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TitlePaleoenvironmental changes across the Carnian/Norian boundary in the Black Bear Ridge section, British Columbia, Canada
 
AuthorOnoue, T; Zonneveld, J P; Orchard, M JORCID logo; Yamashita, M; Yamashita, K; Sato, H; Kusaka, S
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 441, pt. 4, 2016 p. 721-733, https://doi.org/10.1016/j.palaeo.2015.10.008
Image
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20160090
PublisherElsevier BV
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
NTS94B/03
AreaWilliston Lake; Nabesche River; Black Bear Ridge; Peace Reach
Lat/Long WENS-123.0833 -123.0000 56.0833 56.0000
Subjectsstratigraphy; paleontology; paleoenvironment; Carnian; Norian; isotope ratios; limestones; strontium strontium ratios; isotopic studies; carbon isotopes; oxygen isotopes; thermal alteration; diagenesis; Upper Triassic; conodonts; Triassic
ProgramGSC Pacific Division
AbstractThe Black Bear Ridge section in northeastern British Columbia, Canada, consists of a continuously exposed sequence of Upper Carnian through Lower Norian (Upper Triassic) continental margin strata. The section has been proposed as a candidate Global Stratotype Section and Point (GSSP) for the Carnian/Norian boundary (CNB). In order to assess Late Carnian to Early Norian environmental changes recorded in the section, we examined stratigraphic variations in 87Sr/86Sr, d13C, and d18O values, and also values of redox sensitive elements (V, Ni and Cr), in the CNB interval. The study section is located along the north shore of Williston Lake, northeastern British Columbia. The Black Bear Ridge section was deposited in a distal ramp environment on the passive western margin of the North American craton.
The strata across the CNB display a positive shift in d13C values and a corresponding increase in the redox indices V/(V + Ni) and V/Cr. The synchronous increase in d13C values and redox indices suggests that burial rates of marine organic carbon increased in response to the development of anoxic conditions in the water column. An increase in d13C values in carbonate rocks across the CNB has also been reported from Upper Triassic sections in the western Tethys (e.g., in the Pizzo Mondello section, Sicily), which suggests that the development of anoxic conditions within the CNB interval was widespread, affecting both the Panthalassan Ocean and Tethyan Sea. The geochemical data from this study, as well as from research into conodont biostratigraphy in the Black Bear Ridge section, show that the onset of oceanic anoxic conditions may have been responsible for the faunal turnover event at the CNB. The cause of this anoxic event is unknown, but the 87Sr/86Sr and d13C isotope data largely exclude the possibility that the event was triggered by dissociation of methane hydrates and degassing related to large-scale volcanic activity.
Summary(Plain Language Summary, not published)
The Black Bear Ridge section in northeastern British Columbia, Canada preserves a sequence of marine strata deposited on the western margin of the North American craton that has been proposed as a global reference for the Carnian/Norian stage boundary (CNB) of the Upper Triassic timescale. In order to assess environmental changes at the boundary, stratigraphic variations in strontium, carbon, and oxygen isotopes and other elements were studied. The results suggest that burial rates of marine organic carbon increased in response to the development of anoxic conditions in the water column at that time. Similar results reported from Upper Triassic sections in the Europe suggests that the development of anoxic conditions were widespread, and may have been responsible for the faunal turnover event identified at the CNB. The cause of this anoxic event is unknown, but the geochemical data excludes large-scale volcanic activity as an explanation.
GEOSCAN ID298852

 
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