Geomorphological Development of a Deepwater Fan: Three-Dimensional Insights from Ultra-High Resolution Seismic Data, East Breaks Basin IV (Upper Fan), Offshore Texas, Gulf of Mexico

Edwards, Chris¹, David Hoyal¹, Benjamin Sheets², Paul Dunn¹ (1) ExxonMobil Upstream Research Company, Houston, TX (2) ExxonMobil Upstream Research Company, Houston,

An ultra-high resolution seismic volume (~200 Hz peak frequency) calibrated by research cores and ODP boreholes provides the foundation for a hierarchical analysis of the geomorphology and stratigraphy of a deepwater fan within a Pleistocene intraslope basin (Basin IV) of the Trinity-Brazos slope system, north-central Gulf of Mexico. In particular, the detailed nature of the transition from tributive to distributive regions of the system is observed. This transition is identified by a down-dip progression from relatively straight (sinuosity indices typically less than 1.1), vertically-amalgamated,tributive trunk channels that can exceed 300 m in width, to distributive systems composed of kilometer-scale depositional lobes, with associated intricate networks of bifurcating distributary channels up to 50 m wide, and smaller scale mouth bars up to 300 m long and 100 m wide. Analysis of the fill history reveals that the trunk channels and the deposition of their linked down-slope components are initiated by autocyclic avulsion events, probably controlled by localized depositional fan gradients, producing a compensational stacking arrangement of the larger-scale lobe features. These avulsion events have been replicated in laboratory deepwater tank experiments, where depositional processes are observed through time-lapse photography, topographic scans and post-experiment sectioning. In these experiments, avulsions result from sediment back-filling into the channel before diverting flow to a new course that ultimately becomes a new extension of the main trunk channel. Collectively, these datasets provide the basis for a hierarchical and statistical analysis of deepwater distributary systems that will lead to improved reservoir models.