湘南晚泥盆世佘田桥期碳酸盐块状流沉积特征

CHARACTERISTICS OF THE LATE DEVONIAN SHETIANQIAO STAGE CARBONATE MASS—FLOW IN SOUTHERN HUNAN

湘南晚泥盆世佘田桥期表现为东西两侧高而中部低陷的古地理面貌。两侧为碳酸盐台地,中间为深水台盆。在台盆、台地之间斜坡地带和台盆边缘,堆积了类型繁多的碳酸盐块状流沉积物。它们由两类在成因和分布上有密切联系的沉积体系组成,一类为重力崩落或滑移体系,包括岩崩、滑动和滑塌沉积,另一类为重力流体系,包括碎屑流、浊流和颗粒流沉积。在层序上它们虽作有规律的组合层序,但并不是完整的类型,而出现较大的变异性。已发现的组合层序有①滑塌沉积—碎屑流沉积,②碎屑流—高密度浊流—低密度浊流沉积,③变密度颗粒流—浊流沉积。它们沿近南北向的台盆的两侧边缘呈条带状分布,东侧位于临武香花岭至桂阳莲塘一带,重力流厚度可达150m左右,西侧位于道县虎岩坝至双牌县城一带,重力流厚只30—50m,反映了台盆边缘两侧构造活动强度不一致,东侧强,西侧弱。

The southern Hunan area in Shetianqiao stage of Late Devonian shows a paleogeographical feature which is high in both east and west sides and lowering down in the middle. The both sides are carbonate platform, while the middle part shows a deepwater interplatform basin. Various kinds of carbonate mass-flow deposits accumulated along the slope zone between the platform and the interplatfrom basin and in the edge of the interplatform basin. They are composed of two sets of sedimentation that are closely connected in the origin and distribution, one of which is gravitational collapse or gliding system, including rockfalls, sliding and collapse deposits; the other is gravity-flow system, including debris-flow, turbidityflow and grain-flow deposits. Although they show regular assemblage sequence in the stratigraphic order, they are not complete assemblage type, while considerable variation occurs. The already-discovered assemblage sequences are:①Collapsedebris flow deposit, ②Debris flow-high density turbidty flow-low density turbidity flow deposit, ③Varying density grain flow-turbidity flow deposit. They distribute zonally along the both side margins of the near meridional interplatform basin. From Xianghualing of Lingwu county to Liantang of Guiyang county along the east side, the thickness of gravity flow deposit reaches about 150m; from Fuyanba of Douxian county to Shuangpai county town along the west side, only 30—50m thick. These reflect the difference in the intensity of tectonic activity between the both sides of the interplatform basin, which is strong in the east side, and weak in the west side.