ABSTRACT: A Conceptual Model of Facies Distribution in Incised-Valley Estuaries

DALRYMPLE, ROBERT, Queen's University, Kingston, Ontario, Canada, BRIAN ZAITLIN, Esso Resources Canada Ltd., Calgary, Alberta, Canada, and RON BOYD, Dalhousie University, Halifax, Nova Scotia, Canada

This presentation describes the first comprehensive facies models for incised-valley estuaries. These models are based on the recognition that estuarine facies distribution is controlled by the interaction of marine processes (wave and/or tidal currents) that decrease in intensity up-estuary, and fluvial processes that become less energetic down-estuary. Because of this, all estuaries exhibit a three-fold subdivision: an outer, marine-dominated portion; a low-energy central zone (where there is net bedload convergence); and an inner, river-dominated (but marine-influenced) part. The relative influence of waves and tides divides estuaries into two distinct but intergradational types with unique facies assemblages. Wave-dominated estuaries have a well-defined tripartite zonation: barrie sand body, fine-grained central basin, and bay-head delta. The tripartite subdivision of tide-dominated estuaries is less obvious because of the relative ease with which tidal energy penetrates the estuary. The marine sand body consists of elongate sand bars and sand flats, and the central zone is represented by a region of tight meanders that pass up and down estuary into straighter, tidal-fluvial channels. No bay-head delta occurs. The extent of the three facies zones depends on various factors including the coastal-zone gradient; the grain size and amount of sediment supplied by the marine and river sources; the shape of the incised valley; and the evolutionary stage of the estuary. Changes in relative sea level control the direction of estuary evolution (expansion or infilling), and the facies stacking pattern.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)