Geology, Palynomorphs Distribution, Stratigraphy and Depositional Environments of Lewumeji and Idogun Wells, Eastern Dahomey Basin Southwestern, Nigeria

Abstract

Selected composited samples from Lewumeji (0-111m) and Idogun (0- 54m) wells, from Abeokuta Group, Eastern Dahomey Basin, Nigeria, were subjected to detailed lithologic and palynological studies. The studies aimed at determining the lithological sequence, relative age, palynological zone and paleoenvironments of deposition. The core samples were subjected to lithological description and palynological analysis using standard procedure in order to determine palynomorphs contents such as pollen, spore and dinoflagellates. The lithologies from both wells consist of reddish to brown clay, reddish to brown colour, rounded to sub rounded sandstone, dark grey shale denoting possibly fluvial, brackish, lagoonal and marine environments. A total of 31 well preserved low to moderate diverse palynomorphs were recovered from the studied area. The palynomorphs frequency percentage distribution shows that both wells have a higher ratio of land-derived pollen and spores to the marine dinoflagellates; (75%, 25% and 61%, 39%) for Lewumeji and Idogun wells respectively. The microfloral assemblages include abundant Cyathidites sp., Cyathidites minor, Tubistephanocolpites cylindricus, Proteacidites sp., Trilete spore, Foveotriletes margaritae, Monocolpites marginatus, Monoporites annulatus, Pteris sp, Distaverrusporites simplex and Laevigatosporites sp. The dinoflagellates recovered were characterized by the likes of Leiosphaeridia sp., Senegalinium sp., Oligosphaeridinium sp., Paleocytodinium sp., Cerodinium sp. and Subtilisphaera sp. The wells fall within Cyathidites Minor zone, characterized by the diagnostic occurrence of Cyathidites minor, Cyathidites sp. and Monocolpites marginatus dated Upper Maastrichtian to early Paleocene. Paleoenvironmental interpretations based on the abundance of freshwater swamps pollen and Spores, diagnostic dinoflagellates cyst and the Palynomorphs Marine Index (PMI) are suggestive of environmental settings that vary from continental to brackish water and shallow marine.