BROGLY, P.J., and MARTINI, I.P., Department of Land Resource Science, University of Guelph, Guelph, Ontario, N1G 2W1, pmartini@uoguelph.ca; and MIDDLETON, G.V., Department of Geology, McMaster University, Hamilton, Ontario, L8S 4M1, middleto@mcmail.cis.mcmaster.ca.

The Upper Ordovician Queenston Formation constitutes the westernmost part of the Taconic clastic wedge of eastern North America. In Ontario, the Queenston Formation consists of a clastic-carbonate mixed succession composed primarily of red silty shale, locally gypsiferous, alternating, in the middle and lower parts of the formation, with thin gray shales and beds of calcareous siltstone and sandstone and bioclastic-rich units. Brachiopoda, some ostracoda and, in the lower beds, bryozoa constitute the body fossil association. Diplocraterion, Scolithus, Chondrites and an occasional large vertical burrow of unknown origin form the ichnofauna. Ripple marks, and occasional swaley and hummocky cross-stratifications are present in calcareous units. Mudcracks, gypsum nodules, occasional halite hopper casts, small local anticlinal, gilgai- like structures typically occur in interval where shales alternate with siltstone and sandstones. In southernmost Ontario, the upper part of the formation is composed by a featureless red shale interval. These features are indicative of prograding muddy shores. Possible continental settings may be represented in the uppermost part, by a featureless, thick red shale interval, which is truncated by the unconformity separating the Ordovician from the Silurian units in this region. This last feature may be in part relatable to eustatic sea-level drop due to the comtemporaneous Saharan glaciation.