STRATIGRAPHIC STANDARDS AND SEQUENCE STRATIGRAPHY

zhazi_hou

2010 GSA link
http://gsa.confex.com/gsa/2010AM/finalprogram/abstract_182372.htm

TRATIGRAPHIC STANDARDS AND SEQUENCE STRATIGRAPHY: THE QUEST FOR FORMALIZATION CONTINUES

ABREU, Vitor1, NEAL, Jack1, BLUM, Mike1, BOHACS, Kevin M.2, DEMKO, Tim2, GARFIELD, Tim1, KENDALL, Christopher3, GESLIN, Jeff1, JONES, Clive1, and KALBAS, James L.4, (1) ExxonMobil, Houston, TX 77210, vitor_abreu@yahoo.com, (2) ExxonMobil Upstream Rsch Co, 3120 Buffalo Speedway, Houston, TX 77096, (3) Geological Sciences, University of South Carolina, Columbia, SC 29208, (4) ExxonMobil Development Company, Houston, TX 77381

Attempts to formalize sequence stratigraphy over the last 2 decades have been challenging and divisive because of model-driven versus observation-based interpretations, cumbersome nomenclature, and imprecise and inconsistently-used definitions. The association between base-level changes, formation of surfaces, and stratal stacking that define systems tracts is at the heart of the confusion. In some cases, terms like "highstand" and “lowstand” have been used to identify systems tracts because of specific stratal stacking, whereas in other cases, stratal stacking has been inferred to reflect relationships to sea level because of the terms themselves. Considering that sea level changes cannot be directly observed from the geologic record, this terminology implies the need of a "model" to interpret geologic data. Moreover, these terms conflict with others that are related to shoreline translation, or processes that can be directly observed from the geologic record, such as "transgression", "regression", "progradation", and “retrogradation".

We propose a "back-to-basics" approach, emphasizing five key observations that can be made from any geologic data: lithofacies, lithofacies association, vertical stacking, stratal geometries and stratal terminations. These observations should be placed in the context of the lateral movement of the shoreline (transgression and regression) and shoreline trajectory (shelfal accommodation creation and destruction). Model-driven terms like highstand, lowstand, maximum flooding surface, and falling stage should be abandoned and replaced by observation-based terms like aggradation-progradation, progradation-aggradation, surface of maximum transgression and degradation, respectively. Finally, after more than 20 years of applications, much basic research remains to be done on the relationship between stratal stacking, and various controls, and on the formation and significance of key surfaces that demarcate changes in stacking patterns.