Abstract

Detrital ooids, from 0.1 to 0.5 mm diameter, almost completely dominate two 0.3 m thick layers between one and two metres depth at a site in clay-size-rich, isostatically uplifted, glaciomarine, Champlain Sea sediments north of Gatineau, Quebec. The ooids, composed of layers of tangentially oriented, platy particles, are physical aggregations of glacially ground, rock flour with the identical mineral suite that constitutes the regional Champlain Sea sediments. The ooids are not cemented and there is no evidence of diagenetic formation of minerals. A hydrodynamic “hail-stone” model, which requires a somewhat turbulent sedimentary environment within the water column, probably created by wind–wave action that kept ooid nuclei in suspension while the flocculating effect of brackish to marine conditions induced particle accretion onto their surface, is proposed for their formation.

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