海洋地质与环境重点实验室知识库

本论文对阿拉伯海东部IODP U1456站和俾斯麦海西部IODP U1486站两个长柱状沉积物岩芯进行了陆源碎屑物质堆积速率、粒度、粘土矿物、Sr-Nd同位素、元素地球化学的综合研究，分别分析了IODP U1456站位和IODP U1486站的物质来源的演变，并与研究区季风降水、海平面、构造活动、冰芯等记录、地球轨道参数及与其它岩芯相关记录进行对比，分别重建了3.8 Ma以来南亚季风控制区不同时间尺度（构造、轨道、千年）上的沉积物输入演化历及其驱动机制与45万年以来澳大利亚季风控制区轨道时间尺度上的沉积物输入演化历史及其驱动机制。

研究结果表明， IODP U1456站位粘土粒级的陆源碎屑物质主要来自印度河和德干高原的输入。

末次冰期以来，海平面变化控制了拉克希米盆地陆源碎屑物质堆积速率，而南亚夏季风强度的变化显著影响着不同源区的陆源碎屑物质向研究区的输入的比例。在末次盛冰期（LGM），印度夏季风的强度降低，海平面处于低位。该时期喜马拉雅山脉西部的侵蚀增加，致使来自印度河的物理剥蚀碎屑沉积物较多。相反，全新世海平面上升和印度夏季风降雨的加剧导致来自德干高原的粘土粒级沉积物（蒙脱石）比例增加。

末次冰期以来，阿拉伯海东部海域的碎屑沉积物来源具有明显的时空差异。基于多钻孔Sr-Nd同位素数据对比可知，在LGM时期，海平面降低导致了北部岩芯（IODP U1456）接收的源自印度河的沉积物比例增加；而东南阿拉伯海沉积物成分变化则是受到了印度次大陆南部片麻岩区沉积物输入的影响，而非传统观点所认为的仅仅是孟加拉湾的输入影响。在全新世季风增强期，季风降水的增多使印度次大陆南部片麻岩区的小河流沉积通量增大，最终对阿拉伯海东南部岩芯（SS-3101G）的沉积物组成产生了重大影响。

60万年以来的轨道时间尺度上，在绝大部分冰期（MIS 14、MIS 12、MIS 10、MIS 8、MIS 6）及部分间冰期（MIS 15、MIS 13），拉克希米盆地的陆源碎屑物质主要来源于印度河。而在其余间冰期（MIS 11、MIS 9、MIS 7、MIS 5），来源于德干高原的碎屑物质明显增多。碎屑物质堆积速率（MAR）与磁化率显著正相关，指示IODP U1456站位的高磁化率主要反映研究站位陆源物质堆积速率较快，而非单一源区（印度河或德干高原）来源的高磁化率物质输入比例增大。晚更新世以来，IODP U1456站位蒙脱石/（伊利石+绿泥石）的比值主要表现为118 kyr周期，斜率（41 kyr）、岁差（23 kyr）也起着一定的控制作用。南亚夏季风强盛的间冰期（MIS 15、MIS 13），该季风主导了源区（特别是德干高原）碎屑沉积物向研究区的输运；而海平面变化是主导冰期及其他间冰期（MIS 11、MIS 9、MIS 7、MIS 5）时碎屑沉积物向海输运的主要因素。

在构造时间尺度上，3.8-3.3 Ma和2.7-1.2 Ma阶段，研究区的碎屑沉积物主要来源于印度河，期间南亚夏季风强度较弱，故沉积物源区的化学风化强度也较低。U1456站在1.7-1.2 Ma异常高的陆源碎屑物质沉积通量表明当时的印度河源区（喜马拉雅山脉）发生了快速剥蚀去顶作用。同时，其与该时期全球性海洋大型盆地沉积通量增加的事件相对应。而在3.3-2.7 Ma和1.2-0 Ma，伴随着更强的南亚夏季风强度，沉积物源区经受了强烈的化学风化作用，德干高原输入的陆源碎屑物质比例增加。由此可见，3.8 Ma以来，南亚夏季风强度一直是控制印度河和德干高原来源的碎屑沉积物向阿拉伯海东部输运比例变化的重要因素。且其还控制了上述碎屑沉积物在源区的风化/侵蚀。此外，在某些阶段，海平面的变化及构造活动等因素也可能对碎屑沉积物向阿拉伯海东部的运输产生了次级影响。

45万年以来IODP U1486站位沉积的碎屑物质主要来源于海拔较高的塞皮克河上游克拉通类碎屑、超镁铁质类碎屑与海拔较低的塞皮克河中下游及拉穆河输入的火山岩类碎屑沉积物的混合。粘土矿物组分含量的变化及碎屑沉积物Sr-Nd 同位素变化皆表现出明显的冰期-间冰期旋回特征。冰期时，塞皮克河上游新几内亚中央山脉的碎屑物质输入比例增加。相反，间冰期时，新几内亚北部塞皮克河中下游流域及拉穆河河流盆地、低海拔海岸山脉来源的火山岩类碎屑物质比例增加。源区陆源物质向IODP U1486站位的输运主要受控于偏心率影响下的山地冰川进退，新几内亚北部陆表风化剥蚀与低纬度过程（如太阳辐射量）及高纬度过程（如冰量）三者之间紧密相关。受岁差控制的而澳大利亚季风降水可能是次一级的控因素。

45万年以来，新几内亚北部塞皮克河中下游河流盆地、低海拔海岸山脉的化学风化与高海拔中央山脉的山地冰川驱动的物理侵蚀变化在冰期-间冰期的循环尺度上可能主导了新几内亚北部风化侵蚀机制的相对强弱变化，并可能对碳循环产生了一定影响。在冰期，新几内亚高地的冰川侵蚀加剧，富含有机物的沉积岩可能会通过氧化过程向大气大气中释放二氧化碳，而塞皮克河中下游河流盆地、低海拔海岸山脉的硅酸盐风化在间冰期增强可能导致了更有效的二氧化碳的储存。

Sediment from IODP Site U1456 in the Eastern Arabian Sea and IODP Site 1486 in 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 (MIS 15, 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. From 3.3-2.7 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 CO₂ sequestration.