Neil E. Tibert

Ostracodes and agglutinated Foraminifera as indicators of paleoenvironmental change in an Early Carboniferous brackish bay, Atlantic Canada

Ostracodes and agglutinated foraminifera characterize lagoonal, estuarine, marsh, and nonmarine depositional systems that span the land/ sea transition. Using microfossil and sedimentary data, high-resolution paleoenvironmental change is documented in an Early Carboniferous marginal marine depositional system that was previously interpreted as nonmarine. There are five main paleoenvironmental phases: (1) low-energy bay dominated by the euryhaline marine ostracode Copelandella novascotica associated with glauconitic shale and primary framboidal pyrite; (2) restricted nearshore dominated by opportunistic paraparchitacean ostracodes (Shemonaella scotoburdigalensis, Shemonaella tatei, and Chamishaella sp.), Cavellina sp., and post-mortem Carbonita scalpellus associated with hummocky cross-stratified siltstone and shale; (3) coastal pond dominated by C. scalpellus and Carbonita rankiniana associated with pedoturbated calcareous mudstones; (4) distal lagoon dominated by paraparchitaceans, Bairdia sp., Geisina sp., and Youngiella sp., all associated with silty glauconitic shale; and 5) coastal marsh dominated by the agglutinated foraminifera Trochammina sp. associated with calcareous mudstones and in situ Iycopsid trees. Low diversity, high dominance, and large populations characterize the microfossil assemblages that resemble modern ecosystems where physical and chemical conditions are unstable. The Horton Bluff Formation records the brackishfreshwater transition at the landward terminus of an Early Carboniferous marine transgression in the Maritimes Basin.

Evidence for marine influence on a low-gradient coastal plain: Ichnology and invertebrate paleontology of the lower Tongue River Member (Fort Union Formation, middle Paleocene), western Williston Basin, U.S.A.

The Paleocene Tongue River Member of the Fort Union Formation contains trace-fossil associations indicative of marine influence in otherwise freshwater facies. The identified ichnogenera include: Arenicolites, Diplocraterion, Monocraterion, Ophiomorpha, Rhizocorallium, Skolithos linearis, Teichichnus, Thalassinoides , and one form of uncertain affinity. Two species of the marine diatom Coscinodiscus occur a few meters above the base of the member. The burrows occur in at least five discrete, thin, rippled, fine-grained sandstone beds within the lower 85 m of the member west of the Cedar Creek anticline (CCA) in the Signal Butte, Terry Badlands, and Pine Hills areas. Two discrete burrowed beds are found in the lower 10 m of the member east of the CCA in the little Missouri River area. Abundant freshwater ostracodes include Bisulcocypridea arvadensis, Candona, and Cypridopsis . Freshwater bivalves include Plesielliptio and Pachydon mactriformis . We recognize four fossil assemblages that represent fluvio-lacustrine, proximal estuarine, central estuarine, and distal estuarine environments. Biostratal alternations between fresh- and brackish-water assemblages indicate that the Tongue River Member was deposited along a low-gradient coastal plain that was repeatedly inundated from the east by the Cannonball Sea. The existence of marine-influenced beds in the Tongue River Member invalidates the basis for the Slope Formation.

HIGH-RESOLUTION ESTUARINE SEA LEVEL CYCLES FROM THE LATE CRETACEOUS: AMPLITUDE CONSTRAINTS USING AGGLUTINATED FORAMINIFERA

Agglutinated foraminifera provide high-resolution proxies for relative sea level change in Late Cretaceous coal-bearing strata. Three foraminiferal assemblages are recognized where Trochammina (trochospiral) occurs in abundance with either one of the following: 1) Miliammina (quinqueloculine) associated with carbonaceous shale, interpreted as the marsh; 2) Ammobaculites (uncoiled) and estuarine ostracodes associated with shelly mudstones, interpreted as the central, muddy estuary; and 3) Verneulinoides and Textularia (serial) associated with gray mudstones, interpreted as distal estuary (open bay). The marsh represents 0–1 m water depth and this approximates absolute mean sea level, the central estuary represents 5–8 m water depth, and the distal estuary (open bay) represents water depths of 10 m or greater. Alternations between foraminiferal associations in a 25-m section of the upper middle Turonian Smoky Hollow Member, Straight Cliffs Formation, indicate sea level amplitude changes that ranged from 1–10 meters.

Revision of the ostracode genus Fossocytheridea Swain and Brown 1964: Mesozoic ancestral root for the modern eurytopic Cyprideis Jones

Abstract The ostracode genus Fossocytheridea Swain and Brown 1964 is emended herein. A summary of the diagnostic characters include: (1) a median sulcus, (2) a tripartite antimerodont hinge with distinct heart-shaped terminal elements, (3) distinct sexual dimorphism; (4) a narrow inner margin that has 20–28 straight radial pore canals, and (5) variability in the external carapace (pore shape, pore density, and patterns of reticulation) that bears close resemblance to Cyprideis. Two new species are described from southwest Utah (U.S.A): Fossocytheridea mosbyense sp. nov. and Fossocytheridea kirklandi sp. nov. and 21 taxa previously assigned to Fabanella, Sarlatina, Ovocytheridea, Dolocytheridea, Antibythocypris, and Cytheridea are assigned to the emended genus. Fossocytheridea resembles Cyprideis with respect to both shell morphology and ecology since it occurs in association with euryhaline biota in coal-bearing strata. Expansion of marginal marine environments during the highest sea level of the Mesozoic saw Fossocytheridea successfully migrate and dominate restricted coastal environments. Since this expansion, the prominent characters of Fossocytheridea have been preserved in descendent genera belonging to the tribe Cyprideidini Kollmann 1960 that are preserved to this day in Cyprideis.

Unconformities and age relationships, Tongue River and older members of the Fort Union Formation (Paleocene), western Williston Basin, U.S.A.

An unconformable relationship is observed within the Paleocene Fort Union Formation in the western Williston Basin at the contact between the Tongue River Member and the underlying Lebo and Ludlow Members. Isotopic dates and pollen biozone data reported here are integrated with previously published data. A new correlation of these facies results in a revised history of localized depositional and tectonic events. One unconformity occurs at this lithological contact in the Pine Hills (PH), Terry Badlands (TB), and Ekalaka (E) areas west of the Cedar Creek anticline (CCA), and another unconformity occurs at the same lithological contact in the Little Missouri River (LMR) area east of the CCA. The two unconformities differ in age by about two million years. The older is the U 2 and the younger is the U 3 , which initially were recognized in the Ekalaka area of southeastern Montana (Belt et al., 2002). The U 2 crops out in the TB, PH, and E areas, where at least 85 m of Tongue River strata bearing palynomorphs characteristic of biozone P-3 are found above the unconformity. Radiometric dates from strata (bearing palynomorphs characteristic of biozone P-2) below the U 2 range in age from 64.0 to 64.73 Ma. The U 2 unconformity west of the CCA thus occurs in strata near the base of the lower P-3 biozone. The U 3 crops out in the LMR area (east of the CCA), where only 13 m of strata characterized by the P-3 pollen biozone occur above it. Radiometric dates from an ash <1 m above the U 3 in that area range in age from 61.03 to 61.23 Ma, and the P-3/P-4 pollen biozone boundary is located 13 m above the ashes. The U 3 thus occurs in strata characterized by upper parts of the P-3 pollen biozone east of the CCA. The U 3 is also identifiable in the middle of the ca. 200 m-thick Tongue River Member west of the CCA, where mammal sites 40 to 80 m above it are Tiffanian-3 in age. The strata below this unconformity are tilted gently to the northwest; strata above the unconformity are flat lying. This mid Tongue River unconformity probably correlates with the unconformity at the base of the Tongue River Member in the LMR area east of the CCA, where a Ti-2 mammal site (the “X-X” locality) occurs <10 m above it. Depositional and tectonic events can be summarized using North American Mammal Age nomenclature as a relative time scale. From latest Cretaceous through Puercan time, paleodrainage was toward the east or southeast, in the direction of the Cannonball Sea. The Black Hills did not serve as an obstruction at that time. During early Torrejonian time, the Miles City arch (MCA) and Black Hills were uplifted and partially eroded, leading to the U 2 unconformity. When deposition resumed, paleodrainages shifted to a northeasterly course. During middle and late Torrejonian time, facies of the lower Tongue River (“Dominy”) sequence and the Ekalaka Member of the Fort Union Formation were

DEPOSITIONAL CONSTRAINTS ON THE LOWER CRETACEOUS STIKES QUARRY DINOSAUR SITE: UPPER YELLOW CAT MEMBER, CEDAR MOUNTAIN FORMATION, UTAH

Abstract: A new mass death assemblage in Lower Cretaceous strata of east-central Utah contains well-preserved skeletons representing an ontogenetic series of individuals of Utahraptor, and at minimum two iguanodont grade ornithischian skeletons. The dinosaurs were entombed in ovoid-lensoidal, fine-grained sandstone sills linked by sandstone pipes and/or dikes and another basal lensoidal mass with scattered and broken iguanodont and sauropod bones and to an underlying gravelly sandstone bed. Exposed in the excavation high-walls are syndepositional normal-faults bounding graded ripple strata. Multiphased fluid over-pressurization in an artesian setting creating the structures. Trapping, killing, and subsequent burial mechanism was generated by variations of pressure in a localized artesian spring system that breached the surface and is the first such mechanism documented with numerous dinosaur victims.