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Eustatic and Neotectonic Controls on Salt Marsh Sedimentation

by Jonathan R. French, Univ Coll London, London, United Kingdom,



Document Type: Proceeding Paper

Part of: Coastal Sediments

Abstract:

This paper presents a revised conceptual model of the long-term evolution of back-barrier marshes on the macro-tidal north Norfolk coast and their adjustment to tidal levels. The present suite of salt marsh deposits has apparently evolved since 2-3000 B.P. under effectively stable eustatic sea level and quasi-linear subsidence at approximately 1mm yr¹. With the aid of a numerical simulation model, calibrated against age/elevation data for 9 marshes, two 'characteristic' sedimentation scenarios are envisaged: 1) Neotectonic control, with marsh surfaces attaining a static absolute elevation determined by subsidence and sediment supply, and 2) Eustatic control, with marsh surfaces attaining equilibrium with both subsidence and changing tide levels such that (assuming linear eustatic rise) absolute marsh surface elevation continues to increase at a constant rate. Simulations using published eustatic sea level projections derived from global warming models suggest that even with no corresponding increase in sediment supply, sedimentation on these macrotidal marshes is capable of maintaining their ecological function - albeit at slightly lower surface elevations relative to tidal levels. It is suggested that under the more probable scenarios of future eustatic sea level rise, on-shore migration of associated barrier structures may be a more important mechanism for salt marsh loss than 'drowning' in a vertical dimension.

Subject Headings: Tides | Sediment | Sea level | Numerical models | Simulation models | Salts | Land subsidence

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