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

Vakarelov, Boyan *1; Ainsworth, Bruce 2; Nanson, Rachel A.2
(1) Australian School of Petroleum, WAVE Consortium, Adelaide, SA, Australia.
(2) Australian School of Petroleum, The University of Adelaide, Adelaide, SA, Australia.

Variables such as basin setting, distance from a shelf edge, local physiography and shoreline shape have first order effect on shoreline architecture, especially when it comes to the effects of waves and tides. Understanding the impact of such parameters may in fact offer more predictive power than sequence stratigraphy, as shorelines in different systems tracts can be exposed to similar combinations of such parameters.

To test the above hypotheses, we performed process-based analysis of 416 modern marginal marine systems from Asian coastlines. Asian shorelines were selected since they exhibit significant variability of basin, shelf and local coastal physiographic conditions. Each system has been characterized in terms of architecture and basin setting facilitating easy comparison.

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 defined by Ainsworth et al., (2011) 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 a wave-dominated category (W, Wf, Wt, Wft, Wtf), with the W and Wf categories greatly dominating. Wave-dominated shoreline 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 show dominance of mixed influence categories. This is important since mixed influence results in increased heterogeneity in the systems. This then escalates the risk of stratigraphic reservoir compartmentalization in the subsurface.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California