Abstract:

Sanchahe area,Luodian County,Guizhou Province,was in the northern margin of Guizhou-Guangxi Sea Basin and to the south of the Bangen atoll during Ladinic stage.A series of beautiful turbidites with distinct rhythm was deposited there,containing small amount of ammonites,Pelecypoda and other organic clastics.These sediments are now described as the Jiangdonggou Forma-tion,which have following characteristics:1.The rhythmic bedding is quite distinct and the Bouma cycle can be clearly distinguished with B,C,D,and E intervals being hingly developed.Among other things,the D-E and B-E sequences are more common.2.Various kinds of underside casts,such as flute casts,groove casts and load casts were developed there.The paleocurrent direction can be determined by the flute or groove casts ranging 268-297°.3.Major component of these sediments is feldspar,and then quartz.The argillaceous material occupies 3-35%,while the calcite matrix (cement) is 1.5-30%.Therefore,the sediments belong in feldsparthic sandstone.The round-ness of particles is poor and grain size are usually more than 4φ.4.As for parameters of grain-size,the average diameter (Mz) of particles isof 4.073φ,belonging to silt size;the standard deviation (σ₁) is of 0.738,indica-ting middle degree of sorting;the mean skewness (SK_I) is of-0.0002,expressing approximate symmetry;the average value of kurtosis (Kg) is 0.9369,showing approximately normal distribution;the average discriminant score (Y) of envi-ronment (river or turbidity flow) is of 7.6725,representing turbidity current.5.In aspect of graphic feature,straight line and simple brokenline are reproduced on probability diagram of grain size with low slope ranging from 32° to 64°,suggesting mainly a graded suspension transport,but a small amount of saltation transport may have taken place.CM diagram shows parallel C=M spacing.According to sedimentary sequence,underside casts,grain-size and graphic feature,it is Presumed that the Jiangdonggou Formation was the distal facies of turbidity current far from its provenance.