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The Lower Cambrian Forteau Formation, southern Labrador and Great Northern Peninsula, western Newfoundland: Lithostratigraphy, trilobites, and depositional setting.
Swedish Museum of Natural History, Department of Paleobiology.ORCID iD: 0000-0001-7366-7680
2017 (English)Report (Other academic)
Abstract [en]

The upper Lower Cambrian Forteau Formation in southern Labrador and the Great Northern Peninsula (GNP) is a successionof shale, limestone, siltstone and sandstone accommodated by rising sea levels during the early drift stages ofNewfoundland’s Laurentian passive margin. Its Dyeran trilobite fauna, characterized by Elliptocephala logani (Walcott, 1910)that ranges throughout the formation, indicates it was mostly deposited in the middle Bonnia‒Olenellus Zone. Its three lithostratigraphicdivisions, the Devils Cove member, Middle shale and Upper limestone, preserve a transgressive system tract(TST; Devils Cove and lower part of the Middle shale) and the early stages of a regressive high-stand system tract (HST; upper Middle shale and Upper limestone) that hosts a carbonate ramp shelf.A mudstone-dominated succession characterizes the TST, comprised of an inner belt of archeocyathid patch reef andcyclic, well-stratified, fine-grained mixed clastic and carbonate shelf rocks in southern Labrador. To the southeast on the GNP,the shale succession along with minor limestone and no reefs suggests a deeper water shelf basin in which shale accumulated across the GNP. Maximum flooding on the GNP is linked to dark shale midway through the basinal succession, and to athick shale bed that overlies the reefal strata in Labrador.Thin-bedded siltstone, sandstone and limestone in Labrador, and extensively bioturbated siltstone, sandstone and rare limestone on the GNP, support a shelf shallowing above storm-wave base as it prograded during the early stages of regression. Shallow-water carbonate of the Upper limestone supports a prograding shelf, at first dominated by an archeocyathid reefal tract and oolitic shoal complex. The reef tract and carbonate sand shoal complex prograded southeastward to justbeyond the northeast-trending Ten Mile Lake–Long Range fault system. Evidence of slumping in the underlying fine clastic sediment in the same area suggest that this fault zone may coincide with a hinge zone, beyond which the shelf steepened intomostly deep-water clastic sedimentation. The archeocyathid tract in southern Labrador is a broad biostromal complex confined within an erosional recess in the shelf. On the GNP, however, the tract is characterized by high-energy bioherms associated with crossbedded grainstone channels that can be traced for over 60 km along a northeast strike length. East of the reef tract‒shoal complex, the succession appears to be dominated by deeper water shelf mudrock, nodular carbonate and little evidence of shallow-water carbonate facies. The facies transition suggests the Forteau Formation insouthern Labrador and the GNP was laid down in a high-energy shallow-water, inner ramp setting that was up to 75 km wide. Above the carbonate sand shoal complex, the succession is marked by decametre-thick parasequences of intercalated carbonateand clastic intervals. The sequences support a shelf of fine grained to grainy carbonate deposited on an open shelframp overlain by intervals dominated by coarsening upward high-energy siliciclastics that suggest barrier complexes alongthe landward margin of the ramp. Thick units of crossbedded quartz arenite, in the upper half of the Upper limestone, suggest terrigenous sediments initially encroached along the inner part of the shelf, and eventually smothered the Forteau shelf leading to the low-stand deposits of the overlying Hawke Bay Formation. Trilobites recovered from this transition throughout the GNP, indicate that it occurred very late in the upper part of the Bonnia‒Olenellus Zone, likely between the Bristolia mohavensis Biozone and the top of the zone.

Place, publisher, year, edition, pages
St. John's, 2017. , 72 p.
Series
Government of Newfoundland and Labrador, Department of Natural Resources, Geological Survey, St. John’s, Occasional Papers, 2017-01
National Category
Natural Sciences
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-2497OAI: oai:DiVA.org:nrm-2497DiVA: diva2:1154734
Available from: 2017-11-03 Created: 2017-11-03 Last updated: 2017-11-03

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http://www.nr.gov.nl.ca/nr/mines/geoscience/publications/reports/Occasional_Papers_2017-01.pdf

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