Sedimentology, stratigraphy and calcretes of the Comrey Member, Oldman Formation (Campanian), Milk River Canyon, Southeastern Alberta

Abstract

The Comrey Member in the Milk River Canyon, southeastern Alberta, is composed of poorly consolidated pale yellowish-olive gray and reddish-brown fine- to mediumgrained sandstones and intraformational conglomerates with minor greenish-gray shale horizons. Sedimentary structures include trough, low-angle (<10°), and planar (>10°) cross-stratification, ripple cross-lamination, and horizontally stratified sandstones. Erosional scour surfaces with calcareous mudstone intraclasts define broad, asymmetric, concave upward lenses indicating multistoried channels without confining banks. Calcrete hardpans and calcrete derived nodules are common throughout the member but are absent from adjacent stratigraphic intervals. The above indicates that the Comrey Member was deposited in a low-sinuosity fluvial system subject to flash floods in a semi-arid coastal plain environment. Paleocurrent data suggests northeasterly paleoflow. However, westerly paleoflow at the easternmost locality and sigmoidal cross-stratification containing tidal bundles in the central study area indicate a marine incursion.