Abstract:

Tertiary basins in Eastern China are mostly consisted of half-grabens,each of them can be subdivided into three tectonic zones,i.e.escarpment,deep sub-sidence and shallow slope.Along the slope,there are many faults varying in strikes and dips,formed at different times.Normal faults which dip antithetic to the basement(Pre-Tertiary)surface are often accompanied by draping structures,other swhich dip in the same direction as the basement are commonly accompanied by reverse drag structures.Up dip of the slope,sediments in the basin become progressively thin,with overlap,offlap and unconformity quite developed.Sand bodies often pinch out in various directions toward argillaceous rocks.In res-ponse to the not deeply buried basements connected with antithetic normal faults as shown in Fig.1 of this paper,stair-faulted blocks were formed,and inevitablly,structural,stratigraphic-lithologic traps are well developed along slope zones constituting an important oil and gas zone.Ten types of oil/gas pools are revealed,they are related to reverse drag structures,drape structures,faulted blocks,stratigraphic overlaps,stratigraphic uncomformities,buried hills,updip pinch-out of sandstones,fault-truncated sandstones,sandstone lens and proper carbonates.Types and enrichment of petroleum depend mainly on features of the slope.They are divided into three types according to their sedimentary blanket andtimes of formation,namely:稤epositional slope,the slope status of its basement exists prior to its suc-cessively overlapping sedimentary blanket.稴tructural slope,the tilting of its basement occurred after the sedimentation of its blanket,the thickness of the later is therefore almost uniform.稴edimento-structural slope,the basement surface tilted originally,but the filting strengthens gradually during the sedimentation of its blanket,within the later,onlap,offlap and erosion surfaces are common. Among them,the latter is of greater importance and possesses most of pool-types.