Cold seeps, where seepage of hydrocarbon-rich fluids occurs in the sea floor, are sites that harbor highly specialized ecosystems associated with distinctive carbonate sediments. Although their Mesozoic record is scarce and patchy, it commonly includes dimerelloid rhynchonellide brachiopods. Here we report a monospecific assemblage of Anarhynchia from a limestone boulder of early Pliensbachian (Early Jurassic) age in the Inklin Formation of the Whitehorse Trough in the Stikine terrane, from a locality at Atlin Lake in northern British Columbia. Specimens are among the largest known Mesozoic brachiopods, up to 9 cm in length, and described here as Anarhynchia smithi n. sp. Early precipitated carbonate cement phases of the limestone have carbon isotopic composition highly depleted in 13C, indicative of the influence of microbial oxidation of methane derived from a cold seep. Carbonate petrography of the banded-fibrous cement and other characteristic components supports this paleoenvironmental inference. Volcanogenic detrital grains in the matrix are indistinguishable from those in the sandstone layers in the siliciclastic sequence, suggesting that the seep carbonate is broadly coeval with the enclosing conglomerate. The new record extends the geographic range and species-level diversity of the genus, but supports its endemism to the East Pacific and membership in chemosynthesis-based ecosystems. The distribution of three distinct but congeneric species suggests that allopatric speciation occurred at separate sites along the active margin of western North America and Anarhynchia was restricted to seep and vent habitats in the Early Jurassic.
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Research Article|
November 06, 2017
A new occurrence of the Early Jurassic brachiopod Anarhynchia from the Canadian Cordillera confirms its membership in chemosynthesis-based ecosystems1
József Pálfy;
a
Department of Geology, Eötvös Loránd University, Pázmány Péter sétány 1/C, Budapest, H-1117 Hungary.b
MTA–MTM–ELTE Research Group for Paleontology, POB 137, Budapest, H-1431 Hungary.Corresponding author: József Pálfy (email: palfy@elte.hu).
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Zsófia Kovács;
Zsófia Kovács
b
MTA–MTM–ELTE Research Group for Paleontology, POB 137, Budapest, H-1431 Hungary.c
Institute of Earth Sciences, University of Graz, Graz, Austria.
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Gregory D. Price;
Gregory D. Price
d
School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, UK.
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Attila Vörös;
Attila Vörös
b
MTA–MTM–ELTE Research Group for Paleontology, POB 137, Budapest, H-1431 Hungary.
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Gary G. Johannson
Gary G. Johannson
e
Coastal Geological Consulting Ltd., RR1, Van Anda, BC V0N 3K0, Canada.
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Canadian Journal of Earth Sciences (2017) 54 (12): 1179–1193.
Article history
received:
28 Aug 2017
accepted:
28 Sep 2017
first online:
13 Dec 2017
Citation
József Pálfy, Zsófia Kovács, Gregory D. Price, Attila Vörös, Gary G. Johannson; A new occurrence of the Early Jurassic brachiopod Anarhynchia from the Canadian Cordillera confirms its membership in chemosynthesis-based ecosystems. Canadian Journal of Earth Sciences 2017;; 54 (12): 1179–1193. doi: https://doi.org/10.1139/cjes-2017-0179
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Index Terms/Descriptors
- Articulata
- Brachiopoda
- British Columbia
- C-13/C-12
- Canada
- Canadian Cordillera
- carbon
- carbonate rocks
- chemical composition
- cold seeps
- isotope ratios
- isotopes
- Jurassic
- Lower Jurassic
- Mesozoic
- microstructure
- morphology
- new taxa
- North America
- North American Cordillera
- O-18/O-16
- oxygen
- paleoecology
- petrography
- Pliensbachian
- Rhynchonellida
- sedimentary rocks
- shells
- stable isotopes
- Stikinia Terrane
- taxonomy
- Western Canada
- Copper Island
- Atlin Lake
- Inklin Formation
- Peregrinellidae
- Anarhynchia smithi
Latitude & Longitude
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