Arun Deo Singh - Academia.edu (original) (raw)
Papers by Arun Deo Singh
IODP Expedition 339 (17 November 2011-17 January 2012) recently drilled 5 sites in the Gulf of Ca... more IODP Expedition 339 (17 November 2011-17 January 2012) recently drilled 5 sites in the Gulf of Cadiz and 2 off the west Iberian margin, and recovered 5.5 km of core with an average recovery of 86.4%. The Gulf of Cadiz was targeted for drilling as a key location for the investigation of Mediterranean Outflow Water (MOW) through the Gibraltar Gateway and its influence on global circulation and climate. It is also a prime area for understanding the effects of tectonic activity on evolution of the Gibraltar Gateway and on margin sedimentation.
Journal of Earth System Science, 2018
The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ... more The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ) at mid-water depths. The Indian margin where the OMZ impinges provides sediment records ideal to study past changes in the OMZ intensity and its vertical extent in response to the changes of monsoondriven primary productivity and intermediate water ventilation. Benthic foraminifera, depending upon their adaptation capabilities to variation in sea floor environment and microhabitat preferences, develop various functional morphologies that can be potentially used in paleoenvironmental reconstruction. In this study, we analysed benthic foraminiferal morphogroups in assemblage records of the last 30 ka in a sediment core collected from the lower OMZ of the Indian margin (off Goa). In total, nine morphogroups within two broadly classified epifaunal and infaunal microhabitat categories are identified. The abundance of morphogroups varies significantly during the late Glacial, Deglacial and Holocene. It appears that monsoon wind driven organic matter flux, and water column ventilation governing the OMZ intensity and sea-bottom oxygen condition, have profound influence on structuring the benthic foraminiferal morphogroups. We found a few morphogroups showing major changes in their abundances during the periods corresponding to the northern hemisphere climatic events. Benthic foraminifera with planoconvex tests are abundant during the cold Heinrich events, when the sea bottom was oxygenated due to a better ventilated, weak OMZ; whereas, those having tapered/cylindrical tests dominate during the last glacial maximum and the Holocene between 5 and 8 ka BP, when the OMZ was intensified and poorly ventilated, leading to oxygen-depleted benthic environment. Characteristically, increased abundance of taxa with milioline tests during the Heinrich 1 further suggests enhanced ventilation attributed probably to the influence of oxygen-rich Antarctic Intermediate Water (AAIW).
Proceedings of the International Ocean Discovery Program, 2016
Scientific Drilling, 2013
Nick Shackleton's research on piston cores from the Iberian margin highlighted the importance of ... more Nick Shackleton's research on piston cores from the Iberian margin highlighted the importance of this region for providing high-fidelity records of millennial-scale climate variability, and for correlating climate events from the marine environment to polar ice cores and European terrestrial sequences. During the Integrated Ocean Drilling Program (IODP) Expedition 339, we sought to extend the Iberian margin sediment record by drilling with the D/V JOIDES Resolution. Five holes were cored at Site U1385 using the advanced piston corer (APC) system to a maximum depth of ∼ 155.9 m below sea floor (m b.s.f.). Immediately after the expedition, cores from all holes were analyzed by core scanning X-ray fluorescence (XRF) at 1 cm spatial resolution. Ca/Ti data were used to accurately correlate from hole-to-hole and construct a composite spliced section, containing no gaps or disturbed intervals to 166.5 m composite depth (mcd). A low-resolution (20 cm sample spacing) oxygen isotope record confirms that Site U1385 contains a continuous record of hemipelagic sedimentation from the Holocene to 1.43 Ma (Marine Isotope Stage 46). The sediment profile at Site U1385 extends across the middle Pleistocene transition (MPT) with sedimentation rates averaging ∼ 10 cm kyr −1. Strong precession cycles in colour and elemental XRF signals provide a powerful tool for developing an orbitally tuned reference timescale. Site U1385 is likely to become an important type section for marine-ice-terrestrial core correlations and the study of orbital-and millennial-scale climate variability.
Scientific Drilling, 2013
IODP Expedition 339 drilled five sites in the Gulf of Cadiz and two off the west Iberian margin (... more IODP Expedition 339 drilled five sites in the Gulf of Cadiz and two off the west Iberian margin (November 2011 to January 2012), and recovered 5.5 km of sediment cores with an average recovery of 86.4 %. The Gulf of Cadiz was targeted for drilling as a key location for the investigation of Mediterranean outflow water (MOW) through the Gibraltar Gateway and its influence on global circulation and climate. It is also a prime area for understanding the effects of tectonic activity on evolution of the Gibraltar Gateway and on margin sedimentation. We penetrated into the Miocene at two different sites and established a strong signal of MOW in the sedimentary record of the Gulf of Cadiz, following the opening of the Gibraltar Gateway. Preliminary results show the initiation of contourite deposition at 4.2-4.5 Ma, although subsequent research will establish whether this dates the onset of MOW. The Pliocene succession, penetrated at four sites, shows low bottom current activity linked with a weak MOW. Significant widespread unconformities, present in all sites but with hiatuses of variable duration, are interpreted as a signal of intensified MOW, coupled with flow confinement. The Quaternary succession shows a much more pronounced phase of contourite drift development, with two periods of MOW intensification separated by a widespread unconformity. Following this, the final phase of drift evolution established the contourite depositional system (CDS) architecture we see today. There is a significant climate control on this evolution of MOW and bottom-current activity. However, from the closure of the Atlantic-Mediterranean gateways in Spain and Morocco just over 6 Ma and the opening of the Gibraltar Gateway at 5.3 Ma, there has been an even stronger tectonic control on margin development, downslope sediment transport and contourite drift evolution. The Gulf of Cadiz is the world's premier contourite laboratory and thus presents an ideal testing ground for the contourite paradigm. Further study of these contourites will allow us to resolve outstanding issues related to depositional processes, drift budgets, and recognition of fossil contourites in the ancient record on shore. The expedition also verified an enormous quantity and extensive distribution of contourite sands that are clean and well sorted. These represent a relatively untapped and important exploration target for potential oil and gas reservoirs.
Proceedings of the International Ocean Discovery Program, 2016
Introduction, background, and operations 6 Lithostratigraphy 11 Biostratigraphy 24 Stratigraphic ... more Introduction, background, and operations 6 Lithostratigraphy 11 Biostratigraphy 24 Stratigraphic correlation 26 Igneous petrology 31 Geochemistry 33 Microbiology 34 Paleomagnetism and rock magnetism 40 Physical properties 46 Downhole measurements 51 References Orientation-alignable retrieving cup Shear pins Inner seals Outer seals Quick release Rod Vents Honed ID drill collar Clear plastic liner Piston head and seal Shoe 3.80 inch bit (ID) 9.5 m stroke Seafloor Core Before stroke to take core After stroke to take core Advanced piston corer Figure F2. Schematic of the XCB system used during Expedition 355. Coring soft sediment Coring hard sediment Outer barrel Latch Coil spring Landing shoulder Spring shaft Quick release Circulating fluid Venturi vent system Liner bearings Nonrotating core liner 7 inch stroke/retraction Cutting shoe Circulation jets Core catchers Max. extension (variable) 6-14 inch Roller cone bit Bit seal Flow to cutting shoe Variable port-size inlet sub Cutting shoe retracted, hard sediment Cutting shoe extended, soft sediment Cutting discharge Cutting discharge Extended core barrel Pulling neck Latch finger Spacer adapter Check valve Core liner Landing support Float valve Core catchers Adjustable latch sleeve Swivel Quick release Nonrotating inner barrel Core size 2.312 inch (6.20 cm) diameter x 31.2 ft (9.5 m) long Bit seals
Palaeogeography, Palaeoclimatology, Palaeoecology, 2017
A sediment core from NE Arabian Sea was studied to reveal the variations in shelf environment of ... more A sediment core from NE Arabian Sea was studied to reveal the variations in shelf environment of western continental margin of India. A multi-proxy analysis based on planktonic foraminifera abundance (PFA), benthic foraminifera abundance (BFA), planktonic-benthic foraminiferal ratio (P/B), CaCO 3 percentage (wt%), Oxygen (δ 18 O G.ruber) and Carbon (δ 18 O G.ruber) isotopes of foraminifera as well as sediment X-ray studies were carried out on 3.4 m long core SK-240/485 recovered from offshore Saurashtra, NE Arabian Sea. The study aims to understand the monsoon variability in the NE Arabian Sea offshore Saurashtra since the late Pleistocene-Holocene transition and how monsoon climate coupled with sea-level change influenced paleo-productivity pattern. Six AMS radiocarbon dates place the core in the time interval 12-1 Ka. Our study reveals that there have been three periods of major changes in the monsoonal climate, productivity and sea level; viz. 12-8 Ka (Younger Dryas and early Holocene); 8-4 Ka (middle Holocene) and 4-1 Ka (late Holocene). The studied time period was also marked by weakened south west monsoon (SWM) during the cold events such as Younger Dryas (YD), Abrupt Event (AE) centring around 9.8 Ka as well as 8.2 and 4 Ka cold events. The Younger Dryas and early Holocene shows the low sea level stand and less Indus river discharge. Thereafter during middle and late Holocene the monsoon strengthened which resulted in raised sea level and increased Indus river discharge. The proxy records broadly suggest relatively low foraminiferal productivity at the core location during the Younger Dryas and early Holocene. We record a moderate foraminiferal productivity during the middle Holocene between 8 and 4 Ka, which suggest the mesotrophic condition. The foraminiferal productivity however was relatively high since 4 Ka suggesting the eutrophic conditions at the core site.
Geological Magazine, 2019
International Ocean Discovery Program Expedition 355 drilled Sites U1456 and U1457 in Laxmi Basin... more International Ocean Discovery Program Expedition 355 drilled Sites U1456 and U1457 in Laxmi Basin (eastern Arabian Sea) to document the impact of the South Asian monsoon on weathering and erosion of the Himalaya. We revised the chronostratigraphic framework for these sites using a combination of biostratigraphy, magnetostratigraphy and strontium isotope stratigraphy. The sedimentary section at the two sites is similar and we divided it into six units bounded by unconformities or emplaced as a mass-transport deposit (MTD). Unit 1 underlies the MTD, and is of early–middle Miocene age at Site U1456 and early Paleocene age at Site U1457. An unconformity (U1) created by emplacement of the MTD (unit 2) during the late Miocene Epoch (at c. 9.83–9.69 Ma) separates units 1 and 2 and is identified by a marked change in lithology. Unit 3 consists of hemipelagic sediment with thin interbeds of graded sandstone of late Miocene age, separated from unit 4 by a second unconformity (U2) of 0.5–0.9 M...
Geological Magazine, 2019
The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Ar... more The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Arabian Sea and winter convective mixing. Therefore, sediments collected from the eastern Arabian Sea can help to understand the long-term seasonal hydrographic changes. We used the planktonic foraminifera census and stable isotopic ratio (δ18O) from sediments drilled during the International Ocean Discovery Program Expedition 355 to reconstruct surface hydrographic changes in the eastern Arabian Sea during the last 350 kyr. The increased abundance of Globigerina bulloides suggests enhanced advection of upwelled water during the latter half of MIS7 and the beginning of MIS6, as a result of a strengthened summer monsoon. A large drop in upwelling and/or advection of upwelled water from the western Arabian Sea is inferred during the subsequent interval of MIS6, based on the rare presence of G. bulloides. The comparable relative abundance of Neogloboquadrina dutertrei, G. bulloides and Globig...
Geological Magazine, Apr 10, 2019
In order to improve the chronostratigraphic framework that is key to examining the 66 evolution o... more In order to improve the chronostratigraphic framework that is key to examining the 66 evolution of the Himalayas and climate from the late Miocene to Holocene, we undertook new 67 biostratigraphic, paleomagnetic and geochemical analyses. Here we present updated 68 chronostratigraphic frameworks for Site U1456 using new magnetostratigraphic data and Site
GSA Bulletin, 2019
A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in v... more A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in volume all but one other known complex on passive margins worldwide. The complex, named the Nataraja Slide, was drilled by International Ocean Discovery Program (IODP) Expedition 355 in two locations where it is ∼300 m (Site U1456) and ∼200 m thick (Site U1457). The top of this mass-transport complex is defined by the presence of both reworked microfossil assemblages and deformation structures, such as folding and faulting. The deposit consists of two main phases of mass wasting, each consisting of smaller pulses, with generally fining-upward cycles, all emplaced just prior to 10.8 Ma based on biostratigraphy. The base of the deposit at each site is composed largely of matrix-supported carbonate breccia that is interpreted as the product of debris-flows. In the first phase, these breccias alternate with well-sorted calcarenites deposited from a high-energy current, coherent limestone bloc...
Proceedings of the International Ocean Discovery Program, 2016
Background and objectives 4 Operations 9 Lithostratigraphy 19 Biostratigraphy 23 Stratigraphic co... more Background and objectives 4 Operations 9 Lithostratigraphy 19 Biostratigraphy 23 Stratigraphic correlation 26 Igneous petrology 30 Geochemistry 35 Microbiology 37 Paleomagnetism and rock magnetism 41 Physical properties 45 Downhole measurements 46 References 222 223
Proceedings of the International Ocean Discovery Program, 2016
Introduction 3 Background 7 Scientific objectives 9 Principal results 20 Expedition synthesis 25 ... more Introduction 3 Background 7 Scientific objectives 9 Principal results 20 Expedition synthesis 25 Preliminary scientific assessment 27 References
Global and Planetary Change, 2015
We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using... more We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ 18 O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic δ 18 O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene ('41-kyr world') when boundary conditions differed significantly from those of the late Pleistocene ('100-kyr world'). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ 18 O surpassed~3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation Global and Planetary Change 133 (2015) 49-64
Geological Magazine
Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite no... more Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite notable studies on the continental and oceanic sedimentary record. The present study investigates the environmental magnetic and geochemical records preserved in the deep marine sediments of the northeastern (NE) Arabian Sea to elucidate the erosion history of the western Himalayas and its link with the prevailing hydroclimatic conditions since the late Miocene. For this, the sediment core retrieved during International Ocean Discovery Program (IODP) Expedition 355 at Site U1457 in the NE Arabian Sea has been explored. The results reveal that the hydroclimatic conditions were predominantly arid during the late Miocene, except for humid intervals from 6.1 Ma to 5.6 Ma. Humid climate conditions in the Indus River Basin returned during the mid-Pliocene and continued to the Pleistocene with an intense chemical weathering regime from 1.9 Ma to 1.2 Ma. The dominant sediment source to the NE Arab...
Journal of Palaeosciences
The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. M... more The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. Mid–depth oxygen depletion profoundly influences the chemistry of thermocline waters (HCO3ˉ, CO32ˉ and pH), which in turn significantly influences the preservation state of carbonates. The carbonate preservation is primarily controlled by the degree of saturation level of seawater with respect to the calcite and aragonite. The seawater in OMZ is undersaturated with respect to the aragonite (a metastable polymorph of CaCO3). Pteropod test being aragonitic in composition is therefore highly susceptible to the dissolution and dissolves completely below the aragonite compensation depth (ACD). Because of the current condition of intense OMZ due to high primary productivity, enhanced respiration of sinking organic carbon and reduced thermocline circulation; the ACD is shallow, lying in the middle of the OMZ. Hence, preservation record of pteropods in sea–floor sediment archives past changes in ...
Productivity in the Arabian Sea is one of the highest in the world. It is controlled by seasonall... more Productivity in the Arabian Sea is one of the highest in the world. It is controlled by seasonally reversing monsoonal wind-driven upwelling of nutrient-rich deeper waters which fuel phytoplankton growth. The detailed history of upwelling-induced productivity in the eastern Arabian Sea is unknown. Here we present paleoproductivity records from a composite sediment core at the millennial scale during the last 80 kyr B.P. These records are based on relative abundance counts of planktonic foraminifera and organic carbon contents, which are shown to mainly vary in concert. The eastern Arabian Sea upwelling-induced productivity was higher in the glacial period than in the Holocene, but it fell repeatedly on millennial timescales. These productivity declines occurred during cold events in the North Atlantic region, with the most pronounced changes prevailing during the Heinrich events. Hence, seasonal monsoon winds that drive upwelling-induced productivity in the east were weak when the N...
IODP Expedition 339 (17 November 2011-17 January 2012) recently drilled 5 sites in the Gulf of Ca... more IODP Expedition 339 (17 November 2011-17 January 2012) recently drilled 5 sites in the Gulf of Cadiz and 2 off the west Iberian margin, and recovered 5.5 km of core with an average recovery of 86.4%. The Gulf of Cadiz was targeted for drilling as a key location for the investigation of Mediterranean Outflow Water (MOW) through the Gibraltar Gateway and its influence on global circulation and climate. It is also a prime area for understanding the effects of tectonic activity on evolution of the Gibraltar Gateway and on margin sedimentation.
Journal of Earth System Science, 2018
The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ... more The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ) at mid-water depths. The Indian margin where the OMZ impinges provides sediment records ideal to study past changes in the OMZ intensity and its vertical extent in response to the changes of monsoondriven primary productivity and intermediate water ventilation. Benthic foraminifera, depending upon their adaptation capabilities to variation in sea floor environment and microhabitat preferences, develop various functional morphologies that can be potentially used in paleoenvironmental reconstruction. In this study, we analysed benthic foraminiferal morphogroups in assemblage records of the last 30 ka in a sediment core collected from the lower OMZ of the Indian margin (off Goa). In total, nine morphogroups within two broadly classified epifaunal and infaunal microhabitat categories are identified. The abundance of morphogroups varies significantly during the late Glacial, Deglacial and Holocene. It appears that monsoon wind driven organic matter flux, and water column ventilation governing the OMZ intensity and sea-bottom oxygen condition, have profound influence on structuring the benthic foraminiferal morphogroups. We found a few morphogroups showing major changes in their abundances during the periods corresponding to the northern hemisphere climatic events. Benthic foraminifera with planoconvex tests are abundant during the cold Heinrich events, when the sea bottom was oxygenated due to a better ventilated, weak OMZ; whereas, those having tapered/cylindrical tests dominate during the last glacial maximum and the Holocene between 5 and 8 ka BP, when the OMZ was intensified and poorly ventilated, leading to oxygen-depleted benthic environment. Characteristically, increased abundance of taxa with milioline tests during the Heinrich 1 further suggests enhanced ventilation attributed probably to the influence of oxygen-rich Antarctic Intermediate Water (AAIW).
Proceedings of the International Ocean Discovery Program, 2016
Scientific Drilling, 2013
Nick Shackleton's research on piston cores from the Iberian margin highlighted the importance of ... more Nick Shackleton's research on piston cores from the Iberian margin highlighted the importance of this region for providing high-fidelity records of millennial-scale climate variability, and for correlating climate events from the marine environment to polar ice cores and European terrestrial sequences. During the Integrated Ocean Drilling Program (IODP) Expedition 339, we sought to extend the Iberian margin sediment record by drilling with the D/V JOIDES Resolution. Five holes were cored at Site U1385 using the advanced piston corer (APC) system to a maximum depth of ∼ 155.9 m below sea floor (m b.s.f.). Immediately after the expedition, cores from all holes were analyzed by core scanning X-ray fluorescence (XRF) at 1 cm spatial resolution. Ca/Ti data were used to accurately correlate from hole-to-hole and construct a composite spliced section, containing no gaps or disturbed intervals to 166.5 m composite depth (mcd). A low-resolution (20 cm sample spacing) oxygen isotope record confirms that Site U1385 contains a continuous record of hemipelagic sedimentation from the Holocene to 1.43 Ma (Marine Isotope Stage 46). The sediment profile at Site U1385 extends across the middle Pleistocene transition (MPT) with sedimentation rates averaging ∼ 10 cm kyr −1. Strong precession cycles in colour and elemental XRF signals provide a powerful tool for developing an orbitally tuned reference timescale. Site U1385 is likely to become an important type section for marine-ice-terrestrial core correlations and the study of orbital-and millennial-scale climate variability.
Scientific Drilling, 2013
IODP Expedition 339 drilled five sites in the Gulf of Cadiz and two off the west Iberian margin (... more IODP Expedition 339 drilled five sites in the Gulf of Cadiz and two off the west Iberian margin (November 2011 to January 2012), and recovered 5.5 km of sediment cores with an average recovery of 86.4 %. The Gulf of Cadiz was targeted for drilling as a key location for the investigation of Mediterranean outflow water (MOW) through the Gibraltar Gateway and its influence on global circulation and climate. It is also a prime area for understanding the effects of tectonic activity on evolution of the Gibraltar Gateway and on margin sedimentation. We penetrated into the Miocene at two different sites and established a strong signal of MOW in the sedimentary record of the Gulf of Cadiz, following the opening of the Gibraltar Gateway. Preliminary results show the initiation of contourite deposition at 4.2-4.5 Ma, although subsequent research will establish whether this dates the onset of MOW. The Pliocene succession, penetrated at four sites, shows low bottom current activity linked with a weak MOW. Significant widespread unconformities, present in all sites but with hiatuses of variable duration, are interpreted as a signal of intensified MOW, coupled with flow confinement. The Quaternary succession shows a much more pronounced phase of contourite drift development, with two periods of MOW intensification separated by a widespread unconformity. Following this, the final phase of drift evolution established the contourite depositional system (CDS) architecture we see today. There is a significant climate control on this evolution of MOW and bottom-current activity. However, from the closure of the Atlantic-Mediterranean gateways in Spain and Morocco just over 6 Ma and the opening of the Gibraltar Gateway at 5.3 Ma, there has been an even stronger tectonic control on margin development, downslope sediment transport and contourite drift evolution. The Gulf of Cadiz is the world's premier contourite laboratory and thus presents an ideal testing ground for the contourite paradigm. Further study of these contourites will allow us to resolve outstanding issues related to depositional processes, drift budgets, and recognition of fossil contourites in the ancient record on shore. The expedition also verified an enormous quantity and extensive distribution of contourite sands that are clean and well sorted. These represent a relatively untapped and important exploration target for potential oil and gas reservoirs.
Proceedings of the International Ocean Discovery Program, 2016
Introduction, background, and operations 6 Lithostratigraphy 11 Biostratigraphy 24 Stratigraphic ... more Introduction, background, and operations 6 Lithostratigraphy 11 Biostratigraphy 24 Stratigraphic correlation 26 Igneous petrology 31 Geochemistry 33 Microbiology 34 Paleomagnetism and rock magnetism 40 Physical properties 46 Downhole measurements 51 References Orientation-alignable retrieving cup Shear pins Inner seals Outer seals Quick release Rod Vents Honed ID drill collar Clear plastic liner Piston head and seal Shoe 3.80 inch bit (ID) 9.5 m stroke Seafloor Core Before stroke to take core After stroke to take core Advanced piston corer Figure F2. Schematic of the XCB system used during Expedition 355. Coring soft sediment Coring hard sediment Outer barrel Latch Coil spring Landing shoulder Spring shaft Quick release Circulating fluid Venturi vent system Liner bearings Nonrotating core liner 7 inch stroke/retraction Cutting shoe Circulation jets Core catchers Max. extension (variable) 6-14 inch Roller cone bit Bit seal Flow to cutting shoe Variable port-size inlet sub Cutting shoe retracted, hard sediment Cutting shoe extended, soft sediment Cutting discharge Cutting discharge Extended core barrel Pulling neck Latch finger Spacer adapter Check valve Core liner Landing support Float valve Core catchers Adjustable latch sleeve Swivel Quick release Nonrotating inner barrel Core size 2.312 inch (6.20 cm) diameter x 31.2 ft (9.5 m) long Bit seals
Palaeogeography, Palaeoclimatology, Palaeoecology, 2017
A sediment core from NE Arabian Sea was studied to reveal the variations in shelf environment of ... more A sediment core from NE Arabian Sea was studied to reveal the variations in shelf environment of western continental margin of India. A multi-proxy analysis based on planktonic foraminifera abundance (PFA), benthic foraminifera abundance (BFA), planktonic-benthic foraminiferal ratio (P/B), CaCO 3 percentage (wt%), Oxygen (δ 18 O G.ruber) and Carbon (δ 18 O G.ruber) isotopes of foraminifera as well as sediment X-ray studies were carried out on 3.4 m long core SK-240/485 recovered from offshore Saurashtra, NE Arabian Sea. The study aims to understand the monsoon variability in the NE Arabian Sea offshore Saurashtra since the late Pleistocene-Holocene transition and how monsoon climate coupled with sea-level change influenced paleo-productivity pattern. Six AMS radiocarbon dates place the core in the time interval 12-1 Ka. Our study reveals that there have been three periods of major changes in the monsoonal climate, productivity and sea level; viz. 12-8 Ka (Younger Dryas and early Holocene); 8-4 Ka (middle Holocene) and 4-1 Ka (late Holocene). The studied time period was also marked by weakened south west monsoon (SWM) during the cold events such as Younger Dryas (YD), Abrupt Event (AE) centring around 9.8 Ka as well as 8.2 and 4 Ka cold events. The Younger Dryas and early Holocene shows the low sea level stand and less Indus river discharge. Thereafter during middle and late Holocene the monsoon strengthened which resulted in raised sea level and increased Indus river discharge. The proxy records broadly suggest relatively low foraminiferal productivity at the core location during the Younger Dryas and early Holocene. We record a moderate foraminiferal productivity during the middle Holocene between 8 and 4 Ka, which suggest the mesotrophic condition. The foraminiferal productivity however was relatively high since 4 Ka suggesting the eutrophic conditions at the core site.
Geological Magazine, 2019
International Ocean Discovery Program Expedition 355 drilled Sites U1456 and U1457 in Laxmi Basin... more International Ocean Discovery Program Expedition 355 drilled Sites U1456 and U1457 in Laxmi Basin (eastern Arabian Sea) to document the impact of the South Asian monsoon on weathering and erosion of the Himalaya. We revised the chronostratigraphic framework for these sites using a combination of biostratigraphy, magnetostratigraphy and strontium isotope stratigraphy. The sedimentary section at the two sites is similar and we divided it into six units bounded by unconformities or emplaced as a mass-transport deposit (MTD). Unit 1 underlies the MTD, and is of early–middle Miocene age at Site U1456 and early Paleocene age at Site U1457. An unconformity (U1) created by emplacement of the MTD (unit 2) during the late Miocene Epoch (at c. 9.83–9.69 Ma) separates units 1 and 2 and is identified by a marked change in lithology. Unit 3 consists of hemipelagic sediment with thin interbeds of graded sandstone of late Miocene age, separated from unit 4 by a second unconformity (U2) of 0.5–0.9 M...
Geological Magazine, 2019
The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Ar... more The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Arabian Sea and winter convective mixing. Therefore, sediments collected from the eastern Arabian Sea can help to understand the long-term seasonal hydrographic changes. We used the planktonic foraminifera census and stable isotopic ratio (δ18O) from sediments drilled during the International Ocean Discovery Program Expedition 355 to reconstruct surface hydrographic changes in the eastern Arabian Sea during the last 350 kyr. The increased abundance of Globigerina bulloides suggests enhanced advection of upwelled water during the latter half of MIS7 and the beginning of MIS6, as a result of a strengthened summer monsoon. A large drop in upwelling and/or advection of upwelled water from the western Arabian Sea is inferred during the subsequent interval of MIS6, based on the rare presence of G. bulloides. The comparable relative abundance of Neogloboquadrina dutertrei, G. bulloides and Globig...
Geological Magazine, Apr 10, 2019
In order to improve the chronostratigraphic framework that is key to examining the 66 evolution o... more In order to improve the chronostratigraphic framework that is key to examining the 66 evolution of the Himalayas and climate from the late Miocene to Holocene, we undertook new 67 biostratigraphic, paleomagnetic and geochemical analyses. Here we present updated 68 chronostratigraphic frameworks for Site U1456 using new magnetostratigraphic data and Site
GSA Bulletin, 2019
A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in v... more A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in volume all but one other known complex on passive margins worldwide. The complex, named the Nataraja Slide, was drilled by International Ocean Discovery Program (IODP) Expedition 355 in two locations where it is ∼300 m (Site U1456) and ∼200 m thick (Site U1457). The top of this mass-transport complex is defined by the presence of both reworked microfossil assemblages and deformation structures, such as folding and faulting. The deposit consists of two main phases of mass wasting, each consisting of smaller pulses, with generally fining-upward cycles, all emplaced just prior to 10.8 Ma based on biostratigraphy. The base of the deposit at each site is composed largely of matrix-supported carbonate breccia that is interpreted as the product of debris-flows. In the first phase, these breccias alternate with well-sorted calcarenites deposited from a high-energy current, coherent limestone bloc...
Proceedings of the International Ocean Discovery Program, 2016
Background and objectives 4 Operations 9 Lithostratigraphy 19 Biostratigraphy 23 Stratigraphic co... more Background and objectives 4 Operations 9 Lithostratigraphy 19 Biostratigraphy 23 Stratigraphic correlation 26 Igneous petrology 30 Geochemistry 35 Microbiology 37 Paleomagnetism and rock magnetism 41 Physical properties 45 Downhole measurements 46 References 222 223
Proceedings of the International Ocean Discovery Program, 2016
Introduction 3 Background 7 Scientific objectives 9 Principal results 20 Expedition synthesis 25 ... more Introduction 3 Background 7 Scientific objectives 9 Principal results 20 Expedition synthesis 25 Preliminary scientific assessment 27 References
Global and Planetary Change, 2015
We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using... more We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ 18 O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic δ 18 O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene ('41-kyr world') when boundary conditions differed significantly from those of the late Pleistocene ('100-kyr world'). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ 18 O surpassed~3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation Global and Planetary Change 133 (2015) 49-64
Geological Magazine
Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite no... more Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite notable studies on the continental and oceanic sedimentary record. The present study investigates the environmental magnetic and geochemical records preserved in the deep marine sediments of the northeastern (NE) Arabian Sea to elucidate the erosion history of the western Himalayas and its link with the prevailing hydroclimatic conditions since the late Miocene. For this, the sediment core retrieved during International Ocean Discovery Program (IODP) Expedition 355 at Site U1457 in the NE Arabian Sea has been explored. The results reveal that the hydroclimatic conditions were predominantly arid during the late Miocene, except for humid intervals from 6.1 Ma to 5.6 Ma. Humid climate conditions in the Indus River Basin returned during the mid-Pliocene and continued to the Pleistocene with an intense chemical weathering regime from 1.9 Ma to 1.2 Ma. The dominant sediment source to the NE Arab...
Journal of Palaeosciences
The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. M... more The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. Mid–depth oxygen depletion profoundly influences the chemistry of thermocline waters (HCO3ˉ, CO32ˉ and pH), which in turn significantly influences the preservation state of carbonates. The carbonate preservation is primarily controlled by the degree of saturation level of seawater with respect to the calcite and aragonite. The seawater in OMZ is undersaturated with respect to the aragonite (a metastable polymorph of CaCO3). Pteropod test being aragonitic in composition is therefore highly susceptible to the dissolution and dissolves completely below the aragonite compensation depth (ACD). Because of the current condition of intense OMZ due to high primary productivity, enhanced respiration of sinking organic carbon and reduced thermocline circulation; the ACD is shallow, lying in the middle of the OMZ. Hence, preservation record of pteropods in sea–floor sediment archives past changes in ...
Productivity in the Arabian Sea is one of the highest in the world. It is controlled by seasonall... more Productivity in the Arabian Sea is one of the highest in the world. It is controlled by seasonally reversing monsoonal wind-driven upwelling of nutrient-rich deeper waters which fuel phytoplankton growth. The detailed history of upwelling-induced productivity in the eastern Arabian Sea is unknown. Here we present paleoproductivity records from a composite sediment core at the millennial scale during the last 80 kyr B.P. These records are based on relative abundance counts of planktonic foraminifera and organic carbon contents, which are shown to mainly vary in concert. The eastern Arabian Sea upwelling-induced productivity was higher in the glacial period than in the Holocene, but it fell repeatedly on millennial timescales. These productivity declines occurred during cold events in the North Atlantic region, with the most pronounced changes prevailing during the Heinrich events. Hence, seasonal monsoon winds that drive upwelling-induced productivity in the east were weak when the N...