Walker, Roger G.¹
(1) Roger Walker Consulting Inc, Calgary, AB

ABSTRACT: Facies Models Re-visited

The term "facies" was introduced by Gressley (1838) to imply the sum total of the lithological and paleontological aspects of a stratigraphic unit. Ideas regarding the lateral shifting of facies were introduced by Walther (1894), who suggested that "only those facies and facies areas can be superimposed primarily which can be observed beside each other at the present time". Thus vertical successions of facies were deposited as depositional environments shifted. This idea re-appeared in the 1960s in the context of coarsening-upward and fining-upward sequences. The concept of "facies models" appeared in the mid-70s, to generalize the characteristics of particular depositional environments. The models for specific systems (e.g., deltas) were constructed from features observed in modern environments and ancient rocks. The resulting models served as a framework for making new observations, as points of reference for subsequent studies, as predictors in new situations, and as a basis for making environmental and hydrodynamic interpretations. Since the mid-70s, earlier static models have become more dynamic, recognizing that environments are strongly influenced by external parameters (e.g., relative sea level fluctuation). However, with more knowledge of the various environments, it has become apparent that the older, simple models are insufficient. In re-visiting "facies models" in this symposium, perhaps we find that environments are too complex for any sorts of models (a negative approach). Alternatively, it might be better to identify the depositional elements that are fundamental to specific environments, and work on understanding the variety of lateral and vertical relationships between the elements.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.