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TitleLocating the Carnian-Norian boundary in the Martin Bridge Limestone, Blue Mountains Province, Oregon: initial results of conodont biochronology and stable isotope geochemistry
AuthorAlbritton, C K; LaMaskin, T A; Lane, C; Orchard, M J; McRoberts, C
SourceGeological Society of America, Abstracts With Programs vol. 46, no. 5, 2014, 17 pages
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20140178
PublisherGeological Society of America
MeetingGeological Society of America, Rocky Mountain (66th Annual) and Cordilleran (110th Annual) Joint Meeting; Bozeman; US; May 19-21, 2014
Mediapaper; digital; on-line
File formatpdf
ProvinceBritish Columbia
AreaBlack Bear Ridge; Blue Mountains Province; Pizzo Mondello; Wallowa Mountains; northeastern Oregon; Canada; United States; Italy
Lat/Long WENS-122.0000 -116.0000 47.0000 44.0000
Subjectsgeochronology; paleontology; biostratigraphy; conodonts; biochronology; isotope geochemistry; stable isotope studies; carbon isotopes; Phanerozoic
ProgramWestern Arctic Sverdrup Basin, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Late Triassic period is one of the most poorly constrained time intervals in the Phanerozoic, lacking both a robust numerical chronology, and a well-defined stable isotope stratigraphy. Work is underway now to define a Global Stratotype Section and Point (GSSP) in British Columbia (Black Bear Ridge) or Italy (Pizzo Mondello) for the Carnian-Norian Boundary (CNB) using both halobiid clam and conodont biostratigraphy. We present new data from an age correlative section of the Martin Bridge Formation in the southern Wallowa Mountains of northeastern Oregon. The type locality of the Martin Bridge Fm. is an excellent location to further define the biostratigraphy and stable isotope stratigraphy of this important time interval, with implication for debate over a ¿long¿ or ¿short¿ Norian Stage. Lithologies consist predominantly of thin-bedded, laminated limestone interpreted to represent deep-marine calcilutite turbidity flow deposits interbedded with calcareous to carbonaceous Halobia-rich shale. Preliminary analysis of conodont elements, halobiid bivalves, and ammonoids collected near the base of the type section suggest an Upper Carnian age. We preliminarily identify Quadralella carpathicus, Q. nodosus, and Parapetella. n. sp. Q on the basis of comparison to conodont elements from the possible GSSP section at Black Bear Ridge. Ammonoids found in the lower half of the section include Tropites cf. T. nevadanus and Tropiceltites? sp.. Halobiid clams from the basal half of the type locality represent Halobia oregonensis. Age assignments for samples near the top of the section are underway. Whole-rock samples for C and O stable isotope analysis have been collected at the decimeter-scale across 30-m of strata. Initial results indicate a robust carbon-isotope signature using 350¿500 µg of powdered material. Existing global stable isotope data appear to show a consistent trend in d 13C starting at ~1¿ at the base of the Carnian, towards more positive values over most of Carnian time. By early Norian time values stabilize around ~4¿, a trend that has been attributed to a long-term increase in global organic carbon burial rates. Results of this study may provide a high-resolution record of stable isotope stratigraphy across the CNB and may help refine an important global correlation tool for Late Triassic time.
Summary(Plain Language Summary, not published)
This study of the Martin Bridge Formation in the southern Wallowa Mountains of northeastern Oregon aims to provide a high-resolution record of stable isotope stratigraphy across the Carnian-Norian stage boundary of the Late Triassic period. Integration of paleontology and geochemistry is provided and new conodont data is correlated with that from the British Columbia standard in order to locate the stage boundary.