Understanding patterns of sclerobiont encrustation: Methodological review and application of sclerobiont facies model in Middle Devonian Appalachian and Michigan Basin paleodepth gradients

Sclerobionts have been a commonly employed litmus test to evaluate a number of paleontological and paleoecological hypotheses. As a result, data compiled on the varied group of organisms have been obtained from highly varied methods, and resulting analyses of sclerobionts are contradictory. Sclerobionts will continue to be used in widely differing studies, but when they are being used to provide insight on community paleoecology or paleoenvironments, it is imperative that scientists use a consistent method for collecting sclerobiont data, or at least understand the biases their chosen method is likely to introduce.;The purpose of this research was twofold: 1) to evaluate the validity of a spatial abundance method, visual estimation, that is both highly valuable as a quick census tool and that has been rigorously employed in Late Ordovician and Modern environments (Smrecak and Brett, 2014; Brett et al., 2012), and suggests that sclerobiont suites may be used as predictive sclerobiofacies models, and 2) to apply visual estimations and other encrustation metrics to evaluate the potential effectiveness of sclerobiofacies in two coeval basins in the Middle Devonian.;Rank abundance of a variety of methods used to assess encrustation was compared on the same sampled sclerobiont assemblage; each method reported significantly different rank orders. The most accurate method for recording sclerobiont encrustation, and baseline for comparison among the other methods, used ArcGIS image digitizing and geospatial data collecting software to precisely quantify the surface area of a host by each sclerobiont taxon. The method that most closely reflected the rank order produced by ArcGIS was visual estimation. Numerical abundance methods produced a rank order that was 20% different from that produced by ArcGIS. Frequency of encrustation rank abundance was nearly 40% different from ArcGIS rank abundance. Grid overlay methods varied widely based on the counting method used and the grid overlay design chosen.;Visual estimation of spatial abundance was the primary method used to evaluate sclerobiont encrustation patterns in the Middle Devonian Appalachian and Michigan Basins. A number of supporting data metrics were also collected, including encrustation frequency, numerical abundance, and per shell richness, to characterize the sclerobiont encrustation patterns in the basins. Sclerobiont suites in both basins behaved in a manner consistent with what would be predicted by a sclerobiofacies model; an overall decline in encrustation was observed with depth. Some sclerobiont taxa are indicative of particular facies.;Rapid influx of sedimentation in the basin also substantially impacted the observed sclerobiont assemblages. Sclerobionts declined predictably with depth in both the Michigan and Appalachian Basins, but in the Michigan Basin sclerobiont spatial coverage declined from 12% (shallow facies), to 5.4% (moderate facies) to 3.6% (deep facies), but in the Appalachian Basin the decline from 4.3% to 2.48% to 1.25% in those environments. Spatial coverage in the Appalachian Basin is substantially dampened by the high levels of sedimentation. Variability observed within samples inferred to have been from high sedimentation environments suggest that there was a threshold effect from the interplay between sedimentation and eutrophication.