Abstract: CONTROLS ON MODERN EROSION AND THE DEVELOPMENT OF THE PEARL RIVER BASIN SINCE THE EOCENE (GSA Annual Meeting in Denver, Colorado, USA

LIU, Chang¹, CLIFT, Peter², CARTER, Andrew³, BONING, Philipp⁴, HU, Zhaochu⁵, SUN, Zhen⁶ and PAHNKE, Katherina⁴, (1)Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, (2)Department of Geology and Geophysics, Louisiana State University, E235 Howe-Russell-Kniffen Geoscience Complex, Baton Rouge, LA 70803, (3)Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London, WC1E 75x, United Kingdom, (4)Max-Planck Research Group for Marine Isotope Geochemistry, ICBM, University of Oldenburg, University of Oldenburg, Oldenburg, 26129, Germany, (5)State Key Laboratory of Geological Processes and Mineral Resources, China Geosciences University, Wuhan, Wuhan, 430074, China, (6)Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China, cliu14@lsu.edu

The Pearl River and its tributaries drain large areas of southern China and has been the primary source of sediment to the northern continental margin of the South China Sea since its opening. Tributaries of the Pearl River flow majorly from three directions, West, East and North. In this study, we use a combination of bulk sediment geochemistry, Nd and Sr isotope geochemistry, and single grain zircon U-Pb dating to understand the source of sediment in the modern drainage and its delivery pattern, as well as the source of sediment to the rift during the Eocene, as sampled by International Ocean Discovery Program (IODP) Expedition 349. A combination of Nd and Sr isotopes show that the Gui, Liu (Rivers from North) and Dong Rivers (River from East) are likely not important sediment sources. Single grain zircon U-Pb dating emphasize the importance of the westernmost tributaries, draining the highest topography and tectonically active areas as the primary sediment producers, namely the Hongshui and Yu Rivers, while also demonstrate the least sediment contribution from Gui and Liu River. Our data also indicate that climate is not the primary control on erosion patterns and intensities during the sedimentary delivery. Discrepancies between this new data and earlier samples make the role of the Dong River hard to determine, with its Nd isotopes suggest that it is not dominant, while zircon U-Pb data composition supporting its importance. The source of sediment during the Eocene at IODP Site U1435 appears to have been a relatively local basement source, or a regionally restricted river only draining nearby areas of the Cathaysia Block, similar in composition with the modern Dong River. Based on the Kernel Density Estimation plots, there is no evidence for a large regional river and we exclude sediment transport from the southwest, from Indochina as proposed by previous studies. Our data are consistent with the idea of small drainage systems dominating the basin until the end of the Oligocene (~24 Ma), after which the Pearl River expanded towards its modern state as a result of headwater capture largely towards the West.

GSA Annual Meeting in Denver, Colorado, USA - 2016

CONTROLS ON MODERN EROSION AND THE DEVELOPMENT OF THE PEARL RIVER BASIN SINCE THE EOCENE