Characteristics Of Source-to-sink Systems Of Depression-sinking Sequence In The Guantao Formation Of The Bodong Area,Bohai Basin

The Guantao Formation in the Bodong area is a favorable experimental area for studing the source-to-sink system of the depression type.Based on the established of the third-order sequence stratigraphic framework of the Guantao Formation,the paper choses the “source-to-sink” system as the main line in the different sedimentary periods of the Guantao Formation,and clarifies the characteristics of the source supply and sedimental channels in different periods.Sedimentary systems and sedimentary filling and evolution characteristics in different periods were also established.By comparing with the source-to-sink system of the Erhai fault basin,the model of the depression-type sequence source-to-sink system was established.The main results obtained in this paper as followings:(1)Based on the east and west branches of the strike-slip faults,the Bodong area are divided into three parts: the extension section control area A,the strike-slip-hold zone B and the stable deep zone C.In the lower section of the Guantao Formation,the internal and external of basin are jointly supplied.The A zone mainly develops braided river sediments,and in the B zone,it is converted into a small braided river delta deposit,which accumulates along the point of the slope,and there are multiple sedimentary centers in the C zone.And the peripheral sand is relatively developed.In the middle section of the Guantao Formation,the internal supplies in the basin are weakened,and are mainly based on the supplies outside the basin.The sedimentary range of the river in the A area is significantly reduced,and it is transformed into the meandering river type.The B area mainly develops the shallow water delta phase,and isthere are multiple sedimentary centers in the C area.In the upper section of the Guantao Formation,the internal and external of basin are jointly supplied,the A zone develops the meandering river sediment,the shallow zone delta sedimentary system of the B zone advances to the basin center,and the shallow water delta of the Jiaoliao uplift belt advances toward the center,and the sedimentary systems exist on both sides.A certain degree of convergence,the mat sand is more developed.(2)The fault-sinking sequence source-to-sink system generally has two types: fracture steep slope type and fault gentle slope type,especially the fault steep slope type is typical.It has the characteristics of “small source,short path and large deposition”,while the depression-type sequence source-to-sink system has the characteristics of “large source,long path and large sediment”.Among them,“source” mainly refers to the relative size of the basin area;“path” mainly refers to the relative size and length of the source transport channel(water system),and the “deposition” mainly refers to the relative size of the sediment area in the sedimentary area.(3)The depression-type lake basin is very easy to develop the interaction system between rivers and lakes in the shallow water background.According to the difference of terrain and water level,it is divided into three parts from the edge of the basin to the center: Area A(river control main area)on the exposed water,Area B(river and lake interaction area)between the flood line and the dry line and the dry In the C area(the main body area of the lake)below the waterline,the various areas show regular changes during different depositional periods,and the model of the source-to-sink system of the depression-type sequence is established.