Control of syndepositional faulting on systems tract evolution across growth-faulted shelf margins: An analog experimental model of the Miocene Imo River field, Nigeria

Abstract

The presence of growth faults on shelf-margin deltas complicates the sequence-stratigraphic interpretation of deltaic successions. This article describes an analog modeling study of a growth-faulted shelf-margin delta. The aim of the project was to obtain a better understanding of the depositional architecture on a systems tract scale on both sides of the growth fault and to evaluate possible hydrocarbon-trapping configurations in such successions. The analog flume experiment incorporated the combined effect of growth faulting, regional subsidence, and eustasy on hanging-wall and footwall blocks. Experimental variables were based on seismic and well data of the Imo River field in the Niger Delta, which was used as a prototype to calibrate the experimental results. The spatial scale of the model, in conjunction with the supply rate, result in a time scaling that models basin-fill processes that operated over more than 5 m.y. in 90 hr of experiment. Digital topography scans, required for the determination of the bulk sediment transport, were made of the landscape at preset time intervals. The resultant experimental sedimentary successions on both sides of the growth-faulted shelf margin were sliced and correlated across the fault. The results first were compared to the Imo River field prototype and subsequently to examples from the Gulf Coast and to extensional basin settings. These comparisons led to the formulation of a conceptual sequence model for growth-faulted margins that relates the systems tract distribution on each side of the fault to eustasy. The hanging-wall succession is composed of falling stage, lowstand, and early transgressive deposits. The footwall succession, in contrast, is characterized by late transgressive, incised valley-fill, and highstand deposits. The conceptual sequence model provides useful analogs for common and several alternative hydrocarbon-trapping configurations in growth-faulted settings.