Scaling, Sedimentologic and Geometric Criteria for Comparing Modern and Ancient Sandy Turbidite Elements

Morris, W.R., Arco Alaska Inc, Anchorage, AK, and W.R. Normark, US Geological Survey, Menlo Park, CA

Abstract

Deep-water depositional systems are formed by combinations of turbidite and basin slope elements, which can be recognized from modern and ancient settings using outcrop observations, seismic-reflection data, or well-log and core data. Elements can be compared between systems to derive general sedimentologic parameters only if like elements are compared, requiring that the physical scales, geometry, and timescales (duration of activity) are reasonably similar. In some deposits, one or more of the elements are represented by several distinct sub-elements, e.g., a succession of both lensoid and wedge-shaped lobe deposits can comprise the lobe element area. The different lobe sub-elements develop in response to shifts in position of the channel mouth and changes in the sediment supply. Turbidite-channel elements are a common reservoir target. An understanding of the dimensions, facies, and stratigraphic development of modern and ancient turbidite channels can provide critical data both for exploration and development of resources occurring within channel systems and for distinguishing them from other similarly appearing, laterally restricted channel-like features such as crevasse-splay channels, channel thalwags, megascours, and megaflutes.

Improvement in our understanding of the geometric and sedimentologic characteristics of specific turbidite elements (e.g., channels, where there is an understanding both of their linkage to coeval elements, such as overbank or lobe deposits, and of the associated depositional processes) can eventually lead to predictive models specific to each basin. This approach is preferred to forcing data to fit overly simplistic, ad hoc models.