Outcrop-Scale Slope Channel Architecture from Eocene Tyee Forearc Basin, Oregon

Deepwater channel-fills form one of the most prolific hydrocarbon reservoirs, which make them important targets for deepwater hydrocarbon exploration. The architecture of deepwater channels has been studied extensively from subsurface data, particularly using 3D seismic images, and much of the present understanding of their architecture comes from 3D seismic data. However, detailed facies architecture of channel sandstone bodies is usually beyond the scale of seismic resolution and documentation of outcrop-scale lithofacies variation in deepwater channels is important for predicting reservoir properties of these reservoirs. Several well-exposed, large (>500m in width, >50m in thickness) slope channel complex sandstone bodies were recorded from deepwater slope succession within the Eocene Tyee Forearc Basin-fill in central part of Coast Range of Oregon. The present study focuses on detailed lihofacies analysis of two well-exposed slope channel outcrops from central part of Tyee Basin. Reconstruction of the Tyee Basin-fill geometry indicates that these two outcrops are located on the upper slope, within clinoforms that are >500m high. The two channel complexes studied belong to the Early Eocene Tyee Formation (Hubbard Creek member) and overlying Middle Eocene Elkton Formation, both of which are predominantly muddy units. The data collected include grain-size measurement from 163 sandstone and mudstone samples, >250m of measured sections, numerous paleocurrent measurements, GPS control points and a number of photomosaics that allowed partial 3D reconstruction of the channel outcrops. Reconstruction shows that these channel complexes are composed of laterally and vertically stacked highly sand-rich channel elements and relatively fine-grained levee deposits. The channel elements are up to 20m thick and show considerable thinning laterally within 100s of m. The individual channel elements also show lateral facies variation from completely amalgamated thick-bedded sandstones (bed thickness 1-3m) to interbedded thin sandstone beds and laminated mudstones. The sandy channel elements are sometimes separated by fine-grained horizons but are more often amalgamated in varying degree indicating significant lateral and vertical connectivity between the sandstones.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California