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Mouth-Bar Element Complexes: Internal Architecture and Effect of Depositional Process on Modern Deltaic Systems

Abstract

A database of modern mouth-bar deposits sheds new light on the internal architecture of deltaic systems. The study illuminates the relationships between (i) sizes, shapes and along shoreline distances between such deposits and (ii) formative fluvial, wave and tide processes, as well as water depth. The dataset can be used for building an improved predictive framework for the high degree of facies variability and heterogeneity commonly observed in deltaic strata.

The database contains 632 mouth bar deposits with maps and metadata, which have been identified through the use of satellite imagery and bathymetric data. Mouth-bar deposits were mapped by identifying shifts in breaker zone locations and other shallow water depth proxies through time based on 30 years of historical imagery. Using data with temporal control illustrates the highly dynamic nature of such deposits. In addition to geospatial measurements (strike extent, dip extent, perimeter, area), each location is also assigned parameters for mean significant wave height, 10 year storm wave height, and mean spring tidal range. Each data point is also assigned values for water depth 5km and 10km seaward from the mouth bar, which are used as proxies for depth of progradation, foreset and shelf gradient, as well as measurements of the distance to the adjacent mouth bar deposits and the angle between the shoreline and the feeder channel.

The mapped mouth-bar deposits can be considered as the seaward portions of active mouth-bar element complexes (WAVE terminology). The shoreline strike extent of the mapped deposits can be used as a direct proxy for the lateral extent of the associated element complexes. The dip extent, in contrast, does not typically correspond to the full progradational length of the parent mouth-bar element complex. This length is determined by a point, typically some distance landward from the shoreline, which refers the site where mouth-bar formation initiates after a new channel avulsion. In distributive systems, this point always corresponds to an element complex set (ECS) boundary.

The mapped deposits show how mouth-bar element complexes develop internally. Such deposits are typically formed by child architectural units (mouth-bar element sets) which control reservoir heterogeneity and have distributions highly affected by local shoreline processes. We apply the key learnings from the new dataset to interpretation of outcrop and the subsurface data.