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GEOREF RECORD

An Ordovician "Lost City"; venting serpentinite and life oases on Iapetus seafloor

Denis Lavoie and Guoxiang Chi
An Ordovician "Lost City"; venting serpentinite and life oases on Iapetus seafloor
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (March 2010) 47 (3): 199-207

Abstract

Highly brecciated carbonate-rich serpentinites (or ophicalcites) of Early Ordovician age in the Dunnage Zone of Quebec are host to fracture-fill, high-temperature (80-230 degrees C) carbonate cements. Away from, or crosscut by the fractures, centimetre- to decimetre-thick crusts made up of massive to laminated micrite, peloidal layers and threads are associated with low-temperature botryoidal calcite cements. The peloidal masses are characterized by a clotted texture that is reminiscent of interpreted fossilized Ordovician microbial communities. The ophicalcite contains carbonate botryoids, morphology commonly found at shallow reefal margins but also at modern cold CH (sub 4) seeps and recently documented at hot CH (sub 4) vents from serpentinite, such as the modern Lost City hydrothermal field in the Atlantic Ocean. The delta (super 18) O (sub VPDB) ratios of the calcite botryoids and peloidal layers indicate formation and (or) precipitation out of cold Ordovician deep-marine waters. To the contrary of botryoids at cold methane seeps, the botryoids associated with the modern and Ordovician hot vents do not show the negative delta (super 13) C (sub VPDB) ratios indicative of microbial isotopic fractionation. Therefore, any microbial-derived HCO (sub 3) has been overwhelmed by the isotopically heavier marine-derived carbon during the open-system diagenesis. Carbonate-rich serpentinites should be carefully revisited in the search for evidence of microbial life in the Precambrian, as the negative delta (super 13) C (sub VPDB) ratios used as fingerprints of biological activity are not always reliable.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 47
Serial Issue: 3
Title: An Ordovician "Lost City"; venting serpentinite and life oases on Iapetus seafloor
Affiliation: Geological Survey of Canada, Quebec City, QC, Canada
Pages: 199-207
Published: 201003
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 44
Accession Number: 2010-062351
Categories: Igneous and metamorphic petrologyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N45°49'60" - N46°40'00", W71°12'00" - W70°15'00"
N47°49'60" - N48°34'60", W67°40'00" - W64°45'00"
Secondary Affiliation: University of Regina, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201034
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