Publisher: Bachudo Science Co. Ltd

Petrography In Relation To Palaeogeography of The Late Cretaceous Limestone Units In Ohafia Area of Southeastern Nigeria

Kalu Kalu Ibe
KEYWORDS: NSUKKA FORMATION. GLAUCONITIC. SPARITES, MARINE .

ABSTRACT:

Petrographic studies have been carried out on the limestone units at the base of the late Maastrichtian Nsukka formation in Ohafia area of south-eastern Nigeria. The aim is to relate petrography with palaeogeography of the limestone sequence. Field studies show that two limestone beds cover over 40 kilometres. They occur as two distinct low hills, in a shale-limestone-shale sequence. The limestones are basically made up of , spary and boisparitic matter, replacing pre-existing aragonitic skeletal matter in the marine organisms that formed the units. Skeletal grains are preserved both as agglutinated, glauconitised, pyritised and calcified fossils, a d,evelopment that not only depicts the fossils as unreworked but points to the completely marne conditions that characterised their formation. The results are found to be in line with results of earlier work on the palaeogeographic reconstruction of southern Nigeria. With calcite forming well over 80 % of the total mineralogical composition of the samples studied, minor ankarite, benthic and a few planktonic foraminifera recorded, shallow to relatively nearshore palaeo-environment is thus proposed for the area. It is thus concluded that the Late Maastrichtian units in Ohafia-Obotme area of south-eastern Nigeria is another facies of the Nsukka Formation of eastern Nigeria. 


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