AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A Process-Based Classification for Marginal Marine Systems: Linking the Ancient and the Modern
(1) Australian School of Petroleum, Adelaide, SA, Australia.
The interactions of wave, tide and fluvial processes at the shoreline produce complex deposits that are known as mixed-process systems. The variability of the depositional products of these process interactions are poorly understood and no classification scheme is currently available to adequately describe them. A process-based classification for marginal marine systems has thus been developed to deal with the complexity exhibited by these systems. It is equally applicable across both ancient and modern coastlines.
The classification scheme has 15 distinct categories that effectively handle mixed-process system variability. The classification system uses an intuitive three-letter abbreviation code, which describes each category. The code is based on the relative importance of preserved depositional elements and facies, in which a process component can be said to be 'dominating', 'influencing' or 'affecting' a system. A system is 'dominated' by the main preserved component (e.g., wave: 'W'). It is 'influenced' by the secondary preserved component (e.g., fluvial: ‘f'), and it is 'affected' by the tertiary and least important preserved component (e.g., tide: 't'). The code of the aforementioned system will therefore be 'Wft', which stands for a wave-dominated, fluvial-influenced, tide-affected system. Each classification category is designated by a unique code, which will describe a given range of marginal marine system architecture. The classification system differentiates between a true wave-dominated end member (W), a wave-dominated end member with some fluvial influence (Wf), a wave-dominated end member with some tide influence (Wt), or a truly mixed-process scenario such as Wft or Wtf.
Application of the process classification to ancient deposits relies on defining stratigraphic architectural units and determining the relative process dominance within those units by calculating the proportions of sedimentary structures generated by the three processes. Application of the classification to modern deposits can be made by mapping of individual depositional elements and calculating the relative areas of elements generated by the three processes. Additionally, a scheme has also been devised to attribute plan-view coastal geometries to dominant depositional processes.
The process-based classification presents a relatively simple methodology to communicate the complexities of mixed-process coastal systems from both ancient and modern settings.