Abstract
Following the first description of living marine stromatolites along the South African east coast, new investigations along the south coast have revealed the occurrence of extensive fields of actively calcifying stromatolites. These stromatolites have been recorded at regular distances along a 200-km stretch of coastline, from Cape Recife in the east to the Storms River mouth in the west, with the highest density found between Schoenmakerskop and the Maitland River mouth. All active stromatolites are associated with freshwater seepage streams flowing from the dune cordon, which form rimstone dams and other accretions capable of retaining water in the supratidal platform. Resulting pools can reach a maximum depth of about 1 m and constitute a unique ecosystem in which freshwater and marine organisms alternate their dominance in response to vertical mixing and the balance between freshwater versus marine inflow. Although the factors controlling stromatolite growth are yet to be determined, nitrogen appears to be supplied mainly via the dune seeps. The epibenthic algal community within stromatolite pools is generally co-dominated by cyanobacteria and chlorophytes, with minimal diatom contribution.
Highlights
The first extant marine tufa stromatolites along the southern African coast were described in the early 2000s from Cape Morgan[1,2] and later investigated in some detail from a geochemical and geomorphological point of view[3]
The closest type to those discovered on the southeast coast of South Africa are the tufa deposits recently reported from the southwest coast of Western Australia[8] and from the Giant’s Causeway of Northern Ireland[9]
In Australia, most tufa formations are associated with inland spring discharges, whereas the South African types are all upper intertidal to supratidal in position, with strong and regular marine influence
Summary
The first extant marine tufa stromatolites along the southern African coast were described in the early 2000s from Cape Morgan[1,2] and later investigated in some detail from a geochemical and geomorphological point of view[3]. Southern African tufa stromatolites are regarded as unique in their nature, because they typically occur at the interface between freshwater seepage points and the marine penetration.[3] The closest type to those discovered on the southeast coast of South Africa are the tufa deposits recently reported from the southwest coast of Western Australia[8] and from the Giant’s Causeway of Northern Ireland[9].
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