Montmorency Falls is located northeast of Quebec City in southern Quebec Province, se Canada. The waterfalls occurs at a major fault. Structurally, the cliff behind the falls has been uplifted, and the rocks in the foreground of the pic below have been downdropped and tilted. The water is falling over Precambrian gneisses (basement rocks). Thin intervals of steeply tilted Trenton Group limestones and Utica Shale occur downstream of the falls (not visible in the photo below). The dark, tilted rocks in the right foreground are basinal black shales of the Lotbinière Formation (Upper Ordovician), which are graptolitic at this locality.
Montmorency Falls (white area near center), cliff of Utica Shale (gray area to the southeast of falls), and Montmorency Promontory exposure (1st area with brown rocks upstream of bridge).
Satellite photo provided by DigitalGlobe & Google Earth.
Upstream of Montmorency Falls is a spectacular exposure of an ancient rocky shore. This is the best place to observe the Montmorency Promontory, a paleotopographic high. It consists of Precambrian gneisses with onlapping Ordovician sedimentary rocks. The Ordovician succession here is mostly shallow-water limestones. Some of the basal onlapping sediments are fills of Ordovician tidal pools.
Above & below: Precambrian gneiss of the Montmorency Promontory, a little upstream of Montmorency Falls, NE of Quebec City, Canada.
The gray limestone shown in the photo below is filling an Ordovician tidal pool developed in Precambrian gneiss. The limestone is a fossiliferous unit informally called the Solenopora gravels (Trenton Group, upper Middle Ordovician). Its name refers to the abundance of Solenopora fossils. Solenopora is an extinct genus of red alga (Rhodophyta, Solenoporaceae). Some of the Solenopora material at this locality is still red.
Note: “Solenopora” is not the correct generic assignment for fossil red algae at the Montmorency Promontory. The type species of Solenopora is from Estonia, and has been demonstrated to be an Ordovician chaetetid sponge. Some Paleozoic fossil red algae formerly assigned to Solenopora are now referred to as Graticula. Mesozoic fossil red algae formerly assigned to Solenopora need a proper generic assignment as well (see, for example, "Solenopora" jurassica from the Mesozoic of Britain).
Above: exposed stratigraphy upstream of Montmorency Falls. The Montmorency Promontory is Precambrian gneiss forming a rocky rapids in the river. Onlapping the Montmorency Promontory is a thin, discontinuous arkosic sandstone. Above that is upper Middle Ordovician Trenton Group fossiliferous limestones, the basal unit of which is the Solenopora gravels.
Above & below: “Solenopora” fossil red algae directly encrusting Precambrian gneiss. This was a rocky shore environment during the late Middle Ordovician.