LATE OLIGOCENE TO EARLY MIDDLE MIOCENE FORAMINIFERAL BIOSTRATIGRAPHY, SEQUENCE STRATIGRAPHY AND PALAEOENVIRONMENT OF WELL – 004 (OML – 34) NIGER DELTA
LATE OLIGOCENE TO EARLY MIDDLE MIOCENE FORAMINIFERAL BIOSTRATIGRAPHY, SEQUENCE STRATIGRAPHY AND PALAEOENVIRONMENT OF WELL – 004 (OML – 34) NIGER DELTA
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Date
2016-01
Authors
ABUBAKAR, Usman
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Abstract
A total of seventy – two ditch cutting samples from well – 004 were described and analyzed for their foraminiferal content. Lithologic description of the samples shows that the entire sediments belong to the paralic Agbada Formation. A total of sixty three foraminiferal species were recovered out of which fourty – five are benthonics and eighteen are planktonics. The planktonic foraminifera index species recovered from the well revealed that the sediments penetrated in the well range in age from Late Oligocene to Early Middle Miocene. Five planktonic foraminiferal zones namely Globigerina ciperoensis Taxon range zone, Orbulina bilobata Interval zone, Globigerinoides altiaperturus – Catapsydrax dissimilis Concurrent range zone, Catapsydrax stainforthi Interval zone, Praeorbulina glomerosa Interval zone were proposed based on First Downhole Occurrences (FDO) and Last Downhole Occurrences (LDO) of the planktonic foraminiferal index forms. Four benthonic foraminiferal zones were also proposed, namely; Epistominella vitrea taxon range zone, Eponides berthelotianus interval zone, Ammonia sp. interval zone and Miogypsinoides sp. taxon range zone. The sediments in the studied well are considered to be of normal marine neritic depositional environment based on the triangular plot of foraminiferal suborders ratio Textulariina (arenaceous), Miliolina (porcelaneous), and Rotaliina (hyaline calcareous) deposited in dysoxic to oxic condition and Palaeobathymetry range from non-marine to outer neritic. Changes in sea level were inferred base on paleobathymetric data, foraminiferal abundance and coarsening upward nature of the study well section. From the sea level curve it can be deduced that the well sequence is characterized by four episodes of sea level rise and fall during late Oligocene to Early – Middle Miocene. The sequence stratigraphic analysis based on the available data shows that the well penetrated eight (8) system tracts made up of one (1) Lowstand Systems Tract (LST), four (4) Transgressive System Tract (TST), four (4) Highstand System Tract (HST), three (4) candidates of Maximum Flooding Surfaces (MFS) were proposed at 4,235 m, 3,906 m, 3,760 m and 3,414m. This reveals the existence of four (4) depositional sequence in the study well. The associated SB occur at 4,144 m, 3,851 m and 3,650 m. One transgressive surface (TS) was identified at 4,016 m.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF A MASTER OF SCIENCEDEGREE IN GEOLOGY DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE AHMADU BELLO UNIVERSITY, ZARIA NIGERIA
Keywords
LATE OLIGOCENE,, EARLY MIDDLE MIOCENE FORAMINIFERAL,, BIOSTRATIGRAPHY,, SEQUENCE STRATIGRAPHY,, PALAEOENVIRONMENT,, WELL – 004,, (OML – 34),, NIGER DELTA,