Browsing by Author "Shailesh Agrawal"

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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.
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.
Early Palaeogene Climate Variability Based on n-alkane and Stable Carbon Isotopic Composition Evidenced from the Barsingsar Lignite-bearing Sequence of Rajasthan
(Springer, 2020) Runcie P. Mathews; Rimpy Chetia; Shailesh Agrawal; Bhagwan D. Singh; Prakash K. Singh; Vikram P. Singh; Alpana Singh
The assessment of variations and the reconstruction of palaeoclimate, based on the distribution of n-alkanes and stable carbon isotope data, during early Palaeogene have been made on the Barsingsar lignite-bearing sequence associated with Palana Formation (Bikaner-Nagaur basin). The distribution pattern of various n-alkanes and the derived indices/ratios have widely been used as palaeoclimate indicators in several depositional realms. The distribution of n-alkanes in the studied sequence varies from C13 to C34. The values of calculated n-alkane parameters range from 26.20–28.39 (aliphatic chain length (ACL) index); 0.32–7.21 (low-to-higher molecular weight (L/H) ratio); 0.42–0.85 (Proxy wax (Pwax)); 0.20–0.67 (Proxy aqueous (Paq)); 0.28–5.22 (terrigenous/aquatic ratio (TAR)); 0.16–0.79 (C23/C29 ratio); 1.14–6.31 (C27/C31 ratio) and 1.47–7.02 (C29/C31 ratio). The δ13C varies from −24.8 to −26.1‰ and the TOC varies from 9.6 to 69.5 wt.%. All these variations indicate the changes in palaeoclimate from dry and warm to cool and wet conditions during the deposition of this lignite-bearing sequence. Further, it is also suggested that the climatic condition was cooler than that of the Palaeocene-Eocene thermal maximum (PETM) event. © 2020, Geol. Soc. India.
Mid-Holocene intensification of the oxygen minimum zone in the northeastern Arabian Sea
(Elsevier Ltd, 2022) Syed Azharuddin; Pawan Govil; Arun Deo Singh; Ravi Mishra; Shailesh Agrawal
The Arabian Sea is characterized by a strong Oxygen Minimum Zone (OMZ) bearing sub-oxic conditions at the intermediate water depth. We analyzed a sediment core near the upper margin of OMZ (174 m water depth) from offshore Saurashtra, northeastern (NE) Arabian Sea to reconstruct multi-proxy biogeochemical response in the area during the Early-Middle Holocene (∼10–4 ka before present). The results indicate lower foraminiferal productivity (both benthic and planktic) and weak sub-surface denitrification causing mild OMZ conditions at the study site during the early Holocene (∼10–8 ka). Subsequently, an increased foraminiferal productivity and sub-surface (both the water column and sediment) denitrification in the area led to intensified OMZ conditions during the mid-Holocene (after ∼8 ka). Our results corroborate other denitrification records from the Arabian Sea, suggesting the large-scale changes in Arabian Sea OMZ during the mid-Holocene. We suggest that the increased nutrient supply with significant freshwater input may have enhanced the primary productivity and further resulted in the intensified OMZ and escalated outgassing of N2O from the area during the mid-Holocene. © 2022 Elsevier Ltd
Monsoon-influenced variations in productivity and lithogenic flux along offshore Saurashtra, NE Arabian Sea during the Holocene and Younger Dryas: A multi-proxy approach
(Elsevier B.V., 2017) Syed Azharuddin; Pawan Govil; A.D. Singh; Ravi Mishra; Shailesh Agrawal; A.K. Tiwari; Kamlesh Kumar
A sediment core from NE Arabian Sea was studied to reveal the variations in shelf environment of western continental margin of India. A multi-proxy analysis based on planktonic foraminifera abundance (PFA), benthic foraminifera abundance (BFA), planktonic-benthic foraminiferal ratio (P/B), CaCO3 percentage (wt%), Oxygen (δ18OG. ruber) and Carbon (δ18OG. ruber) isotopes of foraminifera as well as sediment X-ray studies were carried out on 3.4 m long core SK-240/485 recovered from offshore Saurashtra, NE Arabian Sea. The study aims to understand the monsoon variability in the NE Arabian Sea offshore Saurashtra since the late Pleistocene-Holocene transition and how monsoon climate coupled with sea-level change influenced paleo-productivity pattern. Six AMS radiocarbon dates place the core in the time interval 12–1 Ka. Our study reveals that there have been three periods of major changes in the monsoonal climate, productivity and sea level; viz. 12–8 Ka (Younger Dryas and early Holocene); 8–4 Ka (middle Holocene) and 4–1 Ka (late Holocene). The studied time period was also marked by weakened south west monsoon (SWM) during the cold events such as Younger Dryas (YD), Abrupt Event (AE) centring around 9.8 Ka as well as 8.2 and 4 Ka cold events. The Younger Dryas and early Holocene shows the low sea level stand and less Indus river discharge. Thereafter during middle and late Holocene the monsoon strengthened which resulted in raised sea level and increased Indus river discharge. The proxy records broadly suggest relatively low foraminiferal productivity at the core location during the Younger Dryas and early Holocene. We record a moderate foraminiferal productivity during the middle Holocene between 8 and 4 Ka, which suggest the mesotrophic condition. The foraminiferal productivity however was relatively high since 4 Ka suggesting the eutrophic conditions at the core site. © 2016 Elsevier B.V.
Pinpointing the Geographic Origin of 165-Year-Old Human Skeletal Remains Found in Punjab, India: Evidence From Mitochondrial DNA and Stable Isotope Analysis
(Frontiers Media S.A., 2022) J.S. Sehrawat; Shailesh Agrawal; Deeksha Sankhyan; Monika Singh; Sachin Kumar; Satya Prakash; Richa Rajpal; Gyaneshwer Chaubey; Kumarasamy Thangaraj; Niraj Rai
In 2014, 157 years after the Sepoy Mutiny of 1857, several unidentified human skeletons were discovered in an abandoned well at Ajnala, Punjab. The most prevailing hypothesis suggested them as Indian soldiers who mutinied during the Indian uprising of 1857. However, there is an intense debate on their geographic affinity. Therefore, to pinpoint their area of origin, we have successfully isolated DNA from cementum-rich material of 50 good-quality random teeth samples and analyzed mtDNA haplogroups. In addition to that, we analyzed 85 individuals for oxygen isotopes (δ18O values). The mtDNA haplogroup distribution and clustering pattern rejected the local ancestry and indicated their genetic link with the populations living east of Punjab. In addition, the oxygen isotope analysis (δ18O values) from archaeological skeletal remains corroborated the molecular data and suggested the closest possible geographical affinity of these skeletal remains toward the eastern part of India, largely covering the Gangetic plain region. The data generated from this study are expected to expand our understanding of the ancestry and population affinity of martyr soldiers. Copyright © 2022 Sehrawat, Agrawal, Sankhyan, Singh, Kumar, Prakash, Rajpal, Chaubey, Thangaraj and Rai.
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.
Reconstruction of landscape and climate of the largest drainage basin in the Ladakh Range, NW Trans Himalaya during the last 7000 years
(Elsevier B.V., 2023) Priyanka Joshi; Binita Phartiyal; Mallickarjun Joshi; Shailesh Agrawal; Pankaj Kumar; Rajveer Sharma
Landform geomorphology and glacial lake deposits in the largest drainage basin of the Ladakh Range i.e. Chang La-Tangtse basin were studied to infer their palaeoclimatic significance. The grain size, mineral magnetism, percentage loss on ignition (%LOI) and organic carbon stable isotope (δ13C) data in combination with total organic carbon (TOC) supported by AMS 14C (calibrated) dates of a 190 cm long section from the Chang La-Tsoltak palaeolake provides a climatic record since the last ∼ 7075 cal yr BP. The χlf, χARM, and SIRM values suggest that the catchment-derived palaeolake sediments predominantly contain magnetically “soft” minerals like magnetite and maghemite. The δ13C values range between −21 and −24 ‰ with an average of –22 ‰ which suggests a mixed C3-C4 plant signature and water stressed ecosystem. The relatively small variations in the δ13C values of organic matter in the entire lake profile suggest a stable climatic condition. The prominent effect of westerlies is seen between 7075 and 6040 cal yr BP with huge detrital influx at the lake bottom indicating a glacial advancement in the region. The affect of Mid-Holocene warm period is evident at 6040 cal yr BP with the advent of ISM. Paradigm shifts in the proxy values are observed at 5710, 4890, 3435, and 2800 cal yr BP. The influence of westerlies gradually reduces at 2800 cal yr BP. The landscape evolution and the climatic variations in the Trans-Himalaya are primarily governed by westerlies and do not correspond to the Indian monsoon variability records, particularly during the Mid-Holocene Thermal Maxima. Several other regions of the Ladakh Range also record similar climatic variations, indicating that the palaeolake sediments also reflect regional climate variations. © 2023 Elsevier B.V.
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.
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.