Satyendra M. Casshyap

Paleocurrents and paleogeographic reconstruction in the Barakar (Lower Gondwana) sandstones of peninsular india

Abstract Data on the attitude of 4100 cross-bedding readings in the Barakar (Lower Permian) sandstones recorded from twenty-two Gondwana coalfields of peninsular India are summarized. The azimuths of the cross-bedding readings show a regional uniformity. The total cross-bedding variance in the typical Barakar sandstones, herein called the lower unit, is uniformly moderate to low commonly ranging between 1500 and 3000. In some coalfields (Raniganj, Jharia, Bokaro, Singrauli) where sandstones of the lower unit are overlain by an upper thick unit of interbedded fine clastics, the total cross-bedding variance exceeds 3000 and is as high as 5500 in one coalfield (Jharia). Based on lithologic and sedimentary characters and total variance of cross-bedding azimuths, it is proposed that the Barakar strata were deposited largely by streams of low channel sinuosity and partly, especially the upper unit wherever developed, by streams of high channel sinuosity (meandering). A regional synthesis of cross-bedding data reveals that at least three major rivers, all draining from southeast to northwest, and their tributaries formed the dominant dispersal system in the Shield area during the deposition of Barakar strata. Of the three Barakar basins, corresponding to each major river, the Damodar Valley basin of eastern India was perhaps remarkably broad, extending far and wide beyond the existing limits of Barakar outliers. A prominent watershed for the major Barakar rivers existed all along and possibly beyond the present eastern coast of India. The study does not support the earlier paleogeographic reconstructions entirely as well as the concept that Gondwana sediments were deposited in “rift” valleys. It proposes some important paleogeographic modifications, and also explains the possible extension and outlet of Barakar drainage.

Fluvial architecture of the Upper Permian Raniganj coal measure in the Damodar basin, Eastern India

Abstract The Upper Permian Raniganj Formation of the Damodar basin consists of an interbedded assemblage of sandstone, shale, carbonaceous shale, and coal facies. The trough cross-bedded sandstone bodies (St facies) formed by migration of dunes in sand bar/point bars are widely developed in the lower part of Raniganj Formation; the planar cross-bedded facies (Sp) of transverse and diagonal bars and massive sandstone of longitudinal bars abound in the upper part of the eastern Raniganj and Jharia coalfields. The succeeding ripple cross-laminated (Sr) facies with or without reactivation surface, alternating with thick beds of fine clastics, suggestive of flood deposits, is widespread in the western Bokaro and North Karanpura coalfields. Markov chain statistics reveals a fining-upward cyclical order of superposition throughout the Raniganj sequence. The integrated results of paleocurrent, channel morphology, texture and petrography suggest that the Raniganj sedimentation was brought about in an extensive unified alluvial plain drained by a system of west-northwest flowing streams whose channel sinuosity increased, and depth decreased progressively in a downcurrent direction from east to west. Post-Gondwana faulting and subsequent erosion account for the disconnected disposition of the coalfields.

Glacial Sedimentation of Late Paleozoic Talchir Diamictite, Pench Valley Coalfield, Central India

Three mappable diamictite units occur in the Lower Gondwana Talchir Formation (Permian-Carboniferous) of the Pench Valley coalfield of Satpura basin, central India. These diamictite units (each about 28 to 45 m thick) are predominantly green, polymictic, and poorly sorted. Portions of the units that are massive diamictite include a variety of twisted and deformed to tabular and wedge-shaped sandstone bodies, as well as thin tenses of conglomerate and sandstone that locally exhibit parallel groove markings on the upper surface. Portions of the units that are stratified diamictite are characterized by “grouped” clasts and thin interbeds of siltstone and sandstone showing fine, parallel grooves (striae) and linguoid ripples where the interbeds occur beneath diamictite. Each diamictite unit is overlain by an assemblage of interbedded green siltstone, shale, and sandstone. Such an assemblage contains a variety of primary depositional structures plus local striated “lonestones.” The upper part of the Talchir Formation, the transitional assemblage, is characterized by horizontally bedded to cross-bedded conglomeratic sandstone in which embedded clasts are more rounded than those of the diamictite. A synthesis of the above features discounts the possibility that turbidity currents or mass flows were the sole formative mechanisms. Alternatively, lithologic and sedimentary characteristics of the lower Talchir strata and their over-all stratigraphic and tectonic setting strongly favor a glacial origin for the diamictite; this corroborates previously published views. We postulate a glaciomarine model, however, to explain the Talchir sedimentation in the study area. The ice sheets may have advanced into central India from the south several times. The overlying transitional assemblage may be glaciofluvial in origin.

Paleocurrent analysis of Lower Gondwana sedimentary rocks, Pench Valley coalfield, Madhya Pradesh (India)

Abstract The Lower Gondwana sequence (mostly Permian) of the Pench Valley coalfield in central India includes three formations as follows in ascending order: Talchir, comprising diamict/?tillite, sandstone and shale; Barakar, largely an assemblage of coal-bearing sandstone; and Motur, representing a sequence mostly of sandstone and mudstone. The paleocurrent study of these formations is based on dimensional pebble fabric of diamicts and cross-bedding dip azimuths of sandstone. The study reveals that the sediment transport during deposition of the Lower Gondwana formations in this area was persistently from the southeast to the northwest direction. Analysis of cross-bedding dip azimuthal data at various levels of sampling reveals that streams which deposited the Barakar and Motur sediments in the Pench Valley Basin had a sinuous regimen. Total variance values of foreset dip azimuth further suggest that the variability was low for streams which deposited the Barakar sand but high for those which laid down the Motur sediments; the former implying, probably, a “braided” pattern, whereas the latter a “meandering” pattern, an inference appropriately supported by the lithology and bedding types of the two formations.

Petrology of the bruce and gonganda formations and its bearing on the evolution of huronian sedimentation in the Espanola-Willisville area, Ontario (Canada)

Abstract In the Espanola-Willisville area, the Bruce Formation is essentially a massive and unstratified diamict—a pebbly conglomeratic muddy sandstone. The Gowganda Formation includes four mappable units as follows, in ascending order: lower diamict, laminated argillite, upper diamict and the intercalated zone of sandstone, argillite and conglomerate. Texturally and compositionally, the Bruce and Gowganda diamicts are strikingly alike. Dispersed phenoclasts are polymictic in composition and often show sharp truncated edges. The enclosing fine-clastic aggregate (matrix) is gray-greenish muddy sandstone: mostly an immature subarkosic wacke ( Casshyap , 1966b). Combined evidence from dimensional fabric, paleocurrents and petrographic study of the entire Huronian succession of the Espanola-Willisville area suggests a northerly sediment transport for the Bruce and Gowganda formations, and a source area comprised of granites and volcanic-schistose complex in the Canadian Shield. Both the Bruce and Gowganda diamicts are attributed a glacial origin. It is suggested that in this area these deposits were laid down, probably, from wet-base glaciers in a terrestrial environment. Evidence from the study of the entire Huronian succession of this area has been used for interpreting the relative importance of rate of subsidence, eustatic movement of sea level and isostatic adjustment of the landmass, and climatic changes in the evolution of the Huronian sedimentary basin in the Espanola-Willisville area.

Entropy in Markov analysis of late paleozoic cyclical coal measures of East Bokaro basin, Bihar, India

Randomness in the occurrence of lithologies in a cyclical succession is evaluated in terms of entropies which can be calculated from a Markov chain matrix. Two types of entropies are linked with every lithologic state; one is the entropy before deposition E(pre)and the other is that after deposition E(post),which together form an entropy set. The entropy sets for pebbly sandstone, sandstone, shale, and coal for the Karharbari coal measures, and sandstone, shale, carbonaceous shale, and coal for the Barakar coal measures were plotted separately and compared with Hattoris idealized plots. These coal measures probably were essentially of symmetrical cyclical pattern (Type-B)of Hattori. The entropy of the whole sedimentation unit readily fits under the broad framework of fluvial cycles.

Cyclicity in early Permian fluviatile Gondwana coal measures: An example from Giridih and Saharjuri basins, Bihar, India

Abstract The Karharbari and Barakar coal measures of Giridih and Saharjuri basins of Bihar, eastern India, comprise an interbedded assemblage of sandstone, shale and coal in variable abundance. The lithofacies composition records a progressive decrease in sandstone and enrichment of shale and coal from Karharbari up to Barakar. Application of first-order embedded Markov-chain statistics to subsurface data of Karharbari (52 borehole logs) and Barakar (10 borehole logs) reveals that deposition in both the coal measures followed a Markovian mechanism with variable probability, to yield a sequence of upward transition from sandstone through shale to coal. The repetitive fining-upward cycles are asymmetrical, i.e. sandstone → shale → coal → sandstone in the case of Karharbari, but symmetrical as sandstone → shale → coal → shale in Barakar. The abundance of sandstone and the asymmetrical nature of Karharbari cycles are attributed to abrupt shifting of channel bars in low-sinuosity anabranching streams. By contrast, the subequal amount of sandstone, shale and coal forming symmetrical cycles in the overlying Barakar Formation is due perhaps to a slow and gradual shift of the stream channels over and across the adjacent subenvironments of the flood plain.

Sedimentological synthesis of permian fluviatile sediments of East Bokaro basin, Bihar, India

Abstract The early Permian Karharbari and Barakar formations of East Bokaro basin comprise the following lithofacies: Lithofacies A, consisting of monomictic cobble- and pebble-conglomerate including pebbly sandstone, with faint crossbeds; deposited mainly by high-velocity aqueous currents as channel-lag deposit or longitudinal bars. Lithofacies B, coarse to medium sandstone, profusely crossbedded; interpreted as channel facies formed by downcurrent migration of sand bars in low-sinuosity streams. Lithofacies C, mainly fine sandstone with interbedded siltstone, characterised by small-scale ripple-lamination; formed in a low-energy environment such as swale-fill and/or overbank deposits. Lithofacies D, including carbonaceous shale and coal, with lack-of-current structures, indicating quiet-water deposition; interpreted as backswamp and lacustrine deposits. The overall context of the Karharbari and Barakar assemblage with relative abundance of pebbly coarse sandstone in the former and fine clastics in the latter, the presence of fining-upward cycles, widespread development of tabular and trough crossbedding and sample to sample variation of foreset azimuths, all suggest a generally alluvial environment. Analysis of crossbedding dip azimuth and dimensional fabric suggest that the sediment milieu in either case consisted of streams flowing persistently from the south-southeast to north-northwest direction. It is inferred that the unidirectional system of streams flowing across the East Bokaro basin changes systematically in channel sinuosity through time.