The Eemian Stratotype Locality at Amersfoort in the Central Netherlands: a Re-Evaluation of Old and New Data

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79 (2/3): 197-216 (2000)

The Eemian stratotype locality at Amersfoort in the central Netherlands: a re-evaluation of old and new data

P.Cleveringa1, 2,T. Meijer1, R.J.W. van Leeuwen1, H. de Wolf1, R. Pouwer1, T. Lissenberg 1 & A.W. Burger 1

1 Corresponding author; e-mail: [email protected] 2 Netherlands Institute of Applied Geoscience TNO – National Geological Survey, PO Box 80015, 3508 TA UTRECHT, the Netherlands

Received: May 2000; accepted in revised form: 6 June 2000

Abstract

In order to obtain a better understanding of the infilling of the Saalian glacial basins during the Eemian, particularly following the recent research in the Amsterdam Basin (Terminal borehole), it was necessary to re-investigate the type locality of the Eemian at Amersfoort. Both published and unpublished data from various biota (diatoms, foraminifers, molluscs, ostracods, pollen) provide new information on the changing sedimentary environments during the Eemian. Although the organic and clastic sediments of the infilling represent nearly all the pollen zones, the sedimentary sequence at Amersfoort is discontinu- ous: four breaks at least are recognised at the type locality. The successive sedimentary environments and the breaks in the record are linked with the transgression of the Eemian sea, the topographic position at the margin of an ice-pushed ridge, and the changes in hydrodynamic conditions. Local conditions, such as a sandy sea bed, shallow water and a reduced water exchange near the North Sea margin, influenced the salinity of the basin. Rib counts of Cerastoderma edule shells indicate a higher salinity at the end of the Taxus (E4b) and the beginning of the Carpinus (E5) zones than that present in the modern North Sea. Local conditions were responsible for the higher salinity following the climate optimum. During the Abies phase (the later part of regional pollen zone E5), the sea level had already fallen. The change from eutrophic peat growth (with Alnus and Salix) to an oligotrophic Ericaceae/Sphagnum community at the end of the Eemian resulted from the change from a marine to a fresh-water environment, probably coherent with a deterioration of the climate.

Keywords: biostratigraphy, climate, Eemian stratotype, fauna, flora, lithology, palaeoenvironment, sea level

Introduction showed a more continuous sedimentary and biostrati- graphical record of the Eemian. Since an even more In 1961, Zagwijn investigated the palynology of the complete record of the stage became available in Eemian deposits in two boreholes drilled close to the 1997 from the ‘Terminal borehole’ in the Amsterdam town of Amersfoort (Fig.1) and proposed them as the Basin (Van Leeuwen et al., 2000 – this issue) it was stratotype of the Eemian stage in the Netherlands. considered necessary to re-evaluate the pollen and With the progressing 1:50,000 geological mapping, foraminifer-content of the type locality at Amersfoort. the knowledge of the Saalian glaciation – more pre- It was also necessary to supplement these analyses cisely the presence of deep glacial basins and their in- with old and new data on the diatom, foraminiferan, filling during the Eemian – increased (Jelgersma & mollusc, ostracod and pollen evidence. This was also Breeuwer, 1975). supplemented with some information on the heavy- Later investigations by Zagwijn (1983) demonstrat- mineral content of the sedimentary filling of the ed that boreholes from the Amsterdam Basin (Fig. 2) Amersfoort Basin.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 197 North Sea North Sea 100

100100 100

50 50

Amsterdam 25 50 Belgium Eem Germany 25 Amersfoort 2 100 Amersfoort Amersfoort 1

Amersfoort

Cleverg. 00ak-02

Fig. 2. The position of the Amersfoort Basin and the Amsterdam Basin in the Netherlands.

Rhine a deeply incised palaeovalley north of the sill. In the deeper part of the basin, south of the sill, a lake formed as a consequence of the rising groundwater table. After the sea level exceeded the height of the sill, Waal the lake evolved gradually into a lagoon. At that mo- Cleverg. 00ak-01 ment, the site of the Amersfoort-1 borehole, at a depth 0 10 km Ice-pushed ridge at surface of –25 m NAP, was still above sea level. Because of the Distribution Eemian marine clay in the Amersfoort Basin sill, the initial marine Eemian sediments were invari- Fig. 1.The Amersfoort Basin and the location of boreholes Amers- ably fine-grained clays and mud. As the sea level rose foort-1 and Amersfoort-2. and the water depth above the sill increased, wave energy became more and more important, however, al- Geological setting though the sediments were still fine-grained clays. On- ly at the margins and in front of the expanding lagoon, Eemian-stage sediments are common in the subsoil of could beaches and spits be formed. the western and northern Netherlands, where they were deposited in depressions of the glacier-moulded Results landscape over which the Eemian sea transgressed. Because of the slow but continuous tectonic subsi- Lithology dence of this region, these deposits have been preserved below the surface, at depths between approx. The lithology of the Eemian sediments in the Amers- 10 and 80 m below NAP (Dutch Ordnance Level = foort-1 and Amersfoort-2 boreholes represents the mean sea level). shallow-marine, marginal facies and thus deviates The Saalian (marine isotope stage 6: MIS 6) ice considerably from the sediments recorded in the cen- cap, which reached as far as the central Netherlands, tral part of the Amersfoort Basin (Zagwijn, 1961; de excavated deep basins surrounded by ridges of ice- Gans et al., 1987). As in the Amsterdam Basin (De pushed sediments. These basins are filled by Saalian Gans et al., 2000 – this issue), the sediments in the lacustrine sediments overlain by Eemian sediments of central part of the Amersfoort Basin consist of clays varying thickness, locally reaching over 50 m. Two (at least 30–40 m) overlain by about 25 m of marine boreholes (Fig. 1), which were proposed as the strato- sands. In the Amersfoort-1 borehole, however, the to- type locality, were put down at the margin of the tal Eemian succession, in which seven lithological Amersfoort Basin. This is the most central of the units are distinguished (Table 1), is about 15 m thick. glacial basins (Fig. 2). The Amersfoort Basin is bounded on its western, Pollen eastern and southern side by ice-pushed ridges. The development of the Eemian succession in the basin is The pollen zonation used in the present contribution basically similar to that of the Amsterdam Basin (De is based on Jessen & Milthers (1928), Zagwijn (1961) Gans et al., 2000 – this issue), both basins being sepa- and Zagwijn & Van Staalduinen (1975). A pollen dia- rated from the open sea by sills at depths of about gram from the recounted Amersfoort-1 borehole, with –40 m NAP.The rising sea flooded the basins through a restricted number of curves, is shown in Figure 3

198 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 Table 1. Lithological units of Eemian deposits in borehole Amers- In boring Amersfoort-2, high percentages of Carpi- foort-1 (borehole 32B119). Depths are indicated in meters below nus (30 %) are found in the sandy sediments below NAP (= Dutch Ordnance Level). L = lithological unit. the clay (Fig. 4), which confirms this local sedimenta- depth (m -NAP) lithology unit tion process during the Carpinus phase.This observa- tion will be discussed below. 25.01-24.44 gyttja, rich in carbonate, with Between –13.30 and –10.80 m NAP, trees decrease freshwater molluscs L1 and are replaced by herbs, in particular Chenopodi- 24.44-23.95 fine-grained organic-rich layer with aceae. This indicates a shift from a lagoonal environ- a brackish marine fauna L2 23.95-23.68 organic-rich sands L3 ment to higher mudflats and saltmarshes during the 23.68-22.60 clay-rich sands with shells L4 later part of the Carpinus phase (E5). Immediately 22.60-14.79 coarse sands with shells L5 above, the spectra with high values of Chenopodi- 14.79-10.51 clays and sandy clays with marine aceae, Alnus and then Salix reach their maximum val- shells, occasionally in living position L6 ues, indicating that the marine environment devel- 10.51-09.90 wood peat with some clays and silty oped into one of eutrophic to mesotrophic fresh- peat intercalations L7 water conditions. The boundary between pollen zones E5 and E6 at (Alnus is not shown); the figure shows also the pollen –10.51 m is drawn where the local vegetation (Salix zonation and the lithology. A striking difference be- and Alnus) becomes important, the clastic sedimenta- tween this new diagram and the older one of Zagwijn tion ceases (unit L7), and peat growth begins. During (1961) is the presence of Taxus in the former (Taxus the peat growth the nutrient availability changed. Af- is a taxon that could not be identified until the late ter a short period Gramineae, Sphagnum and Eri- 1960s). caceae became important taxa, indicating a eutrophic The pollen sequence in Amersfoort-1 begins in peat development changing rapidly into an olig- pollen zone E2, where the gyttja (unit L1) shows a otrophic one. In this oligotrophic peat, only Pinus and dominance of Pinus. This gyttja development con- Betula pollen were trapped. The replacement of the tinues in pollen zone E3, which is (from 24.75–24.44 deciduous forests by a boreal arctic tree vegetation in m) characterised by the presence of Quercus and Ul- pollen zone E6 is thus recorded. The cause of the rel- mus, whereas Corylus increases in the upper part of atively rapid transition from a brackish marine into a this zone. fresh-water environment will be discussed later. The first marine influence, at –24.44 m NAP (unit L2), is assigned to pollen zone E4a (maximum of Molluscs Corylus). In the upper part of this zone, Taxus is already present at low percentages (2–3%). At this Seventeen samples from the Amersfoort-1 borehole point, the accumulation of organic matter is replaced between –24.80 and –10.90 m NAP (units L1–L6) by clastic sedimentation (unit L3). During pollen zone have been investigated. Most of the shells encoun- E4b (Taxus phase), Carpinus appears and is present tered were very well preserved and are considered to at low percentages in the spectra from 23.85 m. The have been in situ or only slightly displaced. A consid- normal Taxus maximum, in which this tree reaches erable part (40–60%) of the assemblages consists of relative high percentages before the arrival of Carpi- juvenile specimens. All assemblages are indicative of a nus, is absent.The reason for this will be discussed be- temperate climate; the marine assemblages show high low. amounts of the lusitanian and mediterranean species In the sandy sediments of unit L5, between –22.60 already present in the first marine sample. Boreal or and –14.79 m, only one spectrum – containing very colder species are absent. few pollen – could be counted. It was assigned to Six units (M1.1–M1.6) are distinguished (Fig. 5). pollen zone E4b on the basis of the low percentage of 1 Unit M1.1 (–24.80 t0 –24.59 m) comprises a tem- Carpinus.The clay (unit L6) overlying the sandy sedi- perate fresh-water assemblage, indicating a shallow, ments represents a part of pollen zone E5 (Carpinus quiet and well-vegetated lacustrine environment phase). Because Abies and Picea are both present, the (Anodonta sp. indet., Bithynia tentaculata, Planorbis clay sedimentation can be assigned to the second part carinatus and Valvata piscinalis). of pollen zone E5. During the main part of the Carpi- 2 Unit M1.2 (–24.28 to –23.95 m) is characterised nus zone, sedimentation and resedimentation of local- by a marine assemblage of low diversity. It is domi- ly eroded sandy material from surrounding ice- nated by Cerastoderma glaucum, which indicates pushed ridges took place in the marginal zone of the very shallow sublittoral conditions with a small Amersfoort Basin. tidal amplitude and low salinity. Quiet and clear

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 199 axus otal of Herbs

Depth (m) below NAP Lithology Pollenzone Betula Pinus Ulmus Quercus Corylus T Carpinus Picea Abies Artemistia Chenopodiaceae T Hystrichosphaeridae

EW? 10.00

E6?

11.00

12.00

E5 13.00

14.00

14.30

14.80 6 26 4 3 3 4 2 2 8 15 21.33 22.61

E4b 23.25

23.68

23.95

E4a

24.44 E3ab

66 68 E2 66

25.00 Cleverg. 00ak-03

20 40% 20 40 60% 5 20 40% 20 40 60 10% 20 40 10 20% 20 5%

peat gyttja

clay shells

sand Fig. 3. Pollen diagram of the Amersfoort-1 borehole (selected species).

200 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 Fig. 4. Pollen diagram of the Amers- foort-2 borehole (selected species).

axus otal of Herbs Depth (m) below NAP Lithology Pollenzone Pinus Picea Hystrichosphaeridae Betula Ulmus Quercus Corylus T Carpinus Chenopodiaceae T

12.10

12.35

12.85

13.10 Cleverg. 00ak-04 10 20% 5 5% 15% 10 20% 5% 10 20 30 40% 5 5 20% 10%

peat gyttja

clay shells

sand

water with a vegetation of seaweed and/or Zostera M1.4 indicate a submersed mode of life for this occurred at the site. predominantly littoral species and do not necessar- 3 Unit M1.3 (–23.65 to –19.80 m) is represented by ily point to nearby intertidal conditions. various marine assemblages. The most dominant 4 Unit M1.4 (–19.80 to –14.85 m) represents a high- species in all assemblages is Modiolus adriaticus. ly divers marine assemblage dominated by Bittium The molluscan faunas point to quiet sublittoral reticulatum, which dominance indicates an increase conditions with high salinity and a larger tidal am- in seaweed and/or Zostera vegetation. The bound- plitude than in unit M1.2. ary with unit M1.3 is arbitrary: both units show a A vegetation of seaweed and/or Zostera is indicated similar species composition, but an increase in the by the presence of, among other species, Bittium abundance of several species is seen at the bound- reticulatum, Rissoa labiosa, Turboella radiata balkei, ary. Besides this change, a remarkable increase in Anisocycla nitidissima, Haminea navicula and Parvi- the number of ribs on the shells of Cerastoderma cardium exiguum. Remains of Zostera have been edule is present. found at the transitional zone (–21.80 to –18.80 m A linear correlation was found for this shell charac- NAP) to unit M1.4. Towards the top of the unit, ter with salinity: more ribs are present at higher the water depth increased. The rather thin-walled salinities (Eisma, 1965; Koulman & Wolff, 1977; shells of Cerastoderma edule in units M1.3 and Eisma et al., 1981). It is not certain whether the

Borehole 32B119 (Amersfoort-1)

marine molluscs

indet.

enerupis aurea senescens imoclea ovata urboella radiata balkei

Mytilus edulis Cerastoderma glaucum V Bittium reticulatum Ostrea edulis T Hinia reticulata Abra ovata Peringia ulvae Spisula subtruncata Abra nitida Cerastoderma edule Ensis Lucinella divaricata Modiolus adriaticus Mysella bidentata Pododesmus squamula Polyplacophora Thracia papyracea T Haminea navicula Odostomia eulimoides Hydrobia ventrosa Macoma balthica

Depth Unit 20 40 60 80 20 40 20 20 40 10 10 10 10 10 10 10 20 10 10 20 40 10 10 10 10 20 10 10 20 40 60 10

10.90 - 11.02 M1.6 11.75 - 11.90 12.75 - 12.90 13.75 - 13.90 M1.5 14.50 - 14.65 14.85 - 15.80 15.80 - 16.80 16.80 - 17.80 M1.4 17.80 - 18.80 18.80 - 19.80 19.80 - 20.80 20.80 - 21.80 21.80 - 22.80 M1.3 23.20 - 23.65 23.95 - 24.15 M1.2 24.15 - 24.28

24.59 - 24.80 M1.1 (Only fresh water species) Cleverg. 00ak-05 Fig. 5. Mollusc diagram of the Amersfoort-1 borehole (selected species)

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 201 rib-number/salinity relationship is linear above Basin are presented, as well as from sites outside these maxima because the data sets of both Eisma this basin. The data outside the Amersfoort Basin (1965) and Koulman & Wolff (1977) did not in- essentially confirm the isohaline pattern of Eisma clude shells that exceed 24 ribs living in salinities of (1965), but the data from the Amersfoort Basin it- approx. 16.5 ‰.The number of ribs found in mod- self conflict with the general trend of increasing ern North Sea shells varies between 22 and 28 salinities towards the North Sea. The numbers of (Van Benthem Jutting, 1943;Tebble, 1966). ribs of Cerastoderma from the Amersfoort samples Eisma (1965) published a map showing tentative (Table 2) are higher than those from samples more isohalines from Dutch Eemian marine deposits. to the west. The conflicting Eemian values from His data were based upon mixed populations of Amerfoort can be explained only by anomalous lo- Cerastoderma edule and C. glaucum, which were at cal conditions during this interval. the time considered to be ecological forms of the 5 Unit M1.5 (–14.65 to –12.75 m) is a low-diversity same species. Koulman & Wolff (1977) showed marine assemblage dominated by Cerastoderma that the positive correlation of rib number with glaucum and Hydrobia sp. (Hydrobia neglecta and salinity only applies to C. edule (which in the mean- Peringia ulvae), indicating shallow sublittoral con- time was considered to be specifically different ditions with a small tidal amplitude and low salini- from C. glaucum). Their revised correlation differs ty. The sharp contrast with the assemblages in the only slightly from the older one, implying that the underlying unit M1.4 is striking. isohaline pattern of Eisma (1965) is essentially still 6 Unit M1.6 (–11.90 to –10.90 m) is a clay with few correct. The isohalines show a general trend to- marine molluscs preserved. Deposition most prob- wards higher salinity values from the coastal zone ably took place in a high inter- to supratidal envi- into the North Sea. Data from the Amersfoort ronment. Basin were not available at the time. The molluscan assemblages of borehole Amersfoort- Here new rib counts of Cerastoderma edule from 1 (Fig. 6) show that the sequence begins as a shallow Eemian deposits (Table 2), from the Amersfoort lacustrine environment and subsequently changes

Table 2. Rib numbers of shells of Cerastoderma edule from Dutch Eemian deposits and from the modern coast. Depths are indicated in meters below surface. n = sample size. boring (code) location/name depth (m -NAP) n mean rib nr

Eemian deposits inside the Amersfoort Basin:

32A437 Eemvalley KW223 9.80-12.00 23 25.8 32A437 Eemvalley KW223 12.00-15.50 27 27.3 32B119 Amersfoort-1 20.50-21.50 60 27.9 32B120 Amersfoort-2 16.70-18.00 100 27.6 32B120 Amersfoort-2 18.00-19.00 92 27.9 32B120 Amersfoort-2 19.00-20.00 31 27.9 32B226 Amersfoort 17.00-18.00 14 27.3 32B226 Amersfoort 20.00 50 28.4

Eemian deposits outside the Amersfoort Basin:

14D62 ’t Veld 31.00-32.00 15 24.5 25A1121 Hoogovens 51.00-53.50 8 23.7 25A1121 Hoogovens 55.00-56.50 16 24.0 25A1121 Hoogovens 59.50-60.00 6 22.3 26D25 Zuid Flevoland 24.20-24.70 12 22.3 30D52 Loosduinen 25.30-28.30 14 24.4 30G262 Den Haag 26.65-31.00 38 24.3 30G629 Nootdorp 25.00-26.00 40 23.5 37C554 Zuurland-2 24.40-25.40 6 24.5 37C554 Zuurland-2 25.40-26.40 11 23.1 37C554 Zuurland-2 27.40-28.40 19 22.3 48A10 Biggekerke Bor. K 23.60-25.70 38 23.1

Modern North Sea: 22-28

202 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 from a brackish into a sheltered marine one. The typical of the boreal faunal province and currently live greatest water depth was probably reached between in the North Sea, Wadden Sea and Baltic Sea. These –17.80 and –16.80 m NAP. Several species suggest areas provide the frame of reference for the environ- clear water, among them Ostrea edulis, the boring mental interpretation of the faunas. In addition, some sponge, Cliona celata, and the mollusc species living lusitanian and mediterranean species (Elphidium on eelgrass (Zostera sp.) or seaweed. Remains of translucens, E. lidoense and Quinqueloculina seminula ju- Zostera have been found in only a few samples. The gosa) occurred. These are normal elements of the epiphytic mollusc species encountered, however, indi- Eemian faunas of NW Europe and their presence is cate the general presence of eelgrass and/or seaweed generally accepted as evidence for climatic conditions vegetation. The marine molluscan assemblages all in- that are warmer than during the Holocene. The dicate lagoonal conditions. In the clay in the upper warm-water indicating species were not present at all part of the sequence (unit L6), the molluscan assem- levels in Amersfoort-1, but this is attributed to varia- blages and their preservation confirm an environmen- tion in environmental conditions rather than climate, tal change from a tidal marsh into a fresh-water envi- as will be discussed later. ronment. Four facies units (F1–F4) are identified (Fig. 9). A The results of the molluscan analyses of borehole description at species level is given in Appendix 2. In 32B120 (Amersfoort-2) are presented separately in the present section,only the derived environmental Appendix 1 (see also Figs. 7 and 12), in which these conditions are summarised. results are compared with those of Amersfoort-1. A The assemblage of unit F1 (–24.41 to –23.80 m) is more sandy facies of the clay (unit L6) developed in interpreted as indicating deposition at very shallow Amersfoort-2 during pollen zone E5, when Abies depth in waters with salinity well below normal ma- pollen was virtually absent. The differences between rine values.To maintain such low salinities, a lagoonal Amersfoort-1 and 2 are explained as sedimentation environment is assumed. E. albiumbilicatum was ab- breaks due to local conditions. This is visualized in sent in the uppermost sample, whereas Buccella frigi- Figure 8. In Amersfoort-1, the clay sedimentation da was abundant.This fauna is considered to be tran- started during a later part of the Carpinus phase, sitional to the overlying unit, F2 (–23.65 to –17.80 when Abies shows a continuous curve; the sedimenta- m). Unit F2 represents the deepening of the lagoon. ry environment represents a tidal marsh. This change Some influence from the inner shelf of the North Sea in environmental conditions is discussed below. can be deduced from the preserved assemblage. The presence of Buccella frigida, together with lusitanian Foraminifers species like Elphidium translucens, is striking. The sands contained only a restricted foraminiferan as- Van Voorthuysen (1957) studied the foraminiferal semblage in the upper part of the unit. faunas of the Amersfoort-1 borehole. To update his Unit F3 (–15.80 to –12.15 m) shows a shallowing work, the original washed residues (fraction >150 of the water. The abundance of Ammonia parkinsoni- mm) were re-examined. Some sample material was ana tepida, Elphidium gunteri and Nonion germanicus still available and three additional subsamples were indicates the presence of mudflats in an estuarine en- taken to fill gaps in the original data set. In his stud- vironment. Unit F4 (–12.15 to –10.65 m) represents ies, Van Voorthuysen examined the unsplit wash the same environment as unit F3. The dissolution of residues, whereas a sodium-polytungstate solution is the foraminiferan tests, however, indicates a lowering used nowadays to concentrate the foraminifers. of the water level, a prolonged period of non-deposi- Species names have changed repeatedly since the tion and non-flooding, and the beginning of soil study by Van Voorthuysen, but the taxonomy of the processes. late Quaternary faunas of NW Europe is now stable. As a rule, we use the same names as Knudsen (1982, Diatoms 1985). The one important exception is the classifica- tion of the morphologically complex group of Ammo- Diatoms were found only between –24.44 and –20.80 nia species, for which the nomenclature of Jorissen m (units L2–L5) in the Amersfoort-I boring. In the (1988) is used. lower part of the sequence, the diatoms were poorly Most of the samples yielded sufficient foraminifers preserved; even the very robust species are ‘broken’. to allow an interpretation, but the uppermost (–10.65 Dissolution of frustules, shortly after sedimentation, to –10.55 m) and lowermost (–25.01 to –24.46 m) is probably responsible for the bad preservation and samples were barren. Apart from a few reworked the absence of diatom fossils. planktics, only benthics were found. Most species are Six units were distinguished (Fig. 10). The flora is

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 203 gp (p)

Depth Unit Specimens / 100 g sample Marine Counted molluscs indet.

enerupis aurea senescens urboella radiata balkei imoclea ovata

400 800 1200 1600 Mytilus edulis Cerastoderma glaucum V Bittium reticulatum Ostrea edulis T Hinia reticulata Hinia pygmaea Abra ovata Peringia ulvae Anisocycla nitidissima Scrobicularia plana Hydrobia neglecta Spisula subtruncata Abra nitida Cerastoderma edule Corbula gibba Dosinia lupinus Ensis Lucinella divaricata Marshallora adversa Modiolus adriaticus Mysella bidentata Odostomia turrita Pododesmus squamula Polyplacophora Semierycina nitida Thracia papyracea T Gastrana fragilis Haminea navicula Abra alba Angulus distortus Hiatella arctica Acanthocardia paucicostata Epitonium clathrus Cerithiopsis nana

10.90 - 11.02 11 1 M1.6 11.75 - 11.90 1 1 12.75 - 12.90 168 4 8 2 1 3 13.75 - 13.90 M1.5 17 4 7 1 14.50 - 14.65 58 16 27 2 1 2 1 2 14.85 - 15.80 6186 144 24 3328 88 226 4 4 104 24 2 16 4 10 2 88 560 16 8 48 52 224 912

15.80 - 16.80 4833 71 12 2112 163 168 5 16 48 68 4 25 52 624 16 28 48 225 1052 4 8 16.80 - 17.80 M1.4 8328 56 40 3650 24 136 26 16 232 94 24 16 26 104 1136 16 739 1816 1 8 17.80 - 18.80 14281 211 35 5786 171 416 89 710 1021 32 99 295 32 272 880 32 49 48 64 2128 1584 38 64 65 32 32

18.80 - 19.80 13000 254 33 3776 294 240 195 1960 548 32 49 458 32 1283 480 40 112 1345 1249 9 97 64 168 16

19.80 - 20.80 8998 24 24 1000 73 184 81 1273 1227 40 48 331 2812 216 24 96 16 376 689 40 56 8 80 16

20.80 - 21.80 12962 113 66 1040 81 432 118 32 240 1429 80 96 560 6990 80 224 240 32 256 385 68 208 64 16 M1.3 21.80 - 22.80 14548 32 98 1360 325 368 412 1026 4174 64 273 536 3651 112 241 16 16 416 594 1 320 16 48 176 16

23.20 - 23.65 7942 130 5 561 1360 116 784 116 1 48 32 16 99 64 907 98 32 80 211 32 1799 16 32 208 80 48 48 65 22 144 96 129 96 82 16 16 23.95 - 24.15 M1.2 265 12 83 55 28 1 21 25 12 3 1 24.15 - 24.28 84 1 38 11 4 2 2 2 1 12 24.59 - 24.80 M1.1 43

Fig. 6 (p. 204-205). Molluscs and other fossil groups in the Amersfoort-1 borehole (selected species).

Molluscs and other fossil groups in the Amersfoort-2 borehole (selected species)

Depth Unit Specimens / 100 g sample Counted molluscs indet.

imoclea ovata enerupis aurea senescens ellimya ferruginosa urboella radiata balkei urbonilla lactea urbonilla rufa

Abra alba Bittium reticulatum Cerastoderma edule Gastrana fragilis Hiatella arctica Hinia reticulata Lucinella divaricata Modiolus adriaticus Mysella bidentata Ostrea edulis Spisula subtruncata Thracia papyracea T Angulus distortus Acanthocardia paucicostata Ensis Chrysallida emaciata Corbula gibba Dosinia lupinus Haminea navicula Marshallora adversa Mytilus edulis Parvicardium exiguum Peringia ulvae Semierycina nitida T T T T Epitonium clathrus Mytilaster lineatus Chlamys varia Hydrobia ventrosa Cerastoderma glaucum Littorina littorea Caecum glabrum Chrysallida spiralis 200 400 600 800 V

13.30 - 14.60 15348 5 5196 1613 77 2 79 336 20 1459 477 871 2151 1728 132 196 6 1 9 12 1 681 5 7 20 1 59 4 3 11 1 4 M2.3 14.60 - 15.60 6758 1169 532 2 1 56 458 1096 346 280 729 1002 644 3 1 148 17 1 2 12 2 2 3 80 2 1 3

15.60 - 16.60 12722 2048 1869 1 16 163 593 4458 288 101 706 828 704 167 32 26 231 96 35 32 32 16 32 M2.2 16.60 - 17.60 10117 49 2283 1372 17 76 137 713 1539 254 267 553 800 315 332 175 1 76 1 1 154 136 1 170 2 15 27 43 134 3 6 17 1 2 1 33 1 1

17.60 - 18.60 19670 320 1984 2117 6 208 834 1489 2312 576 1750 642 960 256 1166 453 136 657 129 387 128 645 256 320 64 96 16 16 129 128 3 195

18.60 - 19.60 M2.1 5348 48 1240 432 56 32 152 368 800 96 323 248 304 32 105 128 16 56 8 24 80 72 16 80 56 168 8 56 64 8 8 16 16 16

19.60 - 20.60 236 4 32 37 5 2 8 17 27 9 14 5 19 5 8 1 4 5

Fig. 7 (p. 204-205). Molluscs and other fossil groups in the Amersfoort-2 borehole (selected species).

204 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 . Fresh water Non Molluscs Depth Land ater indet. arious species} arious remains} {Boreholes} . indet. arious species indet Echinocyamus pusillus Asteroidea {Leaf remains} arious species . arious species arious species. Verruca stroemia arious indet. arious species indet. arious species arious species Cliona celata indet arious species {Leaf and wood remains} arious species {Seeds}

indet. Zostera orms: V

alvata piscinalis ertebrata: Fish remains {V ertebrata: Fish remains {Otolites}

urbonilla lactea ellimya ferruginosa urbonilla rufa ymnaeidae Cirripedia: Decapoda: V Echinodermata: Echinodermata: Irregular Echinoidea {Fragments} W Echinodermata: Porifera: Mollusca: Gastropoda land indet. L Mollusca: Gastropoda Fresh W Ostracoda: V Plants: V Plants: V V Minerals: V Foraminifera: V V Minerals: Gypsum Echinodermata: Irregular Echinoidea {Scales} Insecta: V Cirripedia: Balanomorpha {V Minerals: Siliconring Euspira poliana Musculus Philine aperta Pododesmus patelliformis Retusa truncatula Rissoa labiosa T Caecum glabrum T Gari depressa Odostomia eulimoides Parvicardium exiguum T Chrysallida indistincta Littorina Hydrobia ventrosa Chrysallida emaciata Nucula Phaxas pellucidus Macoma balthica Retusa obtusa Mollusca: marine Anodonta Bithynia tentaculata Pisidium/Sphaerium Planorbis carinatus V Bryozoa: V Echinodermata: V Plants:

2 8 1 1 2 12 10.90 - 11.02

76 10 4 11.75 - 11.90

110 1 39 2 1 6 1 12.75 - 12.90

1 1 1 2 1 1 1 7 13.75 - 13.90

1 2 4 4 1 1 3 14.50 - 14.65

12 10 168 2 106 8 8 8 16 16 40 8 16 24 8 8 8 14.85 - 15.80

4 16 4 28 8 8 16 8 8 24 40 8 80 24 47 15.80 - 16.80

96 72 16 304 56 161 128 119 16 16.80 - 17.80

16 16 64 32 32 3552 2 32 16 32 2314 289 157 112 17.80 - 18.80

96 17 96 8 8 8 33 2744 16 3335 160 300 1 64 80 16 18.80 - 19.80

24 72 32 16 40 80 32 64 1656 32 112 1425 8 55 1 128 8 19.80 - 20.80

32 32 32 16 32 2304 192 2049 1 89 1 32 20.80 - 21.80

16 32 17 190 16 48 16 2704 32 592 3521 60 16 32 21.80 - 22.80

16 16 16 1 16 16 112 160 224 48 64 16 1648 16 16 32 64 320 1153 128 96 1 23.20 - 23.65

24 32 7 2 2 2 23.95 - 24.15

11 10 325 24.15 - 24.28

1 1 11 8 10 6 3 3 5 2 3 65 1 24.59 - 24.80

Fig. 6 (continued). ater

Marine Non Molluscs Depth Fresh W arious species} arious remains} {Boreholes} spec. {Boreholes} Echinocyamus pusillus Asteroidea arious species {Bone remains} arious species {Bone remains} arious species erruca stroemia indet. arious species V arious species indet. Cliona celata arious species {Leaf and wood remains} arious species {Seeds}

Polydora orms: orms: V ertebrata: Fish remains {Otolites} ertebrata: V ertebrata: Fish remains {V V W Hinia pygmaea Mya truncata Odostomia eulimoides Odostomia turrita Pododesmus squamula Polyplacophora Gari depressa Anisocycla nitidissima Cerithiopsis cf tubercularis Cerithiopsis nana Euspira poliana Macoma balthica Musculus Philine aperta Pododesmus patelliformis Rissoa labiosa Angulus tenuis Bithynia tentaculata Bryozoa: V Echinodermata: Echinodermata: Irregular Echinoidea {Fragments} Echinodermata: Irregular Echinoidea {Scales} V Minerals: Siliconring Echinodermata: Echinodermata: Ophiuroidea {Fragments} Plants: V Plants: V V Decapoda: V Mammalia: V Porifera: W Cirripedia: Balanomorpha {V Cirripedia: Mollusca: Pearl Odostomia Rissoa labiosa/membranacea Circulus striatus Spisula elliptica Abra ovata Astarte excurrens Bittium scabrum Cylichna cylindracea Phaxas pellucidus Retusa truncatula Scrobicularia plana Mollusca: Marine indet.

3 3 35 3 70 4 1 3 26 1 1 1 1 3 2 1 23 1 183 397 217 1 1 2 1 1 17 8 2 13.30 - 14.60

27 1 1 1 26 3 2 1 51 53 4 4 141 1 14.60 - 15.60

40 208 480 896 896 64 8 16 8 15.60 - 16.60

1 1 5 1 27 42 1 16 1 1 1 1 16 16 1 1 1 276 624 1568 2372 16 1 16 1 48 16.60 - 17.60

1292 320 2625 1536 1 1 64 17.60 - 18.60

216 64 1968 744 8 24 8 8 18.60 - 19.60

25 1 6 5 49 82 1 1 5 4 1 2 19.60 - 20.60 Cleverg. 00ak-10

Fig. 7 (continued).

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 205 Euhaline Ribs Salinity Depth Unit Fig. 8. Comparison of the salinity dia- 50% Polyhaline grams from boreholes Amersfoort-1 10.91 - 11.03 and Amersfoort-2. Mesohaline 1.6 11.76 - 11.91 Oligohaline 12.76 - 12.91 Fresh Water 13.76 - 13.91 1.5 Salinity groups 14.51 - 14.66 14.86 - 15.81 15.81 - 16.81 Unit Depth Salinity Ribs 16.81 - 17.81 1.4 27.9 17.81 - 18.81 50% 18.81 - 19.81 13.32 - 14.62 27.6 19.81 - 20.81 2.3 break 14.62 - 15.62 27.9 20.81 - 21.81 1.3 15.62 - 16.62 27.9 21.81 - 22.81 2.2 break 16.62 - 17.62 23.21 - 23.66 17.62 - 18.62 23.96 - 24.16 1.2 2.1 18.62 - 19.62 24.16 - 24.29 19.62 - 20.62 24.60 - 24.81 1.1

Cleverg. 00ak-06 32B120 (Amersfoort-2) 32B119 (Amersfoort-1) considered to be allochtonous because it contains Ostracods species of different environments: epiphytic, epipsammic and planktonic species were found in the same Ostracods were found in six samples from the Amers- assemblage. The diatoms were probably washed to- foort-1 borehole that were collected for molluscan gether in the shallow-marine environment near the analysis (units L1–L6).Three assemblages can be dis- coast. tinguished (Table 3): unit O1 (–24.80 to –24.59 m), At a depth of –23.11 to –22.61 m, lusitanian di- unit O2 (–23.65 to –23.20 m) and unit O3 (–20.80 to atom species are present. The assemblage as a whole –14.85 m). Unit O1 represents a fresh-water environ- points to clear-water conditions and a water depth ment. The fauna of unit O2 is typical of shallow, not exceeding 10 m. The diatom assemblages are de- brackish water with a vegetation of eelgrass and/or scribed in more detail in Appendix 3. seaweed. Unit O3 represents the same environmental conditions as unit O2. Only the presence of Aurila aff. prasini is remarkable. This species is known only

Table 3. Ostracods of the Amersfoort-1 borehole. Depths are indicated in meters below NAP.

Ostracod species Depth (m -NAP)

14.85-15.80 17.80-18.80 18.80-19.80 19.80-20.80 23.20-23.65 24.59-24.80 (unit O3) (unit O3) (unit O3) (unit O3) (unit O2) (unit O1)

Cyprideis torosa 1* 1 – 1 40 – Callistocythere cf. praecincta 1 – – – – – Hirschmannia viridis 1 4 – – – – Loxoconcha rhomboidea 3 2 2 3 31 – Hemicythere villosa 2 2 – – – – Loxoconcha elliptica 1 – – – – – Pontocythere elongata – 7 4 F 7 – Aurila aff. prasini – 8 F F 3 – Xestoleberis depressa – – – 1 – – Semicytherura acuticostata – – – 1 1 – Carinocythereis cf. whitei – – – 1 3 – Semicytherura sella – – – 1 – – Leptocythere sp. – – – – 1 – Leptocythere castanea – – – – 1 – Semicytherura striata – – – – 1 – Xestoleberis aurantia – – – – 1 – Limnocythere inopinata – – – – – 6 Candona neglecta – – – – – >100 Darwinula stevensoni – – – – – 1

* = only small valves; F = only fragments.

206 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 a

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1 1 - k a 0 0 . g r e v e l C

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o o o 5 p p p w / / / o n n n l l e e e r r r a r r r 0 h a a a 4 s b b b 0 a 3 n m m a i i u l u n n c u t-1 borehole (selected species). i o o s s i n s s r

a 0 m n e e i r 2 t a m k i p l n r r a l i e e u a d i d g g p w

p . . . . . sfoor e 0 E N A t N E 1 r Amer e % b 0 2 m u n

s 0 e i 1 c e p s % 0 4 ) g 0 0 0 1 3 / s o h t 0 n 2 e b ( g o l 0 1

9 5 3 8 7 8 2 2 4 6 6 7 9 2 9 5 2 2 5 9 0 1 4 d e t n u o c r e b m u n 4 2 4 9 0 1 2 5 5 2 4 0 0 6 5 9 9 1 1 6 1 1 1 1 1 2 2 1 1 2 1 1 1 1 1 1 0 9 1 8 5 5 5 5 0 0 0 0 5 5 5 5 5 0 5 5 0 0 5 w 0 8 5 4 2 1 9 6 9 8 8 8 8 8 5 1 6 7 3 1 7 4 9 6 o ...... l e 5 4 4 4 4 4 3 3 2 2 1 8 5 4 4 4 3 2 2 2 1 1 0 0 e c 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1

------f

r h 0 9 6 8 5 5 0 0 0 0 0 0 5 5 0 0 5 5 5 5 5 7 5 5 t u 9 5 4 2 1 9 8 2 8 8 8 8 8 7 4 9 5 6 1 0 6 2 6 5 p s ...... e 4 4 4 4 4 3 3 3 2 1 0 7 4 4 4 3 3 2 2 2 1 1 0 0 d 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 Benthic foraminiferan assemblages from the 9. n n s t e e 1 i 4 2 3 r r n r r F F F F u a a b b Fig.

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 207 Table 4. Heavy-mineral composition (in percentages) of the Amersfoort-1 borehole. Depths are indicated in meters below NAP.

Mineral Depth (m -NAP)

14.50-14.65 16.80-17.80 19.80-20.20 23.20-23.65 25.01-25.80 tourmaline 5.5 5.5 9.5 3.0 8.0 sillimanite – 1.5 0.5 0.5 – andalusite 0.5 2.0 3.0 0.5 – kyanite 0.5 1.0 1.0 1.5 1.0 staurolite 2.0 2.0 3.5 3.0 2.0 topaze – – – – – pumpellyite – – – – – sphene s.l. 0.5 – 0.5 0.5 – anatase 6.0 1.5 1.0 2.5 1.0 rutile 4.5 0.5 2.0 2.5 3.0 zircon 6.0 1.5 1.0 4.5 4.5 other volcanic minerals – 0.5 – – – hornblende (brown and basaltic) – 4.0 1.0 – 0.5 hypersthene – 0.5 2.5 0.5 – augite 0.5 5.5 10.0 2.0 4.0 chloritoid – – 0.5 0.5 – hornblende 23.5 15.0 14.5 18.0 17.5 alterite 1.5 12.5 14.0 10.0 8.0 saussurite – 2.5 2.0 – – epidote 31.0 14.5 14.0 22.0 18.0 garnet (cloudy) 0.5 0.5 – – 1.0 garnet (clear) 17.5 29.0 19.5 28.5 31.5 from the Eemian of Denmark and Middle Pleistocene water to a brackish-water environment, the drowning interglacial deposits in southern England (Penney of the area, increasingly marine conditions caused by 1989). the continuing sea-level rise, followed by a silting-up of the basin margin with mudflats and salt marshes, Heavy minerals to end with peat growth at the top of the sequence. With the exception of the basal zone E1, all zones The results of the heavy-mineral analyses are given in of the Eemian are represented in these sediments. Table 4. Three units are distinguished: unit H1 Zagwijn (1961), who designated this sequence as the (–25.80 to –23.20 m), unit H2 (–20.80 to –16.80 m), type locality for the Eemian in the Netherlands, later and unit H3 (–14.65 to –14.50 m). Units H1 and H2 reported that the pollen record of the Valkenweg bail- comprise local heavy-mineral associations derived er boreholes of the Amsterdam Basin were more com- from reworking of older outcropping sediments of the plete (Zagwijn, 1983). Thanks to the detailed pollen ice-pushed ridges near the margins of the glacial record of the new Amsterdam-Terminal borehole basin. Unit H3 has a Scandinavian/Baltic composi- (Van Leeuwen et al., 2000 – this issue) it is possible to tion, which also most probably represents reworked recognise and to date breaks in the Amersfoort type sediment from the ice-pushed ridges. The composi- sequence. tion differs from the mineral association of units H1 Because of the undulating morphology of the ice- and H2.This is most probably due to the kind of sedi- pushed ridges, the rising groundwater table locally ments that are reworked: Saalian glaciofluvial and ae- changed the area into fresh-water marshes with small olian material. lakes. The gyttja at a depth of –25.01 to –24.44 m NAP in Amersfoort-1 records this phase. Drowning is Discussion indicated by fresh-water molluscs (unit M1) in the gyttja, the high numbers of the ostracod Candona, by Stratigraphical breaks and depositional environments sklerotoids of Nymphaea counted on the pollen slides, and by the increasing values of Alnus. Among the tree At first sight, the Amersfoort-1 stratotype section pro- pollen, Pinus values decrease in favour of those of Al- vides a continuous record of the Eemian transgres- nus and Quercus. The drowning of the area can there- sion in the Netherlands. The record shows the initial fore be dated as the second half of pollen zone E2. Al- flooding by sea water with the transition of a fresh- nus colonised the wet localities, while Quercus was

208 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 24 22 23 21 depth (m) below NAP growing on slightly higher and drier ground on the 0

10 Actinoptychus undulatus hills. The lacustrine conditions continued into pollen zone E3, when Quercus and Corylus were the most im- 0 Grammotophora oceanica 10 portant trees.

20 The transition from a lacustrine to a brackish envi- 30

40 ronment in Amersfoort-1 took place during zone

50 E4a. The transition was not gradual: it represents an erosional break or an interval of non-deposition. The 0 Melosira sulcata 10 sudden transition at –24.44 m NAP (Fig. 3) is 20 demonstrated by an abrupt increase from approx. 30

40 20% to more than 40% of the Corylus curve. In the

50 pollen record from the Amsterdam-Terminal site, this 60 increase is gradual and occurs over a sediment thick- 70

80 ness of half a meter. The conspicuous change in molluscan assemblages between units M1.2 and M1.3 al- 0 Cymatosira belgica 10 so supports this phenomenon. On top of the fine-grained, organic-rich layer at 0 Stephanopyxis turris –23.95 m, a third break is observed.The Corylus curve 10

20 (Fig.3) shows the break again most clearly: values de- 30 crease from over 50 to less than 30%. This decrease is

0 – just like the one described above – much more grad- Cymatosira belgica 10 ual in the Amsterdam-Terminal borehole (Van

0 Leeuwen et al., 2000 – this issue). The presence of Cymatosira belgica 10 Carpinus at low values, immediately above this bound- 0 Cymatosira belgica 10 ary, provides another argument to suggest a break. In 20 the Amsterdam-Terminal sequence, the first occur- 30 rence of Carpinus coincides with the Taxus maximum 0 Cymatosira belgica (±10 %). At Amersfoort, the arrival and, in particular, 10

0 the gradual decrease and eventual disappearance of

10 Cymatosira belgica Taxus are recorded, but its maximum is absent (Fig.

0 11). The Taxus-maximum pollen zone, which is miss- Cymatosira belgica 10 ing in Amersfoort, is represented by 3 m of laminated 0

10 Cymatosira belgica clay in the Amsterdam-Terminal borehole. According to Zagwijn (1983), the Eemian sea-level 0

10 Cymatosira belgica highstand was attained at the end of pollen zone E4b, slightly after the Taxus pollen maximum, with the first 0

10 Cymatosira belgica arrival of Carpinus. This indicates, together with the 20

0 evidence based on the mollusc, ostracod and

10 Cymatosira belgica foraminifer faunas, that the third break reflects ero- 0

10 Cymatosira belgica sion and non-deposition because of the upward shift of the facies zones with the rising sea level. 20.80 25.00 24.44 24.15 23.77 23.68 The coarsening-upward sequence of shell-rich Depth (m) below NAP t-1 borehole (selected species). sands (unit L5) between –22.60 and –14.79 m NAP oceanica A B C D E Diatom Zone belgica Paralia sulcata (poor) Cymatosira

barren Paralia sulcata Grammatophora

sfoor represents the transition of pollen zone E4b and the greatest part of pollen zone E5. The sands are devoid Amer of pollen, so that the position of the boundary to pollen zone E5 could not be well established. A sample of clayey sand at a depth of –21.33 m NAP gave a ram of the shallow water (beach) or very Marine shore interpretation Environmental marine tidal poor pollen spectrum (Fig. 3). Because of the relatively low value of Carpinus, this spectrum suggests tom diag

Cleverg. 00ak-07 that the sand was deposited during pollen zone E4b.

Dia The clays and sandy clays (unit L1) overlying this

10. sandy sequence at a depth of –14.79 to –10.51 m

Fig. NAP were deposited during the second half of pollen

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 209 Fig. 11. Comparison of the pollen zones of the Amsterdam-Terminal borehole (van Leeuwen et al., 2000 – this issue) and the Amersfoort-1 borehole.

zone E5. This is deduced from the presence of Abies probably responsible for the upward coarsening of the occurring in low percentages in the sediments. Abies sand. The percentage of foraminiferan tests in the frequencies increase upwards in the clay and sandy sandy sequence is therefore limited. The absence of clays to values of 5%. diatoms in these sands might be ascribed to the same During pollen zones E4b (the end) and E5, over 20 process, but chemical dissolution of the diatom frus- m of clay was deposited in the Amsterdam-Terminal tules in the SiO2-unsaturated seawater seems more borehole. The same interval (pollen zones E4b and likely. E5) is represented at Amersfoort by about 8 m of The upward coarsening of the sands and the coarse shelly sands. As already mentioned in the sec- abrupt change at the top of these sandy sequences in- tion above on the molluscs, these coarse sands were to a clay suggests at least a fourth break. This fourth deposited discontinuously. Because of the restricted break became visible by comparison of the pollen resolution of the pollen only the molluscs of Amers- zones of Amsterdam-Terminal and Amersfoort-1 foort-1 and Amersfoort-2 (see also Appendix 1) indi- (Fig. 11). This break will be discussed below, because cate two hiatuses in the sands (Fig. 8). The ostracods it is manifest by a change in the depositional environ- also showed changes in environmental conditions at ment at the end of the Eemian.The sandy sequence is these depths (Table 3). probably the result of local reworking of older out- In Amersfoort-2, clay sedimentation started earlier. cropping sediments in the ice-pushed ridges near the It was dated to pollen zone E5, when Carpinus still margin of the glacial basin, as indicated by the heavy reached values of about 30 (Fig. 4). Because of the minerals. These shelly sands were, as mentioned be- presence of Abies in one of the spectra, the end of fore, deposited discontinuously. The fourth break is the sandy sequence can, however, be dated to the therefore complex. younger part of pollen zone E5, as in Amersfoort-1. The matter of the occurrence of Abies in the Nether- Relative sea-level rise lands will be discussed below. The water depth at the basin margin never exceed- The rise of the groundwater table and the drowning ed 10–15 m during the Eemian highstand. Wave ac- of the area during the second half of pollen zone E2 tion and related hydrodynamic circumstances were were probably not caused by a rising sea level. At the

210 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 Borehole 32B120 (Amersfoort-2)

marine molluscs

imoclea ovata enerupis aurea senescens ellimya ferruginosa urboella radiata balkei

Depth Unit 10 20 10 10 10 10 10 20 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

13.30 - 14.60 M2.3 14.60 - 15.60

15.60 - 16.60 M2.2 16.60 - 17.60

17.60 - 18.60

18.60 - 19.60 M2.1 19.60 - 20.60 Cleverg. 00ak-09 Fig. 12. Mollusc diagram of the Amersfoort-2 borehole (selected species). time, sea level was still below –60 m NAP, as indicat- during the Eemian are in no way similar to the begin- ed by sequences in the western Netherlands and the ning of the Holocene (see also De Gans et al., 2000 – Southern Bight of the North Sea (unpublished data this issue). NITG-TNO). It is highly unlikely that a sea level at this depth would influence a groundwater table at –25 Depositional environment and climate m NAP. This suggests that the drowning of the area reflected a normalisation of the groundwater situation As already discussed, sedimentation began with car- after the Saalien glaciation, and probably also an in- bonate-rich gyttja deposited in a nutrient-rich, shal- crease in precipitation. low lake.The change to brackish conditions is accom- In the Amsterdam Basin, the top of the –40 m deep panied by some erosion. Cerastoderma glaucum is the sill was flooded during pollen zone E3 (De Gans et dominant mollusc species in the fine-grained organic- al., 2000 – this issue; Van Leeuwen et al., 2000 – this rich layer between –24.44 and –23.95 m NAP. This issue). In the Amersfoort-1 borehole, the first marine and some other species point to deposition in water of sediments date from pollen zone E4a. This depth of only a few metres deep, under varying temperature –24.44 m NAP is an important height for the Dutch and salinity conditions. The fauna (molluscs, ostra- Eemian sea-level curve. According to Zagwijn (1983) cods and foraminifers) in the organic-rich sands and the Eemian highstand reached –15 m NAP. It is dated overlying shell-rich clays and sands between –23.95 to pollen zone E4b. and –20 m NAP, indicate a further increase of the wa- The clays and sandy clays (unit L6) deposited at a ter depth during pollen zone E3/E4a. The abundance depth of –14.65 to –10.90 m, at the top of the coarse of Nonion depressulum and Cerastoderma edule show, shelly sands (unit L5) in the Amersfoort-1 borehole, however, that a lagoonal environment with varying suggest a still rising sea level during pollen zone E5 salinity conditions persisted. (Abies). The molluscan and foraminiferan assem- The organic-rich sands and overlying shell-rich blages in the clays and sandy clays, however, indicate clays and sands between –23.95 and –20 m NAP rep- a shallowing of the lagoon, which developed into an resent the transition from the Taxus E4b zone to the estuary-like water body surrounded by mudflats.This Carpinus E5 zone, the Taxus maximum being absent suggests a lowering of the sea level during the second in the Amersfoort-1 borehole. During the Taxus phase half of pollen zone E5. The change of the environ- (pollen zone E4b), the Eemian sea-level highstand mental conditions can be explained only as resulting reached about 10 m below NAP (Zagwijn, 1983). from lowering of the sea level.The clay trapped in the This means that the water depth of the basin at the deeper parts of the glacial basins during the Carpinus Amersfoort-1 site did not exceed 10–15 m during this pollen zone (E5), settled during the latter part of phase. This is confirmed by the presence of epiphytic pollen zone E5, near the margins of the glacial basins. faunas (molluscs such as Bittium and Turboella, and In the Amersfoort Basin, the genesis of the coastal ostracods) and epiphytic diatoms. Besides, the vegeta- area shows no similarity with the Holocene. Both the tion of Zostera and algae indicates clear-water condi- steeper relief after the Saalian glaciation and the (lo- tions, and consequently little suspended material.The cal and regional) morphology in the coastal zone area presence of oysters confirms these environmental cir-

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 211 cumstances. A significant phenomenon is the pres- rich succession between –14.79 and –10.51 m NAP ence of lusitanian and even warmer species in all in- was deposited in a shallow-marine, intertidal and vestigated biota. probably also supratidal environment.The peat above The Cerastoderma edule at a depth between –20.00 the clays demonstrates that the marine environment and –15.00 m NAP has an equal number of ribs as changed finally into a fresh-water environment during the (rarely found) maximum of modern specimens pollen zones E5/E6. The fall of the sea level became (Table 2). Using the relationship found by Koulman obvious at the end of the Eemian, when fresh-water & Wolff (1977) between number of ribs and salinity, conditions prevailed again. the salinity would have been of the order of 40–45 ‰. After the salt-marsh vegetation had changed into a Because these values are beyond the tolerance of the fen-marsh during the Abies/Picea phase of pollen zone species occurring in the Eemian deposits of Amers- E5, the environmental conditions soon became foort, these values are very improbable. This leads, in favourable for oligotrophic peat growth. The begin- combination with the arguments given earlier, to the ning of the Ericaceae/Sphagnum peat development conclusion that salinity was well above salinity values has been assigned to the Weichselian stage (Zagwijn, of the open, present-day North Sea, but not as high as 1961) but it appears from the pollen evidence in the suggested by the rib-number/salinity formula. The Netherlands’ glacial basins that the oligotrophic peat abundant presence of Mysella, a species living be- growth had already begun in some places during the tween the spines of Echinocardium, indicates that the Carpinus phase (pollen zone E5). Picea was already salinity showed little variation, as Echinocardium is an represented as a local element in this oligotrophic echinoid of open-marine waters. Echinocardium can peat. Outside the glacial basins, also in areas with this tolerate a higher salinity very well. oligotrophic peat growth, Picea was also present in In the Amersfoort borehole, the molluscan assem- pollen zone E4b. In the general scheme of the blage of the sandy sequence between –20.00 and Netherlands’ pollen zonation of the Eemian, Picea is –15.00 m NAP is generally considered to represent placed, however, in pollen zone E5 (Zagwijn & van the warmest interval of the Eemian. According to De Staalduinen, 1975). Beaulieu & Reille (1992), Van Andel & Tzedakis Pollen zone E5 is in this scheme, apart from the (1996) and Tzedakis (1999), the major expansion of presence of Carpinus and Picea, also characterised by the mediterranean forest characterised by Olea and the occurrence of Abies. The question at what time evergreen oak was synchronous with the Taxus phase Abies became an important tree during the Eemian in in the rest of Europe and represents the time of maxi- the Netherlands was already mentioned by Vermeer mum summer insolation. Louman (1934) and Van der Vlerk & Florschütz The present authors consider that local geographi- (1953). At Amersfoort, Abies became important to cal conditions – in particular the position of the bore- the end of zone E5 and probably also during the first hole at the margin of a sheltered bay of the Eemian part of pollen zone E6. Elsewhere in Europe, Abies Sea – are responsible for a higher water temperature was an important woodland element even in the first and therefore also a higher salinity at the end of part of the Carpinus phase. pollen zone E4b and the first part of pollen zone E5. Because of the change in the environmental condi- They agree with De Beaulieu & Reille (1992) and Van tions as recorded at Amersfoort, it is presumed that Andel & Tzedakis (1996) that the Taxus phase repre- Abies reached its western limit in the Netherlands sents the warmest phase of the Eemian. during the late Eemian. In particular, the sediments The abrupt change from coarse sands into a clay of new intertidal areas near the margins of glacial represents a hiatus at –14.79 m, as discussed. The basins, which developed during the second part of the coarse shelly sands were deposited at a depth of ap- Carpinus phase, favoured the preservation of the Abies prox. 10 m. The change in depositional environment, pollen. In the Amsterdam Basin succession (Van especially of the hydrodynamic conditions, starts in Leeuwen et al., 2000 – this issue), Abies is also found the second part of pollen zone E5. The presence of in the uppermost sediments dated as Eemian. Cerastoderma glaucum, Hydrobia neglecta and Peringia Whether these intertidal areas were a favourable ulvae suggests shallow sublittoral conditions, and low- biotope for Abies trees, and therefore influenced the er salinity. In addition, the foraminiferan assemblage representation of Abies in the pollen zone E5 and (abundance of Ammoni parkinsiniana tepid, Elphidium probably E6, is still an open question. gunteri and Nonion germanicus) indicates a decrease of It can safely be said that the lowering of the sea lev- the water depth. Both the molluscs and the el must have coincided with an extension of the ice foraminiferan assemblages indicate the presence of caps in Europe and North America. The extent to tidal marshes. It is concluded therefore that the clay- which Abies gained advantage from the changes in ‘at-

212 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 mospheric conditions’ is still unclear. In comparison mum of the Eemian was longer. Local environmental with Picea, Abies does not appreciate cold winters and circumstances, resulting from the morphology and cold springs. Indirectly, the presence and expansion hydrodynamic conditions near the margins of the of Abies to its western limit can be explained as the glacial basins, created a specific biotope that favoured maintenance of the oceanic climate during the last the growth of lusitanian species also after the Taxus part of the Carpinus zone (E5). Colder winters and maximum. Therefore, it is thought that the climate short cold periods during spring finally resulted in a during the first part of the Eemian was already a few decrease of Abies, and, in turn, favoured the conifer- degrees warmer than during the Holocene.The Taxus ous species Pinus and Picea of the evergreen boreal pollen maximum represents the Eemian climatic opti- forest. mum (cf.Tzedakis et al., 1999). Finally, it is concluded that Abies reached its west- Conclusions ern limit in the Netherlands at the end of pollen zone E5. A lowering of the sea level during the interval that The stratotype locality is situated in the predominant- Abies became an important tree is deduced from the ly sandy marginal facies of a bay of the Eemian North change in environmental conditions, which also led to Sea in the central part of the Netherlands. The bore- the development of mudflats and salt marshes near hole consists of an Eemian sequence of about 15 m the margins of the glacial basin,. Locally, eutrophic thick, in which all the northern European Eemian peat growth started on these mud flats and salt pollen zones are present, except E1 (Betula zone). marshes. These eutrophic peats (under fresh-water The pollen record is punctuated by a number of short conditions) changed into oligotrophic peats at the breaks, resulting from erosion and/or non-deposition end of the Eemian and/or during the first part of the during the marine transgression. The position and Early Weichselian. While Abies disappeared, Picea and relative length of these breaks are evident when the Pinus became the dominant trees in the area with record is compared with that from the Amsterdam- oligotrophic peat growth. Terminal borehole in the Amsterdam Basin (Fig. 11). The latter consists of a clay-rich Eemian sequence of Acknowledgements over 40 m thick, representing the deeper central part of a similar basin (Van Leeuwen et al., 2000 – this is- We thank NITG-TNO for supporting our research sue; De Gans et al., 2000 – this issue). It can there- on the Eemian of the Netherlands. We are very grate- fore be concluded that the resolution of the pollen ful to Dr. D.J. Beets for fruitful discussions on the record of the Amersfoort-1 type locality is limited. biostratigraphic and sedimentary aspects of the Eemi- Amsterdam-Terminal seems to be a good parastrato- an in the glacial basins. type locality for the northern and central Nether- We also thank Rob van Galen, Ria Veldkamp and lands. Rita Vreugdenburg for preparing and counting the Because of a restricted exchange between the pollen slides, Heleen Klaver-Koolmees and Marianne North Sea and the glacial basins, specific environ- Koolen-Eekhout for the preparation of the forami- mental conditions occurred in the basins throughout niferal samples and their identification, and Ingrid the marine phase of the Eemian in the Amersfoort Geutskens for the identification of the diatom assem- Basin.The presence of Cerastoderma edule, with an in- blages. Finally, we are grateful to Phil Gibbard, Aleid creased number of ribs on its shells, is an expression Bosch, Nienke Cleveringa and Rob van Galen for text of these specific conditions. Lusitanian and mediter- correction. ranean species are present throughout the marine sequence. At the transition from pollen zone E4b to E5, References and probably during the very first part of pollen zone E5 (the highstand of the Eemian sea) sand was erod- De Beaulieu, J.L. & Reille, M., 1992. Long Pleistocene pollen se- ed from the ice-pushed ridges, as is indicated by quences from the Velay Plateau (Massif Central France), l. Rib- ains Maar.Vegetation History and Archaeobotany 1: 223-242. heavy-mineral analyses. The coarse sands were trans- De Gans, W., De Groot, Th. & Zwaan, H., 1987. The Amsterdam ported to the shallow waters of the basin margin, basin, a case study of a glacial basin in the Netherlands. In: which resulted in the maintenance of a sandy floor J.J.M. van der Meer (ed.): Tills and glaciotectonics. Proceedings and particular environmental conditions in the bay. of an INQUA symposium on genesis and lithology of glacial de- The persistence of the lusitanian faunas, after the posits (Amsterdam, 1986): 205-216. De Gans,W., Beets, D.J. & Centineo, M.C., 2000. Late Saalian and Taxus maximum (pollen zone E4b) confirm this spe- Eemian deposits in the Amsterdam glacial basin. In: Van Kolf- cific environment with higher water temperatures. It schoten, Th. & Gibbard, P.L. (eds.): The Eemian – local se- does not imply that the duration of the climatic opti- quences, global perspectives. Geologie en Mijnbouw / Nether-

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 213 lands Journal of Geosciences 79: 147-160 (this issue). base of the sub-division of the Pleistocene in The Netherlands. Eisma, D., 1965. Shell-characteristics of Cardium edule L. as indica- Verhandelingen van de Koninklijke Akademie van Wetenschap- tors of salinity. Netherlands Journal of Sea Research 2: 493-540. pen 1e reeks, 20 (2): 1-58. Eisma, D., Mook,W.G. & Laban, C., 1981. An early Holocene tidal Van Leeuwen, R.J., Beets, D., Bosch, J.H.A., Burger, A.W., Cle- flat in the Southern Bight. International Association of Sedimen- veringa, P.,Van Harten, D., Herngreen, G.F.W., Langereis, C.G., tologists Special Publication 5: 229-237. Meijer,T., Pouwer, R. & De Wolf, H., 2000. Stratigraphy and in- Haake, F.W., 1962. Untersuchungen an der Foraminiferen-Fauna tegrated facies analysis of the Eemian in the Amsterdam-Termi- im Wattgebiet zwischen Langeoog und dem Festland. Meyniana nal borehole, the Netherlands. In: Van Kolfschoten, Th. & Gib- 12: 25-64. bard, P.L. (eds.): The Eemian – local sequences, global perspec- Jelgersma, S. & Breeuwer, J.B., 1975. Toelichting bij de kaart tives. Geologie en Mijnbouw / Netherlands Journal of Geo- glaciale verschijnselen gedurende het Saalien, 1 : 600.000. In: sciences 79: 161-196 (this issue). Zagwijn,W.H. & Van Staalduinen C.J. (eds.):Toelichting bij geo- Van Voorthuysen, J.H., 1957. Foraminiferen aus dem Eemien logische overzichtskaarten van Nederland. Rijks Geologische (Riss-Würm-Interglazial) in der Bohrung Amersfoort-1 (Locus Dienst (Haarlem): 93-103. typicus). Mededelingen van de Geologische Stichting 11: 27-39. Jessen, K. & Milthers, V., 1928. Stratigraphical and paleontological Van Voorthuysen, J.H., 1960. Die Foraminiferen des Dollart-Ems- studies of interglacial fresh-water deposits in Jutland and North- Estuarium.Verhandelingen van het Koninklijk Geologisch Mijn- west Germany. Danmarks Geologiske Undersøgelse II Raekke bouwkundig Genootschap 19: 237-269. 48: 1-379. Vermeer–Louman, G.G., 1934. Pollen-analytisch onderzoek van Jorissen, F.J., 1988. Benthic foraminifera from the Adriatic Sea; den Westnederlandschen bodem. Ph.D. thesis Amsterdam Uni- principles of phenotypic variation. Utrecht Micropaleontological versity: 184 pp. Bulletin 37: 176 pp. Zagwijn, W.H., 1961. Vegetation, climate and radiocarbon datings Knudsen, K.-L., 1982. Foraminifers. In: Olausson, E. (ed.): The in the Late Pleistocene of the Netherlands. Part I: Eemian and Pleistocene/Holocene boundary in south-western Sweden. Early Weichselian. Mededelingen van de Geologische Stichting, Sveriges Geologiska Undersøkning C 794: 148-177. Nieuwe Serie 14: 15-45. Knudsen, K.-L., 1985. Foraminiferal faunas in Eemian deposits of Zagwijn, W.H., 1983. Sea-level changes in the Netherlands during the Oldenbüttel area near the Kiel Canal, Germany. Geologi- the Eemian. Geologie en Mijnbouw 62: 437-450. sches Jahrbuch A 86: 27-47. Zagwijn, W.H. & Van Staalduinen, C.J. (eds.), 1975. Toelichting bij Konradi, P.B., 1976. Foraminifera in Eemian deposits at Sten- geologische overzichtskaarten van Nederland. Rijks Geologische sigmose, southern Jutland. Danmarks Geologiske Undersøgelse Dienst (Haarlem): 134 pp. II Raekke 105: 55 pp. Koulman, J.G. & Wolff, W.J., 1977. The Mollusca of the estuarine Appendix 1: Molluscs from Amersfoort-2 region of the rivers Rhine, Meuse and Scheldt in relation to the hydrography of the area.V.The Cardiidae. Basteria 41: 21-32. Lutze, G., 1965. Zur Foraminiferen-Fauna der Ostsee. Meyniana In borehole 32B120, (Amersfoort-2) pre-Eemian 15: 75-142. glaciofluvial deposits occur between –24.60 and –20.60 Matoba, Y., 1970. Distribution of Recent shallow water m. Seven samples of the overlying sandy deposits be- foraminifera of Matsushima Bay, Miyagi Prefecture, Northeast tween –20.60 and –13.30 m. have been re-investigated. Japan. Science Reports Tohoku University Series 2 42: 1-85. The overlying marine clay was not included in the mol- Murray, J.W., 1971. An atlas of British Recent foraminifers. Heine- luscan analysis (Fig. 12). Most of the shell material is mann (London): 244 pp. Penney, D.A., 1989. Microfossils (Foraminifera, Ostracods) from rather well to very well preserved; only a minor part of an Eemian (last interglacial) tidal flat sequence in South-West the shells shows traces of leaching. All molluscan assem- Denmark. Quarternary International 3/4: 85-91. blages (Fig. 7), therefore, are considered to be present in Richter, G., 1967. Faziesbereiche rezenter und subrezenter Wat- situ and to be (par)autochthonous. tensedimente nach ihren Foraminiferen-Gemeinschaften. Senck- The environmental conditions are quite similar to enbergiana Lethaea 48: 291-355. those from units M1.3 and M1.4 of borehole 32B119 Tebble, N., 1966. British bivalve seashells. British Museum (Lon- (Amersfoort-1), although some differences are apparent. don): 212 pp. Tzedakis, P.C., 1999. The last climatic cycle at Kopais, central The assemblages are predominantly high sublittoral (be- Greece. Journal of the Geological Society of London 156: 425- tween the wave base and the lowest low watermark) and 434. point to euhaline salinities. Several rib counts on speci- Tzedakis, P.C. & Bennett, K.D., 1995. Interglacial vegetation suc- mens of Cerastoderma edule point to ‘hypersaline’ values cession a view from southern Europe. Quarternary Sience Re- (Table 2). views 14: 967-982. Bittium reticulatum is the dominant species in most Uffenorde, H., 1982. Zur Gliederung des klastischen Holozäns im samples, indicating seaweed and/or eelgrass vegetation. mittleren und nordwestlichen Teil der Deutschen Bucht (Nord- see) unter besonderer Berücksichtigung der Foraminiferen. Other eelgrass (epiphytic) species occur as well: Turboella Eiszeitalter und Gegenwart 32: 177-202. radiata balkei, Haminea navicula, Parvicardium exiguum, Van Andel, T.H. & Tzedakis, P.C., 1996. Palaeolithic landscapes of etc. Although other species dominate in several samples, Europe and environs, 150.000-25.000 years ago: an overview. they do not indicate significant environmental change. Quarternary Science Reviews 15: 481-500. All the investigated molluscan assemblages indicate a la- Van Benthem Jutting, T., 1943. Mollusca (I) C. Lamellibranchia. goonal environment. Fauna van Nederland: 12. A.W. Sijthoff’s Uitgeversmaatschappij N.V. (Leiden): 477 pp. Differences between both Amersfoort boreholes are Van der Vlerk, I.M. & Florschütz, F., 1953. The palaeontological most obvious at two levels. These differences are ex-

214 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 plained as resulting from breaks in sedimentation. Two The fairly common occurrence of E. lidoense in the lower breaks can be recognised.The first is located in borehole sample also indicates a deeper-water environment. Amersfoort-1 at the transition between units M1.2 and Although the salinity may be comparable to that of M1.3. It is thought that the assemblages between –20.60 the modern North Sea, open-marine conditions did not and –17.60 NAP of the Amersfoort-2 borehole correlate prevail. Species of the open sea (such as Ammonia becca- with this break in Amersfoort-1. The second break is rii and Elphidium gerthi) did occur, but were few and present at the top of the sandy facies of Amersfoort-2 at scarce. Another argument is the abundance of Nonion a depth of 13.30 m. The assemblages between –20.55 depressulum. This is considered a lagoonal rather than an and –17.55 m NAP in Amersfoort-1 are considered to inner shelf species, as supposed by Murray (1971), be- represent this break in Amersfoort-2. These two breaks cause it is characteristic of the Wadden Sea rather than can be recognised in the species composition of the as- the North Sea (Haake, 1962; Richter, 1967). Richter semblages in both boreholes, but also in the ecological (1967) reported N. depressulum as characteristic of low- change as indicated by the assemblages. This is exempli- lying sandy tidal flats, close to the open sea. Data regard- fied here by the change in salinity preference of the as- ing its distribution in Holocene and Eemian sediments semblages in both boreholes (Fig. 8). in the Netherlands suggest, however, that N. depressulum is best described as a lagoonal species that lives at or be- Appendix II: foraminiferan zonation in the Amers- low the low-water level. foort-1 borehole It is not clear how the abundance of Buccella frigida should be interpreted. The distribution of this taxon in Unit F1 the Eemian of the Netherlands suggests that its depth habitat lies between that of relatively deep-living species Unit F1, ranging from -24.41 to -23.80 m NAP, yields such as E. excavatum s.l., and that of shallow-living rich faunas with a low diversity. The interval is charac- species such as N. germanicum. B. frigida is nowadays terised by high numbers of Ammonia parkinsoniana tepi- rare in the North Sea, the Wadden Sea and the Baltic. da, Elphidium albiumbilicatum, Elphidium williamsoni and The reason is probably that temperatures are too high, Nonion germanicum except in the uppermost sample (see because it is generally considered to be a boreo-arctic or also Fig. 9). The assemblage has no modern analogue in arctic species (Konradi, 1976). The apparent preference the nordic seas. E. albiumbilicatum is typical of shallow of B. frigida for relatively low temperatures makes its co- brackish waters of the Baltic (Lutze, 1965), whereas occurrence with lusitanian species such as E. translucens both A. parkinsoniana tepida and N. germanicum are char- remarkable. As an explanation, a very large seasonal acteristic of the Wadden Sea intertidal flats (e.g., Van contrast in temperature could be invoked. This sugges- Voorthuysen, 1960; Haake, 1962). Only E. williamsoni is tion arises from observations in NE Japan; Matoba abundant in both areas. This species seems to be a good (1970) reported that both B. frigida and Ammonia, which indicator of water depths because it lives close to the indicates relatively warm water, occur abundantly in high-water level in sheltered parts of the Wadden Sea shallow lagoonal bays where temperatures are high in (e.g., Richter, 1967) and at very shallow depth in the la- summer (August: 25–29°C) and much lower in winter goonal and estuarine parts of Kiel Bay (Lutze, 1965). (January: 1–3°C). Both A. parkinsoniana tepida and E. albiumbilicatum The number of foraminifers decreases upwards and are definitely associated with low salinities. The latter the upper two samples are almost barren. The low num- species is probably indicative of very brackish conditions bers are taken as an indication of repeated reworking of since it flourishes at salinities as low as 6–9‰ (Lutze, the sediments (cf. Uffenorde, 1982). 1965). Unit F3 Unit F2 Unit F3, ranging from –15.80 to –12.15 m, comprises Unit F2, ranging from –23.65 to –17.80 m NAP, yields various faunas with a fairly high number of individuals. faunas with a lower number of individuals but more The differences with unit F2 are large. A. parkinsoniana species than unit F1. The high abundances of Buccella tepida, Elphidium gunteri and Nonion germanicum are frigida and Nonion depressulum are particularly character- abundant and jointly comprise 50-90% of the fauna. A istic here. The assemblage is no longer of brackish-water comparable fauna occurs today in the mud flats of the character: A. parkinsoniana tepida and E. albiumbilicatum estuarine parts of the Wadden Sea (Van Voorthuysen, are virtually absent. On the other hand, Quinqueloculina 1960; Haake, 1962; Richter, 1967). seminula s.l., a stenohaline species (Murray, 1971) is Elphidium gunteri is especially abundant in the upper consistently present. The increase in salinity was proba- part of the unit. In contrast to the other species men- bly coupled to an increase in water depth because E. tioned, the habitat of E. gunteri is restricted to the mud williamsoni is only a subordinate element in the faunas. flats of the Wadden Sea. The change towards higher

Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000 215 abundances might therefore be attributed to a shallow- live on seaweed. The diatom assemblage from this unit ing of the environment. represents various biotopes in the basin and is allochtonous. Unit F4 Unit D3 (–23.72 to –23.68 m NAP) consists of two samples, both poor in diatoms. Paralia sulcata is still the Unit F4, ranging from -12.15 to -10.65 m NAP, is char- dominant species; most of its frustules are broken. In the acterised by a fauna that almost exclusively consists of lower sample, the epipsammic Dimerogramma minor and N. germanicum and E. gunteri.The number of individuals the epiphytic Cocconeis disculoïdes are found. Sedimenta- is low and the tests indicate evidence of dissolution. tion probably occurred under similar environmental The assemblage closely resembles the faunas that ac- conditions as described for unit D2. Because of synsedi- tually live on the mud flats in the estuarine parts of the mentary dissolution, only the most robust frustules of Wadden Sea. Both Haake (1962) and Richter (1967) the diatom flora have been preserved. have shown, indeed, that there are systematic differences Unit D4 is represented by a sample taken from a core between the biocoenoses and thanatocoenoses of the (–23.23 m) and by a bailer sample (–23.20 m). In con- Wadden Sea. In general, characteristic features of the trast to unit D3, Grammatophora oceanica is found here thanatocoenoses are a higher proportion of Ammonia again in the diatom assemblage. In addition to this epi- and a higher number of species. A specific feature of the phytic species, epipsammic species are present. For the thanatocoenoses of the mud flats is their much lower first time in the record, Stephanopyxis turris was found; it percentage of E. gunteri.These differences give the fauna occurred in the stratified deposits of the Amsterdam- of this unit a strong resemblance to a mudflat biocoeno- Terminal borehole (Van Leeuwen et al., 2000 – this is- sis and that of the underlying unit a close similarity to a sue). The diatom assemblage is partly a result of the re- thanatocoenosis. working of the older, organic deposits at the basin mar- The change towards a more autochthonous signal im- gin. plies a decrease of hydrodynamic energy. This is inter- The samples from unit D5 (–23.11 to –22.61 m NAP) preted in this context as a shallowing of the environ- are rich in diatoms, most of which are lusitanian species. ment. In this sandy environment, the percentages of epipsammic diatom species (Dimerogramma minor, Catenula ad- Appendix 3: diatoms from Amersfoort-1 herens, Achnanthes delicatula and Opephora parva) are high, indicating. Some epiphytic species, such as Coc- In unit D1 (–24.44 to –24.22 m NAP), Grammatophora coneis scutellum and C. disculoïdes, are also present; they oceanica, Actinoptychus undulatus and Dimerogramma mi- point to a vegetation of Zostera and/or algae. The assem- nor are the dominant diatoms. The preservation of these blage suggests clear water with a depth of less than 10 very robust diatom species is poor. Most of the diatoms m. are partly broken and dissolved. The flora is considered Unit D6 is represented by two bailer samples (–22.55 to be allochtonous since it consists of species character- to –21.80 and –21.80 to –20.80 m NAP). The coarse istic of strongly varying environments. Epiphytic, epip- sands are very poor in diatoms. The presence of Ra- sammic and planktonic species are found together in a phoneis minutissima and Cymatosira belgica points to more single assemblage. Diatom floras from different niches in open-marine conditions. the basin were probably washed together in shallow-marine water at the margins of the basin between the ice- pushed ridges. The fossilised flora is therefore allochtonous. The presence of Grammatophora oceanica and Hyalodiscus scoticus, at the base of the marine succession in the Amersfoort-1 borehole, is not well understood. In the Amsterdam-Terminal borehole, as well as in other boreholes from the same basin, however, the species are found at exactly the same stratigraphical position, i.e. the base of the marine sequence in pollen zone E4a. The interval of unit D2 (–24.22 to –23.87 m NAP) shows a dominance of the planktonic diatom Paralia (Melosira) sulcata, but epipsammic (Dimerogramma mi- nor) and epiphytic species (Cocconeis disculoïdes) have also been preserved. Campylodiscus echeneis, Rhopalodia constricta and Glyphodesmis distans are present in low percentages in all samples.These species indicate a shallow- marine, near-shore environment. Some of these species

216 Geologie en Mijnbouw / Netherlands Journal of Geosciences 79(2/3) 2000