PALEOECOLOGY OF SILICEOUS SPONGES IN COASTAL MARINE SETTINGS ALONG WESTERN PANGEA USING DEPOSITIONAL MODELS FROM PERMIAN CHERTS OF NORTHWESTERN UTAH

The Permian chert record in northwestern Utah offers the opportunity to study biological activity in marine systems along western Pangea. Siliceous sponges are thought to have played important ecological engineering roles in benthic communities along inner and middle ramp zones in shallow, temperate ecosystems during this time. This is evidenced by abundant, thick beds of spiculitic chert, many over a thousand meters thick, in Utah outcrops. An investigation of Permian units spanning the transition from marine carbonates to biogenic cherts will reveal environmental conditions and ecological processes that contributed to the initiation and proliferation of siliceous sponge colonies along western Pangea.

We present an investigation of this shift from detailed analyses of environmental and biotic conditions from outcrop- to bed-scale units in northwestern Utah to constrain rates and mechanisms of sponge expansion along coastal zones of western Pangea, including geological mapping, stratigraphy, and microfacies analysis. Preliminary results confirm that many cherts contain abundant spicules, or exhibit evidence that spicules existed at the time of original deposition but have since been recrystallized or replaced through diagenetic processes. We developed eight lithofacies from stratigraphic measurements in lower to middle Permian units. Inner-ramp facies include mixed carbonate-chert fossiliferous grainstone and carbonate grainstone with abundant chert-filled burrows. Middle to outer ramp facies increase in chert content, with spiculitic chert filling larger nodules and lenses, and eventually composing entire beds. Stratigraphic trends are generally consistent between field sites in the northwest desert.

Microfacies analyses show evidence of deposition in moderate- to high-energy environments between offshore shelf to lower shoreface zones. We present initial interpretations for bed-scale models of sedimentation and depositional models of outcrop, local, and regional scale features. Further analysis will determine the geographical extent and depths of siliceous sponge colonies along continental ramps of western Pangea and interpret how sponges contributed to sedimentation and ecological engineering in benthic communities at this critical time in Earth history.