DETRITAL ZIRCON GEOCHRONOLOGIC CONSTRAINTS ON INTRA- AND EXTRABASINAL SEDIMENT SOURCES, PALEOGENE PEARL RIVER MOUTH BASIN, NORTHERN SOUTH CHINA SEA

A major challenge in provenance and source-to-sink analysis is deciphering local versus regional sediment sources and influences. This issue is well-exemplified by the Paleogene Pearl River Mouth Basin (PRMB), South China Sea, whose provenance reflects a combination of sediments eroded from the Cathaysia Block, southeastern China, and from intrabasinal structural highs. Here we report 428 new concordant detrital zircon U-Pb ages from the Enping and Zhuhai formations, acquired from seven deep boreholes in the Baiyun sag, southern PRMB. We also compile published detrital zircon U-Pb ages from major rivers across the Cathaysia Block, to better understand spatial differences in sediment source regions and the influence of drainage systems on provenance. Detrital zircons from the upper Eocene-lower Oligocene Enping Formation are dominated by Mesozoic ages, with a 125-110 Ma age-group, absent in the modern river data, that may be diagnostic of intrabasinal sediment sources. In the northern part of the basin, the zircon age spectra show increasing numbers of Paleozoic and Precambrian grains, a pattern also recognized for late Oligocene Zhuhai Formation samples, suggesting a major change in provenance likely related to sediment transport from the Cathaysia Block. Spatial analysis of the results suggests that during deposition of the Enping Formation, long-distance sediment transport was not uniform and that the basin’s architecture strongly influenced provenance. Structural highs within the PRMB acted as both sediment sources and barrier to sediment transport from the Cathaysia Block; whereas structural lows, with clear extrabasinal influence, functioned as corridors for sediment transport. Such spatial differences are lost in samples from the Zhuhai Formation and their provenance suggests that the paleo-Pearl River and processes in the Cathaysia Block likely dominated deposition thereafter.