Origin of megarhythms in flysch sequences of the Quebec Appalachians

Abstract

The cyclic and positive sequences observed in the External Domain of the Quebec Appalachians between L'IsIet and Grosses Roches have been interpreted as facies of deep-sea fans that result from progradation. In these conglomerate-bearing sequences, the composition of the detritus changes up-section, which suggests that uplift of the source area played an important role in their vertical evolution. In early and (or) Middle Cambrian time, the source consisted of sedimentary, igneous, and metamorphic terranes. This provenance was rejuvenated in Late Cambrian – Early Ordovician time, and the Lower – Middle Cambrian shelf wa.s uplifted. The stratigraphic evolution of composition observed in these flysch sequences cannot be explained by deep-sea fan progradation.In recent years the general trend in flysch-sequence analysis has been away from tectonic and towards sedimentological interpretations. The stratigraphic evolution of flysch sequences may be due to both tectonic and sedimentary processes. Studies of rock composition, generally neglected by most workers, could be used to make the distinction.