The development of stratification in vegetated coastal sand dunes, Sable Island, Nova Scotia

Abstract

<p>Sable Island is the emergent portion of Sable Island Bank, located on the edge of the continental shelf about 200 km from the mainland. The island is made up of wide, flat beaches, overwashed spits, brackish and freshwater ponds and vegetated and unvegetated sand dunes. The dunes are organized into a fairly continuous north ridge which is punctuated by blowouts and a less continuous south ridge which ring the island's main body and are vegetated predominantly with Ammophila breviligulata and a variety of woody species of the Shrub Heath community. The spits are covered with low hummock dunes vegetated primarily with Honkenya peploides. A description of the stratification within the dunes provides a basis for an interpretation of the processes operating throughout their history. Particular importance is attached to the role of vegetation because each plant community has an associated set of structures which are the signature of deposition within, around, and in the lee of that group of plants. These sedimentologic signatures are combined to create a sequence which describes the history of deposition in the dunes. Distinct sequences are presented for morphologically different dunes. There are two types of foredunes, which develop in place, that have their own sequence of sedimentologic signatures. Three types of dunes develop from the migration of dune ridges over an area. Of particular importance on Sable Island are the parabolic dunes which move through the body of the island on a west-northwest to east-southeast axis. The structures in the dunes can be used to help explain the surface morphology.</p>