From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005

Basin-Scale and Local Stacking Patterns of the Carboniferous Ross Sandstone, Western Ireland: Applications to Northern Gulf of Mexico Minibasin Reservoirs

David Pyles

Abstract:

A regional data set in the Carboniferous Ross Sandstone of western Ireland illustrates that: 1) the locus of the depocenter of submarine-fan strata did not change through time, 2) depositional area increased through time, 3) sediment supply to the basin increased through time, and 4) the entire Ross correlates up paleocurrent direction into an unconformity. These observations demonstrate that the Ross filled an actively subsiding, structurally confined basin, basin-scale stacking patterns were aggradational, and submarine-fan strata were deposited basinward of an “out-of-grade” basin margin.

Locally, at the center of the basin, the Ross Sandstone contains several systematic upward trends including: 1) increasing paleocurrent diversity, 2) increasing channel-form bodies, 3) increasing chaotic-contorted bodies, and 4) decreasing sandstone. These systematic upward trends may be related to the following temporal changes in basin-scale conditions: 1) increasing sediment supply, 2) increasing depositional area through time/decreasing confinement, 3) increasing steepness of the proximal slope, 4) decreasing accommodation, and 5) increasing contribution of a western provenance.

The Ross Sandstone and “ponded” strata in Gulf of Mexico minibasins have numerous attributes in common: 1) deposition during high-frequency, high-amplitude, eustatic changes in sea level; 2) deposition in structurally confined basins of similar shape and size; 3) thickness of third- and fourth-order stratigraphic cycles; 4) aggradational basin-scale stacking patterns; 5) 0.5 to 5 degree gradients on the proximal slope; 6) subsidence focused at the basin-center position; and 7) high percent sandstone submarine-fan strata. Therefore, the Ross Sandstone is considered and excellent outcrop analog to Gulf of Mexico minibasin reservoirs.