a Closely-spaced set of parallel erosional grooves are described from the Ottawa Limestone. They are interpreted as originating in a similar manner to one type of modern spur-and-groove system found in some shallow-water carbonate bank, atoll, and reef areas. The grooves are formed by bottom scour produced by vigorous undertow, possibly as rip-currents, associated with the breaker zone of a shallow sloping shelf. A comparable paleoenvironment is envisaged for these Middle Ordovician structures, which are clearly of value as environmental and paleogeographic indicators.

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