The Cretaceous Stratum:Pedogenesis Recognition And Paleoenvironmental Analysis, In Shicheng Basin, Jiangxi Province

The Danxia red beds widely distribute in China. It has long been considered to be formed in the environment of rivers and lakes, and the red Color are secondary. Here we work on the Cretaceous red beds HYC, GYY and JSC in Shicheng basin in middle of Wuyi Mountain. The features of mixed thick gravel and fine sand poor sorting and uncontinuous stratification at the HYC, suggest that it develops in semi-arid diluvium deposition basin. GYY and JSC profile are Compose of red fine silt clay with homogeneous structure and calcium layer. Such alluvial material accumulation indicates the profiles form in a semi-arid environment and are away from the mountain pass and near the center of the basin.The calcium plates or calcium layers is proved to be the result of leach and deposit from overlying fine-grained clay layer; Micromorphology images conformed the existence of pedogenesis characteristics, such as root marks suggesting from drab haloes and illuviation argillans, red clay and colloid development along pore wall and secondary calcite; The 2?m-63?m grain size component occupies 65.25%, which is similar to that of Quaternary or Neogene loess-paleosol; Elements analysis shows different degrees of element enrichment and losses. In section JSC, The mean value of Chemical index of alteration(CIA) are 72.59, it is stronger than that of the Quaternary loess in Luochuan and Neogene red clay at Xifeng. The chemical and physical features of the clay layer in Shicheng Cretaceous red beds are similar to that of the Quaternary paleosols and Neogene red clay on the Chinese Loess Plateau, it enable us to suggest that red clay in Shicheng is very likely to be red paleosol. Futhermore, we reconstruct the annual paleo-precipitation for the Shicheng red-beds deposition using four independent methods, each profile are different, JSC profile roughly 530mm, HYC profile should be between 530-800mm, the mean value of GYY profile is between 585-865mm can be referenced.After magnetic measure, we found that Hematite is the main ferromagnetic minerals, the correlation between Fe2O3 content and a* of JSC section samples present Positive, means that hematite controls its red color. Chondrite-normalized REE concentrations for representative samples in Shicheng red beds profile are between Quaternary loess and the south river sediments, negative anomaly of Eu in Shicheng showed abnormal behavior, as it assume the bivalent being migrated, means Shicheng red layer form more humid than the northern loess. Synthesize the experimental results, it is speculated that the Cretaceous red beds were results of long term oxidation in low latitude when the planetary wind system driven by uplift of Tibetan plateau was not yet formed. The bedding and cross-bedding are formed due to temporary water flow, while the red color of ferric iron oxides was formed in long term arid oxidation environments.