Abstract:

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.

Key words: redefining Heishantou Formation, Aketamu Formation, Early Carboniferous, Junggar stratigraphic region