Structures and Petrology of the Rocks around Ekori, Western Ikom – Mamfe Embayment, Southeastern Nigeria

Abstract

Ekori and adjoining areas is located in western part of the Ikom – Mamfe embayment. Sedimentary rocks such as sandstones, limestone, shale and few mudstones make up the sedimentary units in this area while intrusive bodies like dolerite sills and gabbro plutons constitutes the igneous rocks in the area. The sedimentary rocks of the study area contain different types of fossils most notably bivalves and brachiopods in sandstones and burrows in limestone. The calcareous sandstone sometimes form semi – caves beneath which grey shale occur. Fresh limestone usually occurs as thin beds within weathered sandstone. The presence of limestone and black shale suggests shallow and deep marine transgression events while the variation in sediment grain size from coarse to fine implies an intercalation of high and low energy depositional environment. Igneous bodies (dolerite and gabbro) intruded the sandstones and shale which baked some of the shales. The gently dipping sedimentary rocks are intensely fractured with NW – SE/ESE – WNW, NNW – SSE, ENE – WSW and NNE – SSW oriented fractures. The complex behaviour of tectonic fractures in this area implies the occurrence of multiple episodes of deformation. Thin section studies indicate the sandstones are lithic sub-arkosic sandstone with igneous or metamorphic parent material.