Architecture and paleogeography of the Early Paleozoic carbonate systems in the east-central Tarim Basin (China): Constraints from seismic and well data

The evolution of the Cambrian-Middle Ordovician carbonate systems in the east-central Tarim Basin, northwestern China, has been investigated using 2D seismic profiles and well data. Interpretation was performed on seismic profiles flattened along an originally horizontal surface (base of the Cambrian), to remove the effects of post-depositional deformations. Six seismic facies differently arranged in six seismic stratigraphic units record four major stages of architectural evolution, from ramp to flat-topped systems, with differences from north to south: (1) the onset of a homoclinal ramp over a clayey unit at the beginning of Early Cambrian; (2) the development of a prograding carbonate platform characterized by restricted (evaporitic) facies in the inner platform domain during Early Cambrian to Late Cambrian; (3) the development of a first prograding and a aggrading (retrograding to the north) platform during Lower Ordovician; (4) the development of a prograding/retrograding to aggrading final platform during Middle Ordovician. The basinward (eastward) progradation of the carbonate platform edge has been reconstructed in time steps, highlighting differences from the north to the south of the study area in terms of amount of progradation, platform-to-basin relief and depositional surfaces, likely controlled by differences in subsidence and environmental factors. The identification of the four major stages in the evolution of the lower Paleozoic succession of the Tarim Basin was likely controlled by changes in the rate of creation/destruction of accommodation space, due to the interplay between eustatic changes and tectonic events. The demise of the Cambrian to Middle Ordovician carbonate system in the study area is associated with a major tectonic event, recorded by a tilting of the succession toward the east (onlapped by sediments coming from the east) and an uplift (bulge) of the western part of the study area.