Presumed chaetetids in Smithian (early Olenekian,
Early Triassic) microbial-sponge limestones, Rock
Canyon, Arizona, USA

Nicolas Olivier, Arnaud Brayard, Bernard Lathuiliere, James F Jenks, Kevin

G Bylund, Daniel A Stephen, Gilles Escarguel, Emmanuel Fara

► To cite this version:

Nicolas Olivier, Arnaud Brayard, Bernard Lathuiliere, James F Jenks, Kevin G Bylund, et al. Pre-
sumed chaetetids in Smithian (early Olenekian, Early Triassic) microbial-sponge limestones, Rock
Canyon, Arizona, USA. Lethaia, 2025, 58 (2), pp.1-23. 10.18261/let.58.2.6 . hal-05111391

HAL Id: hal-05111391

https://hal.science/hal-05111391v1

Submitted on 13 Jun 2025

**HAL** is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# Presumed chaetetids in Smithian (early Olenekian, Early Triassic) microbial-sponge limestones, Rock Canyon, Arizona, USA

NICOLAS OLIVIER, ARNAUD BRAYARD, BERNARD LATHUILIERE, JAMES F. JENKS, KEVIN G. BYLUND, DANIEL A. STEPHEN, GILLES ESCARGUEL AND EMMANUEL FARA

LETHAIA

<figure><img src="image_3.png" /></figure>

Outcrops in Rock Canyon (northwestern Arizona) show a Smithian (early Olenekian, Early Triassic) sedimentary succession recording a marine transgression over fluvial conglomerates and leading to several metre-thick microbial limestones. These microbial limestones are associated with a diverse sponge assemblage including keratose demosponges, halichondrids, geodiids, lyssacine hexactinellids, and presumed chaetetids, suggesting that Early Triassic sponge communities were more diverse than previously thought. A presumed chaetetid (hypercalcified demosponge) specimen, identified by its lamellar 3D structure, shows slightly raised, subcircular domal structures formed by narrow, joining tubes arranged in a bush-like pattern. Microscopic observations also reveal residual tabula and sparse spicules. Other presumed chaetetid specimens show intense recrystallization that obliterates most of their characteristic skeletal structure. Although chaetetid sponges are well-documented in the Palaeozoic, they were absent until now from the Late Permian to Late Triassic record. Occurring about 2.5 myr after the Permian-Triassic extinction, the specimens from Rock Canyon would be the first Early Triassic chaetetids and the oldest known in the Mesozoic record. The rarity of Early Triassic chaetetids may be due to sampling and taphonomic biases. Their intense recrystallization and elongated shape exhibit a morphological convergence with large fenestrae commonly found in microbial limestones. During the Early Triassic, builds composed of microbial limestones and sponges were widespread, occuring in the Panthalassa, Neotethys and Palaeotethys oceans across various depositional settings, from saline lagoons to open marine environments of varying depths. This broad distribution questions the view that these microbial-sponge communities were confined to localized refuge settings or stressful environmental conditions in the aftermath of the Permian-Triassic crisis. *Chaetetids, sponges, microbialites, taphonomy, palaeoenvironments, Early Triassic, Smithian*

Nicolas Olivier [nicolas.olivier@uca.fr], Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France; Arnaud Brayard [arnaud.brayard@u-bourgogne.fr], Emmanuel Fara [emmanuel.fara@u-bourgogne.fr], Université Bourgogne Europe, CNRS, Biogéosciences UMR 6282, 6 Boulevard Gabriel 21000 Dijon, France; Bernard Lathuilière [Bernard.Lathuilière@univ-lorraine.fr], Université de Lorraine, CNRS, Lab. GeoRessources UMR 7359, BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex, France; James F. Jenks [jenksjimruby@gmail.com], 1134 Johnson Ridge Lane, West Jordan, Utah 84084, USA; Kevin G. Bylund [kgbylund@gmail.com], 140 South 700 East, Spanish Fork, Utah 84660, USA; Daniel A. Stephen [Daniel.Stephen@uvu.edu], Utah Valley University, Department of Earth Science, Orem, Utah 84058, USA; Gilles Escarguel [Gilles.Escarguel@univ-lyon1.fr], Université Claude Bernard Lyon 1, LEHNA UMR 5023, CNRS, ENTPE, F-69622, Villeurbanne, France; manuscript received on 18/11/2024; manuscript accepted on 19/02/2025; manuscript published on 11/06/2025 in *Lethaia* 58(2).

Following the Permian-Triassic mass extinction – the most severe Phanerozoic biotic crisis – the Early Triassic is often portrayed as an interval of a long and delayed marine ecosystem recovery (Hallam 1991; Erwin 1998; Algeo et al. 2011; Song et al. 2011; Benton 2018). Among others, this 5-myr-long interval records marked perturbations of the global carbon cycle (Payne et al. 2004; Galfetti et al. 2007; Caracava et al. 2017; Widmann et al. 2020; Li et al. 2023), associated

with several episodes of extinctions (Brayard et al. 2006, 2009; Orchard 2007; Stanley 2009; Song et al. 2013, 2014). These successive Early Triassic perturbations are tentatively linked to extensive volcanic degassing from the Siberian Traps, which significantly affected both the climate and the oceans (Campbell et al. 1992; Payne et al. 2004). Even if the precise causes of these events are still debated, they are likely to be multiple. The persistence or episodic harsh
environmental conditions, including potential anoxia, euxinia, marine acidification, and global warming or cooling, repeatedly disrupted Early Triassic marine ecosystems (Wei et al. 2015; Goudemand et al. 2019).

Over the last decade, the study of several Early Triassic fossiliferous exposures and their depositional settings in the western USA basin has led researchers to revisit some Early Triassic paradigms, such as the scenario of a slow and delayed recovery for metazoan reefs (Brayard et al. 2011; Morenco et al. 2012), the persistence of poorly diversified ecosystems (Brayard et al. 2017; Smith et al. 2021), the Lilliput effect in some fossil groups (Brayard et al. 2010, 2011, 2015), and the anachronic and disasterous character of regional microbialite deposits (Vennin et al. 2015; Olivier et al. 2016, 2018). All these studies show that these paradigms are not as straightforward as initially proposed or are simply inaccurate, highlighting the fragmentary nature of current knowledge about Early Triassic ecosystems. For instance, following the pioneering work of Schubert & Bottjer (1992), it has been confirmed that Smithian microbial limestones developed under normal marine conditions without any environmental stress (Olivier et al. 2018). It has also been shown that some metazoan reefs and complex ecosystems were present in the western USA basin at least during the Smithian and Spathian, respectively (Brayard et al. 2011, 2017).

These discoveries and the refined knowledge of the Early Triassic rock record in this basin suggest that the observed patterns may reflect a regional phenomenon only corresponding to exceptional refuge ecosystems. However, similar discoveries made worldwide further emphasized the limited knowledge of the Early Triassic fossil record (e.g. Friesenbichler et al. 2021; Dai et al. 2023). A potential taphonomic bias resulting from skeletal mineralogy and differential fossil preservation is frequently discussed in the literature (Erwin & Pan 1996; Stanley 2003; Fraiser & Bottjer 2005; Allison & Bottjer 2011; Pruss et al. 2015; Jattiot et al. 2018). This bias is illustrated by numerous examples of carbonate rocks from the Triassic, Palaeozoic, and even Neoproterozoic that were originally identified as exclusive microbial deposits but are now being reinterpreted as bioconstructions in which sponges played a significant frame-building role (Pratt 1982; Brayard et al. 2011; Luo & Reitner 2016; Lee & Riding 2018, 2021; Pham et al. 2021; Turner 2021; Pei et al. 2022). These studies suggest that the common microbialite fabrics, characterized by frequent fenestrae and various precipitation processes—including diagenetic recrystallization and replacement—may obscure the original metazoan framework, making it difficult to identify some organisms with certainty (Neuweiler

et al. 2022). These studies also underscore the importance of new field exploration and research that could challenge existing knowledge of Early Triassic ecosystem composition and diversity.

The present study describes a diverse microbial-sponge assemblage from the Smithian (early Olenekian) peritidal environments of the western USA basin (northwestern Arizona). This assemblage yields the first presumed Early Triassic chaetetid sponges and highlights sampling and taphonomic biases. Specifically, it reveals morphological convergences among some presumed recrystallized chaetetids and large fenestrae, which may complicate the identification of these hypercalcified sponges in the rock record. Additionally, the compilation of currently known depositional environments for Early Triassic microbial-sponge limestones, along with these new findings, indicate that such ecosystems can hardly be considered as potential refuges or indicators of stressful settings.

## Stratigraphical, geographical and geological contexts

The Early Triassic is commonly subdivided into two (Induan and Olenekian; Kiparisova & Popov 1956) or four stages (Griesbachian, Dienerian, Smithian and Spathian; Tozer 1967). The Induan crudely corresponds to the Griesbachian and Dienerian, while the Olenekian corresponds to the Smithian and Spathian. The Sub-commission on Triassic Stratigraphy adopted the two-fold subdivision, but it remains controversial among Triassic workers for practical reasons. This is mainly due to its definition in two different and distant realms: the Tethyan domain, with its type locality in the Salt Ranges (Pakistan), which defines the Induan, and the Boreal domain, represented by the Olenek River region (Siberia), which defines the Olenekian. Therefore, correlation of the Induan/ Olenekian boundary across the Boreal and Tethyan realms is not obvious and still discussed (Krystyn et al. 2007; Ware et al. 2017; Zhao et al. 2008). As the late Smithian extinction and turnover (i.e. intra-Olenekian) is far more intense than potential similar events at the Induan/Olenekian boundary, the widely used four-stage subdivision is followed in this work, with boundaries well-defined by ammonoids and conodonts (Jenks & Brayard 2018; Zhang et al. 2019; Leu et al. 2022). The time resolution is higher, and correlation easier when using the four-stage subdivision, especially considering that the Spathian represents about half the duration of the Early Triassic
(Widmann *et al.* 2020). Therefore, each mention of the Smithian or Spathian corresponds to the 'early' and 'late' Olenekian in the official ICS subdivision, respectively.

During the Early Triassic, the western USA basin was likely a foreland basin that developed concurrently with the Sonoma orogeny (Stewart *et al.* 1972; Collinson *et al.* 1976; Dickinson 2013; Caravaca *et al.* 2018). Situated along the western margin of Pangea (Fig. 1A), this open epicontinental basin, covering present-day eastern Nevada, Utah, Idaho, Western Wyoming, and Southwestern Montana, was positioned in the northern intertropical zone. It recorded a variety of both terrestrial and marine deposits (Blakey *et al.* 1993; Paull & Paull 1994). The basin experienced frequent sea-level fluctuations, including a significant third-order transgressive-regressive cycle during the Smithian (Paull & Paull 1993, 1997; Embry 1997; Lucas *et al.* 2007; Brayard *et al.* 2013; Olivier *et al.* 2014; Vennin *et al.* 2015; Jeffrey *et al.* 2019). In the area under study, this transgressive-regressive cycle is recorded in the Sinbad Formation and is primarily associated with a global mid-Smithian warming followed by the late Smithian to early Spathian cooling (Goudemand *et al.* 2019). These climatic fluctuations are thought to have contributed to the late Smithian extinction (e.g. Brayard *et al.* 2020).

The study area is situated in the northwesternmost part of Arizona, in Mohave County, less than 3 km from the Utah border and 21 km south of Hurricane, Utah (Fig. 1B). It is located on the western portion of the Uinkaret Plateau, near the Hurricane Ledge, which is a prominent eroded fault scarp of the Hurricane Fault (Billingsley 1992). The rocks under study crop out on the hillsides along Short Creek, just east of its confluence with Cottonwood Creek, upstream from Rock Canyon.

Along Short Creek (Fig. 2), the observed sedimentary succession loosely parallels those described from southwestern Utah (Washington and Kane Counties) and northwesternmost Arizona (Mohave County). The succession begins with Permian cherty limestones of the Harrisburg Member of the Kaibab Formation (Reeside & Bassler 1922; Gregory 1950; Poborski 1954; Stewart *et al.* 1972; Blakey 1979; Jenson 1986; Nielson 1991; Billingsley 1992; Lucas *et al.* 2007; Olivier *et al.* 2014, 2018; Clark 2021). These Lower Permian rocks are characterized by locally incised valleys filled by the Lower Triassic Rock Canyon Conglomerate Formation (Fig. 2A, B). The transition between the Rock Canyon Conglomerate and the overlying microbial carbonates of the Sinbad Formation is marked by a conformable contact characterized by a gradual decrease in detrital pebbles

within the first decimetres of the limestones (Nielson 1991; Olivier *et al.* 2018). In both Rock Canyon and in the far northern Workman Wash, ammonoids found in the uppermost beds of the Sinbad Formation correspond to a typical prionitid assemblage indicative of an early late Smithian age (Olivier *et al.* 2018; Brayard *et al.* 2020). These ammonoids, belonging to the genera *Anasibirites* and *Wasatchites*, are assigned to the regional Unitary Association Zone (UAZ) 5 as defined by Jattiot *et al.* (2017). In contrast, the lower beds of the Sinbad Formation in Rock Canyon contain the ammonoid genus *Guodunites*, which suggests a middle Smithian age and the presence of the regional UAZ 4 (Jattiot *et al.* 2017; Brayard *et al.* 2020).

## Studied section, material and methods

The studied sedimentary succession was logged on the south side of Short Creek (base: 36°58'32.77'N, 113°15'43.13'W; top: 36°58'27.66'N, 113°15'43.33'W), just east of the entrance of Rock Canyon (Figs 1, 2). Panoramas were used to interpret unconformities, sedimentary geometries, and lateral facies variations. The logged section, which is slightly over 14 metres thick, includes 3 metres of conglomeratic limestone at the base, followed by 11 metres of microbial-sponge limestones (Fig. 3). The conglomeratic limestone unit exhibits significant lateral variation in thickness, ranging from 1.5 to 4 metres, and rests on the Permian Kaibab Formation with an erosive, channelized basal surface (Fig. 2A, B). This detrital unit is part of the Rock Canyon Conglomerate Formation and is conformably overlain by the microbial-sponge limestone unit of the Sinbad Formation. Lithological and facies analyses of the 14-metre-thick succession were conducted both in the field and in the laboratory using thirty polished slabs and fifteen thin sections. The proportion of quartz grains in the thin sections was estimated using the diagrams of Baccelle & Bosellini (1965).

The studied presumed chaetetid specimens include a three-dimensional slab and seven additional rock samples. The 3D specimen was collected as a loose rock sample approximately 10 metres from the base of the section (Fig. 2C). The remaining specimens are *in situ* rocks (samples Roc i, k, b, c, d, e, f), originating from an interval between 3.4 and 12 metres (Fig. 3). To analyse the internal structure of presumed chaetetids, transverse and longitudinal sections were examined in both polished slabs and thin sections. One horizontal and two vertical thin sections were prepared from the
<figure><img src="image_4.png" /><figcaption>Fig. 1. A, Early Triassic palaeogeographical map with the position of the Sonoma foreland basin of southwestern USA along the Pangea margin (after Brayard *et al.* 2013); B, location of the study area (Short Creek) in the northern part of Arizona (Mohave County).</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 2. A, field view and B, line drawing of the sedimentary succession in Short Creek, upstream of Rock Canyon. The Sinbad Formation forms the top of the landforms and lies conformably on the Rock Canyon Formation, which is itself unconformable on the Permian Kaibab Formation. C, photograph illustrating the position of the logged section and the position of the sampled 3D chaetetid specimen (UBGD.030499).</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 3. Log of the studied interval on the left bank of Short Creek. The floated 3D specimen (UBGD.030499) was collected at a height of around 10 m above the base of the section. Structures suggesting the presence of additional chaetetids were observed in seven other thin sections (samples Roc b–f, i, k,) positioned at different locations (black arrows on the right side of the erosional profile) along a 9-m-thick stratigraphical interval of the sponge-microbial limestone unit (Sinbad Formation).</figcaption></figure>

edge of the 3D chaetetid specimen. This specimen was
also analysed using Synchrotron µXRF for elemental
mapping to investigate the distribution of major and
trace elements, which allowed for the identification

of some internal anatomical features (see Gueriau
et al. 2018 for details on the principles of Synchrotron
µXRF elemental mapping and the advantages of syn-
chrotron light for fossil imaging). Synchrotron µXRF
maps were obtained at the PUMA beamline of the SOLEIL synchrotron (Gif-sur-Yvette, France), using a monochromatic X-ray beam of 12.5 keV, following the protocol outlined in Saucède *et al.* (2023).

## Description of the main facies

### Conglomerate limestone

This facies consists of beds ranging from decimetres to metres in thickness, featuring channel geometries that can extend over tens of metres (Fig. 2). Within these channel forms, lateral accretion of several sigmoidal units with erosive and reactivation basal surfaces is observed. The conglomerate, which is several metres thick, comprises poorly sorted clasts (ranging from millimetres to decimetres), predominantly subrounded (some subangular), and polygenic (carbonate and chert). According to Nielson (1991), the conglomerate contains clasts of cherts (60%), limestone (20%), dolostone (10%), sandstone (5%), and gypsum (5%). Microscopically, this facies displays very well-sorted (0.5–1 mm) and subrounded quartz grains, comprising 2.5 to 3% of the sample. The cement is predominantly calcite, with minor amounts of silica and hematite (Fig. 3; Nielson 1991). Locally, equant cement crusts are observed along the lower surface of some grains, and intergrain areas primarily consist of coarser calcite spar, with some micrite also present.

### Peritidal facies

The various sediments observed in the microbial-sponge limestone unit can be classified within a peritidal facies (sensu Flügel 2004; Fig. 3). This facies is subdivided into two main subfacies, which include a range of frame-building organisms, carbonate grains, and structures. The first subfacies is a microbial-sponge boundstone with fenestrae, while the second is a non-bioconstructed sediment corresponding to a pel-fenestral limestone (Fig. 4). Stratigraphical and lateral facies variations occur on a centimetric scale between these two subfacies. Here, only a brief and general description of these subfacies characteristics is provided. For more details on microbial structures and reef-building metazoans, readers can refer to the corresponding Sections below.

### Microbial-sponge boundstone with fenestrae

This subfacies consists of an association of various microbial deposits and structures (bacterial filaments and biofilms) with reef-building metazoan organisms

(presumed chaetetids, siliceous sponges, and microconchids). It corresponds to beds that are several decimetres thick and that can locally form small biothermal morphologies (Fig. 2C). Additional metazoan organisms observed in this subfacies include gastropods, bivalves, ostracods, and ammonoids. Ostracods are locally common and appear either as small pocket accumulations or as isolated forms within the microbial micrite. Fenestrae are abundant and morphologically diverse. Associated with flat, well-laminated stromatolites, fenestrae exhibit relatively large planar and elongated shapes (Fig. 4A). In association with columnar stromatolites, they form a vertical network (Fig. 4B). In other instances, smaller and elongated fenestrae highlight a less pronounced stromatolitic lamination (Fig. 4C). Shrinkage structures, circumgranular cracks and vertical cracks are common (Fig. 4D). Intraclasts, brecciation, neptunian dykes, and pedotubule structures are also observed (Fig. 4E, F). Radiaxial fibrous cements are locally present in some large fenestrae or on bioclasts and encrusting microconchids (Fig. 5A). Some intraclasts have a micritic coating, and some large fenestrae exhibit micritic pendant cements (Fig. 5B). The margins of fenestrae typically show isopachous rims of radiaxial or equant cements, while the remaining space is filled with granular or blocky cements. In some fenestrae, blocky cement is observed cannibalizing the fibrous cement. Locally, some fenestrae display dogtooth cements. Recrystallized chaetetid skeletons are commonly infilled with granular cements. Isolated or mesh-like calcitic needles may be present on some stromatolite laminations (Fig. 5C), and these needles can locally form laterally continuous crusts (Fig. 5D). Botryoidal cements are observed both on some fenestrae walls and on stromatolite laminations (Fig. 5E). Additionally, some dolomite rhombohedrons are observed locally.

### Pel-fenestral limestone

This subfacies is characterized by abundant peloids, common intraclasts, and some aggregates, ooids and oncoids. Gastropods and ostracods are also present. Small, moderately sorted, subangular to angular quartz grains can be relatively common, constituting up to 10% of the sediment. The intergrain area, composed of micrite or sparry cement, contributes to packstone to grainstone textures. Locally, circumgranular cracks, irregular nodular textures (palaeocaliche), and intraformational breccia are observed (Fig. 4G). Fenestrae exhibit a range of forms, with elongated fenestrae featuring flat bottoms and jagged to slightly digitate roofs being common (Fig. 4H). The base of these fenestrae is typically infilled with silty micrite, and micritic cements are occasionally found along their roofs or
<figure><img src="image_7.png" /><figcaption>Fig. 4. Thin sections showing the microbial-sponge boundstone with fenestrae (A-F) and pel-fenestral limestone (G, H) subfacies. A, flat stromatolites with flattened subhorizontal fenestrae. B, columnar stromatolites with more vertical fenestrae. C, small fenestrae with an elongated horizontal shape (white arrow). D, domal stromatolites with shrinkage structures (white arrows). E, domal stromatolite with local brecciation. F, pedotubule (black arrow) and shrinkage structure (white arrow) observed alongside a domal stromatolite growing on the right of the photograph. G, micritic coating (black arrow), shrinkage structures (white arrow) and local brecciation (palaeocaliche). H, irregular nodular texture (black arrow; palaeocaliche) and elongated fenestrae with a flat basal surface and more irregular roof. Note the silty micrite (white arrow) infilling the base of the fenestrae.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Fig. 5. Illustrations of various cements and structures in the microbial-sponge boundstone with fenestrae subfacies observed in thin section. A, fibrous aragonite, originally surrounding the microconchid tubes and preserved in its acicular form, replaced by calcite. B, large fenestrae with endostromatolites made of dense micritic cements (white arrows). Note the local alternation of dense micritic cements with crystal silt cements. The rest of the fenestrae is infilled with radiaxial cements (black arrow) and finally with blocky calcite. C, isolated and mesh of needles (white arrow). D, needle-like crusts (white arrow). E, botryoidal cement (white arrow). F, vertical filaments (porostromate microstructures, white arrows) in laminated microbial micrite.</figcaption></figure>

walls. Other fenestrae are irregularly shaped, and
less commonly ovoid. Generally, fenestrae are filled

initially with a rim of radiaxial cement, followed by
blocky spar. Some grains show micritic coatings.
# Description of the boundstone framework

## Microbial structures

In the microbial-sponge boundstone subfacies, microbial structures are quite diverse, primarily consisting of stromatolites, endostromatolites, and microbial filaments.

**Stromatolites.**- Stromatolites are widespread throughout the peritidal limestone unit (Fig. 3). They are associated with various metazoans, including diverse siliceous sponges, presumed chaetetids, gastropods, ammonoids, ostracods, and microconchids. These metazoans either provided support for the microbial crusts or were encrusted by them. Stromatolites exhibit inframillimetric laminations composed of alternating layers of more or less dark micrite (Fig. 4A-F). In terms of shape or fabric, stromatolites show considerable diversity. They can be relatively flat with internal, small, wavy laminations, sometimes featuring elongated fenestrae (Fig. 4A). Stromatolites may also form domal structures ranging from millimetres to several centimetres in scale, occasionally displaying mudcracks, shrinkage, and brecciation features (Fig. 4D, E). Additionally, they can present columnar shapes (Fig. 4B).

**Endostromatolites.**- Some elongated and plurimillimetre-thick fenestrae feature encrusting laminated structures of dense micrite. Differentiating these crusts as microbial structures or diagenetic cements can be challenging (Granier 2020). However, in this study, the observed crusts exhibit growth in all directions, which permits their classification as cavity-dwelling stromatolites or endostromatolites (*sensu* Monty 1982). These structures are found on both the roof and basal surfaces of the fenestrae (Fig. 5B), forming small (sub-millimetric) columns that are relatively discontinuous laterally. In some fenestrae, these endostromatolite crusts alternate with thin layers of sparitic cement.

**Porostromate microstructures.**- Discrete filaments (porostromate microstructuressensu Monty 1981) can be identified within the stromatolitic microfabric. These filaments are found in laterally restricted areas, measuring one to two millimetres across, and consist of a few isolated filaments within micritic and laminated layers (Fig. 5F). These filaments cross two to five micritic layers, ranging in length from 150 to 750 µm and in width from 10 to 18 µm. The tubes are not perfectly straight but exhibit slight

irregularities, with a generally constant width that tapers slightly at both ends. These filaments appear as simple tubes filled with microspar, without any visible micritic or sparitic rim. In the studied stromatolites, there is a notable relationship between filament orientation and lamination. Most observed filaments are oriented perpendicular to the lamination, while a few show a slight inclination of just a few degrees or a more oblique orientation. Dense or open networks of filaments within micritic laminae are not observed.

## Sponges

**Chaetetids (hypercalcified demosponges).**- The first observation of the presumed chaetetid specimens was made on a 3D macroscopic sample (Fig. 6A, D) housed in the palaeontological collections of the Université de Bourgogne, Dijon, France (UBGD.030499). This specimen has an almost complete lamellar form, measuring approximately 16 cm in width, 10 cm in length, and 2 cm in thickness (3D photogrammetric model in the Supplementary Files). Although the upper surface of this specimen exhibits signs of minor erosion, it reveals thirty-four slightly raised, subcircular domal structures, each around 1 cm in diameter (Fig. 6B), highlighting its 3D geometry. From a top view, these mamelons display an internal skeletal organization with a radial pattern resembling septa (Fig. 6C). In vertical section, several subhorizontal lines with irregular distribution and thickness are also present, likely corresponding to growth bands of the skeleton (Fig. 6D). The internal skeletal structure consists of a juxtaposition of narrow, joining tubes forming a bush-like pattern. Individual tubes are 0.2 to 0.5 mm wide, with a diameter that tends to increase from the base to the top (Fig. 7A). Near the upper surface, the tubes locally exhibit a tendency toward a curved growth trajectory (Fig. 7B). They have joined walls preserved as brown micrite, and their central parts are filled with calcite crystals. In some areas, some tubes show fine dark micritic laminae, likely corresponding to residual traces of tabulae (Figs 7C, 8A). Additionally, thin elongated structures that may correspond to spicules are observed on the periphery of some tubes (Fig. 8B).

The juxtaposition of subcylindrical tubes with a bushy growth pattern, along with some tubes showing curved growth directions, clearly supports a biological rather than abiotic origin. The presence of a series of thin, elongated tubes, whose diameter increases during ontogeny, along with tabulae,
<figure><img src="image_9.png" /></figure>

Fig. 6. A, 3D chaetetid (UBGD.030499) viewed from above, displaying numerous small dome-shaped morphologies. The four black arrows indicate the locations of two thin sections (a and b) in the vertical plane. B, close-up of two mamelons, highlighting the radial arrangement of upright, bush-like tubes. C, synchrotron µXRF elementary map scanned at the PUMA beamline, SOLEIL. Greenish colour corresponds to strontium incorporated into the skeleton calcite (blue colour) highlighting the tube contours. Note that the tubes diverge to a direction nearly perpendicular to the growth surface of the mamelon, and their diameters increase during growth. D, vertical section view of the chaetetid shown in A. Note the bush-like tubes, separated by micritic walls (in brick red) that are visible in some areas (white arrows). The black arrow highlights the probable growth bands of the skeleton.

<figure><img src="image_10.png" /></figure>

Fig. 7. A, vertical thin section (position a on Fig. 6A) showing the internal structure of the presumed chaetetid (UBGD.030499). B, close-up of the tubes near the specimen distal surface. Note the increase in diameter and the curvature of some tubes. C, close-up portions of tubes that have preserved probable tabulae (white arrows).
<figure><img src="image_11.png" /><figcaption>Fig. 8. Close-up views of a thin section (position b on Fig. 6A) analysed under blue light. A, probable preserved tabulae in some tubes (arrows). B, set of potential spicules (arrows) located around the central lumen of a tube, within the wall near the upper surface of the specimen.</figcaption></figure>

supports identifying this specimen as a probable
chaetetid (West & Georges 1983; Almazán-Vásquez
et al. 2007; Stanton et al. 2016), rather than another
organism (e.g., red algae, bryozoans, or tabulate
corals) that could develop a relatively similar skel-
etal organization. However, the state of preservation
of the observed specimen, with intense recrystalli-
zation, does not permit a more precise taxonomic
identification.

Polished slabs prepared from various samples
(Roc b–f, i, k) taken along the microbial-sponge
limestone unit revealed seven additional occurences
of potential chaetetids (Fig. 3). The criteria for a
solid diagnosis of these structures as chaetetids
remain limited and debatable, as they are highly
dependent on the quality of preservation (see below).
Typically, these structures correspond to large, pluri-
centimetre fenestrae, which are strongly recrystal-
lized, as observed in sample Roc e (Fig. 9A). Thin
section observations of this sample reveal a signifi-
cant neomorphic fabric with enlarged calcite crystals
of varying sizes replacing the original tubes. Despite
this intense recrystallization, these fenestrae-like
morphologies still exhibit bushy protrusions and
potential vestiges of tabular structures that have not
been completely erased by diagenesis (Fig. 9B, C).
On a smaller scale, observation of some other thin
sections locally shows small clusters of crystals that
also display an organization compatible with chaetet-
ids, including elongated crystal shapes that increase
in width during growth, as well as a general radiate
shape (Fig. 9D). Such observations suggest that these
fenestrae-like structures could likely correspond to
very poorly preserved chaetetids.

*Network microfabric of non-spicular sponges (demo-sponges).*- A specific microfabric is commonly observed throughout the peritidal limestone unit, characterized by a vermiform sparry network running through a surrounding micrite (Fig. 10A-E). Such networks delimit micritic clumps that many authors have associated with the skeletal elements encountered in some non-spicular sponges (Szulc 1997; Brayard *et al.* 2011; Luo & Reitner 2014, 2016; Vennin *et al.* 2015; Olivier *et al.* 2016, 2018; Friesenbichler *et al.* 2018; Baud *et al.* 2021; Pei *et al.* 2021; Gischler *et al.* 2021; Lee & Riding 2021; Pham *et al.* 2021; Turner 2021; Luo *et al.* 2022; Wu *et al.* 2024). Indeed, some demosponges assigned to the Keratosa group have skel-etons consisting of fiber networks made of spongin and lack siliceous or calcareous spicules (Erpenbeck *et al.* 2012). The fossil preservation of these non-spicular sponges implies a calcite-cemented fabric left by the fibrous network, while the micritic clumps may reflect an automaticritic permineralization process (Reitner *et al.* 1995; Luo & Reitner 2014; Lee & Riding 2021). This led some authors to use the term keratolite for carbonates dominated by keratose sponge micro-fabrics (Lee & Riding, 2021). However, other authors are more cautious, arguing that the diagnostic crite-ria for firmly identifying fossil keratose demosponges are not sufficiently supported; that the spongin com-ponent is unlikely to resist sponge tissue decay and diagenesis; and that various microbial or sedimentary processes can also generate vermicular microfabrics (Neuweiler *et al.* 2022).

The studied thin sections reveal common micro-
fabrics that replicate the skeletal architecture and
form of non-spicular sponges (Fig. 10A-E). Along
<figure><img src="image_12.png" /><figcaption>Fig. 9. A, polished vertical slab revealing a large fenestrae-like structure attributed to a probable chaetetid specimen (sample Roc e), which is strongly recrystallized within the microbial-sponge boundstone with a fenestrae subfacies. B, thin section made in the horizontal plane of this presumed chaetetid (B line in A), showing the strong recrystallization of the tubes, which nevertheless preserved a radial organization. C, thin section made in the longitudinal plane of this presumed chaetetid (C line in A), with probable vestiges of the tabulae (black arrow) preserved in some tubes. D, thin section showing a smaller structure with longitudinal tubes that increase in width during growth (white arrow), as well as a general radiate shape. Note the presence of rounded tubes in cross-section (grey arrow) at the medium part of the structure, (sample Roc b). E, fan-like cements (white arrows) at the base of a presumed chaetetid preserved as a large fenestra (sample Roc b).</figcaption></figure>

their margin, these sparry networks can form a line consistent with a coherent collagen layer that delimits pores where the ostia open (Fig. 10A; De Vos *et al.* 1991). Some specimens display a relatively

shapeless, vermiform microfabric with tubular bulges developing along its edge (Fig. 10B, C). Other examples of vermicular microfabrics appear as encrustations on ammonoid shells (Fig. 10D).
<figure><img src="image_13.png" /><figcaption>**Fig. 10.** Thin section illustrations of some network microfabric of non-spicular sponges (demosponges). A, fibre networks of a keratose sponge conform to the bedding, embedded in microbial micritic laminae, and associated with a presumed chaetetid (ch.). Note the marginal line that could reflect a layer of coherent collagen delimiting pores (white arrow). This network is affected by a macroboring organism (black arrow). B, C, fibre networks of a keratose sponge with a tube shape. Note the ostracod shell in the sponge (black arrow) and the line at the sponge margin (white arrows) that may represent a layer of coherent collagen delimiting pores in which opened the ostia. D, fibre networks of a keratose sponge encrusting an ammonoid. Note the tubular cavities in the sponge fibre network (arrow). E, fibre networks of a keratose sponge (arrow) encrusting the wall of a Neptunian dyke (dy.). F, rounded-shape lyssacine hexactinellid (ly.) on a putative cortical layer with densely packed sterraster microscleres (black arrow) and some prostalia marginalia of pointed monaxon spicules (white arrows), characteristic of the family Geodiidae (Geo.; Delecat *et al.* 2001). The cortex outer layer of the lyssacine sponge displays isolated, non-fused spicules in transverse (grey dashed arrow) and longitudinal (black dashed arrow) section. G, partially preserved skeleton of a non-rigid species sponge. Mainly large monaxon megascleres (oxea) assigning the species to the group of Lyssacinosida. H, same thin section as G, few mm to the right, same Geodiidae specimen with pore or tubular systems (black arrows) and non-fused spicules of a probable lyssacine hexactinellid (white arrow).</figcaption></figure>
A cave-dwelling distribution of these sparry networks is also suggested, as they are found occupying the internal space of microconchid tubes or encrusting the walls of neptunian dykes (Fig. 10E). These sparry network microfabrics exhibit tubular cavities consistent with the presence of aquiferous canals (Fig. 10D). All these observations strongly suggest that the observed vermiform microfabrics were originally non-spicular sponges. Furthermore, the presence of ostracod shells within the sponge networks played in favor of an automicritic mineralization process for the micritic clumps, as these micro-crustaceans are commonly associated with the development of microbialites (Forel 2013; Forel et al. 2013; Foster et al. 2019).

*Non-fused spicule accumulations (lyssacine hexactinellids and halichondrid demosponges).* - A few strongly recrystallized, rounded structures (<3 mm in diameter) are also observed locally. In Figure 10F, the illustrated specimen shows preserved transverse and longitudinal sections of spicules, most prominently along their borders. Sponge skeletons composed of isolated, non-fused spicules may belong to the Lyssacinosida group (Delecat & Reitner 2005; Delecat et al. 2011). The illustrated specimen is encrusted with columnar stromatolites and appears to be attached to a larger skeletal sponge (Geodiidae, see below), highlighting its role in contributing to the bioconstruction (Fig. 10F). Similar spheroidal lyssacine hexactinellids have been previously described by Brayard et al. (2011) in Smithian and Spathian deposits from the western USA basin.

Other soft body sponges characterized by a non-rigid skeleton with thin, isolated, and non-fused spicules are also observed. Some specimens appear as poorly-preserved or collapsed skeletons, primarily composed of monaxon megascleres (oxea) (Fig. 10G, H). They form body masses with no well-defined contours, and spicules may display plumose structures. Skeletons exclusively composed of fusiform monaxons are characteristic of halichondrid demosponges (Delecat et al. 2001). These unattached spicule masses are observed within the stromatolitic laminae and sometimes mark erosive surfaces with reworked material (Fig. 10G). In other cases, spicules are found accumulated in small depressions on the surface of larger skeletal sponges (Geodiidae), associated with other detrital peloidal grains (Fig. 10H).

*Geodiidae (demosponges).* - The observation of densely packed sterraster microscleres forming a cortical

layer suggests the presence of other non-rigid demosponges from the geodiid group (Piuz 2004; Reid 2004; Delecat et al. 2011). In association with these sterrasters, geodiids may also exhibit prostalia marginalia of pointed monaxon spicules (Delecat et al. 2001). Figure 10G shows a probable Geodiidae demosponge with a poorly preserved cortical layer and long, needle-like spicules within a strongly recrystallized mesohyl. An unfavorable section likely prevents the observation of the triaen nature of these spicules (Gaillard 1983). The sponge body also reveals some tube-shape voids infilled with blocky calcite, which probably correspond to water canals of the aquiferous system.

## Microconchids

Common spirorbiform tubes ranging from <0,2 mm to 2 mm in diameter are observed in association with laminated microbial deposits. These tubes are externally smooth and lack ornamentation, and they may have an oval aperture (Fig. 11A). The internal lamellar microstructure of the tube walls, which is locally wavy, is characteristic of microconchids (Taylor & Vinn 2006; Yang et al. 2015; Fig. 11B). The tightness of the coiling of these tubes is highly variable. Some tubes are slightly involute with successive overlapping whorls, while others are more erect, showing a clear elevation above the substrate. This observation implies that some of these microchonchid specimens developed an upward growth. Locally, these tubes form small buildups within the stromatolite laminaion (Fig. 11A-D). Microconchids are attached to various substrates, including similar tube specimens, ammonoid and bivalve shells, or stromatolite laminae (Fig. 11E, F). These encrusting organisms have been frequently reported from various Lower Triassic deposits of the western USA basin, but their taxonomic diversity appears to be relatively low and remains to be precisely determined (Brayard et al. 2011; Fraiser 2011; Zaton et al. 2013).

## Interpretation of regional and local sedimentary settings

During the Early Triassic, the studied locality was part of a vast north-south epicontinental sea (Goodspeed & Lucas 2007; Brayard et al. 2013), which is commonly interpreted as a foreland basin associated with the Sonoma orogeny. This event involved the thrusting of an oceanic terrane (i.e.,
<figure><img src="image_14.png" /><figcaption>Fig. 11. Thin section illustrations of micoconchids. A, micoconchids that form a small buildup. The isolated specimen (white arrow, top left corner) displays a spirally coiled tube with an aperture. B, close up of A with the internal lamellar (locally wavy) microstructure (white arrow) of the tube walls characteristic of microconchids. C, spirorbiform tubeworms that form a small buildup in a laminated micritic stromatolite. Note the microconchid specimen with a broad tube base (black arrow) cemented on the stromatolitic substrate and the presence of porostromate filaments (white arrow). D, spirorbiform tubeworms that form a small buildup in a laminated micritic stromatolite, which also contains some porostromate filaments (white arrows). E, F, encrusting microconchids on bivalve (E) and ammonoid (F) shells. Note the fibre networks of some keratose sponges (ker.) both encrusting or infilling microconchid tubes.</figcaption></figure>

the Golconda Allochthon) over the continental margin of North America (Speed 1979; Ingersoll 2019). During the Smithian, the varying topographic loads exerted by the Golconda Allochthon, combined with the heterogeneous rheology of the basement, likely

led to lower subsidence rates in the southern part of the Sonoma basin compared to the northern part (Caravaca et al. 2018). As a result, the southern part of Utah and the northern part of Arizona were characterized by relatively shallow environments with
significant coarse clastic sedimentation (Nielson 1991). Although quite far from the Golconda, where only a few remnants (i.e. Spathian 'Koipato volcanics') are now found in central Nevada (Dickinson 2006; Ingersoll 2008), the Permian formations in southern Utah and northern Arizona exhibit an erosional surface with residual karst topography and overlying conglomerates (Blakey 1979; Jenson 1986). This indicates the presence of local upland areas (Gabrielse et al. 1983).

In Rock Canyon, the basal deposits of the studied succession are conglomerates that Nielson (1991) interpreted as point bars formed in stream channels with drainage flowing to the northeast. Field observations reveal massive beds of conglomerates mainly composed of subrounded, locally imbricated clasts. These flat-bedding conglomerates laterally transition to lateral and vertical accretionary units that developed on large, scoured surfaces (Fig. 2). Such flat stratification in conglomerates can be interpreted as longitudinal bars, commonly found adjacent to lateral accretion conglomerates (Ramos & Sopeña 1983). This facies evolution may reflect the progressive migration of relatively stable longitudinal bars into channels on a braided plain, positioned slightly more distally than an alluvial fan system (Ramos et al. 1986). The landforms were likely not far away, as a minimum transport distance of a few kilometres can produce rounded pebble surfaces (Williams et al. 2013). Additionally, downstream roundness tends to increase relatively quickly in limestone pebbles due to their high susceptibility to erosion (Mills 1979). Previous studies have suggested that some palaeogeographical highs were located about ten kilometres to the west, featuring an alluvial plain and transitioning to the Smithian Sinbad Limestone along a shoreline parallel to the present Hurricane Cliffs, with the open sea further to the north and northeast (Blakey 1979). This coastline was probably not a simple north-south line, as indicated by the presence of debris flows a few kilometres further north at Workman Wash (Olivier et al. 2018), suggesting the presence of tributary fans and closer reliefs.

The Rock Canyon Conglomerate deposits are overlain by microbial limestones that still contain sparse gravels and pebbles, indicating a progressive gradation between these two facies types (Nielson 1991; Olivier et al. 2018). A piedmont plain with a relatively flat depositional profile was likely prone to recording minor changes in relative sea level through rapid lateral facies migrations (Olivier et al. 2014). Once the transgression was complete, both the microbial-sponge boundstone with fenestrae and the pel-fenestral limestone subfacies, which make up the

microbial limestone unit, exhibit common structures (e.g., pedotubules, palaeocaliches; Fig. 4) indicative of brief emersions. However, the presence of various metazoans, such as sponges and ammonoids, suggests subtidal marine settings, while the peloidal grainstone texture indicates shallow, well-agitated waters. These sedimentary structures and subfacies can laterally pass from one to another over very short distances (Olivier et al. 2016, 2018). This is consistent with a mosaic environment characterized by low-relief, locally emersive banks surrounded by shallow subtidal areas, typical of a peritidal setting (Pratt & James 1986).

## Discussion

### Exploring Early Triassic chaetetids and implications for their stratigraphical range

Hypercalcified demosponges with a chaetetid skeleton have been reported unambiguously as far back as the Silurian period, while occurrences from the Cambrian and Ordovician are questioned (West 2015; Kershaw & Leon 2024). Indeed, the systematics of these early chaetetid-like sponges remain controversial due to their skeletal morphology being similar to that of other major benthic clades, such as tabulate corals and bryozoans (West 2011, 2015). West (2012a, 2015) confidently identified chaetetids from the Middle Devonian to the Holocene. Chaetetids were significant contributors to reef building during the Carboniferous and Permian periods (Fagerstrom 1987; Wood 1990; West 2015), yet their generic diversity remained extremely low throughout the Palaeozoic, with only three genera considered as valid taxa by West (2015). The latest Palaeozoic chaetetids are known from Upper Permian sponge reefs in the Changhsing Formation of western Hubei, South China (Weidlich 2002). Chaetetids were not documented from the Early and Middle Triassic until now, but they occur in the Norian and Rhaetian with a relatively high taxonomic diversity, as 10 genera are currently documented (West 2015). Associated with corals and other coralline sponges, they actively contributed to reef building during the Norian and Rhaetian ages (Bernecker 1996; Flügel 2002; Martini et al. 2004; Senowbari-Daryan & Maurer 2008; Martindale et al. 2012). Overall, the presence of presumed chaetetids in Rock Canyon fills a ~30-myr gap in the fossil record between the latest Permian and the Late Triassic, thus likely representing the oldest known record of Mesozoic chaetetids. Furthermore, the few additional specimens observed within a 10-metre thick interval
(Fig. 2) indicate that chaetetids were not rare in this
area at the end of the middle Smithian. This presence
dates to approximately 2.5 myr after the Permian-
Triassic boundary extinction, suggesting a relatively
rapid recovery of these organisms, or their mainte-
nance at least regionally.

Sampling and taphonomic biases

The sedimentary succession studied here represents a peritidal facies with various sponge groups including keratose demosponges, halichondrids, geodiids, lyssacine hexactinellids and presumed chaetetids. However, observing these sponges, both in the field and in thin sections, proves difficult and reveals complex, differential taphonomic pathways. For example, siliceous sponges exhibit diverse biostratinomic and diagenetic pathways that are notably influenced by their environments (Brachert et al. 1987; Reolid 2007; Łukowiak 2020). Demosponges, which have perishable collagen, typically undergo rapid disintegration, leading to the dispersal of their spicules into the sediment (Łukowiak et al. 2013). In Rock Canyon, the shallow peritidal setting with intermittent high-energy conditions during tides or storms likely caused significant sediment reworking, which may explain the rare accumulations of free spicules of halichondrid demosponges, such as those found in small depressions behind obstacles (Fig. 10G, H). The poor preservation of siliceous sponges also results from the instability of silica spicules, which can dissolve quickly during or shortly after the sponge death (Land 1976; Webb 1999; Pisera 2006). During the degradation of sponge tissues, bacterial activities that lead to carbonate precipitation can enhance preservation potential, preventing the collapse of the molds after spicule dissolution (Reitner et al. 1995). The observed vermicular structures (Fig. 10A-E), attributed here to the spongin fibers of keratose sponges, were also found to be associated with early organomineralization within decaying sponge tissues (Delecat et al. 2001; Pei et al. 2022).

In Rock Canyon, the diverse sponge community
was situated in a depositional setting where microbial
deposits flourished. Consequently, the rapid growth
of biofilms may have played a protective role in pre-
serving these non-rigid sponges. However, these
microbial deposits are part of a peritidal facies that
also contains abundant and varied types of fenes-
trae, which complicates the identification of sponges.
The formation of fenestrae can result from different
sedimentary processes and can present very similar
fabrics to those of putative keratose sponges (Fig.
4C; Neuweiler et al. 2022). When recrystallization

is extensive and skeletal elements are not preserved,
it becomes difficult to differentiate them from some
large fenestrae (Fig. 9A). The role of sponges, in
terms of diversity and abundance as framebuilders
may therefore be significantly underestimated in the
Lower Triassic deposits of the western USA basin
and potentially in other basins worldwide. A similar
taphonomic pathway has also been invoked for some
Early to mid-Palaeozoic microbial buildups, where
the degradation of sponges and their cementation
were proposed to explain the formation of cavities
in sediments (Bourque & Boulvain 1993; Coulson &
Brand 2016; Lee & Riding 2021).

The chaetetids, which are hypercalcified sponges,
are expected to have high preservation potential.
However, their preservation in the sedimentary record
is relatively rare due to the mineralogy of their skele-
tons, which often appears to be initially aragonitic or
high-Mg calcite (Cuif 1974; Gautret & Razgallah 1987;
Gautret & Cuif 1989; Cremer 1995; Fabre & Lathuilière
2007; West 2012). The internal structure of the speci-
mens sampled in Rock Canyon is rarely preserved due
to extensive recrystallization (Figs 7, 8). Microscopic
observations show that strong diagenesis obliterates
most of their internal structure, making it difficult to
identify the series of laterally connected longitudinal
tubes, which are replaced by long, radiating calcite
crystals (Fig. 9B, C). Depending on the orientation of
the section within the presumed chaetetids, particu-
larly on their surface where the sketon may form
small reliefs, recrystallized tubes may appear more or
less fan-shaped. This general growth shape can lead to
chaetetid skeletons resembling other biogenic struc-
tures, such as rivulariacean-like cyanobacteria (Bucur
et al. 2020). Distinguishing them from botryoidal or
fan-like cements (Fig. 5E) is also challenging, espe-
cially since such cements might be found just below
some of the presumed chaetetids (Fig. 9E) and could
be biogenically produced. Indeed, a close associa-
tion between some calcareous red algae and radially
arranged fans of aragonite crystals surrounded by
organic tissue is known from modern contexts (Wray
1977; Walker & Moss 1984). In these cases, the algal
thallus produced botryoidal cements that serve as a
support. Similar associations have been reported in
Late Palaeozoic reefs, where biogenically produced
cements may have lost their original structure due to
diagenesis (James et al. 1988; Tucker & Wright 1990).
Some authors also consider that Early Triassic calcium
carbonate crystal fans may reflect abiotic processes
that promoted precipitation on the sea floor (Woods
2014; Friesenbichler et al. 2018), while others propose
that diagenetic and abiotic precipitation of aragonite
botryoids occurs within sediments in marine phreatic
waters (Woods & Baud 2008). When diagenetic overprints affect sponges such as chaetetids, their accurate identification becomes problematic, leading to potential oversight in the field or confusion with various abiotic and post-depositional structures.

## Diverse Early Triassic framebuilders and the missing corals

The participation of sponges as Early Triassic framebuilders was unknown until about a decade ago. The first reports of their presence within various microbial-metazoan bioconstructions challenged the paradigm of an Early Triassic metazoan reef gap (Brayard et al. 2011; Marenco et al. 2012). Since then, several studies have documented the presence of diverse sponges associated with microbial deposits in various locations and over long intervals in the Early Triassic (Luo & Reitner 2014, 2016; Olivier et al. 2014, 2016, 2018; Vennin et al. 2015; Friesenbichler et al. 2018; Baud et al. 2021; Pei et al. 2022; Gischler et al. 2021; Turner 2021; Luo et al. 2022; Wu et al. 2022).

In the western USA basin, a relatively diversified sponge community, including some lyssacine hexactinellids, sphinctozoan demosponges, and calcarea, was the first to be reported as participating in Early Triassic microbial reefs (Brayard et al. 2011). Deposits in Rock Canyon show the presence of additional sponge groups, including some halichondrid and keratose demosponges, geodiides, and presumed chaetetids. Moreover, sponges are not the only regional Early Triassic framebuilders associated with microbial deposits, as micro-conchids and bivalves are also present (Pruss et al. 2007; Brayard et al. 2011; Vennin et al. 2015).

Despite this newly recognized diversity of Early Triassic framebuilders, the challenge remains to find evidence for corals, which have still not been reliably reported from the Early Triassic (Flügel & Senowbari-Daryan 2001; Lathuilière & Marchal 2009). Recent phylogenies proposed for Scleractinia (Lathuilière et al. 2024) and molecular data suggesting a very ancient (Palaeozoic) origin for this clade (Stolarski et al. 2011) both indicate that discovering Early Triassic corals is a reasonable expectation. The discovery of potential chaetetids opens new perspectives, as some authors have hypothesized that this group occupied the ecological niche of corals during the Early Triassic (West 2015). However, the distinction between corals and chaetetids can really be difficult due to their morphological resemblance, which also can be exacerbated by taphonomic processes (see above). Indeed, some domal chaetetids have a superficial skeleton with a honeycomb structure made of hexagonal tubes, somewhat resembling the corallites of scleractinian corals (Ereskovsky & Lavrov 2021).

Upon exposure to weathering, the discovered 3D chaetetid specimen displays domal structures composed of bushy tubes, which indeed evoke either the radial symmetry of septa in scleractinian corallites or the divergence of corallites in a scleractinian domal or hummocky colony (Fig. 6, and 3D photogrammetric models in the Supplementary Files). This morphological similarity is particularly striking when considering that some chaetetids and some corals have tabulae, but chaetetids show only reduced septa or none (Lee & Riding 2018), while some corals have only poorly developed septa (Gretz et al. 2015). Such a skeletal convergence between corals and chaetetids is notably observed in some Lower Jurassic specimens, particularly if diagenesis affects their preservation (Boivin et al. 2020).

## Palaeoenvironmental meaning of Early Triassic microbial-sponge associations

The presence of some sponges in the aftermath of the Permian-Triassic mass extinction is sometimes attributed to their broad environmental tolerance to stressful conditions, such as anoxia (Liu et al. 2013; Wu et al. 2022, 2024). Others authors suggested that Early Triassic sponge-microbial buildups may have survived in specific refuges (Baud & Richoz 2013). Although they currently appear to be restricted to the intertropical area (Martindale et al. 2019), these Early Triassic buildups, regardless of the dominant component (sponge or microbe) in this association, are found in various parts of the Neotethys, Palaeotethys, and Panthalassa oceans (Marenco et al. 2012; Baud et al. 2021; Wu et al. 2022). Furthermore, these buildups developed in a large range of depositional settings, including deep marine settings below the photic zone in Oman (Woods & Baud 2008; Baud & Richoz 2013), outer ramp environments in the western USA (Vennin et al. 2015), open marine mid-ramp environments in Armenia (Luo et al. 2022), and shallow peritidal environments in the western USA (Brayard et al. 2011; Olivier et al. 2016; this study). They have also been reported in a saline lagoonal setting in Germany (Pei et al. 2022). These environments—whether shallow or deep, wave-agitated or calm, restricted or open to the ocean— found in different parts of the world, clearly highlight and confirm the high ecological tolerance of these communities. However, it is difficult to assign a deleterious connotation to any one of these environments in particular, or even to all of them, whether in terms of oxygenation, salinity, trophic conditions, temperature, or even turbidity. Therefore, it seems inappropriate to use microbe-sponge associations as indicators of stressful conditions or as refuge environments during the post-crisis PT recovery phase.
Conclusions

In Rock Canyon (Arizona, USA), middle and late
Smithian exposures of the Sinbad Formation provide
the first record of presumed Early Triassic chaetetid
sponges. The discovery of chaetetids in Early Triassic
deposits both fills a major gap in the fossil record, as
these organisms were previously unknown from the
Early and Middle Triassic, and highlights the remain-
ing significant gaps in our understanding of this
pivotal period in life history following the Permian-
Triassic mass extinction.

Taphonomic and sampling biases make it difficult
to identify with certainty these presumed chaetet-
ids in the studied sedimentary succession. Extensive
recrystallization often obliterates the characteristic
structures of chaetetids, whose elongated shape look
like some fenestrae common within microbial facies.

The co-occurrence of chaetetids with other
sponges, such as lyssacine hexactinellids, halichon-
drid, and keratose demosponges, and geidiids high-
lights that this community is even more diverse than
previously thought. These sponges are associated with
microbial deposits and contribute to the framework
of buildups that developed local and small bioherms.
Locally, some microconchids also contributed to
these bioconstructions.

The studied sedimentary succession reveals a
transition from a fluvial to a peritidal setting, where
microbial-sponge buildups developed following a
transgression. Alongside other similar and contem-
poraneous consortia worldwide, this newly identi-
fied association of microbial deposits with sponges
highlights the widespread occurrence of such Early
Triassic bioconstructions across diverse marine envi-
ronments, from saline lagoons and peritidal settings
to open marine environments of various depths. This
diversity of marine settings questions the paradigm
that microbial-sponge associations could characterize
local refuges or stressful environments in the after-
math of the Permian-Triassic mass extinction.

Acknowledgments. — Thanks to Nicolas Goudemand and Pauline Guenser for help in the field. We thank Sylvaine Jouhannel (LMV) for her help with the acquisition of some photographs of the macroscopic samples, and Lucie Masson (Biogéosciences) for her help in producing thin sections. We thank Jean-David Moreau for his help with 3D reconstructions. We acknowledge the SOLEIL synchrotron for provision of beamtime and we thank Sebastian Schöder (SOLEIL synchrotron, Paris-Saclay, France), Mathieu Thoury and Pierre Gueriau (Ipanema, Saint-Aubin, France) for assistance at the PUMA beamline. We sincerely thank the editor, Peter Doyle, for his guidance and support throughout the review process. We are also deeply grateful to the three reviewers, including George Pleš and two anonymous reviewers, for their constructive comments and valuable suggestions, which improved the quality of this manuscript. This work was supported by the ANR project AFTER (ANR-13-JS06-0001-01), the French ‘Investissements d’Avenir’ program (project ISITE-BFC: ANR-15-IDEX-03), and received funding from the programme

Tellus of the Institut National des Sciences de l'Univers, CNRS.
Sample management and valorization benefited from ANR-11-INBS-0004-RECOLNAT and from the help of Jérôme Thomas.
This work is also a contribution to the e-Col+ project funded by the
Programme d'Investissements d'Avenir (ANR 21 ESRE 0053).

Supplementary Information

*Supplementary Files.* Photogrammetric 3D reconstructions of the presumed chaetetid UBGD.030499. The software Agisoft Metashape Professional 2.0 was used to align and combine several dozens of digital photographs taken by an Olympus TG-5 camera. This led to the generation of the 3D textured model (A), digital elevation model (B) and digital elevation model in false colours (C). The three figures represent the specimen viewed from above. The full model that can be freely oriented digitally is available here https://search-data.ubfc.fr/FR-13002091000019-2024-11-12_3D-Model-Fossil-Chaetetid.html

References

Algeo, T.J., Chen, Z.Q., Fraiser, M.L. & Twitchett, R.J. 2011: Terrestrial–marine teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems. *Palaeogeography, Palaeoclimatology, Palaeoecology* **308**, 1–11.

Allison, P.A. & D.J. Bottjer. 2011: Taphonomy: bias and pro-
cess through time. *In*: Landman, N.H. & Harries, P.J., (eds): *Taphonomy*. Springer, Heidelberg, 1–17.

Almazán-Vázquez, E., Buitrón-Sánchez, B. E., Vachard, D., Mendoza-Madera, C. & Gómez-Espinosa, C. 2007: The late Atokan (Moscovian, Pennsylvanian) chaetetid accumulations of Sierra Agua Verde, Sonora (NW Mexico): composition, facies and palaeoenvironmental signals. *Geological Society, London, Special Publications* **275**, 189–200.

Baccelle, L. & Bosellini, A. 1965: Diagrammi per la stima visiva della composizione percentuale nelle rocce sedimentarie. *Annali dell'Università di Ferrara, N.S. Sez. IX*, 59-62.

Baud, A. & Richoz, S. 2013: The Smithian (Early Triassic) red
ammonoid limestone of Oman, refuge for sponge-microbial
build-ups during recovery phase. *In*: GSA Annual Meeting in
Denver, abstract. Paper No. 399-5.

Baud, A., Richoz, S., Brandner, R., Krystyn, L., Heindel, K., Mohtat, T., Mohtat-Aghai, P. & Horacek, M. 2021: Sponge takeover from end-Permian mass extinction to Early Induan time: Records in Central Iran microbial buildups. *Frontiers in Earth Science* **9**, 586210.

Benton, M.J. 2018: Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction. *Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences* **376**, 20170076.

Bernecker, M. 1996: Upper Triassic reefs of the Oman Mountains: data from the South Tethyan margin. *Facies* **34**, 41–76.

Billingsley, G.H. 1992: Geologic map of the Rock Canyon quadrangle, northern Mohave County. Arizona. *US Geological Survey Open-File Report* **92-449**.

Blakey, R.C. 1979: Oil impregnated carbonate rocks of the Timpowea Member, Moenkopi Formation, Hurricane Cliffs area, Utah and Arizona. *Utah Geological Association Publication* **6**, 45–54.

Blakey, R.C., Bashem, E.L. & Cook, M.J. 1993: Early and Middle Triassic paleogeography, Colorado Plateau and vicinity. In: *Aspects of Mesozoic Geology and Paleontology of the Colorado Plateau*, Morales, M. (ed.), *Museum of Northern Arizona, Bulletin* **59**, p. 13–26.

Boivin S., Vasseur R., Lathuilière B., Lazar I., Durlet C., Martindale R. C., El Hmedi K. & Martini R. 2019: A little walk between Early Jurassic sponges and corals: A confusing morphological convergence. *Geobios* **57**, 1–24.
Bourque, P.A. & Boulvain, F. 1993 : A model for the origin and petrogenesis of the red stromatactis limestone of Paleozoic carbonate mounds. *Journal of Sedimentary Petrology* 63, 607–619.

Brachert, T.C., Dullo, W.C. & Stoffers, P. 1987: Diagenesis of siliceous sponge limestones from the Pleistocene of the Tyrrhenian Sea (Mediterranean Sea). *Facies* 17, 41–49.

Brayard, A., Bucher, H., Escarguel, G., Fluteau, F., Bourquin, S. & Galfetti, T. 2006: The Early Triassic ammonoid recovery: paleoclimatic significance of diversity gradients. *Palaeogeography, Palaeoclimatology, Palaeoecology* 239, 374–395.

Brayard, A., Escarguel, G., Bucher, H. & Brühwiler, T. 2009: Smithian and Spathian (Early Triassic) ammonoid assemblages from terranes: paleoceanographic and paleogeographic implications. *Journal of Asian Earth Sciences* 36, 420–433.

Brayard, A., Nützel, A., Stephen, D. A., Bylund, K. G., Jenks, J. & Bucher, H. 2010: Gastropod evidence against the Early Triassic Lilliput effect. *Geology* 38, 147–150.

Brayard, A., Vennin, E., Olivier, N., Bylund, K.G., Jenks, J., Stephen, D.A., Bucher, H., Hofmann, R., Goudemand, N., Escarguel, G. 2011. Transient metazoa reefs in the aftermath of the end-Permian mass extinction. *Nature Geoscience* 4, 693–697.

Brayard, A., Bylund, K.G., Jenks, J., Stephen, D., Olivier, N., Escarguel, G., Fara, E. & Vennin, E. 2013: Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography. *Swiss Journal of Palaeontology* 132, 141–219.

Brayard A., Meier M., Escarguel G., Fara E., Nützel A., Olivier N., Bylund K.G., Jenks J.F., Stephen D.A., Hautmann M., Vennin E. & Bucher H. 2015: Early Triassic Gulliver gastropods: spatio-temporal distribution and significance for the biotic recovery after the end-Permian mass extinction. *Earth-Science Reviews* 146, 31–64.

Brayard, A., Krumenacker, L.J., Botting, J.P., Jenks, J.F., Bylund, K.G., Fara, E., Vennin, E., Olivier, N., Goudemand, N., Saucède, T., Charbonnier, S., Romano, C., Doguzhaeva, L., Thuy, B., Hautmann, M., Stephen, D.A., Thomazo, C. & Escarguel G. 2017: Unexpected Early Triassic marine ecosystem and the rise of the modern evolutionary fauna. *Science Advances* 3, e1602159.

Brayard, A., Olivier, N., Vennin, E., Jenks, J.F., Bylund, K.G., Stephen, D.A., McShinsky, D., Goudemand, N., Fara, E. & Escarguel, G., 2020: New middle and late Smithian ammonoid faunas from the Utah/Arizona border: new evidence for calibrating Early Triassic transgressive-regressive trends and paleobiogeographical signals in the western USA basin. *Global and Planetary Change* 192, 103251.

Bucur, I. I., Rigaud, S., Del Piero, N., Fucelli, A., Heerwagen, E., Peybernes, C., Peyrotty, G., Verard, C., Chablais, J. & Martini, R. 2020: Upper Triassic calcareous algae from the Panthalassa Ocean. *Rivista Italiana di Paleontologia e stratigrafia* 126, 499–540.

Campbell, I. H., Czamanske, G. K., Fedorenko, V. A., Hill, R. I. & Stepanov, V. 1992: Synchronism of the Siberian Traps and the Permian-Triassic boundary. *Science* 258, 1760–1763.

Caravaca G., Thomazo, C., Brayard A., Vennin E., Olivier N., Cocquerez T., Escarguel G., Fara E., Jenks J.F., Bylund K.G., Stephen D.A. & Brayard A. 2017: Early Triassic fluctuations of the global carbon cycle: New evidence from paired carbon isotopes in the western USA basin. *Global and Planetary Change* 154, 10–22.

Caravaca, G., Brayard, A., Vennin, E., Guiraud, M., Le Pourhiet, L., Grosjean, A.-S., Thomazo, C., Olivier, N., Fara, E., Escarguel, G., Bylund, K.G., Jenks, J.F. & Stephen, D.A. 2018: Controlling factors for differential subsidence in the Sonoma Foreland Basin (Early Triassic, western USA). *Geological Magazine* 155, 1305–1329.

Clark, R.A. 2021: Stratigraphy, lithology, and depositional environments of the Lower Permian Kaibab Formation, Northwestern Arizona. *Arizona Geological Survey Contributed Report* CR-21-E, 87 pp.

Collinson, J.W., Kendall, C.G.S.C. & Marcantel, J. B. 1976: Permian–Triassic boundary in eastern Nevada and west-central Utah. *Bulletin of the Geological Society of America* 87, 821–824.

Coulson, K.P. & Brand, L.R. 2016: Lithistid sponge-microbial reef-building communities construct laminated, upper Cambrian (Furongian) 'stromatolites'. *Palaios* 31, 358–370.

Cremer, H. 1995: Spicule pseudomorphs in Upper Triassic (Norian) chaetetid sponges from the western Taurids (Antalya-Region, SW Turkey). *Geobios* 28, 163–174.

Cuif, J.P. 1974 : Rôle des Sclérosponges dans la faune récifale du Trias des Dolomites (Italie du Nord). *Geobios* 7, 139–153.

Dai, X., Davies, J.H., Yuan, Z., Brayard, A., Ovtcharova, M., Xu, G., Liu X., Smith, P.A., Scweitzer C.E., Li M., Perrot M.G., Jiang S., Miao L., Cao Y., Yan J., Bai R., Wang F., Guo W., Song H., Tian L., Corso J.D., Liu Y., Chu D. & Song, H. 2023: A Mesozoic fossil lagerstätte from 250.8 million years ago shows a modern-type marine ecosystem. *Science* 379, 567–572.

Delecat, S. & Reitner, J. 2005: Sponge communities from the Lower Triassic of Adnet (Northern Calcareous Alps, Austria). *Facies* 51, 385–404.

Delecat, S., Peckmann, J. & Reitner, J. 2001: Non-rigid cryp-tic sponges in oyster patch reefs (Lower Kimmeridgian, Langenberg/Oker, Germany). *Facies* 45, 231–254.

Delecat, S., Arp, G. & Reitner, J. 2011: Aftermath of the Triassic-Jurassic boundary crisis: spiculite formation on drowned Triassic Steinplatte reef-slope by communities of hexactinellid sponges (Northern Calcareous Alps, Austria). *In*: Land, L. & Reitner, J. (eds): *Advances in Stromatolite Geobiology*. Lecture Notes in Earth Sciences 131. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-10415-2_23

De Vos, L., Rützler, K., Boury-Esnault, N., Donadey, C. & Vacelet, J., 1991: *Atlas of sponge morphology. Atlas de morphologie des éponges*, Smithsonian Institution Press, Washington & London.

Dickinson, W.R. 2006: Geotectonic evolution of the Great Basin. *Geosphere* 2, 353–368.

Dickinson, W.R. 2013: Phanerozoic palinspastic reconstructions of Great Basin geotectonics (Nevada-Utah, USA). *Geosphere* 9, 1384–1396.

Embry, A.F. 1997: Global sequence boundaries of the Triassic and their identification in the western Canada sedimentary basin. *Canadian Petroleum Geology Bulletin* 45, 415–433.

Ereskovsky, A. & Lavrov, A. 2021: Porifera, 19–54. *In*: LaDouceur, E.E.B. (ed.): *Invertebrate histology*. Wiley-Blackwell, Hoboken, https://doi.org/10.1002/9781119507697.ch2

Erpenbeck, D., Sutcliffe, P., Cook, S.D.C., Dietzel, A., Maldonado, M., van Soest, R.W., Hooper, J.N. & Wörheide, G., 2012: Horny sponges and their affairs: On the phylogenetic relationships of keratose sponges. *Molecular Phylogenetics and Evolution* 63, 809–816.

Erwin, D.H. 1998: The end and the beginning: recoveries from mass extinctions. *Trends in Ecology & Evolution* 13, 344–349.

Erwin, D.H. & Pan, H.Z. 1996: Recoveries and radiations: gastropods after the Permo-Triassic mass extinction. *In*: Hart, M.B. (ed.): *Biotic Recovery from Mass Extinction Events*. Geological Society of London Special Publications 102, 223–229.

Fabre, C. & Lathuilière, B. 2007: Relationships between growth-bands and paleoenvironmental proxies Sr/Ca and Mg/Ca in hypercalcified sponge: A micro-laser induced breakdown spectroscopy approach. *Spectrochimica Acta B* 62, 1537–1545.

Fagerstrom J.A. 1987: The evolution of reef communities John Wiley and Sons, New York.

Flügel, E. 2002: Triassic reef patterns, 391–463. *In*: Kiessling W, Flügel & Golonka J (eds): *Phanerozoic Reef Patterns*. SEPM Special Publication 72, SEPM Press, Tulsa.

Flügel, E. 2004: *Microfacies of Carbonate Rocks: Analysis, Interpretation and Application*. Springer, Berlin Heidelberg, New York.

Flügel, E. & Senowbari-Daryan, B. 2001: Triassic reefs of the Tethys, 217–249. *In*: Stanley, G.D. (ed), *The History and Sedimentology of Ancient Reef Systems*, Springer, Heidelberg.

Forel, M.B. 2013: The Permian–Triassic mass extinction: ostracods (Crustacea) and microbialites. *Comptes Rendus Geoscience* 345, 203–211.
Forel, M.B., Crasquin, S., Kershaw, S. & Collin, P.Y. 2013: In the aftermath of the end-Permian extinction: the microbialite ref-uge? *Terra Nova* 25, 137–143.

Foster, W.J., Lehrmann, D.J., Yu, M. & Martindale, R.C. 2019: Facies selectivity of benthic invertebrates in a Permian/Triassic boundary microbialite succession: implications for the ‘micro- bialite refuge’ hypothesis. *Geobiology* 17, 523–535.

Fraiser, M.L. 2011: Paleoecology of secondary tierers from Western Pangean tropical marine environments during the after- math of the end-Permian mass extinction. *Palaeogeography, Palaeoclimatology, Palaeoecology* 308, 181–189.

Fraiser, M.L. & Bottjer, D.J. 2005: Restructuring in benthic level- bottom shallow marine communities due to prolonged envi- ronmental stress following the end-Permian mass extinction. *Comptes Rendus Palevol* 4, 583–591.

Friesenbichler, E., Richoz, S., Baud, A., Krystyn, L., Sahakyan, L., Vardanyan, S., Peckmann, J., Reitner, J. & Heindel, K. 2018: Sponge-microbial build-ups from the lowermost Triassic Chanakhchi section in southern Armenia: Microfacies and stable carbon isotopes. *Palaeogeography, Palaeoclimatology, Palaeoecology* 490, 653–672.

Friesenbichler, E., Hautmann, M. & Bucher, H. 2021: The main stage of recovery after the end-Permian mass extinction: Taxonomic rediversification and ecologic reorganization of marine level-bottom communities during the Middle Triassic. *PeerJ* 9, e11654.

Gabrielse, H., Snyder, W.S. & Stewart, J.H. 1983: Sonoma orogeny and Permian to Triassic tectonism in western North America. *Geology* 11, 484–486.

Gaillard, C. 1983: Les biohermes à spongiaires et leur environne- ment dans l'Oxfordien du Jura méridional. *Documents du Laboratoire de Géologie de Lyon, 90*. Université Lyon 1, Lyon.

Galfetti, T., Bucher, H., Ovtcharova, M., Schaltegger, U., Brayard, A., Brühwiler, T., Goudemand, N., Weissert, H., Hochuli, P.A., Cordey, F., Guodun, K. 2007: Timing of the Early Triassic carbon cycle perturbations inferred from new U–Pb ages and ammonoid biochronozones. *Earth and Planetary Science Letters* 258, 593–604.

Gautret, P. & Razgallah. S. 1987: Architecture et microstructure des Chaetétides du Permien du Jebel Tebaga (Sud-Tunisie). *Annales de Paléontologie* 73, 59–82.

Gautret, P. & Cuif, J.P. 1989: Les démosponges calcifiées des bio- hermes du Jurassique supérieur du sud Tunisie (Oxfordien de la région de Tataouine). *Geobios* 22, 49–63.

Gischler, E., Fuchs, A., Bach, W. & Reitner, J. 2021: Massive cryptic microbe-sponge deposits in a Devonian fore-reef slope (Elbingerode Reef Complex, Harz Mts, Germany). *Paläontologische Zeitschrift* 95, 683–707.

Goudemand, N., Romano, C., Leu, M., Bucher, H., Trotter, J.A. & Williams, I.S. 2019: Dynamic interplay between climate and marine biodiversity upheavals during the Early Triassic Smithian-Spathian biotic crisis. *Earth-Science Reviews* 195, 169–178.

Granier, B.R. 2020: The biosignature of sparite permits the dis- tinction between gravitational cement and endostromatolites. *Carnets de Géologie* 20, 407–419.

Gregory, H.E. 1950: Geology and geography of the Zion National Park region, Utah and Arizona. *Geological Survey Professional Paper* 220, 1–200.

Gretz, M., Lathuilière, B. & Martini, R. 2014: A new coral with sim- plified morphology from the oldest known Hettangian (Early Jurassic) reef in southern France. *Acta Palaeontologica Polonica* 60, 277–286.

Gueriau, P., Jauvion, C. & Mocuta, C. 2018: Show me your yttrium, and I will tell you who you are: implications for fossil imaging. *Palaeontology* 61, 981–990.

Hallam, A. 1991: Why was there a delayed radiation after the end-Palaeozoic extinctions? *Historical Biology* 5, 257–262.

Ingersoll, R.V. 2008: Subduction-related sedimentary basins of the USA Cordillera, 395–428. *In: Hsu, K.J. & Miall, A.D. (eds): The Sedimentary Basins of the United States and Canada. Sedimentary basins of the world 5, Elsevier, Amsterdam.*

Ingersoll, R.V. 2019: Subduction-related sedimentary basins of the US Cordillera, 477–510. *In: The sedimentary basins of the United States and Canada*. Elsevier, Amsterdam

James, N.P., Wray, J.L. & Ginsburg, R.N. 1988: Calcification of encrusting aragonitic algae (Peyssonneliaceae); implications for the origin of late Paleozoic reefs and cements. *Journal of Sedimentary Research* 58, 291–303.

Jattiot, R., Bucher, H., Brayard, A., Brosse, M., Jenks, J.F. & Bylund, K.G. 2017: Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin. *Palaeontographica. Abteilung A: Palaeozoologie-Stratigraphie* 309, 1–89.

Jattiot, R., Brayard, A., Bucher, H., Vennin, E., Caravaca, G., Jenks, J.F., Bylund, K.G., Escarguel, G. 2018: Palaeobiogeographical distribution of Smithian (Early Triassic) ammonoid faunas within the western USA basin and its controlling parameters. *Palaeontology* 61, 881–904.

Jeffrey, B.M., Elrick, M., Atudorei, V. & Lucas, S.G. 2019: Facies architecture and across-shelf variability of an extensive Lower Triassic (Smithian) microbial carbonate mound complex in the western U.S. *Palaeogeography, Palaeoclimatology, Palaeoecology* 521, 42–56.

Jenks, J. F. & Brayard, A. 2018: Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: taxonomy, biostratigraphy and biogeography. *New Mexico Museum of Natural History Bulletins* 78, 175.

Jenson, J. 1986: Stratigraphy and facies analysis of the Upper Kaibab and Lower Moenkopi formations in Southwest Washington County, Utah. *Brigham Young University Geology Studies* 33, 1–21.

Kershaw, S. & Jeon, J. 2024: Stromatoporoids and extinctions: A review. *Earth-Science Reviews* 252, 104721.

Kiparisova, L.D. & Popov, Y.N. 1956: Subdivision of the lower series of the Triassic system into stages. *Doklady Academy Sciences U.S.S.R.* 109, 842–845.

Krystyn, L., Bhargava, O. N., Richoz, S. 2007: A candidate GSSP for the base of the Olenekian stage: Mud at Pin Valley; District Lahul & Spiti, Himachal Pradesh (Western Himalaya), India. *Albertiana* 35, 5–29

Land, L.S. 1976: Early dissolution of sponge spicules from reef sediments, North Jamaica. *Journal of Sedimentary Research* 46, 967–969.

Lathuilière, B. & Marchal, D. 2009: Extinction, survival and recovery of corals from the Triassic to Middle Jurassic time. *Terra Nova* 21, 57–66.

Lathuilière, B., Huang, D. & Corallosphere group 2024: Deciphering the evolutionary history of early Mesozoic fossil corals. *Acta Paleontologica Polonica* 69, 249–262.

Lee, J.-H. & Riding, R. 2018: Marine oxygenation, lithistid sponges, and the early history of Paleozoic skeletal reefs. *Earth-Science Reviews* 181, 98–121.

Lee, J.-H. & Riding, R. 2021: Keratolite-stromatolite consortia mimic domical and branched columnar stromatolites. *Palaios* 571, 110228.

Leu, M., Bucher, H., Vennemann, T., Bagherpour, B., Ji, C., Brosse, M. & Goudemand, N. 2022: A Unitary Association-based conodont biozonation of the Smithian–Spathian boundary (Early Triassic) and associated biotic crisis from South China. *Swiss Journal of Palaeontology* 141, 19.

Li, H., Wignall, P.B., Jiang, H., Zhang, M., Wu, X. & Lai, X. 2023: A review of carbon isotope excursions, redox changes and marine red beds of the Early Triassic with insights from the Qinling Sea, northwest China. *Earth-Science Reviews* 300, 104623.

Liu, G., Feng, Q., Shen, J. U. N., Yu, J., He, W. & Algeo, T. J. 2013: Decline of siliceous sponges and spicule miniaturization induced by marine productivity collapse and expanding anoxia during the Permian-Triassic crisis in South China. *Palaios* 28, 664–679.

Lucas, S.G., Krainer, K. & Milner, A.R., 2007: The type section and age of the Timpowap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah. N. M. Mus. *Natural History Sciences Bulletin* 40, 109–117.
Łukowiak, M. 2020: Utilizing sponge spicules in taxonomic, eco-
logical and environmental reconstructions: a review. *PeerJ* 8,
e10601.

Łukowiak, M., Pisera, A & O'Dea, A. 2013: Do spicules in sed-
iments reflect the living sponge community? A test in a
Caribbean shallow water lagoon. *Palaios* 28, 373–85.

Luo, C. & Reitner, J. 2014: First report of fossil 'keratose' demo-
sponges in Phanerozoic carbonates: preservation and 3-D
reconstruction. *Naturwissenschaften* 101, 467–477.

Luo, C. & Reitner, J. 2016: 'Stromatolites' built by sponges and microbes – a new type of Phanerozoic bioconstruction. *Lethaia* 49, 555–570.

Luo, C., Pei, Y., Richoz, S., Li, Q. & Reitner, J. 2022: Identification and current palaeobiological understanding of 'Keratosa'-type nonspicular demosponge fossils in carbonates: with a new example from the lowermost Triassic, Armenia. *Life* 12, 1348.

Marenco, P.J., Griffin, J.M., Fraiser, M.L. & Clapham, M.E. 2012: Paleo-ecology and geochemistry of Early Triassic (Spathian) microbial mounds and implications for anoxia following the end-Permian mass extinction. *Geology* 40, 715–718.

Martindale, R.C., Corsetti, F.A., Bottjer, D.J. & Senowbari-Daryan, B. 2012: Microbialite fabrics and diminutive skeletal bioconstructors in Lower Norian Summit Point reefs, Oregon, United States. *Palaios* 27, 489–508.

Martindale, R. C., Foster, W.J. & Velledits, F. 2019: The survival, recovery, and diversification of metazoan reef ecosystems following the end-Permian mass extinction event. *Palaeogeography, Palaeoclimatology, Palaeoecology* 513, 100–115.

Martini, R., Zaninetti, L., Lathuilière, B., Cirilli, S., Cornée, J.J. & Villeneuve, M. 2004: Upper Triassic carbonate deposits of Seram (Indonesia): palaeogeographic and geodynamic implications. *Palaeogeography, Palaeoclimatology, Palaeoecology* 206, 75–102.

Mills, H.H. 1979: Downstream rounding of pebbles; a quantitative review. *Journal of Sedimentary Research* 49, 295–302.

Monty, CL. 1981: Spongiostromate vs. porostromate stromat-
olites and oncolites, 1-4. *In:* Monty C. (ed.): *Phanerozoic
Stromatolites*. Case Histories, Springer-Verlag, Berlin.

Monty, C.L. 1982: Cavity or fissure dwelling stromatolites (endostromatolites) from Belgian Devonian mud mounds (extended abstract). *Annales de la Société Géologique de Belgique* 105, 343–344.

Neuweiler, F., Kershaw, S., Boulvain, F., Matysik, M., Sendino, C., McMenamin, M. & Wood, R. 2022: Keratose sponges in ancient carbonates – a problem of interpretation. *Sedimentology*, https://doi.org/10.1111/sed.13059

Nielson, R.L. 1991: Petrology, sedimentology and stratigraphic implications of the Rock Canyon Conglomerate, southwestern Utah. *Utah Geological Survey Miscellaneous Publication* 91-7, 65 pp.

Olivier, N., Brayard, A., Fara, E., Bylund, K.G., Jenks, J. F., Vennin, E., Stephen, D.A. & Escarguel, G. 2014: Smithian shoreline migrations and depositional settings in Timpowear Canyon (Early Triassic, Utah, USA). *Geological Magazine* 151, 938–955.

Olivier N., Brayard A., Vennin E., Escarguel G., Fara E., Bylund K.G., Jenks J.F., Caravaca, G. & Stephen D.A. 2016: Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery. *Geological Journal* 51, 600–626.

Olivier N., Fara E., Vennin E., Bylund K.G., Jenks J.F., Escarguel G., Stephen D.A., Goudemand N., Snyder D., Thomazo C. & Brayard A. 2018: Late Smithian microbial deposits and their lateral marine fossiliferous limestones (Early Triassic, Hurricane Cliffs, Utah, USA). *Facies* 64, 13.

Orchard, M.J. 2007: Conodont diversity and evolution through the latest Permian and Early Triassic upheavals. *Palaeogeography, Palaeoclimatology, Palaeoecology* 252, 93–117.

Paull, R.A. & Paull, R.K. 1993: Interpretation of Early Triassic nonmarine-marine relations, Utah, U.S.A. *New Mexico Museum of Natural History and Science Bulletin* 3, 403–409.

Paull, R.K. & Paull, R.A. 1994: Shallow marine sedimentary facies in the earliest Triassic (Griesbachian) Cordilleran miogeocline, U.S.A. *Sedimentary Geology* 93, 181–191.

Paull, R.K. & Paull, R.A. 1997: Transgressive conodont faunas of the Early Triassic: an opportunity for correlation in the Tethys and the circum-Pacific, 158–167. *In:* Dickinson, J.M., Zunyi, Y., Hongfu, Y., Lu- cas, S.G. & Acharyya S.K. (eds): *Late Palaeozoic and Early Mesozoic Circum-Pacific Events and their Global Correlation*. Cambridge University Press, World and Regional Geology 10.

Payne, J.L., Lehrmann, D.J., Wei, J., Orchard, M.J., Schrag, D.P. & Knoll, A.H. 2004: Large perturbations of the carbon cycle during recovery from the end-Permian extinction. *Science* 305, 506–509.

Pei, Y., Duda, J. P., Schoenig, J., Luo, C. & Reitner, J. 2021: Late Anisian microbe-metazoan build-ups in the Germanic Basin: aftermath of the Permian–Triassic crisis. *Lethaia* 54, 823–844.

Pei, Y., Hagdorn, H., Voigt, T., Duda, J. P. & Reitner, J. 2022: Palaeoecological implications of Lower-Middle Triassic stromatolites and microbe-metazoan build-Ups in the Germanic Basin: Insights into the aftermath of the Permian–Triassic crisis. *Geosciences* 12, 133.

Pham, D., Song, J. & Lee, J.-H. 2021: Keratose sponge–microbial consortia in stromatolite-like columns and thrombolite-like mounds of the lower Ordovician (Tremadocian) Mungok Formation, Yeongwol, Korea. *Palaeogeography, Palaeoclimatology, Palaeoecology* 572, 110409.

Pisera, A. 2006: Palaeontology of sponges—a review. *Canadian Journal of Zoology* 84, 242–261.

Piuž, A.D. 2004: *Micropaléontologie d'une plate-forme bioclastique échinodermique: les calcaires à entroques du Bajocien du Jura méridional et de Bourgogne.* Doctoral dissertation, University of Geneva.

Poborski, S.J. 1954: Virgin formation (Triassic) of the St. George, Utah, area. *Geological Society of America Bulletin* 65, 971–1006.

Pratt, B.R., 1982: Stromatolitic framework of carbonate mud mounds. *Journal of Sedimentary Petrology* 52, 1203–1227.

Pratt, B.R. & James, N.P. 1986: The St George Group (Lower Ordovician) of western Newfoundland: tidal flat island model for carbonate sedimentation in shallow epeiric seas. *Sedimentology* 33, 313–343.

Pruss, S.B., Payne, J.L., & Bottjer, D.J. 2007: *Placunopsis* bioherms: the first metazoan buildups following the end-Permian mass extinction. *Palaios* 22, 17–23.

Pruss, S.B., Payne, J.L. & Westacott, S. 2015: Taphonomic bias of selective silicification revealed by paired petrographic and insoluble residue analysis. *Palaios* 30, 620–626.

Ramos A. & Sopeña, A. 1983: Gravel bars in low-sinuosity streams (Permian and Triassic, central Spain). *Special Publications of the International Association of Sedimentologists* 6, 301–312.

Ramos, A., Sopena, A. & Perez-Arlucea, M. 1986: Evolution of Buntsandstein fluvial sedimentation in the northwest Iberian Ranges (Central Spain). *Journal of Sedimentary Research* 56, 862–875.

Reeside, J.B.Jr. & Bassler, H. 1922: Stratigraphic sections in Southwestern Utah and Northwestern Arizona. *U.S. Geological Survey, Professional Paper 129-D*, 53–77.

Reid, R.E.H. 2004: Mesozoic and Cenozoic choristid demo-
sponges, 449–556. *In:* Kaesler R.L. (ed.): *Treatise on Invertebrate
Paleontology, Part E, Porifera (revised)* 3. Geological Society
of America and University of Kansas, Boulder, Colorado and
Lawrence.

Reitner, J., Neuweiler, F. & Gautret, P. 1995: Modern and fossil
automicrites: implications for mud mound genesis. In: Reitner,
J. & Neuweiler (coord): Mud Mounds: A poligenetic spectrum
of fine-grained carbonate buildups. *Facies* 32, 4–17.

Reolid, M. 2007: Taphonomy of the Oxfordian–Lowermost Kimmeridgian siliceous sponges of the Prebetic Zone (Southern Iberia). *Journal of Taphonomy* 5, 71–90.
Saucède, T., Smith, C., Olivier, N., Durlet, C., Gueriau, P., Thoury, M., Fara, E., Escarguel, G. & Brayard, A. 2023: A new Early Triassic crinoid from Nevada questions the origin and palaeobiogeographical history of dadocrinids. *Acta Palaeontologica Polonica* 68, 155-166.

Schubert, J. K. & Bottjer, D. J. 1992: Early Triassic stromatolites as post-mass extinction disaster forms. *Geology* 20, 883-886.

Senowbari-Daryan, B. & Maurer, F. 2008: Upper Triassic (Norian) hypercalcified sponges from the Musandam Peninsula (United Arab Emirates and Oman). *Facies* 54, 433-460.

Smith, C.P.A., Laville, T., Fara, E., Escarguel, G., Olivier, N., Vennin, E., Goudemand, N., Bylund, K.G., Jenks, J.F., Stephen, D.A., Hautmann, M., Charbonnier, S., Krumenacker, L.J. & Brayard, A. 2021: Exceptional fossil assemblages confirm the existence of complex Early Triassic ecosystems during the early Spathian. *Scientific Reports* 11, 19657, https://doi.org/10.1038/s41598-021-99056-8

Song, H.J., Wignall, P.B., Chen, Z.Q., Tong, J.N., Bond, D.P.G., Lai, X.L., Zhao, X.M., Jiang, H.S., Yan, C.B., Niu, Z.J., Chen, J., Yang, H. & Wang, Y.B. 2011: Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction. *Geology* 39, 739-742.

Song, H., Wignall, P. B., Tong, J. & Yin, H. 2013: Two pulses of extinction during the Permian–Triassic crisis. *Nature Geoscience* 6, 52–56.

Song, H., Wignall, P.B., Chu, D., Tong, J., Sun, Y., Song, H., He, W. & Tian, L. 2014: Anoxia/high temperature double whammy during the Permian–Triassic marine crisis and its af- termath. *Scientific Reports* 4, 4132

Speed, R.C. 1979: Collided Paleozoic microplate in the western United States. *The Journal of Geology* 87, 279-292.

Stanley Jr, G.D. 2003: The evolution of modern corals and their early history. *Earth-Science Reviews* 60, 195-225.

Stanley, S.M. 2009: Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions. *Proceedings of the National Academy of Sciences of the United States of America* 106, 15264-15267.

Stanton, R.J., Lambert, L.L., Webb, G.E. & Lustig, L.D. 2016: Chaetetes morphology, environment, and taxonomy. *Facies* 62, 1-21.

Stewart, J.H., Poole, F.G. & Wilson, R.F. 1972: Stratigraphy and origin of the Triassic Moenkopi formation and related strata in the Colorado Plateau region. *Geological Survey Professional Paper* 691, 1-195.

Stolarski, J., Kitahara, M., Miller, D.J., Cairns, S.D., Mazur, M. & Meibom A. 2011: The ancient evolutionary origins of Scleractinia revealed by azooxanthellate corals. *Evolutionary Biology* 11, 316, 1-10.

Szulc, J. 2007: Sponge-microbial stromatolites and coral sponge reef recovery in the Triassic of the western Tethys domain. *In:* Lucas, S.C. & Spielmann, J.A. (eds) *The Global Triassic New Mexico Museum Natural History Sciences Bulletin* 41, 402.

Taylor, P.D. & Vinn, O. 2006: Convergent morphology in small spiral worm tubes ('Spirorbis') and its palaeoenvironmental implications. *Journal of the Geological Society* 163, 225-228.

Tozer, E.T. 1967: A standard for Triassic time. *Geological Survey of Canada Bulletin* 156, 1-103.

Tucker, M.E. & Wright, V.P. 1990: *Carbonate Sedimentology*. Blackwell, Oxford.

Turner, E.C. 2021: Possible poriferan body fossils in early Neoproterozoic microbial reefs. *Nature* 596, 87-91.

Vennin, E., Olivier, N., Brayard, A., Bour, I., Thomazo, C., Escarguel, G., Fara, E., Bylund, K.G., Jenks, J.F., Stephen, D.A. & Hofmann, R. 2015: Microbial deposits in the aftermath of the end-Permian mass extinction: a diverging case from the Mineral Mountains (Utah, USA). *Sedimentology* 62, 753-792.

Walker, R. & Moss, B. 1984: Mode of attachment of six epilithic crustose Corallinaceae (Rhodophyta). *Phycologia* 23, 321-329.

Ware, D., Goudemand, N., Bucher, H., Schneebeli-Hermann, E., Hochuli, P. A., Brühwiler, T. & Roohi, G. 2017: A proposal for a multiproxy definition of the Induan–Olenekian boundary and

its corresponding GSSP candidate at Nammal Nala (Salt Range, Pakistan). *Géologie Alpine* 14, 133-134.

Webb, G. E. 1999: Youngest Early Carboniferous (late Visean) shallow-water patch reefs in eastern Australia (Rockhampton Group, Queensland): combining quantitative micro-and macro-scale data. *Facies* 41, 111-139.

Wei, H., Shen, J., Schoepfer, S.D., Krystyn, L., Richoz, S. & Algeo, T.J. 2015: Environmental controls on marine ecosystem recovery following mass extinctions, with an example from the Early Triassic. *Earth-Science Reviews* 149, 108-135.

Weidlich, O. 2002: Middle and Late Permian reefs—distributional patterns and reservoir potential, 339–390. *In:* Kiessling, W., Flügel, E. & Golonka, J. (eds) *Phanerozoic Reef Patterns*. SEPM Special Publication 72. SEPM Press, Tulsa.

West, R.R. 2011: Part E, Revised, Volume 4, Chapter 2C: Classification of the fossil and living hypercalcified chaetetid-type Porifera (Demospongiae). *Treatise Online* 22, 1-24.

West, R.R. 2012: Part E, Revised, Volume 4, Chapter 2D: Evolution of the hypercalcified chaetetid-type Porifera (Demospongiae). *Treatise Online* 35, 1-26.

West, R.R. 2015: Paleogeography and biostratigraphy of the hypercalcified chaetetid-type Porifera (Demospongiae), 179-191. *In:* Selden, P.A. (ed.): *Treatise on Invertebrate Paleontology. Part E. (Revised) Porifera. Hypercalcified Porifera.* The University of Kansas Paleontological Institute, Lawrence.

West, R.R. & Clark, G. R. 1983: Chaetetids. Series in Geology, *Notes for Short Course* 7, 130-140.

Widmann, P., Bucher, H., Leu, M., Vennemann, T., Bagherpour, B., Schneebeli-Hermann, E., Goudemand, N. & Schaltegger, U. 2020: Dynamics of the largest carbon isotope excursion during the Early Triassic biotic recovery. *Frontiers in Earth Science* 8, 1-16. https://doi.org/10.3389/feart.2020.00196

Williams, R.M., Grotzinger, J.P., Dietrich, W.E., Gupta, S., Sumner, D.Y., Wiens, R.C. & Fabre, C. 2013: Martian fluvial conglomerates at Gale crater. *Science* 340, 1068-1072.

Wood, R. 1990: Reef-building sponges. *American Scientist* 78, 224-235.

Woods, A.D. 2014: Assessing Early Triassic paleoceanographic conditions via unusual sedimentary fabrics and features. *Earth-Science Reviews* 137, 6-18.

Woods, A.D. & Baud, A. 2001: Anachronistic facies from a drowned Lower Triassic carbonate platform: Lower member of the Alwa Formation (Ba’id Exotic), Oman Mountains. *Sedimentary Geology* 209, 1-14.

Wray, J.J. 1977: Late Paleozoic calcareous red algae, 167-176. *In:* *Fossil Algae: Recent Results and Developments*. Springer Berlin Heidelberg.

Wu, S., Chen, Z.Q., Su, C., Fang, Y. & Yang, H. 2022: Keratose sponge fabrics from the lowermost Triassic microbialites in South China: Geobiologic features and Phanerozoic evolution. *Global and Planetary Change* 211, 103787.

Wu, S., Reitner, J., Harper, D.A., Yu, J. & Chen, Z.Q. 2024: New keratose sponges after the end-Permian extinction provide insights into biotic recoveries. *Geobiology* 22, e12582.

Yang, H., Chen, Z. Q., Wang, Y., Ou, W., Liao, W. & Mei, X. 2015: Palaeoecology of microconchids from microbialites near the Permian–Triassic boundary in South China. *Lethaia* 48, 497-508.

Zhang, L., Orchard, M. J., Brayard, A., Algeo, T. J., Zhao, L., Chen, Z. Q. & Lyu, Z. 2019: The Smithian/Spathian boundary (late Early Triassic): A review of ammonoid, conodont, and carbon-isotopic criteria. *Earth-Science Reviews* 195, 7-36.

Zhao, L. S., Tong, J. N., Sun, Z. M., & Orchard, M.J. 2008: A detailed Lower Triassic conodont biostratigraphy and its Implications for the GSSP candidate of the Induan–Olenekian boundary in Chaohu, Anhui Province. *Progress in Natural Science* 18, 79-90.

Zatoń, M., Taylor, P. D. & Vinn, O. 2013: Early Triassic (Spathian) post-extinction microconchids from western Pangea. *Journal of Paleontology* 87, 159-165.