塔里木盆地孔雀河斜坡上新统库车组沉积环境及找铀意义OA

The Pliocene Kuqa formation in the Tarim basin has become a hotspot for uranium exploration in recent years.However,the research on the Kuqa formation in the Kongquehe area at the northeastern margin of the basin,especially on the sedimentary facies and sedimentary environments,is seldom reported,which restricts the evaluation of regional uranium metallogenic potential.This study systematically collected 37 mudstone samples to investigate the paleosalinity,paleoredox conditions,paleoclimate and provenance background during the deposition of the Kuqa formation by analyzing trace element and rare earth element(REE).Environment-sensitive ratios(Sr/Ba,Th/U,V/Cr,Ni/Co),δCe and δEu anomalies,and REE distribution patterns were adopted for comprehensive discussion.Combined with sedimentary facies characteristics and uranium metallogenic geological conditions,we analyzed the regional uranium metallogenic prospects.The results show that the Kuqa formation in the study area is dominated by braided fluvial delta plain deposits,vertically characterized by multi-stage sedimentary rhythms of"distributary channel-interchannel"and frequent sand-mud interbeds.Oxidized bands and gypsum veins are visible in cores,indicating an oxidized depositional environment of transitional marine-continental facies under arid conditions.The average Sr/Ba ratio is 0.46(generally<0.5),and the B/Ga ratio is concentrated in the range of 3-6,jointly indicating a brackish to semi-saline depositional environment.The assemblage of V/Cr,Ni/Co,U/Th,and δCe indicate that the sedimentary water column was overall suboxic-oxic,with weak reducing conditions developed only in local intervals.The average Sr/Cu ratio is 8.87,revealing that the paleoclimate was dominated by semi-arid to arid conditions accompanied by multi-stage warm-humid climatic cycles.The total REE content averages 155.01×10-6,characterized by the enrichment of LREE and flat distribution of HREE.The average δEu value is 0.68 with a distinct negative anomaly,indicating a single and stable provenance,mainly derived from felsic rocks(intermediate-acid metamorphic and volcanic rocks)of the Kuruktag fault uplift to the north.Comprehensive analysis suggests that the Kuqa formation in the Kongquehe area is generally an oxidizing environment,providing long-term and stable migration pathways for U-bearing oxygenated fluids.Warm-humid climatic episodes can form local reducing conditions and gray sandbodies,which favor uranium precipitation and enrichment.Future exploration should focus on the identified braided fluvial delta plain subfacies,trace the exposed gray intervals,and expand toward the inner front subfacies of the basin.