Sequence-Tectonics-Paleo-geomorphology Features Of Paleogen And Their Constraints Relationship In The East Of Liaohe Beach Area

The beach area of Liaohe Oilfield locates in the northern part of Liaohe-Liaodong bay basin. It is the continental fault depression which formed under an extensional, strike-slip background during the Mesozoic-Cenozoic period, and it is the transition zone between the Liaohe depression and Liaodong bay. In order to systematically analyze the features and the controlling factors of the continental fault depression’s sequence stratigraphy, the thesis applied the analytical method of sequence stratigraphy, structural geology, sedimentology and three-dimensional geomorphological modeling technology. This paper systematically analyzed the sequence stratigraphic characteristics, structural features and paleo-geomorphology of the Palaeogene stratum in the eastern region of the beach area of Liaohe Oilfield, indicated that the episodic tectonic activities have led to the change of the basin and its adjacent area’s paleo-geomorphology, and controlled the development of sedimentary sequences and the formation and distribution features of favorable sand.Paleogene in the east of Liaohe beach area experienced episodic rifting, which can be divided into four intensive stages of tectonic evolution: the stage of extensional rifting, the stage of the first post-rifting thermal subsidence, the stage of strike-slip extensional re-rifting and the stage of rift convergence. Influenced by different activities of main basement control-basin faults, the basin tectonic characteristics in stage of extensional rifting from south to north presented as follows: a half graben with down faulting at the eastern boundary and overlapping at the western boundary-a half graben with own faulting at the western boundary and onlapping at the eastern boundary - double fault with graben; the characteristics in stage of first post-rifting thermal subsidence presented with double fault with graben; the characteristics in stage of strike-slip extensional re-rifting and rift convergence integrative presented with depression except for local rifting activities.Based on core, drilling, logging , palaeophyte data and 3D seismic, in the east of Liaohe beach area, two first-order sequence boundaries, two second-order sequence boundaries and six third-order sequences boundaries were identified in Paleogene, so the paleogene system could be divided into nine third-order sequences(SQ1～SQ9). The research of the sequence -tectonic framework in the whole area shows that two rifting sedimentary filling sequence cycles developed, controlled by episodic rift. The characteristics of them were different with sedimentary centre and subsidence center migration regularly. Horizontally, the developing characteristics were different between sequences in different periods and different structural position. Vertically, the basin developed 2 large sets of lake flooding of SQ1 and SQ5, which formed the orderly superposition of different sequences.By adopting the comprehensive methods of qualitative analysis on 3D seismic materials, the timing sequence stratigraphic framework, the tectonic evolution, quantitative analysis on palaeothickness and visualization mapping of 3D geomorphological modeling, the thesis recovers the 3D paleo-geomorphology map of nine third-order sequences in sequence stratigraphic framework of Paleogene in eastern beach area of Liaohe, and analyses the paleo-geomorphology characteristic and evolution history of every period. The systematic analysis of constraints relationship between sequence stratigraphy, tectonics, and paleo-geomorphology indicates that the characteristics of tectonic movement in different tectonic evolutional stage in eastern beach area of Liaohe controlled the assemble types of paleo-geomorphology units in each period, and controlled the development of sedimentary sequence and the formation and distribution of sedimentary systems. According to the characters of tectonic movements, we established the sedimentary sequence pattern under the various ancient paleo-geomorphology background in different tectonic epochs. Through the detailed anatomy of the sequence structure, stacking pattern and stratigraphic features of ancient paleo-geomorphology in key areas, we concluded that the distribution of favorable sand was controlled by palaeo-geomorphic characteristics in the plane and vertically controlled by systems tract, and most of favorable sand develop in lowstand systems tract.