CAJ | 학술논문

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-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(王龙潍组与九里岗组接触)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.
삼협지구상삼첩통왕룡탄조(혹수가하조)초복재하삼첩통가릉강조、중삼첩통파동조혹상삼첩통구리강조등불동시대적지층지상,량자간존재-명현적침적간단면.여하리해해계면적성질화발생시한,대우정학인식인지구조운동재해구적작용형식화과정구유관건작용.근년래,재장강삼협지구개전적기출지질조사연구공작중,대해계면적지질특정진행료전면관찰화연구,대기유료경심입적인식:상삼첩통왕룡탄조(혹수가하조)여하복지층간적침적간단면이발육충쇄구조화잔존소량풍화각위특정,침적간단발생재잡니기중후기지낙리기초기(약225～216.5 Ma).수인지운동영향,잡니기중후기,지각정체태승,포괄연구구재내적중양자지구만장적해상침적역사결속,원유침적조수풍화박식、지형이평;잡니기말기-낙리기초기,지각태승속솔취연가극、지형상대고차변대、하류회춘,대하복지층쾌속하절.저충하절작용횡향변화교대,박식정도차이명현,종이형성재불대적범위내하복지층종무명현결실(왕룡유조여구리강조접촉)지대량결실(왕룡탄조여가릉강조접촉)저일특수지질현상.총적간래,해침적간단계면겸구고폭로박식면、충쇄침식면화하류회춘작용면3충성질,시대인지운동Ⅲ막(연구구내인지운동주막)적침적향응.
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 Camian 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).