Dispersal Patterns of the Late Cretaceous to Early-Tertiary Sediments in the Southern Anambra Basin, Southeastern Nigeria

Samuel O Onyekuru,Godwin I Nwankwor,Cyril E Ukaonu,Nathaniel N Onu,Chukwuma J Iwuagwu

doi:10.4236/ijg.2013.43054

Abstract

The dispersal patterns of the Late Cretaceous to Early Tertiary sediments in southern Anambra Basin were studied to delineate spatial facies distributions for improved mapping and hydrocarbon prospectivity. Seven lithofacies distinguished from eleven outcrop sections aided the interpretation of depositional environments for the different depositional units. Interpreted paleoenvironments ranged from estuarine/lagoonal to tidal delta and shallow marine depositional environments. Sequence stratigraphic interpretation of the deposits using vertical relationships between the delineated facies and foraminiferal and palynofacies assemblages and the interpreted environmental setting identified two complete sequences (SEQ-1 and -2) and two incomplete sequences (SEQ-3 and -4) in the study area. The sequiences are enveloped by three Type-1 Sequence Boundaries (SB), two Transgressive Surfaces of Erosion (TSE) and four Maximum Flooding Surfaces (MFS). The identified surfaces were used to delineate formation boundaries and as such would assist in the improved mapping of the Anambra Basin and adjoining depocenters. The massive sand units of the Highstand and Transgressive Systems Tracts constitute good (potential) reservoirs, while the transgressive shales would constitute seals for potential traps in the study area. The delineation of these petroleum system elements, especially those associated with the Transgressive and Highstand Systems Tracts has conferred great hydrocarbon prospectivity potential on the sedimentary sequences in the Basin. The absence of deep marine and slope complexes of the Lowstand Systems Tract (LST) in the interpreted sequences is indicative that the study area is the up-dip section of the Anambra Basin.

Highlights

The Anambra Basin extends over a roughly triangular territory, estimated at about 95,000 km2 wide [1]
To realize optimal hydrocarbon exploration, recovery and production will require the understanding of the depositional setting and location of play elements within the depositional setting for a realistic or near realistic representation of the subsurface and paleo environmental conditions within the basin. This present study provides a sequence stratigraphic framework for the definition of potentially profitable stratigraphic surfaces, sequences and structures for better mapping and improved predictability of play elements in the southern Anambra Basin
Interstratified Calcareous Mudstone and Shale Facies (AF). This lithofacies was observed in the Mamu Formation exposure at Ohafia, KMs 52 and 76, on the Enugu-Port Harcourt Expressway

Summary

Introduction

The Anambra Basin extends over a roughly triangular territory, estimated at about 95,000 km wide [1]. It is believed to occupy a geographic position among the Benue Trough, the Middle Niger depression, the Niger Delta and the Abakiliki Anticlinorium (Figure 1). The dispersal patterns of the Anambra sedimentary fills have not been clearly established, the difficulty in demarcating its geographic boundaries from adjoining Nigerian coastal basins. The northern limit of the basin is arbitrarily placed around 8 ̊N Latitude while its southern limit is not clear, being masked by the younger Niger Delta deposits [2]. [1], attempted a demarcation of the Anambra Basin from the Benue Trough using lithostratigraphical studies. The basin had been described as Late Cretaceous to Early Tertiary, a delimitation based on time [3]

Methods

Results

Discussion

Conclusion