新疆准噶尔盆地中、晚侏罗世多重地层研究

摘要

This paper presents the results of a comprehensive study of lithostratigraphy, biostratigraphy, chronostratigraphy, cyclostratigraphy and magnetostratigraphy of the Middle–Upper Jurassic strata in the Junggar Basin, Xinjiang. The main findings are as follows: the Toutunhe Formation consists of the uppermost part of the Bathonian, Callovian and the Lower–Middle Oxfordian; the ages of the base and top of this formation are 166.2 Ma and 160.8 Ma respectively, and its sedimentary interval is about 5.4 Ma. The age of the top of the Qigu Formation is estimated at around 155.3 Ma, and the sedimentary interval of this formation is about 5.5 Ma, suggesting the upper Oxfordian and middle Kimmeridgian. The top horizon of the Qigu Formation is almost coeval to that of the Tiaojishan Formation in northern Hebei and western Liaoning provinces. This means that the Qigu Formation is lower than the Tuchengzi Formation in northern Hebei and western Liaoning. The Kalaza Formation is assigned to the late Kimmeridgian, and the overlying Tugulu Group is early Cretaceous in age, which indicates an obvious unconformity with the existence of a stratigraphic gap from the Tithonian to the possible lowermost part of the Cretaceous, and the missing strata are equal to over 7 Ma between the Jurassic and the Cretaceous in the study area. The strata through the Jurassic/Cretaceous boundary are absent.%对新疆维吾尔自治区沙湾县玛纳斯河红沟侏罗系剖面开展了生物地层学、同位素年代地层学、旋回地层学和磁性地层学等的综合研究。研究结果表明,头屯河组的时代为中侏罗世中晚期到晚侏罗世早期,包括巴通阶的最顶部、卡洛维阶和牛津阶的中下部；其底界年龄约为166.2 Ma,顶界线年龄约为160.8 Ma,沉积时间约5.4 Ma。齐古组顶部年龄值为155.3 Ma,沉积时间约5.5 Ma,包括了牛津阶的上部和基默里奇阶的中下部,其顶部与东部冀北、辽西地区髫髻山组顶部大体相当,比土城子组层位低。喀拉扎组的时代为晚侏罗世基默里奇期晚期,而其上覆地层吐谷鲁群的时代为早白垩世早期,两者之间存在一个相当大的不整合,缺失了晚侏罗世提塘期以及可能包括早白垩世最早期的地层,有超过了7 Ma的地层缺失量。侏罗系与白垩系的界线为此不整合面,侏罗纪/白垩纪之交的地层未保存。