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From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Houston, Texas, April 9–12, 2006 Hierarchical Stacking of Submarine Channels and
Abstract: The Carboniferous Ross Sandstone of western Ireland contains some of the world's best exposures of submarine channels and lobes. A detailed study of the Ross Sandstone at Loop Head Peninsula was carried out to address the vertical stacking of these architectural elements. Locally at Loop Head Peninsula, channel-form bodies increase upward from 3 to 7% (by cross-sectional area). Although the proportion of channel-form bodies increases upwards, lobe-form bodies remain the dominant architectural element in the Ross Sandstone. A regional cross section demonstrates that the upward increase in proportion of channel-form bodies does not reflect changes in distance from the shelf edge or changes in the physiographic position. Rather the basin-scale stacking patterns are aggradational and strata at Loop Head Peninsula always record medial basin-floor strata. Regardless of stratigraphic position, outcrops of the Ross Sandstone at Loop Head Peninsula contain the same architectural association. That association is (1) highly erosional channel-form bodies with master erosional surfaces (2) weakly erosional channel-form bodies with serrate margins and (3) lobe-form bodies. The juxtaposition of highly erosional and depositional architectural elements is interpreted to result from a hierarchical stacking of submarine channels and their basinward lobes on an aggrading distributary landform. The hierarchy includes three levels: individual channel-lobe systems (6th order), distributary channel-lobe systems (5th order), and distributary channel-lobe complexes (4th order). The external shape of each system is the same in plan view; however, size and time span of existence increases by the hierarchical level. |