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The Rangit Gondwana Basin of Sikkim in the lesser Himalaya witnessed a wide span of climate change during the Permo-Carboniferous period. The principal objective of the present study is to document this Permo-Carboniferous climate change in the form of a geochemical signature preserved in the siliciclastic facies of the Rangit Pebble Slate Formation. The stratigraphic sequences of the Rangit Gondwana Basin are categorically well defined and subdivided into upper and lower sequences on the basis of their depositional environment. The lower sequences of the Rangit Gondwana basin are comprised of massive diamictite with large stromatolitic dolomite boulders and dropstone embedded in the coarser sandstone which indicate the cold glaciomarine environment of deposition, whereas upper sequences consist of repeated alternate beds of sandstone, black shale and coal seam with a regular interval depicting the fluvial and deltaic environment of deposition. The enrichment of SiO2, Al2O3, TiO2, MnO, MgO, and K2O indicates that these sediments were mostly derived from felsic rock source areas. Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) CaO + Na2O + K2O/Al2O3, and SiO2 vs. (Al2O3 + K2O + Na2O) values suggest that the sediments maturity and paleoclimatic environment deposition of the sediments of lower sequences was cold and semi-humid whereas the deposition of sediments of upper sequences was warm and humid. The A-CN-K ternary plot and CIA vs ICV binary plot also indicate and verify that the source areas were subjected to prolonged intense chemical weathering from low to high grade due to shifting of cold to warm humid paleo-climatic condition.

High-resolution proxy records help to understand natural forcing of climate variability and improving our capability to predict climate variability on decadal to centennial time scales. Present study from the Mawmluh cave, northeastern India shows sudden shifts in speleothem oxygen isotope values, indicating several abrupt changes in the Indian summer monsoon (ISM) during ~212 BCE to 1986 CE. Moderate ISM conditions prevailed during ~212 BCE to 400 CE punctuated with weak intervals, strong ISM during 400 and 500 CE and from 640 to 1060 CE, whereas weak ISM conditions prevailed during 520–540 CE, 820–850 CE and 940–980 CE and after 1060 CE. The interval from 1060 to 1986 CE witnessed decreased precipitation than the previous millennium. The latter phase of the Medieval Climate Anomaly (MCA; 1060 to 1200 CE) was quite drier in contrast to the earlier intervals. The ISM was generally weak during the Little Ice Age (LIA; 1350 to 1850 CE) with short-term pulses of high precipitation when sun-spot activity was high. The data shows the weakest ISM condition during 1640–1740 CE (Maunder Minimum) of the last two millennia. Variations in extra-tropical northern hemisphere temperatures due to volcanic activity and solar insolation, and accompanying northward/southward shifting of the Inter-Tropical Convergence Zone played a pivotal role in modulating the strength of the ISM during the past two millennia.

Recent cloud bursts and Glacial Lake Outburst Flood ( GLOF ) in the Uttarakhand Himalaya have triggered catastrophic landslides. Heavy monsoon precipitation lashed Uttarakhand causing devastation and series of new landslides in the region. The Surbhi Resort Landslide is located near the hill station of Mussoorie in Garhwal Himalaya, India, in the Upper Krol Limestone. After intense rain in August 1998, the Krol sedimentary deposits suddenly gave way as a deep-seated landslide, blocking the main Mussoorie-Kemptyartery for 15 days. In 2005, the velocity of the slide was determined to be 4–14 mm/year by previous workers, thus it was still active with a modest intensity. Recently in 2018, during monsoon there was heavy rainfall in the Mussoorie and mud flow in the Kemty Fall area. Huge amounts of quaternary debris are still lying on the slope, another high intensity rainfall or cloud burst in future could trigger another large-scale failure. Based on our recent detailed investigations, following mitigation and bioengineering measures are suggested. To lower the ground water table, a series of horizontal drains should be installed at the base of the crown portion of the slide. This would generate an additional discharge which has to be channeled down Rangaon-ka-Khala, the natural channel, down the slope to the Aglar River flowing in the valley below. To prevent further surface erosion, it is suggested that the Rangaon-ka-Khalamust be bioengineered with shrubs and grasses such as Eriophorum comosum, Saccharum spontanum, Pogonatherum spp. And Wood fordia fruticosa while the surrounding slope must be reforested with Quercus leucotrichophora, Alnus napelensis , Pinus spp.and Cedrus spp. Check dams must be constructed on the entire 3.5 km stretch of the Rangaon-ka-khala to lower the velocity of thewater. This could be done either as gabions or in the form of live fascines of Salix tetrasperma or Dalbergia sissoo. The catchmentarea above the Mussoorie-Kempty road can be expected to collect 60,000 m3 in 24 hours in a 25-years reoccurrence cloud burst. Thus proper drains (0.40 m in dia.) on the inside of the road must be installed. The flow velocity at these extreme events would be 4.8 m/switch is slightly above the recommended value. If this water is allowed to flow down the Rangaon-ka-Khala it will most certainly lead to a major debris slide with a vertical velocity of almost 100 m/s with huge erosive power. For this reason, this discharge should be channeled down in plastic or cement lined pipes, preferably to the west of the Siyagaon Village which is reported as stable rather than in the landslide zone itself. It is concluded that these mitigation measures and bioengineering plantation would certainly help stabilize the Surbhi landslide area to prevent further disaster in future that destroyed the water mills, fields of the surrounding villages and mud flow in popular Kempty Fall area. These measures may also be applicable for the other active landslide zones in the NW(Jammu and Kashmir) and NE ( Darjiling-Sikkim ) Himalaya.

The Permo-Carboniferous depositional sequence of Lower Gondwana in Sikkim Lesser Himalaya was investigated through an integrated approach of lithological, petrological, and geochemical studies. Lithologically, it is characterized by glacial diamictite at the base and shale-sandstone facies at the top of a sequence which is interpreted as a glaciomarine deposit. Coarser sandstone and massive diamictite composed of quartz, feldspar, muscovite, zircon, and other lithic fragments are observed in thin section. Geochemistry of all studied samples from the Rangit Pebble Slate Formation shows the dominance of silicon dioxide compared to other elemental oxides. The tectonic discrimination diagram positively infers passive margin sedimentation from a felsic-rich provenance. Chemical Index of Alteration was used to depict the weathering trends of all studied samples which reflect paleo-sedimentation under humid to sub-humid climatic conditions.

As one of the most prominent seasonally recurring atmospheric circulation patterns, the Asian Summer Monsoon (ASM) plays a vital role for the life and livelihood of about a third of the global population. Changes in the strength and seasonality of the ASM significantly affect the region, yet the drivers of change and the varied regional responses of the ASM are not well understood. In the last two decades, there have been a number of studies reconstructing the ASM using stalagmite-based proxies such as oxygen isotopes (18O). Such reconstructions allow examination of the drivers and responses, increasing monsoon predictability. In this review paper, we focus on stalagmite 18O records from India at the proximal end of the ASM region. Indian stalagmite 18O records show well dated, high amplitude changes in response to the dominant drivers of the ASM on orbital to multi-centennial timescales and indicate the magnitude of monsoon variability in response to these drivers. We examine Indian stalagmite records collated in SISAL_v1 (version 1) database (http://researchdata.reading.ac.uk/139/) and support the database with a summary of record quality and regional climatic interpretations of the 18O record during different climate states. We highlight current debates and suggest the most useful time periods (climatic events) and locations for further work using tools such as data-model comparisons, spectral analysis methods, multi-proxy investigations and monitoring work

For the foreseeable future, the search for evidence of past life in rocks acquired from other planets will be constrained by the amount of sample available and by the fidelity of preservation of any fossils present. What amount of rock is needed to establish the existence of past life? To address this question, we studied a minute amount of rock collected from cherty dolomites of the Proterozoic Buxa Formation in the metamorphically altered tectonically active northeastern Himalaya. In particular, we investigated 2 small petrographic thin sections-one from each of 2 bedded chert horizons exposed in the Ranjit River stratigraphic section northwest of Rishi, Sikkim, India-that together comprise an area of approximately 5 cm(2) (about the size of a US postage stamp) and have a total rock weight of approximately 0.1 g. Optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy and imagery demonstrate that each of the thin sections contains a rich assemblage of 3-dimensionally permineralized organic-walled microfossils. This study, the first report of Proterozoic microfossils in units of the Ranjit tectonic window, demonstrates that firm evidence of early life can be adduced from even a minuscule amount of fossil-bearing ancient rock.