天津大港歧口凹陷及邻区奥陶纪岩相古地理特征

Ordovician Lithofacies Paleogeography of Qikou Sag and Its Adjacent Area in Dagang Area,Tianjin

寒武-奥陶纪时期华北地台是一个广阔的陆表海,位于南半球低纬度区,气候炎热,蒸发作用强。歧口凹陷区是华北地台内部的一个小地块,奥陶纪歧口凹陷区总体上以开阔台地相沉积为主,大致构成4个自下而上由蒸发-局限到开阔台地相的旋回沉积。旋回上部为高海平面沉积,以发育开阔台地灰坪微相为主;下部为低海平面沉积,在开阔台地相的背景下间或发育局限台地云坪微相,甚至蒸发台地膏云坪与膏质洼地微相。

During Cambrian-Ordovician period,North China platform is a broad epicontinental sea,which is located in the low latitudes of Southern Hemisphere,where the climate is hot,and the evaporation is strong.The Qikou sag area is a small plot of the internal North China platform.The comprehensive research of the existing drilling,well logging and logging data combined with the core analysis and regional geological background considers that the Ordovician Qikou sag area is mainly an open platform facies sedimentary.It roughly constitutes four cyclic deposition,from bottom to top,there are evaporation-limited to open platform facies.The upper part of the cycle is the high sea level deposition,mainly limestone micro-facies on open platform.The lower part is the low sea level deposition,under the background of the open platform.It develops dolomitic plateau on restricted platform,and even develops the micro-facies of gypsodolomite flat and gypsum topographic low on evaporative carbonate platform.