鄂东南地区早三叠世中晚期沉积相和沉积古地理

鄂东南地区早三叠世大冶群为一套以碳酸岩为主的地层。在发育较全的阳新龙港新屋铺剖面可以划分出10个岩性段。本文着重探讨早三叠世中、晚期的沉积相特征。早三叠世鄂东南地区为下扬子海域的一部分,推测早三叠世早期奉区与赣西北为统一的开放海,可能与分隔华北和扬子大陆的秦岭-大别山海域相连。沉积物以深水盆地相和陆棚相泥质页岩和灰岩为主,夹风暴成因的砾屑灰岩和重力流成因的碎屑灰岩。早三叠世中期,大别山、九岭山古陆成为局限盆地,发育潮坪、渴湖、障壁丘和鲕粒滩;晚期因周期性的海平面变化导致形成局限浅水盆地、蒸发岩沉积和深水盆地泥岩和重力流沉积。这些变化与Haq等人(1988)提出的全球海平面变化曲线相吻合。

MIDDLE AND LATE EARLY TRIASSIC SEDIMENTARY FACIES AND PALAEOGEOGRAPHY IN SOUTHEASTERN HUBEI

The Lower Triassic Daye Group dominated by the carbonate strata in southeastern Hubei may be divided into 10 lithologic members in the Xinwupu section, Yangxin County. The present paper gives an interpretation of the characteristics of the middle and late Early Triassic sedimentary facies. It is inferred that the southeastern Hubei-northern Jiangxi area was a part of the Lower Yangtze sea area during Early Triassic, and a northward open shelf sea which might be linked with the Qinling-Dabieshan sea area in the early stage of Early Triassic. The deposits here are dominated by the deep-water basin facies and shelf facies muddy shales and limestones intercalated with calcirudite of storm origin and elastic limestones of gravity-flow origin. In the middle stage, the Dabieshan and Jiulingshan palaeocontinents were uplifted and became a restricted basin in which tidal flats, lagoons, barrier mounds and oolitic shoals were developed. Till the late stage, the periodic sea-level changes resulted in the formation of the evaporite deposits in restricted shallow-water basin and mudstones and gravity-flow deposits in deep-water basins. These changes coincide with the global sea-level curves proposed by Haq et al.(1988).