【摘要】 此文根据有孔虫化石群系统分类、古生态及分布的研究结论,并参考遗迹化石、沟鞭藻及其它化石类别的研究成果,讨论本区海相白垩系的最低层位及海侵开始时间,指出最早海侵时期的海水分布范围和古环境特征;提出各组时代归属的初步意见,并同国内、外有关层位进行对比;探讨海水进退规程及沉积环境演变。本区白垩纪共经历四次较为明显的海水进退旋回,在森诺曼中、晚期至土仑早期形成高潮。更多还原

【Abstract】 The western part of the Tarim Basin in Xinjiang is one of the main areas where the marine Cretaceous is well developed. A quite detailed study has been made on the Upper Cretaceous Yingjisha Group, which is represented mainly by sediments of littoral, near-shore neritic and estuarine facies and divided in ascending order into the Kukebai Formation, the Oytak Formation, the Ygezya Formation, and the Tuvlouk Formation. This paper deals with problems concerning the process of marine transgression and regression, especially the time of earliest transgression of the Cretaceous sea, the geochronology of Cretaceous marine formations and their environments of deposition in the western part of the Tarim Basin.For about thirty years, the basal beds of the Kukebai Formation have been considered to be the lowermost marine horizon of the Cretaceous there, which represents the earliest transgression of the Cretaceous sea into this region. Recently, some evidence indicating marine facies was found in the upper and middle parts of the Kezlesu Group underlying the Kukebai Formation.In 1985, some marine trace fossils such as Ophiomorpha nodosa and O. tuberosa and Thalassinoides? spp. were found in abundance and fine preservation by one of the authors in the brownish-red sandstone of uppec subcycle of the Kezlesu Group in the Kuzgongsu area, the same trace fossils were also found in horizons from the upper part of the lower subcycle to the upper subcycle of the group in the Kangsu area.Both Ophiornorpha and Thalassinoides are fossil burrows or a burrow system of crustaceans. In view of an analogy between Ophiomorpha and its modern counterparts, this trace fossil may be considered to be indicative of near-shore shallow marine to brackish water environments. Thalassinoides is also common in littoral intertidal deposits. The distribution of its population is helpful for locating the shore line.As a result, it may be noted that the strata including the middle and upper parts of the Kezlesu Group and lower part of the Kukebai Formation may represent a complete cycle of sedi mentation.The Yingjisha Group is subdivided into four formations, and the lithological character, fossil content and chronological correlation of each formation are given in Table 3.The West Tarim Gulf was a branch of the Tethys, extending deeply inland. Its communication with the open sea was controlled by the tectonic movement and had decisive influence over the evolution of organisms and development of sedimentation in the gulf. The Cretaceous marine strata deposited in it comprises the following four distinct cycles of sedimentation:(Ⅰ) from the upper part of the Lower Cretaceous to the Lower Membcr cf the Kukebai Formation; (Ⅱ) from the middle part of the Kukebai Formation to the Lower Member of the Oytak Formation;(Ⅲ) The Middle and Upper Member of the Oytak Formation;(Ⅳ) the Ygezya and Tuylouk Formations.Each cycle indicates a change in sedimentary environment from littoral or neritic to supralittoral and lagoonal regime.更多还原