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TitreNew molluscan and radiolarian fossil collections from Lower Cretaceous strata of southern British Columbia: Implications for basin depositional environments and biochronology
AuteurHaggart, J W; Carter, E S
SourceCanadian Paleontology Conference Proceedings no. 6, 2008 p. 28-29
Séries alt.Secteur des sciences de la Terre, Contribution externe 20080349
Réunion18th Canadian Paleontology Conference; Winnipeg, MN; CA; Septembre 19-21, 2008
Documentpublication en série
SujetsCrétacé inférieur; assemblages fossiles; distribution de fossiles; fossiles; sédiments marins; stratigraphie paléontologique; assemblages fauniques; milieu sédimentaire; Groupe de Jackass Mountain ; Bassin de Methow-Tyaughton ; Radiolarie; Radiolaires; Groupe de Taylor Creek ; Ammonites; paléontologie; Mésozoïque; Crétacé
ProgrammeDendroctone du pin ponderosa, Réponse géoscientifique pour le dendroctone du pin ponderosa
Résumé(disponible en anglais seulement)
New collections of molluscan fossils from the Lower Cretaceous Jackass Mountain Group (JMG) of the Tyaughton-Methow basins of southern British Columbia have provided the first definitive recognition of Aptian marine strata within the region. Other molluscan collections from JMG, in association with previous collections from the temporally-equivalent Taylor Creek Group (TCG), and have allowed development of a molluscan biochronology for marine strata of most of post-Hauterivian Early Cretaceous time of the Intermontane region of the Canadian Cordillera. In addition, radiolarian fossils collected from Albian strata of the basin are the first radiolarians to be reported from the Cretaceous Intermontane basins.

Strata exposed along the canyon of the Fraser River south of Lytton are assigned to the JMG and have yielded the heteromorph ammonite Shastoceras sp., within an assemblage of marine bivalves and other ammonites. The faunal assemblage and outcrop sedimentology suggest the strata bearing these fossils formed in shelf environments in the Methow-Tyaughton basin, in contrast to the submarine fan environment usually ascribed to the JMG. Shastoceras has been reported previously from the Aptian of northern California, where it is diagnostic of the stage, as well as the Russian Far East; it is also represented in unpublished collections from Queen Charlotte Islands, British Columbia. This is the first find of the genus in the Intermontane region of British Columbia, and the first definitive evidence of Aptian marine strata within the JMG. Barremian (possibly early?) fossils previously known from the JMG include the ammonites Ancyloceras (Acrioceras) sp., Shasticrioceras? sp., and Protetragonites, as well as belemnites. Early Albian fossils known from the TCG include the widespread ammonites Leconteites lecontei and Anagaudryceras sacya. Younger strata within the basinS are represented by the ammonite Cleoniceras (Grycia) cf. perezianum in the JMG and the TCG, suggestive of mid-Albian, while the ammonites Marshallites? and Desmoceras (Pseudouhligella) sp. from the TCG are suggestive of late Albian (to early Cenomanian?). Thus, a five-fold zonal succession for Barremian, Aptian, and Albian marine strata can be proposed for the basin.

Strata exposed near Mount Tatlow are assigned to the Beece Creek succession of the Taylor Creek Group and are temporally equivalent with Jackass Mountain Group strata but separated from them by the dextral strike-slip Yalakom fault. Marine fossils have not been collected previously from the Mount Tatlow section of the TCG, which has been interpreted as largely terrestrial to shallow-marine in origin. Nassellarian radiolarians collected from this section in 2007 include a single specimen of Dictyomitra, possibly D. montisseri or D. urakawaensis, and several specimens of Obeliscoites (?O. perspicus), and ?Crolanium. The faunal assemblage suggests the sample is probably no older than mid-Albian, nor younger than Cenomanian. The assemblage further indicates that these strata are or marine origin.