准噶尔盆地西北缘克百断裂带晚石炭世火山岩成吉思汗山组新认识及其地质意义OA

The Kebai fault zone is a critical area for the Late Paleozoic tecto-stratigraphic evolution and hydrocarbon exploration along the northwestern margin of the Junggar Basin.The stratigraphic assignment of the Carboniferous volcanic rocks in the fault zone has long been a controversial issue.The volcanic rock sequence encountered in well Baiwu 21 within the Kebai fault zone,previously assigned to the Early Permian Jiamuhe Formation,was selected as the research object.Integrated lithologicalassociation analysis,LA-ICP-MS zircon U-Pb dating,and seismic profile interpretation were conducted on this sequence to redefine its stratigraphic assignment.As indicated by the research results,(1)the volcaniclastic zircon U-Pb ages obtained from two tuffaceous sandy conglomerate samples of the volcanic rock sequence in well Baiwu 21 are(311.9±2.2)Ma and(311.6±2.2)Ma,respectively,indicating a formation age of the late stage of Late Carboniferous and reassigning the sequence to the Chengjisihanshan Formation(C2c).(2)The rock suite is dominated by amygdaloidal andesite and basaltic andesite,exhibiting subalkaline,sodium-rich,and potassium-poor geochemical characteristics that are regionally consistent with those of the C2c,but markedly distinct from those of the Jiamuhe Formation(P1 jm).(3)Seismic profile interpretation confirms that this stratigraphic unit has an angular unconformity contact with the underlying Lower Carboniferous Baogutu Formation(C1b),mirroring the basal structural boundaries of the regional C2c rather than the sequence stacking pattern of P1 jm.Consequently,these multiple lines of evidence justify the redefinition of this volcanic rock sequence as part of the Chengjisihanshan Formation.This new insight resolves the long-standing controversy over stratigraphic division in the area,refines the Late Paleozoic stratigraphic framework along the northwestern margin of the Junggar Basin,and provides fresh chronological constraints on the closure timing and tectonic evolution of the western Paleo-Asian Ocean.Furthermore,it opens up new strata and horizons for deep Carboniferous hydrocarbon exploration in the northwestern margin of the Junggar Basin.