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<jats:title>ABSTRACT</jats:title> <jats:p>The Bighorn Dolomite is a massive, cliff-forming dolostone unit found across the state of Wyoming and adjacent areas that records the transition from greenhouse to icehouse conditions during the Late Ordovician. The basal Steamboat Point Member of the Bighorn Dolomite contains cm-scale mottled fabrics often attributed to the ichnogenus Thalassinoides, but their origin remains enigmatic in Upper Ordovician strata. The development of mottled fabrics may have significant implications for marine chemistry and paleoecology. We analyzed cm-scale mottled fabrics from the basal Steamboat Point Member of the western Teton Mountains to determine their origin and develop criteria for identification of similar mottled fabrics found in other Upper Ordovician strata. In vertical cross-section, massive, m-scale exposures display vertical columns (approximately 1 cm in diameter) that anastomose and maintain decimeter-scale vertical continuity. Microscopically, the columns are composed of micro-peloidal micritic textures surrounded by spar and microspar, whereas the intercolumnar matrix is composed of dolomicrite grains, skeletal clasts, and intraclasts. We interpret the microscopic peloidal texture as a product of benthic microbial calcification that coalesced to form mesoclots—diagnostic features of thrombolitic microbialites. Paragenetic analyses reveal evidence for early lithified microbial biofilms despite dolomite replacement and aggrading neomorphism. These observations indicate the Steamboat Point Member of the Bighorn Dolomite was deposited in seawater that was highly supersaturated with respect to carbonate, consistent with other studies that suggest deposition during greenhouse conditions prior to the end-Ordovician glaciation. We present a novel ternary diagram that contains criteria to help differentiate between burrows, microbialite textures, or physical processes that may result in mottled fabrics in the rock record.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Cruziana and Rusophycus are commonly assumed to be trilobite trace fossils, although associated exoskeletons are almost invariably absent from host strata. In the lower Cambrian Dallas Bugt Formation of Ellesmere Island, Arctic Canada, high-energy, cross-laminated sandstones locally with dense populations of large Skolithos are overlain by thin-bedded, bioturbated, argillaceous, medium-grained glauconitic sandstones of lagoonal aspect, yielding Rusophycus along with an assortment of other “worm” burrows. Some specimens of Rusophycus are located over small Skolithos shafts and the bottoms of Arenicolites, suggesting a predator-prey relationship. Many preserve the impression of a strongly vaulted carapace with a broad, triangular dorsal outline between 1 cm and 7 cm across. A blunt anterior “prow” projects slightly forward and arches dorsally, forming a keyhole-shaped notch. The arthropod dug into the sediment up to 5 cm deep with an antero-posterior angle of up to ∼ 45° from the sea floor; in some cases it dug obliquely laterally and rarely sideways. Retroverse scratches—preserved in hyporelief as sharp-crested ridges—suggest about 20 pairs of endopodites tipped by a pair of small claws typically dug in unison, the anterior ones starting with a V-angle of 140° and decreasing posteriorly to 90°, in rare cases more tightly. Limb length increased posteriorly, although none extended beyond the carapace. Leg muscles were strong enough to rake through the muddy sand and pull inwards either straight or in a slightly forward-curving arc, but were also slightly flexible to wiggle around obstacles. Some specimens show subsequent re-burrowing which produced cross-cutting and opposed scratches. No evidence for exopodite brushings is present. Successive carapace imprints and scratches organized in transverse rugae in some specimens suggest repeatedly plunging and digging as the arthropod pulled backward in the sediment. This was likely aided by a stout trunk and a fan-shaped uropod-like structure flanking the telson which increased grip and leverage. A pair of eye stalks may have projected from the anterior notch, and these could have been retracted during digging, but there is no evidence for antennae. The tracemaker was not a trilobite but an unrelated crustacean-like arthropod, although there is no known late early Cambrian body fossil to which it can be ascribed. The specimens are classified as Rusophycus jenningsi (Fenton and Fenton, 1937) and a neotype is selected for this ichnospecies from the Gog Group near where it was first collected. Its range extends from the southern Canadian Rocky Mountains north along depositional strike to Victoria Island and northwest to Ellesmere Island and northern Greenland. Two new ichnofamilies are established: Rusophycidae and Cruzianidae.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>The early Eocene Okanagan Highland fossil sites of Washington (USA) and British Columbia (Canada) contain exquisitely preserved plant and insect fossils that showcase a critical time and place in the evolution of the Northern Hemisphere temperate deciduous biome. A comprehensive understanding of the dynamics of fossil deposition and preservation at these sites is not fully resolved but is critical for reliable reconstructions of these ancient forests. To expand on previous interpretations (e.g., deep, stratified, anoxic lake bottoms) and address uncertainties about the environment of deposition (e.g., distance to shore, influence of diatoms), we analyzed sediment samples from three Okanagan Highland fossil sites—McAbee, Falkland, and Driftwood Canyon—for organic biomarkers, their stable carbon isotopic compositions, and glycerol dialkyl glycerol tetraethers (GDGTs; at McAbee only). Terpenoids suggest relative trends in gymnosperm abundance between sites that agree with prior macrofossil evidence, though absolute values may overestimate local gymnosperm abundance. A combination of biomarker evidence indicates a predominantly autochthonous aquatic source (e.g., diatoms) for organic matter in shale and mudstone samples, even contributing to long chain n-alkanes and likely to branched GDGTs, which are often assumed to be terrestrially sourced. In combination with biomarker evidence for anoxia and stratification, fossiliferous shales are interpreted to have been deposited offshore in deep and mesotrophic lakes that were thermally stratified with an anoxic hypolimnion, away from in-flowing tributaries, while a coal horizon at Driftwood Canyon was deposited in a shallower, eutrophic, anoxic wetland. Anoxic conditions likely minimized some degradation-based biases and promoted high quality fossil preservation. Deposition of sediment and fossil remains offshore and away from inflowing tributaries suggest fossil plants were locally sourced but highlights the need for careful consideration of transport-induced biases.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits are scarce. The Upper Jurassic–Lower Cretaceous Vaca Muerta Formation from Argentina constitutes an important unconventional reservoir that displays dm- to m-thick, laminated, rippled and bioturbated, crinoidal mudstone and fine to coarse mudstone deposited by wind- and thermohaline-driven contour currents. Four ichnofabrics were recognized in three facies associations. The Palaeophycus heberti ichnofabric is dominant in facies association 1, forming highly bioturbated intervals. The Palaeophycus heberti, Nereites isp., and Phycosiphon incertum ichnofabrics are present in facies association 2, displaying highly, moderately and sparsely bioturbated intervals, respectively. This association is locally characterized by m-thick successions comprising an upward decrease and then increase in bioturbation index, which may have a similar origin to bigradational sequences. The Equilibrichnia-Fugichnia ichnofabric mostly occurs in facies association 3 and less commonly in 2, forming distinctive bioturbated intervals within sparsely bioturbated successions. Benthic activity was controlled by food distribution, oxygenation, hydrodynamic energy, and water turbidity. Food was delivered to the surface or in suspension by currents, promoting deposit- or suspension-feeding strategies in the infauna, respectively. Oxygen levels increased during contour current activity yet remained relatively low (upper dysoxic). Hydrodynamic energy controlled bioturbation intensity, resulting in lower degrees of bioturbation during higher energy events. Suspension-feeding strategies suggest that water turbidity was relatively low during current transport. The herein example increases our understanding of environmental controls of shallow-water contour currents, supporting the fact that high bioturbation levels are typical of contourite deposits and providing an example of muddy contourites showing high preservation of sedimentary structures due to oxygen deficiency in bottom waters.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>The sedimentary-stratigraphic record is regularly considered only in the context of regional climate, tectonic configuration, and sea-level. In this study we provide examples of how biotically influenced autogenic processes may come to be overprinted on these extrinsic, allogenic controls. A sedimentological analysis is given for the Mississippian (Visean) siliciclastic strata which crop out in counties Donegal and Mayo in NW Ireland. Eleven sedimentary facies record deposition of dominantly clastic and humic organic sediments which accumulated in alluvial, fluvial, estuarine, and fully marine environments. The preserved architecture of the sedimentary deposits is shown to be dependent on local autogenic dynamics, processes that were in turn modified or entirely controlled by biota (“biosphere signatures”). Sedimentological criteria, specifically the type and distribution of preserved biosphere signatures, suggests deposition occurred in a dominantly wet, humid environment in keeping with Laurussia's proposed equatorial position but potentially at odds with previous suggestions of seasonal aridity. The humid climate and resultant perennially active water conduits facilitated the widespread preservation of inclined heterolithic stratification (IHS). Allogenic and autogenic processes are ultimately linked, with external factors such as sea-level, tectonics, and climate all impacting the spatial distribution, abundance and prevailing forms of biota. The flooding of the Laurussian continent is accompanied by a shift from plant-induced to animal-induced biosphere signatures basinwards of the estuary funnel. In this way, the interplay between allogenic and autogenic processes is recorded at sedimentary outcrop through the capacity of extrinsic forcings to influence the rates and locations of intrinsic life-sediment interactions.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>By colonizing drylands, plants fundamentally changed continental deposition and, thus, intensified the interaction between life and sediments. Fossil large woody debris in epiclastic strata is a key archive of this environmental turnover, although its interpretation remains challenging due to taphonomic biases. We review voluminous fluvial red-bed successions with sizeable silicified trunks that characterize Middle Pennsylvanian–lower Permian strata of east-central Europe. The stratigraphic occurrence, petrography, architecture of the deposits, and the preservation and nature of the fossil wood are discussed in the context of the tectono-climatic and vegetational evolution of the central-Pangean low latitudes. The log-bearing successions are assigned to five distinct, regionally traceable stratigraphic levels between the middle Moscovian and early Asselian. Up to 20 m long, mostly decorticated trunk fragments occur isolated in more or less feldspathic channel deposits, the architectures and dimensions of which point to large-scale river systems with highly variable discharge. Wood anatomy and floodplain adpression-fossils show that the trunks were derived from cordaitaleans, conifers, and arborescent sphenopsids in more diverse, gymnosperm-dominated dryland floras. The fossil record is biased towards successions formed in large-catchment river systems and, thus, does not accurately document the genuine nature of plant-distribution patterns. Rather, the strata show that large woody debris preservation depended on fluvial style and hydrological regime, hence turning the woody deposits into climate archives. The strata elucidate the climate development in equatorial Pangea, paralleling the acme of the Late Paleozoic Ice Age.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Wildfire has been implicated as a potential driver of deforestation and continental biodiversity loss during the end-Permian extinction event (EPE; ∼ 252 Ma). However, it cannot be established whether wildfire activity was anomalous during the EPE without valid pre- and post-EPE baselines. Here, we assess the changes in wildfire activity in the high-latitude lowlands of eastern Gondwana by presenting new long-term, quantitative late Permian (Lopingian) to Early Triassic records of dispersed fossil charcoal and inertinite from sediments of the Sydney Basin, eastern Australia. We also document little-transported fossil charcoal occurrences in middle to late Permian (Guadalupian to Lopingian) permineralized peats of the Lambert Graben, East Antarctica, and Sydney and Bowen basins, eastern Australia, indicating that even vegetation of consistently moist high-latitude settings was prone to regular fire events. Our records show that wildfires were consistently prevalent through the Lopingian, but the EPE demonstrates a clear spike in activity. The relatively low charcoal and inertinite baseline for the Early Triassic is likely due in part to the lower vegetation density, which would have limited fire spread. We review the evidence for middle Permian to Lower Triassic charcoal in the geosphere, and the impacts of wildfires on sedimentation processes and the evolution of landscapes. Moreover, we assess the evidence of continental extinction drivers during the EPE within eastern Australia, and critically evaluate the role of wildfires as a cause and consequence of ecosystem collapse. The initial intensification of the fire regime during the EPE likely played a role in the initial loss of wetland carbon sinks, and contributed to increased greenhouse gas emissions and land and freshwater ecosystem changes. However, we conclude that elevated wildfire frequency was a short-lived phenomenon; recurrent wildfire events were unlikely to be the direct cause of the subsequent long-term absence of peat-forming wetland vegetation, and the associated ‘coal gap' of the Early Triassic.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Palynological study of the Permian–Triassic boundary has typically focused on the pollen grain and spore content to reconstruct vegetation, with fungal remains either left unidentified or set aside for future research. Paleozoic fungal microfossil records in particular are lacking. The Zechstein Group (∼ 258–252 Ma; Lopingian) is a remarkable stratigraphic sequence of stacked carbonates and evaporites. High-resolution palynological analysis of new borehole cores through the Zechstein Group of northeast England has revealed its entire sedimentological history and enabled a new reconstruction of vegetation dynamics in central-western Europe preceding the Permian–Triassic boundary. Assemblages composed of conifers, pteridosperms, pteridophytes, sphenopsids, and cycads/ginkgoes were recovered alongside fungal remains throughout the entire sequence. Four fungal morphologies were observed, the most common being smooth-walled spheroidal inclusions of an endobiotic Chytridiomycota or Hypochytridiomycota affinity. Other evidence of fungi includes epiphytic Callimothallus-type fungi (Family Microthyraceae), the dematiaceous Chaetomium-like mold (Family Chaetomiaceae) found associated with soil, cellulose and plant debris, and possible evidence of chytrid-induced pitting on the surface of plant cuticle. This is the first study to highlight the fungal content of Zechstein palynological preparations and while occurrences are rare, they provide new insight into the composition of the Zechstein forest understory, reinforcing the interpretation that the upper Zechstein environment was humid. This work improves our understanding of the taxonomic and functional diversity of fungal taxa associated with evaporite systems during the Lopingian, and highlights the exceptional preservation potential of halite, combating underestimates of fungal richness in the fossil record.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>During the mid-Pliocene (Zanclean, ca. ∼ 3.9 Ma), parts of the Canadian High Arctic experienced mean annual temperatures that were 14–22°C warmer than today and supported diverse boreal-type forests. The landscapes of this vegetated polar region left behind a fragmented sedimentary record that crops out across several islands in the Canadian Arctic Archipelago as the Beaufort Formation and correlative strata. Paleoecological information from these strata provides a high-fidelity window onto Pliocene environments, and prominent fossil sites yield unparalleled insights into Cenozoic mammal evolution. Significantly, many of the strata reveal evidence for life-sediment interactions in a warm-climate Arctic, most notably in the form of extensive woody debris and phytoclast deposits. This paper presents original field data that refines the sedimentological context of plant debris accumulations from the anactualistic High Arctic forests, most notably at the ‘Fyles Leaf Beds' and ‘Beaver Pond' fossil-bearing sites in the ‘high terrace deposits' of central Ellesmere Island. The former is a remarkably well-preserved, leaf-rich deposit that is part of a complex of facies associations representing lacustrine, fluvio-deltaic and mire deposition above a paleotopographic unconformity. The latter yields tooth-marked woody debris within a peat layer that also contains a rich assemblage of vertebrate and plant fossils including abundant remains from the extinct beaver-group Dipoides. Here we present sedimentological data that provide circumstantial evidence that the woody debris deposit at Beaver Pond could record dam-building in the genus, by comparing the facies motif with new data from known Holocene beaver dam facies in England. Across the Pliocene of the High Arctic region, woody debris accumulations are shown to represent an array of biosedimentary deposits and landforms including mires, driftcretions, woody bedforms, and possible beaver dams, which help to contextualize mammal fossil sites, provide facies models for high-latitude forests, and reveal interactions between life and sedimentation in a vanished world that may be an analogue to that of the near-future.</jats:p>