The origin of metalliferous argillites in the Shoal Arm Formation of north-central Newfoundland
The Middle Ordovician Shoal Arm Formation, which is located in the central volcanic belt of north-central Newfoundland, is a tripartite assemblage of hematitic argillites, grey cherts, and black shales directly underlying a flysch sequence. The hematitic argillites are enriched in Fe, Mn, Ni, Pb, an...
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Scholars Archive
1992
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| Online Access: | https://scholarsarchive.library.albany.edu/cas_daes_geology_etd/16 https://scholarsarchive.library.albany.edu/context/cas_daes_geology_etd/article/1015/viewcontent/bruchertmstxt.pdf |
| Summary: | The Middle Ordovician Shoal Arm Formation, which is located in the central volcanic belt of north-central Newfoundland, is a tripartite assemblage of hematitic argillites, grey cherts, and black shales directly underlying a flysch sequence. The hematitic argillites are enriched in Fe, Mn, Ni, Pb, and Co. Factor analysis and principal component analysis indicate the presence of a hydrothermal component, presumably derived from hydrothermal activity in the coeval Lawrence Head volcanics. Unusual, (?) calcareous Mn-Fe-oxide nodules are present in the top parts of turbidites in the hematitic argillites. Electron microprobe analysis of a color transition from a red to a green argillite indicates fractionation of Mn from Fe by diagenetic mobilization of Mn and subsequent precipitation as Mn-carbonate in adjacent green, calcareous argillites. The detrital component of the Shoal Arm Formation is influenced by several, geochemically different, clastic sources. The top part of the Shoal Arm Formation is characterized by a Zr-, Nb-, and Y-rich clastic component that may reflect either erosion or volcanic activity of lateral equivalents of the Lawrence Head volcanics. The hydrothermal component disappeared with erosion of these volcanics. The overlying grey, mottled and laminated cherts reflect a biogenic bloom, which preceded euxinification of the depositional basin. Synchronous and diachronous depositional models are proposed to explain the tectonic history of the Shoal Arm Formation. The synchronous model emphasizes the high biological productivity and limited circulation in a restricted basin as the cause for the observed euxinification. The diachronous model explains the black shale facies with a prograding, deep-water anoxic layer that developed during rapid basin subsidence as the result of thrust-loading. In this model, the black shales were deposited in front of flysch sediments derived from a southeastward prograding thrust stack. The Middle Ordovician Taconic sequence of New York (i.e., the upper part of the ... |
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