SEDIMENTARY CHARACTERISTICS AND EVOLUTION OF A MIDDLE AND LATE DEVONIAN INTERPLATFORM BASIN IN SOUTHERN HUNAN

The Devonian strata are the first cover deposited posterior to the Caledonian movement in southern Hunan Province where the Middle and Upper Devonian strata are characterized by the prevailing carbonate rocks and variable sedim entary facies types and palaeogeographic features. By means of rock types, textures and structures and biologic assemblages, four sedimentary facies types are recognized, platform facies, interplatform basin facies, platform-margin slope facies and elastic tidal-flat facies, the former three of whic are dealt with in this paper.
The Lingshan-Hengyang interplatform basin, a NE-trending linear strike-slip basin, is a special basin which was developed on a shallow-water carbonate platform, and may be divided into two parts: the Lingshan-Hexian portion controlled by the strike-slip faults and the southern Hunan portion as a tensional-rifted basin. Five stages are identified for the formation and evolution of the interplatform basin. (1) The initial marine basin stage—the Early Devonian to the early Middle Devonian; (2) The primary stage of the interplatform basin differentiation—the late Middle Devonian (the early Qiziqiaoian); (3) The shrinking stage-of the interplatform basin—the late Middle Devonian (the late Qiziqiaoian); (4) The expanding stage of the interplatform basin—the early Late Devonian (the Shetianqiaoian), and (5) The closing-filling stage of the interplatform basin—the late Late Devonian (the Xikuangshanian).