Development of a braided-fluvial facies model for the Devonian Battery Point Sandstone, Québec

Abstract

Eight distinct facies have been defined in a 110 m thick section of the Lower Devonian Battery Point Sandstone near Gaspé, Québec. The first is a scoured surface overlain by massive sandstone with mudstone intraclasts. Facies A and B are trough cross-bedded sandstones, with poorly- and well-defined stratification, respectively. Facies C and D consist of large isolated, and smaller multiple, sets of planar cross-stratified sandstones, respectively. Facies E comprises large sandstone-filled scours, facies F comprises ripple cross stratified fine sandstones with interbedded mudstones, and facies G comprises sets of very low angle cross-stratified sandstones.The overall context of the Battery Point Sandstone, the presence of rootlets, and the abundance of trough and planar-tabular cross bedding, all suggest a generally fluvial environment of deposition. Analysis of the facies sequence and interpretation of the primary sedimentary structures suggest that channel development began by scouring, and deposition of an intraclast lag. Above this, the two trough cross bedded facies indicate unidirectional dune migration downchannel (vector mean direction 291°). The large planar tabular sets are associated with the trough cross bedded facies, but always show a large (almost 90°) paleoflow divergence, suggesting lateral movement of in-channel transverse bars. The smaller planar tabular sets occur higher topographically in the fluvial system, and the rippled silts and muds indicate vertical accretion. Because of the very high ratio of in-channel sandy facies to fine-grained vertical accretion facies, and because of the evidence of lateral migration of large in-channel bars, the Battery Point River appears to resemble modern braided systems more than meandering ones.