MULTIVARIATE COMMUNITY ANALYSIS OF THE MID TO LATE PERMIAN PHOSPHORIA BASIN

Absolute-age dating of the Meade Peak Phosphatic Shale has upset the well-established biostratigraphic interpretations of the iconic Permian Phosphoria Basin, making the Meade Peak and its overlying units an estimated ~8-10 myr younger than previously thought. With this new temporal context, it is relevant to reevaluate our current understanding of regional benthic community structure, and to determine if long-standing interpretations of bioassociation are still applicable. To accomplish this, we have integrated historical paleontological collections of the greater Phosphoria Rock Complex (PRC) with modern stratigraphic and sedimentological data. We use this robust dataset to assess biotic and environmental trends at a basin-wide scale. The PRC is composed of the Park City Formation, the Park City Group, and the Phosphoria Formation (outcropping in eastern Nevada, northern Utah, western Wyoming, and southern Idaho). This region is broadly sampled geographically, with depositional environments including: (1) basinal cherts and muds to the north; (2) shallow-marine carbonates to the west and southeast; and, (3) shallow-marine siliciclastics to the east. Deposition of the PRC takes place over three primary transgressive-regressive cycles. Cycles are generally defined by the upward shallowing of basal phosphates, to cherts, to shelf carbonates or siliciclastics. Using non-metric multidimensional scaling (NMDS), we determined that benthic fauna track an onshore-offshore gradient corresponding to depositional environment/depth during each of the three stratigraphic cycles. Preliminary results suggest distinct separation of benthic communities from the east to west across the basin. This may be related broadly to lithologic preference (siliciclastic to the east; carbonate to the west), or to patterns in ocean circulation.