BIOSTRATIGRAPHY OF THE STRATA PENETRATED BY GBOKODA-1 WELL, NIGER DELTA

Abstract

A study of the biostratigraphy of Gbokoda-1 well in the western Niger delta was carried out to unravel the age, paleoenvironment and palaeoecology of the strata penetrated by the well. Standard micropaleontological techniques were used. Sedimentological study shows that the analysed section belongs to the transitional, paralic Agbada Formation. The foraminiferal assemblage consists of thirty-two foraminiferal species, comprising three planktonics, Globigerinoides quadrilobatus, Globigerinoides sacculiferus and Globigerinodes spp and twenty-nine benthics among which are Hanzawai strattonii, Heterolepa floridana, Heterolepa inornata, Quinqueloculina lamarckiana, Amphistegina lessonii, Quinqueloculina microcostata, and Cribroelphidium decipens. A total of fifty eight (58) palynomorph species were also recorded among which are Zonocostites ramonae, Monoporites annulatus, Sapotaceapollenites sp, Retitricolporite irregularis, Retibrevitricolporites protundens, Botryococcus braunii and Laevigatosporites spp. Two major benthic informal foraminiferal zones were recognized. They are the Hanzawaia Strattonii / Amphistegina lessonii zone (1216–1838m) and the Amphistegina Lessonii / Cribroelphidium Decipens Zone (1838-2057m). The studied interval of the well falls within the broad pan tropical Echitricolporites/ Spinosus zone and dated middle Miocene to late Miocene. Four paleobathymetric environments of deposition were deduced, namely: coastal deltaic, inner neritic, inner neritic-middle neritic and middle neritic. From the percentage composition of Monoporites annulatus and Zonocostites ramonae, the sequences were deposited under alternation of wet and dry climatic conditions