The Permian high-frequency sequence stratigraphy in western Shandong

The Permian strata in the western Shandong are composed of epicontinental and terrestrial deposits. There are four kinds of depositional systems: tidal flat, barrier-lagoon, river-controlled shallow water delta and lacustrine composite depositional systems. The high-frequency sequences are identified on the basis of recognition of the event surfaces caused by high-frequency sea level changes, and events represented by peat swamping, flooding, extensive erosion and exposure pedogenesis. The third-, fourth- and fifth-order sequences have been identified in the Permian of the western Shandong coalfields. The cyclic changes of the accommodation space caused by episodic tectonic subsidence in the continental lacustrine basin play principal controls on the development of these sequences. The periodicity of the spreading and withering of lake water is closely related to the Milankovitch periods.