Paleogene-Neogene filling sequences and sedimentary environments in the Gunan sag, Shengli Oil Field, Shandong

The Gunan sag is a Cenezoic secondary depression within the Zhanhua sag of the Jiyang depression. The differences of the boundary faulting resulted in the formation of a half graben-like morphology of the sag, which is overlapped in the north and faulted in the south. The polyphase tectonic activities once gave rise to the polystage uplifting, erosion and subsidence of the lake basin. The Paleogene-Neogene filling sequences may be divided into four structural sequences that correspond to four tectonic episodes in the study area. The depositional systems consist of fluvial, fan delta, delta and lacustrine systems. The sediments within the Gunan sag are generally controlled by syndepositional tectonism and provenances.