Geology and sedimentology of the Upper Devonian Escuminac Formation, Québec, and evaluation of its paleoenvironment: lacustrine versus estuarine turbidite sequence

Authors

  • Reinhard Hesse Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada
  • Hemdat Sawh Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada

DOI:

https://doi.org/10.4138/1867

Abstract

The Escuminac Formation of-the Upper Devonian Miguasha Group at the western end of Chaleurs Bay, Québec, famous for its fossil fish fauna, is a turbidite sequence whose environment of deposition has been a matter of debate. Interpretations vary with different authors between lacustrine or brackish to coastal marine. It is possibly of estuarine origin. Its total stratigraphic thickness of 117 m has been divided into eight lithostratigraphic units on the basis of vertical changes in sands tone: shale ratio. A lacustrine setting is feasible in view of the association with fluvial formations below (Fleurant Formation) and above (Bonaventure Formation), although these are separated by a disconformity or an angular unconformity from the Escuminac. The lack of any shelly marine invertebrate fauna is negative evidence indirectly favoring a lacustrine origin. Periodically stagnant bottom-water conditions evidenced by the preservation of laminites are compatible with a lake environment. The fossil fish fauna, however, contains elements which point toward brackish or marine environments. Geochemical evidence also seems to support brackish conditions, although it is not clear to what extent the geochemical signature may have been inherited from older marine detrital clays. A silled estuary would best accommodate the different lines of evidence, but poses problems of fitting into the broadscale paleogcographic picture of the Upper Devonian Old Red Continent. RÉSUMÉ La Formation d'Escuminac du Groupe de Miguasha du Dévonien supérieur, dans la partie ouest de la baie des Chaleurs, Québec, célèbre pour sa faune de poissons fossile, est une séquence de turbidites dont l'environnement de déposition a fait l'objet de discussions. Les interprétations varient suivant les différents auteurs entre lacustre ou saumatre à marin côtier. C'est possiblement d'origine estuarienne. Son épaisseur totale de 117 m a été divisée en huit unités lithostratigraphiques sur la base de variations verticales dans le rapport grès:shale. Un milieu lacustre est possible en regard de l’association avec les formations fluviatiles en-dessous (Formation de Fleurant) et au-dessus (Formation de Bonaventure), bien qu'elles soient séparées de l’Escuminac par une inconformité ou une discordance angulaire. L'absence de toute faune marine invertébrée à coquille est un argument négatif favorisant indirectement une origine lacustre. Des conditions d'eau de fond périodiquement stagnante, indiquées par la préservation de laminites, sont compatibles avec un environnement de lac. La faune de poissons fossile, cependant, contient des éléments qui pointent vers des environnement saumatres ou marins. Les données géochimiques semblent aussi appuyer des conditions saumâtres, bien qu'il ne soit pas clair jusqu'à quel point la signature géochimique ait pu être héritec d'argiles marines plus anciennes. Un estuaire endigué accomoderait le mieux les diverses données, mais rencontre des difficultés à s'incrire dans le cadre paléogéographique à grande échelle du continent Old Red du Dévonien supérieur. [Traduit par la journal]

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Published

1992-11-01

How to Cite

Hesse, R., & Sawh, H. (1992). Geology and sedimentology of the Upper Devonian Escuminac Formation, Québec, and evaluation of its paleoenvironment: lacustrine versus estuarine turbidite sequence. Atlantic Geoscience, 28(3). https://doi.org/10.4138/1867

Issue

Vol. 28 No. 3 (1992)

Section

Articles

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