The short-term base-level cyclic sequences in the Xujiahe and Penglaizhen Formations in the southern part of western Sichuan depression

The short-term base-level cyclic sequences in the Xujiahe Formation-Pengliazhen Formation in the southern part of western Sichuan depression are separated, according to the criteria for the recognition of the short-term base-level cyclic boundaries, into two types:"deepening"-upward asymmetrical (A type)and deepening-and then shallowingupward symmetrical (C type)types, and five subtypes according to the sizes of accommodation spaces and thickness of upper and lower semicycles:"deepening"-upward asymmetrical (A₁ type)of low accommodation spaces; "deepening"-upward asymmetrical (A₂ type)of high accommodation spaces; rising semicycle-dominated incompletely symmetrical type (C₁ type); nearly completely to completely symmetrical type (C₂ type), and falling semicycle-dominated incompletely symmetrical type (C₃ type).