Sequence stratigraphic study of the Late Oligocene to Early-Middle Miocene in Niger delta, Nigeria: Application of palaeobathymetry analysis and biostratigraphy

Abstract

Stratigraphic studies that incorporated biostratigraphic and lithofacies data during the Late Oligocene to Early Middle Miocene time in the Niger Delta are scanty and therefore presents a difficult exploration target. In order to develop a high-resolution sequence stratigraphic model of this time-interval and determine its impact for hydrocarbon exploration, a sequence stratigraphical study was carried out using biostratigraphic, palaeobathymetric and lithofacies data. The sequence consists of alternating sandstones and shales, with subordinate silts. The shales are dark brown to grey. The sandstones are mostly very fine-to coarse-grained, rounded to subrounded and moderately well sorted to well sorted. The foraminiferal recovered from these strata were grouped as shallow to deeper marine environments. The palaeobathymetric interpretation shows that the sediments were deposited in a shallow, inner to outer neritic environment. Eight chronostratigraphic bounding surfaces were identified, including one transgressive surface, four maximum flooding surfaces and three sequence boundaries, the latter allowing the interval to be divided into four third-order depositional sequences (1–4). These bounding surfaces were correlated to Niger Delta palynological and foraminiferal zones, indicating that the study interval was deposited during the Late Oligocene to Early Middle Miocene. Depositional Sequences 1, 3 and 4 consist only of transgressive and highstand systems tracts, while sequence 2 consists of a lowstand, transgressive, and a highstand systems tracts. These sequences were deposited during four cycles of sea-level rise and fall during the Late Oligocene to Middle Miocene.