内蒙古林西地区晚二叠世—早三叠世沉积演化及构造背景

LATE PERMIAN EARLY TRIASSIC SEDIMENTARY EVOLUTION AND TECTONIC SETTING OF THE LINXI REGION, INNER MONGOLIA

在林西地区新发现的叶肢介和介形虫等化石，证实了大兴安岭南部存在早三叠世地层。这套地层为具有红层性质的河—湖环境产物，与下伏上二叠统林西组沉积有较大的差异。林西组中—下部以海相沉积为主，并发育浊流沉积，反映直到晚二叠世中期大兴安岭南部仍有残余海盆存在，应是造成晚二叠世南北植物化石仍保持区系特征的主因。林西地区晚二叠世—早三叠世的沉积—构造演化特征揭示，大兴安岭南部的晚古生代板块构造活动一直到印支构造旋回才结束。

Early Triassic strata in the southern Da Hinggan Mountains has been evidenced by discovery of fossils of ostracods, conchostracans and bivalves in the Linxi region, Inner Mongolia. The Lower Triassic is of fluvial lacustrine facies with red bed features and notably different from its underlying Upper Permian Linxi Formation. Before this work the sedimentary facies of the Linxi Formation was considered as Late Permian non marine deposits. Sedimentological, paleontological and oxygen carbon isotope studies suggest that the mid lower sequences of the Linxi Formation consist mainly of marine deposits with turbidity current deposits, which reflects the existence of a remnant sea basin in the southern Da Hinggan Mountains till the middle Late Permian. This should be the main cause why the Late Permian plants on both sides of the Xar Moron River still maintain the features of different floras. An analysis of Late Permian Early Triassic sedimentary evolution and tectonic setting in the Linxi region shows that the Late Paleozoic plate tectonic movement in the southern Da Hinggan Mountains continued till the Indosinian tectonic cycle.