Phytoplankton dynamics across the Ordovician/Silurian boundary at low palaeolatitudes: Correlations with carbon isotopic and glacial events

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Delabroye A, Munnecke A, Copper P, Tribovillard N, Joachimski MM, Desrochers A, Servais T., VECOLI, MARCO
• Other Authors: Delabroye, A, Munnecke, A, Vecoli, Marco, Copper, P, Tribovillard, N, Joachimski, Mm, Desrochers, A, Servais, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Ice Sheet
• Online Access: http://hdl.handle.net/11584/63806; https://doi.org/10.1016/j.palaeo.2011.09.011

The Late Ordovician culminated in a major glacial period that has been related to one of the strongest mass extinctions recorded during the Phanerozoic. During this interval, Anticosti Island (Quebec, eastern Canada) was located at low to intermediate palaeolatitudes (15-30 degrees S) on the eastern margin of Laurentia. It displays a relatively complete section across the Ordovician-Silurian (O/S) boundary. Upper Ordovician to Lower Silurian strata of Anticosti studied here comprise the Vaureal (Katian), Ellis Bay (Hirnantian) and Becscie (latest Hirnantian-Rhuddanian) formations. Phytoplankton dynamics inferred from the acritarch content of these strata are locally compared with new geochemical environmental proxies (delta(13)C), with recent palynological data from Baltica and also with phytoplankton dynamics as described from near-polar, high latitude localities of the Gondwana region. Two positive excursions of the carbon isotope record have been identified in the lower and upper Ellis Bay Formation. Overall, phytoplankton trends are as follows: (1) as with chitinozoans, conodonts, brachiopods and corals, acritarchs from Anticosti display a major turn-over during the early Hirnantian (uppermost Vaureal Formation-lower Ellis Bay Formation), with the appearance of taxa that exhibit Silurian affinities (e.g. Tylotopalla sp., Ammonidium sp., Oppilatala sp., Evittia sp., Dilatisphaera spp.). High polymorphism for some common taxa is observed in the interval corresponding to the first delta(13)C positive excursion. Using sequence stratigraphy, this period may be related to a first glacially driven sea-level drawdown corresponding to terrestrial ice-sheet growth on Gondwana, such as recorded in Morocco. (2) Subsequently, during the late Himantian of Anticosti (uppermost Ellis Bay Formation), phytoplanktic communities suffered a crisis, exemplified by the disappearance of several typical, large Late Ordovician taxa (i.e., Orthosphaeridium spp., Peteinosphaeridium spp., large Baltisphaeridum spp., Sacculidium sp.). ...