--> Microbial Mounds in the Timpoweap Member of the Lower Triassic (Smithian) Moenkopi Formation, Hurricane Cliffs, SW Utah

AAPG ACE 2018

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Microbial Mounds in the Timpoweap Member of the Lower Triassic (Smithian) Moenkopi Formation, Hurricane Cliffs, SW Utah

Abstract

In the study area on top of the Hurricane Cliffs located 25 km SE of St. George, Utah, the 5 meter-thick Timpoweap Member of the Moenkopi Formation is comprised of a series of microbial mounds separated by stratified inter-mound strata. The Timpoweap is continuously exposed over a 50 meter traverse in a dry gully bottom. Nine domal buildups with massive cores and tilted flanking beds are exposed along the traverse. The mounds are approximately 2.3 meters high and average approximately 6 meters wide. The mound cores are massive in outcrop and comprised of microbial boundstone with variable abundances of non-skeletal carbonate grains, chiefly oncoids and pisoids. Flanking and inter-mound beds are dominated by non-skeletal grains with lesser amounts of microbial material. The mounds represent an interplay between biological and vadose diagenetic processes that developed on a shallow subtidal shelf in the aftermath of the Permo-Triassic extinction. Syndepostional vadose diagenesis resulted in cracking of ooid cortices and rapid cement stabilization of the mounds.