Revisiting the Cretaceous Mancos Group in Utah—problems, previous methods, and new perspectives on a world-class Cretaceous marine section

The Mancos Group is an upper Cenomanian-middle Campanian lithostratigraphic unit that records large-scale changes in sedimentation patterns associated with the incursion of the Western Interior seaway across western Colorado into central Utah. Understanding the stratigraphic relationships in this unit is of critical scientific importance to understanding marine stratigraphic sequences across the globe. This field trip focuses on synonymizing units into consistent lithostratigraphic packages in the framework of biostratigraphy and currently available geochronology. Field trip stops emphasize the hierarchical division of each Mancos unit, the information present/absent for correlation, and fossil occurrences and how they relate to paleoenvironment and index fauna, as well as disparate sedimentological characteristics (grainsize, bioclastic content, glauconite abundance, cementation)

Census of currently known specimens of the Late Jurassic sauropod Haplocanthosaurus from the Morrison Formation, USA

Currently known from two valid species, Haplocanthosaurus priscus and H. delfsi, the Late Jurassic sauropod Haplocanthosaurus (Morrison Formation, Western United States) has often been described as an enigmatic sauropod taxon due to its unstable phylogenetic position and paucity of specimens. Here, we quantify the number of Haplocanthosaurus specimens known from the literature and in collections. Although most regions of the postcranial skeleton are known, the most commonly found elements of Haplocanthosaurus are vertebrae (dorsals and caudals) and tibiae. Our investigation identified twelve individuals of Haplocanthosaurus from ten localities across four states, Colorado, Utah, Montana (private specimen), and Wyoming, making Haplocanthosaurus spatially widespread in the central part of the Morrison Formation. The existence of twelve individuals across four states indicates this genus was widely distributed and more abundant than historically thought. Haplocanthosaurus has been characterized as a ‘primitive’ sauropod restricted to the lower half of the Morrison Formation, but the identification of Haplocanthosaurus in the Dry Mesa Dinosaur Quarry confirms that the genus was also present within the upper part of the Morrison Formation

Claron basin provenance shift from Sevier-Laramide compression to Basin and Range extension: Detrital zircon geochronology from the Eocene-Oligocene Brian Head Formation, Utah

The Eocene-Oligocene Brian Head Formation is the basal volcanic unit throughout much of the southern Marysvale volcanic field but rests atop Sevier-Laramide synorogenic strata of the Claron foreland basin in southern Utah. The Brian Head Formation reaches 300 m in thickness and consists of light-colored volcaniclastic sandstone, siltstone, mudstone, and minor conglomerate and airfall tuff; in northern exposures, the upper part locally contains a volcanic section of lava flows, ash-flow tuff, and volcanic mudflow breccia. These rocks were deposited in a slowly aggrading fluvial to lacustrine depositional environment distal tothe Indian Peak caldera complex to the west. We sampled three volcaniclastic sandstone units near the top of the formation, specifically near Haycock Mountain and along the southern and western flanks of the Sevier Plateau near Casto Butte and Blind Spring Mountain. The sandstone beds are compositionally and texturally immature and classify as lithic and arkosic wacke. U-Pb geochronological data for samples from the three sites were obtained on zircon by inductively coupled plasma mass spectrometry (ICP-MS) at the University of Arizona Laserchron Center. A total of 370 zircon crystals were analyzed. Most zircons were pale, translucent, and euhedral. The detrital zircon age spectra of the three sites are statistically indistinguishable. Each sample contained greater than 80% Paleogene zircons and had prominent age peaks of about 34.5 Ma. We interpret that the maximum depositional age is about 33.4 Ma. Older zircons range from Mesozoic to Archean in age. We suggest that the Brian Head Formation was sourced from the IndianPeak caldera and its environs, which are greater than 150 km to the west. Thus, Brian Head deposition in the Claron basin represents the transition from a Sevier-Laramide foreland basin characterized by the synorogenic Claron Formation to a system dominated by more distally derived sediments from the Indian Peak caldera complex, which is probably the most prominent eruptive center on the Nevadaplano uplift

Faunal extirpations, range shifts, and extinctions in the western Bonneville basin, 17,500 to 5500 cal yr BP: Paleobiogeography of Bonneville Estates Rockshelter and Siblings East Shelter

We analyzed faunal remains from two rockshelters in the far western Bonneville basin of eastern Nevada: Bonneville Estates Rockshelter and Siblings East Shelter. The analysis focused on paleobiogeographic changes between 17,500 and 5500 cal yr BP. Bonneville Estates Rockshelter contains faunal remains dating to the Heinrich 1 Stadial (18,000 to 14,700 cal yr BP), whereas both shelters contain faunal remains dating to the Bølling-Allerød Interstadial (14,700 to 12,900 cal yr BP), Younger Dryas Stadial (12,900 to 11,700 cal yr BP), Early Holocene (11,700 to 9300 cal yr BP), and Middle Holocene (9300 to 5500 cal yr BP). Identified faunal remains from these records indicate cool and either moist or dry climate compared to today between 17,500 and 10,200 cal yr BP, and increasingly warm temperatures impacting animal biogeographies beginning in the latter stages of the Younger Dryas and first one-half of the Early Holocene, culminating in xeric-adapted species like today by 9300 cal yr BP. Bonneville Estates Rockshelter also contains specimens of either gray wolf (Canis lupus) or the extinct dire wolf (Aenocyon dirus) and one felid phalanx of either puma/cougar (Puma concolor) or the extinct North American “cheetah” (Miracinonyx trumani), whereas Siblings East Shelter contains a rib of an extinct large horse of the genus Equus. Radiocarbon dated faunal remains were found directly atop Lake Bonneville beach gravels deposited inside Siblings East Shelter on the Provoterrace of Lake Bonneville, suggesting the lake dropped from this elevation prior to 14,300 cal yr BP

Stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the Late Cretaceous (Campanian-Maastrichtian) of southwestern North America

After the return of giant sauropod dinosaurs in the form of titanosaurids to North America in the Campanian of the Late Cretaceous, Alamosaurus sanjuanensis is generally considered to have been the sole taxon on the continent over a few million years. The possibility of one species existing that long is very low because sauropods often exhibit taxonomic diversity in the same habitat. The fossils from the southwestern states and northern Mexico are all incomplete, overlapping elements are often scarce, and sometimes differ in ontogenetic development. The fragmentary New Mexican A. sanjuanensis material from the early Maastrichtian lower Ojo Alamo Formation shows significant distinctions from the much later partial skeletons from the late Maastrichtian lower North Horn Formation of Utah. The latter is therefore made the holotype of Utetitan zellaguymondeweyae. Some late Maastrichtian Texas fossils can be assigned to U. zellaguymondeweyae, others cannot. Fossils from the middle Campanian cannot be assigned to either genus. Southwestern North America supported a diversity of titanosaurids, which may have formed a Utetitan miniclade as they evolved in semi-isolation from the global titanosaurid fauna. Past calculations that these titanosaurids were among the most massive in the group are not borne out by scaling of skeletal restorations

A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah

This study investigates the depositional environment, sedimentological dynamics, and tectonic influences that shaped the Quarry Sandstone within the Brushy Basin Member of the Upper Jurassic Morrison Formation in Dinosaur National Monument, Utah. Characterized by laterally extensive, multistory sandstone bodies, the origin of the Quarry Sandstone has been a subject of ongoing debate. By synthesizing new field data and revisiting existing interpretations, this research challenges prevailing hypotheses and offers new perspectives on the geological history of the Morrison Formation at the Monument. Whereas the Morrison Formation, deposited in a foreland basin setting on the Colorado Plateau, is generally well understood, the Quarry Sandstone's unique width-to-thickness ratio sets it apart from other sandstone units in the Brushy Basin Member. This distinct feature suggests a depositional history that cannot be fully explained by traditional foreland basin models. To address this anomaly, the study places the sandstone within its stratigraphic framework, emphasizing the critical role of accommodation space in shaping its deposition. A key finding of this research is the proposed influence of a proto-Split Mountain anticline on the sedimentation patterns of the Quarry Sandstone. This minor structural feature, likely generated by oblique compressional forces associated with regional tectonics on the Colorado Plateau, appears to have played a pivotal role in reducing accommodation space during the deposition of the sandstone. Evidence for this reduction includes localized thinning of stratigraphic units and increased lateral connectivity of braided channel sandstones. The structural uplift caused by the proto-Split Mountain anticline likely created an asymmetrical depositional setting. This uplift restricted accommodation, triggering a transition in fluvial systems from single-threaded sinuous channels to multithreaded braided rivers with frequent avulsions. The interconnected nature of these braided channels over time reshaped sediment distribution patterns, producing the distinctive characteristics of the Quarry Sandstone

Great Salt Lake wetland vegetation and what it tells us about environmental gradients, drought, and disturbance

Great Salt Lake (GSL) wetlands support more than 300 species of migratory birds and provide many ecosystem functions, including flood and drought attenuation, dust mitigation, and water quality improvement. Wetland vegetation is a key factor in providing those services and can also tell us about how healthy a wetland is. From 2103 to 2022, 135  GSL wetlands were surveyed to develop a multi-metric index of GSL wetland condition. That wetland condition data, along with environmental variables like soil and water chemistry and physical disturbance, are summarized here as 1) an ecological characterization of the three main types of GSL wetlands, 2) a description of how the plant community differs across environmental and anthropogenic disturbance gradients, and 3) assessment of the major risks to GSL wetland health. GSL wetland plant species are generally resistant to environmental disturbance because of the anatomical and physical adaptations that allow them to survive in dynamic wetland environments. However, land use conversion and the rapid expansion of invasive species, the major threats to GSL wetland health, have seriously degraded wetland condition around GSL. In addition to being useful in wetland monitoring and assessment, the results presented here can also identify wetlands in need of enhanced protection or those with restoration potential as well as setting realistic wetland restoration goals for the region

Radiocarbon Chronology/Growth Rates of Ooids from Great Salt Lake, Utah

Ooids (calcium carbonate coated grains) are common in carbonate environments throughout geologic time, but the mechanism by which they form remains unclear. In particular, the rate of ooid growth remains elusive in all but a few modern marine environments. In order to investigate the rate of ooid growth in a non-marine setting, we used 14C to date ooids from Great Salt Lake, Utah, a well-known site of aragonitic ooids. Bulk ooids obtained from the northern shore of Antelope Island and the northeast shore of Great Salt Lake near Spiral Jetty were sieved into different size fractions and produced mean ages ranging between 2728±15 and 4373±20 14C yr BP. Larger ooids were older than smaller ooids, implying that larger ooids grew in the environment for a longer duration, with the caveat that bulk age dating integrates the growth history of an ooid. To better resolve growth history, ooids from the coarse fraction were sequentially dissolved, and 14C ages were obtained for each dissolution step to create a time series of ooid growth. The results of the sequential dating indicate that the coarse Great Salt Lake ooid growth began between 5800-6600 ± 60 14C yr BP while their outer cortices are nearly modern. Sequentially dated ooids from the South Arm of Great Salt Lake at Antelope Island record a nearly linear growth history (~ 10-15 µm/kyr), whereas ooids from Spiral Jetty record somewhat faster growth between ~6000 and 4000 years ago (0.03 – 0.06 µm/yr) followed by a 10x slower growth history for the remainder of their lifespan (0.003 – 0.008 µm/yr). The lifespan of Great Salt Lake aragonitic ooids is two to six times longer than those from modern marine environments, and thus provides a unique end member for understanding the mechanisms behind ooid formation. The ooid age range indicates that geochemical parameters measured from bulk ooid dissolution integrates over ~6000 years and thus does not represent a geochemical snapshot in time, as some previous studies have suggested

Wave dynamics and sediment transport in Great Salt Lake: A model-data comparison

Great Salt Lake is a natural laboratory to test and refine ideas about the relationship between sediment transport by waves and the characteristics of shoreline carbonate sediments, in particular ooid sands and microbialite mounds. In this chapter, we present a year-long series of wave data collected from July 2021 through June 2022 and use these wave data to assess the performance of a US Army Corps of Engineers wave model previously used to estimate bed shear velocity and intermittency of sediment transport in Great Salt Lake (Smith and others, 2020). We use this model-data comparison to identify the strengths and weaknesses of the existing model for both geological and ecological applications, and areas of improvement for future model development. We also use shallow sediment cores and Unmanned Aerial Vehicle (UAV)-based orthomosaics collected from shorelines near each buoy to assess how the wave climate along two parts of the lake shore influences the stratigraphic record and the surface morphology of the lakebed

The Holocene Great Salt Lake and Pleistocene Lake Bonneville System: Conserving our Geoheritage for Future Generations

The modern (Holocene-age) Great Salt Lake (GSL) and Pleistocene Lake Bonneville of the Bonneville Basin (BB) together make a geosite (GSL-BB system) of exceptional scientific, cultural, aesthetic, and societal value. GSL is the largest saline lake in the Western Hemisphere and a sensitive recorder of climate. For millennia, this distinctive salty water body has been a dynamic and complex natural ecosystem, including an important waterway for birds and other wildlife and an archive of environmental change and history. Lake Bonneville is a seminal part of the history of science in the United States through the work of G.K. Gilbert, who in the 1870s and 1880s developed both critical scientific concepts (e.g., isostasy) and methods (e.g., multiple working hypotheses), which are still employed today. GSL is a major tourist attraction, an economic driver, and a place of scientific exploration. Yet today, the GSL is in grave danger of near total desiccation due to a combination of factors: human removal of waters that would normally replenish the lake, climate change, and other environmental pressures. Over the past few decades there has been a growing international movement to recognize and respect our geoheritage, by raising visibility and protection of high-priority geosites. The GSLBB system is a geoheritage site that urgently needs our protection