Abstract

Enigmatic calcareous microfossils that belong to the Ovummuridae Munnecke, Servais, and Vachard, 2000 are present in ten cores through the upper part of the Escarpment Formation and Alexandra Formation in the Hay River area of the Northwest Territories, Canada. These Late Devonian (Frasnian) siliciclastic, mixed carbonate– siliciclastic, and carbonate ramp deposits accumulated on the western margin of Laurussia. Finding ovummurids in these deposits is significant because it provides the first formal documentation that these microorganisms existed in the Devonian and confirms that the stratigraphic range of the family extends from the Lower Silurian to Upper Permian. The microfossils, which are of unknown biological affinity, include Minourella gotlandica, previously known only from Silurian strata, Ovummurus duoportius, and Minourella cameroni sp. nov. The preservation potential of these microfossils was markedly enhanced by thick cement overgrowths, akin to the syntaxial overgrowths that are common on Paleozoic crinoid fragments. The distribution of ovummurids in these ramp deposits is significant because it demonstrates that ovummurids were capable of inhabiting turbid, likely nutrient-enriched marine environments, with significant siliciclastic influx, that were unsuitable for most other carbonate-secreting organisms in the Paleozoic.

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