Predicting Stratigraphic Architecture from Local Basin and Physiographic Settings: A Process-Based Analysis of Asian Shoreline Systems

Vakarelov, Boyan ¹; Ainsworth, Bruce ²
(1) WAVE Consortium, SedPortal Ltd, Sofia, Bulgaria. (2) Australian School of Petroleum, The University of Adelaide, Adelaide, SA, Australia.

Sequence stratigraphy is often used to link coastal depositional style to specific systems tracts. Even though such an approach has merit, it is argued that other variables, such as basin setting, distance from a shelf edge, local physiography and shoreline shape are more useful for predicting shoreline architecture, especially when it comes to the effects of waves and tides. This is because shorelines in different systems tracts can be exposed to similar combination of processes, which have a first order dependence on the shape of the marine basin fronting them.

To test the above notions, we performed process-based analysis of 416 modern marginal marine systems from Asian coastlines, which show large variability of basinal, shelfal and local coastal physiographic conditions. Each system has been characterized in terms of architecture and basin setting, which can then be compared.

Architecture is defined using a check-list of geomorphologic criteria such as presence of beach ridges and beach ridge sets, presence of tidal channels, degree of tidal funneling visible at the mouths of fluvial channels, presence of tidal flats, measure of lobateness of the shoreline, among others. Using such criteria, the systems have been placed into one of fifteen process classification categories (W; Wt, Wf; Wtf; Wft; T; Tw; Tf; Twf; Tfw; F; Fw; Ft; Fwt; Ftw) that reflect the relative impact of wave (w), tide (t), and fluvial (f) influence at a shoreline.

Basin setting parameters describe whether a system occurs on a narrow shelf (<75km), wide shelf (>75km), small embayment (<50km), large embayment (50-500km), a seaway (>500km), a combination of these, as well as additional parameters describing levels of shoreline protection (partially protected; protected; enclosed).

The results of the study show statistically significant, probabilistic relationships between basin setting and process classification. It is shown that over 90% of systems on narrow shelves belong to one of the wave-dominated categories (W, Wf, Wt, Wft, Wtf), with the vast majority of these belonging to the W and Wf category. It is also shown that the wave-dominated proportion significantly decreases on wide shelves, large embayments and continental seaways, where wave-dominated systems occur only 55-65% of the time, with tide-dominated and fluvial dominated systems becoming proportionally more important. Such systems also show overwhelming dominance of mixed influence categories.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.