Depositional Environments of Ireton Formation, Central Alberta

Abstract

In the Woodbend Group of central Alberta, shales of the Ireton Formation occupy the basinal areas between the Leduc reefs. Within the shales are thin limestone beds which can be traced as electric-log markers over large areas. These markers probably approximate time lines, and they show a distinct westward divergence from the Ireton-Nisku contact. Their stratigraphic behavior has allowed subdivision of the Ireton Formation into rocks typical of the three critical environments of deposition established by Rich (1951a). Studies of cores and well cuttings corroborated the conclusions about environment which were reached by the study of the stratigraphic behavior of the marker beds. The lithologies described by Rich for the unda, clino, and fondo environments are present in the Ireton. The sediments of the Ireton are composed of terrigenous clay transported over a shelf area in the east, combined with fine carbonate derived from the scattered reefs throughout the area. The carbonates of the Upper Ireton are indigenous to the shelf environment. The pattern of shifting environments indicates that the inter-reef area was filled progressively from east to west. The paleogeography of a restricted area during Woodbend time has been deduced in a generalized manner by the application of Rich's concepts.