|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
GEOLOGIC NOTE |
1 Geological Studies Unit, Indian Statistical Institute, 203 B. T. Road, Kolkata 700108, India; sarbani{at}isical.ac.in
2 Geological Studies Unit, Indian Statistical Institute, 203 B. T. Road, Kolkata 700108, India; asru41{at}rediffmail.com
Sarbani obtained her B.Sc. and M.Sc. degrees in geology from the University of Calcutta. She joined the Geological Studies Unit of the Indian Statistical Institute in 1992 with a doctoral program on sedimentology and stratigraphy of a Neoproterozoic cratonic basin. She received her Ph.D. from the University of Jadavpur, Kolkata, in 2001. Since then, Sarbani has been working as a sedimentologist in the Proterozoic research group of the institute, specializing in facies, environment, and stratigraphy. Her interests also include provenance studies and tectonics.
Asru Chaudhuri was a professor in the Geological Studies Unit of the Indian Statistical Institute, and currently, he is an emeritus scientist in the same department. He studied geology in the University of Jadavpur, Kolkata, and received his M.Sc. degree in 1964. He received his Ph.D. from the University of Calcutta in 1970 on the basis of his work on sedimentology and stratigraphic evolution of a Proterozoic cratonic rift basin in south India. His interests include stratigraphy and evolution of Proterozoic cratonic basins and tectonics of the Indian craton.
A thick wedge of immature siliciclastics characterizes the basal part of the basin-fill succession in the eastern part of the Neoproterozoic Chattisgarh Basin. It comprises a mosaic of mass-flow–deposited conglomerate and pebbly sandstone, coarse-grained sandy braided stream deposits, wave-lag pebble sheets, high-energy, wave-dominated foreshore and upper shoreface facies, and wave- and tide-dominated lower shoreface facies. The succession is characterized by strong lateral and vertical facies variation. The facies associations and stacking pattern point to the development of an alluvial-fan to fan-delta complex, with outbuilding of delta lobes onto a high-energy shallow-marine shelf via a high-gradient, narrow delta plain. The delta-front deposits of coarse-grained sand interfinger and grade into prodelta mud in the seaward direction. The dominance of coarse-grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate. The sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf. A critical balance between progradation, aggradation, and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin.
Repeated fault-controlled uplift of the source, followed by subsidence and transgression, generated multiple fining-upward cycles and a retreating fan-delta system. The marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution. The accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences. Intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering, generated a large amount of detritus, and resulted in forced regressions, repeatedly disrupting the fining-upward pattern. The controls of source rock lithology or climate were of secondary importance to tectonic effects. Retreating fan deltas are rarely reported and may be a stratigraphic response of marine-connected rift basins at the early stage of extension.
The delta stratigraphy is analogous to the submarine fan stratigraphy. In the case where basin shales act as hydrocarbon sources, the fan deltas are potential hydrocarbon reservoirs. The coarse-grained lobes can be excellent reservoirs, with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon. The coarse-grained deposits of the delta plain and proximal delta front, occurring as laterally coalesced, large sand bodies blanketed by transgressive prodelta mud, might also form good reservoirs.
This article has been cited by other articles:
|
|
 |
|
  S. PATRANABIS-DEB, J. SCHIEBER, and A. BASU Almandine garnet phenocrysts in a ~ 1 Ga rhyolitic tuff from central India Geological Magazine, January 1, 2009; 146(1): 133 - 143. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
