|Titel:||Evolution of Cretaceous sediments in the Mamfe Basin, SW Cameroon: Depositional Environments, Palynostratigraphy, and Paleogeography||Sonstige Titel:||Die Entwicklung der kretazischen Sedimente im Mamfe Becken im Südwesten Kamerun: Ablagerungsmilieu, Palynostratigraphie und Paläogeographie||Sprache:||Englisch||Autor/Autorin:||Ajonina, Humphrey Njeatih||Schlagwörter:||Mamfe Becken; Südwesten Kameruns; Ablagerungsmilieu; Palynostratigraphie; Paläogeographie; Mamfe Basin; SW Cameroon; Depositional Environments; Palynostratigraphy; Paleogeography||Erscheinungsdatum:||2016||Tag der mündlichen Prüfung:||2016-05-11||Zusammenfassung:||
The Mamfe Basin is a WNW-ESE trending half-graben in southeastern Nigeria that extends into southwestern Cameroon. This basin is the southernmost part of the West and Central African rift system that resulted from the breakup and subsequent separation of South America from Africa during the early Cretaceous. It is located about 150 km to the northeast of the meeting point of the early Cretaceous Benue Trough-Equatorial Atlantic-South Atlantic rift system triple junction.
The sedimentary infill of the Mamfe Basin is over 4500 m thick and formerly referred to as the Mamfe Formation. Until date, the Mamfe Formation lacks any direct or clearly defined age determination in geological and paleontological literature. The formation has over the years been correlated with Albian-Cenomanian sediments in the adjoining southern Benue Trough on the basis of presumed lithological similarities, and is mapped as the basal unit of the Asu River Group.
This research was undertaken to characterize the depositional environments and age of the sedimentary infill of the Mamfe Basin within the context of the early Cretaceous paleogeography of the eastern Gulf of Guinea region from southern Benue Trough to northern Gabon. Sedimentological, palynofacies, organic geochemical, palynological, and foraminiferal analyses were carried out on outcrop samples that were collected from the Cameroonian sector of the Mamfe Basin.
Results of this research indicates that the sedimentary infill of the Mamfe Basin includes siliciclastics, carbonates, evaporites, and volcaniclastics. Twenty macrofacies were identified and grouped into nine facies associations: proximal alluvial fan, floodplain, palustrine marshes, fluvio-lacustrine, moderate to deep (sublittoral-profundal) lake, littoral-shoreline marshes, deltaic swamps, medial alluvial fan, and fluvial channel/overbank. Based on the vertical and lateral relationship of the facies associations, a revised lithostratigraphic framework consisting of five formations is proposed for the Mamfe Basin. These formations from bottom to top are Etuko, Nfaitok, Manyu, Okoyong, and Ikom-Munaya. These formations are partitioned by unconformities into three depositional sequences.
The basal (pre-rift) depositional sequence overlies the Pan-African basement, and consists of non-fossiliferous proximal alluvial fan debris flow deposit that outcrop in the northeastern margin of the basin in and around Etuko. This unit is dated as pre-middle Barremian based on the palynological age of the overlying depositional sequence.
The middle (syn-rift) depositional sequence is underlain by an erosional unconformity and is named the Mamfe Group. This group consists of three formations, which from bottom to top are Nfaitok (fluvio-palustrine), Manyu (lacustrine), and Okoyong (fan-delta). Micropaleontological analysis of samples from the Mamfe Group yielded 128 pollen and spores taxa with many new previously undescribed species, very rare foraminifera and no dinoflagellates. Angiosperm pollen grains are rare, and Dicheiropollis etruscus and elater-bearing pollen are absent. Age-diagnostic palynomorphs within the microflora assemblage suggests that the Mamfe Group is younger than early Barremian and older than middle Albian. The palynoflora assemblage correspond to the West Africa regional palynostratigraphic reference section and zones CV to CIX of SNEA (P) in Gabon, and palynozones P-190 to P-280 in South America (Brazil) that have been assigned a middle Barremian-early Albian age. The Aptian age of the lacustrine facies of the Manyu Formation suggests that the Mamfe Basin was part of the Barremian-middle Albian Medio-African and NE-Brazilian Great Lakes. A late Aptian-early Albian marine ingression into the Mamfe Basin from the Douala Basin is represented by halite dominated evaporites and rare Praebulimina sp. and Hedbergella sp. The evaporites deposit in the Mamfe Group represent the northernmost fringes of the South Atlantic salt province.
The upper (post-rift) depositional sequence is underlain by a regional angular unconformity that coincides with the opening of the Equatorial Atlantic and Benue Trough. It consists of non-fossiliferous fluvial deposits in the western part of the basin that have been named Ikom-Munaya Formation.
Lithofacies, palynofacies, microflora, and clay mineral composition of the studied sedimentary succession of the Mamfe Basin indicates a progressively shift from a warm and dry arid to semi-arid climate in the fluvio-palustrine and lacustrine units towards a more humid and wet climate in the fan-delta and fluvial successions at the top. The age of the sediments in the Mamfe Basin indicates that the basin is not a rift-splay segment of the Benue Trough as earlier suggested. Vitrinite reflectance, thermal alteration index, and illite crystallinity paleothermal data all suggest burial depths of between 1200 and 4000 m. The westward younging of sediments in the Mamfe basin is due to uplift and erosion in the eastern part of the basin rather than the previously reported westward migration of depocenter.
|URI:||https://ediss.sub.uni-hamburg.de/handle/ediss/7010||URN:||urn:nbn:de:gbv:18-82601||Dokumenttyp:||Dissertation||Hauptberichter:||Betzler, Christian (Prof. Dr.)|
|Enthalten in den Sammlungen:||Elektronische Dissertationen und Habilitationen|
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