Palynological and calcareous nannofossil biostratigraphy of OM-4 and OM-A wells, Western Niger Delta, Nigeria

Abstract

Palynological and calcareous nannofossils analyses were carried out on 50 ditch cutting samples each from two wells OM-4 and OM-A, Western Niger Delta, Nigeria with the aim of establishing their biozones. Studied intervals in both wells ranged from 8200 – 11350 ft. Acid method was used for palynomorph processing while smear slide method was used for calcareous nannofossil. The palynomorphs yielded 51 and 44 species in OM-4 and OM-A wells respectively while the calcareous nannofossils had a poor yield of 1 species in OM-4 well and 17 species in OM-A well. Based on the contained diagnostic marker palynomorphs and calcareous nannofossils present in the wells, three palynomorph zones, Retibrevitricolporites protrudens/obodoensis – Verrutricolporites sp. Zone (T1), Monocolporites sp. – Magnastriatites howardi Zone (T2) and Crassoretitriletes vanraadshooveni Zone (T3) were identified OM-4 well, while an indeterminate Zone(T4), Peregrinipollis niericus – Cyperaceaepollis sp Zone (T5) and Psilatriporites sp – Retitricolporites sp. Zone (T6) were identified for the OM-A well. The informal T1, T2 and T3 zones established OM-4 well corresponded to the P650, P670-P680 and P720 subzones. Also, the three zones, T4, T5 and T6 established in OM-A well, correspond to the P830, P840 and P850 subzones and the Echitricolporites spinosus pan tropical palynological zone. No calcareous nannofossil zone was established in OM-4 well due to very poor recovery, while Discoaster berrigrenni Zone (NN11) was identified in OM-A well. The wells were assigned Miocene Epoch based on the presence of Miocene markers.