Sequence stratigraphy and depositional systems in the Caohu depression, Tarim Basin, Xinjiang

The Jurassic strata in the Caohu depression, Tarim Basin, Xinjiang are divided, on the basis of well logs and regional tectonic evolution, into two third-order sequences J-SQ1 and J-SQ2. During the deposition of J-SQ1 sequences, the climates were warm and humid. The sequence displays the complete rising-falling semicyclic deposits. Till the deposition of J-SQ2 sequences, the climates turned into hot and semiarid ones. The sequences display only the rising semicyclic deposits, and consists of oxidized lacustrine depositional systems in which the littoral-shallow lacustrine sand-mud beach deposits are developed. The braided channel sandstones in J-SQ1 sequences are believed to be the favourable reservoir rocks in the study area due to tremendous thickness, better physical properties and moderate to thick overlying lacustrine mudstone.