Can Sequence Stratigraphic Concepts Be Applied in Mudrock Systems?

Abstract

The concepts of sequence stratigraphy have become well-established approaches for defining and predicting facies architecture in sandstone/shale and carbonate systems since their development began in the 1970's. In recent years, there have been many attempts to apply these same concepts in mudrock systems. However, a review of recent literature reveals substantial departures from original concepts of both terms and application in all sedimentary systems, but especially in mudrocks. Confusion and inconsistencies exist in the usage of basic terms (e.g., sequence, sequence boundary, transgression, maximum flooding, etc) as well as in the types of data necessary to define such surfaces and events. Equally significant problems exist in the interpretation of facies stacking patterns in terms of depositional environments and accommodation. A fundamental difference between many mudrock successions and carbonate and sandstone/shale systems is the fact that the latter are defined largely by variations in sediment supply and accommodation observed along a gradient (i.e., depositional dip). These changes can typically be related to changes in sealevel, climate, tectonics, or sediment supply. Some mudrock successions, in contrast, may show no such variations, instead, being a function of geographically largely in situ variations in sediment genesis and deposition. So can we apply sequence stratigraphic concepts in mudrock systems in a way that will result in improved understanding of facies architecture? Yes, No, and Maybe. The answer depends on available datasets. Critical to success are detailed data on sediment type and origin, a depositional model that predicts changes in sediment distribution (i.e., facies) along depositional gradient, and a data set that demonstrates lateral changes in facies geometries driven by dip-related variations in sediment supply. The potential for applying sequence stratigraphy is greatest in proximal areas of mudrock systems where platform shedding of shallow water clastics and carbonates is most common and poorest in distal settings where these deposits are rare or absent.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017