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<jats:title>ABSTRACT</jats:title> <jats:p>During the late Cambrian–Early Ordovician interval the predominant non-microbial reef builders were sponges or sponge-like metazoans. The lithological and faunal composition of Cambro-Ordovician sponge-dominated reefs have previously been analyzed and reviewed. Here we take the relationship between reef aggregation pattern at reef to seascape scale into account, and look for changes during the Early–Middle Ordovician interval, in which metazoans became dominant reef builders. In a comparison of sponge-rich reefs from eight sites of the Laurentia paleocontinent three different seascape level reef growth patterns can be distinguished: (1) mosaic mode of reef growth, where reefs form a complex spatial mosaic dependent on hard substrate; (2) episodic mode, where patch reefs grew exclusively in distinct unconformity bounded horizons within non-reefal lithological units that have a much larger thickness; and (3) belt-and-bank mode, where reefs and reef complexes grew vertically and laterally as dispersed patches largely independent from truncation surfaces. The distinct modes of growth likely represent specific reef forming paleocommunities, because they differ in content and abundance of skeletal metazoan framebuilders, bioturbation intensity of non-skeletal reef sediment matrix, and in association of reef growth with underlying hard substrate. We suggest, based on a review of Laurentian reef occurrences, that the mosaic mode dominated in Early Ordovician strata and that the dominance shifted toward the belt and bank mode from Middle Ordovician strata onward.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Free-living forms of crustose coralline algae (rhodoliths) accumulate on shallow-water marine shelves in many regions worldwide. They form their own benthic habitats termed ‘rhodolith beds' and their deposits are well preserved in the rock record. Characteristics of rhodolith deposits can be used to interpret ancient water depths, light levels, and water energies. Accurate paleoceanographic interpretations rely on large-scale, detailed studies of living rhodolith beds, but these studies are scarce. Spencer Gulf in South Australia has the largest living rhodolith beds in southeastern Australia (∼ 3,000 km2). Documentation of these rhodolith deposits includes facies analysis, coralline algal taxonomy, characterization of growth forms and morphometrics, and integration with oceanographic data. Extensive oceanographic data and hydrodynamic modeling enable comparisons between rhodolith morphologies and bottom water energies with unprecedented accuracy. Rhodolith deposits in the gulf are intermixed with carbonate sands and muds under diverse hydrodynamic conditions, with current speeds up to 1.04 m s−1. At least five coralline algal genera construct rhodoliths in Spencer Gulf. Growth forms include fruticose, lumpy, and warty. Rhodolith morphologies imply that water energy is not the only thing affecting rhodolith movement and growth; rhodoliths can also be shifted by fish and invertebrates. Linear regression models in this study evaluate relationships between rhodolith morphometrics (mean diameter, sphericity, and branch density) and maximum bottom water speeds in Spencer Gulf and their results support the idea that water energy is not a major control on rhodolith morphology under these water energy conditions. Previous studies have revealed that the relationship between rhodolith morphologies and water energy levels is complicated and many authors have cautioned to not rely solely on rhodolith morphologies to interpret paleoceanographic conditions. Results of this study demonstrate that accurate paleoceanographic interpretations cannot be made based on rhodolith morphologies alone, but should also include sedimentology, coralline taxonomy, and associated biota.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Tectonic changes have influenced the evolution of the marine community by changing the land and seaway configuration through time. Two such events during the Oligo-Miocene—the closure of the Tethyan seaway due to development of the Gomphotherium Landbridge leading to separation of the Arabian Sea from proto-Mediterranean Sea (∼ 19 Ma) and significant uplift of the Tibetan Plateau marking the initiation of the monsoon (∼ 16 Ma)—represent a classic case of tectonic shift influencing the regional environment of the Indian subcontinent. We investigated the taxonomic and body-size related response of the shallow marine fauna to this regional change using bivalves from 11 time-constrained shellbeds of the Kutch Basin (western India) from three formations—Maniyara Fort (Chattian), Khari Nadi (Aquitanian) and Chhasra (Burdigalian-Langian) representing a time span of ∼ 9 Ma (24.4–15 Ma).</jats:p> <jats:p>Our collection of over 2000 individuals represents a total of 15 families and 61 morphospecies. The fossils are predominantly calcitic in nature and families of aragonitic composition are often preserved as molds indicating a potential negative effect of diagenesis. The taphonomic nature, however, does not vary substantially across shellbeds and hence, less likely produced a temporal pattern. The five most abundant species, Ostrea latimarginata, Ostrea angulata, Talochlamys articulata, Anomia primaeva, and Placuna lamellata occur in all the formations. The species composition of the Maniyara Fort Formation is substantially different from those of the younger formations, implying the possible effect of biogeographic separation. The absence of proto-Mediterranean taxa in Oligocene shellbeds supports limited faunal exchange between the Mediterranean-Iranian Province (MIP) and the western Indian Province (WIP) as early as ∼ 24.4 Ma (Chattian). Faunal exchange, however, continued between the WIP and the adjacent Eastern African-Arabian Province (EAAP). Formation-specific evenness shows a monotonic decrease from the Maniyara Fort to the Chhasra Formation. However, shellbed-specific analyses of diversity and body size do not show a strong directional trend through time and supports the stasis model. Although it is difficult to rule out the negative influence of taphonomy on the diversity of the studied fauna, the Oligo-Miocene marine bivalve fauna of the Kutch Basin demonstrates little or no influence of the Tethyan closure and Himalayan upliftment on the diversity through time.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Although empirical testing of Cope's rule, the tendency for size to increase over time, has received significant attention in the last few decades, there is no consensus about the applicability of this rule across taxonomic levels. In the present study, we investigate the distribution of body size of Trigoniida bivalves, at order-, family-, genus- and species-level, through the Middle Jurassic and Early Cretaceous of the Kutch region in India. Our data suggest that the body size of Trigoniida bivalves did not vary significantly in the Middle–Late Jurassic, followed by an increase after the Jurassic–Cretaceous mass extinction boundary and a reduction in the late Early Cretaceous. Changes in relative sea-level and associated sedimentary facies composition generally exhibit poor correlation with the overall stasis, or no net body size change, displayed by Trigoniida bivalves. Body-size analysis across taxonomic hierarchy reveals that order-level trends are not a simple aggregation of trends at lower taxon levels. An important observation of our study is the body-size increase immediately in the aftermath of the Jurassic– Cretaceous mass extinction, a deviation from the general observation that size reduction occurs in post-extinction communities. We argue that this increase may be result of both ecological competition and evolutionary faunal turnover.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>The Hell Creek region of northeastern Montana is an excellent study system to explore the rise to dominance of mammalian faunas after the Cretaceous–Paleogene (K–Pg) mass extinction. The Tullock Member of the Fort Union Formation exposed in that region was deposited during the first 1.2 Ma after the Chicxulub bolide impact. Some aspects of post-K–Pg mammalian succession remain obscure, however, due to a lack of finer stratigraphic resolution between vertebrate fossil localities. Here, we present a new stratigraphic model for the lower and middle Tullock and identify a stratigraphic succession of five mammal-bearing sedimentary units that span the first ∼ 900 ka of the Paleocene. Most notably, we find that middle Tullock fossil localities, which were previously thought to be deposited by a single, large fluvial channel complex, are derived from two temporally and lithologically distinct sedimentary units: the Biscuit Springs unit (BS) and the Garbani channel (GC). The top of the GC is stratigraphically above the top of the BS, but in some places cuts through the entirety of the BS, a relationship that previously complicated interpretations of their relative age. This cross-cutting relationship reveals that the BS is older than the GC. Thus, the BS local fauna represents a potential intermediate between the older local faunas from the post-K–Pg ‘disaster' interval and the younger, more taxonomically/ecologically diverse GC local fauna. This new stratigraphic framework sets the stage for future studies focused on the pattern and timing of biotic recovery in the aftermath of the K–Pg mass extinction.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>The Murdock Mountain Formation crops out across northern Utah and Nevada as part of the Park City Group; a unit within the greater Phosphoria Rock Complex. The Murdock Mountain is a hundreds-meters-thick section of mixed chert, dolomite, and siltstone. This unit is the southernmost expression of the widespread Permian Chert Event and offers unique views of sedimentology and paleoecology during this event. Previous researchers have described shallow-water facies dominated by biosiliceous sedimentary production as glass ramps. This framework has been speculatively applied by others to the units of the Park City Group in northern Utah and Nevada. In this study, we test whether the glass ramp depositional framework accurately represents the strata of the Murdock Mountain Formation. We use stratigraphic, hand sample, and thin section data to describe the sedimentological character of the Murdock Mountain Formation and the overlying Gerster Limestone. Four chert facies and one carbonate facies are recognized based upon the presence of silt, sponge spicules, carbonate bioclasts, and evaporites. The Murdock Mountain Formation shares many characteristics with other reported glass ramp localities. We interpret the transition from chert to carbonate-rich strata as an alternation between stable states with silica-producing fauna dominating the Murdock Mountain and carbonate-producing fauna dominating the Gerster. The takeover of biosiliceous deposition by carbonate highlights the termination of a glass ramp and the onset of a carbonate ramp regime.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Aberrant forms of many different spore and pollen taxa (sporomorphs) are often used to assess timings and extent of environmental stress at major extinction/climate events. However, little is known about the normal level of malformations in these taxa. Malformation can manifest in several different ways, including significant size differences (± from the accepted range for the species), retention of pollen/spores within tetrads, and unusual and inconsistent morphological aberrations. This study analyses one commonly used pollen genus, Classopollis, and its aberrant forms, from the Bajocian of Argentina. Tetrads, including those incorporating malformed/aborted pollen grains, are found to be common, showing that tetrads of Classopollis are not a reliable signal of major environmental disturbance. The results and discussion presented here emphasize why palynological data must be interpreted in context of the depositional dynamics, facies changes and how they affect the assemblages in conjunction with understanding variations in the strategies of individual flora.</jats:p>