About This Item
Share This Item
Symposium Abstracts: Paleoecology
Body Fossils of Tide- and Wave-Dominated Continental Shelves: Abstract
Important evidence on the provenance of sandstones can come from the study of their associated faunas. Analysis of the sediments and faunas of the offshore tidal sand sheet and sand bank facies on the tidal-current-dominated northwest European continental shelf has demonstrated several criteria that should be widely applicable to paleoenvironmental studies of sandstone successions and to basin analysis. The bed forms that are present in the sand sheet facies and which are related to decreasing tidal-current strength are furrows, sand ribbons, large and small sand waves, small sand waves alone, rippled sands and sand patches. Each bed form supports a characteristic fauna of potential body fossils consisting mostly of molluscs, echinoderms and crustaceans. Potential trace fossils are provided by polychaetes, echinoderms and other groups. Sand ribbons are unlikely to be preserved, but the underlying and adjacent gravel floor supports a moderately diverse fauna, which could be preserved. Large sand waves (with small sand waves on them) support a low diversity fauna comprising few individuals with low preservation potential. Diversity is greatest in the zone of rippled sand and its associated gravel sheet, and the preservation potential is much higher. Evidence currently available suggests that differentiation between active sand banks with sand waves on them and active sand wave fields is difficult if only faunal criteria are used. Bed forms on wave-dominated shelves are generally much more uniform and are broadly analogous to the rippled sand zone. By analogy, these wave-dominated sand sheets support a diverse fauna of both body and trace fossils with high preservation potential. Detailed studies are required to identify geologically significant differences between faunas of wave-dominated sand sheets and those of tidal-current-dominated rippled sands. The effects of storm-generated waves on the faunas of both tidal and wave-dominated shelves can be catastrophic and could therefore increase the preservation potential of both faunas. The leaching of body fossils in such sandstones during diagenesis causes additional problems, which must be taken into consideration.
Acknowledgments and Associated Footnotes
1 Institute of Oceanographic Sciences, Wormley, Godalming, Surrey GU8 5UB, U.K.
Copyright © 2008 by the Canadian Society of Petroleum Geologists