3-D Stratigraphic Architecture of Distributary Channel-Lobe Systems: Outcrop Analysis of the Bridges of Ross Exposure, Carboniferous Ross Sandstone, Ireland

David R. Pyles¹, Renaud Bouroullec¹, and David Jennette^2
1Department of Geology, Chevron Center of Research Excellence, Golden, CO
²Apache Oil Corporation, Houston, TX

Structurally confined submarine fans constitute significant hydrocarbon reservoirs hydrocarbons in many parts of the world including Gulf of Mexico and west Africa. These fans often contain sinuous channels and their connected lobes that compensationally stack in a distributary pattern. Although seismic data sets are exceptional for characterizing landscape features, other attributes such as facies and stratigraphic architecture are below seismic resolution. Outcrop analogs remain the primary data set from which to study facies and stratigraphic architecture in submarine landscapes.

The Carboniferous Ross Sandstone of Ireland is a submarine fan that was deposited in a structurally confined basin. This study focuses on the Bridges of Ross outcrop. The outcrop contains 20m of coeval strata that crop out on 4 peninsulas in an area of 2km x 0.5km. Data acquired to evaluate the outcrop include: (1) photopanels, (2) 3D ground based LiDAR data, (3) 100's of paleocurrent measurements, (4) stratigraphic columns, (5) architectural element boundaries, (6) facies distributions, and (7) strikes and dips of bedding.

The Bridges of Ross exposure contains seven architectural elements (1 slump, 4 lobes, 2 channels). These elements stack in a compensational pattern that is interpreted to reflect a distributary plan view pattern. Three dimensional mapping of one of the channels across the four peninsulas reveals a sinuous plan form. The channel truncates into the axis of an older lobe. Furthermore, the channel contains facies and architectural asymmetry that is associated with a channel sinuosity of 1.05. Laterally accreting bar forms occur on the inner margins of channel bends. These bar forms are associated with increased channel sinuosity and erosion. The greatest amount of facies diversity and lowest net:gross strata occurs at channel margins.

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