Deep-water sediments and evolution of the Lower Triassic Xikou Formation in southwestern Fujian, China

The Lower Triassic Xikou Formation in southwestern Fujian, China is a set o f complex deep-water sediments' which includes turbidites, sandy contourite s and isolated olistoliths. Five facies and seven subfacies are recognized in the deep-water turbidites, which are considered to belong to five facies associations of upper, middle and lower fans, respectively. The sandy cont ourites, which occur within turbidites as isolated thin layers with structu res of traction current, are formed by reworking turbidites. They occur in discrete units, not as a part of a vertical sequence of structures, such as Bouma sequence. Paleocurrent directions derived from sandy contourites are perpendicular to or at a large angle of those derived from turbidites. In some areas, within the Formation there exist large oolitic limestone blocks slided from shallow sea. The temporal-spatial distribution of three types of sediments mentioned above and the related evidences could indicate that a passive continental margin from shallow sea to bathyal-abyssal region, di pping toward southeast, once occurred in study area during the early Triass ic. The early Triassic represents a period of sealevel uprising. The uprisi ng of sea level and the development of isolated olistoliths probably imply gradual shrinking of an ocean basin at that time.