STRUCTURAL STYLE AND ITS RELATION TO HYDROCARBON EXPLORATION IN THE SONGLIAO BASIN, NORTHEAST CHINA

The Songliao basin in northeast China is a Mesozoic rift basin charact erized by Mesozoic and Cenozoic hydrocarbon systems. The Songliao basi n was initiated by southeast-to-northwest lithospheric extension durin g the late Jurassic. The extensional phase was dominated by two fault sets, (1) 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 pha se occurred during the early Qingshankou (early Albian, 100 to 97 Ma). Faults that occur in the Quantou Formation and the Qingshankou Format ion are growth faults (T-2 faults), which trend mostly NNW, and occur predominantly at the sites of basement faults, and structural bend zon es (located between sag and uplift), and basement uplifts. The basin b roadly subsided during the Denglouku-Quantou (Aptian, 125 to 100 Ma) a nd 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 th e Songliao basin. These are classified into two types: positive invers ion structures controlled by reactivation of early normal faults, and inversion structures not controlled by earlier faults. The major exten sional structures exerted a range of controls on both sedimentation an d deformation during the subsequent phases of basin evolution. Two the rmotectonic rifting events during the late Jurassic and early Qingshan kou play a major role in organic matter thermal evolution. The timing of formation of structural traps in the basin matches that of hydrocar bon generation and migration. Structural traps formed during late Jura ssic, early Qingshankou, and late Cretaceous to Paleocene (73 to 56 Ma ). Late Jurassic organic-rich source rock reached its peak oil generat ion from the time of deposition of Member Deng 3,4 of the Denglouku Fo rmation (119 to 116 Ma) to that of Member Qing 1 of the Qingshankou Fo rmation (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 Form ation to that of the upper Yi'an Formation and from the time of deposi tion of the Taikang Formation to that of deposition of the Quarternary , respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.