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The stratigraphic and geochemical imprints of Late Ordovician glaciation onfar-field neritic carbonates, Anticosti Island, eastern Canada

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The storm-dominated, open marine neritic carbonate facies, continuously exposed in coastal cliffs and widerocky tidalflat exposures at the western end of Anticosti Island, form a 315-m-thick, expanded section spanningthe Ordovician-Silurian boundary. These carbonate facies display deepening-shallowing trends of different or-ders, resulting in a hierarchical stacking of sedimentary cycles. The carbonate facies within these multi-ordercycles represent sediments that were deposited from shoreline to deeper outer carbonate ramp (> 80 m in waterdepth) and exhibit sea-level changes of several tens of metres in magnitude. Field, petrographic and geochemicalevidence support a well-preserved primaryδ18O signal in close equilibrium with the original paleoenviron-mental conditions. Theδ18O intracycle variations, up to 1.0‰in magnitude, reveal repeated decreasing andincreasing values during the transgressive and regressive portions of decametre TR cycles respectively. Althoughtemperature, salinity, and ice volume influenced the recorded primaryδ18O signal, orbital scale glacioeustasyultimately controlled facies and cycle development andδ18O signal during the Katian immediately before thelatest Ordovician (Hirnantian) glaciation. The ~3.5 myr-longδ18O signal recorded by our entire successionsupports a protracted period of cooling leading into the main phase of latest Ordovician (Hirnantian) glaciation.Spectral analysis of theδ18O record also reveals decametre variations, which are associated with decametre scaletransgressive-regressive (TR) cycles; possibly reflecting eccentricity orbital signals. Our study shows the im-portance of a thick expanded stratigraphic succession sampled at the highest resolution possible to decipherpotential linkages between facies changes, multi-order stratigraphic cycles,δ18O signal and the Earth's orbitalparameters.
Tijdschrift: Palaeo
ISSN: 0031-0182
Volume: 543
Jaar van publicatie:2020
CSS-citation score:2
Toegankelijkheid:Open