ReBecca Hunt-Foster

A U/Pb age for the Mygatt-Moore Quarry, Upper Jurassic Morrison Formation, Mesa County, Colorado

The bromalite record of the western United States is quite limited, especially in contrast to the Triassic and Cretaceous records of the same region. Indeed, there are only a handful of well documented vertebrate bromalites from the Jurassic strata of the western USA, including: (1) coprolites from the nonmarine Early Jurassic Glen Canyon Group; (2) consumulites and evisceralites from the Middle Jurassic Todilto and Sundance formations; and (3) consumulites, putative coprolites and pseudobromalites from the nonmarine Upper Jurassic Morrison Formation. Early Jurassic red beds are notably less fossiliferous than those of the Triassic (e.g., contrast the fossil record of the Chinle and Glen Canyon groups). The Middle Jurassic of the region includes several eolianites and sabkha-like deposits representing environments that preserve few bromalites. The Upper Jurassic Morrison Formation contains abundant vertebrate body fossils and many tracks but very few bromalites in contrast to many broadly similar fluvial deposits of Triassic and Cretaceous age in the same region. The global bromalite record also appears to be depauperate in the Jurassic, with a few exceptions such as marine shales and lithographic limestones in Europe (e.g., Lower Jurassic of England, Upper Jurassic Solnhofen Limestone of Bavaria). This relative lack of a global Jurassic bromalite record may in part be more a result of a lack of collection and study. However, the relative lack of nonmarine bromalites is clearly influenced by high sea levels in the Early Jurassic, a paucity of Middle Jurassic nonmarine vertebrate-bearing units and a lack, or lack of recognition of, bromalites in major Upper Jurassic nonmarine vertebrate faunas (e.g., China, Tanzania, Portugal, etc.). In the Western United States there is clearly a need for more detailed examination of known specimens (e.g., putative Morrison coprolites) and a focus on collecting more examples. 1 Flying Heritage Collection, 3407 109thSt SW, Everett, WA 98204; e-mail: adrianhu@flyingheritage.com 2 New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104; e-mail: spencer.lucas@state.nm.us JURASSIC BROMALITES IN THE WESTERN UNITED STATESThe Springdale Sandstone records a large number of reversals of the geomagnetic field. Forty-three percent of the 60 m section investigated showed 25 polarity intervals. These frequent reversals follow the nearly constant normal polarity of the underlying Whitmore Point strata. Comparison of the reversal sequence of the Springdale Sandstone with a core from the Paris Basin suggests that the Springdale Sandstone spans an interval extending possibly from as early as late Hettangian to early-mid Sinemurian time. The paleomagnetic pole calculated from Springdale paleomagnetic directions is statistically identical to that of the underlying Whitmore Point Member of the Moenave Formation, and considerably different from that of the overlying Kayenta Formation. This similarity suggests that the Springdale Sandstone should be retained as a member of the Moenave Formation, not considered part of the Kayenta Formation.Two partial skeletons of allosaurid theropods belonging to an adult and a juvenile from the Upper Jurassic (Tithonian) Morrison Formation of McElmo Canyon in Montezuma County, southwestern Colorado, were discovered in 1953 by the late Joseph T. Gregory and David Techter. The adult specimen consists of several isolated cranial and postcranial skeletal elements that are exceptionally well-preserved and include the left premaxilla, maxilla, dentary, teeth, quadratojugal, two caudal vertebrae, pubic peduncle, ischium, proximal tibia, a nearly complete left foot, and several isolated teeth, whereas the juvenile specimen is represented by the distal portion of the right dentary and a fragmentary splenial. The specimens represent a new species of Allosaurus , here named Allosaurus lucasi , which differs from Allosaurus fragilis by having a relatively short premaxilla and robust quadratojugal with short jugal process and a short quadrate process of the quadratojugal that is at the same level as the rostral quadratojugal ramus. The presence of a new species of Allosaurus in the Tithonian of North America provides further evidence of the taxonomic and morphological diversity of the Allosauridae clade and their continuous evolutionary success, which extended to the Cretaceous.To evaluate the utility of high-resolution micro-computed tomography (micro-CT) in observing radiolarian fossils, we examined the skeleton of the Jurassic radiolarian fossil Protunuma ? ochiensis Matsuoka using a micro-CT device. Although this species is a closed Nassellarian with a thick exterior wall, important taxonomic characters on the interior and exterior of the shell were represented almost perfectly in the acquired three-dimensional computer graphic images. These characters include those documented in the original description, such as the height and width of the skeleton, the outline, the number of segments, the pore arrangement and other features. In addition, the structure of the initial spicule of this species was revealed newly. An enlarged plaster radiolarian model printed using the laminated modelling method was useful for detailed observation. Nondestructive omnidirectional observation is an advantage of this method, which is not possible with scanning electron microscopy or optical microscopic investigations. Micro-CT technology would become an effective observational tool for radiolarian studies in the near future. method of visualising and measuring the internal geometries of opaque objects. Micro-CT is specialised for visualising the structures of micrometreto centimetre-sized objects with greatly increased resolution. This developing technoloINTRODUCTION X-ray computed tomography (CT), which is commonly used for medical and industrial purposes, is a nondestructive 1 Gas Hydrate Research Laboratory, Meiji University, Kanda-Surugadai 1-1, Chiyoda-ku, Tokyo, 101-8301, Japan; phone and fax: +81-3-3296-4582; e-mail: nao.ishida21@mbn.nifty.com. 2 Department of Mechanical Engineering, Faculty of Science and Engineering, Setsunan University, Neyagawa 572-8508, Japan; phone: +81-72-839-9165; e-mail: kishimoto@mec.setsunan.ac.jp. 3 Department of Geology, Faculty of Science, Niigata University, Niigata 950-2181, Japan; phone and fax: +81-25-262-6376; e-mail: amatsuoka@geo.sc.niigata-u.ac.jp. 4 Research and Development Center for Global Change (RCGC), JAMSTEC, Yokosuka, Kanagawa 237-0061, Japan; phone: +81-46-867-9436; e-mail: kimopy@jamstec.go.jp. 5 Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan; phone and fax: +81-25-262-7640; e-mail: kurihara@geo.sc.niigata-u.ac.jp. 6 Department of Mechanical Engineering, Faculty of Science and Engineering, Toyo University, Kawagoe, Saitama 350-8585, Japan; phone: +81-49-239-1396; e-mail: tyoshino@toyo.jp. 78 Naoto Ishida et al. gy is being applied to a wide range of geological and palaeontological investigations (e.g. Ketcham, Carlson, 2001). To evaluate the potential of micro-CT imaging technology in investigating microfossils, the authors have experimentally examined the skeletons of foraminifers, ostracodes, diatoms and radiolarians. For example, Matsuoka et al. (2012) reported the exact pore number of a specimen of the genus Pantanellium and represented its pore distribution on a spherical shell based on three-dimensional (3D) scanning data. Furthermore, Yoshino et al. (2014) presented a method that uses 3D information to automatically determine the pore numbers of spherical radiolarian skeletons. In this study, we present the results of 3D scanning of the Jurassic radiolarian Protunuma ? ochiensis Matsuoka using a high-resolution micro-CT scanner. Although closed Nassellarians, including this species, are commonly recovered from Jurassic sediments, conventional methods cannot be used for nondestructive observation of a combination of both their surface textures and their internal structures. Observation using high-resolution micro-CT overcomes this difficulty. This study introduces the observation of radiolarian fossils using 3D imaging methods and emphasises the utility of high-resolution micro-CT for palaeontological investigations. METHODS AND MATERIALSThe thick and relatively complete Jurassic succession of eastern Greenland provides a unique biostratigraphic record for the North Atlantic region. The main biostratigraphic control for the succession has been provided by molluscs, especially ammonites and to a lesser extent by bivalves and belemnites. The late John Callomon and colleagues recognised 93 Boreal ammonite-bearing horizons in the Mid to Late Jurassic. This provides a reliable backbone to the biostratigraphy of these strata, prompting a palynological colleague to comment that they are the “Policemen of Jurassic Stratigraphy”. Other biostratigraphically significant microfossil and palynological groups, can be calibrated against this standard, but on their own cannot achieve the same precision.​ The Early Jurassic of eastern Greenland does not have such fine control as later parts of the period. No single biostratigraphic group can be used successfully throughout the interval, and there are only three significant ammonite faunas during this period. Reliance on various different organisms is necessary to cope with the changing range of marine to non-marine environments. CASP field-work from 1990 to 2012 has resulted in the collection of much biostratigraphic material. In this article, published data are summarised together with previously unpublished data in the form of a unified table. The integrated chart shows detailed columns for the whole eastern Greenland Jurassic. It demonstrates the ammonite, palynological and microfossil events/biozones and horizons which are correlated by time. More limited information is available on belemnites, bivalves and macroflora. This is the first time such an integrated biostratigraphic scheme has been assembled for the Jurassic of eastern Greenland. It will be of value to the offshore oil-industry in the northern North Atlantic and on the Barents Shelf as well as to field geologists in Greenland.Measured sections of Jurassic San Rafael Group strata correlated by lithostratigraphy along an ~60 km transect between Bluff and the Abajo Mountains in southeastern Utah indicate that: (1) the Carmel Formation is continuous and disconformable on the Navajo Sandstone (J-2 unconformity); (2) the Entrada Sandstone (Slick Rock Member) is continuous and conformable on the Carmel; (3) the Summerville Formation is continuous and does not intertongue with the Entrada (its base is the J-2 unconformity); (4) the Bluff Sandstone grades northward into the upper Summerville south of the Abajo Mountains; (5) the Recapture Member of the Bluff is physically continuous with at least part of the Tidwell Member of the Summerville; and (5) the base of the Salt Wash Member of the Morrison Fm. is a pervasive unconformity (J-5) with demonstrable local stratigraphic relief of up to 14 m. These observations counter previous claims of extensive Entrada-Summerville intertonguing in southeastern Utah and do not support recognition of depositional sequence boundaries in the Entrada and Summerville lithosomes. Though Entrada deposition may have been by a wet eolian system, its southeastern Utah outcrops are well to the south/ southeast of any marine and paralic facies with which the Entrada intertongues. 1 New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104 USA; e-mail: spencer.lucas@state.nm.us fornia and left eolian sandstone up to 660 m thick called in different regions Navajo Sandstone, Nugget Sandstone or Aztec Sandstone. Later, during the Middle Jurassic (Callovian), the Entrada erg extended from Utah to Oklahoma and from New Mexico to Wyoming. The last Jurassic erg, the Bluff sand sea, accumulated during the Middle-Late Jurassic transition and was primarily located in the Four Corners. The two younger ergs – Entrada and Bluff – accumulated at a time when a Jurassic Cordilleran seaway was present to the northwest, in what is now Idaho and parts of northern and western Utah. The ergs were landward of that seaway and their deposits interfinger to the northwest with its marine and paralic facies. In southeastern Utah, O’Sullivan (1980) INTRODUCTION Jurassic strata of the American Southwest include some of the most intensively studied eolian strata on the planet. These strata document several extensive sand seas (ergs) of Jurassic age that covered many thousands of square kilometers, including the largest of all Phanerozoic ergs, the Navajo erg (e.g., Kocurek, Dott, 1983; Blakey et al., 1988). The Jurassic erg history in the southwestern USA begins with the Wingate erg, which covered the Four Corners during the Triassic-Jurassic boundary interval. Next youngest is the Navajo erg, which extended at least from Wyoming to Cali-