Cobble Beaches Along The Coastlines Of The Georgian Bay Islands

Abstract

<p> This report is the only detailed study concerning the fresh water cobble beaches of the Georgian Bay Islands. It includes extensive studies on the morphological characteristics, especially the platform development and profile configuration, and the sedimentary provenance of the cobbles. </p> <p> It was found that the platform configuration (step topography) acts as a substrate control for the cobble beaches. The presence of two cobble generations, angular and well-rounded, indicate that t he shore platform is the source for these cobble beaches. </p> <p> The roundness values of these cobble generations depends on t heir mode of transport. Evidence indicates that longshore movement of cobbles increases their roundness values, but their angular shape i s indicative of their lack of transport. </p> <p> Very little proof was found within this study to correlate relict cobble beaches with any specific stage of the Lake Huron Basin, although it was possible to generalize and state that the relict cobble beaches were generated by high-energy wave events during the transition from the Algoma stage to Lake Huron. </p> <p> Clast analysis determines the relationship between the length of the wave fetch and its related energy environment. It was found that high-energy coastal environments have oblate cobbles with a high roundness and low sphericity. In each case, the samples were associated with a large fetch. Those cobbles of a low-energy coastal environment have a high sphericity, low roundness, and are associated with smaller fetches. </p> <p> The steepness of the beach profile results from the increase in wave height, generated by an increase in shallowness. It also depends upon the volume of backwash. The backwash is reduced by the increased percolation rates through the cobbles, thus reducing the combing down effect of the backwash. </p> <p> This study also provides a discussion on the minor morphological features such as sinkholes and imbrication. </p>