Contrasting Nature of Petroliferous Mesozoic-Cenozoic Basins in Eastern and Western China

Abstract

Onshore petroliferous basins of Mesozoic-Cenozoic age in China include two distinct geographic-geotectonic groups: eastern extensional (rifted) basins and western compressional (orogenic) basins. Eastern basins are faulted depressions and crustal sags that formed where incipient intracontinental rifting thinned the crust and developed tilted fault blocks and half grabens bounded by normal faults. Western basins are flexural downbows that were depressed under the tectonic load of adjacent thrust sheets associated with the folded mountain ranges of central Asia. Source beds in both groups of basins are dominantly dark lacustrine mudstones of terrestrial facies associations, and reservoirs are mainly fluviodeltaic sandstones. Hydrocarbon traps in the eastern basins include e tensional rollover anticlines, compactional drape anticlines, diapiric salt domes, buried-hill highs in the substratum, and stratal pinch-outs on the flanks of buried highs. Simple or faulted anticlinal traps are dominant in the western basins. Multiple reservoir horizons are characteristic of oil fields in both groups of basins. Orogenic compression, which developed the western basins, is attributed to the successive collision of microcontinents with the southern edge of the composite Eurasian continental mass. Crustal extension, which developed the eastern basins, is attributed to incipient rifting within and behind magmatic arcs along the margin of the Pacific Ocean basin.