Browsing by Author "Anupam Sharma"

Now showing 1 - 15 of 15

Biostratigraphy, palaeoenvironment and sea level changes during pre-collisional (Palaeocene) phase of the Indian plate: Palynological evidence from Akli Formation in Giral Lignite Mine, Barmer Basin, Rajasthan, Western India
(International Union of Geological Sciences, 2020) Vandana Prasad; Prem Raj Uddandam; Shailesh Agrawal; Sunil Bajpai; Indrabir Singh; Ashish K. Mishra; Anupam Sharma; Madhav Kumar; Poonam Verma
Giral Lignite Mine succession (Akli Formation) from Barmer Basin, Rajasthan yielded rich assemblage of dinoflagellate cysts and compared with the global dinoflagellate zonation schemes, and a Danian- Thanetian age is proposed. Within a precise biostratigraphic control, changes in the terrestrial and marine palynomorphs allowed the construction of relative sea level fluctuation curve and the development of depositonal succession in a sequence stratigraphic framework. Based on the lithological and palynological content, the Giral Lignite Mine succession is divided in to five units. Unit 1 (lower 7.8 m) is interpreted as transgressive deposit formed in an open bay setting during rise in the relative sea level representing the Transgressive Systems Tract (TST). The age is Danian on the basis of dinoflagellate cyst assemblages. Unit 2 (16.5 m) consists of 5-6 laterally occurring lignite bands. It is deposited during decrease of sea level and increased detritus supply in essentially salt marsh environment during Highstand Systems Tract (HST). Unit 3 (3.42 m) is shallow marine facies of Thanetian age deposited in a restricted setting represents a Transgressive Systems Tract. Unit 4 (0.9 m) is marked by a return to coastal marsh depositional conditions, possibly representing a Highstand Systems Tract. The erosional surface at the top of Unit 4 is interpreted as a Sequence Boundary. Unit 5 (9.3 m) is highly oxydized and is devoid of any organic matter content. Two major marine flooding surfaces identified in the Giral Lignite Mine succession can be correlated with the Maximum Flooding Surfaces (MFS) at 60.7 Ma and 57.9 Ma corresponding to the eustatic curve. Based on the dinoflagellate biostratigraphy Danian- Thanetian age has been assigned to the lignite bearing succession of Giral Mine. Western Indian margin consist of large-scale lignite deposits in Kutch, Cambay and Rajasthan Basin. The proposed Danian-Thanetian age of lignite bearing succession of Giral Mine is much older than the late Thanetian-early Ypresian age of lignite successions of Cambay and Kutch Basins of Gujarat. The present study suggests a significantly diachronous development of lignite deposits on the western peninsular margin of India. © 2020 International Union of Geological Sciences. All rights reserved.
Characteristics of modern biotic data and their relationship to vegetation of the Alpine zone of Chopta valley, North Sikkim, India: Implications for palaeovegetation reconstruction
(SAGE Publications Ltd, 2018) Jyotsna Dubey; Ruby Ghosh; Shailesh Agrawal; M.F. Quamar; P. Morthekai; R.K. Sharma; Anupam Sharma; Pratima Pandey; Vaibhava Srivastava; Sheikh Nawaz Ali
We examined the modern pollen palynomorphs (PP) distribution complemented with non-pollen palynomorphs (NPP) and stable carbon isotopic data of soil organic matter (SOM) to explore relationships of these proxies to vegetation communities in the Chopta valley, a closed valley in alpine zone of the North Sikkim, India, in an attempt to check the efficiency for reconstructing past vegetation and climate. A total of 24 surface soil samples were collected from both the windward and leeward sides of the valley and they did not show any significant difference in the palynoassemblages. The average value of δ13C is −26.6%, which clearly indicates a C3-dominated vegetation in this valley which is also corroborated by the palynological data. However, signature of upthermic wind transport was evident by the significant presence of extra-local and regional forest elements in the palynoassemblages. NPP data indicated grazing activity in the valley and is in conformity with the present-day scenario. Furthermore, cluster analysis (CA) and principal component analysis (PCA) done on the PP and NPP data broadly grouped the samples according to the location of collection to some extent and reflected the relationships among the taxa with the extant vegetation. This study provides a basis for future palaeovegetation and palaeoclimate reconstruction from the region. © 2017, © The Author(s) 2017.
Characterization of lignite deposits of Barmer Basin, Rajasthan: insights from mineralogical and elemental analysis
(Springer Science and Business Media B.V., 2023) Om Prakash Kumar; P. Gopinathan; Amiya S. Naik; T. Subramani; Prakash K. Singh; Anupam Sharma; Sudip Maity; Sujan Saha
The geochemistry of fly ash produced from the combustion of coal at thermal power plants presents a significant challenge for disposal and environmental impact due to its complex mineralogical and elemental composition. The objective of this study was to investigate the mineralogical and elemental distribution of thirty lignite samples from the Barmer Basin using advanced techniques such as X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analysis revealed the presence of minerals such as haematite (Fe2O3), nepheline, anhydrite, magnesite, andalusite, spinel and anatase. Other minor minerals included albite, siderite, periclase, calcite, mayenite, hauyne, pyrite, cristobalite, quartz, nosean and kaolinite. XRF analysis demonstrated that the most abundant elements in the Barmer Basin lignite ash were iron oxide (Fe2O3), sulphur oxide (SO3), calcium oxide (CaO), and quartz (SiO2) followed by minor traces of toxic oxides (SrO, V2O5, NiO, Cr2O3, Co2O3, CuO) that are known to have adverse effects on human health and the environment. The rare earth element (REE) composition showed higher concentrations of Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc at the Giral and lower concentrations at Sonari mine. The Barmer lignites recorded higher concentration of trace elements such as V, Cr, Co, Ni, Cu and Sr while lower concentration of Rb, Cs, Ba, Pb, As, Th and U were observed within optimal range. The study findings revealed the predominant mineral concentration, elemental makeup, trace elements and rare earth elements associated with lignite reserves in the Barmer Basin. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.
Conifer-mixed tropical rainforest in the Indian Paleogene: New evidences from terpenoid signatures
(Elsevier B.V., 2022) Rimpy Chetia; Runcie P. Mathews; Prakash K. Singh; Anupam Sharma
The Paleocene sediments from Barsingsar lignite mine section of Bikaner-Nagaur Basin in Rajasthan, India were subjected to gas chromatography–mass spectrometry (GC–MS) analysis to resolve its botanical history in relation to its terpenoid composition. The terpenoid suite was characterised by sesquiterpenoids, diterpenoids, and sporadic triterpenoids. The presence of sesquiterpenoids along with drimane, norcadalenes, cadalenes and their related compounds hint to higher plant input. High abundance of diterpenoids and their temporal universality imply a significant gymnosperm input. The diterpenoid-class of terpenoids, primarly comprises of conifer-derived abietane, phyllocladane, kaurane, pimarane/isopimarane and podocarpane-class compounds. It further point to Southern Hemisphere conifer families, Podocarpaceae and Araucariaceae. Exceptional void of phenolic abietane and labdane derivatives rule out the probability of Pinaceae as the source of these terpenes. A very low abundance of pentacyclic terpenoids like oleanane-derivatives suggest low angiosperm-derived terpenoid contribution. The average value of pristane/phytane in the realm, 1.7 indicated oxic to suboxic depositional setting. The values of ar-AGI (aromatic Angiosperm/Gymnosperm Index), t-AGI 1 and t-AGI 2 spans over 0.01 to 1, 0.009 to 1.23, and 0.002 to 0.34 respectively for the section. The research provided evidence of the occurrence of a tropical rainforest where conifers were a significant element or remained a refugia in the midst of emerging angiosperms as life stabilized in the Paleogene after the devastating Cretaceous-Paleogene (K/Pg) boundary. © 2022
Constraints of lithostratigraphy on the landscape evolution in response of erosion, climate and tectonics in the Marginal Ganga Plain, India
(Elsevier Ltd, 2021) Rupa Ghosh; Uma Kant Shukla; Pradeep Srivastava; Anupam Sharma
The Marginal Ganga Plain (MGP) exhibits up to 160 m thick fluvial sedimentary record of the Late Quaternary forebulge dynamics. The mineralogical composition of sediments from forty boreholes reveals three major depositional sequences (DS1, DS2, and DS3) and four sequence boundaries Sb1, Sb2, Sb3 and Sb4 representing where different tectonic and climatic conditions exercised parental control. These sequence boundaries are demarcated by the shift in facies architecture. The Sb1 sequence boundary is locally developed over the basement rocks. The lowermost DS1 represents a thick floodplain and low sinuosity channel association at > 114 ka under stable landscape. This DS1 indicates a low rate of sedimentation and High Accommodation Systems Tract (HAST), characterized by positive > 1 A/S (Accommodation to Sediment) ratio. The sequence boundary Sb2 lies between DS1 and overlying DS2 implies a regional unconformity in the MGP and negative A/S ratio. Further, laterally extensive asymmetrical DS2, developed between ~ 80–54 ka with an erosional base overlies the DS1 and represents Low Accommodation Systems Tract (LAST) with A/S < 1. The Sb3, present between DS2 and DS3 denotes a sharp transition in facies architecture. The DS3 made up of the interfluves sequence shows an upward fining sequence deposited by vertically aggrading minor channels developed after 54 ka and is characterized as HAST where A/S > 1. The Sb4 represents the top surface of the DS3 and is currently getting degraded by ravinement processes. The varying pattern of alluvial architecture in the MGP defines variable A/S ratio and infer forebulge tectonic signature shaping the fluvial landscape. © 2021 Elsevier Ltd
COUPLED ROLE OF CLIMATE AND TECTONICS IN THE DEPOSITION OF THE LATE QUATERNARY SEDIMENTARY SEQUENCE IN THE SOUTHERN MARGIN OF THE CENTRAL GANGA PLAIN, INDIA
(SEPM Society for Sedimentary Geology, 2024) Mukesh Yadav; U.K. Shukla; G.P. Gurumurthy; Sajid Ali; Kamlesh Kumar; Anupam Sharma
The Ganga Plain’s sedimentation is primarily controlled by Himalayan tectonics, variations in monsoon intensity, and glacier size. However, the significance of intrabasinal tectonics, which is an interplay of the Himalaya tectonics and basement tectonic configuration of the Ganga Plain, in comprehending the late Quaternary Ganga Plain sedimentation remains unclear. In this study, the sediment provenance and extent of weathering experienced by the sediments are studied using the mineralogical and geochemical (major, trace, and rare earth elements) composition of a sedimentary cliff sequence exposed at the Ramnagar locality near the cratonic peripheral bulge in the southern Ganga Plain. In the Ramnagar cliff sediment section, two sediment packages, designated SP-A and SP-B, are identified based on mineralogy, texture, and geochemistry. These packages of sediments show mild chemical weathering and distinct geochemical compositions. The lower part (SP-A) of the Ramnagar cliff section is characterized by higher contributions from mafic sources (pyroxene, feldspar, and mica as dominant minerals), while the upper part (SP-B) is predominately derived from felsic sources (mica and feldspar as dominant minerals), which are supplied via the peninsular and the Himalayan rivers, respectively. The southern part of the central Ganga Plain shows evidence of a shift in the sediment provenance from mafic to felsic source rock at 40 ka. This study demonstrates how weathering and sedimentation are controlled by both regional tectonics and climate in the southern margin of the central Ganga Plain.; The Director of the BSIP, Lucknow, is thanked by the authors for providing all infrastructural (SAIF) and administrative support to complete the assignment. This work is a part of MY’s doctoral thesis, supported by the funding received from the University Grants Commission (CSIR-UGC JRF fellowship, Roll No. 207693) and recorded as BSIP/RDCC/Publication no. 24/2024-25. The authors also thank Dr. Sheikh Nawaz Ali, Dr. Arvind Kumar Singh, Dr. Naimisha Vanik, Harshita Srivastava, Dr. Masud Kawsar, and Dr. Abhisek Kumar for their constructive suggestions that helped to make the manuscript better. UKS is thankful to the Head of the Department of Geology for providing the working facilities of the Department. We thank editor Dr. Kathleen Marsaglia, Associate Editor Dr. Alberto Resentini, and anonymous reviewers for constructive comments on our manuscript. Ó 2024, SEPM (Society for Sedimentary Geology)
Diversity of diatom and carbon isotope characterization of soil organic matter in extreme climate, Sikkim Himalaya, India
(Indian Academy of Sciences, 2020) Jyotsna Dubey; Biswajeet Thakur; Shailesh Agrawal; Anupam Sharma; P. Morthekai; Vaibhava Srivastava; S. Nawaz Ali
Analysis of spatial variation of diatom assemblages and characterization of carbon isotopic composition of surface soil/sediment samples along three high-altitude transects (Chopta, Lashar and Gurudongmar valleys) in North Sikkim, Higher Himalaya have been done to delineate the ecological information (modern analogue). We have studied the variation in the distribution of diatom species and stable carbon composition in three different valleys having variable climatic conditions ranging from sub-humid to semi-arid. The results reveal that the biotic components respond appreciably towards varying environmental conditions. The spatial distribution of diatoms in surface sediments seems to be controlled by physical parameters such as temperature, water and nutrient availability. The overall δ13C values vary from -25% to -29%, suggesting a C3-dominated vegetation in the region. Higher δ13C values are observed in Gurudongmar samples that are characterized by less moisture and low temperature. The δ13C values suggest that the source of organic matter in soil/sediment is contributed by open grasslands (C3 grasses). The isotope values clearly demonstrate an increase in δ13C values along with a progressive increase in elevation and decrease in precipitation. The present data will serve as an important archive for future correlations in palaeoclimatic studies. © 2020 Indian Academy of Sciences.
Geochemical and mineralogical assessment of environmentally sensitive elements in Neyveli lignite deposits, Cauvery Basin, India
(Springer, 2024) Pramod K. Rajak; P. Gopinathan; Aniruddha Kumar; Om Prakash Kumar; Ishwar C. Rahi; Anupam Sharma; Prakash K. Singh; Amit Karmakar
This research work presents an examination of the concentrations and modes of occurrence of environmentally sensitive elements within lignite deposits, located in Neyveli, within the Cauvery Basin of India. Coal is one of the most complex geologically formed materials, consisting of organic and inorganic matter. The inorganic mineral matter including the crystalline minerals, non-crystalline mineraloids, and elements with non-mineral associations. These lignite samples underwent complete analysis encompassing macroscopic, microscopic and geochemical assessments. The analysis reveals that the total mineral matter (MM) content, comprising significant proportions of sulphides, carbonate and argillaceous components. Geochemical characterization further elucidates the lignite’s properties, with proximate analysis yielding values such as ash, volatile matter and fixed carbon and the Ultimate components analysis reveals the carbon, hydrogen, nitrogen, sulphur and oxygen. Inorganic mineral matters play a significant role in coal utilization, and also such modes of occurrence of elements provide useful geochemical information on coal formation and coal-bearing basin evolution. In this paper, we assess the associations of elements and minerals, as well as the associations of selected elements including environmentally-sensitive (e.g., S, As, U, and Hg), and some major elements (e.g., Ca, Mg, Fe, Al, and Ti) that have largely occurred in non-mineral forms in these low-rank coals. And also, comparative analysis is conducted between the concentrations of elements within the lignite samples and the values reported for World Clarke Brown Coals (WCBC). Particularly, some of these elements exhibit significantly high environmental sensitivity, demanding careful consideration in lignite extraction and utilization practices. © The Author(s), under exclusive licence to Springer Nature B.V. 2024.
Geochemistry of the siliciclastic sediments from the Raniganj Gondwana basin, West Bengal, India, and its geological implications
(Science Press, 2025) Yumlembam Priyananda Singh; Oinam Kingson; K. Milankumar Sharma; Raghavendra Prasad Tiwari; Rajeev Patnaik; Prosenjit Ghosh; Anupam Sharma; Jitendra K. Pattanaik; Pankaj Kumar; Harel Thomas; Ningthoujam Premjit Singh; Prem Chand Kisku; Nongmaithem Amardas Singh
Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering, paleoclimate, provenance, and tectonic setting of the basin. Records for Permo–Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins. Nevertheless, our understanding on sedimentation, provenance, and regional tectonics of the Raniganj Basin, a Gondwana basin in the eastern India is poor. Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering, paleoclimate, provenance, and tectonic settings of the basin. This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area, while the Barakar, Raniganj, and Panchet formations had prevailing semiarid climates. The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex (CGGC). Further, the geochemical results suggest a rift-like (passive) tectonic setting for the Raniganj Basin, while few samples represent the collision tectonic setting of the basement CGGC, formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time. © The Author(s), under exclusive licence to Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Glacial Geomorphology and Landscape Evolution of the Thangu Valley, North Sikkim Himalaya, India
(Springer, 2019) Jyotsna Dubey; Sheikh Nawaz Ali; Anupam Sharma; P. Morthekai; Rupendra Singh; R.K. Sharma; Pratima Pandey; Biswajeet Thakur; Vaibhava Srivastava
The present study describes glacial-geomorphological landforms in and around Thangu area, North Sikkim, India, and also provides significant insights about the evolution of pro- and paraglacial landscapes. Paraglacial processes are the governing mechanism of landscape evolution in deglaciating valleys and are now studied to understand the deglacial and postglacial landscape dynamics. We here present and describe detailed glacial geomorphology of Lashar and Chopta valleys as the area is strongly modified by the erosional and depositional imprints of late Pleistocene glaciations (MIS 2). Using geomorphological and stratigraphical methods, field surveys, SRTM DEM, Landsat ETM + and Google Earth Pro data, we have mapped glacial and glaciofluvial landforms and established moraine stratigraphy in the study area. Based on the morphostratigraphical mapping of the moraines supported by limited optical chronology, four events of glaciations have been identified in the in the Lashar, Chopta and Kalip valleys and date back to last glacial maximum and advocate for a widespread ice cover with large outlet tributary glaciers. The disposition of the lateral and terminal moraines has been used to estimate the area of paleoglacial extent and their corresponding ice volume during different stages. The presence of proglacial lakes, sensitive indicators of climate change, suggests that the glaciers in the region are melting and radically responding to global warming and are potentially vulnerable for generating glacial lake outburst floods. © 2019, Indian Society of Remote Sensing.
Occurrence of pseudotachylites in the vicinity of South Almora Thrust zone, Kumaun Lesser Himalaya
(2011) K.K. Agarwal; Anupam Sharma; Nigar Jahan; Chandra Prakash; Amar Agarwal
Thin veins of pseudotachylites are observed within the South Almora Thrust (SAT) zone of the Almora crystallines, Kumaun Lesser Himalaya. The SAT zone presents a relatively wide variety of mylonite types. Within this zone thin, dark-coloured veins of pseudotachylites are found. Folded veins of irregular thickness are also observed. The pseudotachylites are formed by rapid crystallization of melts. Intense deformation and friction-related heating is generated during the thrust sheet movement, which is responsible for producing the melts. Small amount of melts generated during the frictional heating cool rapidly in association of the wall rock and form thin veins, which have sharp boundaries (or folded) within the wall rock. Quartz, K-feldspar and plagioclase occur as porphyroclasts in the host rocks.
Presence and implications of petrogenic organic carbon in High Himalayan Crystalline lake sediment
(Cambridge University Press, 2024) Priyanka Singh; Vijayananda Sarangi; Ravi Bhushan; S Nawaz Ali; Shailesh Agrawal; Pooja Tiwari; Masud Kawsar; Prasanta Sanyal; Kamlesh Kumar; Biswajeet Thakur; M.C. Manoj; Veerukant Singh; Ankur Dabhi; Anupam Sharma; Kuldeep Prakash; P. Morthekai
Twelve lacustrine sediment samples from a relict lake in the Kalla Glacier valley were co-dated using AMS radiocarbon (14C) and infrared stimulated luminescence (IRSL) dating methods. In general, the radiocarbon ages of bulk organic matter were older by a minimum of 1500 years compared to (age depth) modeled luminescence ages after fading corrections. This is observed for the first time in the lake sediments of High Himalayan Crystalline zone. A combination of lipid n-alkane data, Raman spectra and geochemical proxies suggested that this was due to ancient organic carbon (OCancient) that is a mixture of pre-aged (OCpre-aged) and petrogenic (OCpetro) organic carbon within older glacial moraine debris that served as sediment source to the lake. Raman spectra suggest the presence of moderate to highly graphitized OCpetro in all the profile samples. The OCpetro contributed 0.064 ± 0.032% to the sediment and the lake stored 2.5 ± 0.7 Gg OCpetro at variable rates during the last 16 kyr, with the mean burial flux 160 kg OCpetro yr-1. This study implies (1) employing another independent dating method in addition to radiocarbon method using bulk sediment organic matter, if the carbon content is low, to observe any discrepancy, and (2) a need to investigate on the fate of OCpetro as many such small lakes become relict in this region. © The Author(s), 2024. Published by Cambridge University Press on behalf of University of Arizona.
Unearthing the PETM in the Indian tropics: n-alkane and bulk carbon isotope records from the Barmer Basin
(Elsevier B.V., 2025) Sneha Mary Mathew; Shailesh Agrawal; M. C. Manoj; Prasanta Sanyal; Ishwar Chandra Rahi; Shalini Parmar; Vandana Prasad; Anupam Sharma; Amiya Shankar Naik
The Paleocene–Eocene Thermal Maximum (PETM) represents one of the most pronounced global hyperthermal events of the Cenozoic, characterized by rapid warming, carbon cycle perturbations, and substantial environmental reorganization. Despite its global significance, tropical terrestrial records remain underrepresented, particularly from the Indian subcontinent. This study presents a high-resolution geochemical and isotopic investigation of Paleogene sediments from the Sonari Lignite Mine (SLM), Barmer Basin of western India, to reconstruct paleoenvironmental responses to the PETM. Bulk organic carbon (δ13Cbulk) and compound-specific n-alkane isotope (δ13Cn-alkane) data reveal a distinct negative Carbon Isotope Excursion (−ve CIE), with δ13C₃₁ reaching a minimum of −40.5 ‰ and a total excursion magnitude of ∼8.6 ‰, among the highest rec orded in terrestrial PETM sequences. Biomarker distributions indicate a mixed organic matter source, dominated by higher plant input, with secondary contributions from aquatic macrophytes and microbial sources. The onset of the CIE at ∼45.95 m is supported by dinocyst-based biostratigraphy, including the acme of Apectodinium augustum. A smaller pre-onset excursion suggests pulsed carbon release prior to the main event. Regional environmental changes include increased humidity, intensified hydrological cycling, and transient sea-level rise, interpreted from declining Carbon Preference Index (CPI) values, reduced terrigenous/aquatic ratio (TAR), and a surge in short-chain n-alkanes. The magnitude of the CIE and associated climatic shifts at SLM reflect a robust expression of PETM-related feedbacks in a low-latitude, monsoon-influenced setting. These results underscore the significance of tropical terrestrial archives in resolving the spatial heterogeneity of PETM climate responses and highlight the importance of the Indian subcontinent as a key region for documenting low-latitude tropical climate and vegetation dynamics during hyperthermal events. © 2025 Elsevier B.V.
Vegetation diversity in response to monsoonal variability in the Eastern Himalaya, India over the past ~13 000 yrs
(SAGE Publications Ltd, 2024) Jyotsna Dubey; S Nawaz Ali; Mohammad Firoze Quamar; Priyanka Singh; P. Morthekai; Ruby Ghosh; Anupam Sharma; Vaibhava Srivastava
Monsoon precipitation plays a crucial role in shaping the diversity of vegetation in the Himalayas, both in terms of temporal and spatial distribution. While palynology has traditionally been employed to reconstruct the past climate of the Himalaya, there has been limited understanding of how monsoon-related changes affect the structure and distribution of vegetation. To address this, we analysed pollen data from a 3 m deep sedimentary profile in the higher Sikkim Himalaya to reconstruct monsoon driven changes in vegetation diversity. Our results show a highly fluctuating trend of pollen and diversity parameters at late-Pleistocene-Holocene transition for which fluctuating hydroclimatic conditions and differential pollen preservation in coarser sediments is attributed. During the Early Holocene (10,438–7934 cal yrs BP) favourable hydroclimatic conditions led to a rapid expansion of mixed broad-leaved forests, marked by higher values of richness and alpha diversity. Between 7934 and 5481 cal yrs BP, the region experienced moderate hydroclimatic conditions that facilitated expansion and diversification of woody taxa, and correlated with the global Holocene Climate Optimum (HCO). Conversely, from 5481 to3949 cal yrs BP, declining total pollen count (TPC), species richness, and alpha diversity indicates significant shifts in vegetation composition under deteriorating climatic conditions, which corresponds with the 4.2 ka event worldwide. From 3949 to 2049 cal yrs BP, an increasing yet variable trend in TPC and diversity indices, suggests warm-humid conditions prevailed in the region. During the last 1086 cal yrs, an increasing trend is recorded in the palyno assemblage and diversity parameters suggesting ameliorating climate, matches well with the Mediaeval Climate Anomaly (MCA). Our inferences suggest that the palyno assemblage and diversity parameters are quiet sensitive to warm and humid conditions. © The Author(s) 2024.
Westerly-monsoon variations since the last deglaciation from semi-arid Ladakh region, Trans Himalaya, India
(Elsevier B.V., 2023) Debarati Nag; Binita Phartiyal; Shailesh Agrawal; Pankaj Kumar; Rajveer Sharma; Kamlesh Kumar; Anupam Sharma; Mallickarjun Joshi
The semi-arid Ladakh region in the Trans Himalaya forms an environmental boundary between North Atlantic and monsoon forcings. Its location in the transient setting of these two climate systems enables to attest slight changes in the dynamics of these components of atmospheric circulation. Variation in climatic conditions from 19.6 to 6.1 ka using multi-proxy investigation (mineral magnetism, stable carbon isotope, palaeoprecipitation, sediment grainsize end member analysis, clay mineralogy and TOC) is studied from Khalsi palaeolake deposit in Ladakh. Considering the inherent uncertainty of radiocarbon chronology, the present study provides millennial to multi-centennial scale resolution of climate variation from the sediment sequence. The results indicate cold arid climate influenced by Westerly circulation for the last 19.6 to 11.1 ka, thereafter from 11.1 to 7.5 ka, monsoon forcings dominated the climate of the region, following the orbitally controlled solar insolation that influenced the position of ITCZ and formed the key driver of the variability of these atmospheric circulations. A short wet phase from ∼17.4 to 16.5 ka within the dominant Westerly period is attributed to the early wet phase of two-fold H1 event. Westerly regained strength from 7.5 to 6.1 ka during the mid-Holocene coinciding with decreasing insolation, weakening monsoon and enhanced El Niño activities. © 2023 Elsevier B.V.