The Division of Zhangjiakou Formation of Later Jurassic at Jibei

Abstract

There is not a unified division scheme on the lithostratigraphic unit of Zhangjiakou formation from later Jurassic at jibei for a long time, so it makes the divisions more confusion, the establishment of the reasonable stratigraphic sequence and regional stratigraphic correlation has been effected. The Zhangjiakou formation is divided into three lithologic members in turn based on lithology combination of the phase sequence at Zhangjiakou by author through the project of “the study of jibei Mesozoic continental volcanic-sedimentary basin 1:250000 mapping method”. The first section mainly includes lithology combination of weak eruption phase sequence. The second section is main the lithology combination of explosive phase sequence; the third section mainly includes lithology combination of the eruption phase sequence. These three sections respectively represent the stage of the initial outbreak, the large-scale outbreak and a caldera collapse deposition. This division method can reflect volcanic tectonic features, establishing reasonable stratigraphic sequence, this contribute to the study of the history of the volcanic evolution. It can also combine the lithostratigraphic units division and volcanic-sedimentary organically.