In the Western Netherlands, in the region to be denoted in a Holocene-geologicaI perspective as the perimarine fluviatile coastal plain (where the vertical space for fluviatile and related organic accumulation was offered by the local water-level rise induced by the Holocene sea-level rise), two small case-study areas were selected for a reconstruction of the paleoenvironmental evolution. This reconstruction has been based on extensive geological mapping, detailed paleobotanical analyses, and numerous radiocarbon dates from several sections. Apart from showing a much more detailed paleoenvironmental picture of the region than hitherto available, the results provide alternatives for several of the existing notions.

In the study areas fluviatile clastic beds (clay- and sand deposits) alternate with organic beds (Phragmites peat and wood peat, partially also detritus gyttja). The loamy top of the braided-river deposits at the base of this clay/peat alternation may have originated as a partly fluvial, partly eolian deposit and thus may be linked genetically with the river dunes that also occur abundantly at the base of the clay/peat alternation and at several places pierce through it (as so-called donken). Both the loam and the river dunes may be dated probably as Late-Weichselian cum early-Holocene. From c. 7400 BP the Holocene (ground-)water-level rise brought constantly moist conditions of a strongly varying nature to the region. After slow initial organic lacustrine deposition, Phragmites-peat accumulation, and precursory fluvial clay deposition, extensive fluvial deposi­tion of clay and sand took place in the middle-Atlantic in the whole region, in a so-called fluvio-lagoonal environment: per­manent open-water surfaces covered the area outside the outcropping river dunes and the wooded natural levees of the many small river branches. An important relative, perhaps partly also absolute water-level fall at c. 6100 BP caused the region to become covered by swamp forest (mainly Alnus swamp) and to a lesser degree Phragmites marsh. These swamp forests per­sisted at many places notwithstanding the continuation of the Holocene water-level rise, probably because of its gradual slowing down in the course of the Holocene. In the more seaward of the two study areas, wetter conditions created many lakes amidst the swamp forests. In these lakes organic (gyttja) accumulation took place, and from c. 5300 BP also clay deposition, in very quiet conditions (the so-called fluvio-lacustrine paleoenvironment). This late-Atlantic/early-Subboreal depositional phase (ending c. 4600 BP in the downstream study area) was followed during several centuries by an environment of closed swamp forest and Phragmites marsh. In the middle-Subboreal (from c. 4100 BP) extensive fluviatile depositional activity returned to the region with an environment much like the middle-Atlantic fluvio-lagoonal one. This phase and the final part of the foregoing phase show some synchrony with the marine depositional (transgressive) phases in the foreland, and this might indicate a temporary marine influence on the perimarine area; this contrasts with the situation in the Atlantic period, when there was no such synchrony. After the slowing down of the main fluviatile depositional activity in the region, around 3800 BP, shallow open-water conditions persisted for several centuries. The ultimate complete covering by swamp forest (mainly Alnus) first took place in the downstream study area, around 3300 BP, and only occurred in the upstream study area six centuries later. In the downstream study area, the local and temporary existence of open sites (with Umbelliferae) in the swamp forest may possibly be related to a temporary increase of the local Holocene water-level rise. The swamp forest persisted at least up to c. 2000 BP.

During the Atlantic and Subboreal evolution of the region, amidst the generally moist environment dry sites, suitable for prehistoric occupation, were offered by the outcropping Late-Weichselian/early-Holocene river dunes, the natural levees of the many small river branches in the middle-Atlantic and middle-Subboreal, and by the stream ridges (channel fills with levees) originating from these river branches. The arboreal vegetation of these dry sites consisted mainly of Quercus, Ulmus and Corylus, and some Tilia on the higher parts of the river dunes. Prehistoric wood cutting, occurring at intervals on these dry sites, seems to have been confined largely to Quercus. Marsh herbs occurring along the margins and at shallow places of the wet basins, and at open sites in the swamp forests, were among others Phragmites (and other hygrophilous grasses), Typha angustifolia, ferns, Scirpus (and other Cyperaceae), Alisma and Umbelliferae.

Legend for these drawings:

Ulmus = elm   Alnus = alder  Quercus = oak   Phragmites = reed

Part of Figure 43 (for whole drawing click here and choose normal size).
c. 6300 years ago.

Fluvio-lagoonal landscape with wooded levees of small river branches amidst waterlogged basins.
River dune outcrop at lower left (in all four pictures).

Part of Figure 50 (for whole drawing click here and choose normal size).
c. 4800-4900 years ago.

Still fluvio-lacustrine but the swamp forest islands have decreased in size due to the water level rise.

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