The Study Of Sequence Stratigraphy And Tidal Sedimentary Systems Of Jiaozhou Bay

The sequence stratigraphy and tidal sedimentary systems is mainly discussed in Jiaozhou Bay area.Based on the analysis of geological and geophysical data in 2003-2004 of Jiaozhou Bay, The sequence stratigraphical model in shore area is formed. The items including the method of identifying the sequence stratigraphy boundary and tracts boundary, the different tracts of sequence, and the various facies of each tract and tidal depositional systems in high sea level system tract are discussed respectively. It is valuable in establishing the depositional systems at similarity bay environment.Firstly, the sea-level changes of study area is mentioned after comparing the sea-level changes in Qingdao area with it in global and climate changes in Qingdao area since LGM. The change can be divided into three periods within 15 ka B.P. â…¢:slowly to rapidly uprising period from15 to 10 ka B.P.. The sea water reached Jiaozhou Bay area gradually. â…¡: slowly wavy climbing period from 10 to 5.5 ka B.P.. The basin was in transgress and sea water upraised maximum level. â… : high sea level period since 5.5 ka B.P..It is very important to identify the sequence boundary. In the studied area, the bottom surface of sequence is an continental-oceanic unconformity surface, it's a transgressive surface also. The top surface is water-sedimentation surface.The method of seeking the boundary (TS and MFS) between system tracts is worked out by studies on the lithology, micropaleontological assemblage characteristics and mineral assemblage of core QDD03. First Transgressive Surface always presents coarse sandy lithology with enriched shell fragments and low abundance of microfossil. Differently, the Maximum Flood Surface characters with fine muddy lithology and high abundance of microfossil.The sequence stratigraphy frame and model is formed based on the core and shallow stratigraphy profile data. There is only one stratigraphy sequence in IiaozhouBay which includes High Sea Level System Tract (HST) and Transgressive System Tract (TST). Fluvial facies and eluvium beneath TS are sedimentation in the continental basin within undepositional interrupted period. The depth of TST is less than 1-2.5 m. Transgression boundary layer (TBL) is much thicker or even missed somewhere. The sedimentary facies in TST include TBL, tidal channel fill, ancient offshore coarse deposition and MFS. The reflected character of TST in profile is parallel or onlap reflection.The lithology of surface sediment can be divided into six main types. Coarse sandy sediment mainly distributes in tidal channel, flood and ebb tidal delta, and river mouth of Dagu-Yanghe delta. Sub-tidal area is fine muddy sediment on the whole because of the weak hydrodynamism. According to the analysis of distribution characteristics of surface sediment, the tidal sedimentary systems in Jiaozhou Bay and offshore of Qingdao is established. The sedimentary environment of studied area can be divided into two main types: one is Dagu-Yanghe tidal-rive complex delta, another is barrier -island depositional environment. Further more , it can be divided into nine sub-environments.The facies in barrier -island depositional environment include tidal channel, flood tidal delta and sand ridge, ebb tidal delta and sand ridge, subtidal sedimentation. It has no barrier-island facies because the inlet of Jiaozhou Bay is surrounded by the rock and it can't swing. There is rock or relict sediment in the main channel and eroded quaternary at the edge of the main tidal. The swing of branch channel bring into fine upward sediment cycle.The outstanding sedimentary body on flood and ebb tidal delta is linear sand ridges at the rim of tidal channel, there are Dagu sand ridge, Center sand ridge and Cangkou sand ridge on the flood tidal delta. Dagu sand ridge between Yanghe channel and Dagu river is a well sorted sand resource. The Center sand ridge is moribund sand ridge covering with fine sediment on the top. Cangkou sand ridge is the biggest one which is almost 16 km long and well sorted also. The North sand ridge and South sand ridge and Dazhu sand ridge are developed on the ebb tidal delta. All of these ridge are well sorted and sand reservoir. The South sand ridge has been mined on thesneak. The movement of North sand ridge is landward.Dagu-Yanghe delta depositional system is discussed . The system includes five sub-environment facies: lower delta plain tidal flat, delta front sand bar, distal bar, interdistributory bay, and pro-delta . Interdistributory bay is located between Dagu river and Yanghe river channel, the sediment is poor sorted sand-silt-clay with organic belt and shell. The bio- disturbance strcture is popular. The river mouth bar is well sorted pure fine sand and full of shell fragment but lack of organism, distal bar is lcated in the front of sand bar, the lithology is silt and clayey silt with bio- disturbance strcture. The formation of Dagu-Yanghe delta is in the high sea level period and later than the formation of sand ridge.