Study on Characteristics of Lower Ordovician Contour Current Deposits in Yuanguping, Northern Hunan, China

Key words: 
• contourite types /
• contourite sequence /
• Yuanguping region /
• Lower Ordovician /
• Panjiazui Formation

Abstract: By measuring and describing the section in detail, it comes to a discovery that the Lower Ordovician Panjiazui Formation in Yuanguping area is composed of deep-water carbonate rocks. The rocks are mainly gray micrite, calcarenite and bioclastic limestone. Three types of sediments are developed, namely, vertical landing sediments, gravity flow sediments and contourites. According to lithological characters, the contourites are divided into three types. They are respectively calcilutitic contourite, calcarenitic contourite, and bioclastic contourite. Among them, calcilutitic contourite is well developed, followed by calcarenitic contourite and bioclastic contourite. The development characteristics and the vertical sequences are summarized. Our study shows that there are three types of incomplete contourite sequences in the study area, namely, a single calcilutitic contourite sequence, a calcilutitic-calcarenitic contourite sequence, and a bioclastic-calcarenitic contourite sequence. In the section, the Panjiazui Formation is divided into three parts according to the type and extent of development. From PartⅠ to Part Ⅲ, the proportion of contourite thickness tends to increase. Considering the regional sedimentary background, the contour current strength of this area varied from weak to strong during the sedimentary period of Early Ordovician Panjiazui Formation on the whole, which should form in the mature period of the contourites, so it is significant to study the formation mechanism of this contourites and to define its distribution range.