The Yankou Formation in the Upper Ordovician of Tonglu County in Zhejiang Province consists mainly of rhythmically thin alternating layers of gray fine|grained sandstones, siltstones and dark|gray mudstones, silty mudstones, in which the typical flaser, wavy, lenticular bedding and rhythmic stratification are well
developed, with 2~3 intercalated beds of gray medium| to thick|bedded conglomerates in the base of the formation. In the past, these conglomerates and the overlapping rhythmically thin alternating layers of sandstones and mudstones had been considered as basal conglomerates and typical ancient tide|flat deposits respectively. The results of geological work in the field and study of regional geological data show that the sedimentary environment of the Yankou Formation should be deep|water slope rather than shallow|water seastrand. The conglomerates of the formation should be matrix|rich debris|flow deposits, and the rhythmically thin alternating layers of sandstones and mudstones should be internal|tide deposits developed on a deep|water slope. These internal|tide deposits have typical and symmetrical graded|couplet succession which may be related to the periodical changes of Neap|Spring tidal dynamics. This internal|tide deposits is the first example of ancient internal|tide deposits found in China. ;
. PETROLOGICAL CHARACTERISTICS AND SEDIMENTARY ENVIRONMENT OF THE YANKOU FORMATIONINTHE UPPER ORDOVICIAN AT TONGLU AREA IN ZHEJIANG PROVINCE[J]. JOPC, 1999, 1(3): 65-72.