Oceanographic Restriction and Deposition of the Permian Park City and Phosphoria Formations, Northeastern Utah and Western Wyoming

WHALEN, MICHAEL T., Syracuse University, Syracuse, NY

Detailed lithofacies analyses of the Permian Park City Formation, in northeastern Utah and western Wyoming, reveal that it was deposited in both open and restricted continental shelf and slope environments bordering the Oquirrh and Sublett basins. The Park City and the intercalated Phosphoria Formation document the interplay between carbonate, clastic, evaporite, and organic-rich sedimentation, fluctuating sea-level and bottom water oxygenation, and oceanic upwelling.

New data from the Park City and Phosphoria formations imply that paleoceanographic models for the deposition of these units must be revised. Both physical and chemical restriction, resulting from paleogeographic constraints, regressive conditions, and the decay of organic matter produced in nutrient-rich upwelled waters, were important to the development of lithofacies patterns. Evidence of restriction includes massive and bedded anhydrite deposits and calcite replaced anhydrite nodules, carbonate facies with low levels of bioturbation and significant quantities of authigenic pyrite, and laminated black, organic-rich shales indicating low oxygen conditions. Lithostratigraphy demonstrates that evaporite sedimentation occurred during low-stands of sea level as evidenced by increased cla tic influx in shelf and slope environments. These units are overlain by transgressive, low oxygen, organic-rich facies of the Phosphoria Formation.

Park City and Phosphoria lithofacies imply that upwelling began during regression that resulted from a glacio-eustatic drop in sea level. This was accompanied by a greater pole-to-equator temperature gradient and intensified atmospheric circulation that induced eastern ocean basin upwelling. Physical and chemical restriction of marginal Permian basins was important in the development of dysaerobic to anaerobic conditions that facilitated the preservation of organic matter. The remnants of the Humbolt Highlands in Nevada and Idaho and Permian volcanic arcs in Oregon and Idaho acted as oceanographic barriers that induced physically restricted conditions during low-stands of sea level.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)