海拉尔盆地乌尔逊凹陷早白垩世沉积特征和沉积–构造演化
Early Cretaceous Sedimentary Features and Sedimento-Tectonic Evolution of the Urxun Sag, Hailar Baisn

乌尔逊凹陷乌南次凹下白垩统的铜钵庙组、南屯组和大磨拐河组一段沉积中发育扇三角洲相、辫状河三角洲相、湖泊和湖底扇相。基于各类沉积相主要特征的总结及其与邻区凹陷的对比，发现乌南次凹沉积–构造演化的两大特点。空间上它是一个极不对称的盆地。西侧有乌西断裂带长期强烈活动，控制了乌西断阶和中央深凹带形成，深湖半深湖和湖底扇的规模相对较大；东侧却是宽缓的稳定斜坡，长期控制辫状河三角洲发育。时间上，乌南次凹的断陷阶段可延续至大磨拐河组一段沉积期，并可细分为4幕：初始伸展–裂陷幕(铜钵庙组沉积期)、主伸展–裂陷幕(南屯组一段沉积期)、再次伸展幕(南屯组二段下部沉积期)和末次伸展幕(大磨拐河组一段上部沉积期)。大磨拐河组二段沉积期是次凹演化的断–坳转换期。
The main sedimentary facies types of the Lower Cretaceous Tongbomiao-Nantun Formations and No. 1 Member of Damoguaihe Formation in the South Sub-Sag, Urxun Sag of Hailar Basin are fan delta, braided river delta, lacustrine and sublacustrine fan. Based on the summarization of characters of each facies type as well as comparison with that of the neighboring sags, two main distinctions for the Early Cretaceous sedimento-tectonic evolution of the South Urxun Sub-Sag can be discovered. Spatially, the Urxun Sag might be an extremely unsymmetrical basin. Its western boundary fault, the Wuxi fracture belt, was a violently activated synsedimentary normal fault, which controlled the creation of the West Fault-Step Belt and the Central Deep-Sinking Belt where the deep lacustrine and sublacustrine fan deposits were relatively better occurred. Whereas the eastern margin of the sag might be a rather gentle and stable slope, along which the braided river deltaic deposits were developed for a long time. In the neighboring sags the Tongbomiao and Nantun Formations are records of faulting-depressing stage of the basin. While in the South Urxun Sub-Sag, the faulting-depressing stage could continue to sedimentary period of the No. 1 Member of Damoguaihe Formation. The stage could be further divided into four episodes: the initial rifting-depressing episode during sedimentary period of the Tongbomiao Formation, the main rifting-depressing episode during sedimentary period of the No. 1 Member of Nantun Formation, the re-extension episode during depositing time of the lower part of the No. 2 Member of Nantun Formation, and the last extension episode during sedimentary period of the upper part of No. 1 Member of Damoguaihe Formation. The sedimento-tectonic evolution of the sag transformed from faulting-depressing stage into the down-warping stage in the sedimentary period of the No. 2 Member of Damoguaihe Formation.