Relations Between Sedimentary Facies and Diagenesis in Frenchman Formation (Maestrichtian) of Southern Saskatchewan: ABSTRACT

The Frenchman Formation of southern Saskatchewan is a fluvial deposit which ranges in thickness from only a few meters to over 70 m in a distance of about 50 km. The detritus was derived from the Cordillera mainly on the west and southwest. The rocks and sediments of the Frenchman Formation are arranged in fining-upward sequences, typically with the following arrangement of sedimentary facies from bottom to top of each sequence: large-scale trough cross-bedding in medium to coarse-grained silty sand; trough cross-bedding with individual sets topped by ripple lamination or parallel-laminated silt with plant remains; ripple cross-lamination in fine sand and silt; parallel-laminated fine-grained silty sand or alternating sand and carbonaceous material; interbedded purple, gr en, and silty clays. Single sequences are up to 40 m thick. The sands are interpreted as channel-fill deposits and the clays as overbank deposits; the ratio of channel to overbank deposits ranges from 0.2 to 5.3. Where exposures permit and the formation is thick enough, sand bodies can be traced for up to 4 km. However, some sands clearly are lenticular and persist in outcrop for less than 1 km. Many parts of the Frenchman sands are cemented with calcium carbonate and the distribution of the cement shows a close relation to the sedimentary facies. In the coarse-grained sands with large-scale cross-bedding, patterns of cementation have been influenced strongly by the anisotropy of permeability; preferred directions of cement development are parallel with the trough axes of cross-bedding a d parallel with the dip of foresets in cross-bedding, and cementation in such zones commonly occurs to the extent that an expanded fabric has developed. In the finer grained sands and silts, development of cements is related principally to the overall direction of bedding, and cements are concentrated in spheroidal concretions whose planes of maximum projection parallel the bedding. End_of_Article - Last_Page 831------------