Du Yuansheng

Characteristics of Devonian sedimentary facies in the Qinling mountains and their tectono-palaeogeographic significance

Abstract Both eastern and western Qinling can be divided into three belts, north, middle and south, based on studies in recent years of the sedimentary facies characteristics, palaeogeographic environments, provenance directions, palaeontologic distributions and geologic event comparisons. Whereas the north belt mainly represents a deep flysch basin on the southern edge of the North China massif, the south belt belongs to the shallow shelf sea on the northern edge of the Yangzi massif. In the middle belt, the Devonian has clear characteristics of a palaeo-island sedimentary system, with a low diversity in coral fauna and some special Upper Devonian geologic events. It represents a micromassif which has been separated from the Yangzi but not yet aggregated to the North China massif. Although the North China and the Yangzi massifs had already had their initial collision during the Caledonian stage, they did not actually converge together to form an unified continent.

Sequence Stratigraphic Delineation and Correlation of the Dongying Formation in the Nearshore and Adjacent Sea Areas, Bohai Bay Basin

Abstract Based on the analysis of well logs, seismic data, core studies, the Dongying () Formation along the nearshore and adjacent sea areas, Bohai () Bay basin has been subdivided into three third-order sequences from base to top: namely, sequences SQ1, SQ2 and SQ3. The three sequences have different wireline (SP) log responses, showing triple-section characteristics with SQ1 being characterized by primarily flat baseline with intercalation of relatively low spontaneous potential, SQ2 generally exhibiting weak or moderate amplitude spontaneous potential with finger-shaped peaks, and SQ3 having relatively high spontaneous potential with funnel-shaped log curves. On the basis of the triple-section characteristics, the stratigraphic sequences can be correlated consistently throughout the entire study area. A stratigraphic and sedimentary model for sequences SQ1 to SQ3 of the Dongying Formation in the study area has been proposed. The accommodation space change in the two sides of the asymmetrical basin was examined and the asymmetrical basin has the feature of the asymmetrical accommodation space change. The asymmetrical physiography is a vital factor to influence the accommodation changes in additional to the lake level change, tectonism and sediment supply. This may have important implications to similar basins in other parts of China or elsewhere.

Geochemistry of the Late Paleozoic cherts in the Youjiang Basin: Implications for the basin evolution

Abstract We analyzed the major and rare earth element compositions of siliceous deposits from the Upper Devonian Liujiang Formation, Lower Carboniferous Luzhai Formation, Lower–Middle Permian Sidazhai Formation and Tapi Formation, which are widely distributed as bedded cherts in the interplatform basinal successions of the Youjiang Basin. The Liujiang Formation and Luzhai Formation cherts generally have high Al/(Al+Fe+Mn) values (0.38–0.94) and are non-hydrothermal cherts. These cherts are generally characterized by moderately negative Ce anomalies and high Y/Ho values relatived to PAAS, indicating that the Youjiang Basin might have evolved into an open rift basin during the Late Devonian–Early Carboniferous. The Sidazhai Formation cherts from Ziyun generally have high Al/(Al+Fe+Mn) values (0.60–0.78), suggesting negligible contribution from a hydrothermal component. The Sidazhai Formation cherts from Hechi and the Tapi Formation cherts from Malipo generally have low Al/(Al+Fe+Mn) values (0.09–0.41), indicating an intense hydrothermal input. Relatived to the Sidazhai Formation cherts, the Tapi Formation cherts have higher Ce/Ce* values (0.68±0.19) and lower Y/Ho values (41.83±13.27), which may be affected by the terrigenous input from the Vietnam Block. The Sidazhai Formation cherts from Ziyun and Hechi exhibit negative Ce anomalies (0.43±0.12, 0.33±0.17, respectively) with high Y/Ho values (57.44±16.20, 46.02±4.27, respectively), resembling the geochemical characteristics of open-ocean basin cherts. These cherts were deposited on a passive continental margin adjacent to the Babu branch ocean, which may have contributed to upwelling. Detailed spatial studies on geochemical characteristics of the Late Paleozoic cherts can unravel the evolution of the Youjiang Basin.