Framework And Evolution Of Cambrian Sedimentary Sequence In Tangshan Area And Ajacent Region

Based on the theories of sedimentology and sequence stratigraphy and combined with regional stratigraphic data,a comprehensive analysis is built in this paper to divide the Cambrian third-order sequences and establish the sequence stratigraphic framework in Tangshan area and ajacent region,the study of the analysis contains the field outcrops of the Zhaogezhuang section in Tangshan and the Xiaweidian section in Western Hills of Beijing as the main line,coupled with rock sections,carbon and oxygen isotopic data at Xiaweidian in Western Hills of Beijing,drilling cores of thirteen wells and logging data of thirty-six wells.Furthermore,it is convenient to analysis the sedimentary facies,sedimentary system and the evolution of sedimentary environment within the stratigraphic framework.Acquired some conclusions as follow:1.The Cambrian in the study area can be divided into six third-order sequences.the top surface boundary of SQI belongs to Type ? sequence boundary,the one of SQ4 belongs to Type ? sequence boundary,whereas others are all type ? sequence boundary.2.The Cambrian lithostratigraphic formations of thirty-six wells in Nanpu Sag are redivided according to the field outcrop,logging data of natural gamma and resistivity,the characteristics of logging lithology,drilling cores and rock sections.The natural gamma can be divided three types:? low--high--low(subtidal deposi-tion);?high--low(subtidal deposition);?low--high(intertiedal deposition-supratidal deposition).Meanwhile the layer division of twenty-nine wells in Nanpu Sag has been adjusted to the sedimentary cycles.3.Comparing the Cambrian third-sequences in the study area with the trend of bulk Carbon and Oxygen isotopic curve of the Xiaweidian section in Western Hills of Beijing,it shows that the trend of bulk Carbon and Oxygen isotope is in agreement with the sedimentary cycle characteristics of each third-order sequences,and indicates that the sedimentary trend is closely related to global sea-level change.4.Five sedimentary models can be discerned in strata of Cambrian within study area:? low-energy open gentle slope deposition of Fujunshan formation;? semirestricted and restricted mixed continental shelf deposition from Mantou formation to Maozhuang formation;?high-energy open gentle slope deposition of Xuzhuang formation and Zhangxia formation;? open rimmed plateform deposition of Gushan formation and Changshan formation;? open rimmed platform-basin deposition of Fengshan formation.Before the end of Zhangxia stage,the main sedimentary models are gentle slope deposition and continental shelf deposition-from Gushan stage to Fengshan stage,the model is rimmed plateform deposition.Fujunshan--Maozhuang formation and Xuzhuang formation--Ordovician Majiagou formation are respectively developed one evolution cycle of extensive and restricted sedimentary environment.