Fates of World Major River-Derived Sediments to the Sea: Along-shore vs Cross-shelf Transport

Dr J. Paul Liu – North Carolina State University

Recent extensive geological and geophysical surveys over the world major river-dominated sea margins indicate that many rivers have developed largest proximal subaqueous deltas, with asymmetrical prodelta lobes, and elongated or detached distal masses of sediment. For example, the Amazon River’s sediment disperses >1500 km along the shore within the water depths of 60-70 m, and reaching the Orinoco River mouth; The Yangtze River sediment has transported ~800 km along the shore into the Taiwan Strait, and Yellow River sediment is deposited more than 700 km into the south Yellow Sea. Beyond the proximal depocenters near their river mouth, both the Yangtze and Yellow systems have developed a 40-m thick distal mud depocenters. The Mekong-derived sediment has also extended >250 km southwestwardly to the tip of the Ca Mau Peninsula, forming a distal mud depocenter up to 22 m thick, and extending into the Gulf of Thailand. Other major river systems, like the Irrawaddy, Mississippi, Nile, Po, Rhone, Pearl, Red, also have a large longshore-transported distal deposit with some typical underwater clinoform features. Only a few of the world major rivers are able to disperse their sediment directly or indirectly to the deep sea through the attached shelf canyon systems, like the Congo and Ganges-Brahmaputra.I will describe the unexpected discovery of pore fluids that, for the first time, appear to represent a direct archive of ancient seawater and to preserve the salinity and isotopic ratios of seawater from a past glacial period, likely the Last Glacial Maximum. These pore fluids were extracted from sediment cores from the Maldives Inner Sea, drilled in 2015 during IODP (International Ocean Discovery Program) Expedition 359 and penetrating late Oligocene to modern sediments. The composition of these fluids carries implications for glacial ocean circulation, water-rock interaction in platform systems, and preservation of carbonate sedimentary geochemistry.