Bengal Fan Research Articles

Convolutional Neural Network based Marine Cetaceans Detection around the Swatch of No Ground in the Bay of Bengal

Convolutional Neural Network based Marine Cetaceans Detection around the Swatch of No Ground in the Bay of Bengal

Contrasting thermal histories for the Indian passive margins during syn‐ and post‐Gondwana break‐up: Insights from apatite fission‐track thermochronology

AbstractNew and published apatite fission‐track data provides evidence for differential exhumation between the eastern and western passive margins of southern India. The eastern margin records significant Late Jurassic to Early Cretaceous rifting‐triggered exhumation in response to Gondwana break‐up and minor Cenozoic cooling. In contrast, Meso–Cenozoic rifting and posterior tectonic events did not deeply exhume the basement of the western margin. The anomalous thick crust of the Western Dharwar Craton might explain why Mesozoic deformation in this area was subdued. In addition, the Cenozoic eastward tilting of the Indian plate and the onset of Bengal Fan sedimentation ca. 23 Ma allowed the accumulation of thick sedimentary sequences in the eastern coastal basins, probably inducing a flexural response of fault reactivation on the eastern margin. More generally, we demonstrate the influence of lithospheric strength and post‐rifting sedimentation to the exhumation history of passive margins.

Development and analysis of a geospatial database for maritime spatial planning in Bangladesh

In this research we collect, prepare and analyze a geospatial database of maritime activities located in the northern Bay of Bengal with the final aim to simulate maritime spatial planning (MSP) - ready information source for future sectoral and multi-sector MSP in Bangladesh. The database is composed of 28 anthropogenic and environmental layers categorized into seven Blue Economy sectors. The database is analyzed with a set of geospatial models aimed at understanding the intensity distribution of human activities at sea and the potential marine use conflicts emerging from the aggregation of human activities. Ecological resources were characterized in terms of marine mammals, lobsters, commercially important and threatened fish species, and pelagic birds and mapped as biodiversity hotspots using geographic cluster analysis. Results show that the most intensely used sea areas are located along the northeastern coast of Bangladesh, as well as in the Swatch of No Ground (SoNG) area, with maximum Marine Use Intensity (MUI) scores ranging from 5 to 8. Offshore waters of Saint Martin's Island have higher MUI scores (≥ 5) as well. The pairwise spatial conflict analysis shows that nature protection sites particularly SoNG Marine Protected Area (MPA), Nijhum Dwip Marine Reserve (MR), and Saint Martin's Island MPA are exposed to the high Marine Use Conflicts (MUC) induced by fishing and shipping activities. Fishing operations generate the highest MUC value (MUC=30) in SoNG MPA, whereas shipping activities produce the highest MUC value (MUC=24) in Nijhum Dwip MR. Both of the MPAs exhibit 6 to 12 MUC scores induced by shipping. The proposed database together with the illustrated analytical techniques used in this study and key findings can provide the first understanding of the priorities for Ecosystem Based Management of Bangladesh's marine space and provide valuable insights on the urgency for MSP process in the country. The study concludes with an outlook on the utility of the database for future analysis.

The formation and development of avulsions and splays of submarine channel systems: Insights from 3D seismic data from the northeastern Bengal Fan

Avulsions and splays of submarine channels are important autogenic responses affecting sediment distribution in deep-water areas; however, their formation and development are still not well understood. Using high-resolution 3D seismic data and spectral decomposition red–green–blue (RGB) color blends, two seismically well-imaged submarine channel systems (SCS1 and SCS2) on the northeastern Bengal Fan are used to document the formation and development of avulsions and splays. The results suggest that avulsions occur mainly during the early evolution stage of submarine channel systems. SCS1 and SCS2 are respectively accompanied by one and four avulsions and accordingly produce two and five independent submarine channels. During this early phase, these channels collectively incise into the underlying stratigraphy but lack levee deposits. Splays, in contrast, develop consistently during the late evolution stage of the submarine channel systems. Three crevasse splays and three overbank splays develop on the overbank areas of SCS1 and SCS2. During that late stage, channel and levee deposits build over the site of former erosion, thus forming the aggradational phase of channel evolution. Crevasse and overbank splays are two different types of splays observed on this part of the Bengal Fan. The former are created by flow breaching of the adjacent levees, producing large-scale elongated shapes; they are related to relatively stable sediment gravity flows, a high-degree of channel instability, and steep levee topography. Overbank splays, however, are created by flow overtopping adjacent levees and produce small-scale, fan-like shapes; they are related to gradually-weaking sediment gravity flows, a low-degree channel unstability, and gentle levee topography.

Hotspot volcanism along a leaky fracture zone contributes the formation of the 85°E Ridge at 11°N latitude, Bay of Bengal

The 85°E Ridge is a prominent linear structure in the northeastern Indian Ocean. Its nature and origin are still controversial due to the coverage of thick Bengal Fan sediments. Here we present a newly collected 400-km-long 2-D seismic reflection profile which crosses the 85°E Ridge near 11°N and shows the basement morphology and internal structures of the ridge. The ridge has a thickened crust characterized by two basement highs rising up to ~2–3 km above the surrounding oceanic crust and a Moho depression with amplitude of ~3–4 km. Typical volcanic structures formed by hotspot volcanism are identified in the ridge. Deep-rooted faults played important roles in the formation of the 85°E Ridge. They acted as the preferred conduit for the upwelling of hotspot melts, but their syn- and post-volcanic reactivations induced the collapse of volcanic sequences and the relative uplift of the East Ridge. These observations support that the 85°E Ridge near 11°N having formed by hotspot magmatism drained along a leaky fracture zone. Combined with previous results, a new single-hotspot formation model of the 85°E Ridge is proposed, in which the entire 85°E Ridge was formed by a weak and pulsating mantle plume acting on the northward drifting Indian Plate. Its along-strike variations in location, morphology, and structure in different segments are interpreted to reflect different elastic strength of the oceanic lithosphere and the existence of a pre-existing fracture zone which laterally redistributed the shallow melts.

Seismic characterization and modelling of the gas hydrate system in the northern Bay of Bengal, offshore Bangladesh

The offshore Bangladesh includes the northern Bengal fan, where sediment supply from the Ganges and Brahmaputra rivers has resulted in the accumulation of up to 20 km of shallow-marine, fluvio-deltaic and slope sediments that have accumulated during rapid tectonic subsidence since the late Miocene. The high sedimentation rates, along with high organic matter content, make this area favorable for the formation of natural gas from both microbial and thermogenic sources. Here we use multichannel seismic reflection profiles and modelling of the gas hydrate stability zone (GHSZ) to present the first evidence for the occurrence of natural gas hydrate in the offshore Bangladesh. First, we analyze the sediments of the shelf and slope areas, which are characterized by downslope sediment transport features and by the presence, in places, of faults/fractures as well as widely distributed amplitude anomalies and seismic facies that we relate to the presence of gas. A high-amplitude reversed polarity reflection of variable continuity that mimics the seafloor and cross-cut stratigraphy is interpreted as a Bottom Simulating Reflector (BSR). The BSR is observed in several areas that are predominantly located in the E-SE of the study area, in water depths of 1300–1900 m and at depths below seafloor of 250–440 m. Sediments above BSR locations generally show higher seismic interval velocities reaching values of ∼1920–1940 m/s, which are consistent with the presence of gas hydrate in shallow marine sediments. Furthermore, the BSR lies at approximately the same depth as the theoretical base of the gas (methane) hydrate stability zone (BGHSZ), calculated assuming a 3.5 % wt pore water salinity and using existing geothermal gradient and seafloor temperature data from the study region. However, in places, the BSR lies deeper or shallower than the base of the modelled BGHSZ. These discrepancies include areas where faults/fractures and seismic evidence linked to fluid flow from deeper reservoirs reach the GHSZ disrupting its stratigraphic continuity. At these locations, we suggest that faults/fractures act as fluid migration pathways causing localized heat-flow perturbations and/or changes in the hydrate-forming gas composition both likely affecting the depth of the GHSZ. Our results provide the first evidence of the gas hydrate potential in the offshore Bangladesh and should drive future research and data acquisition aiming to understand the composition, saturation and thickness of the gas hydrate-bearing sediments in this region.

Heavy metal pollution and ecological risk assessment in the surface water from a marine protected area, Swatch of No Ground, north-western part of the Bay of Bengal

The primary intends of the study was to ascertain the degree of pollution, spatial distribution, and prime sources of heavy metals in a marine protected area, Swatch of No Ground, north-western part of the Bay of Bengal. Six heavy metals were considered, and their concentrations were found in the decreasing order of Fe > Pb > Cu > Zn > Ni > Cd. Several indices namely Heavy metal pollution index (HPI), Heavy metal evaluation index (HEI) and Nemerow pollution index (NPI), Potential ecological risk index (PER), Hazard quotient (HQ), and Hazard index (HI) were measured to portray the degree of pollution and risk assessment, respectively. HPI, HEI, and NPI suggested that the surface water of North-western Bay of Bengal is under moderate to high degree of pollution due to the higher concentration of Pb, Cu, and Cd. In addition, heavy metal pollution is moderate according to PER, and human health hazards are comparatively low according to HQ and HI. Principal component analysis, hierarchical cluster analysis, and correlation analysis result further reveal that anthropogenic activities are primly influencing the heavy metal accumulation in the study area. Moreover, all of the heavy metals had surpassed the background value of natural surface water in their concentrations. Three of the six heavy metals exceed the lowest biological chronic safety limit, except for Zn, Cd, and Ni recommended by the National Oceanographic and Atmospheric Administration. Hence, to conserve the balance of marine ecology, the local authorities must implement proper treatment of domestic and industrial waste management policies before causing excessive risk.

Spatio-temporal deposition profile of an experimentally produced turbidity current with a continuous suspension supply

A turbidity current is a turbulent, particle-laden gravity current that is driven by density differences resulting from the presence of suspended sediment particles. The current travels downslope, bearing a large amount of sediment over a great distance, and forms fluvial and submarine bedforms. Knowledge of the spatio-temporal deposition profile of turbidity-deposited sediment is important for a better understanding of sediment transport by turbidity currents. In the current study, the depositional process of experimentally produced quasi-steady turbidity currents in an inclined flume was investigated using an electrical-resistance-based depositmeter. It was found that the amount of sediment deposited along the flume bottom increases linearly with time at a specific rate, and decreases exponentially in the downstream direction. Inspired by this observation, the mass conservation law was modified for the suspension layer and a simple theoretical model was proposed involving two parameters, the initial sedimentation rate and the decay constant. The proposed model reproduces the observed data from the flume experiment with high accuracy, and is consistent with the sediment transport distance of a natural example, the Bengal Fan. It was concluded that the two parameters that govern the sedimentation process are the key to estimating the deposition profile of fluvial systems.

Different avulsion events throughout the evolution of submarine channel-levee systems: A 3D seismic case study from the northeastern Bengal Fan

As very common deep-water phenomena, submarine channel avulsions have been paid considerable attention recently. The differences among them are, however, rarely noted, nor their relationship to the evolution of submarine channels. A seismically well-imaged channel-levee system from the Pliocene Bengal Fan, named target channels (TCs) and consisting of three independent channels (Tc1-Tc3), has been selected as a case to address these issues. Using high-resolution 3D seismic data along with spectral decomposition and RGB color blending techniques, this study images TCs from initiation to abandonment and recognizes three different types of avulsion events: regional avulsion, local avulsion and bank crevasse. In the early evolution stage of TCs, the regional avulsion and the local avulsion successively occurred, promoting TCs to obtain a stable flow course and then undergo a significant evolution. Moreover, coupled with those regional and local avulsion events, TCs were growing respectively in the form of individual channel and amalgamated stacking. In the late evolution stage of TCs, only bank crevasses occurred and led to the formation of crevasse splays in the overbank setting, which coincided with the aggradational stacking of TCs developing. This new evolution model of channel-levee systems, which acknowledges different avulsion events, may provide insights on the understanding of analogue deep-water deposits and in turn can be applied to guide the hydrocarbon exploration and development.

Different types of gravity-driven flow deposits and associated bedforms in the Upper Bengal Fan, offshore Myanmar

This study uses 3D reflection seismic data to investigate how sediment gravity flows contribute to the evolution of the lower continental slope of the Myanmar margin that is part of the Bengal Fan, the largest deep-water fan system in the world. Seafloor and subseafloor data show large sediment wave fields that developed on both flanks of an extensive submarine canyon. The sediment waves exhibit asymmetric stoss and lee sides, wave lengths and heights of 850–3000 m and 25–70 m, respectively, and an upslope direction of migration. Seismic data reveals the presence of multiple fields of vertically stacked sediment waves, interbedded with units characterised by a chaotic seismic facies that accumulate mainly in the troughs of the sediment waves and can be tracked laterally to the adjacent canyons. According to their seismic facies, geometry, and internal architecture these chaotic units are interpreted as debrites. Seismic attributes extracted from different horizons indicate that the sediment waves are dominated by fine-grained sediment, while the debrites are probably associated with coarser-grained deposits. The debrites fill the troughs of the sediment waves, as well as the downstream portions of canyon thalweg, thus flattening the paleo-seafloor. The sediment waves are interpreted as cyclic steps formed by low-density turbidity currents flowing across the slope down to the basin floor, where the change in gradient favours the formation of hydraulic jumps and the transition from supercritical to subcritical flow conditions. A conceptual model for the sediment wave evolution was proposed for the study area, in the transitional environment on the lower slope, with low-density gravity flow deposits and high-density debris flow deposits alternatively accumulating on the major gravity flow conduits.

Frequency of deep-sea turbidity as an important component of the response of a source-to-sink system to climate: A case study in the eastern middle Bengal Fan since 32 ka

The Bengal Fan is world famous for its developed turbiditic system. This study identified turbidite records in a gravity core (BoB-104) taken from near a currently inactive channel (E4) based on lithology, geochemical and mineralogical parameters. This core contained turbidite and hemipelagic layers in this core. This study identified 21 turbidite layers which exhibited consistent provenance with the hemipelagic layers, showing a two end-member mixing pattern and indicating consistent sources since the last glacial period. Typical turbidite layer analysis was used to study the possible turbidite deposition mechanism. Features such as the lithology break interface, normal graded sequence, a consistent pattern of a sharp increase and gradual decrease in the variation of the mean grain size (Mz), and median grain size (D50) and Si/Al ratios commonly implied a continuous deposition in accordance with variations in densities and particle sizes. This study identified long-term evolution of turbidite deposition in the eastern middle Bengal Fan that appears to be the last and indispensable part of the systematic response of the “Bengal depositional system” to the climate. Four stages were identified from the turbidite records and all the identified intervals showed synchronous changes with the entire system. The Indian summer monsoon (ISM) played a dominant role in the system interactions. The sea level affects the turbidity system by regulating the transition of the deposition center between the deep-sea and the shelf, whereas the migration of the main channel to the “Active Valley (AV)” between 14.5 ka to 10.4 ka almost halted the deposition of turbidites along the E4 channel. Thus, turbidity activity in the eastern middle Bengal Fan is not an isolated incident but part of a comprehensive system resuling from global and regional changes at different scales.

Hydrologic Changes Drove the Late Miocene Expansion of C4 Grasslands on the Northern Indian Subcontinent

AbstractModern tropical and subtropical C4 grasslands and savannas were established during the late‐Miocene and Pliocene, over 20 Myr after evolutionary originations of the C4 photosynthetic pathway. This lag suggests environmental factors first limited and then favored C4 plants. Here, we examine the timing and drivers for the establishment of C4 grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant‐wax n‐alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C4 ecosystems in the Ganges‐Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C4 grasslands with further drying at the onset of C4 expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C4 grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C4 ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO2, beginning at 10.2 Ma and strengthening through the late Miocene.

Late Miocene C4 Grassland Fire Feedbacks on the Indian Subcontinent

AbstractFire dynamics potentially account for the asynchronous timing of the expansion of C4 grasslands throughout the Mio‐Pliocene world. Yet how fire, climate, and ecosystems interacted in different settings remain poorly constrained because it is difficult to quantify fires and fuel source over these timescales. Here, we apply molecular proxies for fire occurrence alongside records of vegetation change and paleohydrology in Bengal Fan sediments (ODP Leg 116) to examine fire feedbacks on the south Asian continent. We employ abundances of polycyclic aromatic hydrocarbons (PAHs) to reconstruct fire occurrence and δ13C measurements of pyrogenic PAHs to constrain fuel source and grassland burning. This combination allowed us to test whether: (1) a fire‐seasonality forcing facilitated the expansion of grassland ecosystems and (2) a fire‐C4 grass burning feedback maintained these systems. PAHs can be sourced from weathered fossil carbon (i.e., a petrogenic source) and from burned terrestrial biomass (i.e., a pyrogenic source). Alkylated and non‐alkylated structure abundance data distinguished pyrogenic from petrogenic sourced samples. A sharp increase in pyrogenic PAHs along with increases in δ2H and δ13C values of plant waxes at 7.4 Ma indicates increased fire coincided with the onset of C4 expansion and hydrologic change in South Asia. The correlated 13C enrichment in PAHs, 13C enrichment in plant waxes, and increased abundances of PAHs suggest burning of C4 grasslands likely maintained open ecosystems. Our results link fire to the initial opening of grassland ecosystems on a subcontinental‐scale and support disturbance as a critical mechanism of terrestrial biome transition.

Marine sedimentary records of chemical weathering evolution in the western Himalaya since 17 Ma

AbstractThe Indus Fan derives sediment from the western Himalaya and Karakoram. Sediment from International Ocean Discovery Program drill sites in the eastern part of the fan coupled with data from an industrial well near the river mouth allow the weathering history of the region since ca. 16 Ma to be reconstructed. Clay minerals, bulk sediment geochemistry, and magnetic susceptibility were used to constrain degrees of chemical alteration. Diffuse reflectance spectroscopy was used to measure the abundance of moisture-sensitive minerals hematite and goethite. Indus Fan sediment is more weathered than Bengal Fan material, probably reflecting slow transport, despite the drier climate, which slows chemical weathering rates. Some chemical weathering proxies, such as K/Si or kaolinite/(illite + chlorite), show no temporal evolution, but illite crystallinity and the chemical index of alteration do have statistically measurable decreases over long time periods. Using these proxies, we suggest that sediment alteration was moderate and then increased from 13 to 11 Ma, remained high until 9 Ma, and then reduced from that time until 6 Ma in the context of reduced physical erosion during a time of increasing aridity as tracked by hematite/goethite values. The poorly defined reducing trend in weathering intensity is not clearly linked to global cooling and at least partly reflects regional climate change. Since 6 Ma, weathering has been weak but variable since a final reduction in alteration state after 3.5 Ma that correlates with the onset of Northern Hemispheric glaciation. Reduced or stable chemical weathering at a time of falling sedimentation rates is not consistent with models for Cenozoic global climate change that invoke greater Himalayan weathering fluxes drawing down atmospheric CO2 but are in accord with the idea of greater surface reactivity to weathering.

Climatic and Tectonic Control on the Bengal Fan Sedimentation Since the Pliocene

AbstractStrontium and Neodymium isotopic analysis of the lithogenic fractions of the hole U1445A (International Ocean Discovery Program‐353) collected from the deep‐water end of the Mahanadi basin (western Bay of Bengal) was carried out to evaluate the sediment sources as well as to understand the link between the temporal variations in the Sr‐Nd isotope ratios and climatic and tectonic forcings during the last 6 Ma. The Sr‐Nd isotopic compositions along with Fe/Al ratios and clay mineralogy show tell‐tale signature of Ganga‐Brahmaputra sedimentation (Bengal fan) in the study area. The significant temporal fluctuations observed in the Sr‐Nd isotopic compositions suggest variation in the relative sediment contribution by the Ganga and Brahmaputra river systems, which in turn are controlled by monsoon intensity variations coupled with orographic effect, glaciation, and multiple tectonic activities. The results show the marked influence of glacial‐interglacials on the relative sediment contribution by Ganga and Brahmaputra rivers during 0–1.8 Ma, while the sedimentation during the 1.8–6 Ma time window was likely influenced by both climatic and tectonic forcings such as uplift of the Shillong plateau, eastern syntaxis development of Indo‐Burma wedge, reorganization of Brahmaputra river system. The present study is the first high resolution (122 samples within 6 Ma) Sr‐Nd isotope ratio analysis from the Bengal Fan. The study has brought to light multiple isotope fluctuations linked to climatic and tectonic forcings. The work also establishes dominant control of Ganga‐Brahmaputra sedimentation along the deep waters of the Indian east coast.

Miocene provenance change in Himalayan foreland basin and Bengal Fan sediments, with special reference to detrital garnet chemistry

AbstractBengal Fan Miocene sediments were collected during International Ocean Discovery Program Expedition 354 and investigated using petrographic and detrital garnet chemistry analyses. The Miocene Siwalik Group, which is composed of sediments deposited in the Himalayan foreland basin, was also analyzed for comparison with the Bengal Fan data for the provenance change during the Miocene. Our petrographic analyses revealed that the Miocene sediments of the Bengal Fan and Siwalik Group consist predominantly of Higher Himalayan Crystalline (HHC)‐derived detritus such as chloritoid, staurolite, sillimanite, and/or kyanite, which appear among the accessory minerals. The chemistry of the detrital garnet varies across the stratigraphy; most of the garnet is rich in almandine and poor in spessartine and pyrope. However, pyrope‐rich garnet, which is considered to originate from the HHC core (granulite facies), was found in the lower to upper Miocene deposits. The deposition of HHC‐derived detrital garnet began before the Middle Miocene (15 Ma) and before the Late Miocene (10–9 Ma) in the Siwalik Group. The Bengal Fan data, by contrast, indicated that pyrope‐rich garnet appeared in the Early Miocene (17.3 Ma) and Late Miocene (8.5–6.5 Ma). We conclude that the Bengal Fan sediments record the erosion of the HHC zone since the Early Miocene that appears in the Siwalik sediments. Furthermore, we found that the HHC‐derived inputs decreased from the late Middle Miocene (12 Ma) to the early Middle Miocene (10 Ma) in both the Nepal Himalaya foreland basin and the Bengal Fan. The disappearance of the HHC‐derived detritus is probably the result of dilution by Lesser Himalayan detritus, which suggests that the Lesser Himalayan zone, which is composed of metamorphosed and unmetamorphosed sedimentary rocks, was uplifted.

Miocene to Recent calcareous nannofossil biostratigraphy in the eastern Bengal Fan (Indian Ocean): Linking turbidites to tectonic activity during the evolution of the Himalayas.

Miocene to Recent calcareous nannofossil biostratigraphy in the eastern Bengal Fan (Indian Ocean): Linking turbidites to tectonic activity during the evolution of the Himalayas.

Sedimentary provenance of the Plio-Pleistocene Nicobar Fan: Complex sourcing revealed through Raman spectroscopy heavy mineral analysis

The Nicobar Fan lies within the north-eastern Indian Ocean between the Ninety-East Ridge and Sunda Arc. The fan forms part of the Bengal–Nicobar Fan System and is among the oldest and largest submarine fans on Earth. Previous U–Pb zircon studies of the Nicobar and Bengal fans indicate the Himalaya as the dominate sediment source, making these fans a major Cenozoic sink for uplifted Himalayan sediment. However, the northwards moving Indian Plate, coupled with mid-Pleistocene collision of the Ninety-East Ridge with the Sunda Arc, has shutdown many sediment pathways linking the Himalaya and Nicobar Fan. Here we use big data Raman spectroscopy heavy mineral analysis along with U–Pb zircon data to better define sediment source regions for the Nicobar Fan during the Plio-Pleistocene following the shutdown of sediment delivery. The detrital zircon spectra for the Plio-Pleistocene Nicobar Fan from this study are consistent with previous work indicating that the original sources of these zircons can be found within both the Greater and Tethyan Himalaya, the Gangdese Arc, and the Indo-Myanmar Ranges. However, the heavy mineral data indicate that a large proportion of sediment has been derived from a more complex array of sources. This is coupled with an abundance of low- and moderate-stability minerals (e.g., amphibole, apatite, clinopyroxene), which are unlikely to have been transported large distances. Suggesting that proximal sources have delivered the majority of lower-stability heavy minerals into the Plio-Pleistocene Nicobar Fan. We show that from the Pleistocene onwards direct sediment delivery into the Nicobar Fan from the Himalaya was largely shutdown, with sediment instead shedding off the uplifting Indo-Myanmar Ranges, the Andaman–Nicobar Accretionary Ridge, and the westwards propagating Ayeyarwady River. This study shows that extensive uplift along the northern Sunda Arc is recorded in the Nicobar Fan alongside the previously reported Himalayan record.

Evolution of sediment provenances and transport processes in the central Bay of Bengal since the Last Glacial Maximum

To investigate the evolution of sediment provenances and transport processes in the central Bay of Bengal (BoB) since the Last Glacial Maximum, we present a comprehensive study on the grain size, clay minerals, rare earth elements, and accelerator mass spectrometry (AMS)14C analyses of the core BoB-24 sediments. Six AMS14C dates were obtained from planktonic foraminiferal Neogloboquedrina dutertrei (N. dutertrei) extracted from the core to reconstruct a reliable age model. The assemblage of clay minerals and the (La/Yb)UCC–δEu relationship indicated that the core contained a mixture of sediments from the Himalayas and Indian Peninsula. These results showed that the Himalayas were the main source of erosional materials during 25–6.5 ka BP, whereas those from the Indian Peninsula increased since the mid-Holocene. Between 25 ka BP and 12 ka BP, the sea level was relatively low, and a large amount of terrigenous detrital material were directly transported from the Himalayas and the Tibet Plateau to the study area by submarine canyons, forming a deposition center on the Bengal Fan. Between 12 ka BP and 6.5 ka BP, the sea level gradually rose and the Indian summer monsoon gradually strengthened, whereas the sedimentation rate and the amount of material transported from the Ganges–Brahmaputra River decreased greatly; the deposition center transferred from the Bengal Fan to the shelf of the BoB. Since 6.5 ka BP, the sea level has risen, reaching its present position. A high sea level and a strengthened East Indian Coastal Current resulted in an increase of material contribution from India, while the deposition center was on the shelf of the BoB. Overall, this study confirmed that both sea level fluctuations and variations of the Indian summer monsoon controlled the evolution of sediment provenances in the central BoB and transfer of the deposition center from the Bengal Fan to the continental shelf. This typical sedimentary pattern observed in the northeastern Indian Ocean improves our general understanding of past land–sea interactions.

Sediment thickness in the Bay of Bengal and Andaman Sea compared with topography and geophysical settings by GMT

Abstract The study presents an analysis of the sediment thickness compared with bathymetric and geophysical settings in the Bay of Bengal and Andaman Sea, Indian Ocean. It uses a combination of the high-resolution data: topographic GEBCO, satellite and marine gravity anomalies, EGM2008 geoid and GlobSed to visualize the correlation between relief, gravity and trends in continent-ocean sediment transport. The results include thematic maps and 3D model showing increased sediment thickness in the Bengal Fan (8,0 to 8,2 km) in NE direction with maximum in Ganges Fan (16,2 km), and southward decrease in the Andaman Sea from Irrawaddy river mouth (6-7 km) to the Strait of Malacca (1-2 km). All maps and 3D model have been plotted by Generic Mapping Tools (GMT) cartographic scripting toolset version 6.0.0.