Cap des Rosiers Formation at Grosses Roches, Quebec—deposits of the mid-fan region on an Ordovician submarine fan
Resedimented deposits in the Ordovician Cap des Rosiers Formation near Grosses Roches, Quebec, are arranged in fining-upwards sequences, each with conglomerate at the base, and argillaceous sandstones, or interbedded sandstones and shales at the top. The conglomerates are primarily cobble-grade, and are poorly sorted; graded bedding and clast imbrication are poorly developed, and internal stratification is uncommon. They pass upwards and laterally to pebbly sandstones and sandstones, most of which are massive, but which contain cross-stratification, parallel stratification, or dish structure in places. The sandstones are overlain by finer-grained sandstones with many load-deformation and water-escape structures and at the top of some sequences there are sandstone and siltstone turbidites. The presence of large sediment slabs and soft clasts in the conglomerates and sandstones, and of the abundant shale chips in the argillaceous sandstones, provides evidence of penecontemporaneous erosion. Load casts, flam...