Sedimentology and Ichnology of the Lower Triassic Moenkopi Formation, Southwestern Utah and Northern Arizona

Scott Mata
Department of Earth Sciences, University of Southern California Los Angeles, CA, U.S.A; [email protected]

The Early Triassic is a time interval characterized by unusual sedimentary facies related to the aftermath of the end-Permian mass extinction, and represents a non-actualistic sedimentary system in that sedimentary features do not fit actualistic models (i.e., models based upon modern environments). It is of the utmost importance to understand and incorporate this non-actualism in order to develop a sequence stratigraphic framework for Lower Triassic strata globally. For example, there is an unusual abundance of Early Triassic offshore microbialites, which would be interpreted as marginal marine using actualistic models, especially if working only with subsurface data, as is the case with a significant portion of petroleum exploration. The Lower Triassic (Spathian) Moenkopi Formation of southwestern Utah and northern Arizona represents deposition in nearshore settings ranging from offshore transition to supratidal and fluvial, and provides an ideal opportunity to develop a sequence stratigraphic framework for a non-actualistic sedimentary system and has the potential to be used as a template for understanding the sequence stratigraphy of other environmentally stressed periods. By analyzing the nearshore sedimentary facies of the formation, it will be possible to place it into a sequence stratigraphic context and document the distribution of facies within this non-actualistic sedimentary system.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid