volcanic events and resultant basic flows and volcaniclastics, succeeded by deposition of interlayered fine clastics and conglomeratic coarse cross-bedded sandstone in the adjoining down warped (? half graben) basin (s) has heralded the onset of Vindhyan sedimentation in a fluctuating shore zone environment in southeastern Rajasthan.

Keywords

Volcanism, Mesoproterozoic pyroclastics, Accretionary Lapilli, Tectono-Magmatic Event, Vindhyan Basin, Chittaurgarh, Rajasthan.

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S. M. Casshyap ¹, B. D. Bhardwaj ¹, M. Raza ¹, A. Singh ¹, A. Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN

Abstract

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.

Keywords

Mesoproterozoic, Cratonic Basin, Sedimentary Facies, Paleocurrents, Beach, Barrier Island, Palaeogeography, Vindhyan, Rajasthan.

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M. Raza ¹, S. M. Casshyap ¹, A. Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN

Abstract

The western margin of the Vindhyan Basin of north Indian shield, is characterized by well developed Mesoproterozoic Lower Vindhyan succession. It contains thick units of shales and sandstonc with minor conglomcratc and limestone at different stratigraphic levels. Five shale units, namely Khardeola Shale (KHS), Palri Shale (PRS), Binota Shale (BNS), Bari Shale (BRS) and Suket Shale (SKS) occurring in chronological order, have been examined for their geochemistry to determine the composition of their source rocks, to understand the environments of weathering and sedimentation and the tectonic conditions at the time of their deposition.

The Lower Vindhyan shales are characterized by high SiO₂, low CaO and MgO, very low Na₂O and very high K₂O/Na₂O ratio relative to average Proterozoic shales. All the shale units are severely depleted in Ca, Na and Sr and slightly enriched in some trace elements such as Co and Nb, relative to the early Proterozoic upper continental crust. It appears that the high field strength and transition elements remained immobile throughout the sedimentary processes and represent the source rock composition. Geochemically, the individual shale units do not show any significant variation with age, excepting the Khardeola Shale that is relatively more enriched in ferromagnesian and large ion lithophile elements.

Geochemical data suggest that sediments of Lower Vindhyan shales had their source in stable continental areas and deposited in intracratonic basin away from active plate boundaries. The immobile trace element data suggest that the source material of these shales have been derived from felsic and mafic components of Banded Gneissic Complex occurring to the west of the Great Boundary Fault in the proportion of about 4: 1. Severe but non-steady-state weathering conditions in the source region having humid, and tropical climate appcar to have prevailed throughout the sedimentation of Lower Vindhyan sequence. The sequence of events suggcsts passive type rifting environment during the Vindhyan Basin formation.

Keywords

Geochemistry, Shales, Vindhyan, Mesoproterozoic, Chittaurgarh, Rajasthan.

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