Palynofacies, sedimentology and palaeoenvironment evidenced by studies on IDA-6 well, Niger Delta, Nigeria

Abstract

Palynofacies and sedimentological analyses of the strata penetrated by Ida-6 well were undertaken with the aim of determining biozones and the palaeoenvironmental conditions. Fifty ditch cutting samples within the intervals of 2679–4051 m were analysed. The analysis yielded low to abundant recovery of pollen and spores, small to large sizes of palynomaceral 1 (irregularly shaped, orange-brown to dark-brown coloured and opaque plant debris), palynomaceral 2 (irregularly shaped, brown-orange coloured platy plant materials), and few occurrences of palynomaceral 3 (pale to brown coloured, cuticular, and translucent plant materials). The lithology showed alternation of shale and sandstone units with few intercalations of siltstone units. The sandstone units consist of fine to medium grains, occasionally coarse to granule sized. The sand grains are mostly sub-angular to sub-rounded, occasionally rounded, and generally poorly to moderately sorted. The accessory minerals are dominated by ferruginous material, shell fragments and carbonaceous detritus with spotty occurrences of mica flakes. The lithologic, textural, and wire line log data indicated that the entire studied intervals in the well belong to the Agbada Formation. The studied intervals were deposited during middle Miocene to late Miocene based on the recovered age diagnostic marker species such as Multiareolites formosus, Verrutricolporites rotundiporus, Crassoretitriletes vanraadshoveni and Racemonocolpites hians. Three interval range zones were established using the international stratigraphic guide for the establishment of biozones. The three established palynostratigraphic zones are Multiareolites formosus Lavigatosporites sp., Racemonocolpites hians–Crassoretitriletes vanraadshoveni and Psiltricolporites crassus—Acrostichum aureum Zones. Coastal-deltaic environments of deposition have been inferred for the studied interval of the well on the bases of the palynofacies association and sedimentological characteristics.