PRELIMINARY DATA FROM OUTCROP STUDIES AND PETROGRAPHIC ANALYSIS OF RELICT PRE-SANTONIAN GRAVELS NEAR AUCHI, EDO STATE, NIGERIA
DOI:
https://doi.org/10.60787/tnamp.v25.716Keywords:
Pre-Santonian, clast-supported gravel, Western Anambra Basin, Sedimentology provenanceAbstract
The western fringe of the Anambra Basin has traditionally been regarded as a stable platform during the pre-Santonian period. This study presents preliminary data on recently discovered pre-Santonian rocks, depicting a more complex paleodepositional history than previously postulated. The pre- antonian rocks occur as poorly sorted, lithified, clast-supported gravels with angular to subrounded clasts, outcropping as boulders distributed along a gently sloping elliptical ridge. Sedimentary structures, including graded bedding and crossbedding with centimetre- to decimetre-scale foresets, observed within the succession, together with the textural characteristics, depict a braided river palaeoenvironment. Furthermore, petrographic analysis reveals monocrystalline quartz as the dominant framework mineral, with minor feldspar, rock fragments, and zircon. The abundance of angular to subangular grains, together with the poor sorting, indicates mmature to submature textural maturity consistent with first-cycle sediments. Similarly, the framework composition reflects immature to submature compositional maturity, derived from felsic provenance, hypothesized as the Precambrian Igarra Schist Belt.
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