Academic literature on the topic 'Ammonoidea - Canada, Western'

The thin-shelled pteriid bivalve Halobia is widely distributed in Upper Triassic (Carnian-mid Norian) marine strata throughout the circum-Pacific region with significant occurrences along the western and arctic margin of North America, northeast Russia, China, Japan, Indochina, islands of the western Pacific, and New Zealand. Halobiids are commonly associated with deep water, black shale facies typically devoid of macrobenthos. This facies occurrence and a thin-shelled, flat-valved morphology suggests an autecology (possibly pseudoplanktic) in contrast to modern benthic pteriids. High speciation and extinction rates of halobiids not only provide an excellent means for dating rocks lacking ammonoids, but they give an independent view of rapidly evolving lineages during Carnian-Norian time.A composite halobiid succession with nearly complete coverage from the earliest Carnian through the late mid Norian is constructed from numerous North American sequences and localities with ammonoid control. Although differences in nomenclature rather then endemism make correlation of the North American succession with other circum-Pacific regions difficult, similar (and quite possibly homologous) morphologies allow limited correlation between these regions. The early Carnian is typified by H. zitteli, which occurs in predominantly boreal strata of Canada and Siberia. By later Carnian time, a variety of similar morphotypes (probably conspecific) belonging to subspecies of H. superba, H. radiata, and several other species are known throughout the circum-Pacific. The earliest Norian Kerri ammonoid zone is recognized by the first appearance of H. beyrichi in North America, and H. styriaca in Asia. In North America and the rest of the circum-Pacific, the latter part of the early Norian is marked by a rapid diversification of forms, including H. cordillerana and H. fallax. By late mid Norian time diversity reached a maximum 5 species. The mid Norian species H. fallax, H. halorica, and H. plicosa are particularly wide-spread; they occur throughout the circum-Pacific where they coexisted with the earliest Monotis. As in the Alpine-Mediterranean region, the remaining halobiids went extinct by the end of the mid Norian.Halobiid speciation and extinction rates exceed other Late Triassic macrofauna except ammonoids. The average North American species duration is fewer than three ammonoid zones (ca. 2.5 MY). The late early Norian is a period of pronounced diversification, whereas the middle early Norian and late middle Norian are times of accelerated extinctions. Instead of catastrophic extinction at the Carnian-Norian boundary, North American halobiids exhibit complex taxonomic turnover. Similar diversity patterns are recognizable in other circum-Pacific halobiid sequences.

The Upper Triassic of the Williston Lake area of northeastern British Columbia is represented by a nearly continuous series of fossil-rich sediments that were deposited in the Western Canadian Sedimentary Basin in an offshore mid-paleolatitude setting on the western margin of cratonic Pangea. The fossils in this report come primarily from the upper Carnian–upper Norian Pardonet Formation, which has been the subject of numerous paleontologic studies on ammonoids and conodonts, yet has received little attention with regard to its bivalve fauna. Fossil bivalves belonging to the thin-shelled bivalve genera Halobia, Eomonotis, and Monotis dominate the benthic macrofauna and occur within unique shell accumulations that are interpreted to represent oxygen-controlled monospecific paleocommumities that have undergone little post-mortem transportation. Systematic analyses of more than 1,000 individual bivalve specimens resulted in the identification of 25 species-rank taxa, a majority of which belong to the pterioid genus Halobia and the pectinoid genera Eomonotis and Monotis. Of these, four new species are recognized, including 1) upper Carnian Halobia tozeri n. sp. characterized by a unique triangular outline; 2) lowermost Norian Halobia selwyni n. sp. closely related to H. beyrichi and first appearing with H. austriaca which is proposed as a potential datum for the Carnian–Norian boundary; 3) Norian Meleagrinella mclearni n. sp., a new name for previously identified species; and 4) upper Norian Otaparia norica n. sp. which has a delicate thin shell, unique outline, and fine ornament. A revised and refined biochronology of Upper Triassic Bivalvia (chiefly Halobiidae and Monotidae) integrated with conodont and ammonoid zones and standard Triassic stages is presented for the Upper Triassic of the Williston Lake area and permits enhanced correlation to coeval faunas elsewhere in the North American Cordillera, and to the Boreal, Panthalassan and Tethyan faunal realms.

Ammonite species of the genera Prionocyclus, Subprionocyclus, and Collignoniceras described here from the Cardium Formation, in combination with scaphitid ammonoids and inoceramid bivalves, allow recognition of all biozones for the Turonian Stage (Upper Cretaceous) established farther south in the United States Western Interior Basin. Although many of the species used in this zonation were endemic to the Western Interior seaway, more cosmopolitan forms at some levels do allow correlation with western European sequences. The presence of Prionocyclus germari Reuss is firmly established in the lower parts of the Leyland Member, confirming the position of the Turonian-Coniacian boundary and earlier proposed constraints on the duration of the Cardinal–Leyland hiatus.

While the Cardium Formation (Turonian–Coniacian, Upper Cretaceous) is one of the major hydrocarbon sources, and consequently one of the most intensely studied siliciclastic formations in the Western Canada Sedimentary Basin, it remains one of the more controversial units in terms of understanding the depositional environments and processes it represents, and correlations between subsurface and outcrop. Proposed subsurface subdivisions based on sequence stratigraphic concepts, and relation of these allomembers to long-established members of the outcrop belt, have provoked further disagreements. The general lack of biostratigraphic data within the Cardium Formation makes it difficult to test different models and to resolve conflicting proposals. This paper provides stratigraphic and taxonomic information on all known scaphitid ammonoids from the Cardium Formation and correlation of these faunas with the Turonian and Coniacian zonal scheme established in the United States Western Interior; future publications will provide similar treatments of the collignoniceratid ammonites and inoceramid bivalves.

Most species of the middle and late Hettangian psiloceratid genusSunrisitesare endemic to the eastern Pacific, where they are common members of ammonoid assemblages. the Taseko Lakes map area in British Columbia yields diverse and well-preservedSunrisitesfaunas which are formally described here for the first time. Three new species are recognized,S. brimblecombei, S. chilcotinensis, andS. senililevis.the new species require an extension of the morphological range of the genus to include forms that become moderately involute at large shell diameters. Signs of sexual dimorphism are apparent within all three new species ofSunrisites.This work extends the stratigraphic range ofSunrisitesto include the latest Hettangian Rursicostatum Zone in North America. The distribution ofSunrisitessuggests that the Hispanic Corridor, which linked the western Tethyan Ocean and the eastern Pacific, may have been open during the Hettangian. Furthermore, occurrences of the genus constrain the Hettangian position of several allochthonous terranes to the northeastern Pacific.

The Upper Devonian (Frasnian) conodont fauna of the Lime Creek Formation of north-central Iowa is dominated by species of Polygnathus. Patterns of species composition and abundance are consistent with the Polygnathus biofacies described from the Frasnian of the Northwest Territories of western Canada. Consequently, the standard Frasnian conodont zones, defined on sequences developed in the Palmatolepis biofacies, are not applicable to the Lime Creek sequence. The Lime Creek conodont sequence correlates with Zones 4, 5 and Faunal Interval 7 of the Frasnian conodont sequence in the Alberta Rockies and with similar sequences in the southwestern United States. The Pb elements of Palmatolepis semichatovae Ovnatanova and Ancyrognathus? deformis (Anderson) are described and illustrated for the first time.In the Lime Creek Formation of north-central Iowa, brachiopods of the lowermost part of the Nervostrophia thomasi Zone of Day (1989a) occur in Zone 4, brachiopods of most of the N. thomasi, Douvillina arcuata, and Cyrtospirifer whitneyi Zones span conodont Zone 5, and the Elita inconsueta and Iowatrypa owenensis Zones occur in Faunal Interval 7. Species of the ammonoid Manticoceras and of the gastropods Floyda, Turbonopsis, and Westerna are restricted to Faunal Interval 7. Species of the calcareous foraminifer Nanicella first occur in Zone 5, and are joined by species of Multiseptida high in Zone 5.