Bridging the Gap between Sedimentology and Sequence Stratigraphy: A New Architectural Classification for Marginal Marine Deposits

A new hierarchical architectural classification for marginal marine systems, based on the process classification of Ainsworth et al.
(2011), is presented. The architectural scheme covers the full range of observation between sedimentology (e.g., core, outcrop) and sequence stratigraphy (e.g., wireline logs, seismic). The classification uses five architectural levels: (i) Element; (ii) Element Complex; (iii) Element Complex Assemblage; (iv) Element Complex Assemblage Set; and (v) T-R Sequence.

Elements (E) are the basic building blocks of depositional systems and represent 3D, mappable small-scale geomorphologic units and their subsurface equivalents (e.g., Beach Ridge Element). Element Complexes (EC) refer to portions of depositional systems that are characterized by limited facies variability and are deposited under similar fluvial, wave and tide process conditions (e.g., W-Beach Complex). Element Complex Assemblages (ECA) are also tied to the process regime at the shoreline but on a more regional scale and typically describe entire depositional systems (e.g., Wf-Complex Assemblage). Significant down dip or along strike changes in process conditions requires the definition of a new assemblage. A list of elements, element complexes, and element complex assemblages that cover most of the variability in marginal marine depositional systems has been compiled.

The last two levels of the classification refer to the more regional distribution of marginal marine deposits in response to transgression and regression. A set of ECAs occurring in a transgressive package will form a Transgressive Element Complex Assemblage Set (TECAS), while its regressive counterpart will form a Regressive Element Complex Assemblage Set (RECAS). A TECAS - RECAS pair will form the highest level of the classification, a T-R Sequence. The five levels of architecture describe the full variability of modern and ancient marginal marine systems. The classification clearly separates process from architecture, clearing some discrepancies existing in current nomenclature.

A modern and an ancient case study are used to illustrate how the classification is applied in practice. Both systems are highly variable, mixed influence and are not effectively described by previous classifications. The structured nature of the new architectural classification is highly suitable for use in geospatial databases. The scheme is also effectively used as a tool for handling uncertainty in the subsurface.

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