Wormer Member

NUNAWO

Formal (Weerts 2003).

Shell-bearing calcareous sands, dominant grain-sizes: 105-210 µm, coarse sand (210-420 µm) in tidal channel deposits. The sands alternate with thin silt and clay-layers, often showing disturbance of the layering by organisms such as molluscs and crustacea (bioturbation structures).

Back-barrier tidal basin behind an ‘open coast’. The open coast featured barrier islands separated by large inlets with ebb and flood-tidal deltas (Beets et al. 2000). The Wormer Member includes five main lithofacies units: sandy point bar deposits, sandy tidal flat deposits, mud flat deposits, supra-tidal flat and tidal marsh deposits, and clayey lagoonal deposits (Van Straaten 1963; De Mulder & Bosch 1982; Westerhoff et al. 1987; Ebbing et al. 2003; Vos & Van Kesteren 2000; Donselaar & Geel 2007).

In most places the Wormer Member overlies with a sharp, erosive contact the Basisveen Bed (Nieuwkoop Formation). Alternatively it overlies fine and coarse-grained Pleistocene sediments.

Usually characterized by a 1-2 m thick blue-grey coloured clay layer in the top, known (in Dutch) as ‘oude blauwe zeeklei’. The Wormer Member is overlain by peat (Hollandveen Member, Nieuwkoop Formation).

Up to about 15 - 20 m in tidal channels.

Widely distributed within the spatial distribution of the Naaldwijk Formation. In the northern Netherlands, particularly in the western part of the Wadden Sea area the unit is not distinguished (similar to the Walcheren Member). All Holocene tidal sediments in that area are interpreted to be ‘Naaldwijk Formation, not differentiated’.

UK: ?; GER: ?; BEL: ?

Holocene (Greenlandian - Northgrippian).

Named after the village Wormer.

Calais Deposits (Doppert et al. 1975), Lower Member A (De Mulder & Bosch 1982).

Wim Dubelaar (2018).

Beets, D.J., Van der Spek, A.J.F. 2000. The Holocene evolution of the barrier and the back-barrier basins of Belgium and the Netherlands as a function of late Weichselian morphology, relative sea-level rise and sediment supply. Geologie en Mijnbouw / Netherlands Journal of Geosciences 79 (1), 3-16.

De Mulder, E.F.J., Bosch, J.H.A. 1982. Holocene stratigraphy, radiocarbon dating and paleogeography of centra land northern North Holland (The Netherlands). Mededelingen Rijks Geologische Dienst 36 (3), 111-160.

Doppert, J.W.Chr., Ruegg, G.H.J., Van Staalduinen, C.J., Zagwijn, W.H., Zandstra, J.G. 1975. Formaties van het Kwartair en Boven-Tertiair in Nederland. In: Zagwijn, W.H., Van Staalduinen, C.J. (eds.): Toelichting bij geologische overzichtskaarten van Nederland. Rijks Geologische Dienst, Haarlem, 11-56.

Ebbing, J.H.J., Weerts, H.J.T., Westerhoff, W.E. 2003. Towards an integrated land–sea stratigraphy of the Netherlands. Quaternary Science Reviews, 22, 1579-1587.

Geel, C.R., Donselaar, M.E. 2007. Reservoir modelling of heterolithic tidal deposits: sensitivity analysis of an object-based stochastic model. Netherlands Journal of Geosciences - Geologie en Mijnbouw, 86 (4), 403-411.

Van Straaten, L.M.J.U. 1963. Aspects of the Holocene sedimentation in the Netherlands. Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig Genootschap. Geologische Serie, 21 (1), 149-172.

Vos, P.C., Van Kesteren, W.P. 2000. The long-term evolution of intertidal mudflats in the Northern Netherlands during the Holocene; natural and anthropogenic processes. Continental Shelf Research 20, 1687-1710.

Weerts, H.J.T. 2003. Beschrijving lithostratigrafische eenheid. Nederlands Instituut voor Toegepaste Geowetenschappen TNO. Utrecht.

Westerhoff, W.E., De Mulder, E.F.J., De Gans, W. 1987. Toelichtingen bij de Geologische kaart van Nederland 1: 50.000 Blad Alkmaar West (19W) en Blad Alkmaar Oost (19O). Rijks Geologische Dienst, Haarlem.