鄂尔多斯盆地奥陶系丘形反射的解释及其与礁的关系

Interpretation of Seismic Reflection Mounds in Ordovician Carbonate Rocks and its relation to Reefs in the Ordos Basin

鄂尔多斯盆地T_9—T_(10)地震反射波组之间的奥陶系碳酸盐岩中存在着许多丘形反射,其中一部分属于以藻类生物为主的藻丘类型,一部分为东部盐凹中的盐丘,一部分为奥陶系顶古风化壳残丘,其它丘形反射为绕射波、回转波、或者为地表静校不当引起的假象。奥陶系的礁丘一般规模很小,岩性以粘结岩为主,其孔隙发育好坏同风化残丘一样,主要取决于次生溶蚀作用。但礁丘生长过程中由于受海面波动影响,曾发生过多次暴露,形成多期溶孔。礁丘和古残丘都是寻找油气的较有利地带。

There are numerous mound-shaped reflections of Ordovician carbonate rocks bounded by T9 and T10 reflection waves on seismic profiles. Some of the mound-shaped reflections belong to reef dominated by algae; some represent salt mounds or residual hills of ancient weathering crust the Ordovician; and others represent diffracted waves and pseudomorphs caused by improper static corrections of terrain or weathered depth in the processing of seismic data. The Ordovician reef mounds are generally small in size and composed mainly bindstones; so, like weathered residual mounds, their porosity development depends mainly on secondary corrosion. But reef mounds may possess a better porosity because they were exposed and eroded repeatedly in their growth under the influence of sea level fluctuation. Both the reef mounds and weathering residual mounds are favorable sites for finding oil and gas.