Global cooling and the establishment of a moderate climate in the Middle Ordovician has been invoked as the primary driver of the tenfold increase in marine biodiversity that characterized the Great Ordovician Biodiversification Event (GOBE). Arguments suggesting that climate change played a significant role in biodiversification purport that the Early Ordovician was dominated by warm (possibly even extremely warm) temperatures. In this scenario, biodiversification occurred only after sea surface temperatures approached the range observed in modern tropical settings. Temperature constraints for the Early Ordovician, however, are limited in number and documentation of short-term climatic trends is lacking. This study aims to begin to address these shortcomings by presenting a new high-resolution phosphate oxygen isotope record of species-specific and mixed conodont assemblages from the Lange Ranch section of central Texas. We document consistently low δ¹⁸O values indicating that the Early Ordovician was characterized by extreme warmth. In addition, variations observed in δ¹⁸O values through the section are consistent with a short-lived (< 4 m.y.) warming event and/or oceanographic shift leading to a decrease in the δ¹⁸O value of local seawater. All new data generated for this study are consistent with very warm temperatures during the Early Ordovician, an important starting condition in arguments that climate played an important role in Middle Ordovician biodiversification, but variation found also demonstrates the need for high resolution studies to constrain conditions on time scales relevant to evolutionary diversification.

The bowl-shaped trace fossil Piscichnus waitemata Gregory 1991 appears in Pliocene sandstones from Santa Maria Island (Azores Archipelago), extensively excavated during a stage of island evolution when the volcanic edifice was a guyot (flat-topped seamount) isolated in the NE Atlantic. The host sediments were deposited at depths from the intertidal zone to fair-weather wave base in a tropical climate under the influence of periodic storms and hurricanes. The traces were produced by ray fishes hunting for polychaetes, crustaceans and bivalves living in the sediment, similar to present-day nearshore, warm waters in the Azores, Baja California Sur (Mexico), and New Zealand, from which examples of feeding depressions are drawn (incipient Piscichnus). While P. waitemata is abundantly present in planar sediments on top of the guyot, far fewer trace fossils occur in sandstone deposited on the guyot's margins. Presumably, the different densities of ray holes in the two sedimentary bodies were a response to lesser availability of prey, lower seawater temperatures (due to greater depths), and a more dynamic environment in which life conditions were less favorable. Moreover, the potential preservation of bowl-shaped depressions was lower in this setting, given the steepness of the seafloor, stronger currents, and constant sediment mobility. The top of the guyot was a more favorable habitat, refuge and/or nursery ground for many ray fishes. Measurement of the diameters of the ray holes indicate three distinct size classes, which may suggest that several species were responsible for their formation.

The value of taphonomic signatures as a source of paleoenvironmental information has been recognized at local and regional environmental scales. In environmentally heterogeneous shallow lakes, the habitat complexity provides an opportunity to evaluate the potential use of taphonomy to uncover environmental differences among within-lake sub-environments. In this contribution, the composition and preservation of diatom assemblages from five sub-environments (free-floating and attached macrophytes, water column, open waters, and littoral sediments) were analyzed in a Pampean shallow lake (Nahuel Rucá, Argentina). Sub-environments differed in depth, macrophyte coverage, and water composition, being these differences reflected both by the composition and preservation of diatom assemblages. Diversity, fragmentation, and dissolution were higher in planktonic and open-waters sedimentary assemblages, whereas fragmentation dominated in littoral sediments. Epiphytic assemblages were the least diverse and showed the best preservation. Compositional and taphonomic indices were significantly correlated, suggesting common environmental controls on the species composition and preservation at local scales. The joint analysis of compositional and taphonomic variations in the recent sedimentary record of Nahuel Rucá demonstrated the usefulness of taphonomic analyses to uncover subtle paleoenvironmental variations, which could be overlooked if only traditional compositional analyses are performed. We concluded that both taphonomic analyses and a holistic consideration of ecologically meaningful taxa should be considered in order to improve paleoenvironmental reconstructions in environmentally heterogeneous shallow lakes.

The Cincinnati Arch contains a suite of Upper Ordovician, mixed siliciclastic-carbonate, shallow marine strata, with alternating packages of packstones and shales that contain exceptionally well-preserved articulated fauna. The Waynesville Formation (C5 sequence) in Eastern Indiana includes distinctive clay-rich shales, which are locally referred to as butter shale. These bluish-green claystones are distinct in comparison to other shales because of their geochemistry, clay mineralogy, bulk composition, and well-preserved and biostratigraphically important fauna. This study focuses on an outcrop with exposed butter shale from the Waynesville Formation at Hanna Creek in Brookville, Indiana. Bulk-rock samples were collected and the geochemical and clay mineralogical composition of the claystones were analyzed using x-ray fluorescence (XRF) and x-ray diffraction (XRD) techniques. On average, the butter shale clay mineralogy is 74% illite, 25% chlorite/kaolinite, and less than 1% smectite. The butter shale lacks expandable smectite, likely from post-depositional alteration of original smectite through illitization and chloritization. The presence of iron in the system as a result of diagenetic processes allowed for the immediate mineralization, and in some cases pyritization, of fossils. Bulk chemical analysis coupled with clay mineral analysis provides an explanation for the Fe substitution into chlorite for the butter shales and supports the interpretation of rapid sediment sealing that allowed for the pristine preservation of articulated fauna and mineralization observed in the butter shale.