Tracing the Vedic Saraswati River in the Great Rann of Kachchh

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 5476, doi:10.1038/s41598-017-05745-8.The lost Saraswati River mentioned in the ancient Indian tradition is postulated to have flown independently of the Indus River into the Arabian Sea, perhaps along courses of now defunct rivers such as Ghaggar, Hakra and Nara. The persistence of such a river during the Harappan Bronze Age and the Iron Age Vedic period is strongly debated. We drilled in the Great Rann of Kachchh (Kutch), an infilled gulf of the Arabian Sea, which must have received input from the Saraswati, if active. Nd and Sr isotopic measurements suggest that a distinct source may have been present before 10 ka. Later in Holocene, under a drying climate, sediments from the Thar Desert probably choked the signature of an independent Saraswati-like river. Alternatively, without excluding a Saraswati-like secondary source, the Indus and the Thar were the dominant sources throughout the post-glacial history of the GRK. Indus-derived sediment accelerated the infilling of GRK after ~6 ka when the Indus delta started to grow. Until its complete infilling few centuries ago, freshwater input from the Indus, and perhaps from the Ghaggar-Hakra-Nara, probably sustained a productive marine environment as well as navigability toward old coastal Harappan and historic towns in the region.The drilling effort and subsequent study of the cores was funded by Department of Science and Technology (DST), Government of India sponsored research project to DMM (Project No. SR/S4/ES-21/Kachchh Window/P1) under the science of Shallow Subsurface Programme (SSS). N. Khonde gratefully acknowledges Indo-US Post-doctoral Fellowship sponsored by SERB-IUSSTF for research work at Woods Hole Oceanographic Institution

Calcretes in semi-arid alluvial systems: formative pathways and sinks

Late Quaternary deposits in Gujarat, western India show an abundant development of calcretes. Three major sinks of carbonate in the alluvial deposits are recognized: (1) groundwater calcretes, (2) pedogenic calcretes, and (3) calcrete conglomerates. Groundwater calcretes originate from carbonate-saturated waters travelling preferentially along stratification planes. Pedogenic calcretes form through soil-forming processes typically in extra-channel areas. Calcrete conglomerates occur as ribbons, sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes. As a result a pathway of calcretization develops that has the route: groundwater calcrete to pedogenic calcrete to calcrete-conglomerate. The formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that (1) apart from aeolian dust, river waters are also a major source of carbonate, and (2) pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre-existing groundwater calcretes. Consequently, the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

The character and genesis of calcrete in Late Quaternary alluvial deposits, Gujarat, Western India, and its bearing on the interpretation of ancient climates

Late Quaternary deposits in Mainland Gujarat contain sediments deposited in subhumid and semi-arid climates. The 30-35 m succession shows the presence of Vertisols at the base and a red-bed horizon (ferric Calcisol when pedogenic in origin) that roughly bisects the succession. A widespread development of calcretes is observed throughout the succession. The various varieties of calcrete include pedogenic calcrete, groundwater calcrete, calcrete conglomerate (transported calcrete) and rhizogenic calcrete. Pedogenic calcrete nodules associated with Vertisols and the red-soil show marked differences in morphology, dimensions and the distribution of microscopic features. These differences arise due to contrasting climate-controlled physicochemical environs under which they formed. Pedogenic calcrete nodules associated with Vertisols acquire large (5-10 cm) dimensions and are characterised by either showing the presence of a nucleus of soil-matter or showing a dense micritic groundmass cut by thick sparitic veins. In contrast, calcrete nodules that formed in the red-soil are <3 cm in size and do not exhibit dense networks of sparitic veins. Calcretes associated with Vertisols and the ferric Calcisol also exhibit differences in the morphology of rhizoliths. These differences also show up in the distribution of microfabrics of calcretes. Grain coats are present in rhizogenic and pedogenic calcretes, but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes. Clotted micrite is present in all types except groundwater calcretes. Sparitic veins, however, are observed in each type, but are relatively less developed in groundwater calcretes. A similar distribution of displacive and replacive textures is also seen, although some grains in groundwater calcretes showed signs of corrosion. The Vertisol-associated calcretes represent a subhumid (500-700 mm) climate, whereas the red-soil calcretes suggest a semi-arid (100-500 mm) climate. Calcretes from the Vertisol association show a range in δ13C composition constrained between −9%. and −5%., whereas the red-soil calcretes exhibit the whole spectrum of values from −9%. to −1%.. Based on mineralogical associations, calcretes, usually taken to reflect semi-arid episodes in the Earth's history, may be classified further. Calcretes, when associated with sepiolite/palygorskite, suggest an arid climate (mean annual rainfall=50-100 mm), when associated with smectite, haematite and the absence of hydromorphism, a semi-arid climate (mean annual rainfall=100-500 mm), and when found in smectitic Vertisols, subhumid climates (mean annual rainfall=500-700 mm)

Variations of the Somali upwelling since 18.5 ka BP and its relationship with southwest monsoon rainfall

Somali upwelling history has been reconstructed for the last 18.5&thinsp;ka&thinsp;BP based on biogenic silica fluxes estimated from a sediment core retrieved from the western Arabian Sea. Surface winds along the east African coast during the southwest monsoon (SWM) cause the Somali upwelling; thus, the intensity of this upwelling has been related to the variability of the SWM. Biogenic silica flux variation suggests periodic weakening and strengthening of the Somali upwelling. Weakened upwelling during the 18.5–15&thinsp;ka&thinsp;BP period and strengthened upwelling during the Bølling–Allerød (15–12.9&thinsp;ka&thinsp;BP) suggest the onset of the SWM. The Younger Dryas (12.9–11.7&thinsp;ka&thinsp;BP) is marked by reduced upwelling strength, with an intensification of the Somali upwelling observed at the beginning of the Holocene and a further decline at 8&thinsp;ka&thinsp;BP. The increase in the upwelling strength recorded since 8&thinsp;ka&thinsp;BP suggests SWM strengthening during the latter part of the Holocene. A comparison of upwelling variations with the SWM precipitation record demonstrates a reversal in the relationship between the strength of the Somali upwelling and SWM rainfall at the beginning of the Holocene. This observed shift has been attributed to the variation in the SWM strength due to the latitudinal shift of the intertropical convergence zone (ITCZ) associated with changes in moisture sources.</p

Holocene Paleoenvironmental Changes in the Lower Mahi Basin, Western India

From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.Evidence of paleoenvironmental changes during the Holocene from the Lower Mahi basin of Western India have been documented. The unpaired S2 surface all along the estuarine zone of the Mahi basin has been identified as an uplifted marine terrace. The terraces have preserved in their lithosections fairly distinct horizons of grayish brown clays rich in marine microfauna. The intervening silty-sand horizons are indicative of freshwater origin. The sedimentary structure and faunal assemblage indicate that these units have been deposited in a marginal marine environment. The 14C ages obtained on these marine mud horizons show that between 3600 and 1700 BP the sea level was higher than at present. The geomorphic evidence suggests that a late Holocene uplift has played a significant role in lowering the relative sea level to its present position.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Coastal geomorphology and tsunami hazard scenario along the Kachchh coast, western India

549-556Geomorphology and coastal configuration plays a vital role during tsunami events as different coastal geomorphic units respond differently to a tsunami hazard. The study of ability of different coastal landforms to respond tsunami surge is very much important for vulnerability mapping of coast. The Kachchh coast that runs for about more than 450 km has conspicuous presence of both, wave as well as tide influenced landforms. Following the classification suggested by Ramasamy et al.1, the geomorphic features for possible response of tsunami event can be classified as facilitators, conveyors, accommodators, absorbers and barriers. Depending upon its action as facilitator, conveyor or accommodator, the geomorphic units like estuary, creek, mudflats and backwater increase the possibility of tsunami run ups and inundation. The beach ridges and wide sandy beaches on the other hand absorb tsunami energy and act as barriers. In view of these six distinct segments have been identified along the Kachchh coast and are described for their possible response to tsunami event. Accordingly, the segment between Jakhau and Suthari has barrier kind of geomorphic set up with presence of backswamps that has higher preservation potential of tsunami deposits. The segment from Suthari to Kanthada has steep beaches and dune ridges that can reduce the intensity of tsunami hazard. The Kanthada - Rawal Pir segment has Rukmavati River mouth that can convey the effect of tsunami to a considerable landward area whereas, the Rawal Pir - Mundra and Mundra – Tuna segments have dominant accommodator type of geomorphic assemblage that also has a higher preservation potential for tsunami sediments. The segment between Tuna and Kandla has relatively much wider mudflats and mangrove swamps which accommodates as well as reduces tsunami energy. However, the configuration suggests much intensified tsunami surge that can devastate the large scale developments in this part. Response mechanism of the coastal geomorphic assemblages will not only help in the disaster risk reduction activities but will also be useful in better understanding of palaeo and historical tsunamis