68 results on '"Achyuthan, Hema"'
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2. Middle to late Holocene alluvial history of the northeast monsoon dominated coastal tropical rivers of south India.
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Achyuthan, Hema
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OPTICALLY stimulated luminescence , *HOLOCENE Epoch , *AGGRADATION & degradation , *WATERSHEDS , *MEANDERING rivers , *MONSOONS , *CLIFFS - Abstract
The region around the coastal Chennai area, India, is drained by three major rivers that rise from the remnants of the Eastern Ghats and receive dominantly the northeast rains. These rivers meander short distances, deposit sediments into the Bay of Bengal and preserve signatures of past phases of sedimentation and incision. In this study, detailed mapping using satellite imageries and extensive field work, logging of the river cliff bank sections was supported by sediment texture and structure and optically stimulated luminescence (OSL) dates. The main objective of this study was to infer the major periods of aggradation and incision in coastal drainage basins receiving dominantly the northeast rains. Integration of all the earlier available dated alluvial sequences (14C ages) and the present study OSL dates reveal that a major period of sedimentation occurred during the early Holocene (9 to 8.3 ka), mid Holocene (7.6–5.5 ka) and late Holocene to recent (2.4 and 1.6 ka, 0.9–0.6 ka and around 0.2 ka) periods. The Koratallaiyar river has preserved older middle Holocene terraces. Younger ages of the south easterly and east flowing rivers such as the Palar and the Coovum signify that they have incised and eroded to the present riverbed levels by catastrophic floods during the late Holocene period. This has resulted in an imbalance between sediment supply and sediment transporting power thus laterally stacking sediments rather than vertically. [ABSTRACT FROM AUTHOR]
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- 2022
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3. Constraining the chronology and ecology of Late Acheulean and Middle Palaeolithic occupations at the margins of the monsoon.
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Blinkhorn, James, Achyuthan, Hema, Durcan, Julie, Roberts, Patrick, and Ilgner, Jana
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MIDDLE Paleolithic Period , *PALEOECOLOGY , *MONSOONS , *PALEOLITHIC Period , *ECOLOGICAL impact , *PHYSIOLOGICAL adaptation - Abstract
South Asia hosts the world's youngest Acheulean sites, with dated records typically restricted to sub-humid landscapes. The Thar Desert marks a major adaptive boundary between monsoonal Asia to the east and the Saharo-Arabian desert belt to the west, making it a key threshold to examine patterns of hominin ecological adaptation and its impacts on patterns of behaviour, demography and dispersal. Here, we investigate Palaeolithic occupations at the western margin of the South Asian monsoon at Singi Talav, undertaking new chronometric, sedimentological and palaeoecological studies of Acheulean and Middle Palaeolithic occupation horizons. We constrain occupations of the site between 248 and 65 thousand years ago. This presents the first direct palaeoecological evidence for landscapes occupied by South Asian Acheulean-producing populations, most notably in the main occupation horizon dating to 177 thousand years ago. Our results illustrate the potential role of the Thar Desert as an ecological, and demographic, frontier to Palaeolithic populations. [ABSTRACT FROM AUTHOR]
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- 2021
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4. Climate Change as Observed in the Bay of Bengal.
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Rajalakshmi, P.R. and Achyuthan, Hema
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CLIMATE change , *HEAT waves (Meteorology) , *OCEAN temperature , *TROPICAL cyclones , *OCEAN acidification , *SEA level , *FOOD chains - Abstract
The Bay of Bengal covers a vast expanse of area, it being warmer, holds signatures of climate change. Its impact and the parameters have been studied in terms of rise in temperature, sea level change, increased rainfall, drought, heat waves, the intensity of tropical cyclones, ocean acidification and ocean productivity. In the last 45 years, sea surface temperature (SST) has risen by 0.2 to 0.3°C and is projected to rise further by 2.0 to 3.5°C by the end of this century. As a result, the sea level is expected to also rise 37 cm by 2050. The Bay of Bengal is witnessing an increase in the intensity of cyclones in the last two decades. Floods and droughts have increased over the years and are a growing threat to plant and animal life. Ocean acidification and increase in the sea surface temperature have made many fish species a major part of the coastal food chain vulnerable to its productivity. Hence, the collection of real time data and its continuous monitoring of the Bay of Bengal is essential to predict and project the future climate change to its accuracy both in space and time. [ABSTRACT FROM AUTHOR]
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- 2021
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5. Understanding the Late Quaternary Paleomonsoon and Paleoenvironmental Shifts of Asia.
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Achyuthan, Hema, Chen, Min-Te, and Liu, Shengfa
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- ASIA
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- 2022
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6. Physicochemical characteristics and spatial distribution pattern of the Yercaud Lake surface sediments, South India.
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Gopal, Veeramalai, Achyuthan, Hema, Shah, Rayees Ahmad, and Jayaprakash, Muthumanickam
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LAKE sediments , *CHEMICAL weathering , *LAKES , *PARTICLE size distribution , *WATERSHEDS , *ANALYTICAL geochemistry - Abstract
Freshwater lakes and sediments need to be monitored continuously for environmental assessment and geochemical explorations. Lake sediments are major sinks for organic matter and for all geochemical elements. In the present study, total organic matter (TOC), nitrogen (TN), and geochemical analysis of major oxides was carried out on Yercaud Lake surface sediments, located at a higher elevation in South India to infer sediment distribution pattern and source for organic matter. Particle size distribution of lake surface sediments suggests that the sediments are predominantly silty sand and sandy silt, poorly to very poorly sorted and symmetrically skewed. TOC/TN ratio (6.54–12.65) reveal that the organic matter (OM) is derived from the in situ lake sources particularly from the vascular plants and lake biota accumulation. Weathering indices that fall from [chemical index of alteration (CIA)] 88.59–93.08 values and A‐CN‐K plot reflects intense chemical weathering of the bedrock exposures in the source area, which was accelerated under warmer and humid climate conditions in the sub‐tropical regions. Al2O3/TiO2 ratio (6.94–26.62) indicates weathering particularly of the exposed charnockite rocks around the lake basin. [ABSTRACT FROM AUTHOR]
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- 2021
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7. Holocene evolution of the Palar river, Southern India: Tracking history of migration, provenance, weathering and tectonics.
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Resmi, M.R., Achyuthan, Hema, and Babeesh, C.
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STRIKE-slip faults (Geology) , *RIVER sediments , *HOLOCENE Epoch , *PROVENANCE (Geology) , *WATERSHEDS , *AGGRADATION & degradation ,HISTORY of India - Abstract
This study examines the catchment and source morphodynamics of the Palar River, Southern Peninsular India. Here, we applied a multidisciplinary approach (Remote sensing Techniques, Lineament Analysis, Geochemistry and Ground Penetration Radar) for a better understanding of its evolution during Holocene times. The lineaments present in the Palar River basin are showing dominantly NE-SW trend. There are five major faults identified in the Palar River basin. Fault F1 (strike slip fault) occurs in the upper part of the Palar River following the NE-SW trend. Other major faults F2 and F3 occurs in the middle reaches with a transition zone where frequent smaller magnitude earthquake occured and fault F4 traverses in parallel to the Cheyyar River. Fault F-5 nearer to the east coast indicates a passive tectonic activity regime. The after-effects of tectonic activity in the basin is further implicit from the GPR Profile. The sediments of active Palar River are dominantly litharenite, arkose, wacke; while, the paleochannels are shale in composition. Weathering proxies such as CIA, PIA, elemental ratios along with A–CN–K plot indicate a post-depositional intense weathering due to climatic variability for paleochannel sediments. Due to ongoing tectonic activity in the sources region along with subsequent aggradation and degradation in fluvial regimes, the sediments of active Palar River shows low to moderate weathering. Moreover, the geochemical data also reveals that the sediments from the Palar River and paleochannels are predominately from active continental and passive continental margins respectively. Moreover, the Major Oxide, Trace Elements and REE elements data indicate that Palar River sediments are from a felsic source while paleochannels are from mafic source. Hence, our study suggests that the catchment area of the Palar River has been shifted to the southward during the Holocene period due to tectonic uplift. Subsequently, the sediments of the paleochannels have undergone post-depositional weathering. Due to ongoing tectonic activity and intense precipitation in the region, enhances rapid erosion in the catchment area results in the deposition of the huge thickness of sediments from the middle to lower reaches of active Palar River. [ABSTRACT FROM AUTHOR]
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- 2021
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8. Palaeoenvironment shifts during last ~ 500 years and eutrophic evolution of the Wular Lake, Kashmir Valley, India.
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Shah, Rayees Ahmad, Achyuthan, Hema, Lone, Aasif, Kumar, Pankaj, Ali, Asif, and Rahman, Abdur
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LITTLE Ice Age , *LAKE sediments , *LAKES , *VALLEYS , *LAKE sediment analysis , *SIXTEENTH century - Abstract
Multi-proxy analysis of lake sediments provides high-resolution and reliable palaeoclimate records. The present study aims to investigate the palaeoenvironmental changes and eutrophic evolution of the Wular Lake, Kashmir Valley spanning the last ~ 500 years. Based on the multi-proxy analysis and supported by radiocarbon chronology, two prominent environmental phases were identified. From 74 to 45 cm, the sedimentation corresponds to the late 15th to early sixteenth century suggests the influence of cold, Little Ice Age (LIA) with nutrient-poor lacustrine environmental conditions. The following climate phase (28–9 cm) reflects the 19th and early twentieth century warmer and wetter environmental conditions. Enhanced TOC and N nutrient inputs in the lake sediments observed during the top 25 cm are likely contributed by anthropogenic sources owing to rapid and sustained anthropogenic land-use of watershed environments. This increase in the lake nutrients has been caused due to intense agriculture and horticulture practices leading to the lake eutrophication. [ABSTRACT FROM AUTHOR]
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- 2021
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9. Holocene palaeoenvironmental records from the high-altitude Wular Lake, Western Himalayas.
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Shah, Rayees Ahmad, Achyuthan, Hema, Lone, Aasif Mohmad, Kumar, Sanjeev, Kumar, Pankaj, Sharma, Rajveer, Amir, Mohd, Singh, Atul Kumar, and Dash, Chinmay
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HOLOCENE Epoch , *LAKES , *CLIMATE change , *RADIOCARBON dating - Abstract
We present a comprehensive record of Holocene (11,590–628 cal. yr BP) climate and hydrographic changes around the Wular Lake located in Kashmir Valley, India. Based on the multi-proxy investigations, we have identified three phases of wet climate conditions that prevailed from the commencement of the Holocene Epoch – 9000 cal. yr BP, 8100–6650 cal. yr BP and 6350–5000 cal. yr BP, whereas periods of dry climate were observed during 9000–8100 cal. yr BP, 6650–6350 cal. yr BP and ~5000 to 4000 cal. yr BP. The results also suggested that the lake widened and deepened significantly around 6350–5000 cal. yr BP. The results indicated desiccation and the exposure of the lake margin around 5000–4500 cal. yr BP. The sedimentation rate since 4500–628 cal. yr BP was quite low for detailed paleoclimate interpretations. Oscillations in lake extension and deepening appear to be due to changing intensity of westerly moisture in the region, and we correlate several of the low lake-level phases to the Bond events caused by North Atlantic ice rafting events. [ABSTRACT FROM AUTHOR]
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- 2020
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10. Environmental Risk Assessment of Lake Surface Sediments Using Trace Elements: A Case Study, the Wular Lake.
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Shah, Rayees Ahmad, Achyuthan, Hema, Lone, Aasif Mohmad, Lone, Suhail Ahmad, and Malik, M. Subzar
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TRACE elements , *ENVIRONMENTAL risk assessment , *LAKE sediments , *WATER pollution , *METROPOLITAN areas , *LAKES - Abstract
Surface sediments were collected from Wular Lake, located in Bandipora district of Kashmir Valley, NW Himalaya to investigate the environmental risk assessment using trace element concentrations. The surface sediments of the lake reveal higher concentration of Cl, Cr, Ni, Cu, Co, Pb, Zn and Th. In order to estimate the impact of metal pollution on the sediments, the trace element data was quantified for enrichment factor (EF), geoaccumulation index (Igeo), pollution load index (PLI) and contamination factor (CF). The average values for Igeo reveal moderate to strong contamination of Ni, Cu, while Cr and Co exhibit moderate to strong contamination in the central part of the lake. EF reveals minor enrichment of Cu, Ni, Cr, Co and Zn in the lake surface sediments. PLI indicate moderate pollution from all the sampling sites. Spatial distribution of the metal in the lake reveals their transport through the sewage from the urbanized areas and the Jhelum river. Since metal pollution in the lake is still at nascent stage, it demands attention of the local authorities and the Lake Conservation Department to take remedial measures for the protection of this freshwater body from further contamination. [ABSTRACT FROM AUTHOR]
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- 2020
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11. Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India.
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Ali, Asif and Achyuthan, Hema
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Kashmir valley receives the rainfall owing to the dominant westerly winds and experiences less impact of the southwest monsoonal rains (SWM). In this valley, loess and loess paleosols occur as a thin veneer covering the landscape. The loess paleosols form an important proxy for paleoclimate reconstruction and understanding the late Quaternary paleoenvironmental shifts. For this purpose, the loess, paleosols within the loess lithosections were lithologged and the sediment samples were subjected to various grain-size textural and geochemical analysis. The U-ratio of the sediments supported by parameters such as TOC, CaCO3 content, ratios of Zr/Rb, Rb/Sr, Ba/Sr, K/Ba, K/Rb, chemical index of alteration (CIA) and clay mineralogy indicate that the loess paleosols have undergone weak to moderate degree of pedogenesis. The U-ratio and Zr/Sr ratio also reflect variations in the wind velocity ranging from weak to moderate conditions for the loess deposition. The Ba/Sr and Rb/Sr ratios signify varied precipitation conditions, particularly with higher precipitation during the paleosol formation. The A–CN–K plot exhibits weaker to intermediate type of weathering of the loess horizons. TiO2% vs. Al2O3% binary plot illustarates mostly basaltic to rhyolite/granite type of rock source and the Panjal Traps is one of the major sources of the loess deposition. The lower end of the exposed Choori and Burzahama lithosections were dated by OSL method to 54 ± 2 ka at 9.5 m depth and 52 ± 2 ka at 8 m of depth, respectively. Geochemical analysis and OSL dating of the Choori and Burzahama lithosections reveal that climate during the marine isotope stage 3 (MIS 3) was dominantly warm and dry (stadial conditions) in Kashmir valley when the loess layers covered the valley and since then the loess horizons have undergone weak to intermediate, moderate type of weathering in cool and dry conditions. [ABSTRACT FROM AUTHOR]
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- 2020
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12. 13th International Earth Science Olympiad 2019, Daegu, Republic of Korea.
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Achyuthan, Hema and Godhavari, K. S.
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EARTH sciences , *SCIENCE museums , *SCIENCE education - Published
- 2020
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13. Paleoenvironmental shifts spanning the last ~6000 years and recent anthropogenic controls inferred from a high-altitude temperate lake: Anchar Lake, NW Himalaya.
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Lone, Aasif Mohmad, Achyuthan, Hema, Shah, Rayees Ahmad, Sangode, Satish Jadgeo, Kumar, Pankaj, Chopra, Sundeep, and Sharma, Rajveer
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WESTERLIES , *LAKES , *ENVIRONMENTAL geochemistry , *WATERSHEDS , *GEOCHEMISTRY , *GRAIN size - Abstract
Integrating multiproxy results (geochemistry, mineral magnetism, grain size, and C/N ratio variability supported by 14C AMS dating), obtained from a 1.4-m sediment core retrieved from high-altitude Anchar Lake, Kashmir Valley, NW Himalaya, we present a 6000-years record of paleoenvironmental and paleolimnological shifts. Phase 1 (6000–4700 cal. yr BP) revealed a wetter climate with a significant terrestrial input corresponding to the gradual strengthening of the westerlies. Phase 2 (4700–3900 cal. yr BP) reflects an overall improved westerly precipitation and autochthonous sources of organic matter (OM). Magnetic parameters also indicate higher lake levels and reducing conditions during this phase. Phase 2 was followed by a gradual diminishing pattern of the westerlies as also represented by phase 3 (3900–2500 cal. yr BP) and phase 4 (2500–1600 cal. yr BP) indicating moderate precipitation conditions, catchment stability, and temperate and/or cold-dry climatic conditions. Phase 5 (1600–500 cal. yr BP) revealed the prevalence of moderately cold/dry and further subdued westerly precipitation. Phase 6 (500 cal. yr BP to present) is represented by reduced westerly precipitation, shrinking lake margins, and significant terrestrial/anthropogenic controls over the lake basin. Mineral magnetic parameters indicate reducing lake bottom water conditions and eutrophication during this phase due to anthropogenic activities. These paleoenvironmental shifts reveal near synchronous changes (within dating uncertainties) with other regional paleoclimate records close to the present Anchar Lake location and reflect the gradual late-Holocene diminishment of the amount of winter/early summer moisture provided by the mid-latitude westerlies. [ABSTRACT FROM AUTHOR]
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- 2020
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14. Incipient Weathering of the ∼74ka Young Toba Tuff (YTT) Biotite Grains, Sagileru Valley, Andhra Pradesh.
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Krishnan, Geethanjali and Achyuthan, Hema
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BIOTITE , *VOLCANIC ash, tuff, etc. , *GRAIN , *NEANDERTHALS , *SCANNING electron microscopes , *ELECTRON probe microanalysis - Abstract
The Young Toba Tuff (YTT) ash containing biotite flakes was once spread over the Indian peninsula, and is now exposed at several sites in the Sagileru river basin in Andhra Pradesh. The ash beds form a distinct marker horizon in the landscape and have been recognized in a variety of sedimentary sequences associated with middle Paleolithic archaeological tools. In the present study, biotite grains from the volcanic ash beds were separated that were collected from Vankamarri (VKM), Porumamilla (PRM) and Jammulamadugu (JMD), sites in the Sagileru river valley, Cuddapah, Andhra Pradesh. The biotite grains were separated to understand the state and stage of weathering since the ash deposition ∼74ka. Electron microprobe data of the biotite grains exhibit low FeO/MgO values. The chemical discrimination diagrams characterizing the physicochemical properties of the biotite flakes from VKM, PRM and JMD sites indicate calc-alkaline composition and in the A-CN-K diagram, most of the samples fall above the plagioclase feldspar zone signifying low degree of alteration. Both the CIA and A-CN-K values depict the low weathering state of biotite, and this probably is owing to long periods of dry, semi-arid to arid climatic conditions since ∼74ka. Scanning Electron microscope (SEM) of the biotite grains reveal micro and nanopores on the surface and many a times these coalesce to form curls along the edges of the biotite grains further supporting incipient but very early stage of biotite weathering since its deposition ∼74ka. [ABSTRACT FROM AUTHOR]
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- 2019
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15. Clay Minerals and Micromorphology of the Loess Paleosols, Kashmir Valley, India.
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Ali, Aasif, Achyuthan, Hema, and Azhardin, Mohamad
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CLAY minerals , *PALEOPEDOLOGY , *LOESS , *QUATERNARY paleoclimatology , *OXIDE coating , *WIND speed , *FERRIC oxide , *SILT - Abstract
Loess paleosols have been often studied to reconstruct late Quaternary past climate changes. In the present study, textural analysis, TOC, CaCO3 content, micromorphology and clay mineralogy of the three loess paleosol profiles from three sites (Choori, Alochibagh and Burzahama), from Kashmir valley are presented. Based on the dates of Burzahama section, the exposed loess paleosols are approximately dated to 45ka. Textural analyses suggest that the sediments are largely fine silt followed by silty loam and silty clay loam. The fine sand component in the loess and paleosols indicate that winds in the valley were strong, but in phases the wind velocity was low. The paleosols are much thicker than loess layers and form several horizons within the lithosections. The increase of CaCO3 content indicates that it has leached in phases and along with total organic carbon (TOC) resulted in mild pedogenesis with variations in the rate of pedogenesis within the paleosols and forming pedocomplexes. Micromorphology of the loess-paleosols indicates the presence of calcite nodules with iron oxide coating indicating sub-aerial weathering and pedogenesis. The presence of channel structures in loess paleosols formed due to root traces and pores probably during the warmer periods. The replacement of chlorite by smectite clays in loess paleosols suggests that the alteration of clay minerals probably took place in cold, dry, warmer climatic conditions in low wind regime. [ABSTRACT FROM AUTHOR]
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- 2019
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16. The Toba tephra as a late Quaternary stratigraphic marker: Investigations in the Sagileru river basin, Andhra Pradesh, India.
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K, Geethanjali, Achyuthan, Hema, and Jaiswal, M.K.
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THERMOLUMINESCENCE dating , *WATERSHEDS , *TEPHROCHRONOLOGY , *EARTH sciences , *BLUE light emitting diodes , *SEDIMENTARY rocks - Published
- 2019
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17. Late Holocene paleoenvironmental changes inferred from Manasbal Lake sediments, Kashmir Valley, India.
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Babeesh, C., Achyuthan, Hema, Resmi, M.R., Nautiyal, Chandra Mohan, and Shah, Rayees Ahmad
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KATABATIC winds , *LAKE sediments , *VALLEYS , *WESTERLIES , *GEOCHEMISTRY , *MONSOONS - Abstract
Paleoclimate investigations and reconstruction using the lake sediment cores of Kashmir Valley have been rarely attempted. The basin is influenced by Indian Summer Monsoon, Westerlies and the local katabatic winds. In the present study, an 80 cm undisturbed sediment core was retrieved from the Manasbal Lake situated in North western Himalaya. Sediments were dated using 14C method, and the age-depth model indicated a depositional history extending from ∼3345 yrs BP to the present. Grain size, major and trace elements, TOC, OM contents C/N ratio and diatom assemblages were applied to reconstruct the paleoenvironmental changes around the area. The A-CN-K diagram displays that the weathering intensity of the Manasbal lake sediments are moderate to highly weathered and the sediments have been derived from nearby and mixed source origin. Several wet and cold phases were identified during ∼3300 yrs BP to ∼2500 yrs BP and ∼1800 yrs BP to ∼1300 yrs BP due to intense precipitation reflect high lake level. These wet phases are marked by higher sand and silt content, C/N ratio and high allochthonous input with less abundance of diatom species, clay, OM, TOC contents and high CIA values. Consequently, low lake level and dry and cold period from ∼3345 yrs BP to ∼3300 yrs BP and ∼2500 yrs BP to ∼1800 yrs BP is observed. These inferences are corroborated with the trace elemental ratios CIA and CWI data. Our data indicate that the Westerlies and localised katabtic winds rather than the Indian summer monsoons played a major role in controlling the past climate around the Manasbal lake, Kashmir Valley. [ABSTRACT FROM AUTHOR]
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- 2019
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18. Tropical Rainforest Dynamics and Palaeoclimate Implications since the late Pleistocene, Nilgiris, India.
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Raja, Priyanka, Achyuthan, Hema, Farooqui, Anjum, Ramesh, Rengaswamy, Kumar, Pankaj, and Chopra, Sundeep
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RAIN forests , *PALEOCLIMATOLOGY , *PLEISTOCENE Epoch , *VEGETATION dynamics - Abstract
A multiproxy study involving sedimentology, palynology, radiocarbon dating, stable isotopes, and geochemistry was carried out on the Parsons Valley Lake deposit, Nilgiris, India, to determine palaeoclimatic fluctuations and their possible impact on vegetation since the late Pleistocene. The 72-cm-deep sediment core that was retrieved reveals five distinct palaeoclimatic phases: (1) Warm and humid conditions with a high lake stand before the last glacial maximum (LGM; ~29,800 cal yr BP), subsequently changing to a relatively cool and dry phase during the LGM. (2) Considerable dry conditions and lower precipitation occurred between ~16,300 and 9500 cal yr BP. During this period, the vegetation shrank and perhaps was confined to moister pockets or was a riparian forest cover. (3) An outbreak in the shift of monsoonal precipitation was witnessed in the beginning of the mid-Holocene, around 8400 cal yr BP, implying alteration in the shift toward warm and humid conditions, resulting in relatively high pollen abundance for evergreen taxa. (4) This phase exhibits a shift to heavier δ13C values around ~1850 cal yr BP, with an emergence of moist deciduous plants pointing to drier conditions. (5) Human activities contributed to the exceedingly high percentage of Acacia and Pinus pollen during the Little Ice Age. [ABSTRACT FROM AUTHOR]
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- 2019
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19. Prof. S. N. Rajaguru (1933–2022).
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Achyuthan, Hema
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COLLEGE curriculum , *ARCHAEOLOGICAL excavations , *EDUCATIONAL sociology - Published
- 2023
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20. Geochemical Signatures of Karlad Lake Sediments, North Kerala: Source Area Weathering and Provenance.
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Babeesh, C., Achyuthan, Hema, and Sajeesh, T.P.
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ANALYTICAL geochemistry , *LAKE sediments , *WEATHERING , *CARBON content of water , *CALCIUM carbonate - Abstract
In the present study, the lake floor sediments of the Karlad lake, located at higher elevation in Wayanad region of north Kerala, were analyzed for textural characteristics, organic matter, calcium carbonate, major oxides and trace elements. This study was carried out to infer the chemical composition, provenance and intensity of chemical weathering of the source rocks in the lake catchment area. Textural studies signify that lake floor sediments are predominantly as clays (38.75%) followed by sand (36.36%) and silt (25.19%) fractions. The C/N ratio of the lake sediments signify that the sediments are both autochthonous and allochthonous in origin. The major oxides average content reveals the order of abundance as follows; SiO2 > Al2O3 > Fe2O3 > TiO2 > MgO > CaO > K2O > P2O5 > Na2O > MnO. Moreover, the various weathering indices such as Chemical Index of Alteration (CIAAvg. 93.5%), PlagioclaseIndex of Alteration (PIA- Avg. 95.6%) and Chemical Index of Weathering (CIW- Avg. 95.76%) suggest an intense chemical weathering of the source area. The A-CN-K diagram is also corroborating the same. Various provenance discrimination diagrams reveal that the sediments are derived from the mafic source rocks. [ABSTRACT FROM AUTHOR]
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- 2018
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21. Lower Palar River Sediments, Southern Peninsular, India: Geochemistry, Source-Area Weathering, Provenance and Tectonic Setting.
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Resmi, M. R. and Achyuthan, Hema
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RIVER sediments , *RIVERS , *GRAIN size , *SEDIMENTS , *FELSIC rocks , *IGNEOUS rocks , *CHONDRITES - Abstract
This present study describes the geochemistry of fluvial sediments of the Palar river (lower reaches), Southern Peninsular India, with an aim to evaluate their provenance, weathering and tectonic setting. The bulk sediment chemistry is influenced by grain size. The river sediments are enriched with SiO2 and depleted in Al2O3, K2O, CaO, Na2O, MgO, P2O5, MnO, Fe2O3 as compared with UCC values. Geochemical classification indicate that the sediments are mainly arkose, wacke and shale in composition. Discriminant diagrams together with immobile element ratio plots reveal that, the Palar river sediments are mostly derived from rocks formed in an active continental margin. Additionally, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate felsic rock sources. The chemical indices of alteration suggest that Palar river sediments are chemically immature and have experienced low chemical weathering effects. This is further supported by the Th/U Rb/Sr ratio and A-CN-K ternary diagram, with most of the sample data points falling close to the plagioclase-smectite line. The bivariate plot of Th/Sc versus Zr/Sc suggest a moderate recycled origin of the sediments. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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22. Northeast monsoon variations during the Holocene inferred from palaeochannels and active channels of the Palar River basin, Southern Peninsular India.
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Resmi, M. R. and Achyuthan, Hema
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GEOCHEMICAL modeling , *OPTICALLY stimulated luminescence , *SEDIMENTS , *MONSOONS , *PALEOCLIMATOLOGY - Abstract
The present-day Palar River and its palaeochannel located in the Southern Peninsular India were investigated with a multidisciplinary approach. The main aim of the study was to reconstruct the palaeoenvironment history of the Palar River basin and to delineate the role of Holocene fluctuations that played a major role in the geomorphological evolution of the region since the Holocene period. The results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence (OSL) dates reveal distinct seven climatic phases since the past ~10 ka. Phase 1 signifies a very high precipitation as attested by the low CWI with high Rb/Sr ratio. Subsequent to Phase 1, a decreasing trend in the northeast monsoon rainfall (NEMR) is observed (Phase 2). Phase 3 (~4.83-3.59 ka) reflects a decrease in NEMR further supported by low Mn/Al, Mg/ Al and Chemical Index of Alteration (CIA) values. Phase 4 (~3.59 ka) is marked by high sand flux, higher K/Al, Ti/Al, Rb/Sr and Ba/Sr ratios coupled with lower values of CaO/MgO, Mn/Al and Fe/Al indicating wetter conditions in the catchment area resulting in the intense weathering of the bedrocks caused owing to the increase in NEMR precipitation. Phase 5 (3.26-2.42 ka) reveals a decline in NEMR precipitation coupled with rapid upstream avulsion because of neotectonic activity that occurred in an intense dry phase. Phase 6 (~1.88-1.44 ka) is marked by an augment NEMR causing higher K/Al, Mg/ Al, Ti/Al ratios, CIA and CWI values. Finally, Phase 7 (~1.44 ka-present) is marked by lowered elemental solubility and mobility reflecting short periods of weaker or deteriorated NEMR. The documented record of the Palar River and palaeochannels suggests Holocene NEMR variability in the study region and is synchronous with the various proxy records of NEMR-dominated regions, however, revealing an inverse coupling with southwest monsoon rainfall (SWMR) during the Holocene period. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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23. Late Pleistocene Paleoflood Deposits Identified by Grain Size Signatures, Parsons Valley Lake, Nilgiris, Tamil Nadu.
- Author
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Raja, Priyanka, Achyuthan, Hema, Geethanjali, K., Kumar, Pankaj, and Chopra, Sundeep
- Subjects
- *
PARTICLE size distribution , *LAKE sediments , *LAKE hydrology , *CARBON isotopes , *FLOODS - Abstract
A study involving grain size analysis was carried out from the Parsons valley lake deposit, Nilgiris, India to determine the depositional environments and paleoflood events since late Pleistocene period (∼29,838 cal yr BP). A 72 cm lacustrine core was collected from the lake and eight organic rich sediment samples were AMS radiocarbon dated. The study reveals variations in the grain size distribution chiefly influenced by regional climatic conditions. Paleoflood events have been identified by the individual sedimentary flood signatures of varying changes in the magnitude of sediment supply from the background silty sediment matrix around ∼29,838 and ∼8405 cal yr BP. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
24. Ferricretes of Sriperumbudur: Micromorphology and Geochemistry.
- Author
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Shah, Rayees Ahmad, Achyuthan, Hema, Jose, Powel, Lone, Aasif Mohmad, and K., Geethanjali
- Subjects
- *
GEOCHEMISTRY , *SOIL micromorphology , *GEOLOGICAL formations , *CHEMICAL weathering , *SEDIMENTARY rocks , *CRETACEOUS Period - Abstract
Earlier studies on the ferricrete of Sriperumbudur Formation were focused on their types of occurrences and mode of formation. However, in the present study, an attempt is made to understand the physico-chemical changes across seven saprolite-ferricrete profiles developed over sedimentary protolith after upliftment to decipher the paleoenvironmental conditions to which the Sriperumbudur Formation was exposed and to understand the processes of ferricretisation. For this purpose, the ferricrete exposures around Sriperumbudur were surveyed and mapped for their occurrences and types of ferricretes, collected samples were examined for various physio-chemical aspects. Geochemical and petrographic studies exhibit a relatively high percentage of iron content. The Fe2O3 content varies from 7.71% to 14.9% followed by the higher concentration of Al2O3 and SiO2 as a result of deep weathering of the Sriperumbudur beds. Other major oxides such as CaO, MgO, Na2O, K2O, MnO and TiO2 show lower concentrations. The bulk X-ray diffraction of the ferricrete samples shows the occurrence of tourmaline, muscovite and magnetite. SEM analysis of the ferricrete samples exhibits solution channels and pits in the matrix, on the limonite, quartz and magnetite revealing intense chemical weathering. Petrographic studies show the occurrence of quartz in a variety of shapes, sizes and sediment sorting, cemented by iron oxides in varying stages. It also reveals iron oxide mobilization due to the alteration of ferruginous sandstone forming a hard ferricrete crust. Iron oxide cementation is due to leaching and re-cementing from the parent sedimentary rock with subsequent re-deposition of the earlier material taking place in a near shore environment and in wetter conditions after the Sriperumbudur beds were exposed since the lower Cretaceous period. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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25. Diatoms, spatial distribution and physicochemical characteristics of the Wular lake sediments, Kashmir valley, Jammu and Kashmir.
- Author
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Shah, Rayees, Achyuthan, Hema, Lone, Aasif, and Ramanibai, R.
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- *
DIATOMS , *SPATIAL distribution (Quantum optics) , *LAKE sediments , *CARBON content of water , *LAKES - Abstract
Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to understand the source of organic carbon (terrestrial or in situ) in lake systems in order to monitor the health of the lake. Wular lake, located in north Kashmir, is one of the largest fresh water lake in India, situated at an average elevation of 1580m ASL. The lake is fed by a number of watersheds that bring a diverse type of sediments and organic matter and thus deposit them into the Wular lake basin. In order to understand sediment distribution pattern, content and source of organic matter, sediment provenance and the persisting environment in the Wular lake, 32 lake floor sediment samples covering the entire lake were collected and analyzed for organic element analysis, CaCO3, organic matter, sediment texture and diatom analysis. The results indicated that sediments in the lake are dominated by silt and silty clay. The organic carbon in the lake ranged from 0.83%-4.52% and nitrogen varied from 0.06%-0.5%. The Carbon to Nitrogen (C/N) ratios (9.04 to 22.03) indicate a mixed source of organic carbon but dominated by in situ lake sources from the vascular and lake biota accumulation. The diatom analysis revealed the occurrence of a diverse type of species along the sampling sites present within the lake. The wide distribution of the diatom species such as Cymbella, Cyclotella and Tabularia etc. in the lake indicate high organic pollution and alkaline fresh water environment prevailing in the lake. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
26. Middle to late Holocene paleochannels and migration of the Palar River, Tamil Nadu: Implications of neotectonic activity.
- Author
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Resmi, M.R., Achyuthan, Hema, and Jaiswal, Manoj Kumar
- Subjects
- *
STRUCTURAL geology , *THERMOLUMINESCENCE dating , *NEOTECTONICS , *MONSOONS , *RIVERS , *MANAGEMENT - Abstract
Geomorphic, tectonic and sedimentary investigations have been carried out to understand the landscape evolution of the Palar River basin, Southern Peninsular India. For this purpose, satellite data interpretations coupled with field investigations, fluvial architecture and optically stimulated luminescence (OSL) dating methods were adopted to infer climatic variations and neotectonic deformation that took place during the mid to late Holocene period. Several paleochannels have been identified in the Northern part of the present day Palar River. The distribution pattern of the Palar paleochannels and its present course indicate its migration towards the south, leaving behind the old Palar River streams as paleochannels. Significant changes in the morphological characteristics, channel width and river pattern in the successive paleochannels reveal evidences of channel movement by avulsion largely controlled by reactivation of pre-existing lineaments and intensified NE monsoon. Based on OSL ages, two major phases of migration have been identified that occurred between 4.83 ka to 1.88 ka. First phase occurred between 3.59 ka to 3.26 ka due to intensified monsoon accompanied with small scale neotectonic activity. The second phase took place between 2.42 ka to 1.88 ka which occurred probably due to the rapid upstream avulsion. This rapid avulsion is due to the close proximity of MPA and the reactivation of the pre-existing lineaments. Moreover, the present Palar River basin exhibits evidences of neotectonic activity such as soft sediment deformation structures, anomalous drainage deflections and reactivation of lineaments and faults further indicating that the Palar River is still draining a tectonically active region. Thus, neotctonics and fluctuations in the intensity of monsoon are largely responsible for sculpting the present landscape. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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27. Comparative petrophysical and geochemical characteristics of thermal and volcanic ash from southeastern India.
- Author
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Krishnan, Geethanjali, Achyuthan, Hema, and Siva, V.
- Subjects
- *
VOLCANIC ash, tuff, etc. , *PETROPHYSICS , *THERMAL analysis , *POLLUTION , *QUARTZ , *X-ray diffraction - Abstract
This paper examines the difference in the geophysical and chemical characteristic of the volcanic ash and thermal fly ash to evaluate environmental pollution. Natural volcanic ash (VA) samples from Sagirelu, Cuddapah dist., Andhra Pradesh and thermal fly ash (FA) samples from the Thermal Power Station, Ennore, Chennai, were collected, analysed and compared. The particle sizes of the ash samples were determined using the laser particle size analyzer and the different surface morphological characters were studied using SEM analyses. The chemical components such as pH, major oxides, trace metals and mineral compositions were determined using pH metre, XRF and XRD methods. pH value of the volcanic ash varies from 8.5 to 8.9 indicating its alkalinity (8.5 to 9) in volcanic ash, while the thermal ash is neutral to mildly alkaline with pH varying from 6 to 7.5. Both the ash samples have higher concentration value in SiO (VA - 69.25%, FA- 46%) in major oxides and Cl (VA - 0.8%, FA - 0.1%) in trace elements. Quartz is the dominant mineral in both the types of ash, however, the volcanic ash has amorphous silica, while the fly ash contains crystalline quartz. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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28. Late Quaternary loess-like paleosols and pedocomplexes, geochemistry, provenance and source area weathering, Manasbal, Kashmir Valley, India.
- Author
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Babeesh, C., Achyuthan, Hema, Jaiswal, Manoj Kumar, and Lone, Aasif
- Subjects
- *
LOESS , *PALEOPEDOLOGY , *GEOCHEMISTRY , *OPTICALLY stimulated luminescence , *CLIMATE change - Abstract
The late Quaternary loess and loess-like deposits in Kashmir Valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region. We present a loess-like paleosol located along the margin of the Manasbal Lake, Ganderbal, which was studied in detail for understanding the pedological processes and reconstructing the late Quaternary soil formation. In this paper we present loess-like paleosol formation of a nearly 10.6 m thick sequence exposed along the margin of Manasbal Lake, Ganderbal District, Srinagar, Kashmir. Geochemical and textural data of this loess-like sedimentary sequence fluctuate reflecting the varied depositional processes operating in the valley, differential intensity of weathering, and processes of pedogenesis. Weathering indices such as chemical index of alteration, chemical index of weathering, and plagioclase index of alteration reveal weak to moderate weathering of the parent material. Provenance discrimination diagrams of the present study disclose that the Manasbal loess-like paleosol sediments are derived from the mixed source rocks suggesting a variety of provenance with variable geological settings, which apparently have undergone weak to moderate recycling processes. The Manasbal paleosol horizons have been dated by the optically stimulated luminescence (OSL) method to the marine isotope stages mid-MIS-3 (41.7 ± 8.0 ka) and late-MIS-2 (14.6 ± 3.8 ka). During the MIS-3 period, the climate was wetter, forming a strong AhBtk paleosol as inferred from the geochemical data. A steady increase in the CaCO3 content and C/N ratio in the paleosols from 6.50 m (MIS-3) indicates arid and drier climatic conditions. The area around Manasbal Lake incised because of climate change and neotectonic activity since post-14 ka. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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29. Early-Holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments, Kukkal Lake, Southern India: Geochemistry and palynology.
- Author
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Rajmanickam, Vijayaraj, Achyuthan, Hema, Eastoe, Christopher, and Farooqui, Anjum
- Subjects
- *
GEOLOGICAL basins , *CLIMATE change , *WEATHERING , *MONSOONS , *FORESTS & forestry , *LAKES - Abstract
The Kukkal basin, Tamil Nadu, India, receives most of its rain from the southwest monsoon (SWM). A sediment core from Kukkal Lake preserves a continuous sediment record from the early-Holocene to present (9000 yr BP to present). The present lake is situated at an elevation of ~1887 m a.s.l., in a small basin that appears to have alternated between a and wetland depositional environment. Climate proxies, including sediment texture, total organic carbon (TOC), total nitrogen (TN), C/N, pollen and geochemical composition indicate a steady progression to wetter conditions, with two stepwise changes at about 8000, and between 3200 and 1800 yr BP. The change at 8000 yr BP appears to correspond to a brief (100–150 years) dry spell recorded elsewhere in India. The change at 3200–1800 yr BP consisted in a rapid intensification of the SWM, and may correlate with the initiation of the ‘Roman Warm Period’. There is no clear evidence of changes at the times of the ‘Medieval Warm Period’ (‘MWP’) and the ‘Little Ice Age’ (‘LIA’). The C/N ratio of the sediments ranges from 14.02 to 8.31, indicating that the organic matter originated from a mixture of lacustrine algae, vascular and terrestrial plants. Chemical weathering indices (Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA)) are consistent with extreme silicate weathering. Pollen data show a development from savanna vegetation prior to about 8000 yr BP, followed by grassland with palms, the appearance of ferns just prior to 3200 yr BP and the establishment of the tropical humid forest between 3200 and about 1800 yr BP. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
30. Palaeoenvironmental dynamics and Palaeolithic occupation at Katoati, Thar Desert, India.
- Author
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Blinkhorn, James, Achyuthan, Hema, Ditchfield, Peter, and Petraglia, Michael
- Subjects
- *
PALEOLITHIC Period , *PLEISTOCENE Epoch , *MONSOONS - Abstract
Late Pleistocene palaeoenvironments in the Thar Desert (India), located at the eastern extent of the Saharo-Arabian desert belt, have fluctuated considerably as a result of the varying range and intensity of the Indian summer monsoon. Phases of widespread Pleistocene aridity are well documented in the Thar Desert, but research focusing on humid proxies is critical to examine how the region may have facilitated population expansions across southern Asia. At Katoati, located on the northeast margin of the Thar Desert, the combination of field recording of sediment sections with detailed analyses (micromorphology, stable isotope, loss on ignition, magnetic susceptibility, and X-ray fluorescence) from an archaeological site identify a series of hominin occupations during phases of enhanced humidity between ~96 and 60 ka. A gradient of humidity on the eastern margin of the Thar Desert during the late Pleistocene is identified, with the periodic humidity evident at Katoati occurring more frequently and with longer duration towards the southern margin. This uneven distribution of humidity in the Thar Desert is likely to have strongly influenced when and where hominin populations could expand into and across the region. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
31. Geochemistry of Vellayani lake sediments: Indicators of weathering and provenance.
- Author
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Nair, Veena and Achyuthan, Hema
- Subjects
- *
LAKES , *RARE earth metals , *SEDIMENTS , *GEOCHEMISTRY , *WEATHERING , *WATERSHEDS - Abstract
The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO, MnO, CaO, MgO, NaO, KO, and PO content while TiO, FeO and AlO are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO is high in coarse fractions while AlO is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
32. 12th International Earth Science Olympiad (IESO) at Mahidol University, Kanchanburi Campus, Thailand.
- Author
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Achyuthan, Hema and Godhavari, K. S.
- Subjects
- *
EVALUATORS , *GOVERNMENT laboratories - Published
- 2019
- Full Text
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33. 10 International Earth Science Olympiad (IESO): 2016, Mie University, Tsu, Japan.
- Author
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Achyuthan, Hema and Godhavari, K.
- Subjects
- *
SCHOOL contests , *SECONDARY school students , *EARTH sciences , *EMISSION control , *FIELDWORK (Educational method) - Abstract
The article discusses the 10th International Earth Science Olympiad that was held at Mie University in Tsu, Japan from August 20 to 27, 2016. The event served as an earth science competition for secondary school students given annually. It tackled ways to reduce greenhouse gas emissions and develop renewable energy sources. Among the team activities conducted at the event were the International Team Field Investigation and Earth System Project.
- Published
- 2016
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34. Organic matter source in the freshwater tropical lakes of southern India.
- Author
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Vijayaraj, R. and Achyuthan, Hema
- Subjects
- *
ALGAE , *LAKES , *ORGANIC compounds , *PARTICULATE matter , *SEDIMENTS - Abstract
In this article, sediment texture, calcium carbonate, organic matter (OM), total organic carbon (TOC), total nitrogen (TN) and C/N ratio analysis of lake floor sediments of the Berijam and Kukkal lakes located nearly 2000 m amsl in the Palani Hills, Tamil Nadu, India are presented. This study was carried out to decipher the spatial distribution, origin of OM and the relationship among the components. TOC, TN% and C/N ratio of the Berijam lake sediments indicate a mixed source of OM (terrestrial and in situ lake algae and other biota), while for the Kukkal lake it is due to algae, aquatic weeds and plant detritus that grow along its margins. The lake margins and lake-bed morphology control the distribution of sediment particulate matter and texture. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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35. th International Earth Science Olympiad (IESO), Cotê d' Azur, Nice, France.
- Author
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Achyuthan, Hema and Godhavari, K.
- Subjects
- *
EARTH sciences , *SECONDARY school students , *GEOLOGY , *HYDROLOGY , *METEOROLOGY , *OCEANOGRAPHY , *ASTRONOMY , *CONTESTS - Published
- 2018
- Full Text
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36. Pozzolanic characteristics of Young Toba Tuff.
- Author
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Siva, V. H. R., Achyuthan, Hema, and Santhanam, Manu
- Subjects
- *
VOLCANIC ash, tuff, etc. , *PORTLAND cement , *POZZOLANIC reaction , *LIMESTONE , *SOLUBILITY - Abstract
Portland Pozzolana Cement (PPC) is widely used to achieve durable and sustainable concrete in modern construction. In the present study, the potential use of natural volcanic ash in the manufacturing of PPC has been studied. Young Toba Tuff (YTT) was collected from Jwalapuram, Andhra Pradesh, India. The pozzolanic performance of this ash was assessed by Strength Activity Index (SAI) and Frattini test. SAI of YTT was found to be above 75% for sufficient pozzolanicity. Further, the results of Frattini test were below the lime solubility curve, indicating that YTT could be potentially useful as pozzolanic material in concrete. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
37. Distribution of sediments and organic matter source: Berijam Lake, Tamil Nadu.
- Author
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Vijayaraj, R. and Achyuthan, Hema
- Subjects
- *
SEDIMENT analysis , *GEOLOGICAL basins , *LAKE management , *ORGANIC compounds , *GRAVITATION - Abstract
Berijam lake, Tamil Nadu, situated at an elevation of 2165 m above mean sea level is a fresh water, irregular linear basin with two major linear arms located in the Palani hills. Lake floor sediments were collected covering the entire aerial extent of this lake basin to understand the sediment pattern distribution and plausible source of organic carbon. Textural pattern, CaCO, Organic matter, TOC, TN content and the C/N ratio of the lake floor sediment samples were analysed and the data generated exhibit a distinct pattern of sediment distribution and deposition. Grain size data indicate that the clay is associated with both sand and silt and the lake is dominantly composed of sandy clay and silty clay. CaCO content is low (2.70 to 0.80%) as there is no major source for CaCO. OM, TOC and TN show positive correlation with silt. C/N ratio varies from (12.2 to 9.6) indicating dominantly algal organic matter. NNW, NNE and SSE region of the lake seems to have supported thick water column as high organic carbon, silt and clay content occur in these directions. C/N ratio indicates that the major source of organic matter is from the lake algae, aquatic weeds and plants. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
38. Middle Palaeolithic point technologies in the Thar Desert, India.
- Author
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Blinkhorn, James, Achyuthan, Hema, and Ajithprasad, P.
- Subjects
- *
PALEOLITHIC Period , *DISPERSAL (Ecology) , *MESOLITHIC Period , *HUMAN ecology - Abstract
Point technologies form a key component of Middle Palaeolithic and Middle Stone Age industries across the Old World. However, only limited attention has been paid to the appearance of point technologies in the South Asian context. Two recent studies have indicated that the lack of Indian point technologies that are analogous to those known from the African Middle Stone Age and Arabian Middle Palaeolithic presents the basis to reject models for modern human dispersals into India associated with Middle Palaeolithic technologies. This study examines the role point technologies play in the Middle Palaeolithic record of the Thar Desert and situates them within the wider context of South Asia and adjacent regions to the west. A synthesis of existing evidence indicates that points form a key component of Middle Palaeolithic industries in the Thar Desert. New descriptions of Middle Palaeolithic artefacts from the Thar Desert highlight the repeated presence of debitage and façonnage approaches which suggest the use of specific reduction strategies in point production, rather than opportunistic or expedient methods. These results are placed in the wider context of the role points have played in Middle Palaeolithic reduction strategies within South Asia. Given the presence of point technologies in the Thar Desert that are comparable with contemporaneous technologies in North Africa and Arabia, we suggest that Middle Palaeolithic dispersal models cannot be rejected on the basis of their absence. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
39. Tafoni along the east coast, Chennai to Mamallapuram, Tamil Nadu.
- Author
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Arjunan, Malarvizhi and Achyuthan, Hema
- Subjects
- *
TAFONI , *GRANITE , *CHARNOCKITE , *SALINE waters , *WEATHERING - Abstract
A study on weathering pits called tafoni was carried out on rock surfaces that age from a few hundreds to millions of years along the east coast between Chennai and Mamallapuram. Tafoni of varying sizes and shapes such as simple circular dots to oblate to prolate, hemispherical to spherical are formed on the granite, granite gneiss, charnockites (acid and mafic) and sandstone both on exposed and inner wall surfaces. In this study, their formation is related to not only tropical weathering processes, but also to sea salt water splays causing salt mineral etching, weathering processes, besides microbial activity, algal and lichen growth accentuating their formation. [ABSTRACT FROM AUTHOR]
- Published
- 2015
40. Late Holocene continental shelf sediments, off Cuddalore, East coast, Bay of Bengal, India: Geochemical implications for source-area weathering and provenance.
- Author
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Keshav, Nisha and Achyuthan, Hema
- Subjects
- *
HOLOCENE Epoch , *SEDIMENTS , *CONTINENTAL shelf , *ANALYTICAL geochemistry , *WEATHERING , *PROVENANCE (Geology) - Abstract
In the present study, a 60 cm sediment gravity core collected off the Cuddalore shore (11°42.419 N, 79°57.993 E) from a water depth of 150 m was radiocarbon dated and analysed for major elements (Si, Al, Na, K, Ca, Mg and P), trace elements (Fe, Cr, Mn, Co, Ni, Cu, Zn and Pb), calcium carbonate, and organic matter content to understand their behavior and probable sources and also to understand the monsoon variability. The sediment core has been radiocarbon dated from around 4100 to 3100 BP. High sand around 4000, 3700, 1500 BP with low CaCO 3 content suggests high sediment flux coupled with higher precipitation corresponding to increased erosion during these periods, and more fresh water runoff from rivers in the late Holocene, thus reflecting intensification of the SW and NE monsoon. The results of the major elemental analyses show the fine-grained, detrital nature of sediments with high values of Si and lower values of Al and Fe. The present study clearly demarcates that the distribution patterns of Cr, Cu, Pb and Zn that are controlled by the distribution of the fine grained fractions. The increased Mn content towards the lower end of the sediment core denotes the allogenic supply of Mn from oxic to-sub-oxic recycling within the sediment column in fine grain sediments. The mean CIA values (56.47) reflect immature, moderately weathered sediments that are mostly derived from sandstone and clay. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
41. Mid-Holocene Indian Summer Monsoon variability off the Andaman Islands, Bay of Bengal.
- Author
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Achyuthan, Hema, Nagasundaram, Mohan, Gourlan, Alexandra T., Eastoe, Christopher, Ahmad, Syed M., and Padmakumari, Veena M.
- Subjects
- *
HOLOCENE Epoch , *MONSOONS , *CLIMATE change , *CHEMICAL weathering , *GEOCHEMISTRY - Abstract
A sediment core retrieved from the Andamans Forearc Basin (AFB) near Landfall Island, North Andaman, provides a record of sediment provenance and climate change during the mid to late Holocene. Radiocarbon ages ranging from 6078 to 1658 indicate that the core represents the interval from 6500 BP to the present. Grain size variation indicates a cyclic variation of wetter and drier conditions corresponding to changes in intensity of the Indian Summer Monsoon (ISM), which was at greatest intensity near 6400, 5300 and 3300–3000 BP. Geochemical parameters including abundance of CaCO 3 , εNd and δ 18 O in Globigerinoides ruber are consistent with a long-term trend from cooler, wetter conditions to the warmer, drier conditions at present. Chemical weathering intensity, which lags behind climate changes on land, shows a pulse of highly weathered sediment deposited at about 4000 BP. During the short-duration pulses of intense monsoon activity, sandy sediment was supplied from the Andaman Islands. The Irrawaddy, Salween, and Sittang rivers of Myanmar are the secondary sediment sources for the study area. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
42. A multi-proxy reconstruction of monsoon variability in the late Holocene, South India.
- Author
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Veena, M.P., Achyuthan, Hema, Eastoe, Christopher, and Farooqui, Anjum
- Subjects
- *
HOLOCENE Epoch , *SEDIMENTS , *MONSOONS , *FRESH water , *GEOCHEMISTRY , *RADIOCARBON dating - Abstract
Abstract: Pookode Lake, Kerala, South India, a fresh water lake situated at an altitude of ∼770 m.a.s.l., receives predominantly rains from the south-west monsoon. A sediment core 125 cm long was investigated for sediment texture, dating and geochemical composition. Radiocarbon dates obtained on the organic carbon rich sediments of the Pookode Lake range in age from the mid-Holocene to more recent (6240–565 14C BP; BC 4786 to AD 1434 cal.). Geochemical data of the sediment cores were corroborated with phytolith and pollen studies. Although phytoliths occur in the entire sediment core, pollen assemblages start occurring only since 1500 14C BP (∼AD 650 cal.). The sediments older than 1500 14C BP were not suitable for the preservation of the pollen assemblages. There is a major change in the lake hydrology, indicating lacustrine conditions subsequent to 1500 BP. Occurrence of diatoms in the upper sediment layers of the sediment core indicates shallowing of the lake. Both the Medieval Warm Period (MWP) and the Little Ice Age (LIA) are represented in the Pookode Lake sediment core. Sediment texture, chemical weathering intensity (CWI) values supported by phytolith and pollen assemblages, indicate that overall warm and dry conditions prevailed during 6200–420 14C BP (BC 4786–AD 1434 cal.) but this was interrupted by short, intense wet phases between ∼3900 and ∼1900 (∼BC 4000–∼AD 300 cal.), ∼1400–∼760 (∼AD 800–∼AD 1200 cal.), and ∼420–∼140 14C BP (∼AD 1570–∼ AD 1860 cal.). The wet events resulted from the strengthening of south-west monsoon (SWM) causing rising water levels and brief expansion of the Pookode Lake margin. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
43. Middle Palaeolithic occupation in the Thar Desert during the Upper Pleistocene: the signature of a modern human exit out of Africa?
- Author
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Blinkhorn, James, Achyuthan, Hema, Petraglia, Michael, and Ditchfield, Peter
- Subjects
- *
PALEOLITHIC Period , *PLEISTOCENE Epoch , *ARCHAEOLOGICAL assemblages , *STONE Age - Abstract
Abstract: The Thar Desert marks the transition from the Saharo-Arabian deserts to the Oriental biogeographical zone and is therefore an important location in understanding hominin occupation and dispersal during the Upper Pleistocene. Here, we report the discovery of stratified Middle Palaeolithic assemblages at Katoati in the north-eastern Thar Desert, dating to Marine Isotope Stages (MIS) 5 and the MIS 4–3 boundary, during periods of enhanced humidity. Hominins procured cobbles from gravels at the site as evidenced by early stages of stone tool reduction, with a component of more formalised point production. The MIS 5c assemblages at Katoati represent the earliest securely dated Middle Palaeolithic occupation of South Asia. Distinctive artefacts identified in both MIS 5 and MIS 4–3 boundary horizons match technological entities observed in Middle Palaeolithic assemblages in South Asia, Arabia and Middle Stone Age sites in the Sahara. The evidence from Katoati is consistent with arguments for the dispersal of Homo sapiens populations from Africa across southern Asia using Middle Palaeolithic technologies. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
44. Stable isotopes and salinity in the surface waters of the Bay of Bengal: Implications for water dynamics and palaeoclimate
- Author
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Achyuthan, Hema, Deshpande, R.D., Rao, M.S., Kumar, Bhishm, Nallathambi, T., Shashi Kumar, K., Ramesh, R., Ramachandran, P., Maurya, A.S., and Gupta, S.K.
- Subjects
- *
STABLE isotopes , *SALINITY , *WATER storage , *PALEOHYDROLOGY , *MONSOONS , *CHEMICAL oceanography - Abstract
Abstract: Surface water mixing in the Bay of Bengal (BOB) inferred from spatio-temporal distribution of δ18O and salinity based on synthesis of 194 new samples together with published data is reported. In general, both δ18O and salinity have low values in northern part of the BOB, progressively increasing towards SW. The lowest values are observed during July–September (southwest monsoon season) and the highest in pre-monsoon. The most prominent δ18O–salinity relationship is seen for samples collected during June to October when the Himalayan river influx dominates. When this influx decreases in other seasons the δ18O–salinity relationship is poor. The δ18O–δD regression of samples north of 10°N is similar to the GMWL. However, for samples south of ~10°N, this regression has a significantly lower slope. This is interpreted as due to absence of direct riverine inflow in this region of the BOB, coupled with –ve (P−E; Precipitation minus Evaporation) almost throughout the year. This study shows that the seasonal distribution of δ18O and salinity over the northern BOB is dominantly governed by the variation in the (P+R−|E|) in spite of the fact that ocean currents transfer several times more water between the two basins of northern Indian Ocean. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
45. Geochemistry of calcretes (calcic palaeosols and hardpan), Coimbatore, Southern India: Formation and Paleoenvironment
- Author
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Achyuthan, Hema, Shankar, Navin, Braida, Martina, and Ahmad, Syed Masood
- Subjects
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GEOCHEMISTRY , *CALCRETES , *TRACE metals , *GROUND vegetation cover , *SOIL profiles - Abstract
Abstract: There is no major chemical variation in the late Quaternary calcic nodules formed within vertisols in the foot-hill regions, and hardpan calcretes (greater than 200 ka) formed over the Precambrian substrate that occur as duricrust horizons in the plains around Coimbatore region, Tamil Nadu, India. The bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in CaO, SiO2, Al2O3 and Fe2O3 content. The trend of trace metal content in calcic nodules and in the hardpan calcrete is Mn > Zn > Ni > Cr > Pb > Co > Cu and Zn > Mn > Ni > Co > Pb > Cu > Cr respectively. PAAS-normalised REE data of the calcretes (calcic nodules and the hardpan) demonstrate a positive Euanomaly. This could be attributed to feldspar, apatite mineral alteration and soil digenetic processes, differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in Eu. The stable isotope values of the calcic nodules do not exhibit a wide range (δ18O −3.39 to −5.84‰ and δ13C −3.01 to −6.64‰), compared to the hardpan calcretes (δ18O −2.91 to −12.98‰) and δ13C (−0.05 to −7.4‰). The palaeoenvironment during the formation of the calcretes nodules was dominated by the C4 plants with sparse vegetation cover and that the parent material/bedrock supported a thin veneer of soil column with sparse vegetation cover as present day. Calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical – groundwater processes in arid – semi-arid conditions over along geological period. During the late MIS3 to the LGM period the south west monsoon was weak with mean annual rainfall (MAR) between 300 and 500 mm/yr, the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
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46. Saluvankuppam coastal temple -- excavation and application of soil micromorphology.
- Author
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Badhreenath, Sathyabhama, Achyuthan, Hema, Haricharan, Smriti, and Mohandas, K. P.
- Subjects
- *
SOIL micromorphology , *GRANITE , *INSELBERGS , *LATERITE , *POTSHERDS - Abstract
The 26 December 2004 tsunami exposed an inscription of the 10th century engraved on a rock boulder at Saluvankuppam, 6 km north of Mamallapuram. The inscription indicates the existence of a Subramanya temple. The temple and the mound around the granite inselberg were excavated by the Archaeological Survey of India, Chennai Circle. The excavation exposed the entire Subramanya temple complex constructed over a period of time (4th/5th CE to 12th/13th CE). The temple complex and the litho sections reveal phases of temple building activity. The cement and lime used for the temple complex contain fragments of shells. Soil micromorphology technique was applied to understand the type of textures and fabric in soil sediments, bricks, potsherds, well rims, bone fragments, etc., using a polarized microscope. Thin sections of the laterite bricks which formed the foundation indicate high content of hematite, magnetite, kaolinite patches and the porosity of the laterite brick varies from 5% to 10% only, whereas thin sections of potsherds indicate that the firing temperature was fairly low and that the pots were well fired. Geoarcheology study of this temple complex indicates that a number of naturally occurring raw materials have been used for constructing this temple that were locally available. [ABSTRACT FROM AUTHOR]
- Published
- 2011
47. Genesis of calcic and petrocalcic horizons from Coimbatore, Tamil Nadu: Micromorphology and geochemical studies
- Author
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Shankar, Navin and Achyuthan, Hema
- Subjects
- *
GRAIN , *EARTH sciences , *OXIDE minerals , *MINERAL aggregates - Abstract
Abstract: Understanding the development of calcic and petrocalcic horizons is important for palaeoclimate reconstruction. The micromorphology and geochemistry of Quaternary calcic and petrocalcic horizons formed in the area around Coimbatore, Tamil Nadu are discussed. The calcic horizons represent the Bk horizons that occur as thick complex profiles (∼300cm thick) in the foothill regions while the laminar petrocalcic horizons representing the K horizon (80–100cm thick) formed on hard rock in the topographic low-lying area. Calcic horizons are represented by powdery, nodular calcrete nodules and root casts with 95.2–64.5% of CaCO3. Laminar petrocalcic horizons are compact with well rounded coalesced nodules and contain 56–64% CaCO3. Micromorphological study of the calcic horizons show the occurrence of alveolar septal structures, calcified filaments, coated grains, spherulites, calcified root cells and calcispheres that indicate biogenic origins, mainly induced by plant root related microbial activity. The calcic nodules within the calcic horizons consist of quartz sand grains cemented by finely crystalline, grain-coating, often glaebular and pore-filling micrite. This development has taken place in phases of soil formation, erosion and reworking. The inter-relationships between these processes have caused variations in the phases of accretion of soil profiles developed in the foothill region. Microfabrics of laminar petrocalcic horizons with detritus hosts show replacement, corrosion, displacement and shrinkage indicating that the laminar petrocalcic horizon formed under relatively semi arid conditions. These characteristics indicate that the laminar petrocalcic horizons formed in a moderately near-surface environment with relatively high rates of evaporation and ground water action and are polygenetic in origin. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
48. Stable isotopic composition of pedogenic carbonates from the eastern margin of the Thar Desert, Rajasthan, India
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Achyuthan, Hema, Quade, Jay, Roe, Lois, and Placzek, Christa
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- *
CARBONATES in soils , *DESERTS , *ISOTOPES - Abstract
Abstract: Pedogenic carbonates in a 19m-thick dune section (16R) at Didwana, and several shorter profiles from the eastern margin of the Thar Desert, Rajasthan, were studied for their stable isotope composition. Carbon isotope results show the C4 biomass (grasses?) has dominated local vegetation for most of the 250,000years represented by the 16R section. Our results display a decrease in δ 18O and δ 13C values during the last interglacial and early glacial periods. The higher δ 13C values in our dune records correlate to episodes in the strong upwelling and decreased sedimentation rates in Indian Ocean cores, probably the result of a strong Asian Monsoon. The high δ 13C values may, therefore, denote the expansion of C4 vegetation in response to warm, wetter monsoon circulation. Conversely, low δ 18O and δ 13C values mark the expansion of C3 vegetation, probably caused by enhanced winter rains and lower temperatures. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
49. Radiocarbon dates and Holocene sea-level change along the Cuddalore and Odinur Coast, Tamil Nadu.
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Hameed, Abbas, Achyuthan, Hema, and Sekhar, B.
- Subjects
- *
CARBON isotopes , *RADIOCARBON dating , *ARCHAEOLOGICAL dating , *HOLOCENE stratigraphic geology - Abstract
Five sediment cores from the tidal flats and estuaries between Cuddalore and Odinur, Tamil Nadu at ∼50-70 cm water depth were collected to study the down core variations in organic matter, calcium carbonate content and sediment texture. Quartz, feldspar and moderately rounded to well-round, garnet-rich sand were present in all cores except core IV collected from Marakkanam. Cuddalore (cores I-III) sediments were coarse-grained and those from Odinur (core V) varied from sand to silty sand to clay. Smectite, kaolinite, illite and vermiculite occurred as clay minerals. High content of organic matter was observed in cores from Marakkanam and Odinur. Radiocarbon dates on shell, organic carbon at the base and at intervals of the cores from Marakkanam (core IV) and Odinur (core V) are 8200 ± 230, 9170 ± 290, 5540 ± 430, 2700 ± 140 yrs BP respectively. The sea-level curve presented for the Marakkanam site indicates a gradual and slow sea-level rise since 9000 to 1800 yrs BP. Data on sediment texture, mineralogy, organic matter content supplemented by radiocarbon dates indicate that the deposition of these sediments has taken place in phases since the early Holocene. Reworking of the inner shelf sediments as a result of the dropping sea-level provided the ultimate sediment source for the progradation of the present coastline. [ABSTRACT FROM AUTHOR]
- Published
- 2006
50. Petrologic analysis and geochemistry of the Late Neogene-Early Quaternary hardpan calcretes of Western Rajasthan, India
- Author
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Achyuthan, Hema
- Subjects
- *
CALCRETES , *PETROLOGY - Abstract
Calcretes formed over bedrock such as Precambrian hornblende-chlorite schist, rhyolite and carbonaceous phyllites in Western Rajasthan, India, were studied for their mineralogical composition and geochemistry. They form a distinct element of the Quaternary landscape of Western Rajasthan, India. The study area is located within the Nagaur–Churu–Jaipur tract of Western Rajasthan. The purpose of this study was to determine the processes governing the development of hardpan calcretes, and to evaluate the local and regional controls on their formation.Micromorphology included pedogenetic and groundwater features within the hardpan calcretes. Thickening of calcite laminae downward and tapering at the sideward edges around the unweathered minerals of quartz and feldspars indicated cumulative and compound pedogenesis, which probably occurred locally, and downward movement of carbonate solution and pore water. Carbonate solutions were probably derived from the upper horizons or surfaces bringing about the process of dissolution and recementation of individual laminae. Occurrence of fibrous palygorskite as coatings around the detrital grains and siderite (oolitic and pisolitic in shape) points to a subalkaline–subacidic process of pedogenesis in a semi-arid to arid climate. Stable δ13C and δ18O isotope data of the hardpan calcrete laminae vary between 0.3‰ to 1.5‰ and −5.9‰ and −1.5‰, respectively indicating their formation at or near surface (capillary fringe), probably supporting a thin column of soil. The source of most of the calcite is groundwater; however, calcite nodule formation was largely dependent on pedogenic processes associated with evaporation, evapotranspiration and /or microenvironmental changes in pH and CO2 partial pressure. Dust is also a major source for carbonate precipitation. Although it is commonly assumed that the powdery calcretes are younger in age compared to the more complex forms, the occurrence of Middle Palaeolithic tools below the hardpan calcrete at Roopangarh and Dayalpura, and above the hardpan calcretes at Mitri, Genana and Rol, indicates that the morphology of calcretes is not a reliable indicator of age. [Copyright &y& Elsevier]
- Published
- 2003
- Full Text
- View/download PDF
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