Vertically

the Ordovician in Tarim basin can be divided into 2 supersequence groups

which can be further divided into 5 supersequences and 18 third-order sequences.Laterally

from west to east

the Ordovician deposits transit successively from platform facies to slope and basin facies

and the development of stratigraphic sequences appear to be progressive progradation resulting in the downlapping of a series of prograded sequences onto a relatively large downlapping surface.Sequence boundaries of various orders have important control on the development of Ordovician carbonate reservoirs in Tarim basin.The transient exposure caused by the third-order sequence boundaries and the synchronous diagenesis would have facilitated the modification of reef-bank facies reservoirs on the edge of the platform corresponding the large unconformities

which correspond to the sequence boundaries of higher levels might be the key factors that have controlled the development of the Ordovician carbonate karstic reservoirs in Tarim basin.