Depositional facies and palynofacies provenance reconstruction of the Danian Nsukka Formation, Southeastern Nigeria

A combined detailed palynofacies and lithofacies analysis was carried out on the Nsukka Formation outcropping Danian (Palaeocene) lithostratigraphic units in the Ikpankwu domain (SE Nigeria) for the first time. Lithological characteristics of grain size textural attributes, sedimentary structure and microflora palynofacies elements were instrumental in deciphering eight lithofacies: carbonaceous shale facies (Shfc), claystone facies (Csf), mudstone facies (Mfm), cross-bedded sandstone facies (Spt), siltstone facies (Fmt), heterolith facies (Fls), structureless sandstone facies (Smc), plane parallel laminated sandstones facies (Pls) and seven sub-facies deposited within low- to high-energy environment. These lithofacies and palynofacies-induced sedimentary attributes were grouped into three facies association (FA1, FA2 and FA3) and palynofacies types to delineate the principle palaeoenvironments, palynofacies provenance and depositional mechanisms triggered by hydrodynamic antics of the Nsukka Formation. The palynomaceral elements display superiority of large to medium-sized well-preserved brown to dark brown Palynomaceral 2 phytoclasts and terrestrial sporomorphs, Palynomaceral 4 and limited number of Palynomaceral 1 and Palynomaceral 3. The lithofacies and palynomaceral hydrodynamic array indicate that the mudrock facies of shale, mudstone and siltstone are deposits of lower deltaic plains or Lagoon with high terrestrial microflora input, while the sandstone facies depicts sediment of the upper deltaic plain (upper shoreface) or coastal tidal settings with overall effective oscillation tendency from tidal flat, lagoon to nearshore with open marine-influenced setting. The lithofacies and palynomaceral provenance prototype suggest terrestrially dominated shallow marine and tidally influenced outer neritic environment signalled from the quality and quantity of land-derived palynofacies components in association with few AOM and Kenleyia spp. and Spiniferites ramosus dinocysts, foraminifera test lining along with Laevigatosporites sp., Longerpertites group and other pollen and spore microflora. Lithofacies and palynomaceral organic matter in fluvial and inner neritic deep marine-influenced paralic strata of the study exhibit a perfect model for appreciating the lithological changes associated with a larger diversity of palynomaceral elements in marine and non-marine settings along with those of fluctuating salinity in the water realm.