Facies development of a Late Ordovician mixed carbonate-siliciclastic ramp proximal to the developing Taconic orogen: Lourdes Formation, Newfoundland, Canada |
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Authors: | Kelly L Batten Hender George R Dix |
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Institution: | (1) Department of Earth Sciences and Ottawa-Carleton Geoscience Centre, Carleton University, Ottawa, ON, K1S 5B6, Canada;(2) PDI Production Inc, Suite 201, 10 Fort William Place, St. John’s NL, A1C 1K4, Canada |
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Abstract: | The Upper Ordovician (late Whiterockian to Mohawkian) Lourdes Formation represents a narrow (tens of kilometers), short-lived
∼5–7 million years (my)], open-ocean (high-energy) mixed siliciclastic-carbonate ramp that onlapped allochthonous strata
along the orogen side of the local Taconic foreland basin. Platform development followed a 6–8 my hiatus during which weathering
had concentrated chemically mature siliciclastics that were admixed with initial carbonate sediments. A cross-platform facies
gradient contains paleokarst and peritidal carbonates and sandstones, shallow-ramp carbonate bioherms and skeletal shoals,
and deeper ramp calcareous shales. Transgressive systems tracts are marked by ramp-wide sheets and shoals of skeletal grainstone
and low accumulation rates, and highstand systems tracts are marked by significant admixture and interbedding of siliciclastics
with cross-ramp carbonate facies. Platform demise coincides with increased siliciclastic input, which is likely tectonically
influenced. The Lourdes platform is equivalent to epicontinental foreland ramps along eastern Laurentia, but its narrower
width precluded formation of oceanographically restricted platform-interior facies. |
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Keywords: | Mixed siliciclastic-carbonate facies Tectonics Lourdes Formation Upper Ordovician Newfoundland |
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