Clay minerals are significant indicators that can be used to identify sources and transport patterns of both fluvial and marine sediments. The Ganges, Brahmaputra, and Surma-Meghna (SM) rivers are ...the most important rivers of the Bengal Basin (BB), loading a large amount of sediments from the Himalayas into the Bay of Bengal. Clay minerals of 132 surface sediment samples from the Ganges-Brahmaputra-Meghna (GBM) river system have been analyzed with X-ray diffraction (XRD) to show the variation of clay mineral assemblages in the sediments from upstream to downstream for the major rivers of the BB and to verify the validity of clay minerals as an important index for sediment provenance in the Bay of Bengal after these sediments are discharged into the neighboring seas. The results show that the clay mineral assemblage in the GBM river system consists dominantly of illite (average 66%), with smaller amounts of smectite, kaolinite, and chlorite (8%, 8%, and 17%, respectively). Smectite is diagnostic in the Ganges River sediments, with a higher content (23%) than that in the Brahmaputra (2%) and the SM River (1%); however, chlorite (21%) is high in the SM River sediments and the Brahmaputra River sediments have a high illite percentage (77%). Downstream, the smectite percentages in the Ganges River increase significantly, but the kaolinite percentages in sediments of the SM River increase slightly. Due to the continuous mixture of first the Brahmaputra River and then the SM River discharge, the clay mineral assemblages of this river system's sediments change greatly, e.g., smectite percentages decrease from 23% in the Ganges River to 8% in the GBM River via the stretch with 12% in the Ganges-Brahmaputra confluence river.
•Clay mineralogy of the Bengal Basin river system was analyzed.•Clay mineral assemblages of this river system's sediments change greatly.•The Ganges River sediments are rich in smectite formed in the Indo-Gangetic flood plain.•The Brahmaputra and Surma-Meghna rivers show similar clay mineral compositions.•The Himalayas represent the main clay mineral source area.
Sediment accumulation and budget in the continental margins provides abundant information of source-sink processes from the land to the sea, including weathering, human activities and sedimentary ...environment. Here we show the distribution of mud areas, modern sedimentation rates and sediment budget in the Bohai Sea, Yellow Sea and East China Sea. Using grain size data of >18,000 surface sediment samples and 210Pb data from 413 sites, we identify five areas with sediments mainly composed of fine-grained fractions (mean grain size >6 φ) and find a relatively high sedimentation rates of >1.5mm/yr in the mud areas. Near the Yellow and Yangtze River deltas sedimentation reaches >95.0mm/yr. Approximately 1185.4×106tons of fine-grained sediment accumulate annually in the mud areas of the east China seas. Atmospheric deposition contributes <2% (18.37×106 tons/yr), while the riverine sediment inputs account for >75% (917×106tons/yr). The remainder comes from all other sources including coastal erosion and resuspension of bottom sediments. In addition, ~45% of the fluvial sediment supply deposits on the subaerial delta, ~40–50% is trapped on the subaqueous delta and shelf, and the remainder <5% escapes the shelf edge. The results will be a strong foundation for understanding of the transport, deposit and preservation of sediment and other relevant material (e.g. carbon and nutrient etc.) of terrestrial materials in the sea.
•Distribution of modern sedimentation rates in the Bohai Sea, Yellow Sea and East China Sea were illustrated.•Five mud deposit areas with sediments mainly composed of fine-grained fractions were identified.•The sediment budget and mass balance within a source-sink perspective was constructed.
Intraplate volcanism initiated shortly after the cessation of Cenozoic seafloor spreading in the South China Sea (SCS) region, but the full extent of its influence on the Indochina block has not been ...well constrained. Here we present major and trace element data and Sr-Nd-Pb-Hf isotope ratios of late Cenozoic basaltic lavas from the Khorat plateau and some volcanic centers in the Paleozoic Sukhothai arc terrane in Thailand. These volcanic rocks are mainly trachybasalts and basaltic trachyandesites. Trace element patterns and Sr-Nd-Pb-Hf isotopic compositions show that these alkaline volcanic lavas exhibit oceanic island basalt (OIB)-like characteristics with enrichments in both large-ion lithophile elements (LILE) and high field strength elements (HFSEs). Their mantle source is a mixture between a depleted Indian MORB-type mantle and an enriched mantle type 2 (EMII). We suggest that the post-spreading intraplate volcanism in the SCS region was induced by a Hainan mantle plume which spread westwards to the Paleozoic Sukhothai arc terrane.
Studying marine sedimentary archives from the Indian Ocean have provided great opportunities to assess the forcing/response relationship between the Indian monsoons, millennial-scale climate ...variability as revealed in Greenland ice cores, and possible roles of the Atlantic meridional overturning circulation (AMOC) changes that are most likely responsible for driving both. Here we present new evidence of sea surface temperature (SST) estimates and δ18O of seawater (δ18Osw, presumably salinity-driven) from the paired data of Mg/Ca and δ18O measured from planktonic foraminifer Globigerinoides ruber (white) in core BoB-24 collected from the central Bay of Bengal (BoB), tropical Indian Ocean. Eleven accelerator mass spectrometry (AMS) radiocarbon dates on planktonic foraminifera Neogloboquedrina dutertrei from the core provide a reliable age model. Our results indicate a gradual surface warming with several short-lived fluctuations since ~42 kyr ago, and a ~3 °C cooling during the Last Glacial Maximum (LGM) and a ~3 °C warming from the last glacial to the Holocene. Our δ18Osw revealed an increased salinity during the Marine Isotope Stage (MIS) 2, which is likely attributable to a weakening of Indian Summer Monsoon (ISM) precipitation and associated river discharge in the BoB. Our record also indicates clearly a phase of strengthening ISM during the mid-MIS 3 (37.5–32 ka) as evidenced by low foraminiferal δ18Osw values of ~0.2‰. Lower than present δ18Osw values during the Bølling/Allerød (B/A) event (14.5–12.6 ka) and the early Holocene (10–5 ka) in core BoB-24 indicate lower salinity that in turn suggest enhanced ISM precipitation and increased freshwater output from the Ganges-Meghna-Brahmaputra-Irrawaddy (GMBI) rivers together with peninsular rivers and Irrawaddy-Salween rivers from Myanmar. This study brings data evidence that implies weakened ISM was linked with Northern Hemisphere cooling events, especially during the MIS 2. Furthermore, the millennial-scale hydroclimate changes in the BoB presented in this study support the dynamic role of AMOC in driving a teleconnection between the North Atlantic and Indian Ocean monsoon regions.
•Millennial-scale climate variability reconstructed by SST and δ18Osw in the BoB.•Weakened ISM have been proved linked with Northern Hemisphere cooling events.•A teleconnection between the North Atlantic and Indian Ocean by dynamic role of AMOC.
We present a sedimentary multi-index comprehensive study on sediment core BoB-56 collected from the central Bay of Bengal (BoB) with an attempt to understand the sedimentary processes and their ...responses to sea level change and the Indian summer monsoon (ISM) since the last glacial period. We revealed the temporal evolution of terrigenous input and provided a brief discussion of the implications of our sedimentary indexes for ocean productivity. Then, we proposed a simple depositional model in the central BoB since the last glacial period. As indicated by the geochemistry, mineralogy and physical indexes, including linear sedimentary rate (LSR), Ti/Ca, Rb/Sr and quartz/calcite ratios, the terrigenous input was higher during the last glacial period than during the Holocene period, and the sea level is suggested to be responsible for this significant distinction through the depositional center transition in the BoB at the glacial-interglacial scale. Similar terrigenous input patterns with solar radiation and precipitation before 18 ka indicated that the monsoon controlled these situations at precession-related scales. Synchronous changes with records in the north Atlantic Ocean during the last deglaciation and early Holocene suggested terrigenous input responses to the climate changes that also recorded by high latitude sedimentary system at millennial scales. Indicated by the element (CaCO3, Ba and Sr) authigenic accumulation rates, the paleoproductivity in the central BoB was at a roughly equivalent level during the last glacial period and the Holocene period. Different terrestrial nutrient inputs and ISM-related ocean surface stratifications were suggested to be responsible for the level of paleoproductivity. This study provides a brief understanding of the sedimentary response to the climate and emphasizes the different roles of the sea level and ISM in the central BoB.
•High-resolution systematic study of the sedimentary characteristics since last glacial period;•The different roles of sea level and Indian summer monsoon in the sedimentation of the Bay of Bengal are clarified;•Sedimentary process during the last deglaciation was in response to climate change in the North Atlantic;•A simple depositional pattern in the central BoB since the last glacial period was built
Downcore geochemical composition of sediment core retrieved from the central Andaman Sea were measured to help understanding the potential connection between chemical weathering and monsoon climate ...since the last glacial period. The age model was confirmed based on twelve accelerator mass spectrometry (AMS) 14C dates on planktonic foraminifera Neogloboquedrina dutertrei. Provenance discrimination results distinguished by Rare Earth Elements pattern and Sc/Th-(La/Yb)UCC diagram revealed that terrestrial sediment from the Irrawaddy River are the dominant input in the central Andaman Sea. Chemical weathering indexes, including chemical index of alteration (CIA), weathering index of Parker (WIP), αAlNa, and a stack of these data were reported and the terrestrial input was assessed using Ti/Ca ratios. These indexes showed general synchronicity with the regional monsoon precipitation and temperature record, the chemical weathering intensity and monsoon precipitation/temperature were stronger/higher during MIS 3 and MIS 1 and weaker/lower during MIS 2, indicating existence of a general “climate-driving weathering” pattern on glacial-interglacial time scales. However, certain anomalies occurred during 18–13 cal. kyr BP and 6–3 cal. kyr BP, when the chemical weathering intensity showed higher and lower values, respectively. The chemical weathering intensity enhanced during 18–14 cal. kyr BP, due to increased isolation and markedly increased temperatures, as well as lower erosion production and sediment transfer rate caused by lower precipitation, whereas the opposite conditions prevailed during 14–13 cal. kyr BP. Indeed, for the weak chemical weathering intensity during 6–3 cal. kyr BP, decreased isolation, relatively high terrestrial sediment supply, slightly lower precipitation and markedly lower temperatures were suggested to be the primary reasons, indicating the presence of a “climate-driving weathering” pattern on millennial time scales. Our findings support the hypothesis that the chemical weathering evolution in the north-eastern Indian Ocean was synchronous with both global and regional climate conditions, representing distinct changes controlled by Indian summer monsoon on different time scales.
•CIA, WIP, αAlNa and Ti/Ca for chemical weathering intensity reconstruction•A “precipitation-induced weathering” mode exists on glacial-interglacial time scales.•A “temperature and terrestrial input controlled” mode on millennial time scales
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