Chapter 7.3 - Tectonic geomorphology and depositional pattern of the Paleozoic central uplift belt in the Tarim Basin

Abstract

The central paleouplift belt in the Tarim Basin was a sizable composite paleouplift and paleoslope belt with complex paleogeomorphic characteristics during the Middle to early Late Ordovician. It was inclined eastward and comprised the Hetianhe, Hetianhedong, Tazhong, and Bachu paleouplifts. The paleouplift belt and its surroundings have been found to contain a number of paleostructural geomorphic features, including high uplift belts, faulted uplift platforms, marginal slopes and slope break zones, surrounding shelf slopes or low relief ramps, shelf slope break zones, and deep basin plains. The uplift belt's flanking marginal slopes and slope break zones restricted the production and deposition of high-energy facies during the Late Ordovician. The southeastern margin of the basin was severely compressed and raised around the end of the Ordovician, causing the Tazhong paleouplift to hinge westward and transform into a snout that dips westward. The tectono-paleogeomorphic framework of the central northern basin during the Early Silurian and the Late Devonian to Early Carboniferous changed remarkably in topography from the initial low in east and high in west to high in northeast and low in southwest. The lowstand sandstones and the early transgressive systems tracts were deposited along the slope of uplift edges, and the gentle ramps formed high yield reservoirs in the basin. The study has shown that the distribution mode of unconformities of the basin are closely related to the characteristics of paleogeomorphic and evolution of the paleo-uplift. The truncated and onlap triangular unconformity belts formed along the slope of the uplift, and are the preferred areas to form stratigraphic trap oil and gas reservoirs.