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A marine origin for the late Mesoproterozoic Copper Harbor and Nonesuch Formations of the Midcontinent Rift of Laurentia
Citation
Jones, SM and Prave, AR and Raub, TD and Cloutier, J and Stueken, EE and Rose, CV and Linnekogel, S and Nazarov, K, A marine origin for the late Mesoproterozoic Copper Harbor and Nonesuch Formations of the Midcontinent Rift of Laurentia, Precambrian Research, 336 Article 105510. ISSN 0301-9268 (2020) [Refereed Article]
Copyright Statement
© 2019 Elsevier B.V. All rights reserved.
Official URL: https://www.sciencedirect.com/science/article/pii/...
DOI: doi:10.1016/j.precamres.2019.105510
Abstract
The c. 1.1 Ga Copper Harbor and Nonesuch Formations of the Keweenawan Supergroup exposed along the
Canadian-United States shorelines of Lake Superior are part of the surface exposures of the Laurentian
Midcontinent Rift. These units have long been considered non-marine in origin and have figured prominently in
ideas regarding the evolution of microbial life and the redox conditions of Earth’s ocean-atmosphere system at
the close of Mesoproterozoic time. However, these rocks also host hydrothermal metal deposits, the emplacement
of which may have compromised primary geochemical signals that are used to underpin those ideas. Here
we highlight new sedimentological observations to provide an independent framework for assessing the depositional
setting and geochemistry of those strata. We show that the totality of sedimentological features leads
to the conclusion that parts of the upper Copper Harbor Formation and the entirety of the Nonesuch Formation
were deposited along tide- and wave-influenced shorelines and in shallow-marine settings under evaporitic
conditions. Evidence for this interpretation includes the abundance of flaser, wavy, linsen and pinstripe bedding,
ubiquity of reactivation surfaces and mud drapes associated with all ripple forms, superposed sets of ripple crosslamination
showing bimodal (herring-bone) sediment transport directions, desiccation cracks and metre-scale
hummocky cross-stratification. Further, evaporite fabrics and pseudomorphs after gypsum in the upper 200m of
the Copper Harbor Formation and in numerous stratigraphic positions within the Nonesuch Formation indicate
that the water body was saline, not fresh. The emerging palaeogeographic image is one of a large, shallowmarine
embayment with fringing sabkha-like shorelines. Ideas about late Mesoproterozoic biospheric evolution
and Earth’s surface redox and oxygenation that rely on the Nonesuch Formation and Copper Harbor stromatolites
having been deposited within a lacustrine setting require reassessment.
Item Details
Item Type: | Refereed Article |
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Keywords: | Midcontinent Rift, Keweenawan Supergroup, Copper Harbor Formation, lacustrine, Nonesuch Formation, Mesoproterozoic |
Research Division: | Earth Sciences |
Research Group: | Geology |
Research Field: | Stratigraphy (incl. biostratigraphy, sequence stratigraphy and basin analysis) |
Objective Division: | Mineral Resources (Excl. Energy Resources) |
Objective Group: | Mineral exploration |
Objective Field: | Copper ore exploration |
UTAS Author: | Cloutier, J (Mr Jonathan Cloutier) |
ID Code: | 136679 |
Year Published: | 2020 |
Web of Science® Times Cited: | 3 |
Deposited By: | CODES ARC |
Deposited On: | 2020-01-14 |
Last Modified: | 2020-04-30 |
Downloads: | 0 |
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