Sequence Stratigraphy And Sedimentary System Analysis Of Xiaganchaigou In Niudong Area, Northern Margin Of Qaidam Basin

The Niudong area on the northern margin of the Qaidam Basin is located in the northwestern part of the Qaidam Basin,in the piedmont zone of the Altun Mountains,above the Niudong nose,and is one of the key exploration blocks of CNPC Qinghai Oilfield Company.This paper comprehensively uses geochemistry,high-resolution sequence stratigraphy,logging geology,sedimentology and other theories and techniques to analyze the sequence stratigraphy and sedimentary system of the Xiaganchaigou Formation in the Niudong area on the northern margin of the Qaidam Basin.The sedimentary environment of xiaganchaigou formation in Niudong area is analyzed.Based on the study of basic data such as drilling logs,cores,geochemistry,etc.,a high-precision sequence stratigraphic framework of the Xiaganchaigou Formation in the Niudong area on the northern margin of the Qaidam Basin was Established,and two three-level sequences(ESQ1 and ESQ2)were identified.And six four-level sequences(Esq1-Esq6)also were identified.And the continuous well stratigraphic comparison in the entire Niudong area.The sequence distribution and evolution of the Xiaganchaigou Formation were summarized.Based on the sequence development characteristics the sequence filling pattern has been obtained.Through the analysis of paleoclimate,paleo-salinity,paleo-redox conditions and other indicators,the sedimentary environment of the Xiaganchaigou Formation in Niudong area during the deposition period was restored more accurately.The lower section of the Xiaganchaigou Formation is considered to be a humid climate,fresh water,and a transitional water environment with a high degree of oxidation;The upper section of the Xiaganchaigou Formation has a humid-semi-arid climate,fresh water-salt water,and a highly oxidized transitional environment.And the sedimentary environment from the lower section of Xiaganchaigou Formation to the upper section of Xiaganchaigou Formation has a strong inheritance.It is concluded that fan delta-lake deposits are mainly developed in the lower section of the Xiaganchaigou Formation.The sediments flowed downhill from the Altyn Mountains and first accumulated in the front of the mountains to form a fan delta plain.With the advance of the river channel,the sediment size became finer and had the effect of a lake.The formation of Shallow Lake sediments.Due to the structural stability of the Xiaganchaigou Formation in the Niudong area during the period,the upper and lower sections of the Xiaganchaigou Formation were generally consistent,but the upper section shrank compared to the lower section and the sedimentary center moved toward the lake basin.