Abstract

A newly discovered molluscan fauna provides an approximate age for a previously undated gravel sequence capping Nose Hill, a relict plateau adjacent to the Bow River in Calgary, Alberta, and constrains the age of the physiographic relief in the area. The fauna consists of a mixed terrestrial–aquatic assemblage whose composition indicates a paleoclimatic regime similar to that of the area today. The fossiliferous sediment, interpreted as a pond deposit, is a pebbly mud within a thick braid-plain gravel sequence. Isoleucine epimerization in the molluscs is not inconsistent with an Early Pleistocene or older age for the deposit. The Nose Hill gravels and an equivalent sequence capping another outlier (Broadcast Hill) located on the other side of the Bow River define an originally extensive paleo-plains surface. Fluvial dissection of the surface, including 175 m of incision by the Bow River and resultant separation of the two outliers, occurred within the last one to two million years.

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