The Karst Geomorphology of Manitoulin Island

Abstract

<p>Manitoulin Island is formed of glacially-abraded dolomite and limestone bedrock widely exposed across the island. The dominant karst landform is dolomite pavement, its form strongly controlled by lithology and classified according to appearance and karren characteristics. Pavement was found to be most extensive and well developed on the Amabel Formation, which also featured a pitted littoral zone along the southern Lake Huron shore. The Fossil Hill Formation featured good pavement only on a limited number of sites .. Other carbonates had only very shallow, limited pavement due to presence of clay or silica rich insolubles, thin beds and frequent shale interbeds. Clint and grike karren forms were the most common on Manitoulin Island pavements. Grikes on these pavements were found to be on average 13 cm wide, 83 cm deep and 367 cm in length, with much variation across pavement types. Grike orientations were dominated by a 90° regional set, with sets at 60°, 1200 , 300 and 150° of secondary importance Investigation of the island's hydrogeology revealed that the main karst aquifer is divided in half by the Cabot Head Shale aquiclude. The northern aquifer is formed of less soluble carbonates and is dominated by fluvial surface drainage. The southern aquifer has developed in highly soluble dolomites and is dominated by holokarstic drainage, mainly diffuse, and several internally draining lakes. A lack of fluvial karst except some immature systems is attributed to few streams crossing the border between the two extremes of drainage type. There is little macro-karst except Mindemoya Cave, indicating there are limiting fa.ctors to karst development on Manitoulin including age since deglaciation, rock solubility and physiography. Tree density on alvars, a sparsE! parkland type vegetation, was examined on the pavemen.ts. Density was directly related to pavement type as a function of amount of debris in grikes which allows trees to take root. The impacts of deforestation likely enhanced erosion, resulting in the development of this type of vegetation. The relationship between hardness and specific conductivity for Manitoulin Island surfac4= and subsurface waters was established in this study. The wat.ers were found to have high hardness, similar to values on the Bruce Peninsula.</p>