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

Bijai Prasad ¹, A. K. Dey ², P. K. Gogoi ², A. K. Maithani ²

Affiliations
1 Regional Geological Laboratories, Oil and Natural Gas Commission, Sibsagar 785640, IN
2 Geology Section, Oil and Natural Gas Commission, Jorhat 785614, IN

Abstract

Selected samples from the intertrappean beds of Abor Volcanics were macerated for palynofossils in an attempt to provide fossil evidence for their age, The palyno-fossils so far isolated are trilete and monolete microspores, radial monosaccates and striated as well as non-striated disaccate pollen of Early Permian age. The fossil evi· dence suggests similar age to the intertrappean beds and lead to the conclusion that the Abor Volcanics of the studied area viz., Yinkiong, Dalbuing and Mariyong of Dihang valley (Arunachal Pradesh) are of Early Permian age.

Full Text

     

Bijai Prasad ¹, A. K. Jain ¹

Affiliations
1 KDM Institute of Petroleum Exploration, Oil & Natural Gas Commission, Dehradun-248 195, IN

Abstract

Triassic palynomorph assemblages are recorded from the subsurface sediments of the Krishna-Godavari Basin. Four palynological assemblage zones, ranging in age from Smithian to Norian are identified in different well sections. These assemblages closely resemble Early to Late Triassic palynoflora of northwestern Australia and represent the Onslow type palynoflora.

It is suggested that the subsurface sedimentary sections in this basin, which have yielded typical Smithian to Norian palynoflora, and are termed as "Chintalapudi Sandstones", be referred to as Maleri sequence or its equivalents.

Keywords

Krishna-Godavari Basin, Stratigraphy, Palaeobotany.

Full Text

     

Bijai Prasad ¹

Affiliations
1 KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporation Limited, 9, Kaulagarh Road, Dehradun - 248 195, IN

Abstract

Abundant specimens of Vendian marker species of Obruchevella, a helically coiled filamentous microfossil, are recorded from the sediments of Bhander Group of western Son Valley and DMH-A well, in Madhya Pradesh. Various species of Obruchevella appear in the Ganurgarh Shale, become abundant in the overlying Nagod Limestone and the Sirbu Shale, and are associated with other characteristic Terminal Proterozoic organic-walled microfossils.

The appearance of Obruchevella parva and O. valdaica in the Ganurgarh Shale, with associated occurrence of Vandadasphaeridizrm reticulaturn and Trachysphaeridium laufeldi, suggests Late Cryogenian-Early Vendian (ca. 650- 590 Ma) age. The abundance of above species of Obruchevella in the Nagod Limestone, along with 0. delicata, is broadly indicative of an Early Vendian (ca. 690 - 570 Ma) age. Yet, the appearance of 0. delicata, Lophospharidiurn rarum and Cymatiosphaera sp. in the Nagod Limestone, having their earliest occurrences from Late Vendian, suggests that the age of the Nagod Limestone extends into the Late Vendian (ca. 570 -560 Ma) also. The persistence of the above species of Obruchevella, and the occurrence of Cristallinium sp., Dictyotidium sp. and 0.parvissima in the Sirbu Shale which generally show their appearances in Early Cambrian, is suggestive of a Late Vendian-Early Cambrian age. However, the abundance of Vendian marker species of Obruchevella and the absence of distinctive Early Cambrian acritarchs in the Sirbu Shale, favours a Late Vendian age.

The recovered microfossils provide a strong evidence for a latest Cryogenian to Late Vendian (ca. 650 - 544 Ma) age-range for the Bhander Group. The presence of Vendian marker species of Obruchevella and other Terminal Proterozoic age-potential organic-walled microfossils in the Bhander Group brackets the upper age limits of the Vindhyan Supergroup to the Late Vendian, and seems that it does not encompass the Lower Paleozoic (Cambrian).

Keywords

Terminal Proterozoic, Organic-Walled microfossils, Bhander Group, Vindhyan Supergroup, Son Valley, Madhya Pradesh.

Full Text

     

P. K. Maithy ¹, Gopendra Kumar ², Bijai Prasad ³

Affiliations
1 Birbal Sahani Institute of Paleobotany, Lucknow, IN
2 Geological Survey of India, Lucknow, IN
3 ONGC Ltd., Dehradun, IN

Abstract

No Abstract.

Full Text

   

Bijai Prasad ¹, Ramson Asher ¹, Bihuti Borgohai ²

Affiliations
1 KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporation Limited, 9, Kaulagarh Road, Dehradun - 248 195, IN
2 Geology Division, Oil India Limited, Jodhpur Project, Jodhpur, Rajasthan, IN

Abstract

Characteristic latest Neoproterozoic and Early Paleozoic acritarchs and associated organic-walled microfossils are recorded from the sediments of Marwar Supergroup encountered in BGW-A well (Bikaner-Nagaur Basin) from 1123-481 m depth. Six distinct acritarch assemblages, broadly comparable with globally known Ediacaran (Vendian) and Cambrian assemblages are recognised. The recovered microfossils provide precise age for different units of the Marwar Supergroup whose ages, till now, were poorly understood due to absence or paucity of invertebrate and other mega and microfossils.

Jodhpur Group (1123-1105 m), the basal unit of Marwar Supergroup, records abundant ornamented sphaeromorphs (Lophosphaeridium spp.) alongwith various species of Leiosphaeridia, suggesting Late Ediacaran age. Occurrence of small micrhystrids (Asteridium spp.) and appearance of Dictyotidium birvetense, Pterospermella solida and Annulum squamaceum in lower part of Bilara Group (1105-1081 m), suggests latest Ediacaran to early Early Cambrian age.Hanseran Evaporite Group (1068-907m) is marked by abundant Retisphaeridium dichamerum, Dictyotidium birvetense, Cristallinium cambriense, Comasphaeridium sp. cf. C. strigosum and Archaeodiscina umbonulata indicating late Early Cambrian to early Middle Cambrian age. Microfossil contents in Nagaur Group (907-727m) are very poor. The succeeding Upper Carbonate Sequence (727-481 m) shows abundant Cristallinium randomense, Cymatiosphaera crameri and Asteridium spp., along with other species of Cymatiosphaera and Cristallinium, and also includes the early Late Cambrian marker forms, such as Striatotheca loculifera and Dorsenidium (Veryhachium) minutum that suggest late Middle Cambrian to early Late Cambrian age.

The recorded acritarch assemblages suggest Late Ediacaran to early Late Cambrian (ca 570-500 Ma) age for the Marwar Supergroup, with demarcation of Precambrian-Cambrian boundary within the lower part of Bilara Group. Associated microfossils indicate Intertidal/Foreshore depositional environment for Jodhpur and Nagaur groups, whereas inner neritic to subtidal for the Bilara, Hanseran and Upper Carbonate units. Occurrence of an Early Permian palynoflora in the succeeding sequence (481-427 m depth) indicates a major hiatus of ca 200Ma between the Marwar and overlying Bap/Badhaura sequences which involves the absence of middle Late Cambrian to Late Carboniferous sediments in this basin.

Latest biostratigraphic data from Ujhani (Ganga Basin) and Bhander (Vindhyan Basin) sediments suggest that the above two sequences are closely comparable with the Marwar Supergroup, and show the prospective exploration challenges as do the Marwar Supergroup.

Keywords

Acritarch Biostratigraphy, Marwar Supergroup, Bikaner-Nagaur Basin, Rajasthan.

Full Text

     

Bijai Prasad ¹

Affiliations
1 KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporation Ltd., Dehra Dun - 248195, IN

Abstract

Palynological studies carried out on the "red beds" encountered in the subsurface sections of Krishna-Godavari Basin establish the occurrence of two distinct red beds; the older of Triassic age, deposited in fluvial intracratonic Pranhita-Godavari Graben and equated with the Maleri rocks of Central India and an younger one of Early Cretaceous (Neocomian - Barremian) age, deposited during synrift stage of the Krishna-Godavari Basin in marginal to shallow marine environment, corresponding to the red claystones of Gollapali Formation. A major hiatus of about 80 Ma is present between the two red beds involving the absence of latest Triassic and major part of Jurassic sediments.

The gaseous pay-sand zones in Mandapeta and Ramchandrapuram structures which lie just below the Cretaceous red beds, belong to the Gollapali Sandstone and indicate Early Cretaceous (Neocomian-Barremian) age. The Cretacous red beds are considered to serve as caprocks for hydrocarbon accumulation in these pay-sands.

Keywords

Energy Resources, Hydrocarbons, Red Beds, Krishna-Godavari Basin, Andhra Pradesh.

Full Text