Intertidal flat sediments and their environments of deposition in the Wash

Abstract

The Wash is an area of extensive intertidal-flat sedimentation. Seven sub-environments of deposition can be distinguished on part of the Lincolnshire coast. They are roughly parallel to the coastline and are, from landward to seaward: the salt marsh; higher mudflats; inner sand flats; Arenicola sand flats; lower mud flats; and lower sand flats. Cutting across these is the sub-environment of creeks and bordering areas. Each sub-environment is characterized by distinctive surface features, associations of organisms and sediments with differing composition, texture, and sedimentary structures. The sediments contain small amounts of calcium carbonate, organic matter, and iron concentrated in the finer-grained sediments. They also contain small amounts of feldspar and heavy minerals. The tidal waters decrease in competency and capacity as they move inland over the intertidal zone, depositing sediments that decrease in grain-size when traced from low- to high-water mark. Secondary agents such as waves and organisms modify this simple arrangement. The deposits of each sub-environment are thought to develop as sheet-like units over these to seaward, the creek and bordering region units cutting across them perpendicularly to the shore. The floors of the North Sea and the Wash and the eroding boulder-clay cliffs and adjacent sea-floors, of Lincolnshire to the north and Norfolk to the east, are thought to be the chief sources of the sediments.