【摘要】 三峡地区上三叠统王龙滩组(或须家河组)超覆在下三叠统嘉陵江组、中三叠统巴东组或上三叠统九里岗组等不同时代的地层之上,两者间存在一明显的沉积间断面。如何理解该界面的性质和发生时限,对于正确认识印支构造运动在该区的作用形式和过程具有关键作用。近年来,在长江三峡地区开展的基础地质调查研究工作中,对该界面的地质特征进行了全面观察和研究,对其有了更深入的认识:上三叠统王龙滩组(或须家河组)与下伏地层间的沉积间断面以发育冲刷构造和残存少量风化壳为特征,沉积间断发生在卡尼期中后期至诺利期初期(约225～216.5,Ma)。受印支运动影响,卡尼期中后期,地壳整体抬升,包括研究区在内的中扬子地区漫长的海相沉积历史结束,原有沉积遭受风化剥蚀、地形夷平;卡尼期末期—诺利期初期,地壳抬升速率骤然加剧、地形相对高差变大、河流回春,对下伏地层快速下切。这种下切作用横向变化较大,剥蚀程度差异明显,从而形成在不大的范围内下伏地层从无明显缺失(王龙滩组与九里岗组接触)至大量缺失(王龙滩组与嘉陵江组接触)这一特殊地质现象。总的看来,该沉积间断界面兼具古暴露剥蚀面、冲刷侵蚀面和河流回春作用面3种性质,是对印支运动Ⅲ幕(研究区内印支运动主幕)的沉积响应。更多还原

【Abstract】 The Upper Triassic Wanglongtan (or Xujiahe) Formation overlies on the strata of different ages such as the Lower Triassic Jialingjiang Formation,the Middle Triassic Badong Formation and the Upper Triassic Jiuligang Formation in Three Gorges area,and an apparent depositional break exists between them. The characteristics and age of this interface are the key to understand the Indosinian Movement and its style and process in the area. During the geological survey,the depositional break interface has been studied extensively and some new knowledge has been obtained. The hiatus is characterized by washing structures and residue of weathered crust,and occurred at the Middle-Late Carnian to the Early Norian(ca.225～216.5Ma). With the development of the Indosinian Movement,the marine deposition history of the Middle Yangtze region was ended in the Middle Carnian,and then it experienced erosion and uplifting. From the Late Carnian to the Early Norian,the crust uplifting speeded sharply,resulting in a big topographic difference and a fast down-cutting with river rejuvenation and forming a special geological phenomenon that the underlying strata were slightly eroded or largely absent. Therefore,this sedimentary discontinuity is a combination of the exposing erosion,washing erosion and the erosion of river rejuvenation,which corresponds to the third episode of the Indosinian Orogeny (the main episode of the Orogeny in the study area).更多还原