PG Department of Geology

During intervals of Pleistocene glaciation, insolation of the high-latitude northern hemisphere was lower than today, particularly during summer. Growth of continental ice sheets resulted in a lowering of sea level by more than 100 m in the Bering Sea. As a result, the Bering Strait was closed and most of the Bering continental shelf exposed. A proposed model predicts that (1) sea-ice formation would occur along the (modern) outer continental shelf, (2)advection would transport the sea ice over the deep basin, and (3) brine would flow into the basin at some intermediate depth to enhance the halocline. The result would be a low-salinity surface layer with a cold, thick halocline and reduced vertical mixing. Diatom microfossils and lithologic changes in sediment cores from the North Pacific Ocean and Bering Sea support the model and suggest that the proposed oceanographic conditions extended into the North Pacific, where the cold low-salinity laycr was enhanced by meltwater from continentally derived icebergs.

The sedimentary beds associated with Deccan Continental Flood Basalt (DCFB) sequences exposed in the volcanic subprovinces of Jabalpur-Mandla-Chhindwara (JMC) regions of Madhya Pradesh and Nand-Dongargaon (N-D) basin and the adjoining areas to the west in Yeotmal-Nanded in Maharashtra were studied for their palynofloral analysis. The sediments were characterized palynologically and changes in the palynoflora are observed at different stratigraphic levels in a number of sections including several new intertrappean localities recorded in recent years. For the purpose of effective correlation of different subprovinces, palynofloras of some of the previously studied intertrappeans are also reviewed. Our studies suggest that before the start of the Deccan volcanic activity, the palynoflora found in the Lameta sediments, was dominated by gymnosperms-angiosperm association. The plant canopy consisted mainly of gymnosperms (Conifers and Podocarpaceae) whereas, the understory members were mostly of palms and herbs (Poaceae and Asteraceae). The eruption of Deccan volcanic flows severely affected the existing floral association and proved fatal for the well established plant community. The immediately overlying sediments associated with the earliest volcanic flows are dominated by pteridophytes and angiosperm taxa (Azolla cretacea, Aquilapollenites bengalensis, Ariadnaesporites sp., Gabonisporis vigourouxii and Triporoletes reticulatus). Higher up in the stratigraphic sequence, similar forms continued with simultaneous appearance of new taxa including Scabrastephanocolpites spp. At still higher stratigraphic levels, abundance of fungi especially the mycorrhizal fungi, concurrent with sharp decline in pollen/spore recovery was observed. In the culminating phase (i.e. Palaeocene) of Deccan volcanic history a new palynofloral assemblage of typical Palaeocene taxa (Dandotiaspora dilata, D. pseudoauriculata, D. plicata, Spinizonocolpites echinatus, Matanomadhiasulcites sp., and Lakiapollis ovatus) was encountered.

Rice and its relatives are a focal point in agricultural and evolutionary science, but a paucity of fossils has obscured their deep-time history. Previously described cuticles with silica bodies (phytoliths) from the Late Cretaceous period (67-65 Ma) of India indicate that, by the latest Cretaceous, the grass family (Poaceae) consisted of members of the modern subclades PACMAD (Panicoideae-Aristidoideae-Chloridoideae-Micrairoideae-Arundinoideae-Danthonioideae) and BEP (Bambusoideae-Ehrhartoideae-Pooideae), including a taxon with proposed affinities to Ehrhartoideae. Here we describe additional fossils and show that, based on phylogenetic analyses that combine molecular genetic data and epidermal and phytolith features across Poaceae, these can be assigned to the rice tribe, Oryzeae, of grass subfamily Ehrhartoideae. The new Oryzeae fossils suggest substantial diversification within Ehrhartoideae by the Late Cretaceous, pushing back the time of origin of Poaceae as a whole. These results, therefore, necessitate a re-evaluation of current models for grass evolution and palaeobiogeography.

Late Cretaceous-Early Paleogene sediments associated with Deccan Continental Flood Basalt (DCFB) sequences of central and western India record the timing of the introduction and extinction of Late Cretaceous dinosaurs in India based on magnetostratigraphy and magnetic susceptibility stratigraphy. Current taxonomy indicates that only two genera of titanosaurs (e.g., Isisaurus and Jainosaurus), at least four species of large-bodied abelisauridae theropods (e.g., Rajasaurus narmadensis, Rahiolisaurus gujaratensis, Indosuchus matleyi and Indosaurus raptorius) and a small-bodied theropod Laevisuchus inhabited India during the Maastrichtian. Their stratigraphic and geographic distribution suggests that these dinosaurs were dominated by titanosauriforme and abelisauridae that first appeared before the advent of Deccan volcanism in the magnetochron C30n and were well established with the acme of breeding and nesting during C30n to maastrichtian C29r. Their decline in diversity and abundance coincides with initiation of DCFB eruptions when most of the early taxa were terminated and only a few titanosauriforme sauropods survived becoming extinct at about 350 kyr before the Cretaceous-Paleogene boundary (KPB). Dinosaur extinction in India is thus directly tied to Deccan volcanism with no evidence of an asteroid impact.

Palynological studies of Deccan volcanic associated sediments of the Sahyadri Group of Nand-Dongargaon basin of Maharashtra, Amarkantak Group of Chhindwara and unclassified Deccan Trap sequences of Saurashtra show the presence of Aquilapollenites pollen. The overall data on this genus from the Indian Late Cretaceous-Early Paleocene indicates that the genus was widely distributed during the Late Cretaceous. A notable decline in abundance in the Early Paleocene may be related to the climatic and environmental changes brought about by the Deccan volcanism.

The Deccan Continental Flood Basalt (DCFB) sequence of India includes the volcanic flows of the Deccan Traps and the intertrappean sedimentary lacustrine deposits that lie in between the flows. The well-preserved arcellinidan taxon Centropyxis aculeata and associated diatoms on their tests are described for the first time in India from palaeolake sediments (Maastrichtian) of the Bagwanya Intertrappean sequence in Central India. Laminated shales and clays yielded diatoms, arcellinidans and sponge spicules, whereas other lithofacies composed mainly of black cherts yielded marker palynomorphs of Maastrichtian age. Diatoms isolated from the sediments include the poorly preserved centric diatom Aulacoseira and other pennate diatoms. Sponge spicules are present in this microfossil assemblage and show similarity with the extant genus Corvospongilla. Five diatom taxa, Cyclotella sp. (? meneghiniana); Pantocsekiella sp. (? ocellata); Achnanthes sp. (? brevipes); Diadesmis sp. (? confervacea); and Oricymba sp. (? tianmuensis), found associated with the tests of Centropyxis aculeata have been described. Palaeoecological interpretation of this palaeolake is based on the information derived from lithology, arecllinidans, diatoms and the palynomorphs. Bagwanya Palaeolake was a perennial, warm water, well oxygenated and very low salinity lake, surrounded by tropical to subtropical terrestrial and aquatic plants along its coast and also under shallow waters. The environment in this lake was under stress due to ongoing and extensive volcanism in the region, leading to SO 2 and CO 2 outgassing. Xenosomes of sand and various species of diatoms on the test of Centropyxis aculeata indicate that the shallow benthic environments of the lake had a sandy substrate.

The megaflora-rich intertrappean cherts near the village Mohgaon Kalan in Chhindwara District, Madhya Pradesh has been known since 1934 when K. P. Rode1 first reported dicotyledonous woods from this intertrappean. Sahni and Rode carried out pioneering work on megaflora of this horizon and during the following seven decades numerous additional megafloral remains, representing pteridophytes, gymnosperms, angiosperms, algae and fungi have been reported.

Eruptions of lava flows of Deccan large igneous province straddled the Cretaceous-Palaeogene boundary (K-Pg). Sediments associated at different stratigraphic levels within the lava piles of Deccan volcanic sequences (DVS) are mainly terrestrial. We studied the sediments of Eastern and Central Deccan Volcanic Province, and the Malwa Plateau for tracking changes in reptilian tetrapods across the volcanism. The reptiles are mainly represented by abelisaurid-titanosaurid dinosaurs, Alethinophidia madtsoiia snakes, Notosuchian crocodylomorph Simosuchus, bothremydid Kurmademydinae turtles and Anguimorph and Scincomorphs lizards. The evidences suggest that the non-avian dinosaurs were adversely affected by the arrival of the first volcanic flows locally in the province either within C30N or C29R Maastrichtian. The abelisaurid theropods became extinct whereas a single or two species of titanosauriforme dinosaurs survived but eventually became extinct at least 350 ky before the K-Pg boundary with increasing volcanism. The madtsooid snakes and crocodylimorphs were also adversely affected with decline in their diversity and abundance, whereas the Bothremydid turtles survived the initial onslaught of Deccan volcanism and continued across the K-Pg boundary.

Micofloral study of Lameta sediments and associated sauropod coprolites in the Nand-Dongargaon basin in Maharashtra was conducted to understand the diet and habitat of sauropods. The study revealed the presence of pollen, spores, algal and fungal remains, well-preserved cuticles of Poaceae, and testate amoebae. Vegetation during Lameta included tall arboreal taxa, such as conifers (Podocarpus and Araucaria), Cycads (Cycas), Euphorian and Barringtonia and herbs and shrubs, such as Cheirolepidiaceae (Classopollis), Arecaceae (Palmaepollenites), Poaceae (Graminidites), Asteraceae (Compositoipollenites), Caryophyllaceae (Cretacaeiporites and Periporopollenites), and Acanthaceae (Multiareolites). Data suggest that the sauropods ate soft tissues of angiosperms and gymnosperms. The intake of testate amoeba, algal remains, sponge spicules, and diatoms might be through water intake.

Presence of charcoal in intertrappean lake sediments associated with the Malwa Group of the Deccan trap, India is recorded. The finding provides the first evidence of palaeofire in the Indian late Cretaceous. Though previous studies have shown the presence of carbonaceous clays and coal bands in the Deccan volcanic associated sediments, the presence of fossil charcoal in the sediments is rarely reported. The fossil charcoal was identified based on optical microscope, Scanning Electron Microscope and Pyrolysis-Gas Chromatography Mass Spectrometer (Py-GC-MS). This study indicates that charcoal is derived from burning of plants caused by forest fire during the Maastrichtian (Chron 30N).

In this study, thermoluminescence (TL) characterization of fossils of sauropod dinosaur bone, dinosaur eggshells, and associated sediments were recorded for the first time. The fossil bone was collected from the Bagwanya intertrappean sediments in the Dhar district of Madhya Pradesh, India. TL was recorded using 60Co gamma ray exposure at different doses. Fossils of dinosaur bone, dinosaur eggshells, and associated sediments were irradiated using 60Co gamma rays at different doses from 0.15 kGy to 19 kGy. The linear dose–response curve of the irradiated sample was obtained for a dose ranging from 0.15 kGy to 9.5 kGy. These geological samples were characterized further using X‐ray diffraction for confirmation with phase, scanning electron microscopy, Fourier transform infrared spectroscopy, and wavelength dispersive‐X‐ray fluorescence for determination of the elemental composition in parts per million to percentage levels.