Provenance Analyses of Lower Cretaceous Strata in the Liupanshan Basin: From Paleocurrents Indicators, Conglomerate Clast Compositions, and Zircon U-Pb Geochronology

The Liupanshan Basin constitutes a major portion of the northern North-South tectonic belt. The Lower Cretaceous strata in the Liupanshan Basin recorded the tectono-sedimentary evolution processes of this area and are pivotal for understanding the original sedimentary appearance of the Liupanshan Basin. In this work, we present a study of provenance and tectono-sedimentary evolution of the Liupanshan Basin during the Early Cretaceous. Integrated-paleocurrent directions, gravel clast compositions, and detrital zircon U-Pb isotopic analysis of the Lower Cretaceous Sanqiao and Heshangpu formations were applied to determine the provenance. The gravel clast compositions of Sanqiao Formation conglomerates(mainly including magmatic rocks, metamorphic rocks and limestones) display various features in different places, revealing different rock components of source areas. The paleocurrent directions of the Sanqiao and Heshangpu formations suggest that the sediments were transported from the basin margin to the center. Detrital zircons of two samples from the Huoshizhai Section(northwestern Liupanshan Basin) yield a dominant unimodal distribution from 420 to 500 Ma, suggesting a single-sourced provenance. Based on the above analyses, comparing to the magmatic records in the Qilian-Qinling orogenic belt, the detritus of the Sanqiao and Heshangpu formations were mainly from the proximal metamorphic and magmatic rocks of the Qilian-Qinling orogenic belt and the limestones of the archaic uplift. Combined with sedimentary characteristics, we concluded that the Liupanshan Basin experienced multi-stage evolution history:(1) the early rifting extension stage(Sanqiao Period),(2) the middle spanning and depression stage(Heshangpu–Early Naijiahe Period), and(3) the late extinction stage(Late Naijiahe Period). The evolution of Liupanshan Basin is closely related to that of Ordos Basin and it is further associated with tectonic transition of the northern North-South tectonic belt.

Major and trace element geochemistry of the mid-Bay of Bengal surface sediments: implications for provenance

The major and trace elements in 110 surface sediment samples collected from the middle of the Bay of Bengal（mid-Bay of Bengal） are analyzed to investigate provenance. Si levels are highest, followed by Al, and the distributions of these two elements are identical. The average CIA＊（chemical index of alteration） value is 72.07,indicating that the degree of weathering of the sediments in the study area is intermediate between those of sediments of the Himalayan and Indian rivers. Factor analyses and discrimination function analyses imply that the two main provenances are the Himalayan and the Indian continent. The inverse model calculation of the Tinormalized element ratios of the Bay of Bengal sediments indicate an estimated average contribution of 83.5%and 16.5% from the Himalayan and peninsular Indian rivers to the study area, respectively. The Himalayan source contributes more sediment to the eastern part of the study area, whereas the western part receives more sediment from the Indian Peninsula than did the eastern part. The primary mechanisms for deposition of sediments in the study area are the transport of Himalayan matter by turbidity currents and river-diluted water and the transport of Indian matter to the study area by a surface circulation in the Bay of Bengal, particularly the East India Coastal Current.

Evolution of the Pearl River and its Implication for East Asian Continental Landscape Reversion

As the link connecting the South China Continent and the northern South China Sea(SCS),the Pearl River is the focus of sedimentology and petroleum geology research.Its evolutionary process and controlling factors are of great significance in revealing the East Asian continental landscape reorganization during the Late Cenozoic.Based on published data,’source-to-sink’provenance analyses allow systematic deliberation on the birth and evolutionary history of the Pearl River.Close to the Oligocene/Miocene boundary,an abrupt shift in the sedimentary composition indicates significant westward and northward expansion of the river’s watershed area,followed by the establishment of a near-modern fluvial network.This sedimentary change generally concurred with a series of regional geological events,including the onset of the Yangtze throughflow,large-scale development of the loess plateau,and formation of the northwestern arid zone and Asian Monsoon system.These major changes in the geology-climate-ecoenvironment system are in close response to the process of the Cenozoic Xizang(Tibetan)Plateau uplift.Consequently,the East Asian continental landscape and most of midCenozoic drainage systems underwent critical reversion into east-tilting,or east-flowing networks.