Sedimentary Evolution In The Eastern Arabian Sea And Western Bismarck Sea Under The Evolution Of The Indian-Australian Monsoon Since 3.8 Ma

Sediment from IODP Site U1456 in the Eastern Arabian Sea and IODP Site 1486in the Western Bismarck Sea of the Western Pacific Warm Pool were used trace the history of sedimentary evolution and its control mechanism based on multiproxy records,including mass accumulation rate（MAR）,laser grain size,clay mineralogy,Sr-Nd isotopes,and elements geochemical analysis and compared with other data including the monsoon precipitation index,sea level,tectonic activity,ice cores,earth orbit parameters,and other sediment core-related records in the study area.The history and driving mechanism of sediment input at different timescales（tectonic,orbital,millennial）in the eastern Arabian Sea under the evolution of the South Asian monsoon since 3.8 Ma.And the history of sediment input and its driving mechanism at orbital timescales in the Bismarck Sea under the evolution of the Australian monsoon over the past 450,000 years were reconstructed.The major conclusions are as follows:Provenance analysis indicates that sediments result from the mixing of two main sedimentary sources corresponding to the Indus River and to rivers draining the Deccan Traps on the millennium scale since the last glacial period,on the orbital scale since 600,000 years,and on the tectonic scale since 3.8 Ma.Since the last glacial,the discharge of sediments transported from the Indus River and the rivers draining the Deccan Traps to IODP Site U1456 were strongly influenced by sea-level fluctuation.Variations of isotopic and mineralogical compositions were used to reconstruct the past changes in the relative proportions of the fine-grained detrital sediments at IODP Site U1456 derived from the Indus River and the Deccan Traps.During LGM reducing Indian summer monsoon intensity combined with low-sea level stand where associated to detrital sediment primarily derived from the Indus River due to the enhanced physical erosion of the western Himalayas.In contrast,when the Indian summer monsoon intensity intensified and rainfall increased during the deglacial,more detrital clay-sized sediments originating mainly from the Deccan Traps.The detrital sediments provenance from the eastern Arabian sea have spatial and temporal variations.Comparison with other detrital Sr-Nd isotopes record from the eastern Arabian sea indicate that during LGM,the provenance of sediments deposited in more northern core（IODP Site U1456）is dominated by the increased proportion of sediments deriving from the Indus river,while the smaller river systems from the Peninsular Gneissic Rock feeding the sinuous channel systems in the southeastern Arabian sea instead of only the sediment from Bay of Bengal also have significant impact on the sediments deposited in more southern area.During the Holocene Intensified Monsoon Phase,the increased flux of the smaller river systems from the Peninsular Gneissic Rock had significant influence of the sediments deposited in more southern core（SS-3101G）with stronger Indian summer monsoon rainfall.At the orbital time scale,during most of the glacial periods（MIS 14,MIS 12,MIS 10,MIS 8,and MIS 6）and some interglacial periods（MIS 15,MIS 13）,the detrital sediments mainly originated from the India river since 600,000 years.In other interglacial periods（MIS 11,MIS 9,MIS 7,MIS 5）,the detrital sediments from the Deccan Traps increased significantly.The siliciclastic MARs is significantly positively correlated with the magnetic susceptibility,indicating that the higher magnetic susceptibility of the IODP site U1456 mainly reflects the increased mass accumulation rate of terrestrial sediment at the study area,rather than the increase input of a single sediments provenance（Indus river or Deccan Traps）.Smectite/（illite+chlorite）ratio of IODP Site U1456 indicate a dominant 118 kyr cycle and moderate obliquity（41 kyr）and precession cycles（23 kyr）during the Late Quaternary.During the interglacial periods with strong Indian summer monsoon（MIS15,MIS 13）,the transport of detrital sediments from the source area（especially the Deccan Traps）to the study core was dominated by the Indian summer monsoon;During other interglacial periods（MIS 11,MIS 9,MIS 7,MIS 5）with weak Indian summer monsoon and the glacial periods,sea level change was the main controlling factor for the transport of detrital sediments to the the eastern Arabian sea.At the tectonic time scale,the sediments in the IODP Site U1456 have mainly been transported from the Indus River between 3.8-3.3 Ma and 2.7-1.2 Ma.Due to a weak Indian summer monsoon,the chemical alteration during those depositional stages were relatively weak.The abnormally high siliciclastic MARs of IODP Site U1456 at 1.7-1.2 Ma suggests that rapid denudation and topping occurred in the Himalayas of the of the Indus River at 1.7-1.2 Ma.In particular,it corresponds to the increase in the siliciclastic MARs of the global large basins during this period.From3.3-2.7 Ma to 1.2-0 Ma,with the stronger Indian summer monsoon,the sediment experienced strong chemical weathering in the the source area,and increased input of sediments from the Deccan Traps.Indian summer monsoon intensity has been the primary factor controlling the relative inputs of weathering and erosion products from the Indus River and Deccan Traps into the eastern Arabian Sea since 3.8 Ma.Silicate weathering/erosion of the detrital sediment transported to IODP Site U1456 was primarily controlled by the monsoon climate during each period.In addition,changes in sea level and avulsion of fan lobes into the Laxmi Basin may have also had a secondary impact on the transport of detrital sediment into the eastern Arabian Sea during some stages.The analysis results of provenance show that the siliciclastic sediment at IODP Site U1486 since 450,000 years was mainly derived from the cratonic and ultramafic detritus of the upper Sepik river flow through the New Guinea Highlands,and the volcanic sediments in the middle and lower Sepik river basin and Ramu river basin.During glacial periods,the proportion of sediment material export of the Central Mountains of New Guinea on the upper Sepik river increased.On the contrary,during the interglacial periods,the proportion of volcanic sediment materials from the middle and lower reaches of the Sepik River and Ramu river and low altitude coastal mountains in northern increased.The change of weathering intensity in the source area and the siliciclastic MARs at the study core are mainly controlled by the glacier growth on the highest mounts in the central Papua New Guinea,which almost controlled by eccentricity.The weathering/erosion of the land surface in northern New Guinea is closely related to low-latitude processes（such as solar insolation）and high-latitude processes（such as ice volume）.the Australian monsoon rainfall controlled by precession,was the second controlling factor.On the tectonic scale,the intensity of monsoon precipitation may have dominated the change in the relative proportion of detrital materials transported to the IODP Site U1486.The climate‐driven erosional glacial-interglacial cycle shifts identified in the northern Papua New Guinea river basins during the last 450,000 years,were also accompanied by the alternation between chemical weathering in the middle and lower reaches of the Sepik River,Ramu river,including low altitude coastal mountains in northern Papua New Guinea,and the physical erosion changes driven by the mountain glaciers in the high-elevation central mountains,may dominated the weathering and erosion regimes in northern Papua New Guinea.And presumably had an impact on the carbon cycle.During glacial periods with cold environment,enhanced physical erosion in the New Guinea Highlands,and its potential influence on the alteration of organic‐rich sedimentary rocks,possibly acted as a net source of CO₂ to the atmosphere through oxidation processes,while enhanced silicate weathering in floodplains during interglacial periods possibly led to more efficient CO₂sequestration.