COMPARATIVE STUDIES OF SOME OF THE ROCKS IN THE SEKONDIAN SERIES – IMPLICATIONS FOR PETRO-MECHANICAL STRENGTH OF THE ROCKS

Abstract

This study petrologically and mechanically assesses and compares five of the seven stratigraphic units of the Sekondi Group comprising Elmina sandstone from Central region; Ajoa, Takoradi, Takoradi Harbour and Essipong shales from the Western region in Ghana. All the studied shales were detrital clastic sedimentary rocks observed to have angular, near rounded and elongated crystal habits which are randomly distributed within fine-grained clay minerals as cementing matrix. These characters were clearly observed in the Ajua shales than the others. Unlike the shales, no chlorite, organic materials or foliations were observed in the Elmina sandstone. Also, the most consisted minerals in the shales were the feldspars (K- and plagioclase) and quartz, whereby the K-feldspar dominated the other crystals in the sandstone. The finer texture of the shales may be inferred that the shales have undergone longer times and distances of transportation process. The UCS test carried out on the Elmina sandstone reveals it to be a weak rock with a strength value of 37.3 MPa whilst the Schmidt Hammer test carried out on the four shale rock samples define the shales to be delaminated with the average rebound value of zero (0) each. Both results confirm the megascopic and microscopic petrological results, since both revealed the occurrences of laminated sections within the rocks, and the fissile property of all the shales. It also proves megascopic observation of Elmina sandstone being the hardest of the rocks observed, although the sandstone is still relatively weak from the rock hardness classification.