Analysis On Sedimentary Characteristics And Its Tectonic Environment Of The Hetaoyuan Formation In Nanyang Sag

This paper analyses the sedimentary facies of Hetaoyuan Formation in Xidagang outcrop by geological section, microcop image analysis and grain size analysis. That the strata are mainly braided delta and lake sediments. Also found that contact interface between E2h22 and E2h21 is sedimentary environment abrupt interface, under this interface is delta deposits, upper this interface sediment transform to deep lake - semi-deep lake deposits. It is showed significant "jump-phase"phenomenon. By X-diffraction and trace element analysis, we found there is so much sedimentary pyrite within the contact interface. These studies suggest that the contact interface between E2h22 and E2h21 is breakup unconformity. Maybe that is the result of strong extension of NE-trend Quwa fault, which caused mutations in depositional environment of up and down interface. The breakup unconformity is the physical performance of this sedimentary and tectonic environmental change.We analyse the sedimentray facies distribution and its development features of Hetaoyuan Formation in Nanyang sag, on the basis of the above analysis,the sedimentary facies analysis of drillings and previous research results. The strata are mainly delta and lake sediments.The sedimentary center is located in the central despression belt of Nanyang sag, in which Niusanmen subprime sag and Dongzhuang subprime sag develop. The above two subprime sags develop deep lake facies. The broad northern slope zone of sag develops river-flood plain facies. There are three large deltas (Shayan delta, Jinhua and Zhangdian deltas) in northern margin of sag. There are many small fan deltas in southern margin of sag. The sedimentary center happened west-to-east migration along with evolution of sedimentary basin.Throng the research of fault activity and sedimentary environment analysis, we find associated systems of extensional fault control the deposition of Hetaoyuan Formation in Nanyang sag. The above breakup unconformity is caused by Quwa fault extensional transition, which is the performance of extensional transition of associated systems of extensional fault. Thus it can be seen that breakup unconformity is the physical performance and geological evidence of this extensional transition in Nanyang sag.According to sedimentary featurs and fault activity featurs of other sags in Nanxiang basin, this study deems the sedimentation of Hetaoyuan Formation and its hydrocarbon source rock are mainly controled by associated systems of extensional fault which is composed by Quwa fault and Xinye fault.