SEDIMENTOLOGICAL CHARACTERIZATION AND PETROGRAPHIC ANALYSIS OF A SEDIMENTARY OUTLIER UNIT AT THE OUTSKIRTS OF IKPESHI AREA
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Abstract
This research is focused on the sedimentological characterization and petrographic analysis of a sedimentary outlier unit at the outskirts of Ikpeshi area. The sedimentological study of sections of the rock units involved the description, measurements and sampling of various sections and samples broken off from the rock unit in situ. The laboratory studies carried out in this research include petrographic analysis involving thin section petrography. This rock unit occurs as boulders on a narrow ridge and they are
surrounded by basement complex rocks, they have a coarse texture, and contain particle size that range from about 1mm – 15mm with a dominant clast size of 2mm, they are poorly sorted and they range from sub-angular to angular in roundness. They contain about 85% quartz, 10% clay minerals and lithic fragments account for the rest. The rock unit was observed to be texturally and mineralogically immature. These rock units have been established as sandstones, made up of very coarse sands – small pebbles mineral grains, they are sub-arkosic in nature which is a function of the percentage of the mineral content and the lithic fragments. The sandstone unit consists of series of sedimentary structures which include cross beds, which formed as a result of sudden rise and fall in the depositional energy, the direction of dips of these cross beds indicates the paleocurrent direction of the transporting medium at the time of deposition. The rock unit outcrops in the Benin flank, the sandstone is described as
Pre-Santonian due to its age, the sandstone is observed to be older than sandstones that were formed in the Anambra Basin. This is evident in the compaction difference or diagenetic process that occurred between the two, the sediments as well as the depositional processes that make up these sandstones is suggested to have come from the lower Benue Trough this can be said to be true as a result of 2 the clear distinct lithological and textural characteristics of the sandstones formed in Anambra Basin and the sandstones that is been examined.
surrounded by basement complex rocks, they have a coarse texture, and contain particle size that range from about 1mm – 15mm with a dominant clast size of 2mm, they are poorly sorted and they range from sub-angular to angular in roundness. They contain about 85% quartz, 10% clay minerals and lithic fragments account for the rest. The rock unit was observed to be texturally and mineralogically immature. These rock units have been established as sandstones, made up of very coarse sands – small pebbles mineral grains, they are sub-arkosic in nature which is a function of the percentage of the mineral content and the lithic fragments. The sandstone unit consists of series of sedimentary structures which include cross beds, which formed as a result of sudden rise and fall in the depositional energy, the direction of dips of these cross beds indicates the paleocurrent direction of the transporting medium at the time of deposition. The rock unit outcrops in the Benin flank, the sandstone is described as
Pre-Santonian due to its age, the sandstone is observed to be older than sandstones that were formed in the Anambra Basin. This is evident in the compaction difference or diagenetic process that occurred between the two, the sediments as well as the depositional processes that make up these sandstones is suggested to have come from the lower Benue Trough this can be said to be true as a result of 2 the clear distinct lithological and textural characteristics of the sandstones formed in Anambra Basin and the sandstones that is been examined.
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