A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Mishra, Diwakar
- Microfacies Analysis of Transgressive Condensed Sequence: a Study from the Oxfordian of Kachchh Basin, Gujarat
Authors
1 Department of Geology, Banaras Hindu University, Varanasi-221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 6 (2007), Pagination: 923-932Abstract
1-9m thick Dhosa Oolite Member of Chan Formation exposed in Kachchh Mainland, western India, represents a condensed transgressive sequence of the Oxfordtan age. It is composed of hard and compact, fossilifeious, sandy/conglomeratic oolitic limestone interbedded with friable, thinly bedded calcareous siltstone/fine sandstone Field&petrographic studies revealed six microfacies namely, (i)sandy/pebbly ironstone(A1), (ii)conglomeratic fossililerous ironstone (A2), (iii)conglomeratic fossiliferous oolitic packstone(B1), (iv) sandy oolitic packstone (B2), (v) siltstone (C1), (vi) fine grained sandstone (C2). These microfacies are grouped in to three microfacies assemblages namely (i)sandy oolitic Packstone-Siltstone assemblage (B2-C1), (ii) Siltstone-Fine grained sandstone assemblage (C1 - C2) and (iii) conglomeratic fossiliferous oolitic packstone - fine grained sandstone assemblage (C2-B1).The study of microfacies suggests that the deposition of the Dhosa Oolite Member took place in an open marine shallow shelf environment with clear proximal-to'distal trend from southeast to northwest. Two transgressive pulses were responsible for its formation. An earlier slow and frequently interrupted transgression together with subsidence is lecordedby abrupt change in clastic grain size, mixing of two lithologies and abundance of siliciclastics in each microfacies Later, rapid transgression is suggested by the extremely reduced thickness, erosive to irregular contacts, development of intraformatjonal conglomerates, multi phase reworked sediments, an increase in the abundance of carbonates and ammonites and negligible sediment input Lateral vanation in the microfacies and their assemblages together with variable extent of marine mega fauna (ammonites) from southeast to northwest marks the depositional slope ot the basin towards northwest during studied interval. The mixed lithologies in this condensed sequence together with the bioturbated nature of sediments suggest that the rate of sedimentation was extremely slow.
Keywords
Microfacies, Transgressive Condensed Sequence, Dhosa Oolite Member, Oxtordian, Kachchh, Gujarat.
- Provenance Study of Siliciclastic Sediments, Jhura Dome, Kachchh, Gujarat
Authors
1 Department of Geology, Banaras Hindu University, Varanasi - 221005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 65, No 6 (2005), Pagination: 703-714Abstract
Provenance of the siliciclastic rocks of Patcharn and Chari Formations (Bathonian to Oxfordian) has been ascertained by means of heavy mineral studies. The study shows abundance of transparent heavies like garnet, zircon, tourmaline, staurofite, rutile, hornblende, andalusite, kyanite, anatase and epidote, in decreasing order, and constitute 26.47 per cent of total heavies. The opaque group is represented mainly by goethite and limonite, which constitute 73.45 per cent. The statistical data of heavies reveals that garnet, zircon and tourmaline are more or less uniform throughout the stratigraphic column and constitute 43.92 per cent, 22.27 per cent and 19.99 per cent respectively. The average percentage of staurolite and rutile is 5.40 and 4.52. The percentage of anatase, kyanite, hornblende, anddusite and epidote is very less. On the basis of distribution pattern of heavy minerals in stratigraphic column, heavies are grouped into two distinct assemblages i.e. (i) Garnet-Staurolite-Hornblende-Kyanite-Epidotaes semblage, (ii) prismatic and rounded to subrounded grains of Zircon-Tourmaline-Rutile assemblage.The presence of heavy mineral assemblages in the stratigraphic column reveals that the sediments of Patcham and Chari Formations have been derived mainly from two 1ithologicalIy different Precambrian terrains; one is dominated by metamorphic rocks and the other is igneous (acid and basic), besides a little contribution of sedimentary source. Source rocks were situated close to basin of deposition in the noflheast and east i.e. Aravalli range and north and northwest dominated by Granite-Syenite suite belonging to Nagar-Parkar Massif. The variable ZTR index indicates manifestation of relief and climatic change in the source area.
Keywords
Heavy Minerals, Provenance, Patcham-Chari Formations, Jhura Dome, Kachchh Basin, Gujarat.- Sedimentology, Sequence Stratigraphy and Syn-Rift Model of Younger Part of Washtawa Formation and Early Part of Kanthkot Formation, Wagad, Kachchh Basin, Gujarat
Authors
1 Department of Geology, Banaras Hindu University, Varanasi - 221005, IN
2 201/C ISM House, Thakur Village, Kandivali (E), Mumbai - 400101, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 73, No 4 (2009), Pagination: 519-527Abstract
The 600 m thick prograding sedimentary succession of Wagad ranging in age from Callovian to Early Kimmeridgian has been divided into three formations namely, Washtawa, Kanthkot and Gamdau. Present study is confined to younger part of the Washtawa Formation and early part of the Kanthkot Formation exposed around Kanthkot, Washtawa, Chitrod and Rapar. The depositional architecture and sedimentation processes of these deposits have been studied applying sequence stratigraphic context.Facies studies have led to identification of five upward stacking facies associations (A, B, C, D, and E) which reflect that deposition was controlled by one single transgressive - regressive cycle. The transgressive deposit is characterized by fining and thinning upward succession of facies consisting of two facies associations: (1) Association A: medium - to coarse-grained calcareous sandstone - mudrocks alternations (2) Association B: fine-grained calcareous sandstone - mudrocks alternations. The top of this association marks maximum flooding surface as identified by bioturbational fabrics and abundance of deep marine fauna (ammonites). Association A is interpreted as high energy transgressive deposit deposited during relative sea level rise. Whereas, facies association B indicates its deposition in low energy marine environment deposited during stand-still period with low supply of sediments. Regressive sedimentary package has been divided into three facies associations consisting of: (1) Association C: gypsiferous mudstone-siltstone/fine sandstone (2) Association D: laminated, medium-grained sandstone - siltstone (3) Association E: well laminated (coarse and fine mode) sandstone interbedded with coarse grained sandstone with trough cross stratification. Regressive succession of facies association C, D and E is interpreted as wave dominated shoreface, foreshore to backshore and dune environment respectively.
Sequence stratigraphic concepts have been applied to subdivide these deposits into two genetic sequences: (i) the lower carbonate dominated (25 m) transgressive deposits (TST) include facies association A and B and the upper thick (75m) regressive deposits (HST) include facies association C, D and E. The two sequences are separated by maximum flooding surface (MFS) identified by sudden shift in facies association from B to C. The transgressive facies association A and B represent the sediments deposited during the syn-rift climax followed by regressive sediments comprising association C, D and E deposited during late syn-rift stage.
Keywords
Sedimentology, Sequence Stratigraphy, Synrift Model, Wagad, Kachchh Basin, Gujarat.References
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