新疆准噶尔地层区黑山头组的重新厘定及阿克塔木组新建

黑山头组在新疆东准噶尔、西准噶尔两个地层分区均有产出,分布最为广泛,可作为两个地层分区对比的标志性地层单位。最初确立该组为一套海相正常陆源碎屑岩,但因最初建组剖面上的黑山头组更名为那林卡拉组,加之补立黑山头组层型剖面中火山地层的并入,特别是对并入火山地层的划分归属分歧和时代争议,使得黑山头组的划分与时代认识出现严重分歧,导致其上覆和下伏多个组级地层单位的使用混乱,引发了这些地层的区域地层划分与对比困难。野外调查确认,原黑山头组的海相正常陆源碎屑岩与并入上部的火山地层岩性差异显著,二分性界面清楚,区域延伸性和可对比性标志清晰,且两者之间发育明显的喷发不整合界面,故建议对其解体和重新厘定。新厘定的黑山头组只保留(原下部)陆源碎屑岩层位,其上的火山地层确信为早石炭世(非前人所述的中泥盆世),故新建早石炭世阿克塔木组。这一新方案为准噶尔地层区石炭系地层的正确划分和区域地层合理对比等提供了重要佐证,提升了黑山头组在两个地层分区的对比价值。

Redefining the Heishantou Formation and defining the Aketamu Formation in West Junggar,Xinjiang

The Heishantou Formation is widely distributed in the stratigraphic regions of East and West Junggar and can be used as a landmark unit for stratigraphic correlation. The Heishantou Formation was initially established as marine terrigenous clastic rock strata; however, the geological section that defined the Heishantou Formation was renamed the Nalinkala Formation with the addition of the volcanic strata in the alternate section, leading to serious disagreement between the classification and timing of the Heishantou Formation. As a result, the use of stratigraphic units overlying and underlying the Heishantou Formation created many confusions. Through a substantial field geological survey, we found the lithology of the initially defined marine terrigenous clastic rocks of the Heishantou Formation are significantly different from that of the volcanic strata added to the upper part of the section. Their lithologic interfaces are clear and comparable in the Junggar area; in addition, there is an evident eruptive unconformity between the two strata. Thus, we suggest to disintegrate and redefine the Heishantou Formation. The newly defined Heishantou Formation retains only the lower strata of the marine terrigenous clastic rocks; the volcanic strata, believed to be the Early Carboniferous (not the Middle Devonian as previously considered), is defined as the Aketamu Formation. This new scheme provides important evidence for the division of the Carboniferous strata in the Junggar stratigraphic region and for the correlation of regional strata, which in turn improves the comparative value of the Heishantou Formation in the two stratigraphic regions.