DOI: 10.5061/dryad.ngf1vhhwm
title: The effect of siliceous sponge deposition on Permian paleocommunity structure

description: A dramatic shift from carbonate-rich to chert-rich marine strata occurred
 during the Permian and is frequently attributed to the increased activity
 of siliceous sponges and their biosiliceous sedimentation. The first-order
 ecological consequences of this transition, if any, remain opaque. We
 analyze fossil occurrence data from the Phosphoria Basin (western North
 America) to test whether the presence of siliceous sponges, which are
 correlated with basin-wide chert strata, influenced the recruitment of
 benthic fauna. We digitized occurrence data from Yochelson and Van Sickle
 (1968), with particular attention to 228 fossil collections with detailed
 lithologic descriptions. We categorized fossil collections by formation,
 facies, and lithology, and used these data to code DCA and NMDS
 ordinations. We also analyzed the clustering of taxa into faunal units
 termed biofacies. Results from these analyses indicate that fossil
 collections occurring in chert and carbonate are closely associated in
 faunal composition and community structure. These collections
 preferentially occur in the inner to mid ramp facies, in agreement with
 previous studies. Although largely similar in composition, changes in the
 frequency and abundance of accessory brachiopod taxa (e.g., Composita and
 Hustedia) reflect greater biosiliceous sedimentary input.
description: We assessed the relationship between paleocommunity and lithology
 using fossil collections digitized from Yochelson and Van Sickle (1968),
 which comprises over 1,500 individual collections made throughout the
 Phosphoria Basin. Major benthic faunal groups present in the Phosphoria
 Basin include: brachiopods, bivalves, bryozoans, and gastropods. Minor
 contributions from anthozoans are also present. Fossils were collected
 from both outcrops and trenches in Wyoming, Montana, and Idaho
 (Supplementary Materials 1). Yochelson and Van Sickle (1968) report that
 no consistent method for sampling abundance was implemented between
 collectors, however, the authors note that relative abundances of fossils
 remains constant from locality to locality. We filtered the digitized data
 to include only fossil collections with detailed lithologic descriptions
 (Sheldon 1963; Cressman and Swanson 1964). Facies assignments were made
 using these lithologic descriptions. Filtering the data by these criteria
 produced a subset of 228 fossil collections and 69 taxa from 35 localities
 (Fig. 1; Table 1 and 2; Supplementary Materials 1).
 Faunal charts from Yochelson and Van Sickle (1968) tabulate
 fossil collections using a semiquantitative abundance scheme. This is: A-
 abundant, greater than 16 individuals; C- common, 6 to 15 individuals; R-
 rare, 1 to 5 individuals; X-  present, used to refer to remains which are
 disarticulated and difficult to count (e.g., disarticulate bryozoan
 branches or crinoid columnals); and, NA- absent. For statistical analyses,
 these have been converted to the following numerical values: A- 4; C- 3;
 R- 2; X-  1; absent- 0 (Supplementary Materials 1). Because of this
 semiquantitative scheme, when presenting our results, we use the terms
 frequent or occurrence in reference to the total collections with a given
 taxon, and abundance in reference to the taxon’s semi-quantitative code
 (See Faunal Composition). When possible, taxa were
 identified to species level (Yochelson and Van Sickle 1968). For
 statistical analyses, we aggregate any species level taxa to genus with
 the exception of any dubious taxon entries (typically denoted with a
 question mark) in Yochelson and Van Sickle’s (1968) faunal charts. These
 entries were removed from this study. Semiquantitative abundances were
 aggregated by taking the highest abundance category of the aggregate
 fossil entry at a particular generic level. For example, if a particular
 sample includes a genus with three species with abundance categories of C,
 R, and R, then the aggregate abundance category for that genus would be
 C. A fossil collection’s lithology was defined based
 upon the dominant lithology in its lithologic description (Supplementary
 Materials 1). Lithologic descriptions containing chert, either as nodular
 in a host rock or as bedded chert, were classified as chert. This
 inclusive definition of chert is appropriate as we seek to identify how
 biosiliceous sedimentation, preserved as chert, contributes to classically
 dominant lithologies (e.g., siliciclastics and carbonates). See Facies
 categorization for a comparison of nodular cherts vs. bedded
 cherts. A composite cool-water carbonate ramp and glass
 ramp model was used to categorize fossil collections by detailed
 lithologic description (Table 2; James 1997; Gates et al. 2004; Blomeier
 et al. 2013). Fossil collections were categorized into three facies: inner
 ramp, mid ramp, and outer ramp. The inner ramp depositional environment is
 defined as coarse to fine sand size clasts composed of bioclasts, quartz,
 or peloids with thick to indeterminate bedding, and light-colored, nodule
 to massive chert. The mid ramp depositional environment is defined as fine
 sand to silt size clasts composed of bioclasts, quartz, or peloids with
 indeterminate to medium bedding, and light-gray to medium gray, nodular to
 massive cherts. The outer ramp depositional environment is defined as
 silty to argillaceous, with limited bioclasts and quartz, thin to medium
 or irregular bedding, and medium-gray to dark-gray, nodular to bedded
 chert. Total fossil collections from each depositional environment were:
 inner ramp- 55; mid ramp- 102; and, outer ramp- 71 (Table 3). The two most
 sampled units in this analysis are the Franson Member (64 collections) and
 the Retort Phosphatic Shale member (70 collections). These two units’
 account for approximately half of all fossil collections analyzed in this
 study. The community matrix was filtered to include
 only taxa that occur in at least two different collections and collections
 that have at least two different taxa. This further reduced the data to
 105 fossil collections and 49 taxa. This procedure filters all collections
 of the Lower Chert, Rex Chert, and Cherty Shale from the community matrix.
 The Lower Chert and Cherty Shale are under-sampled as compared to the
 other units in the Phosphoria Rock Complex. The Grandeur contains many
 singletons. For some multivariate analyses, we subset the data by
 depositional cycle to explore how community structure changed through
 time. In these analyses, we use the same filtering procedure as for the
 entire dataset. This resulted in 49 collections and 32 taxa in the Franson
 cycle, and 56 fossil collections and 32 taxa in the Ervay cycle
description: This dataset includes the unfiltered faunal charts from USGS
 Professional Paper 313-D that correspond with stratigraphic sections
 reported in USGS Professional Papers 313-B and 313-C. Faunal charts were
 digitized following the procedure in methods. Data from stratigraphic
 sections and faunal charts should be joined using the collection ID
 number. This file also contains the results of ordination analyses
 presented in Wistort and Ritterbush (2022).