. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] ESTUARIES, DELTAS, SHELF, SLOPE 629 this book). In the coastal marshes and estuaries bordering the North Sea from Zeeland to the Elbe mouth, the combination of subsidence and eustatic shifts of sea-level has resulted in most complicated stratigraphy. The marine deposits related to the last two interglacial periods, which are referred to as the Hol- steinian (or Needian) and the Eemian deposits (Woldstedt, 1950), are depressed under the marshes, while they stand as subaerial terraces in coastal areas where no subsi
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] ESTUARIES, DELTAS, SHELF, SLOPE 629 this book). In the coastal marshes and estuaries bordering the North Sea from Zeeland to the Elbe mouth, the combination of subsidence and eustatic shifts of sea-level has resulted in most complicated stratigraphy. The marine deposits related to the last two interglacial periods, which are referred to as the Hol- steinian (or Needian) and the Eemian deposits (Woldstedt, 1950), are depressed under the marshes, while they stand as subaerial terraces in coastal areas where no subsidence occurs. During the last 10,000 yearsâthe Holoceneâthe follow- ing strata were laid down in order (Fig. 7): a layer of peat (the lower peat), deposited before the post-glacial sea-level was high enough to reach these countries; the older tidal flat deposits and marine clays, deposited behind barrier beaches; the upper peat, which may tentatively be related to a fall of sea-level by a few metres after the post-glacial climatic optimum; and young .Young dunes sand bars Young marine cloy. X A A '^ â ^ X X ^ Pleistocene sand Lower peat Fig. 7. Diagrammatic section through tlie Holocene deposits of Holland. (Simplified from Pannekoek, 1956.) marine clays and sands, resulting from the fact that the small lowering of sea- level was finally surpassed by the subsidence, which led to invasions of the peat bogs by the sea. Such alternations of marine and terrestrial deposits, with peat layers in the sub-surface, have morphological consequences in the coastal marshes (see below). If we consider now the processes acting today, we must describe separately the deltas, the estuaries and the related marshes. a. Deltas Deltas (see, for example, Russell and Russell, in Trask, 1955) consist of a complex of distributary channels, natural levees bordering the channels, and shallow lakes or swamps lying between them at a slightly lower level. The coarser elements are concentrated in the chann
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