5. Westboro Beach
Stromatolites, orthocones and trace fossilS
Westboro Beach
Kichi Zībī Mīkan, Ottawa, Ont.
Bumps on the exposed surface of the limestone outcrop are the tops of fossilized domal stromatolites.
Photo by Q. Gall.
Stromatolite domes (colonies of cyanobacteria) grew at least 20 cm above the surrounding Ordovician seafloor (bottom of scale card).
Photo by Q. Gall.
Stromatolites are biosedimentary structures built up during sedimentation by cyanobacteria. Layers were built up as the cyanobacteria grew up through successive depositions of lime muds to create rounded, domed structures. At Westboro Beach, the bedrock shows vertical cross-sections through these fossils. These stromatolite limestones are part of the Ordovician Pamelia Formation, and can be correlated with the stromatolite limestone on the Quebec side of the Champlain Bridge (STOP 4). Orthocone fossils and trace fossils can be seen in the limestone stair steps.
Block of stromatolitic limestone showing vertical evolution (upward) from small to larger domes. Top of block shows circular plan sections through a few stromatolite domes.
Photo by Q. Gall