Structural style and its relation to hydrocarbon exploration in the Songliao basin, northeast China

Abstract

The Songliao basin in northeast China is a Mesozoic rift basin characterized by Mesozoic and Cenozoic hydrocarbon systems. The Songliao basin was initiated by southeast-to-northwest lithospheric extension during the late Jurassic. The extensional phase was dominated by two fault sets, (l) shallow to moderately dipping normal faults, and (2) steeply dipping transfer faults. The extensional structures are characterized by half-grabens. A second short extensional tectonic overprinting phase occurred during the early Qingshankou (early Albian, 100 to 97 Ma). Faults that occur in the Quantou Formation and the Qingshankou Formation are growth faults (T 2 faults), which trend mostly NNW, and occur predominantly at the sites of basement faults, and structural bend zones (located between sag and uplift), and basement uplifts. The basin broadly subsided during the Denglouku-Quantou (Aptian, 125 to 100 Ma) and the late Qingshankou (late Albian, 97 to 94 Ma) to Yaojia-Nenjiang (Cenomanian to Campanian 94 to 73 Ma), respectively. Positive inverted structures developed during the late Cretaceous to the Cenozoic in the Songliao basin. These are classified into two types: positive inversion structures controlled by reactivation of early normal faults, and inversion structures not controlled by earlier faults. The major extensional structures exerted a range of controls on both sedimentation and deformation during the subsequent phases of basin evolution. Two thermotectonic rifting events during the late Jurassic and early Qingshankou play a major role in organic matter thermal evolution. The timing of formation of structural traps in the basin matches that of hydrocarbon generation and migration. Structural traps formed during late Jurassic, early Qingshankou, and late Cretaceous to Paleocene (73 to 56 Ma). Late Jurassic organic-rich source rock reached its peak oil generation from the time of deposition of Member Deng 3,4 of the Denglouku Formation (119 to 116 Ma) to that of Member Qing 1 of the Qingshankou Formation (100 to 97 Ma). Qing 1 of the Qingshankou Formation and Nen 1 of the Nenjiang Formation organic-rich source rocks reached their peak oil generation from the time of deposition of the upper Mingshui Formation to that of the upper Yi'an Formation and from the time of deposition of the Taikang Formation to that of deposition of the Quarternary, respectively.