Vandana Prasad

Dinosaur Coprolites and the Early Evolution of Grasses and Grazers

Silicified plant tissues (phytoliths) preserved in Late Cretaceous coprolites from India show that at least five taxa from extant grass (Poaceae) subclades were present on the Indian subcontinent during the latest Cretaceous. This taxonomic diversity suggests that crown-group Poaceae had diversified and spread in Gondwana before India became geographically isolated. Other phytoliths extracted from the coprolites (from dicotyledons, conifers, and palms) suggest that the suspected dung producers (titanosaur sauropods) fed indiscriminately on a wide range of plants. These data also make plausible the hypothesis that gondwanatherian mammals with hypsodont cheek teeth were grazers.

Early Eocene warming events and the timing of terrestrial faunal exchange between India and Asia

The timing of initiation of continent-continent collision between Asia and India is controversial, but this major tectonic event is generally thought to have occurred in the Early Eocene, ca. 50 Ma. New and independent data from strontium isotopes, stable carbon isotopes, microfossil biostratigraphy, and mammal fossils from an Early Eocene marginal marine sequence (Cambay Shale) at the Vastan Lignite Mine of western India indicate that terrestrial faunal exchanges, and therefore continental collision, between Asia and the Indian subcontinent took place before 53.7 Ma. This age coincides with the second Eocene Thermal Maximum (ETM2), a short-lived warming episode that followed the Paleocene-Eocene Thermal Maximum (PETM) ca. 55.5 Ma. Our data also document, for the first time, a clear record of the ETM2 in terrestrial organic material from a low-latitude site, which is represented by a 3‰−4‰ carbon isotope excursion (CIE) in lignite and dispersed organic carbon δ13C values. The magnitude of the CIE at this location closely matches that observed in marine cores from the Arctic Ocean, which supports an interpretation that this hyperthermal event, though of lower magnitude, was similar in character to that of the PETM, being a global phenomenon that affected both terrestrial and marine ecosystems.

Evidence of Late Palaeocene-Early Eocene equatorial rain forest refugia in southern Western Ghats, India

Equatorial rain forests that maintain a balance between speciation and extinction are hot-spots for studies of biodiversity. Western Ghats in southern India have gained attention due to high tropical biodiversity and endemism in their southern most area. We attempted to track the affinities of the pollen flora of the endemic plants of Western Ghat area within the fossil palynoflora of late Palaeocene-early Eocene (∼55–50 Ma) sedimentary deposits of western and northeastern Indian region. The study shows striking similarity of extant pollen with twenty eight most common fossil pollen taxa of the early Palaeogene. Widespread occurrences of coal and lignite deposits during early Palaeogene provide evidence of existence of well diversified rain forest community and swampy vegetation in the coastal low lying areas all along the western and northeastern margins of the Indian subcontinent. Prevalence of excessive humid climate during this period has been seen as a result of equatorial positioning of Indian subcontinent, superimposed by a long term global warming phase (PETM and EECO) during the early Palaeogene. The study presents clear evidence that highly diversified equatorial rain forest vegetation once widespread in the Indian subcontinent during early Palaeogene times, are now restricted in a small area as a refugia in the southernmost part of the Western Ghat area. High precipitation and shorter periods of dry months seem to have provided suitable environment to sustain lineages of ancient tropical vegetation in this area of Western Ghats in spite of dramatic climatic changes subsequent to the post India-Asia collision and during the Quaternary and Recent times.

Evidence of enhanced winter precipitation and the prevalence of a cool and dry climate during the mid to late Holocene in mainland Gujarat, India

The Kothiyakhad sedimentary sequence of Mahi estuary in mainland Gujarat, India, contains valuable information on late- to mid-Holocene climatic conditions as inferred by phytolith, palynofacies, magnetic susceptibility and clay mineralogical studies. Three distinct climatic regimes, ie, Phase I, II and III, were established. Phase I (3660—~3400 yr BP) shows a gradual weakening of SW monsoonal activity, though overlapped by enhanced western disturbances which led to the development of cool climatic conditions. The coupled effect of SW monsoon and enhanced winter precipitation produced improved hydrological conditions, which supported the agrarian society of the Indus Valley civilization until the beginning of Phase II (~3400—~3000 yr BP). During Phase II the SW monsoon was in a state of severe recession, leading to severe drought-like conditions, other than for a brief but intensely warm and humid pulse recorded at ~3320 yr BP, associated with SW monsoonal activity. In Phase III (~3000—2850 yr BP), SW precipitation fluctuated greatly with a considerable increase in warm summer conditions, similar to present-day conditions. The weak SW monsoonal activity ~3500 yr BP also coincided with a global cool and arid phase and this probably explains the timing as well as the cause of why the population of the Indus civilization migrated to more humid areas to sustain their livelihoods.

Characteristic modern pollen assemblages in relation to vegetation types in the East Khasi Hills, northeast India

ABSTRACT This paper presents characteristic modern pollen assemblages in relation to various vegetation types from one of the wettest regions of the world. Four characteristic modern pollen assemblages were recorded based on the major pollen taxa recovered from the surface samples. The Pinus—Tsuga—Betula—Quercus—Rhododendron—Chenopodiaceae assemblage was observed in pine forests under cold and wet climate in the region. The broad leaved forests were characterised by the Quercus—Betulaálnus—Rhododendron—Pinusímpatiens assemblage. The evergreen forest assemblage Castanopsis—Mesua—Betula—Magnoliaceae—Dipterocarpaceae—Nepenthes was suggestive of a cold and wet climate due to seasonally high rainfall activity. Grassland was identified by the recovery of a Poaceae—Cyperaceaeásteraceae—Chenopodiaceae—cerealia assemblage in the surface samples under relatively dry climate with seasonal rainfall. The study revealed that the grasslands of East Khasi Hills are not the primary vegetation, but that it is converted from the primary dense forest as evidenced by the recovery of pollen from evergreen and broadleaved taxa in the surface samples. The presence of cerealia in almost all samples strongly indicates human activity in and around the study areas. Ferns, especially Cyathea, Gleichenia and Pyrrosia, in the palynoassemblage were suggestive of wet conditions in the region. Fungal remains such as Meliola, Microthyriaceae and Xylaria along with high organic matter in the palynoassemblage also suggest the same. The thrust of this study was to investigate the characteristic pollen assemblage in the surface samples in relation to the present vegetation of northeast India.

Multi-proxy evidence for an arid shift in the climate and vegetation of the Banni grasslands of western India during the mid- to late-Holocene:

Tropical semi-arid grasslands are a widespread and ecologically and economically important terrestrial biome. Here, we use paleoecology to understand woodland–grassland transitions across the mid- to late-Holocene period in the Banni grassland, western India. Multi proxy analyses involving palynology, phytoliths and elemental geochemistry were carried out on two sediment cores retrieved from wetlands (Chachi and Luna), to understand temporal fluctuations in vegetation, moisture availability and other environmental parameters. Based on the results, the Chachi core was divided into two major climatic phases. Phase 1 (4600–2500 cal. yr BP) was characterised by high precipitation and abundance of pollen types and phytolith morphotypes that indicate the presence of woody savanna, and mesic herbaceous taxa. Phase 2 (2500 cal. yr BP to the present) was characterised by lower precipitation, lower abundance of mesic taxa and an increase in grass phytolith abundance. However, the period from ~1000 cal. yr BP to the present was characterised by the increased abundance of leguminous taxa, dryland herbs/shrubs and a decline in grass phytolith abundance. The Luna core (~1000 cal. yr BP to the present) also showed results matching with the Chachi core for this latter period. Overall, moisture availability in the ecosystem appears to have declined since 4600 cal. yr BP, and the vegetation has responded to this. Although the balance between tree, shrub and grass elements has fluctuated, overall, the region has remained as an open ‘grass and shrub savanna’ with sparse woody vegetation throughout this period. Our study provides insights into the vegetation dynamics and environmental settings in a poorly understood tropical arid-grassland ecosystem from Asia during the mid-late-Holocene.

Palynofacies Study of Lakadong Limestone (Late Paleocene) of Mawsynram Area, Shillong Plateau, India: Implications for Sequence Stratigraphy

Subtle paleoenvironmental fluctuations are difficult to detect in sedimentologically uniform carbonate rocks, however, study of relative increase and decrease of marine and terrestrial organic matter content provides a useful tool for deciphering the deepening and shallowing cycles in these successions. Lakadong Limestone Member in Khasi and Jaintia hills in South Shillong Plateau is late Paleocene in age and forms part of the carbonate platform. It represents deposition during High Stand Systems Tract. In the present study palynofacies analysis were carried out in two Lakadong Limestone sections i.e., Dohsniang (Kurtinsiang) (KPL) and Laitmowksing (LTL) from Khasi hills for detailed palaeoenvironmental interpretations, for the correlation and for the identification of higher order sea level cycles. Both the sections have been dated as late Paleocene based on the characteristic larger benthic foraminiferal assemblages belonging to the Tethyan Shallow Benthic Zones SBZ 3. For palynofacies analysis various type of organic matter were characterized and counted. The study shows cyclicity pattern in the organic matter types in both the sections which may be linked to the sea level changes of higher order cycles. Based on the variation in the organic matter content both the sections were subdivided into distinct palynofacies units. Each palynofacies unitsstart with high proportion of black oxidized palynomaceral along with dinoflagellate cysts representing a transgressive surface, followed by high quantity of degraded brown and cuticle organic matter from terrestrial source. Each palynofacies unit thus represent progradational deposit of High Stand Systems Tract starting with the deepening facies followed by shallowing facies of more terrestrial origin. Four progradational sequences have been identified in the KPL and three in the LTL section that can be correlated. Palynofacies study thus offers a logical approach for the study of uniform carbonate facies. Based on the present palynofacies criteria it has been possible to identify higher order sea level cycles in the Lakadong Limestone exposed at KPL and LTL section in Khasi Hills.

Rare earth element distribution in tropical coastal wetland sediments: a case study from Vembanad estuary, southwest India

Rare earth element (REE) geochemistry of sediments from Vembanad Coastal Wetland, southwest India, shows that light rare earth elements (LREEs) are the more abundant compared to middle rare earth element (MREE) and heavy rare earth element (HREE). We suggest that the textural parameters and the biochemical processes lead to the REE variation in this coastal wetland environment. Variations in the REE abundance are mainly controlled by the source materials deposited by riverine input. REE records in sediments showed spatial heterogeneity due to the influence of the physico-chemical conditions like, sedimentological conditions, salinity and depositional flux of the sediments along the wetland. Enriched values observed along the northern and southern stations are due to the increased riverine input. The REE ratios and enrichment factor values suggest that the abundance is in the order of LREE > MREE > HREE. Positive Eu anomaly is linked to the source sediments brought down from the catchment areas of the Periyar River and Muvattupuzha River. However, Ce anomaly suggests no significant variation in the oxidation condition at the sites of deposition.