2.6.1: Sources of sediments deposits

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Judith Bosboom & Marcel J.F. Stive
Delft University of Technology via TU Delft Open

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These lecture notes focus on depositional coastal environments. With that we mean coastal environments consisting of soft or loose material (mainly sand or mud) that has been deposited there at some point in the past. At present these materials might be subject to either erosion or accretion due to the impact of waves and tides. The loose material is present in the form of shorefaces, beaches and accompanying dunes and barriers. Besides by dunes, the beach can also be backed by rocky material. The loose material that we find on our coasts can have various origins. We can distinguish between continental sediments and carbonate sediments:

Continental sediments are the major type of sand of the coastal area and are formed from weathered continental rock, usually granite. They are composed of silicate minerals, with quartz and feldspar being the most abundant. Quartz is very resistant, feldspar easily weathers into fines. Granite and basalt are also the source of heavy minerals (with a density larger than quartz). Streaks and patches of dark coloured grains – rich in heavy minerals – can be found of on some beaches. The larger part of continental sediments found in coastal deposits is not from current rivers but consists of older Holocene sediments or Pleistocene sediments reworked during the Holocene by marine processes.

Carbonate sediments form of calcium carbonate. Most of these grains are fragments of shells or remains of marine life. Marine carbonates are the second major source of sands to the coast.