高密度流与湖南泥盆纪沉积相分异

SEDIMENTARY FACIES DIFFERENTIATION RELATED TO HIGH-DENSITY FLOW DURING DEVONIAN IN HUNAN

湖南泥盆纪陆表海的沉积相分异 ,尤其是台地相和台盆相的分异与当时发育的高密度流有密切的关系 ,高密度流的流动和沉积又与地形及海侵海退有关。高密度流使台盆区形成与相邻的台地区完全不同的沉积 ,形成的沉积差异反过来又使海底地形发生进一步的变化。在这种反复作用的过程中 ,湖南泥盆纪的岩相分异经历了一个形成、发展。

The Devonian Sea in Hunan was an epicontinental sea, with several interplatform basins, extending from SSW to NNE, sandwiched in the platforms. The high density flows from the Mufu Oldland could run easily into the concave areas, since the paleocurrent was just parallel the relief trending. In the Early Qiziqiao Period, the terrigenous materials in the high density flows decreased with the transgression. The sands carried by the high density flows deposited in the areas surrounding the oldlands, and the argillaceous materials were carried farther and deposited in the interplatform basins. Carbonates deposited mostly on the platforms, where various benthic organisms flourished and formed some biostromes. Sometimes the high density flows covered on the convex areas and argillaceous sediments deposited. In the Middle Qiziqiao Period, the terrigenous materials in the high density flows decreased continuously. The deposits decreased in the interplatform basins, but the carbonate deposits increased very quickly on the platforms. The relief differentiation of the sea bottom became larger and lager. The relief controlled the sedimentation, and the sedimentation, in turn, laid an important role in the reformation of the relief, which accelerated the facies differentiation. The Late Qiziqiao Period was a time of the largest transgression. Small amount of argillaceous materials, carried by the high density flows, deposited in the interplatform basins. The interplatform basin facies was characterized with argillaceous and siliceous sediments formed in a stagnant environment. The platform facies was featured by various carbonate deposits with considerable thickness. Reefs formed along the margins of the carbonate platforms, resulting in the differentiation of sedimentary facies further. The regression enlarged rapidly in the Late Shetienchiao Period. Great quantities of terrigenous materials were carried into the interplatform basins by the high density flows, so as to fill the interplatform basins gradually. In the Xikuangshan (Hsikuangshan) Period, the high density underflows occurred on the even sea floor, which stopped the differentiation of the platform facies and interplatform basin facies.