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

M. Masroor Alam ¹, A. H. M. Ahmed ², M. Haris A. Khan ²

Affiliations
1 Geology Section, Department of Civil Engineering, Aligarh Muslim University, Aligarh - 202 002, (U.P.), IN
2 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, (U.P.), IN

Abstract

The lower Jurassic Lathi Formation forms the lower part of the Jaisalmer basin and comprises 360 m thick succession of medium to coarse grained sandstones with interbeds of shale, claystone and occasional lignite. The rocks are exposed amidst desert sand as low mounds and in shallow stone quarries. The sandstones were deposited in shallow marine to deltaic depositional environments. Our study deals mainly with the identification of various diagenetic features such as cements and their paragenesis, compaction, depth of burial and porosity evolution. The sandstones are marked by iron oxide, calcite, silica and dolomite cements. Compaction is mainly mechanical with a depth of burial in the range of 725-1125 m. The sandstones show good amount of porosity with an average of 13.3%. Porosity reduction is mainly due to early stage of mechanical compaction and subsequent pervasive calcite and iron oxide cementation.

Keywords

Lathi Formation, Diagenetic Features, Compaction, Cementation, Porosity, Depth of Burial.

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M. Masroor Alam ¹, M. E. A. Mondal ², A. H. M. Ahmad ²

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

Abstract

This study mainly deals with the sandstone lithofacies and petrofacies of Jahaj-Govindpura Formation of the Raialo Group, rich in volcaniclastics, exposed near Hathori village. These cross and planar bedded sandstones are medium grained poorly sorted, and are cemented mainly by iron oxide, carbonate and by matrix rich in phyllosilicates and vitrofelsitic material. The sandstone petrofacies arc rich in detrital modes suggestive of metamorphic source terrain as well as juvenile volcanic 1ithic fragments with textual and mineralogical characteristics typical of neo-volcanic source which was very near to the basin. The underlying clastics of Raialo Group and the overlying formations represented by the Alwar and Ajabgarh Groups of the Jahaj-Govindpura volcanics respectively, do not have a notable amount of volcanic lithics. This suggests that the volcanism was intrabasinal, took place for a shorter time period and was not vety explosive. While the sedimentation continued in this basin, detritus from the highs exposing the BGC and Aravalli Supergroup of rocks in SE and SW were mixed with intrabasinal volcaniclastics. These volcanic highs then may have been carapaced by younger sediments which were deposited in linear rift zones and were eroded from an "Accreted Basement Provenance" comprising Banded Gneissic Complex and Aravalli Supergroup in a short time span.

Keywords

Syn-Depositional Volcanism, Sandstone, Lithofacies, Petrofacies, Tectonic Setting, Bayana Basin, Aravalli-Delhi Fold Belt, Rajasthan.

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A. H. M. Ahmad ¹, M. Masroor Alam ², M. Haris Azim Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, Uttar Pradesh, IN
2 Geology Section, Department of Civil Engineering, Aligarh Muslim University, Aligarh-202 002, Uttar Pradesh, IN

Abstract

The Bayana Sub-Basin comprises thick sequence of metavolcanics and metasedimentary rocks belonging to Delhi Supergroup. The deposition of sediments took place in response to vertical tectonism during Middle Proterozoic in fluvial and shallow marine environments. The rocks are mainly clastics and include conglomerate, sandstone and shale.

The conglomerate lithofacies and petrofacies were studied with a view to understand the tectonic setting of the provenance and the basin. The conglomerate matrix consist of framework detrital grains such as several varieties of quartz followed by rock fragments, mica, feldspar, and heavy minerals. The Qt-F-L, Qm-F-Lt, Qp-Lv-Ls and Qm-P-K diagrams suggest continental block, recycled orogen provenance, rifted continental margin type of basin setting and overall maturity and stability of the continental block provenance. The cement phases in conglomerate matrix consist of iron oxide, silica, carbonate and barite. Dominance of floating, point and long contacts indicates that the sand grains did not suffer much pressure solution.

Keywords

Conglomerate, Petrofacies, Diagenesis, Bayana Sub-Basin, Delhi Supergroup, Bharatpur, Rajasthan.

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A. H. M. Ahmad ¹, M. Masroor Alam ², M. Haris Azim Khan ¹, A. Shahab M. Saeed ³

Affiliations
1 Department of Geology Aligarh Muslim University, Aligarh - 202 002, U P, IN
2 Geology Section, Department of Civil Engineering, Aligarh Muslim University, Aligarh - 202 002, U P, IN
3 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, U P, IN

Abstract

The studied rocks form a part of Upper Rewa Sandstone, which overlies the Kaimur Sandstone in northwest part of the Vindhyan basin, exposed in various isolated ridges around Baretha area of Bayana, Bharatpur district of Rajasthan The sandstones are medium to fine grained and moderately well sorted to well sorted The sandstones consist of various types of quartz followed by feldspar, rock fragments, mica and heavy minerals The petrofacies in Qt-F-L, Qm-F-Lt, Qp-Lv-Ls and Qm-P-K ternary diagrams suggest mainly basement uplift source of craton intenor in rifted continental margin type basin setting with very low input from recycled orogen provenance

The sandstones are well compacted and dominated by interpenetrative contacts and are mainiy cemented by silica with very small amount of carbonate and Iron oxide Quartz overgrowths are well developed on monocrystalline quartz than polycrystalline ones Coarser fraction of detrital quartz grains have sequestered authigenic overgrowths covering more of its grain boundary and are thicker as compared to finer grains Dissolution of quartz along gram boundaries and silica rich compaction pore water seems to be the main source of silica.

Keywords

Sedimentary Petrology, Petrofacies, Diagenesis, Rewa Sandstone, Vindhyan Basin, Rajasthan.

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M. Masroor Alam ¹

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

Abstract

Petrofacies of the Middle Jurassic Jaisalmer sandstones has been analysed in the light of known geotectonic evolution of the Precambrian Aravalli-Delhi fold belt. Various factors responsible for modification of the original detrital composition of the sandstones have been critically examined. In addition, heavy minerals have also been studied to strengthen the interpretation of the provenance.

The Jaisalmer sandstone petrofacies plot in the 'mature craton interior field' rather than the expected 'recycled orogen' and/or 'basement uplift provenance', in accordance with the recent models of orogenic evolution of the Aravalli- Delhi fold belt. The granite-gneiss from the basement uplift as well as the metamorphic and sedimentary rocks of recycled orogen (Aravalli and Delhi Supergroups) acted as the provenance for the Jaisalmer sandstones. The first cycle and recycled detritus were further intensely modified as a result of weathering under warm humid climate and transport before burial, thereby providing mineralogical maturity to the Jaisalmer sandstones.

Keywords

Sandstone Petrofacies, Generic Provenance, Tectonics, Middle Jurassic, Jaisalmer Formation, Rajasthan.

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Saif ud Din ¹, M. Masroor Alam ²

Affiliations
1 Natural Resources and Environmental Research Institute, NRERI/PEC, King Abdul Aziz City for Science and Technology, P.O. Box No. 6086, Riyadh - 11442, SA
2 Department of Civil Engineering, A.M.U., Aligarh - 202 002, IN

Abstract

No Abstract.

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