Carbonate platform-margin architecture and its influence on Cambrian-Ordovician reef-shoal development, Tarim Basin, NW China

Abstract

Six types of carbonate platform marginal slope have been identified in the Cambrian-Ordovician of Tarim Basin. These include a progradational carbonate ramp platform, a progradational carbonate rimmed platform, an aggradational rimmed carbonate platform, a retrogradational rimmed carbonate platform, an aggradational margin on an isolated carbonate platform and a retrogradational margin on a submerged carbonate platform. Various platform margin architectures and reef-shoal characteristics occur in different areas of the Tarim basin. A progradational carbonate ramp platform margin began in the Early Cambrian in the Tarim basin. A progradational rimmed platform margin developed in the Middle Cambrian time in the northern Tarim basin, whereas contemporaneously a progradational ramp platform margin developed in the southwestern and central Tarim basin. A retrogradational rimmed carbonate platform developed in the northern Tarim basin, whereas an aggradational rimmed carbonate platform occupied the central Tarim basin in the Early Ordovician time. An aggradational margin on an isolated platform and a retrogradational margin on a submerged platform developed mainly during the Late Ordovician in the central Tarim basin. Platform margin-slopes migrated continually throughout the Cambro-Ordovician. The broad platform area (western Tarim Platform) that occupied most of the northwestern and central Tarim Basin in the Early Cambrian time was split by an east-west oriented shelf seaway that began to develop along the eastern and western margins of the platform in the Early Ordovician time and completely transected the platform by Late Ordovician time. The resultant central Tarim Basin platform area was much reduced, elongate east-west around the Central Tarim paleo-uplift, and terminated eastward towards region of the Late Ordovician basinal deposition across the eastern Tarim Basin. Affected by platform margin structure, Climate and paleodepth, algal reefs and shoals developed mainly in the Cambrian, and intraclastic shoals developed mainly in the Early Ordovician, followed by reef-building of framestone or bafflestone in the Late Ordovician.