| Mixed-siliciclastic-carbonate sediments and "Source-to-sink" system are two relatively independent research fields developed in recent 20 years.The study of mixed sediments mainly focuses on the lithofacies classification,the description of sedimentaryreservoir-diagenetic characteristics,and the analysis of main controlling factors in typical mixed sediments developed areas in sedimentary basins.It mainly focuses on the case anatomy and the summary of phenomena,and focuses on the analysis of microscopic reservoir structure and diagenesis,with little consideration of macroscopic factors.Moreover,the genesis of mixed sediments is jointly controlled by terrigenous clastic and carbonate forming elements,and the specific genetic mechanism is affected by complex factors such as tectonic background,sedimentary environment,provenance,paleoclimate,etc.,so that the study on the genetic mechanism of mixed sediments has not formed an analytical thinking and process from macroscopic "source-sink" to microscopic "reservoir-diagenesis" integration.However,the "source-to-sink" system is closely related to the development of mixed sediments,and macro "source-sink" factors such as the type of parent rock,tectonic background and sedimentary facies all play an important role in controlling the development of mixed sediments.Therefore,the study of mixed sediments is very suitable to be included in the "source-to-sink" system.This paper mainly focuses on the characteristics and coupling relationship of "source-sink-diagenesis-reservoir" of Paleogene mixed sediments in Huanghekou Sag of Bohai Bay Basin.The Bohai Bay Basin is by far the most developed mixed sedimentation area in China,and unique mixed-siliciclastic-carbonate deposition has been found in many tectonic zones,including the Huanghekou Sag.This paper is mainly guided by sequence stratigraphy,"Source-to-sink" system,seismic geomorphology,reservoir geology,with the help of 3-D seismic data,drilling/well logging,core,thin sections,element geochemistry data,to carry out the study on the characteristics of "Source-tosink" system in the Paleogene sedimentary period and the recovery of lithologypaleogeomorphology in the Huanghekou sag,and systematically analyze the sedimentological,petrologic and geochemical characteristics of different mixed sediments in study area.The main achievements and understandings of the thesis are as follows:(1)The lithological characteristics of the parent rocks in different periods of the Paleogene Shahejie formation in Bonan low uplift were restored.During the sedimentary period of the Shahejie-3 Formation,the southern part of the western branch of the Bonan low uplift was dominated by the Archaean metamorphic granite,the western part of the eastern branch of the uplift was dominated by the Archaean metamorphic granite,the Paleozoic carbonate rock,the Mesozoic igneous rock and the conglomerate of the Kongdian formation.The eastern part of the eastern branch was dominated by the Archaean metamorphic granite.The distribution of parent rocks in the second period of Shahejie formation was inherited from the third period,and the area of metamorphic rocks in the west branch was enlarged,while the area of igneous rocks in the east branch was decreased.In the first period,the exposed area of the metamorphic rocks of the west branch continued to expand,while the exposed area of the carbonate rocks in the east branch expanded.(2)The technique and method of paleogeomorphology restoration have been established,and the paleogeomorphology restoration has been completed for different periods of Paleogene Bonan low uplift.The technical process of paleogeomorphology restoration mainly includes four steps: obtaining the thickness data of the present residual strata,systematically division and parameter statistics of the “Source-sink” system,recovering the denudation amount of strata,and reconstructing the paleogeomorphology.Based on the identification,characterization and parameter statistics of the "denudation zone","overstripping zone" and "sedimentary zone" of the eastern and western branches of the Bonan low uplift,the paleogeomorphology restoration of the uplift in different periods of the Paleogene system was completed.The results showed that the maximum height difference of the eastern branch of Bonan low uplift was continuously larger than that of the western branch,and the denudation range of the eastern branch and the western branch was continuously reduced and the maximum height difference was continuously reduced during the deposition period from Shahejie-3 to Shahejie-1 formation.(3)The plan distribution of typical mixed rocks in the first and second period of the Shahejie formation in Huanghekou depression is described.The seismic reflection characteristics of the mixed rocks in the Paleogene period of Huanghekou sag are mainly characterized by moderate to high amplitude,moderate-high frequency and moderate-high continuous reflection,which are obviously different from those of the surrounding strata.The results show that the large-scale fan delta system in the south of Bonan low uplift was distributed in the second period of Shahejie formation,the mixed beach was only locally developed,and the overall scale was small.During the first period,the fan delta was smaller than the second period,and was the peak period for the development of mixed beach,and large-scale mixed sediments were developed in several parts in the south of Bonan low uplift.(4)The reservoir characteristics of typical mixed rock development area in Huanghekou sag were analyzed.Calcareous cementation sandstone and glutenite with thin layers of bioclastic dolostone are developed in the structural areas of BZ27-2 and BZ29-4,while calcareous cementation sandstone and bioclastic dolostone are vertically interbedded in the structural areas of BZ36-2.Secondary pores,such as the inner pores of living debris grains,mold holes and cementite dissolution pores,are the main pore structure types developed in the mixed rock.The overall reservoir physical property of BZ36-2 zone is greater than BZ29-4 zone than BZ27-2 zone.The reservoir quality of bioclastic dolostone is better than that of calcareous cementation sandstone,glutenite and other terrigenous dominated mixed reservoirs.(5)The main diagenetic processes affecting the physical properties of mixed rock reservoirs was summarized.The diagenetic characteristics and mechanisms of calcareous compaction cementation,dolomitization and dissolution have been identified.Based on the observation of petrography and the analysis of the diagenesis product characteristics,it is concluded that there have been two cementation processes(destructive diagenesis)and two dissolution processes(constructive diagenesis)in the study area.(6)The typical sequence of the mixed rock and the "multi-stage cyclicity" sedimentary sequence in the BZ36-2 structural area were established.Based on the Bouma series in turbidite,the typical sequence of lacustrine mixed rock was established,which consists of five strata(A-E)with fine lithology from bottom to top.The systematic division of the sedimentary sequence in the BZ36-2 structural area was completed,and it was divided into two long-term cycles.Among them,long-term cycle 1 included three moderate-term cycles,and some short-term cycles could be subdivided within the moderate-term cycles.The long-term,moderate-term and short-term cycles controlling factors are the change of sediment supply pattern,the difference of terrigenous detrital supply intensity,and the periodic cessation of terrigenous supply,respectively.(7)The controlling effects of the sub-systems of "source","sink" and "diagenesis" on "reservoir" were summarized,and two coupling models of "exogenous injection type" and "endogenous interaction type" were established.Influenced by the strong supply of terrigenous detritus and the of calcareous compact cementation,the "exogenous injection type" coupling model of the mixed rocks develops shallow-water bioclastic shoals for a short time,and the overall reservoir is relatively compact.The "endogenous interaction type" coupling model is weakly affected by the sedimentation of terrigenous debris and calcareous cementation,and the shallow-water bioclastic shoals develop on a large scale for relatively long period,and the whole reservoir is in good condition after several stages of dissolution. |
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