贵州瓮安地区上震旦统碳同位素特征

Late Triassic—Middle Jurassic strata and their sedimentary environments of Jingzhou area,Hubei

贵州瓮安磷矿上震旦统碳同位素组成显示，δ１３Ｃ值在垂向地层序列中的变化有明显的规律性。陡山沱组底部白云岩δ１３Ｃ为负值，向上碳同位素值发生显著正飘移，然后，除在陡山沱组中部δ１３Ｃ值有所下降外，δ１３Ｃ值基本上保持在＋２‰左右，一直持续到灯影组。瓮安地区上震旦统碳同位素剖面表现出与湖北峡东及世界其它地区同期碳同位素剖面极大的相似性，显示它们反映了末元古代海水碳同位素值的长期变化趋势。

The characteristics of the Late Triassic—Middle Jurassic strata suggest that the Jingzhou area was a foreland basin which was formed in the foreland south of the Qinling Orogenic Belt. The sedimentary features and the contact relationships show that they are a Ⅰ grade sequence. Based on different graded beddings and formations, the Triassic and Jurassic strata can be divided into two Ⅱ grade sequences, composed of three and seven Ⅲ grade sequences respectively. The studies of the stratigraphic sequences and sedimentary features in this area suggest that the Jinzhou foreland Basin underwent three evolutional stages, namely, the flexural deformation (T 3j), the viscoelastic deformation (T 3w) and later foreland basin evolution (J 1-2 ). The subsidence center and forebulge of the foreland basin are of longitudinal migration, the scale and subsidence range of the basin indicate a regular transforms in different stages.