|Title||Cool eastern rim of the north Pacific during Late Cretaceous time: a seep-carbonate paleothermometry from the Nanaimo Group, British Columbia, Canada|
|Author||Jenkins, R G; Hasegawa, T; Haggart, J W; Goto, A S; Iwase, Y; Nakase, C|
|Source||Palaeogeography, Palaeoclimatology, Palaeoecology vol. 487, 2017 p. 407-415, https://doi.org/10.1016/j.palaeo.2017.09.027 Open Access|
|Alt Series||Natural Resources Canada, Contribution Series 20170274|
|Media||paper; on-line; digital|
|Lat/Long WENS||-125.0000 -124.0000 50.0000 49.7500|
|Subjects||sedimentology; 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|
|Illustrations||location maps; photographs; tables|
|Program||GSC Pacific Division|
|Released||2017 09 28|
|Abstract||A 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.