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Paleoenvironmental Reconstruction and Sequence Stratigraphic Analysis Using Element Geochemical Analysis in Pear River Mouth Basin, South China Sea


Geochemical data is not commonly used in the reconstruction of ancient depositional environment because a lot of valuable information may be lost during the laboratary chemical analysis. Here we present one case study of paleoenvironmental reconstruction and sequence stratigraphic analysis using primarily element geochemical analysis in the Pear River Mouth Basin, China. Forty-three mudstone samples and 37 carbonate samples from 10 wells of Tertiary Zhuhai Formation (paleogene) to Hanjiang formation (Neogene) of Pearl River Mouth Basin have been tested for C, O isotopic and other geochemical analysis. The results show that the paleoclimate became more arid from Zhuhai stage to Hanjiang stage of this area, and the palaeosalinity increased from Zhuhai to Hanjiang formation. Paleoenvironment in Zhuhai stage is mainly oxidized, but became reductive during Zhujiang and Hanjiang stages. The paleosalinity increased during early and then decreased at the late stage of Zhujiang period. The paleotemperature of sea water was between 18–24degree Celsius, varied in the same tendency as the paleosalinity of this area. The paleo-sea level rised and then falled from the early to the late during this period. The paleosalinity, the paleotemperature, and the paleo-sea level reached to their highest value at the time of NSQ3 during Zhujiang period. The values of 1000×Sr/Ca, V/Cr, 100×(MgO/Al2O3), Sr/Ba, CIA, and MgO/CaO reveal that the water depth, the paleosalinity of the sea, and the paleoclimate of the source areas are variable at different parts of the basin. The paleoenvironmental condition changed from oxidizd during Zhuhai period to reductive during the period of Zhujiang and Hanjiang. Elemental Fe and Al tend to be rich on the sequence boundaries and are mainly oxidized in northern Baiyun Depression of the Basin. The ratio of Th/U is high and the ratio of Sr/Ca is low. The values of Th/U, Cr/V, Co/Ni, Sr/Ba and δ(Ce) increased gradually during the sea-level lowstnad (LST) and decreased gradually during transgression (TST), reaching their minimum at the maximum flooding surface and then gradually increased during the sea-level highstand (HST). The values of Mn/Fe, Mn/Ti, Sr/Ca, ∑REE, and (La/Ce)N decreased gradually during the sea-level lowstand (LST) and increased gradually during transgression (TST), reaching their maximum at the maximum flooding surface and then decreased gradually during the sea-level highstand (HST).