Advances in the research on Carboniferous deep‐water marine deposits in western Junggar, northwestern China

Abstract

Carboniferous deep‐water marine strata have been insufficiently studied in western Junggar, NW China where the deep‐water facies successions have long been disputed in terms of age constraints, sequence and palaeoenvironmental reconstruction. This paper introduces some views in the light of new materials obtained from this region in recent years. The presence of the Visean plant fossils from the upper Ta'erbahatai Formation in the Tarbgatay Mountains indicates that the formation can be extended to the Early Carboniferous epoch in age. This unit also displays obvious diachroneity, which is of Late Devonian to Early Tournaisian age in the Saur Mountains and Late Devonian to Visean age in the Tarbgatay Mountains. The Xibeikulasi, Baogutu and Tailegula formations are widely distributed in northwestern Karamay areas. The scouring structures and graded bedding near the boundaries between the three formations confirm the stratal sequence that they were originally assigned, namely the Xibeikulasi, Baogutu and Tailegula formations in ascending order. The ‘fossil chaos’ of the three formations is due to mistaking fossils of other stratigraphic units for fossils of these three formations. After revision, only the Early Carboniferous fossils are considered reliable, and combined with the newly found plant fossils, the Xibeikulasi, Baogutu and Tailegula formations are re‐assigned to the early Visean, late Visean, and latest Visean to Serpukhovian ages, respectively. An extension of the lower Hala'alate Formation was recognized in the southwestern Hala'alate Mountains. The presence of the latest Early Carboniferous brachiopods constrains the Hala'alate Formation as late Serpukhovian to Bashkirian in age, bearing the mid‐Carboniferous boundary. Copyright © 2013 John Wiley & Sons, Ltd.