Currently accepted depositional models of coastal facies derive mostly from studies of modern depositional systems combined with interpretations of ancient successions. Two factors, however, can limit the efficacy of such facies models. First, Holocene coastal settings differ significantly from those in which many, if not most, ancient coastal sediments accumulated. Second, input to a model from the rock record commonly is specific to a particular tectonic and oceanographic setting (which may be poorly constrained) and is not fully exportable to other settings. This paper explores how these factors impact our interpretive capability.
Many, if not most, ancient shoreface deposits accumulated under conditions of progradation, a process relatively uncommon among the world’s present shorelines. Instead, many modern postglacial coasts experience rising sea level and reduced sedimentation, which enhances barrier-island development and influences the shoreface-to-shelf bottom profile and sand–mud distributions. Ignoring these differences promotes inaccuracy in our facies models.
Often overlooked in the application of coastal facies models are variations imposed by texture, energy level, and tectonism. Sedimentary structures on fine-grained sandy coasts differ substantially from those on a coast underlain by coarse-grained sediment. Deposits on a high-energy coast are unlike those in a low-energy setting. Differing degrees of accommodation influence the nature of the preserved succession. Some of the problems inherent in current facies models can be obviated by considering them as end members within a continuum of models that incorporate different energy regimes, textural characters, and preservational modes.
Figures & Tables
Facies Models Revisited
Conference of the Canadian Society of Petroleum Geologists) and in Dallas in 2004 (Annual Conference of the American Association of Petroleum Geologists). These sessions, entitled Facies Models Revisited, were intended to capture the state of the art with respect to facies modeling in several key depositional environments. This volume is focused on clastic depositional settings including continental (aeolian and fluvial), estuarine, shoreface, deltaic, shelf, and deep water. The approach that they encouraged with the authors to follow was a first-principles rather than a model-driven approach. Their philosophy was to provide the reader with the tools and rules to create their own models rather than providing them with “canned” models or “templates”. Following this approach, they believe that geoscientists will develop better and more predictive facies of depositional models. The editors believe this volume will find a niche with both academic as well as industry and government geoscientists.