Pyles, David R.1
(1) University of Colorado, Boulder, CO
ABSTRACT: On the Stratigraphic Evolution of a Structurally-Confined, Submarine Basin—Carboniferous Ross Sandstone, Western Ireland
The Carboniferous Ross Sandstone was deposited as a submarine fan in a structurally-confined basin. This study utilizes a multi-scale dataset comprising structural, biostratigraphic, and paleocurrent data for the entire Ross outcrop; one well log; and detailed correlation panels, photopanels, and ILRIS data of five laterally-continuous exposures of the Ross. These exposures represent a continuum from basal to upper Ross strata.
The 400m-thick Ross Sandstone displays a systematic, vertical change in net:gross, diversity of architectural elements, diversity of facies, amount of erosional surfaces, and distribution of paleocurrents. The net: gross in the Ross shows an increasing then decreasing trend from 0.2 in the basal Ross, increasing to 0.9 in the middle Ross, decreasing to 0.6 in the upper Ross. The diversity of architectural elements increases vertically from slumps and tabular mudstone sheets in the basal Ross, to lobe-form bodies and tabular mudstone sheets in the lower Ross, to channel-form bodies, lobe-form bodies, slumps, and tabular mudstone sheets in the upper Ross. The diversity of facies increases vertically, from 5 facies in the basal Ross to 13 in the upper Ross. The number of erosional surfaces/meter increases vertically from 0.2 in the lower Ross to 1.0 in the upper Ross. The distribution of paleocurrent directions increases vertically from 20 degrees in the basal Ross to 110 degrees in the upper Ross.
These systematic changes are interpreted to reflect temporal changes in the depositional landscape as the basin filled. These changes include increasing depositional area, decreasing accommodation, decreasing potential energy, and decreasing confinement.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.