Stratigraphic Research Articles

Refined geochronology and revised stratigraphic nomenclature of the Upper Cretaceous Wahweap Formation, Utah, U.S.A. and the age of early Campanian vertebrates from southern Laramidia

The Western Interior of North America preserves one of the most complete successions of Upper Cretaceous marine and non-marine strata in the world; among these, the Cenomanian-Campanian units of the Kaiparowits Plateau in southern Utah are a critical archive of terrestrial environments and biotas. Here we present new radioisotopic ages for the Campanian Wahweap Formation, along with lithostratigraphic revision, to improve the geological context of its fossil biota. The widely accepted informal stratigraphic subdivisions of the Wahweap Formation on the Kaiparowits Plateau are herein formalized and named the Last Chance Creek Member, Reynolds Point Member, Coyote Point Member, and Pardner Canyon Member (formerly the lower, middle, upper, and capping sandstone members respectively). Two high-precision U-Pb zircon ages were obtained from bentonites using CA-ID-TIMS, supported by five additional bentonite and detrital zircon LA-ICP-MS ages. Improved geochronology of the Star Seep bentonite from the base of the Reynolds Point Member via CA-ID-TIMS demonstrates that this important marker horizon is over a million years older than previously thought. A Bayesian age-stratigraphic model was constructed for the Wahweap Formation using the new geochronologic data, yielding statistically robust ages and associated uncertainties that quantifiably account for potential variations in sediment accumulation rate. The new chronostratigraphic framework places the lower and upper formation boundaries at 82.17 +1.47/-10.63 Ma and 77.29 +0.72/-0.62 Ma, respectively, thus constraining its age to the first half of the Campanian. Additionally, a holistic review of known vertebrate fossil localities from the Wahweap Formation was conducted to better understand their spatio-temporal distribution including revised ages for early members of iconic dinosaur lineages such as Tyrannosauridae, Hadrosauridae, and Centrosaurinae. Chrono- and lithostratigraphic refinement of the Wahweap Formation and its constituent biotic assemblages establishes an important reference for addressing questions of Campanian terrestrial paleoecology and macroevolution, including dinosaur endemism and diversification throughout western North America. • New high-precision age for the Star Seep bentonite extends age of the Wahweap Fm. • Subdivisions of the Wahweap Formation are formally recognized. • A detailed age-stratigraphic model was generated including uncertainty. • Robust ages with uncertainty produced for any stratigraphic level in the formation. • Oldest members of key dinosaur lineages found to be older than previously thought.

EOCENE-OLIGOCENE CLIMATE BASED ON PALYNOLOGICAL RECORDS

This study is a part of the investigation on Tertiary paleoclimate conducted by LEMIGAS Stratigraphy Group. The paleoclimate reconstruction covers most area of western Indonesia including South Sumatra Basin, Sunda-Asri Basin, Northeast Java Basin South Kalimantan and Northeast Java Basin, West Natuna and South Sulawesi (Figure 1). This paper is aimed to figure out the regional paleoclimate of western Indonesia which occurred during Eocene-Oligocene. In fact, the knowledge of paleoclimate is useful to define sea level changes which are believed to have relationship with stratigraphy and sedimentology of these areas. The paleoclimate interpretation can be approached using different tools such as biostratigraphy and geochemistry. In this study, paleoclimate is interpretated based on biostratigraphy (microfossil evidences) including palynomorph and foraminifer. Palynomorphs were mainly applied on the non-marine to transitional sections, whilst foraminifers were used in interpreting shallow to deep marine sediments. In fact, most interpretations rely on palynological evidences as these simply provide suitable data for paleoclimate analysis. In case of both microfossils appear in the same section, the paleoclimate interpretation based on palynomorph can be placed in a certain stratigraphic level which is defined based on the occurrence of the age-restricted foraminifer. The paleoclimate interpretation of certain strati- graphic level is based on the compilation of palynological and foraminiferal data deriving from different areas. This method is used to obtain representative picture of paleoclimate which occurs in the selected stratigraphic range of the western Indonesia

New data on the theropod diversity from the Middle to Late Jurassic of the Vaches Noires cliffs (Normandy, France)

Dinosaur remains found at the Vaches Noires cliffs (Calvados, Normandy) have usually been discovered by amateur palaeontologists. The bones come from carcasses which drifted away from a nearby land (Armorican Massif) during the upper Callovian and lower Oxfordian. Most of these bones belong to private collections and are hardly accessible. Consequently, many of these bones were never described. Thus, and for the first time, private and public collections are gathered to obtain a global vision of theropod remains from the Vaches Noires cliffs. Most of the dinosaur remains from this locality belong to theropods. Some bones are from the same individual but have been isolated as a result of cliff erosion and tidal action which also mixed specimens from different stratigraphic levels. This over-representation of theropod remains is enigmatic because it is not found in other similar deposits. A specific way of life is likely to explain that fact, but it could also be a simple statistical effect due to a limited sample. At least 3 taxa are tentatively identified: Streptospondylus altdorfensis Meyer, 1832, another megalosauroid and an allosauroid.

Deep-sea hiatuses track the vigor of Cenozoic ocean bottom currents

Abstract The deep-sea stratigraphic record is full of gaps. These hiatuses track changes in ocean circulation and chemistry, but determining their timing and causes has been limited by sparse data and incomplete knowledge of ocean gateway evolution in earlier studies. We combine a significantly expanded, age-calibrated deep-sea stratigraphic database with a global tectonic and paleo–water depth model to investigate the distribution of >400 Cenozoic hiatuses longer than ~0.2 m.y. We find that only a small number of hiatuses are due to carbonate dissolution. The majority of hiatuses were, by implication, caused by mechanical erosion and redistribution of sediments by bottom currents into regions of increased sedimentation such as contourite drifts. We link peaks in regional hiatuses to changes in ocean circulation and intensification of deep-water formation. Widespread hiatuses in the South Atlantic, South Pacific, and southern Indian oceans between ca. 34 Ma and 30 Ma are attributed to the coeval widening and deepening of the Drake Passage and the opening of the deep Tasman Gateway. A peak in hiatuses in the Atlantic in the early Miocene is linked to the initiation of a proto–Atlantic Meridional Overturning Circulation driven by the complete opening of the deep Drake Passage and the progressive closure of the Tethys seaway. A long-term 30% decline in hiatus frequency since ca. 14 Ma is synchronous with post–Miocene Climate Optimum cooling, suggesting the slowing of abyssal circulation. Our synthesis of deep-sea hiatuses could be used to track the fate of deep-sea sediments and to ground-truth deep-ocean circulation models.

The post-Caledonian thermo-tectonic evolution of Fennoscandia

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides only partial documentation of the geological evolution. A more complete understanding is obtained by also considering evidence of rocks that were formerly present but have since been removed. We report apatite fission track data and associated thermal history constraints in 331 samples of Precambrian basement, younger sedimentary cover, Paleozoic and Mesozoic igneous rocks from outcrops and boreholes (up to 6 km depth) across Fennoscandia, which define thirteen phases of cooling (each representing kilometre-scale exhumation) over the last 1100 Myr. Key post-Caledonian episodes began in the intervals 311–307 Ma (late Carboniferous), 245–244 Ma (Middle Triassic), 170–167 Ma (Middle Jurassic), 102–92 Ma (mid-Cretaceous) and 23–21 Ma (early Miocene). These episodes, varying in magnitude, are recognised across Fennoscandia, and their effects are documented in the stratigraphic record and as prominent regional peneplains. The results define a history involving repeated episodes of regional burial and exhumation. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasising the tectonic nature of the history. Results from Finland record the same events recognised in Norway and Sweden (though less pronounced), and are not consistent with long-term cratonic stability. The lack of preserved Phanerozoic sedimentary cover in Finland is interpreted to be due to complete removal during multiple episodes of denudation. In southern Norway and Sweden, early Miocene exhumation led to creation of a peneplain, which in Pliocene times was uplifted and dissected, producing the modern landscape. Post-Caledonian exhumation episodes defined here are broadly synchronous with similar events in Greenland, the British Isles and North America. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.

Sauropod Trackway Morphometrics: An Exploratory Study Using Highway A16 Excavation at the Courtedoux-Tchâfouè Track Site (Late Jurassic, NW Switzerland)

Ichnogeneric classification of sauropod trackways is determined using qualitative and quantitative descriptions of morphological parameters. More recently, the validity of several of these parameters has been called into question (e.g., trackway gauge). This paper aims to test traditional and more novel landmark-based geometric morphometric (GM) analysis to describe sauropod tracks and trackways. The Courtedoux-Tchâfouè (TCH) tracksite, in NW Switzerland, has been used as a test site because it hosted several Late Jurassic sauropod track-bearing levels, over a short time period (∼40 ka), creating a time capsule of sauropod activity. Exploratory statistical analyses suggest that the TCH trackway dataset can be partitioned into clusters based on trackway parameters (e.g., width of pes angulation pattern/pes length) that demonstrate differences between trackways. Nevertheless, clustering reflected a moderate degree of intercluster similarity and a continuum in TCH trackway morphologies. The GM analysis of TCH pes impressions, from several trackways, indicates a similar morphotype and did not significantly differentiate pes tracks from various stratigraphic levels. Currently, the results indicate that neither linear nor landmark-based geometric morphometric methods strongly segregate tracks at TCH nor show a time-control (i.e., via stratigraphic level) over the short interval studied. The methods reinforce that sauropod pes impression shape is conservative and that combining morphological methods to be inclusive of sauropod trackway data is important. The TCH site demonstrates that variability may reflect morphological continuums and behavioural factors and does not unambiguously differentiate unique sauropod trackmakers. More exploration on the minimum number of trackway parameters as predictors of sauropod ichnotaxonomy is needed. Integrating complementary techniques will provide more insight and practical means of identification and delineation of sauropod tracks and their trackways.

Seismic evidences of recurrent volcanism across the North Brazilian and the Fernando de Noronha ridges – Brazilian Equatorial Atlantic Ocean

ABSTRACT. This study, based on the interpretation of LEPLAC (the Brazilian Continental Shelf Survey Project) deep seismic lines (~16.0 s twtt), reveals for the first time across the Brazilian Equatorial Atlantic Ocean seismic evidences that buried portions of individual volcanic edifices of the North Brazilian and the Fernando de Noronha volcanic ridges are laterally coupled with a series of volcanic wedges. Our analyses evidence that these magmatic occurrences are presented as layered volcanic bodies as wide as 80 km and as thick as 1.2 s (twtt) close to the volcanic edifices. Volcanic wedges occur as layered prograding bodies stemming directly from the major volcanic edifices of both ridges. Seismic analyses also reveal that numerous layered volcanic accumulations associated to a same individual volcanic edifice may occur along variable stratigraphic levels. These occurrences indicate that the evolution of the North Brazilian and the Fernando de Noronha volcanic ridges is followed by a long history of recurrent volcanic activities that may have possibly been synchronous in distinct volcanic edifices distant apart.Keywords: seamounts, guyots, volcanic seismic facies, volcanostratigraphy, intraplate volcanic ridges.

Acritarch biostratigraphy of the Lower-Middle Cambrian boundary in the Iberian Chains, province of Soria, northeastern Spain

The Lower and Middle Cambrian age acritarch assemblages are reported from a continuous succession of the siliciclastic-carbonate Ribota, Huermeda and Daroca Formations in the Iberian Chains, northeastern Spain. One new genus and four new species are described, one of them in open nomenclature. The microfossil assemblages allow to recognize the Lower Cambrian Heliosphaeridium dissimilare-Skiagia ciliosa and Volkovia dentifera-­Liepaina plana acritarch zones, and to discuss an informal lowermost Middle Cambrian acritarch zone. These zones correspond respectively to the Holmia kjerulfi, Prorolenus and Acadoparadoxides oelandicus trilobite zones, identified in the Acado-Baltic faunal province. The first appearance of Eliasum llaniscum, Celtiberium dedalinum and Retisphaeridium dichamerum, which are age-diagnostic for the Middle Cambrian, in the upper Daroca Formation is interpreted to point the Lower-Middle Cambrian boundary. This stratigraphic level underlies the previously established trilobite-based boundary. The depositional environments and biostratigraphy of the concerned strata are discussed.

Exploring the application of blue and red thermoluminescence for dating volcanic glasses

Tephras are significant markers in the stratigraphic record and play a key role in establishing paleoenvironmental and paleoclimate histories worldwide. Despite burgeoning research focused on tephra characterization and correlation techniques, there are still few techniques that allow for the direct dating of tephra, particularly below the lower age limit of K/Ar and Ar/Ar dating methods. In this study, we test different thermoluminescence (TL) dating approaches on the 4–11 μm volcanic glass constituents of three different independently different tephras. By comparing against independent age control, we demonstrate the utility of both blue (320–450 nm) and red (587–651 nm) TL emissions for dating volcanic glasses using single aliquot regenerative (SAR) dose techniques. We find that both blue and red TL emissions from the volcanic glass shards are dim but reproducible and show no evidence for significant sensitivity changes occurring between the natural TL and the first test dose during the SAR protocol. Fading tests on the blue TL signal show that g-values range from 1.6 ± 1.0 to 2.9 ± 1.1%/decade and are statistically indistinguishable with zero at 2σ for the red TL. Bleaching experiments show that both blue and red TL signals are sensitive to light exposure, with sensitivity corrected signals declining by ∼40% over a 2-h period. For all three tephras, both the fading-corrected blue and red SAR-TL ages are consistent with age expectation. These successful results demonstrate the effectiveness of TL techniques for determining the eruption ages of tephra deposits in primary position between ∼1 and at least 30 ka.

The Whale Point Formation: A stratigraphic record of high-frequency climate and sea-level fluctuations in the Bahamas during Marine Isotope Stage 5a (ca. 80 ka BP)

In this paper, we formally define a series of bioclastic eolianites and protosols exposed on high-energy bank margins throughout the Bahamas archipelago as the Whale Point Formation (WPF). The position of this new lithostratigraphic unit above and seaward of deposits dated to Marine Isotope Stage (MIS) 5e and below Holocene sediments constrains its age to the latest Pleistocene, more precisely to MIS 5a (ca. 88–74 ka BP). This age is further corroborated by amino-acid racemization data calibrated with UTh ages. Based on their sedimentological characteristics, the WPF eolianites are interpreted as landward-advancing dunes decoupled from their source beaches. Relying on the faunal content, the maximum elevation of relative sea level during MIS 5a can be roughly estimated at ca. 9 ± 2 m below the present stand. The WPF includes two phases of eolian deposition separated by an interval of negative sediment budget and pedogenesis. These different facies possibly reflect millennial-scale sea-level and climate instability during MIS 5a, the latter being likely related to shifts in the mean annual position of the intertropical convergence zone and associated rainfall belt.

The feasibility of high-temperature aquifer thermal energy storage in Denmark: the Gassum Formation in the Stenlille structure

File replaced 2022–02–24: Erroneous stratigraphic levels in figures 8, 9, 10 and 11 of the original publication are now correct Heat storage in the Danish subsurface is gaining increasing interest for optimiz-ing the use of energy resources, but no deep heat storage facilities have yet been established. As an analogue we study the Gassum Formation in the Stenlille structure that is presently used for gas storage. This allows us to discuss geological and technical characteristics of an aquifer relevant for heat storage in Denmark. We develop a 3D model for a high-temperature aquifer thermal energy storage sys-tem using analysis of geological core data, sedimentological description, geophysi-cal data including well logs and seismic lines, as well as a finite difference model to calculate the recovery efficiency, heat storage capacity and thermal breakthrough time. Based on geostatistical methods we made three realisations and found similar results for the three cases. In accordance with results from published simplified models we found a high recovery efficiency of 70% after 4 years and 69% after 20 years, a high heat storage capacity of 1.8×1018 J, and a long thermal breakthrough time of 66–77 years. These results reflect the excellent reservoir properties of the Gassum Formation in Stenlille, characterised by a uniformly layered sand/shale sedimentology, a high average porosity of 25% and a high permeability of 1000 to 10 000 mD of sandstone intervals.

Morphological evolution of menardiform globorotalids at Western Pacific Warm Pool ODP Hole 806C (Ontong-Java Plateau) Evolution morphologique du groupe de Globorotalia menardii au Site ODP 806C (Ontong-Java Plateau, Pacifique tropical occidental)

The morphological evolution was investigated in the tropical Neogene planktonic foraminiferal lineage Globorotalia menardii, G. limbata and G. multicamerata during the past 8 million years at ODP Hole 806C (Ontong-Java Plateau, western equatorial Pacific). This research is an extension of several similar studies since 2007 from the Caribbean Sea, the tropical Atlantic and the Eastern Equatorial Pacific. The goal is to find empirical and quantitative confirmation for morphological speciation – splitting or phyletic gradualism or accelerated evolution – in planktonic foraminifera with the above lineage as model objects. The present study from ODP Hole 806C serves as a test to discriminate between these evolutionary scenarios.In the western equatorial Pacific warm and stable environments prevailed back to Pliocene times, and potential influences of Northern Hemisphere Glaciation are thought to bear less severely on shell size evolution than in the Atlantic Ocean. A slow and gradual pattern of shell size increase is therefore expected in the western tropical Pacific, in contrast to the intermittent rapid menardiform shell size increase during periods of intensified formation of warm water eddies in the southern to tropical Atlantic.For this study a total of 11,101 specimens from 37 stratigraphic levels extending over the past 8 million years were morphometrically investigated thanks to the AMOR robot for imaging and microfossil orientation. Of those, 6080 specimens comprise the G. menardii–limbata-multicamerata plexus. Special attention was given to trends of spiral height (δX) versus axial length (δY) in keel view, for which bivariate contour- and volume-density diagrams were constructed to visualize speciation and evolutionary trends.The investigation at Hole 806C showed, that G. menardii evolved in a more gradual manner than in the Atlantic. Contour plots of δX versus δY reveal modest bimodality between 3.18 Ma – 2.55 Ma with a dominant branch consisting of smaller G. menardii (δX<∼300 μm) persisting until the Late Quaternary, and a less dominant branch of larger G. menardii (δX>∼300 μm) until 2.63 Ma. There is evidence for cladogenesis – splitting with subsequent morphological divergence in the Late Pliocene G. menardii-limbata-multicamerata lineage, and which may be linked to changes in the thermocline. Due to the general scarcity of G. multicamerata at Site 806, the divergence was less clearly expressed than originally expected. Up-section, bimodality vanished but G. menardii populations shifted towards extra large shells between 2.19-1.95 Ma.The morphological evolution of Pacific menardiform globorotalids contrasts the one observed in the Atlantic. This inter-oceanic asymmetry may indicate possible long-distance dispersal of G. menardii, at least during intermittent phases. For plankton biostratigraphy this implies, that correlating events represent more often than previously thought large scale environmental perturbations with local morphological ecophenotypic adaptations and nuances.

The stratigraphic significance of self‐organization: Exploring how autogenic processes can generate cyclical carbonate platform strata

AbstractAutogenic spatial self‐organization can produce coherent patterns of ordered cyclical strata through interaction of system components, independent of initial conditions and without external forcing. Previous numerical modelling work that partially explored self‐organized cyclicity in carbonate strata is expanded, refined and tested using a different numerical model formulation of an existing carbonate forward model ‘CarboCAT’. Results show that cross‐platform sediment transport creates a series of self‐organized prograding islands and shorelines that generate upward‐shallowing autocycles, defined by strong statistical evidence for ordered facies successions. A subtidal factory in front of each shoreline supplies sediment that drives shoreline progradation and these subtidal supply‐zone widths are also self‐organized to an optimal characteristic width due to island progradation, such that an accommodation creation/sediment supply ratio of around one maintains self‐organized shoreline progradation. The resulting island progradation rate determines autocycle thickness, which is very different from the accommodation control assumed in most sequence stratigraphic and cyclostratigraphic interpretations. This self‐organization process is comparable to the reaction–diffusion model first suggested by Alan Turing. The simplest possible combination of processes that leads to self‐organization are water‐depth‐dependent production, straight long‐distance cross‐platform transport and uniform subsidence. Additional more complex processes can produce self‐organization, but also more diverse island morphologies, less ordered autocyclic strata and more variable lateral facies continuity. Exploration of the model parameter space shows that self‐organization occurs for only a limited range of accommodation creation/sediment supply ratios. The modelling is calibrated and checked for realism against shoreline progradation rates measured on the Peros Banhos carbonate platform, British Indian Ocean Territory, and a Holocene Abu Dhabi shoreline, suggesting that this is a realistic and perhaps ubiquitous process in geological history. Given the fundamental nature of processes modelled here, and the match with observed processes in modern depositional systems, it seems possible that similar autogenic, self‐organizing processes have operated on many carbonate platforms and are an important component in the stratigraphic record.

The response of foraminifera to rapid sea-level rise from tidal restoration of Ni-les'tun marsh, Oregon, U.S.A

Foraminifera preserved in saltmarshes are widely used to reconstruct relative sea-level change (RSL), and inferred from this, coseismic vertical coastal motions following an earthquake. However, how quickly foraminifera respond to rapid changes in RSL is poorly understood. Here, we present a six-year foraminiferal study of the tidal restoration of Ni-les'tun marsh and a comparison of modern and fossil assemblages. We installed eight stations on the marsh and sampled these stations for live foraminifera prior to and during the first six years after tidal restoration (2011–2017), and we extruded one short core at station 1 in 2016. At stations 1 to 7, tidal flat/low marsh assemblages, dominated by Miliammina fusca, colonized 10 months to 2.5 years after tidal restoration. At station 8, the first living mixed assemblage of foraminifera, dominated by Haplophragmoides wilberti, was found 2 years after tidal restoration. Our observations suggest that M. fusca, and to some extent H. wilberti, are opportunistic species (r-strategists), able to increase their standing crop rapidly after invading a new habitat (to up to ~3600 specimens per 10 cm3 sediment volume). Potential causes for the delay in foraminifera colonization include their reproductive cycle and/or limited food availability due to the slow response of the vegetation community and soil development to tidal restoration. However, the similarity among assemblages and concentrations of agglutinated foraminifera between the fossil and modern sediments, indicate that post-depositional taphonomic processes have minimal influence when incorporated in the stratigraphic record. Although foraminifera have shown a delayed response to tidal restoration in the Ni-les'tun marsh, the similarities between the modern and fossil assemblages indicate that the delayed response of foraminifera to tidal restoration is undetectable in study areas with low sedimentation rates (in this case 3.3 mm/yr) after tidal restoration. In the case of high post-earthquake sedimentation rates, sampling a few cm higher rather than immediately above an earthquake contact could avoid uncertainties of coseismic vertical motions when foraminifera have a delayed colonization.

Coral assemblages of the Serpukhovian–Bashkirian transition from Adarouch (Morocco)

The Carboniferous outcrops from Adarouch (central Morocco) are composed of siliciclastic and carbonate rocks, and the latter have yielded abundant fossils. The upper part of the marine succession in the Idmarrach Formation and its laterally equivalent Tirhela Formation belong to the Bashkirian. More recent investigations of poorly preserved coral assemblages from the upper part of Idmarrach 2 section and the upper part of the Tirhela Formation are here described. The assemblage from the upper Idmarrach Formation comprises several typical Mississippian taxa, such as Aulophyllum fungites, Dibunophyllum bipartitum, Koninckophyllum interruptum, Siphonodendron scaleberense and Lithostrotion decipiens, and some highly evolved forms previously undescribed of Mississippian genera such as Haplolasma sp., Arachnolasma sp., Siphonodendron sp., Diphyphyllum sp., Solenodendron sp., Clisiophyllum sp. and a new species Corwenia tirhelensis sp. nov. In addition, an undetermined petalaxid has been also recorded. Similarly, the assemblage from near the top of the Tirhela Formation yielded some species regarded usually as Mississippian, such as Palaeosmilia murchisoni and Lithostrotion decipiens. We also identified the long-ranging tabulate Syringopora sp., Corwenia tirhelensis sp. nov., and a single species of the fasciculate rugosan, Siphonodendron tindoufense, previously described from Bashkirian rocks in the Tindouf Basin (southern Morocco). The presence of the latter taxon in both the Idmarrach and Tirhela sections implies a communication between the Adarouch region and the Saharan basins. The occurrence of S. tindoufense at the approximately same stratigraphic level in Tindouf, Taoudenni, Reggan-Ahnet and Adarouch, demonstrates its important regional stratigraphic value in North Africa.

Evaluating the taphonomic consistency of microvertebrate assemblages at Natural Trap Cave, Wyoming, USA

Paleontological sites composed of small vertebrate specimens can contain hundreds-of-thousands of identifiable fossils, which can reveal community responses to environmental and trophic changes. However, the composition of these communities may be skewed if the taphonomic signatures of the deposits change over time and across strata. Here, we discuss the taphonomic processes that led to dense deposits of microvertebrate fossils at Natural Trap Cave, Wyoming, USA. We then evaluate the nature and consistency of the taphonomic signature across stratigraphic layers using bone breakage rates and bone processing information. Natural Trap Cave is a pitfall cave that has an excellent record of vertebrate communities over the last 35,000 years. Along the North Wall of the excavation site, microvertebrate fossils form a dense accumulation, raining down from a packrat (Neotoma) nest located ∼20 m above the floor of the cave. Using the breakage rates of micromammal limb bones, we evaluate whether the accumulation mechanism appears consistent across strata. We demonstrate that the variation in breakage rates from Natural Trap Cave's strata cluster together when compared to breakage rates for different predator types (mammalian carnivores, raptors, and owls). We then demonstrate that the variation in breakage rates from the three strata is less than would be expected if it were the result of a change in major predator type across the strata. Our analysis of depositional taphonomy at Natural Trap Cave provides confidence in the reliability of the microvertebrate community record, paving the way for future paleoecological analyses.

Boron proxies record paleosalinity variation in the North American Midcontinent Sea in response to Carboniferous glacio-eustasy

Abstract Salinity variation in ancient epicontinental seas has long been challenging to reconstruct. We determined salinity variation in the Late Pennsylvanian North American Midcontinent Sea based on normalized boron concentrations (B/Ga) and isotopic compositions (δ11B) of bulk shale. We analyzed the Stark Shale Member of the Missourian Stage Dennis Limestone cyclothem in the Charleston core (CC) from the Illinois Basin (eastward, more proximal) and the Iowa Riverton core (IRC) from the Midcontinent Shelf (westward, more distal). Both cores exhibited the same pattern of secular variation, with lower B/Ga and δ11B values at their base and top, recording less saline conditions during lower sea-level stands, and higher values in their middle part, recording more saline conditions at highstands—a pattern that conforms to conventional sequence stratigraphic and glacio-eustatic interpretations of Midcontinent cyclothems. At equivalent stratigraphic levels, B/Ga and δ11B values are systematically lower at CC relative to IRC, reflecting the generally lower salinity conditions of the Illinois Basin relative to the Midcontinent shelf, which is consistent with greater freshwater influence from the east due to heavy river runoff into the Appalachian foreland basin. Our findings serve to demonstrate the utility of paired B concentration and isotope data for paleosalinity analysis of deep-time shale formations.

Submarine Channel Mouth Settings: Processes, Geomorphology, and Deposits

Observations from the modern seafloor that suggest turbidity currents tend to erode as they lose channel-levee confinement, rather than decelerating and depositing their sediment load, has driven investigations into sediment gravity flow behaviour at the mouth of submarine channels. Commonly, channel mouth settings coincide with areas of gradient change and play a vital role in the transfer of sediment through deep-water systems. Channel mouth settings are widely referred to as the submarine channel-lobe transition zone (CLTZ) where well-defined channel-levees are separated from well-defined lobes, and are associated with an assemblage of erosional and depositional bedforms (e.g., scours and scour fields, sediment waves, incipient channels). Motivated by recently published datasets, we reviewed modern seafloor studies, which suggest that a wide range of channel mouth configurations exist. These include traditional CLTZs, plunge pools, and distinctive long and flared tracts between channels and lobes, which we recognise with the new term channel mouth expansion zones (CMEZs). In order to understand the morphodynamic differences between types of channel mouth settings, we review insights from physical experiments that have focussed on understanding changes in process behaviour as flows exit channels. We integrate field observations and numerical modelling that offer insight into flow behaviours in channel mouth settings. From this analysis, we propose four types of channel mouth setting: 1) supercritical CMEZs on slopes; 2) plunge pools at steep slope breaks with high incoming supercritical Froude numbers; 3) CLTZs with arrays of hydraulic jumps at slope breaks with incoming supercritical Froude numbers closer to unity; and, 4) subcritical CLTZs associated with slope breaks and/or flow expansion. Identification of the stratigraphic record of channel mouth settings is complicated by the propagation, and avulsion, of channels. Nonetheless, recent studies from ancient outcrop and subsurface systems have highlighted the dynamic evolution of interpreted CLTZs, which range from composite erosion surfaces, to tens of metres thick stratigraphic records. We propose that some examples be reconsidered as exhumed CMEZs.

The paleoenvironment of southeastern São Paulo: contributions from Itapeva shelter to a discussion on anthropic and natural insertion

Paleoclimate reconstitution for the state of São Paulo results from past and ongoing research efforts in palynology, anthracology, and stable isotope studies. In cases such as southern São Paulo, however, researchers are required to extrapolate data from the states of Paraná, Santa Catarina, and Rio Grande do Sul for comparisons. Phytoliths and seeds were collected from sediments retrieved from excavation units D18 and G6 at the Abrigo de Itapeva [Itapeva Shelter] archeological site and analyzed. Seed results indicate that Ocotea (Lauraceae) is present in the initial levels, whereas Syagrus romanzoffiana predominates at all other stratigraphic levels. The former is a species of Atlantic Forest that occurs in Araucaria Forests; the latter is a palm species found in southeastern and southern Brazil. Phytoliths analysis reveals a change from a drier climate with grassland vegetation to a woody forest in the later periods of shelter occupation. As such, grassland and forest vegetation types occur from base stratigraphic levels up to level seven, dating from 5,510 cal BP to 730 cal BP. Conversely, from level seven up to the surface levels, dated from 730 cal BP to 560 cal BP, we see species linked to Araucaria Forest proliferation which may indicate the presence of Jê groups in the study area, thus corroborating studies on the possible anthropization of São Paulo forests from 1,000 BP.

A glimpse of a Gondwanan postglacial fossil forest

The rooted nature of vegetation allows for individual plants or entire communities to be buried in life position under exceptional geological conditions, thereby preserving their ecology and spatial distribution in the stratigraphic record. Upright lycopsids are not uncommon within paleoequatorial Carboniferous coal-bearing deposits, but they are rare in mid- to high-paleolatitude Gondwana, where they have only been found in lower Permian strata. An exceptionally well preserved in situ Brasilodendron-like lycopsid forest is described from an early Permian postglacial paleolandscape of western Gondwana (Paraná Basin, Brazil). The forest depicted here is unique given its extratropical location, as well as the exceptional preservation of abundant specimens and their morphological and paleoecological aspects. Over 150 lycopsid stumps, with a clustered spatial organization, were mapped. The host succession, overlying glaciomarine diamictites by a few tens of meters, captures the terminal deglaciation in the Paraná Basin, and shows that these forests could establish dense communities on poorly developed soils in postglacial times. Sedimentological data suggest that the death and burial of these lycopsids in life position were caused by crevasse splay progradation over the colonized interdistributary bay areas as a consequence of a major river flooding event.