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TitleCool eastern rim of the north Pacific during Late Cretaceous time: a seep-carbonate paleothermometry from the Nanaimo Group, British Columbia, Canada
AuthorJenkins, R G; Hasegawa, T; Haggart, J W; Goto, A S; Iwase, Y; Nakase, C
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 487, 2017 p. 407-415, Open Access
logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170274
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92F/15; 92F/16
AreaHornby Island
Lat/Long WENS-125.0000 -124.0000 50.0000 49.7500
Subjectssedimentology; craters; carbonates; carbonate mounds; intertidal environment; intertidal zones; carbon isotopes; oxygen isotopes; paleotemperatures; methane; gas seeps; depositional environment; paleoenvironment; Northumberland Formation; Nanaimo Group; Phanerozoic; Mesozoic; Cretaceous
Illustrationslocation maps; photographs; tables
ProgramGSC Pacific Division
Released2017 09 28
AbstractA crater-shaped carbonate body newly recognized in the uppermost Northumberland Formation (Nanaimo Group) of the Canadian Pacific coast, is identified as a remnant of methane seepage during latest Campanian time in the northeastern Pacific region. A two meter-long elliptical mound with central concavity is found on a Cretaceous bedding plane observed at Hornby Island, British Columbia, exposed on an expansive intertidal platform. Microstructures characteristic of carbonate associated with methane seepage are readily observed
within the rock body and indicate it was formed near the sediment-water interface. Carbon isotope values of the carbonate range between - 45.5 and +4.9 (permil), where the lowermost values characterize anaerobic oxidation of biogenic methane as the primary process that controlled the carbonate precipitation. Oxygen isotope values also exhibit a wide range of values, from -9.8 to +0.6 (permil). Areas preserving features of earliest precipitation (i.e., radiaxial bladed calcite and micrite with clotted fabric) on cross-sections exhibit the highest delta18O values and indicate a paleotemperature 8.0 ± 0.7 °C for seawater at the seafloor. Development of cool water on uppermost bathyal or outer shelf depths in the northeastern North Pacific is thus implied during the Campanian- Maastrichtian transition. This paleotemperature determination shows a significant variance with those obtained from similar paleo-water depths of the northwestern North Pacific.
Summary(Plain Language Summary, not published)
The authors have studied a locality of sedimentary rocks of Late Cretaceous age, about 72 million years old, preserved on Hornby Island in the Strait of Georgia, British Columbia. Isotopic geochemical analysis of the rocks at the locality show that the sediments were deposited in relatively cool (approximately 10dC) bottom waters of the Late Cretaceous ocean at the time. This temperature contrasts with temperatures from similar rocks deposited at the same time in the NW Pacific region (Japan), where the water at the sea-bottom was approximately 15dC. The authors explain this variation as a result of oceanic circulation patterns in the North Pacific region during Late Cretaceous time.

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