1 - Odumodu, Chukwuemeka F.; 1 - Ikegwuonu, Okechukwu N.; 2 - Mode, Ayonma W.

1 - Department of Geology, Chukwuemeka Odumegwu Ojukwu University, Anambra State E-mail: raluchukwu@yahoo.com; okeynick2010@yahoo.com

2 - Department of Geology, University of Nigeria, Nsukka E-mail: wilfred.mode@unn.edu.ng

A set of twelve (12) outcrop samples of Late Cretaceous and Earliest Paleogene from  Ihube, Okigwe-Arondizuogu, and Umuasua road sections in the Anambra Basin were palynologically examined to re-evaluate their age and reconstruct their paleoenvironments of deposition. Palynological analysis was carried out, using the standard conventional method of acid maceration for recovering the acid-insoluble organic-walled microfossils from sediments. Four (4) main lithological units were encountered which include, carbonaceous shale, sandstones, mudstones, and siltstones. Result from the palynological examination shows high dominance of terrigenous microflora (spores and pollen), especially the mangrove pollen over marine microplanktons in the samples from Ihube and Okigwe/Arondizuogu sections, whereas samples from the Umuasua section yielded more marine species, mostly the dinoflagellates with proximate cyst affinity, than the terrigenous forms. Age control was achieved based on the selected key stratigraphic index palynomorph assemblages recovered. A Latest Maastrichtian age was assigned to the samples from Ihube and Okigwe-Arondizogu sections, with the following index species: Longapertites marginatus, Proxapertites operculatus, Proxapertites cursus, Retidiporites magdalenensis, Cingulatisporites ornatus, Proteacidites dehaani, Spinizonocolpites baculatus / echinatus, Mauritidites crassibaculatus, Distaverrusporites simplex, Foveotriletes margaritae, Constructipollenites ineffectus, and Longapertites microfoveolatus. This assemblage has been attributed to the palmae and belongs to the tropical – subtropical Senonian Palmae Province of South America and African region. Samples from the Umuasua section signal Early Danian based on Cordosphaeridium varians, Damassadinium californicum, Fibrocysta licia, Carpatella cornuta, Eisenackia circumtabulata, Carpatella septata, Senoniasphaera inornata, Tectatodinium rugulatum, Kenleyia leptocerata, and Palynodinium grallator. A mangrove swamp / or near shore brackish water environment of deposition was proposed based on the important environmentally significant miospore taxa such as those belonging to the palmae. Marine microplanktons such as the peridinioid (proximate cyst) dinocyst which occurred in high abundance over the gonyaulacacean (chorate cyst) species also demonstrated strong evidence of nearshore brackish water depositional condition, with reduced salinity fluctuation. The paleogeographic conditions suggested by the miospores association indicated a warm and humid climate in the region.

Keywords: Anambra Basin, Dinoflagellates, Paleoenvironment, Sporomorph, Palmae