Chapter 133: Architectural Elements in a Ponded Submarine Fan, Carboniferous Ross Sandstone, Western Ireland

Abstract

Abstract The Carboniferous Ross Sandstone of western Ireland is constructed of four architectural elements: channels, lobes, chaotic-contorted bodies, and mudstone sheets. The elemental amounts in the Ross exposures studied are 5%, 56%, 12%, and 27%, respectively. Each architectural element is unique in terms of its cross sectional shape and aspect ratio, and each occupies a unique domain on a thickness-versus-width plot. Lobes are the dominant architectural element in the Ross Sandstone. The architectural elements are formed by distinct paleobathymetric features. Channels are formed by submarine channels. Lobes are formed by deposition that occurs basinward of submarine channels. Chaotic-contorted bodies are formed by slumps. Mudstone sheets are formed by dilute turbid flows and blankets of fine-grained, pelagic and hemipelagic sediments. Architectural element analysis of outcrops provides a method for studying how ancient submarine landscapes evolve over geologic time scales. Of the four architectural elements, only the channels and mudstone sheets are observed to stack in a hierarchical manner. The hierarchical levels of channels include: channel story, channel element, and channel complex. Channel elements record a distinctive phase of downcutting and filling. The hierarchical levels of mudstone sheets are sheet and sheet complex. Mudstone sheets do not contain goniatites, and their correlation lengths are less than 18 km (11.2 mi). Mudstone sheet-complexes contain goniatites, and they can be correlated around the entire basin (>40 km [>25 mi]). The four different architectural elements in the Ross Sandstone contain unique attributes that allow them to be distinguished using one-dimensional data sets (e.g., core, gamma-ray, and dip-magnitude data). The distinguishing one-dimensional attributes of architectural elements in the Ross Sandstone may apply to architectural elements in the ponded phase of northern Gulf of Mexico minibasin-fill successions. The Ross Sandstone and the ponded phase of individual northern Gulf of Mexico minibasin-fill successions have numerous similarities including basin size, shape, architectural elements, depositional processes, and thickness. If architectural elements can be interpreted using one-dimensional data sets, the cross sectional dimension of reservoir bodies may be predictable using thickness-versus-width plots from the Ross Sandstone.