New Insights on the Impact of Tidal Currents on a Low-gradient, Semi-enclosed, Epicontinental Basin—the Curtis Formation, East-central Utah, USA

Based on a methodic sedimentological analysis, the Late Jurassic (Oxfordian) Curtis Formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. This unit crops out in east-central Utah, between the eolian deposits of the underlying Middle Jurassic (Callovian) Entrada Sandstone, from which it is separated by the J-3 unconformity, and the conformable overlying supratidal Summerville Formation of Oxfordian age. A high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (FA) with six sub-facies associa¬tions. Based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the Curtis Formation into three sub-units: the lower, middle and upper Curtis. The J-3 unconformity defines the base of the lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud-domi¬nated (FA 3a) and sand-dominated heterolithic subtidal flat (FA 3b), sand-rich sub- to supratidal flat (FA 4a) and correlative tidal channel infill (FA 4c). It is capped by the middle Curtis, which coincides with the sub- to intertidal channel-dune-flat complex of FA 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the Major Transgressive Surface (MTS). This surface suggests a potential correla¬tion between the middle and the upper Curtis and the neighboring Todilto Member of the Wanakah Forma¬tion or Todilto Formation. The upper Curtis consists of the heterolithic upper sub- to intertidal flat (FA 6) and coastal dry eolian dunes belonging to the Moab Member of the Curtis Formation (FA 7), and it conformably overlies the middle Curtis.
The spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. In sector 1, the Curtis For¬mation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper Curtis, and sector 3 encompasses the extent of the Moab Member of the Curtis Formation.
This study also highlights the composite nature of the J-3 unconformity, which was impacted by various processes occurring before the Curtis Formation was deposited, as well as during the development of the lower and middle Curtis. Local collapse features within the lower and middle Curtis are linked to sand fluid over¬pressure within a remobilized sandy substratum, potentially triggered by seismic activity. Furthermore, the occurrence of a sub-regional angular relationship between the middle Curtis and substratum implies that the area of study was impacted by a regional deformational event during the Late Jurassic, before the deposition of the middle Curtis.

The Upper Jurassic Morrison Formation in north-central New Mexico–Linking Colorado Plateau stratigraphy to the stratigraphy of the High Plains

Most study of the Upper Jurassic Morrison Formation has focused on its spectacular and extensive outcrops on the southern Colorado Plateau. Nevertheless, outcrops of the Morrison Formation extend far off the Colorado Plateau, onto the southern High Plains as far east as western Oklahoma. Outcrops of the Morrison Formation east of and along the eastern flank of the Rio Grande rift in north-central New Mexico (Sandoval, Bernalillo, and San­ta Fe Counties) are geographically intermediate between the Morrison Formation outcrops on the southeastern Colorado Plateau in northwestern New Mexico and on the southern High Plains of eastern New Mexico. Previous lithostratigraphic correlations between the Colorado Plateau and High Plains Morrison Formation outcrops using the north-central New Mexico sections encompassed a geographic gap in outcrop data of about 100 km. New data on previously unstudied Morrison Formation outcrops at Placitas in Sandoval County and south of Lamy in Santa Fe County reduce that gap and significantly add to stratigraphic coverage. At Placitas, the Morrison Formation is about 141 m thick, in the Lamy area it is about 232 m thick, and, at both locations, it consists of the (ascending) sandstone-dominated Salt Wash Member, mudstone-dominated Brushy Basin Member, and sandstone-dominat­ed Jackpile Member. Correlation of Morrison strata across northern New Mexico documents the continuity of the Morrison depositional systems from the Colorado Plateau eastward onto the southern High Plains. Along this transect, there is significant stratigraphic relief on the base of the Salt Wash Member (J-5 unconformity), the base of the Jackpile Member, and the base of the Cretaceous strata that overlie the Morrison Formation (K unconfor­mity). Salt Wash Member deposition was generally by easterly-flowing rivers, and this river system continued well east of the Colorado Plateau. The continuity of the Brushy Basin Member, and its characteristic zeolite-rich clay facies, onto the High Plains suggests that localized depositional models (e.g., “Lake T’oo’dichi’) need to be re-eval­uated. Instead, envisioning Brushy Basin Member deposition on a vast muddy floodplain, with some localized lacustrine and palustrine depocenters, better interprets its distribution and facies.

Permo-Pennsylvanian shark teeth from the Lower Cutler beds near Moab, Utah

Several shark teeth have been collected from limestones in the marine-nonmarine transitional zone of the lower Cutler beds in the Shafer Basin near Moab, Utah. The shark teeth include the Pennsylvanian pet­alodontiform Petalodus ohioensis, which is the first described from the state, and the Permo-Carboniferous cladodontomorph Cladodus sp. The Petalodus specimens are compared with the holotype P. hastingsae Owen, P. acuminatus (Agassiz), P. ohioensis (Shafer), and P. alleghaniensis (Leidy). Several of these key taxa are illustrated with photographs for the first time.

Evidence for niche partitioning among ground-height browsing sauropods from the Upper Jurassic Morrison Formation of North America

Two tooth-bearing snout fragments from a diplodocid sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic) excavated from the Mygatt-Moore Quarry in Rabbit Valley, Colora­do are described. The Mygatt-Moore Quarry has produced thousands of vertebrate fossils from the Brushy Basin Member, with the diplodocid Apatosaurus cf. louisae and the tetanuran Allosaurus fragilis dominat­ing the assemblage. Additionally, remains of another diplodocid, Diplodocus sp., have been found near the quarry within Rabbit Valley. Both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (CT) scans. This is inconsistent with the genus Diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. The presence of eight replacement teeth per alveolus has previously only been reported in the Cretaceous rebbachisaurid Nigersaurus taqueti, which has been interpreted to have occupied a similar ground-height browsing feeding strategy to both Diplodocus and Apatosaurus. This is the first report of this type of high-count replacement teeth in a diplodocid sauropod from the Morrison Formation. The high number of replacement teeth in a close relative to the contemporaneous Diplodocus provides evidence for niche partitioning among the contemporary ground-height browsing diplodocid sauropods of the Late Jurassic Period in North America.

Paleontology, taphonomy, and sedimentology of the Mygatt-Moore Quarry, a large dinosaur bonebed in the Morrison Formation, western Colorado—Implications for Upper Jurassic dinosaur preservation modes

The Mygatt-Moore Quarry is a deposit of several thousand dinosaur bones in the Brushy Basin Member of the Morrison Formation in western Colorado. The site has been worked for more than 30 years and nearly 2400 mapped specimens have been collected. This study gathered data about the quarry from many sources to investigate the origin of the deposit. The Mygatt-Moore Quarry appears to be an attritional deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in a vernal pool deposit in an overbank setting. Bone modification was mostly by corrosion and breakage by trampling; scavenging was abundant. The paleofauna is dominated by Allosaurus and Apatosaurus (MNI and NIS), with the polacanthid ankylosaur Mymoorapelta less common. The matrix of the main quarry layer includes abundant carbonized fragments of plant material, and the mud during the time of deposition may have been often at least damp and occasionally acidic and dysoxic. The Cleveland-Lloyd Dinosaur Quarry is a close correlate of the Mygatt-Moore Quarry in terms of lithology and taphonomy, but demonstrates significant differences upon close inspection of matrix details and bone modification. Large quarries of fine-grained facies in the Morrison Formation possess a very different preservation mode as well as different taxon and relative abundance profiles from those in coarser sediments, which suggests that more may be learned in the future from taphofacies study of large quarries in mudstone beds.

First unambiguous dinosaur specimen from the Upper Triassic Chinle Formation in Utah

Triassic dinosaurs represent relatively rare but important components of terrestrial faunas across Pangea. Whereas this record has been well studied at various locales across the American West, there has been no previous systematic review of Triassic material assigned to Dinosauria from Utah. Here, we critically examine the published body fossil and footprint record of Triassic dinosaurs from Utah and revise their record from the state. In addition, we describe a sacrum from a locality within the Upper Triassic Chinle Formation of southeastern Utah. _is specimen represents the only unambiguous Triassic dinosaur body fossil from Utah. MWC 5627 falls within the range of variation known for sacrum morphology from Coelophysis bauri. Based on a literature review and examination of specimens available to us, we restrict the Triassic Utah dinosaurian record to _eropoda from the Chinle Formation. Preliminary reports of Triassic dinosaurs from other clades and formations in Utah are unsubstantiated.

Source within the seal—Distribution and implications of organic shale-bearing stringers within the Onion Creek diapir, northern Paradox Basin, Utah

The Onion Creek diapir is one of the best exposures of a dissected salt diapir in the world, offering a unique opportunity to better understand the internal character of heterolithic diapirs that are common in sedimentary basins worldwide. Large amounts of interbedded shale, carbonate, and evaporites are incorporated into the diapir as stringers or boudins, and excellent three-dimensional exposure allows us to document the nature, size, deformation, and distribution of these stringers. Blocks range in size from single, disaggregated layers of dolomite to several meters of coherent stringers that contain multiple cycles of dolomite- shale-evaporite and are upwards of 20 m thick and more than 100 m in observed length. The largest blocks are most commonly located along the margins of the exposed diapir, though stringers are common throughout the exposed caprock. In areas devoid of large stringers, there is more extensive deformation of the gypsum caprock, suggesting that the presence of stringers leads to a more heterolithic distribution of stress within the salt as it diapirically rises. These observations can help to better characterize similar diapirs elsewhere that are not well exposed at the surface. Black shale is present in all observed large stringers of the Onion Creek diapir. These shale beds are interpreted to have been deposited in a shallow, restricted marginal marine environment along with the interbedded carbonate and evaporite strata. Pyrolysis analysis of 13 samples from within the stringers shows a range of 2.56 to 60.22% total organic carbon (TOC), with an average value of 16.93%. These strata contain Type I/Type II hydrocarbon source facies, consistent with a restricted shallow marine environment. Tmax data suggest that these source rock facies have been exposed to sufficient thermal energy to generate hydrocarbons (average = 437o C), as evidenced by common hydrocarbon staining of intra-stringer carbonate strata and evaporite beds surrounding the stringers. Twelve additional samples were collected from these stained strata and pyrolysis analysis shows that all are enriched in free oil, as shown by elevated S1 peaks, high production index ratios, and TOC values of 0.64 to 1.66%. This hydrocarbon staining is found around stringers near the center of the exposed caprock, as well as stringers along the margins. Near the margins in particular, extensive alteration can be seen across tens of meters of evaporitic strata, showing that hydrocarbons are effectively generating within and migrating away from stringers fully encased in the anhydrite caprock of the Onion Creek diapir. This has important implications for potential seal integrity of diapiric caprocks, as well as providing a potential mechanism for caprock carbonate formation suggested by other researchers.

Shorelines and vertebrate fauna of Pleistocene Lake Bonneville, Utah, Idaho, and Nevada

Pleistocene Lake Bonneville created many classic examples of lacustrine shoreline landforms, which preserve a wide variety of vertebrate fossils. _is _eld guide provides a review of the published literature for a sampling of the lake’s world-class localities. _is guide also provides a brief overview of modern Great Salt Lake and its microbialites recently exposed by near-record low lake levels. Stops include G.K. Gilbert Geologic View Park, Draper spit, Steep Mountain beach, Point of the Mountain spit, American Fork delta, Stockton Bar, and Great Salt Lake State Park.

Upper Triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern Utah

The Chinle Formation and the lower part of the overlying Wingate Sandstone and Moenave Formation were deposited in fluvial, lacustrine, paludal, and eolian environments during the Norian and Rhaetian stages of the Late Triassic (~230 to 201.3 Ma), during which time the climate shifted from subtropical to increasingly arid. In southern Utah, the Shinarump Member was largely confined to pre-Chinle paleovalleys and usually overprinted by mottled strata. From southeastern to southwestern Utah, the lower members of the Chinle Formation (Cameron Member and correlative Monitor Butte Member) thicken dramatically whereas the upper members of the Chinle Formation (the Moss Back, Petrified Forest, Owl Rock, and Church Rock Members) become erosionally truncated; south of Moab, the Kane Springs beds are laterally correlative with the Owl Rock Member and uppermost Petrified Forest Member. Prior to the erosional truncation of the upper members, the Chinle Formation was probably thickest in a southeast to northwest trend between Petrified Forest National Park and the Zion National Park, and thinned to the northeast due to the lower Chinle Formation lensing out against the flanks of the Ancestral Rocky Mountains, where the thickness of the Chinle is largely controlled by syndepositional salt tectonism. The Gartra and Stanaker Members of the Ankareh Formation are poorly understood Chinle Formation correlatives north of the San Rafael Swell. Osteichthyan fish, metoposaurid temnospondyls, phytosaurids, and crocodylomorphs are known throughout the Chinle Formation, although most remains are fragmentary. In the Cameron and Monitor Butte Members, metoposaurids are abundant and non-pseudopalatine phytosaurs are known, as is excellent material of the paracrocodylomorph Poposaurus; fragmentary specimens of the aetosaurs Calyptosuchus, Desmatosuchus, and indeterminate paratypothoracisins were probably also recovered from these beds. Osteichthyans, pseudopalatine phytosaurs, and the aetosaur Typothorax are especially abundant in the Kane Springs beds and Church Rock Member of Lisbon Valley, and Typothorax is also known from the Petrified Forest Member in Capitol Reef National Park. Procolophonids, doswelliids, and dinosaurs are known but extremely rare in the Chinle Formation of Utah. Body fossils and tracks of osteichthyans, therapsids, crocodylomorphs, and theropods are well known from the lowermost Wingate Sandstone and Moenave Formation, especially from the St. George Dinosaur Discovery Site at Johnson Farm.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.