Annual Report 2011-2012 - Birbal Sahni Institute of Palaeobotany

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EBIRBAL SAHNI INSTITUT 1946 OF PALAEOBOTANY Annual Report 2011-2012 Distribution of sedimentary organic matter, Tirap Colliery brackish water (marine) influence. Raised mires, autochthonous swamps and allochthonous organic matter accumulations comprise the vitrinite-rich high volatile bituminous B coals. The upper third of the section represents upper delta plain environments with high sediment pass-through. Here standing fossil ‘forests’ attest to frequent inundation and recovery of the arborescent inter-fluvial vegetation. A dominance of spores attributed to the Cyatheaceae and other fern taxa indicate tree ferns and other pteridophytes were a major component of the vegetation throughout the environments represented by the section, despite the absence of ferns in the megafossil record. Nypa and mangrove mega remains together with mangrove pollen and Acrostichum spores attest to the presence of a mangrove community similar in composition to those of modern south-east Asia. Palms and megathermal tree taxa such as those belonging to the Malvaceae, Meliaceae, Alangiaceae, Anacardiaceae and Pellicieraceae inhabited the interfluve and swamp forests. Palynofacies analysis shows a dominance of anoxic/dysoxic environments with a small part of the lower part of the section exhibiting more oxic conditions associated with circumstantial evidence for mild marine, possibly tidal, influence. Most palynodebris fluoresce only weakly consistent with the relatively high rank for coals of this age. A small number of reworked Gondwanic (Permian) grains suggest sediment erosion from the highlands to the north. The late Oligocene tropical delta vegetation has much in common with modern lowland wet megathermal forests from south-east Asia. (jointly with N.C. Mehrotra, R.C. Mehrotra, Gaurav Srivastava, R.A. Spicer & T.E. Spicer). In addition, macerated samples collected from Jagun coal mine and well drilled for tracing coal seams along the Namphuk River, Assam N # 4, N # 7 and N#11. Slides of productive samples have been prepared and scanned. Madhav Kumar Project 5.6: Palynological investigation of Miocene sediments of Mizoram and Tripura A rich and diversified palynofloral assemblage has been recorded from the Bhuban Formation exposed along Kanchanpur road cutting section (north of Tripura). The palynoassemblages are assigned to an early Miocene in age, based on marker taxa, such as Spinizonocolpites echinatus, Striatriletes susannae, Pteridacidites tripuraensis, Osmundacidites wellmanii, Acanthotricolpites brevicolpus, Retitrescolpites typicus, Hibisceaepollenites robustispinosus, etc. The other associated palynotaxa are Malvacearumpollis sp, Trisyncolpites ramanujamii, Chenopodipollis sp, Piceapollenites excellensus, Abiespollenites cognatus, Pinuspollenites crestus, Operculodinium centrocarpum, Cleistosphaeridium diversispinosum, Spiniferites mirabilis, Oligosphaeridium complex, Densoisporites velatus, Callialasporites sp, Cannanoropollis trilobatus and Cuneatisporites rarus. The significant taxa of the palynoflora have been compared to those of the extant members of the family Microthyriaceae, Cyatheaceae, Osmundaceae, Schizeaceae, Parkeriaceae, Acaceae, Parkeriaceae, Polypodiaceae, Pteridaceae, Malvaceae, Pinaceae, Podocarpaceae, etc. The sediments were deposited in a marginally marine environment under terrestrial influence, as indicated by the presence of very rare dinocysts and significant amount of cuticular material. The presence of Spinizonocolpites suggests a shoreline inhabited by mangroves. The occurrence of pollen mangrove taxa 18 www.bsip.res.in
EBIRBAL SAHNI INSTITUT Annual Report 2011-2012 1946 OF PALAEOBOTANY which belongs to a coastal marsh vegetational community, support the presence of tidal swamps near the area of deposition. The diversity of angiosperm palynoflora, which forms the bulk of assemblage, is thought to indicate a dense low land vegetation cover. The taxonomic diversity of palynofloral associations indicate that the deposition of Miocene sediments took place in high energy, brackish water and reducing conditions. Recorded palynotaxa indicate the prevalence of a moist, subtropical climate in the studied area. In addition, field work is conducted in Tripura and its adjoining areas, and collected 185 palynological samples for study. B.D. Mandaokar Project 5.7: Palynological investigations of the Disang Group its palaeofloristic trends, palaeoecological and palaeogeographical interpretations Completed palynological study of Disang Group exposed along Silchar-Haflong Road, North Cachar Hills district, Assam. Disang Group exposed along the road is predominantly made up of shales which are generally black to dark steel grey, weathering to reddish brown. This is laminated, highly fissile to splintery. The Disang shales are assumed to be fluvial, non-marine, flood plain deposits formed in a narrow trough. Recovered and identified palynofossils like Cyathidites australis, C. minor, Todisporites major, T minor, Lygodiumsporites, pachyexinus, L. eocenicus, Intrapunctisporis intrapunctis, Baculatisiporites wellmanii, Monolites mawkmaensis, Polypodiisporonites repandus, P. tuberculensis, Laevigatosporites tertiarus, Hammenisporis micoverrucosus, Pinuspollenites crestus, Densiverrupollerites eocenicus, Pellicieroipollis langenheimii, Favitricolporites magnus, Palmaepollenites ovatus, besides reworked Gondwana palynofossils like Cingulatisporites sp., Indotriradites sparsus, Vitreisporites densus, Lundbladispora sp., Callialasporites segmentatus. The palynological assemblage recovered is dominated by pteridophytes particularly those belonging to family Cyatheaceae, Polypodiaceae, Parkeriaceae, Schizaeaceae, Matoniaceae and Osmundaceae. Presence of gymnospermous bisaccate pollen, Pinuspollenites, suggests that the topographically elevated areas were not far away from the basin of sedimentation. The recorded assemblage indicates that the area enjoyed moist, warm, humid, tropical to subtropical climate and the sedimentation seem to have taken place in fresh water environment with ponding conditions nearby. The upper recorded palynoassemblage indicates Late Eocene age to these Disang sediments. Additionally, scanned slides of the samples of Disang Group collected from Jotsoma village, near Kohima TV Station, Nagaland. Recovered and identified palynofossils like Cyathidites australis, Lygodiumsporites lakiensis, Gleicheniidites senonicus, Monolites mawkmaensis, Lavigatosporites tertiarus, Polypodiisporonites oligocenicus, Hammenisporis susannae, H. multicostatus, Pinuspollenites crestus, Lakiapollis ovatus, Dermatobrevicolpites dermatus, Margocolporites tsukadae. G.K. Trivedi Thrust Area: Project 6.1: INTEGRATIVE MICROPALAEONTOLOGY, BIO-PETROLOGY AND ORGANIC FACIES: RELEVANCE TO FOSSIL FUEL CHARACTERIZATION & EXPLORATION (Integrated approach to realizing economic potential in prospective basins) Marine Micropalaeontology Group High resolution biostratigraphy, biotic turnover, palaeoclimate and relative sea level changes during Late Cretaceous-Early Palaeogene (~80-35 Ma) in South Shillong Plateau, Meghalaya, northeastern India Within a precise sedimentological framework palynofacies analysis of Mahadek Formation (late Cretaceous), Cherrapunji area has been studied. Lithofacies in different sections of the Mahadek Formation have been determined and interpreted in terms of depositional processes. The sedimentological study shows formation of fan delta complex during earliest marine incursion in South Shillong plateau. Palynofacies study of fine grained sediment succession in between the boulder conglomerate facies of Mahadek Formation indicate www.bsip.res.in 19
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Page 5 and 6: Contents Foreword .................
Page 7 and 8: Foreword The Birbal Sahni Institute
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Annual Report 2011-2012 - Birbal Sahni Institute of Palaeobotany

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