Composition and grain-size distribution of the Holocene Dutch “sloef” (Almere Member of the Groningen Formation)

Sedimentary Geology, 13 (1975) 237--251 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

COMPOSITION AND GRAIN-SIZE DISTRIBUTION OF THE HOLOCENE DUTCH "SLOEF" (ALMERE MEMBER OF THE GRONINGEN FORMATION)

A.J. VAN LOON and A.J. WIGGERS Instituut voor Aardwetenschappen der Vrije Universiteit, Amsterdam (The Netherlands) (Submitted October 22, 1974; revised and accepted January 10, 1975 )

ABSTRACT Van Loon, A.J. and Wiggers, A.J., 1975. Composition and grain-size distribution of the Holocene Dutch "sloef" (Almere Member of the Groningen Formation). Sediment. Geol., 13: 237--251. The Almere Member of the Groningen Formation, usually indicated by the lithostratigraphic name of "sloef", was deposited in a lagoon, which covered approximately the same area as the present IJsselmeer (the former Zuiderzee). Archeological finds show that this sediment dates from 0--1600 A.D. Microfossils indicate an oligohaline to ~-mesohaline environment. Most of the material consists of silt. As a result of peptisation the ratio between the 0--2 pm and the 0--16 pm is abnormally low. In the SE part of the lagoon the average grain size is much smaller than in the NE. This is interpreted as a result of transport from the main source area, the Waddenzee, to the SE. The percentage of organic material, derived from the underlying eroded peat and detritus-gytt]a, decreases in an upward direction. A few scattered pebbles have been encountered in these deposits. They are assumed to have been deposited by ice during winter.

INTRODUCTION In a previous p a p e r (Van L o o n a n d Wiggers, 1 9 7 5 a ) it was m e n t i o n e d t h a t a t y p i c a l grain-size d i s t r i b u t i o n exists in t h e " s l o e f " , a H o l o c e n e l a g o o n a l d e p o s i t in t h e f o r m e r D u t c h Zuiderzee (Fig. 1). O t h e r characteristics are t h e fine l a m i n a t i o n , t h e small grain size even in layers with a l o w l u t u m c o n t e n t , a n d t h e u p w a r d decrease in t h e a m o u n t o f organic m a t t e r ( K o o p s t r a , 1 9 6 2 ) . T h o u g h h a r d l y m e n t i o n e d in t h e literature, a possibly even m o r e characteristic f e a t u r e is p r e s e n t e d b y t h e f r e q u e n t o c c u r r e n c e o f syn- a n d postsedim e n t a r y d i s t u r b a n c e s (Fig. 2). We shall deal w i t h these s t r u c t u r e s (as well as w i t h various erosional features) in s o m e f u t u r e papers. This p a p e r s h o u l d be c o n s i d e r e d as a review o f t h e p r e s e n t state o f sedim e n t a r y p e t r o g r a p h i c research, t h e results o f w h i c h are n o t generally acces-

238

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Fig. 1 Location o f the IJsselmeer region and the four reclaimed areas.

sible, since they are mainly contained in internal reports, often written in Dutch. Some new results are added. The sedimentary petrographical properties of the "sloef" vary in lateral directions. These changes have permitted the reconstruction of a fairly accurate picture of this lagoonal area. Since also vertical changes occur, the lithostratigraphy gives information about the sedimentary history.

239

Fig. 2 Metasedimentary disturbance of mainly silt-sized laminae. Section 7.

STRATIGRAPHY

In a recent paper (Van Loon and Wiggers, 1975b) an extensive review was given of litho-, bio-, and chronostratigraphic aspects of the "sloef". In accordance with the thesis of Roeleveld (1974) the term " s l o e f " was rejected, and the name of "Almere Member of the Groningen F o r m a t i o n " was introduced. We will continue to use this more acceptable name in the future. In the Almere Member seven beds can be distinguished in the area of the Noordoostpolder, on the basis of lithological variations (Fig. 3). The lowest, highly humic bed has been eroded in most places. Possibly it has n o t been deposited in other parts of the lagoon (Ente and Segeren, 1969). This lowermost bed is indicated by the symbol S1 III b . The bed above it (S1 III a) often contains a layer, usually at its top, with a concentration of shells. Since the fresh-water snarl Valvata piscinalis dominates, this shell bed is k n o w n as the Valvata layer (Fig. 4). The paleontological c o n t e n t of the various beds has been investigated by various authors, the most important of which are Muller and Van Raadshoven (1947), Middelhoek and Wiggers (1953), Wagner (1957) and Ente et al. (1961). Comparison of their results indicates that during deposition of the Almere Member shallow marine, brackish conditions (oligohaline to ~-meso-

240

Fig. 3 Nearly completely developed sequence in the Almere Member. The S1 III b bed probably has been eroded; the S1 IIIa bed is only represented by a thin Valvata layer, overlying the detritus-gyttja (d.g.) of the Flevomeer Member. The top of the section is formed by sediments of the Zuiderzee Member (Z.M.). Section 5.

241

Fig. 4 Typical facies of the Valvata layer, showing small shells of Valvata piscinalis and larger shells of Unio tumidus. Photograph by the "Rijksdienst voor de IJsselmeerpolders".

haline) existed in an area surrounded by tidal marshes. This is in accordance with the lagoonal interpretation based on paleogeographical and sedimentological arguments. Dating of these sediments was n o t possible with the 14 C-method, since m o s t of the organic material has been washed in, derived from older sediments, mainly the underlying peat and detritus-gyttja (Flevomeer Member of the Groningen Formation). Fortunately, various beds have been dated by archeological finds. Especially wrecks with their contents (e.g. coins) have been very helpful. Fig. 5 indicates in which way a correlation might be made between the age of the wreck and the age of the sediments surrounding the ship. The wreck sinks, touches the b o t t o m , and subsides due to rocking, caused by wave action, until a strong layer is reached. Afterwards the ship is rapidly filled by sediments, and within a few years b o t h the ship and the surrounding sediments are covered by an undisturbed layer above them. The most important datings concern the base of the Almere Member, which must have been deposited about 0 A.D. The first bed(S1 III b ) ended in the 12th century. The Valvata layer of the next bed (S1 III a) may be dated as middle of the 13th century (Wiggers, 1955) or end of the 12th century {Ente, 1973). Deposition of the Almere Member ended at the transition from the 16th to the 17th centuries.

242

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Fig. 5 Shipwreck within the Almere Member (A) and schematic picture of sedimentation in the wash-out around it (B). Photograph by the "Rijksdienst voor de IJsselmeerpolders". DISTRIBUTION

The location of the lagoon in which the Almere Member was deposited corresponds to that of the present IJsselmeer. Although mapping in this lake is very well possible (methods are described by Smits and Wiggers, 1959), most information a b o u t the distribution of the various sediments was obtained from the reclaimed areas (Wieringermeer, N o o r d o o s t p o l d e r , Oostelijk Flevoland and Zuidelijk Flevoland). The distribution of this deposit in the

243

second and third polders has been published on detailed maps: the "Bodemkundige Code- en Profielenkaart van de N o o r d o o s t p o l d e r " (1947--1956) and the "Bodemkundige Code- en Profielenkaart van Oostelijk Flevoland" (started in 1968). On the basis of the data n o w available, the following -- schematic -picture of the distribution of the Almere Member can be made. In the northern part of the IJsselmeer no typical "sloef" is present, since sediments of the same age have been either eroded, or are of a much coarser nature (Zuur, 1936). In all other parts of the IJsselmeer, however, this t y p e of sediment is present (Muller and Van Raadshoven, 1947). In the southernmost part the grain-size distribution is n o t very characteristic, since the deposits there contain more lutum (Zuur, 1948a). Generally speaking, an increase of the lutum content can be observed from N or NW to S or SE. The a m o u n t of humus (derived from eroded older deposits), which needs quiet water to settle, also increases towards the SE (Koopstra, 1962). At some localities the Almere Member is represented b y a hiatus i.e., those cases where the position of the older deposits with respect to the sea level was t o o high, e.g. along the border of the Veluwe (Zuur, 1948a). Elsewhere,

/ ~

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Fig. 6 D i s t r i b u t i o n a n d t h i c k n e s s o f t h e A l m e r e M e m b e r . In t h e NW n o d a t a are s h o w n , since t h e s e d i m e n t s t h e r e lack t h e t y p i c a l " s l o e f " c h a r a c t e r . A f t e r P o n s a n d Wiggers

(1959--1960).

244

the thickness of this member in Zuidelijk Flevoland ranges from 75 to 400 cm, in most localities from 200 to 300 cm (Ente and Wiggers, 1963). These variations strongly depend on the topography during sedimentation: the lower boundary undulates; this is also the case with the boundary between the humic and the sandy facies. The top, however, usually located some 35 to 60 cm below the surface, is fairly plane. This levelling might be due to synsedimentary subsidence (Ente, 1964). In the Noordoostpolder, where the top lies at a depth of 25--50 cm, this deposit is 0--300 cm thick, most frequently 50--150 cm. It is present almost anywhere, except in the northeast, where it has disappeared by erosion (Wiggers, 1955). In the southern part of this polder it is locally absent as

10 -'I • ''''''o'o

percentage of lulum

~

1

transition into coarse coastal sands

Fig. 7 Distribution and l u t u m c o n t e n t of t h e S] I b bed. After Wiggers (1955).

245

well, partly due to the mixing with coarse deltaic sands, especially in the younger beds. An almost identical picture can be observed in Oostelijk Flevoland, where the depth below the surface (15--90 cm) gradually increases from NW to SE (De Koning and Wiggers, 1955), accompanied by a decrease in grain size into the same direction (Koopstra, 1961). A generalized map of the distribution of the Almere Member has been published already by Pons and Wiggers (1959--1960; Fig. 6). The distribution of the separate beds is quite different: some beds (e.g. the S1 1b ) occur in large areas (Fig. 7), while other beds are laterally very restricted. COMPOSITION AND GRAIN-SIZE ANALYSIS

In addition to the mineral components there is a considerable a m o u n t of organic matter from eroded peat and gyttja, as well as calcium carbonate. The most characteristic property of the Almere Member (to which it owed its former name of "sloef"), however, is the frequent occurrence of grains in the 2--16 ~zm range with respect to those in the 0--2 pm fraction (Zuur, 1943; 1954). The bulk of the material is somewhat coarser, and belongs to the 16--50 ~m fraction (Wiggers et al., 1962). Changes in the grain-size distribution occur both horizontally and vertically. From the central part of the lake towards the edges the material changes from a sandy to a silty character (Ente, 1971). A gradual increase in grain size occurs from SE to NW. In the northwestern part of the Noordoostpolder this leads sometimes to a significant percentage of grains in the 50--75 pm fraction (Muller and Van Raadshoven, 1947). Also in Oostelijk Flevoland only the NW part contains some sand (Zuur, 1950). The ratio of the 0--2 pm fraction and the 0--16 #m fraction is indicated by the symbol " R " . It is determined by the formula R = 1 0 0 . % 0--2 pm/% 0--16 pm. In the Noordoostpolder it reaches a value of 35, but locally it may go up to 60. In Oostelijk Flevoland the average value of R is 46 (De Koning and Wiggers, 1955); it varies from about 30 in the NE to 60 in the SW. In Zuidelijk Flevoland the average value is 55 (Ente and Wiggers, 1963), decreasing from 60 in the NW to 45 in the SE. In the vertical sequence changes occur as well. The humus content generally decreases upwards (Wiggers, 1955; De Koning and Wiggers, 1955), whereas the a m o u n t of calcium carbonate increases (Wiggers et al., 1962). Variations occur also in the lutum content and in the t y p e of layering. This allows the previously mentioned division into beds, which can be mapped easily in most cases. This paper will not treat these changes for the entire IJsselmeer region. In order to show an example of the changes some data by Wiggers (1955) for the Noordoostpolder are reproduced. Wiggers mentions an average composition for the seven beds, such as shown in Table I. The frequency diagrams of lutum, organic matter and CaCO3 are reproduced in Fig. 8.

246 lutum

C~O 3

organ~ matter

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Fig. 8 F r e q u e n c y d i a g r a m s o f l u t u m , organic m a t t e r a n d CaCO 3 in t h e various beds. Vertical scale: p e r c e n t a g e o f samples. H o r i z o n t a l scale: c o n t e n t in p e r c e n t a g e s o f dry m a t t e r , n = n u m b e r o f samples. M = a r i t h m e t i c m e a n . A f t e r Wiggers ( 1 9 5 5 ) .

247 TABLE I Average c o m p o s i t i o n o f t h e various b e d s in t h e N o o r d o o s t p o l d e r ( A f t e r Wiggers, 1 9 5 5 ) Bed

C o n t e n t s in % o f d r y m a t t e r

R-value

CaCO 3

organic m a t t e r

0--2 p m

0--16 pm

16--2000 pm

11.2 9.5 8.5 7.2 7.0 6.4 4.5

2.2 3.3 2.9 7.5 12.4 4.7 13.1

6.8 9.9 4.9 9.1 14.0 4.6 10.9

18.8 25.7 13.9 26.1 34.2 11.0 27.0

67.8 61.5 74.7 59.2 46.4 77.9 55.4

36.1 38.5 35.3 34.9 36.3 41.9 40.4

Total number of samples 1297

1297

1522

1365

1365

1365

Sl I a S11 b Sl II a Sl IIb Sl II c S1 IIIa Sl III b

SOURCE

A decrease in average grain size of the Almere Member appears to exist from NW to SE, which would indicate a source area in the NW. This assumption is supported by the decrease in thickness of various sand layers towards the SE (Koopstra, 1961; Ente and Wiggers, 1963). Palaeogeographic information makes it clear, that material may have been supplied by the Waddenzee, which was situated in the NW. This would especially have taken place after the inlet, which connected these two areas, had widened considerably (boundary Sl IIIb--S1 III a) (Zuur, 1948b). Transport of material from the Waddenzee towards the bays or lagoons (such as the former Zuiderzee) which were connected with it, is certainly possible. This has been shown for recent sediments of the Dollard--Eems estuary along the boundary between The Netherlands and Germany (Favejee, 1960; Van Straaten, 1960; Wiggers, 1960). This transport takes place through several phases. The question of the source of the material in the Waddenzee has already been solved. Based on the heavy-mineral content (investigated by Crommelin: Favejee, 1951), and on the relative ratios of the various clay minerals (Favejee, 1960), it had been postulated that this material was derived from the North Sea, possibly by erosion of Pleistocene deposits. Convincing proof was given by Van Straaten (1963), who showed the presence of spines of Echinocardium cordatum in the Wadden sediments. This echinoderm lives exclusively in open seas and tidal inlets. Since these spines are absent in older sediments of the Waddenzee, reworking is impossible. Therefore the spines must have been brought in from the North Sea.

248

Thus the mineral components of the Almere Member originated probably for the most part form the North Sea. During short periods, local supply by rivers may have been important along the borders of the IJsselmeer. Since this member is very fine grained, it is almost impossible to extract information on the source area by an analysis of the heavy minerals. Only deposits surrounding local Pleistocene "highs" {such as cover sands, e.g. in our section 5: see Van Loon and Wiggers, 1975a) may contain coarse material in somewhat larger quantities, but the source of these sediments cannot be considered as characteristic for the main part of the Almere Member. The occurrence throughout the whole member of scattered pebbles is interesting. During recent investigations specimens up to 9 cm were found. This grain size is in strong contradiction with the whole sedimentological pattern. In addition, many specimens show extremely sharp rims that exclude the possibility of bed load transport (Fig. 9). Indications for mass transport have n o t been found either. We assume therefore, that these pebbles have been picked up during winter from high parts in the neighbourhood by drifting ice, or from the lake b o t t o m by ground ice. During spring, when the ice melted, the pebbles were dropped into the fine-grained b o t t o m sediment. This might explain the random distribution throughout this member. A concentration of pebbles is present in the Valvata layer (S1 IIIa), which has an erosive character, and in which the pebbles might be considered to represent the residue of an eroded sequence. The boulder clays from the "highs" of Urk and Schokland may be thought of as a probable source area of these pebbles. The mineralogical composition of the pebbles (85% of glacial material) confirms this hypothesis.

Fig. 9 P e b b l e s f r o m t h e A l m e r e M e m b e r .

249 ORIGIN OF THE LOW LUTUM CONTENT

In the marine Quaternary sediments of The Netherlands the ratio R always ranges from 65 to 70 (Hissink, 1929; Van Straaten, 1963). In fluvial clays R is more variable, and ranges from 40 to 65, usually from 60 to 65, which might indicate a mechanical depositional process rather than a colloid-chemical sedimentation (Poelman, 1965). At some locations R m a y even reach values of 80 (Stichting voor Bodemkartering, 1973). The constant ratio between the various grain sizes in marine clays exists also between the various subfractions smaller than 16 /am (De Ridder and Wiggers, 1959). According to Favejee (1951} the constant granulometric composition (and the uniform mineralogical content) of the finer fractions in marine sediments can be explained by coagulation in consequence of the high electrolyte content of the seawater. These coagulated particles are supposed to have a diameter of a b o u t 40 lam {Van Straaten, 1963). When these particles reached the fresh or slightly brackish water of the lagoon, peptisation t o o k place, with the exception of the particles of 0 - - 2 / a m (De Ridder and Wiggers, 1959). The finest particles could not settle because of the turbulence in the water, which resulted from currents and especially from wave action. After some time they were carried back to the sea in suspension. The low ratio R is therefore n o t due to an excessive a m o u n t of the 2--16/am fraction, b u t to a lack of lutum. Muller and Van Raadshoven (1947), Zuur (1951), Wiggers (1955) and Zonneveld (1960) assumed already earlier that peptisation plays an important role. ACKNOWLEDGEMENTS

The authors wish to express their thanks to Dr. H. Rijckborst and Prof. M.J.S. Rudwick for their comments and correction of the English text. The kind permission by the "Rijksdienst voor de IJsselmeerpolders" to inspect several internal reports, and to reproduce some of their photographs is gratefully mentioned.

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250 silbfractie van enkele Kenozofsche afzettingen in Nederland. Geol. Mijnbouw, 21: 416--433. Ente, P.J., 1964. Thickness variations of the sandy Almere deposits (Holocene) in the former Zuiderzee area (The Netherlands). In: L.M.J.U. van Straaten (Editor), Deltaic and Shallow Marine Deposits (Developments in Sedimentology, 1). Elsevier, Amsterdam, pp. 123--128. Ente, P.J., 1971. Sedimentary geology of the Holocene in Lake IJssel region. In: J.D. de Jong (Editor), Sedimentology--Research on Sedimentology and Sedimentary Geology in The Netherlands. Geol. Mijnbouw, 50 (3): 373--382. Ente, P.J., 1973. De IJsseldelta. Kamper Almanak, 1973: 137--164. Ente, P.J. and Segeren, W.A., 1969. Toelichting bij de bodemkundige code- en profielenkaart en de grondwaterstandskaarten in Oostelijk Flevoland. Flevobericht, 6 5 : 4 8 pp. Ente, P.J. and Wiggers, A.J., 1963. Over de bodemgesteldheid van Zuidelijk Flevoland. Van Zee tot Land, 3 4 : 5 6 pp. Ente, P.J., Van Straaten, L.M.J.U., Wiggers, A.J., Van Voorthuysen, J.H., Wagner, C.W. and Van der Werff, A., 1961. Sedimentation and micropalaeontology of the Holocene of Eastern Flevoland. Excursion Guide 7th Eur. Micropaleontol. Colloq. (The Netherlands and Belgium), 13 pp. Favejee, J.Ch.L., 1951. The origin of the "Wadden" mud. Meded. Landbouwhogesch. Wageningen, 51 : 113--141. Favejee, J.Ch.L., 1960. On the origin of the mud deposits in the Ems-Estuary. In: J.H. van Voorthuysen and Ph.H. Kuenen (Editors), Das Ems-Estuarium (Nordsee) - Ein Sedimentologisches Symposium. Verb. K. Ned. Geol. Mijnbouwkd. Genoot., 19: 147-151. Hissink, D.J., 1929. De bodemkundige gesteldheid van den Andijker Proefpolder in het jaar 1927--1928. Meded. Comm. Advies Proefpolder Andijk, 1. Koopstra, R., 1961. Over de bodemgesteldheid van het noordwesten van Oostelijk Flevoland (noordelijk deel). Rapp. Kartering Oostelijk Flevoland na Droogvalling, 1 0 : 1 9 PP. Koopstra, R., 1962. Een vergelijking van de geologische indelingen van Noordoostpolder en Oostelijk Flevoland. Rapp. Kartering Oostelijk Flevoland na Droogvalling, 1 1 : 2 1 PP. Middelhoek, A. and Wiggers, A.J., 1953. A research into the microflora and microfauna of the Holocene sediments in the north-eastern polder. Biol. Jaarb., 20: 235--291. Muller, J. and Van Raadshoven, B., 1947. Het Holoceen in de Noordoostpotder. Tijdschr. K. Ned. Aardrijksk. Genoot., 2e Reeks, 64: 153--185. Poelman, J.N.B., 1965. De lutum-slibverhoudingen in rivierkleigronden. Boor en Spade, 14: 196--213. Pons, L.J. and Wiggers, A.J., 1959--1960. De Holocene wordingsgeschiedenis van NoordHolland en het Zuiderzeegebied. Tijdschr. K. Ned. Aardrijksk. Genoot., 7 6 : 1 0 4 - - 1 5 2 and 77: 3--57. Roeleveld, W., 1974. The Groningen Coastal Area. Part B: The Holocene Evolution of the Groningen Marine-Clay District. Thesis, Vrije Universiteit, Amsterdam, 252 pp. Smits, H. and Wiggers, A.J., 1959. Soil survey and landclassification as applied to reclamation of sea bottom land in the Netherlands. Int. Inst. Land Reclam. Improv. Publ., 4: 60 pp. Stichting voor Bodemkartering, 1973. Bodemkaart van Nederland, schaal 1 : 50 000, blad 39 west en oost, Rhenen. Wageningen. Van Loon, A.J. and Wiggers, A.J., 1975a. Holocene lagoonal silts (formerly called "sloef") from the Zuiderzee. Sediment. Geol., 13: 47--55. Van Loon, A.J. and Wiggers, A.J., 1975b. Litho-, bio-, and chronostratigraphy of the Holocene Dutch "sloef" (Almere Member of the Groningen Formation). Meded. Werkgr. Tert. Kwart. Geol., 12: 3--24.

251 Van Straaten, L.M.J.U., 1960. Transport and composition of sediments. In: J.H. van Voorthuysen and Ph.H. Kuenen (Editors): Das Ems-Estuarium -- Ein Sedimentologisches Symposium. Verh. K. Ned. Geol. Mijnbouwkd. Genoot., 19: 279--292. Van Straaten, L.M.J.U. 1963. Aspects of Holocene sedimentation in The Netherlands. Verh. K. Ned. Geol. Mijnbouwkd. Genoot., 21: 149--172. Van Straaten, L.M.J.U. (Editor), 1964. Deltaic and Shallow Marine Deposits. (Developments in Sedimentology, 1). Elsevier, Amsterdam, 464 pp. Van Voorthuysen, J.H. and Kuenen, Ph.H. (Editors), 1960. Das Ems-Estuarium -- Ein Sedimentoligisches Symposium. Verh. K. Ned. Geol. Mijnbouwkd. Genoot., 1 9 : 3 0 0 pp. Wagner, C.W., 1957. Sur les ostracodes du Quaternaire r~cent des Pays-Bas et leur utilisation dans l'6tude g~ologique des d~p6ts Holoc~nes. Thesis, Univ. Paris, 259 pp. Wiggers, A.J., 1955. De wording van het Noordoostpoldergebied. Van Zee tot Land, 14: 1--216. Wiggers, A.J., De Jong, F.H. and Spanjer, K., 1962. De bodemgesteldheid van de Noordoostpolder. Van Zee tot Land, 3 3 : 1 3 9 pp. Zonneveld, I.S., 1960. De Brabantse Biesbosch, Een Studie van Bodem en Vegetatie in een Zoetwatergetijdendelta. Thesis, Landbouwhogeschool Wageningen, 210 pp. Zuur, A.J., 1936. Over de Bodemkundige Gesteldheid van de Wieringermeer. Minist. van Waterstaat, 's-Gravenhage, 113 pp. Zuur, A.J., 1943. Over de betekenis van de fracties 0---2 and 0--16 mu voor de indeling der zwaardere gronden in de Noordoostpolder. Intern Rapp. Bodemk. Afd. Directie Wieringermeer (Noordoostpolderwerken}, Kampen, 13 pp. Zuur, A.J., 1948a. Over de bodemkundige gesteldheid van de zuidelijke kom van het IJsselmeer. Intern Rapp. Bodemk. Afd. Directie Wieringermeer (Noordoostpolderwerken), Kampen, 8 pp. Zuur, A.J., 1948b. Over de bodemkundige gesteldheid van het westelijke gedeelte van de Noordoostpolder, Intern Rapp. Directie Wieringermeer (Noordoostpolderwerken), Kampen, 5 pp. Zuur, A.J., 1950. Over de bodemkundige gesteldheid van de toekomstige oostelijke polder in het IJsselmeer. Jaarb. 1950 Alg. Bond Oud-Leerlingen Inrichting Middelbaar Landbouwonderwijs, pp. 1--8. Zuur, A.J., 1951. Ontstaan en aard van de bodem van de Noordoostpolder. Van Zee tot Land, 1 : 1 9 pp. Zuur, A.J., 1954. Over de betekenis van de fracties 0--2 and 0--16 mu voor de indeling van de zwaardere gronden in de Noordoostpolder. In: Langs Gewonnen Velden. Veenman, Wageningen, pp. 131--142.