Sedimentation and stratigraphy of part of the Rice Lake Group, Manitoba

Abstract

The extrusive and volcanic-derived sedimentary rocks of the Rice Lake Group, Manitoba, have been subdivided into eight formations. These units are named and identified here for the first time. Sedimentary rocks within the lower part of the group were deposited in a rapidly subsiding basin, with syn-depositional volcanic activity. Three lithofacies have been delineated within the group. They outline the proximal, transitional, and distal facies. These three are persistent throughout the stratigraphic column. Their stratigraphic persistence shows that volcanic activity was localized and consistent throughout the history of the basin... Primary sedimentary structures typical of turbidites occur throughout the lower part of the stratigraphic sequence and indicate that the major mechanism of deposition was by turbidity currents... Differentiation of the parent magma at depth is reflected in both the volcanic products, and in the upward increase in the percentage of detrital quartz in the derived sand-sized sediments. Welded tuffs and agglomerate clasts close to one source show that deposition was at least in part subaerial during the late stages of basinal development... Sources of sedimentary material can be delineated from the paleocurrrent pattern, changes in lithology, and clast size variations. Two possible volcanic sources have been located in this manner. Correlation of the sediments and volcanic rocks in the vicinity of Rice Lake area with those of the Beresford Lake area is very tenuous... However, the stratigraphic succession in each locality is quite similar, and a tentative correlation is proposed.