--> Abstract: Sequence-Stratigraphic Analysis of Middle Miocene Paralic Deposits (Agbada Formation), Ewan and Oloye Fields, Central Niger Delta, by Abimbola A. Durogbitan and Rob L. Gawthorpe; #90078 (2008)

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Sequence-Stratigraphic Analysis of Middle Miocene Paralic Deposits (Agbada Formation), Ewan and Oloye Fields, Central Niger Delta

Abimbola A. Durogbitan and Rob L. Gawthorpe
Earth Sciences, University of Manchester, Manchester, United Kingdom

We analyse depositional environments and sequence stratigraphy of the middle Miocene, north-western Niger delta based on cores, well logs and 3D seismic data. Log motif analysis, calibrated by core was used to define log facies associations which were used to identify stacking patterns and key stratal surfaces. At least six depositional sequences have been identified.

Core sedimentology and ichnology of specific intervals from two boreholes has allowed identification of three facies associations; mudstone-dominated, heterolithic and sandstone-dominated. Well log and core data indicate that the depositional environments range from lower delta plain to inner shelf.

In general, sequences are widespread and dominated by progradational HST that make up about 75% of a sequence. TST are thin but widespread, and LST are restricted to within valley fills typically 5km wide and an average 40 m deep, trending N-S. Outside the LST valleys, transgressive surfaces and sequence boundaries are coincident on interfluves. This suggests that during LST times most of the area was subaerially exposed. Sequences mapped over the study area show local variation associated with growth faults and slope scars. Typically, individual sequences are 10-15% thicker, and LST fluvial incision is greater, in the hanging wall of the growth faults.

There is strong local growth fault control on sequence variability. Individual sequences can be mapped across the study area and biostratigraphic data allow tentative correlation with regional sea level. A further local control on sequence geometry is slope collapse structures which have a strong geomorphological impact on the area. The slope scars act as a locus for fluvial lowstand incision and affect sequence thickness. The additional accommodation space above slope scars allows local development of thick HST with seismically resolvable clinoforms

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas