Early Cretaceous Sedimentary Filling,Structural Style And Evolution Of The Tonghua-Liuhe Basin

Basin filling sequences are sedimentary responses to structural style and tectonic evolution of basins,especially in specific sequences with event deposition.These sedimentary records of volcanic events and earthquakes can be used as one of the important means of sedimentary basin analysis.The purpose of this thesis is to study the oil and gas exploration layer of the Early Cretaceous TonghuaLiuhe Basin in southern Jilin Province based on cores,field outcrops,well logging and seismic profile.We focused on the problems about peperite and seismite in perspective of the volcanism-induced sedimentation and seismically-induced sedimentation,and analyzed the characteristics of sequence stratigraphy and sedimentary fillings in the Hengtongshan Formation of the Tonghua Basin and the Yingzuilazi Formation of the Liuhe Basin in order to illucidate the formation mechanism,controls of tectonic activities on sedimentary filling and evolution of the Tonghua-Liuhe Basin in different periods through the integrated analysis of basin structural style,dominant facies and successions of peperite and seismite.This study can provide reference for oil and gas exploration and basin research in areas of southern Jilin province.The following achievements and conclusions have been achieved through this study:(1)The featured volcanism-induced sedimentation and peperite were developed in the Hengtongshan Formation of the Tonghua Basin.Using the methods of observation of cores and outcrops and identification and counting of components,three types of lithology and 12 kinds of lithofacies were distinguished based on the pyroclastic content and sedimentary structure.The lithofacies related to volcanism consist of lava rocks and pyroclastic rocks.In the lava rocks,there are four kinds of lithofacies including rhyolite with fluidal structure,rhyolite with massive structure,andesite with convex-concave boundary and andesite with massive structure,which are named as typical peperite.In the pyroclastic rocks,there are five kinds of lithofacies including tuff breccia-tuff with welded texture,tuff breccia-tuff with scour-graded bedding,tuff breccia-tuff with hummocky and trough cross bedding,tuffaceous sandstone with hummocky and trough cross bedding and tuffaceous sandstone and tuff with wavy and parallel bedding,which are named as peperite sensu lato or mixedsediment rocks.In addition,there are three lithofacies associated with weathering including pebbly sandstone with scour-graded bedding,sandstone with graded,parallel,and wavy bedding and sandstone or pebbly sandstone with cross bedding and reverse graded bedding.These twelve kinds of lithofacies with genetic significance were used to constitute nine kinds of successions which can reflect specific sedimentary environment,and the spatial distribution of these lithofacies associations and successions exhibited a mixed model of source to sink system.(2)The seismically-induced sedimentation and seismite were developed in the Yingzuilazi Formation of the Liuhe Basin.Through the obversion of structures in cores and outcrops,three types of seismite and nine kinds of seismogenic structures were identified based on the development stage and morphological characteristics.The first type is the syn-depositional structure,which is divided into two kinds according to the layered structure,namely debris flow and turbidity current flow.The second type is penecontemporaneous deformation structure,which is divided into four kinds according to the morphological features,namely sand dyke structure,flame structure,ball-pillow and pillow structure and pseudomass structure.The third type is post-sedimentary structure,which is divided into three kinds according to the deformation degree,namely fold structure,microfracture structure,fault structure and seismic parabreccia.These nine earthquake-related structures with genetic significance reflect the tectonic-sedimentary succession from autochthonous seismite to allopatric-accumulated seismite,and there is a tectonic interface between the two lithofacies.(3)The Hengtongshan Formation were divided into three sequences based on the lithofacies association,abrupt changes on logging curves and cyclic variations of the pyroclastic content.In S1 stage,the architecture of well T4 is composed of fine-coarse-coarse beds with dominant facies of andesitic mixed subaqueous fan;the dominant facies in well T2 is weathered epiclastic fan deltasubaqueous fan;the architecture of well T1 is characterized by coarse-fine-coarse beds with dominant facies of rhyolitic mixed subaqueous fan.In S2 stage,the architecture of well T4 is composed of alternating fine-coarse beds with dominant facies of andesitic mixed fan delta-subaqueous fan;the architecture of well T2 is composed of alternating fine-coarse beds with dominant facies of rhyolitic mixed subaqueous fan;the architecture of well T1 is characterized by coarse-fine-coarse beds with dominant facies of weathered epiclastic subaqueous fan.In S3 stage,the architecture of well T4 is composed of fine-coarse-coarse beds with dominant facies of weathered epiclastic subaqueous fan;the architecture of well T2 is composed of fine-coarse beds with dominant facies of rhyolitic mixed subaqueous fan;the architecture of well T1 is characterized by fine-coarse beds with dominant facies of rhyolitic mixed subaqueous fan.(4)The upper member of the Yingzuilazi Formation were divided into two sequences based on the association of seismite,abrupt changes on logging curves and stratigraphic architectures of the seismic profile.In S3 stage,the dominant facies shows the alternation of the fan delta and the subaqueous fan along F4.The architecture of well L2 is characterized by alternating fine-coarse beds with dominant facies of subaqueous fan,and the architecture of well L1 which is located in F5 is characterized by coarse-fine-coarse beds with dominant facies of subaqueous fan.In S3 stage,the dominant facies migrated along the F4,but still presented the alternating characteristics of fan delta and subaqueous fan.The architecture of well L2 is characterized by alternating fine-coarse beds with dominant facies of fan delta front,and the architecture of well L1 which is located in F5 is characterized by coarse-fine-coarse beds with dominant facies of fan delta front.(5)Based on the analysis of the structural style of the Tonghua-Liuhe Basin,migration of the dominant facies and architecture of the sequences,we concluded that the different volcanicsedimentary sequences,multiple filling architectures and lotus basin structure developed in the Tonghua Basin are the result of wrench tectonics,while the migrated dominant facies,multiple filling architectures and flower structure developed in the Liuhe Basin are the result of strike-slip extension(transtension).The Liuhe Basin and the Tonghua Basin exhibit a basin combination constituted of the narrow and the rhomboid-shaped basins,indicating that this basin group is controlled by the strikeslipping and associated wrench mechanism in the large fault system.(6)Considering the influence of strike-slipping and associated wrenching on basin tectonic evolution and sedimentation and the evaluation of source rocks and reservoirs in the Tonghua-Liuhe Basin,it is considered that the Tonghua Basin has two favorable hydrocarbon traps,namely well T2 area and well T1 area,which are fault-block type oil reservoirs.In the Liuhe Basin,there is a favorable hydrocarbon trap in Xiangyang depression,which may have shale gas reservoir.