Tectonic Responses of Triassic Sequence Stratigraphy in the Large-Scale Compressional Down-Warped Lacustrine Basin of Inner Tarim Basin

As the regional stress field transferred from extension to compression in the Triassic, a large-scale down-warped lacustrine basin developed in the interior Tarim basin. According to seismic sequence interpretation, four third-order sequences were identified in the Triassic. Both top and bottom surfaces of the Triassic were regional truncation unconformities. Besides a few terminal types of truncate, up-lap and incised valley, top-lap was the widespread mark of sequence boundary. Furthermore, sequences correlations among wells reveals that sequences were very special in depositional evolutions as follows: in their lake-expanding systems tracts, large-scale braided river deltas had usually developed with coarse sediment and thick sandbodies; contrarily, in their high-stand systems tracts, the deltas were small with much finer sediments. Presumedly, stratigraphic sequences were dominated by episodic compressive tectonism, which gradually intensified and then weakened. Responding to violently compressive action in lake-expanding systems tracts, the lithosphere had flexed and as a result the basin rapidly expanded; on the other hand, the surrounding forebulges and orogenic belts had intensely uplifted, and the sediment supplies had been largely accelerated so that it exceeded the accommodation increment which caused that the braided river deltas had extensively developed.