Jiyang Depression Tertiary Geological Structure Features

Based on study of structural geometry and kinetic features of Jiyangdepression, the paper reconstructed its evolutional history. Jiyang Tertiarysedimentary basin was a north-east extending down-faulted basin which wasdeveloped on a basement with north-west compressing structural layer andnorth-west striking negative reverse half-graben. The basement structural layerfirstly experienced compressing during pre-Jurassic and caused the forming ofthrust faulted belt. The north-west extending positive structural beltsexperienced weather and corrosion during early and middle Jurassic. Negative reverse action happened to the thrusted faulted belt during Yanshanian, andMesozoic north-west striking half-graben appeared. The sedimentary period ofKongdian Formation was a transform period and the main deposition centerand subsidence center was located in Huimin and Dongying sags while somesmall sags were scattered in the north part of Jiyang depression. Afterdeposition of the fourth member of Shahejie Formation (Es4) the structurepattern were featured by north-east spreading half-graben and resulted in manynorth-easting striking fault system. At the end of Himalayan period localcompressing of Dongying movement caused the forming of positive reversestructures. Jiyang depression experienced entirely downwarping movementduring late Tertiary. Therefore, there were many kinds of structural trapscontrolled by compressing movement, tensile movement and composite of theboth. The positive reverse structure provided a new kind of trap forexploration. Tensile extension movement caused many slop-plateau faults andassociated rollover anticlines were the most important trap type. Cutted bynorth-east striking Tertiary faults the lower structural layer and basement layerin north-west spreading negative reverse structure could connected withCenozoic oil resource, and forming buried hill reservoir with Cenozoicresource and Paleozoic reservoir bed. This kind of buried hill reservoir isprofitable targets to increase reserves and production.