KONINKRIJK BELGIE

IVIINI . RIE VAN ECONOMISCHE ZAKEN Administratie der Mijnen - Geologische Dienst van Belgie Jennerstraat, 13- 1040 Brussel

STUDIES IN TERTIARY BENTHONIC FORAMINIFERA IN BELGIUM

door H.J.F. HOOYSERGHS

PROFESSIONAL PAPER 1985/6 Nr 219 BELGISCHE GEOLOGISCHE DIENST - PROFESSIONAL PAPER 1985/6 - N° 219

STUDIES IN TERTIARY BENTHONIC FORAMINIFERA

IN BELGIUM

H.J.F. HOOYBERGHS

Instituut Aardwetenschappen f,. K.U.Leuven Redingenstraat 16b 3000 LEUVEN -1-

CONTENTS.

I. Quantitative distribution and paleoecology of benthonic foraminifera in the Brussels Formation, the Lede Formation and the Asse Formation (Eocene) at Haacht (Belgium).

II. Quantitative distribution and paleoecology of benthonic foraminifera in the Eocene Brussels Sands Formation at Diegem (Belgium).

III. Quantitative distribution and paleoecology of benthonic foraminifera in the Eocene Lede Formation at Balegem (Belgium).

IV. Quantitative distribution and paleoecology of benthonic foraminifera in the Wemmel Sands Member of the Asse Formation (Eocene) at Strombeek Bever (Belgium).

V. Quantitative distribution and paleoecology of benthonic foraminifera in the Asse Formation and Kallo Formation at Assenede (Belgium). -2-

Quantitative distribution and paleoecology of benthonic foraminifera in the Brussels Formation, the Lede Formation and the Asse Formation (Eocene) at Haacht (Belgium)

H.J.F. HOOYBERGHS. -3-

CONTENTS.

I. Abstract. 2. Introduction. 3. Lithological description of the deposits. 4. Distribution of benthonic foraminifera in well P.3. 5. Triangular plot of suborders. 6. Similarities. 7. Diversity index or Fisher a index. 8. Dominance index. 9. Percentage dominance. 10. Paleoecological interpretation of the taxa. 11. Conclusions. 12. Acknowledgements. 13. References. -4-

0 5 10Km. LEUVEN

Fig. 1 Location map. -5-

Log Formations

ASSE FORMATION

LED£ FORMATION ·==-·.., ...... ~:~~~~~~ ·v=:=~vr:::::Jlv • ·.·:·~···· • c;:, ·"'"-J' ••• •• c:::::~· ...... s::=l...... ·=·=·.·.· I vv vI Bioturbations .·=·=·~ . . ... ·==·=·.C::::J' .:= . . • . • c:::=:l...... • . .• . •. ~ Bivalvia ... ~-c::a •• I=§] Sandstone 'c:::.::=!~·.· ~ ...... BRUSSELS . . . . . I -=-1 Clayey sand .....::.· llli:=o". • •• C:;:J. • • . FORMATION 1,.: 1!ll io iw·o "Gres fistuleux .. .~-~-··· Ic:!:>l

(J] Fine sand

...... Coarse sand . . . ~ ...... • •• ...... 0 •• Grovel c::::l. ·.:.; •• • ••••••••• • • • • • • .. ..·~ ...... , .·.. ..·· ...... ·. :.·.. ·• ...... • • • • • .• • ·:~·.;·.·~.-...... • . •--a.. . • . lEPER FORMATION

Fig. 2: Development of the Brussels. Lede and Asse Formations in well P.3 -6-

l. ABSTRACT.

The ben.thonic foraminiferal populations in the Brussels Sands, the Lede Sands and the Wemmel Sands have been studied in a borehole at Haacht. Quantitative countings of up to 200 individuals per sample are made. By successive use of the following methods : quantitative distri­ bution, triangular plot of suborders, similarities, Fisher a index, dominance index, percentage dominance and paleoecological significance of the occurringtaxa, it has been possible to interpret the faunal assemblages paleoecologically.

2. INTRODUCTION.

The "Nationale Maatschappij der Waterleidingen" bored several wells in the vicinity of Haacht for ground water exploration. One of these wells, P.3 is treated here. This well is situated in the Dijle valley, near the hamlet of Wakkerzeel (fig.l, location map). Three different deposits have been sampled in detail : the Brussels Sands, the Lede Sands and the Wemmel Sands. The samples were washed on a 0,074mm sieve. In each residue, countings to 200 individuals of benthonic foraminifera have been made. For a systematic description of the taxa, we refer to KAASSCHIETER (1961).

3. LITHOLOGICAL DESCRIPTION OF THE DEPOSITS.

Three lithological units have been studied in the P.3 well at Haacht : the Brussels Formation, the Lede Formation and the Asse Forma­ tion (KAASSCHIETER, 1961). In the Asse Formation, only the Wemmel Sands Member was sampled (text.fig.2). -7-

1) Brussels Formation.

The Brussels Sands are developed between-67.25m and -33m. They overlie the sandy top of the leper Formation. In the lower part of the Brussels Sands, between- 67.25m and -61.50m, a coarse glauconitic sand is observed. Irregular sandstone concretions, known as "gres fistuleux" occur at-63m. Between-61.50m and -33m, fine calcareous yellow-grey sands are developed. At different levels, sandstone beds and "gres fistuleux" concretions occur. The level at-6lm is rich in Nummulites. Bivalvia have been observed at-Slm. In the upper part of the Brussels Sands, at- 34.50m, the deposit is bioturbated.

2) Lede Formation.

The Lede Sands occur between-33m and -25.25m. At the base of these sands, a fine gravel bed is observed. It contains irregular quartz grains, shell fragments and partly reworked Nummulites. Higher up, the Lede Sands are silty and homogeneous, green-grey in colour, with scattered Nummulites. Calcareous sandstone layers are developed at different levels.

3) Asse Formation.

The Wemmel Sands Member of the Asse Formation in well P.3 is developed between-25.25m and -l3.50m. The lowermost part contains a fine gravel layer with shell fragments and reworked Nummulites. These sands in P.3 are fine glauconitic, slightly clayey and grey-green in colour. Nummulites occur in the whole interval. At lesser depths, the deposit becomes more and more clayey.

4. DISTRIBUTION OF BENTHONIC FORAMINIFERA IN WELL P.3.

Table 1 shows the quantitative frequencies of the benthonic -8-

MILIOLINA

ROTALIINA TEXTULARIINA

Fig. 3 : Triangular plot of the three suborders in the Brussels Sands. -9-

MILIOLINA

ROTALIINA TEXTULARIINA

Fig. 4 : Triangular plot of the three suborders in the Lede Sands. -10-

MILIOLINA

ROTALIINA TEXTULARIINA

Fig. 5 : Triangular plot of the three suborders in the Wemmel Sands. -II-

foraminifera in 200 individuals per sample. Table 2 gives the relative abundance of the taxa. We shall discuss here the fluctuations in the frequencies of the species in. til! different deposits.

I) Brussels Formation.

The Brussels Sands contain a rather homogeneous population in the diffEH:ent samples. Those populations are dominated by several species of the genus Cibicides : C. lobatulus (0-4%,), C. mauPicensis (4-21%), C. propPius acutimargo (2-12%), C. propPius propr,iZf8 (15-::44%), C. sp (0-14%), C. sulzensis(0-4%), C. taUahatensis (0-14%), c. tenelZUs (0-21%) and C. westi (2-21%). The fluctuations in the frequency c,>f C. teneUus, which shows three maxima : 21% (depth 67.20m), 20% (depth 45.60m) and IS% (depth 33.80m) are noteworthy. The genus Elphidium is a fairly important component of the associations E. subnodosum (1-19%) and less frequently E. laeve (0-3%). Rotalia audouini represents a maximum of 10% of the populations, in which some other perforated calcareous benthonic foraminifera occur regularly : Guttulina lactea (0-4%), Gyroidina octocamerata (0-4%), Hanzawaia boueana (G-3%), Trifarina wilcoxensis (0-2%), Globulina gibba (0-2%) and AstePigerina bartoniana (0-2%).

2) Lede Sands.

The Lede Sands are characterized by a remarkably high frequency of C. tenellus (39-59%). Other Cibicides species occur regularly but less frequently : C. lobatulus (2-6%), C. mauPicensis (0-4%), C. propPius acuti­ margo (1-3%), C. propPius propPius (0-3%}~ C. sp (3-8%), C. tallahatensis (0-2%) and C. carinatus (0-3%). Different perforated calcareous taxa occur regularly in the succeeding samples : Bolivina anglica(0-5%), Elphidium laeve (0-3%), Eponides schreibersi (1-5%), Guttulina lactea (0-?%), Rotalia audouini (0-3%), Bolivina carinata (0-5%), Reussella limbata (0-2%), Nonionella wemmelensis (0-6%) and Reussella terquemi (G-6%). -12-

2~ 3 3 8 1 1 2 16 2 8 18 3 , 8 5 2 9 12 1 , 23 8 4 ' 1 11 1 2 60 2 1 7 2 4 2 24 19 2 6 2 6 40 5 8 3 3 1 3 73 1 1 1 7 2 I X 9 8 ' 2 2 1 61 1 ' 1 ' 1 257 6 1 4 1 5 3 13 5 113 6 3 1 2 1 6 3 26 11 6 1 t1 3 2 8 m 3 11 1 3 3 2 268 5 1 8 2 2 12 2 84 2 10 , 7 6 , 5 27.5 '2 1 2 , 7 5 1 7 3m 2 2 9 I 6 1 5 1 5 2 1 5 8 86 1 t1 3 4 2 1 28.1 7 8 I 5 3 ' 181 3 7 I, 7 3 2 6 16 1 18 3 1 6 1 10 3 1 6 I 4 28!1 3 3 , 8 3 3 7 8 118 2 5 1 1 2 2 1 29-295 2 8 1 7 3 7 3 12 1 87 1 1 1 7 2 2 , 2 1 3 2 I, I 2 2 1 5 30!1 1 9 7 4 6 12 88 3 8 3 ' 32 2 t1 5 6 3 3 t1 198 5 t1 5 1 4 I 7 17'0 1 1 13 9 6 6 7 3 89 6 1 3 6 2 " 33.8 2 4 2357952 5 31 13 2 8 1 3 7 2 34.2 11 171171152 11 5 16 11 4 5 1 4 2 1 35 I 8 111246215 9 20 18 25 , 4 1 1 3 1 35.7 17 18852193 15 4 23 23 1 7 1 3 1 .liS 7 137355296 '15 7 28 1B 1 7 2 1 37.2 6 21.1153143 16 12 20 21 3 3 6 5 1 38.i 12 21145711.1 11. 2 32 15 3 4 4 3 1 38.7 8 18117491 9 8 43 8 2 4 1 2 1 .3!15 12 151276185 16 4 27 10 1 1 1 398 15 221055113 7 7 33 22 1 2 3 4 l.fJ.2 7 2J "· 79 12 9 16 4 13 1 13 2 6 1 407 3 27885181 16 5· 11 13 1 2 3 1 1 1.1 4 271088171 19 3 12 I 7 2 1 41.3 3 21877162 17 10 24 12 2 2 4 2 41.7 6 258 71162 19 4 29 I 13 2 5 1 , 2 42.2 12 21746511.5 13 10 ZJ 10 , , 2 4 3 1 3 435 5 227355166 1026 14 , 16 1 1 1 3 45.6 36125121/, 8 40 8 3 1 1 4 1 8 2 45,9 "25849215 12 16 19 , 6 1 , 3 3 4 4 .u;..3 3231559214 7 31 7 2 4 1 1 1 1 I 1 11 49.3 1 9181656182 1 21 2J 2 9 I 3 6 , 2 1 1 4&4 9111647152 5 11 26 2 15 2 6 8 1 1 13 3 , 4!Ui 1101170261, 13 12 10 3 25 4 3 , , 49,9 7 8 9 7D 73 3 7 19 19 2 18 2 2 5 4 1 , 7 , 50.2 131521,65204 6 10 73 11 , 6 2 2 1 1 50.7 514118525 7 8 ,, 1 12. 2 2 2 •4 51,1. 141778221 10 14 12 1 5 2 2 2 1 1 7 517 2 8 21 8 66 26 1 12 10 18 2 3 7 2 4 523 8111074234 10 18 7 2 " 1 4 3 1 53 110121173151 12 8 23 3 15 1 2 4 1 ' 5l8 4111077184 15 10 26 ., , 2 4 1 ' 55 8 18.73 5323 2 21 8 12 122 1 3 5 1 ' 55.7 41566634 12 4 20 20 2 3 1 3 3 3 56 1 5 13 9 54 27 10 5 21 271 5 2 4 3 1 2 3 57.1 1 41676622 4 11 5 19 3 24 t 1 5 4 9 1 58,1 2 51186013 2 15 5 21. 36· 2 1 9 5 1 5 1 59 61996620 5 22 9 4 20 1 1 2 4 5 3 1 59.2 8 26 9 $ 15 6 16 7 26 10 2 8 5 3 1 3 , 2 59.8 9 20 12 60 10 4 13 10 16 21 2 1 1 6 5 2 60.2 52820465 3 ZJ 7 21 1 13 1 2 1 3 3 6 7 60.3 2 122524571 5 18 4 "· 5 16 2 2 2 1 2 61.5 2 3 29 15 56 9 7 16 5 24 1 12 1 4 1 7 1 62-6.?.1 122187015 3 7 11 13 7 9 1 1 7 1 9 ' , 6275 1 743178313 7 28 1 5 7 8 8 1 64 1 133216716 7 16 17 5 15 2 2 2 64.6 2 21031145112 5 10 6 18 2 13 4 1 2 4 6 1 65 5 5 923716613 7 22 12 2 7 2 3 2 3 , 1 , 67 1 3 71474312 3 7 23 20 I 23 1 2 2 1 4 20 4 21 3 7 2 2 3 2 2 67.2 1 2 1 271'5113014 ' 11. 43 5 ' ' 1 ..

T.Jblt~ 7 : Ou.Jntit.ati'llfl distribution of lnnthonic foraminift~ra. -13-

, 0 , 5 2 J , , 7 5 , 2 2 '7 ' 'J 2 ' 6 6 5 , J 2 , , ~ ; 2 2 16 If) J , I. J ' , 2 , , 2 7 ' 1 JO J , 9 4 , 6 4 , , 2 7 2 2 , , J , 6 2 , 2 , , J , , J 2 , 5 1 2 2 , 2 , 6 , 5 , 9 , , 1 ,, :1 :1 , 338 2 31.2 1 , , 1 35 , , 35:1 36.5 :P2 38.2 2 38.7 J!l5 39.8 1.02 IJl7 2 ,, 3 , 'J,J J.t7 1.22 4l5 2 2 4S6 459 3 '43 2 2 3 .49.3 3 49,4 2 '!i6 , 2 49!J 502 !11.7 2 St-' , 517 2 3 2 523 1 , ' , 53 , 2 SJ.B , 1 2 S5 2 , 1 I 1 SS7 , 56 ' , , 57.1 2 , 58.1 , 59 , 5'!12 2 59.8 2 1 I «J.2 , , " , , 60.:1 1 61.5 2 2 6}.62J ' , 6275 64 , 2' 61..6 , 2 65 67 ' 1 67.2 -14-

22$ 5 26 3 , IS 23 1 3 10 5 , 3 24 1 11 5 , , 4 , 2 25 3 IJ 1 2 , 2 2 , ' 25.7 , 2 ' 2 1 , 1 26 , , 3 , 2 2 2 , I , 268 I. , , 2 1 , Zl.S , 2 IS 6 , 3 28.1 6 I. 13 11 217 3 , , 11 2 2 2 28!1 5 , 2 13 29-a; 2 I. 5 13 3 1 :11!1 , 3 5 11 , 4 32 Ill 32.5 3 'f , ff3 , , 33.8 31.2 35 35.7 ~ 372 38.2 38.7 .3!15 39/J 1.0.2 1.0.7 41 1.(3 41.1 1.2.2 4.l5 1.5.6 1.5,9 1.6.3 49.3 4&4 496 ~ 50.2 SlU 51/. 517 52.3 53 538 55 557 56 57.1 58.1 59 59;1 59.8 612 61.3 61.5 6U2I 62.15 64 64.6 65 61 61.2 ii:' ~ BRUSSELS LED£ ASS£ FORMATIONS "'

~~~~~~~~@~~~~~~~~~~~~~~~~~~iese~&E~c~&~~~~~~~~~~~bl~t::fi! l ~~~~~~~tU!tt!t!J~(m TAXA i Lagena 5lflolo Ent050iemo ortugnyona Di5corbis limboto I Outnqul'loculino c05toto ~ ...... ,.. RfNsello llmboto t ,...I Spiro/QOJ/ii!Q ITICQTII!OtQ be/91QJ Trifortna murolts f. - Nollloll sazp/IIJm Arttcultna terq<.~emt ~ .. ~ '-1 ._,.._ Mtlioloceo ~: u-' O...tnqtJelocul•na semtnulum f.-l-1 J "-L{J Bilormo selseyens•s Boltvmo cr.,.,lolo ~ BIJiimtMIIG pulchro .. -- U'1 OlondiJimo /oew!i/Oto I ~Ia w.mme/lensts _.-~ 1....l...}-J -u-u - 1 r"LJ-LJ R~t~JSelloterquem1 TriiOOJiino tri!iiO"'JIO Astef'lgerino sp - - CtbiCtdes pygmeus Qumque/ocultno JUieono - Lomorcktno crtstelloroides - Spfrolocultno ITfCOTfnalo Spiroloculina cosltgero

Bolivmo cooJ

I -~~ _....., ~ Etphtdium laeVC~ ~ - - - Etphtdtum subnodosum t 1.-LJ.~ """1-.J f ·~~ ~ Epotl#des schretbesl

~ Eponttles toulmtfll 3 Globu/lfiQ gtl>bo ~: ~ L.J Guttultno lacteo J - L..J ...... - -..... ~ w f-''-LJ Guttulma pulchelta i Gyratdma ()(:tocamerala 0'1 -1-J~ .._.- ...... - ...... --...... L.J I - - I --- bouea~>a '-J' w - - - ~ - Hanzawata - NolliOII off'"" - Noii/OMita spisso Rotalta audoutnt -u ...... LJ-1_ -L....r~ ...... u ~

U-U Trtlartno INIIcaxeMtS

Gullulma putcllella "\_J L.J ~ ~ Ctbtctdes canna/us - - Guttullna trregutarts L«oticutina sp ~ Textularta aggluttnans Outquetocultna cartnata ~ ...... , Bolivina carmata Glabutma gravtda

...... EpotlldeS umbonatus SaltVtna brabonttea .. ~ BRUSSELS LED£ ASS£ FORMATIONS ~

a~~!~mlem!~~~!~~~~~~~~~~!~&leea&&eee~&m~•~~s~~~t~~~~~~-~~~~~~~~~TAXA ~i' Asterigerma barlotliana

AslerigentlfJ d guerra1 I Bolivina ang11ca ~ Cancris auriculus primit1vus i Cibicides dulemp/fH I Cibicicks lobatu/us g­ I I I I 1 I I I I I I I I l I I I I I I I I I I I Ll I I I I I I I I I I I I I I I I I I I I I I I c::;::: I Cibicides mauricensts ~ s· f Cibic1cks propr1tJ$ acutimargo

-....1 Cib1C1des propr1us propr1us I

Cibicides sp.

Cib1c1des sulzensis Cib1Cides tal/ahatensis

Cibicides tenellus -18-·

Asterigerina bartoniana occurs especially in the upper part of the Lede Sands (0-5%). Less important taxa are Cancris auriculus primitivus (0-2%), ElphidiUm subnodosum (0-1%), Globulina gibba (0-1%), Quinque­ loculina seminula (0-2%), Bolivina crenulata (0-3%), and Buliminella pulchra (0-2%). The appearance of ~liolacea (0-4%) is of note.

3) Wemmel Sands.

The frequency of C. tenellus in the Wemmel Sands is lower (9-30%). Other Cibicides species occur less frequently : C. lobatulus (0-4%), C. sp (1-8%) and C. proprius acutimargo (2-8%). A number of perforated calcareous benthonic foraminifera appear regularly in The Wemmel Sands : Asterigerina cf. guerrai (1-3%), Asterigerina sp. (2%), Trifarina wilcoxensis (0-6%), Textularia agglutinans (2-6%), Nonion scaphum (0-3%), Bifarina selseyensis (1-8%), Bolivina cookei (1-3%) and Eponides umbonatus (0-2%).

Some taxa from the Lede Sands still occur in the Wemmel Sands ~ Asteri­ gerina bartoniana (1-8%), Bolivina anglica (2-7%), Elphidium laeve (0-2%), Elphidium subnodosum (0-4%), Guttulina lactea (3-8%), Rotalia audouini (0-4%), and Nonionella wemmelensis (4-13%). We also note the presence of ~liolacea (0-8%), Quinqueloculina seminula (0-5%) and Spiroloculina tricarinata belgica (0-2%).

5. Triangular plot of suborders.

The foraminiferal populations represent three suborders : Textu- lariina, Miliolina and RotaZina (LOEBLICH & TAPPAN, 1964), which can be plotted on a triangular diagram. MURRAY (1973) marks out the fields for the different possible environments in this diagram. In the deposits studied here, the different assemblages can be situated near the Rotci.Ua corner (figs.3,4,5). According to the interpretation by MURRAY, these assemblages can occur in the following environments : hypersaline marshes, normal marine marshes, hypersaline lagoons, continental shelf and hypersaline lagoons and marshes. -19-

33,8 JJ,j 35 35.7 36.5 37.2 38.2 38.7

~5 39.8

1,().2

/,().7 " "·3 41,7 42.2 22.6 4l5 23 416 24 ] 45,9 2S I I O'Hi SO 'Hi 700% t.IU .I.!U WENMEL SANDS .1.!14 t.!l6 49.9 50.2 5/),7 57,4 51,7 52.3 25.7 53 26 53.8 26.8 55 27.5 55,7 28.1 56 28.7 57.7 28.9 58.1 29-29.5

59 ~ 59.2 32

5!l8 32.5 I O'Hi 700% flU 60.3 LEDE SANDS 61.5 62-62.1 62.75 64 64.6 65 67 67.2 50% 100%

BRUSSELS SANDS

Fig. 6 · Similanty mdex. -20-

6. SIMILARITIES.

This method of SANDERS (1960) measures the similarity between the successive samples in a section. To compare two samples, the percentage occurrence of the species common to the two samples are listed. For each species common to the two samples, the lowest percentage is noted. The total value of all these lowest percentages gives the similarity index. The populations in the two samples are nearly identical when the total value is higher than 80. The associations differ progressively as the similarity index diminishes.

The similarity inde~ for the succeeding samples in the three different deposits is given in fig.6.

In the Brussels Sands, most of the values are between 70% and 93%. Those high values underline the homogeneity of the populations within this deposit. The similarity index is only lower between samples -67 and -65 60%.

In the Lede Sands, the values are slightly lower than in the Brussels Sands : between 67% and 88%, but the species associations remain still rather homogeneous.

In the Wemmel Sands, the similarity index lies between 57% and 66%. Those values are lower than in the two other deposits. The similarity index decreases progressively in the successive deposits and the population differences increase progressively.

7. DIVERSITY INDEX OR FISHER a INDEX.

The diversity index or fisher aindex gives the relationship between the number of individuals and the number of species in a population. The avalue can be determined by plotting the number of species against the number of individuals in the base-graph constructed by FISHER, CORBETT & WILLIAMS (1943). WRIGHT & MURRAY (1972) and MURRAY (1973) draw up the interpretation of the different environments corresponding to the various avalues. -21-

70 iJ 1/ I v II I V;) v 1/ 65 ~ v I I v 1/ v I~~ I v I '/ IJ vVj i/ 1/ v 1/ 1/l/i/ II 55 1 I I/ ~ v1/l/1/ v v [/ 1/1/ v I [/ vV; I / 50 I v 7 lv / v v / I ~'I ~ / I V; / v 45 v v 1.1 I I / / v v/ / vv :! 40 /; ~ ~ v -~ v v v / I-' vI I ~ I J v / v '0 35 va ~ v I v I v ~ I / / .;' (///; / .;' 30 / v / E ~ v I v ~ / v (/ / 1/ v / / v 25 ~ v v vv 1-- v v ~---~--- v v v v "' .-"" 20 ~ v v v v !--' .... 1-- 1-- ~ v :,.... 1- 15 ...... v ~ / / ~ / 1-- ~~--- 10 ___...... - 1- ,.--~ -

~ ~--- 5 ~ - --

0 100 500 1000 5000 10000 Number of individuals

Fig. 7: Fisher o<:. index in the Brussels Sands. ·-22-

70 i/ / I 1/ I II!J I l 65 l v J / l I vI I /lj~ !/ 60 / I !/ v v v II 1/ llvv I'J; J I !/ 55 ll 1/ VI/I/ v v lJ l/1/ lJ I 1/ I / so I VI 17 v I I Vv !/ v / 1/ v v V; [/ 45 / I ~ v / v v 1/ vI I / v v /; 1/ v v/ / 1/ ~ 40 ~ ~ I v -~ v v v I vI I ~ 7/A ~ I / v ..... ~ 35 / I / v I / / ~ f) v il / /; / / / / E 10 v ~ v 1// / ~ / / / / / / v 25 ~ v v,.... [/ v v 1---'J..- ""' l/ v v v 20 ~ v v 17 / / v v v ""' 1--- ..... ""' 15 v v v v ~ - 1--- 1-- (){..:: 1 10 r::- v - i--1- ~ ~ - 1- 5 - ~ -- --

0 100 500 1000 5000 10000 Number of individuals

Fig. 8: Fisher o<:: index in the Lede Sands. -23-

70 J v II V'j; 1/ II 1/ v: I II I i/ I I v v I 1/ V/; I I I 60 I / 1/ lljj '/ I v i/ lv I I I I 55 /I I v I I I / I I / !J /; I /, 50 I I I I I / :; I v / I vI/ 1/ 1/; / v 45 I ~ v vI/ vv v l! v ,.Y /; v II ll v/ / v ~ v v II / vv I _,/ / I / / '0 35 !/A ~ / i/ I v / / / v / ~ ~ / / / / / v / v v / / / / ~/ / 25 ~ v v v v I' v v ~--~ v v v / """ / v 2f) ~ / / f.-v .... v .... / v ...... ~~-- 15 ~ ,...- - v ~ / ...... ~ ..... ~.-- / ...... 1- __, 10 __...... _..... - _....- -- - 1- 5 - !------

0 100 500 1000 5000 10000 Number of individuals

Fig. 9: Fisher IX. index in the Wemmel Sands. -24-

33.8 342 35 35.7 36,5 37.2 38.2 38.7 J!l5 39.8

~2 IJJ,7

41

41,3 1.1,7 1.2.2 22.6 u.s 23 4S6 21.

4U 25 ' 0 5 10' 46.3 15 Ml3 WENMEL SANDS. 49,4

4~ 49.9 50.2 50,7 51,4 51,7

52.3 25.7 53 26 53.8 26.8 55 27.5 5S7 28.1 56 28.7 57.1 28.9 58,1 29-29.5 59 30.9

5~2 32 59.8 32,5 0 5' IS' 60.2 60.3 LEDE SANDS 61,5 62-62.1 62,75 61. 64.6 65 67 67.2 0 5 10

BRUSSELS SANDS

Fig.IO : Dominance mdt:x. -25-

Fig.7 shows the avalues in the Brussels Sands. The a index varies between 3.5 and 9. The possible environments are a hyposaline and nearshore shelf sea or lagoon and a shelf sea of normal salinity. The avalues in the Lede Sands are given in fig.8. The aindex lies between 6 and 12.5, distinctly higher than in the Brussels Sands. These values fall in the field of the shelf seas of normal salinity. The salinity was probably higher than in the Brussels Sanes. The avalues in the Wemmel Sands (fig.9) are still higher : between 10.8 and 16. They correspond to a shelf sea of normal salinity. The higher values could indicate a greather depth than in the other two deposits (BANDY & ARNAL, 1960).

8. DOMINANCE INDEX.

This index gives the number of species in 80% of the total population. The percentages are summed starting whit the most abundant species. When a total of 80% is reachedt the number of species needed is noeed (WRIGHT, 1972). High values, corresponding to many species whit low percentages, indicate a stable environment. A low index corresponds to an unstable or marginal environment. Fig.IO shows the dominance index in the Brussels Sands, in the Lede Sands and in the Wemmel Sands. In the Brussels Sands, the values lie between 4 and 10. The index increases in the Lede Sands (8 to 13) and reaches maximum values in the Wemmel Sands (13 to 17). We conclude that the environment becomes gradually more and more stable in the successive deposits.

9. PERCENTAGE DOMINANCE.

The percentage dominance corresponds to the percentage of the most abundant species in .a sample. WALTON (1964) notes that this percent percentage dominance depends of the sea. It increases with decreasing depth. -26-

22.6 23 21.

25 I 0% so" WEMMEL SANDS

S0,7 51,, 51.7 52,3 25.7 53 26 53.8 ..268 55 27.5 55.7 211.1 56 28.7 57.1 211.9 58.1 29-29.5 59 30.9 5512 32 598 32,5 . 0% 6Q2 100" 60.3 LEDE SANDS 61.5 62-62.1 62.75 64 64.6 65 67 67.2 0% SO% 100%

BRUSSELS SANDS

Fig. 11 : PercM~toge domiii011CII. -27-

The percentages dominance in the different deposits are given in fig. II. In the Brussels Sands, the values vary between 2I% and 44%. In the Lede Sarlds the percentages are higher : 39% to 59%, but in the Wemmel Sands they decrease distinctly : 9% to 30%. The fairly high values in the Brussels Sands indicate a rather shallow marine environment. The sea depth probably decreases slightly in the Lede Sands, while the Wemmel Sands were deposited in a more open marine environment whifua greater sea depth.

IO. PALEOECOLOGICAL INTERPRETATION OF THE TAXA.

Studies on Recent foraminiferal associations prove the influence of the environment on the composition of the benthonic populations. We can accept that, especially at the generic level, the influence of the different facies did not change significantly during the Tertiary. Information on the (paleo-)ecological significance of the occurring taxa is found in e.g. : PHLEGER (1960), BANDY (I960, 1964), WALTON (1964), WRIGHT & MURRAY (I972), MURRAY (1973), WRIGHT (1972- 1973), MURRAY & WRIGHT (I974), BOLTOVSKOY & WRIGHT (1976) and GERITS, HOOYBERGHS & VOETS (1981).

I) Brussels Sands.

The population in the Brussels Sands are dominated by Cibiaides. This is a common inner shelf genus living in a wide variety of tempe­ rature and salinity conditions. It is attached to all types of substrates : vegetation, stones, shells, living animals. Cibiaides occurs from arctic to tropical areas, but is currently most abundant in temperate seas: Especially C. lobatulus occurs most frequently in the transition zone between a protected bay and the open ocean. The absence of ~liolina indicates a normal salinity orhyposaline conditions The presence of planktonic foraminifera (HOOYBERGHS, 1983) indicates the proximity of open marine conditions. Another important genus is Elphidium. It occurs most abundantly in very shallow environments : tidal marshesand lagoons or nearshore, -28-

but in oxygen-rich water. A few other hyalin calcareous taxa occur regularly but less frequently in this deposit. Guttulina and Gyroidina

are typical genera in shelf environments. Hanz~~ia and Rotalia occur most frequently ·in rather shallow, nearshore to inner shelf conditions.

i) Lede Sands.

Cibiaides is still a dominant genus in the Lede Sands. The

presence of ~lioLids indicates higher salinities : normal marine to hy­

persaline. The ~lioUds, particula.rlyQuinqueloaulina and Triloaulina become abundant in shallow shelf seas and in channels and bays. They rarely occur in hyposaline conditions. The temperature also becomes

higher in the Lede Sands. ~liolids especially occur in temperate to

tropical waters. The frequency of broken ~liolids indicates a rather turbulent environment. Rotalia and Guttulina still occur regularly in the Lede Sands. A few new genera appear significantly in this deposit. Small smooth species of Bolivina (B. angliaa, B. aarinata, B. arenulata) prefer a inner shelf

zone with normal salinities (33% ~ 37%). Buliminella mainly occurs on the shelf in normal marine, temperate con­ ditions. Nonionella preferably appears in temperate to subtropical waters in normal marine conditions. Eponides and Reussella occur in an inner shelf to bathyal environment. Asterigerina, which appears especially in the upper part of the Lede Sands, normally dominates in an inner shelf zone under conditions of stable salinity.

3) Wemmel Sands.

Different taxa from the Lede Sands still occur in the Wemmel

Sands : Bolivina, Elphidiwn, Guttulina, Rotalia, ReusseUa, ~Uolaaea, Quinqueloculina (lower part), Buliminella and Nonionella. The frequency of Asterigerina increases in an environment with more stable salinity. -29-

Cibicides occurs less frequently, being replaced by the other hyalin calcareous benthonic foraminifera. A few species appear for the first time at a significant frequency. Trifarina and TextuZaria occur in

normal marine e~vironments on the shelf and in the upper bathyal zone. Nonion is a common genus on the shelf of normal marine seas. The presence of striate BoZipina's (B. cookei) indicates an increasing sea depth (central and outer shelf) in subtropical to tropical areas.

11. CONCLUSIONS.

The Brussels Sands were deposited in a sea with moderate temperature and salinities on an inner to central shelf (50- lOOm). The seawater was rich in • An important vegetation probably favoured o2 the development of Cibicides. The presence of planktonic foraminifera indicate an opening to the ocean. The regression of the Brussels sea was followed by a new transgression. The salinity of the sea increased slightly during deposition of the Lede Sands to normal marine or hypersaline conditions. At the same time the temperature increased to

tropical-subtropical values. The sedimentation took place on an inn~r shelf environment, where the water was more turbulent than in the Brussels sea. The depth of the sea increased quickly in a new trangression of the Wemmel sea to a central to outer shelf environment (100-lSOm), which is indicated by the occurrence of striate BoZivina's. The salinity and the temperature remained fairly high.

12. ACKNOWLEDGEMENTS.

The author owes gratitude to the "Nationale Maatschappij der Waterleidingen" and to Dr. P. Laga of the Belgian Geological Survey for permission to study the samples from the borehole at Haacht. ;- ;\t30- '

13. REFERENCES.

BANDY, O.L. 1960- General correlation of foraminiferal structure with environment. Int. Geol. Congres, Report 21, Sess. Nordon 1960, P.XXII, 7-19, 9 figs.

1964- General correlation of foraminiferal structure with environment. In "Approaches to Paleoecology", Imbrie & Newell, 75-95.

BANDY, O.L. & ARNAL, R.E. 1960- Concepts of foraminiferal paleoecology. Bull. Am. Ass. Petr. Geol., 44 (12), 1921-1932, 14 figs.

BOLTOVSKOY & WRIGHT, R. 1976 - Recent foraminifera. 515 p.

FISHER, R.A., CORBET, A.S. & WILLIAMS, C.B. 1943 - The relation between the number of species and the number of individuals in a random sample of an animal population. Journ. Animal Ecol., 12, 42-58, 8 figs., 9 tab.

GERITS, M., HOOYBERGHS, H. & VOETS, R. 1981 - Quantitative distribution and paleoecology of benthonic

foraminifera recorded from some Eoc~ne deposits in Belgium.

Prof. Paper, 1981/3, nr. ~82, 53 p., 6 figs., 19 tab.

HOOYBERGHS, H.J.F. 1983 - Middle Eocene planktonic foraminifera recorded from the Brussels Sands Formation at Haacht (Belgium). Tert. Res., 5(1), 9-24, Z text-figs., 4 pl. -31-

KAASSCHIETER, J-P.H. 1961 - Foraminifera of the Eocene of Belgium. Memoires Inst. r; Sci. Nat. Belg., 147, 271 p., 8 tab., 16 figs., 16 pls.

LOEBLICH, A.R. & TAPPAN, H. 1964 - Treatise on Invertebrate Paleontology. Part C : Protista : vol. 1, 1-510. vol. 2, 511-900, 653 figs.

MURRAY, J. W. 1973 - Distribution and ecology of living benthic foraminiferids. 274 p., 102 figs.

MURRAY, J.W. & WRIGHT, C.A. 1974 - Palaeogene foraminiferida and palaeoecology, Hampshire

and Paris B~sins and the English Channel. Spec. Papers in Paleontology, 14, 129 p., 47 text-figs., 20 pls.

PHLEGER, F.B. 1964 - Ecology and distribution of Recent foraminifera. 297 p., 79 figs., 11 pls.

SANDERS, H.L. 1960 - Benthic studies in Buzzands Bay. II. The structure of the solft-bottom community. Limnol. Oceanogr., 5(2), 138-151.

WALTON, W. R. 1964 - Recent foraminiferal Ecology and Paleoecology. In : IMBRIE & NEWELL "Approaches to paleoecology", 151-237, 29 figs. -32-

WRIGHT, C.A. 1972 - The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proc. Geol. Ass., 83(4), 413-420.

1972 - Foraminiferids from the London Clay at lower Swanwick and their paleoecological interpretation. Proc. Geol. Ass. 83(3), 337-347, 4 figs.

1973 - Foraminiferids from the Lutetian at Ronquerolles (Val d'Oise) and their paleoecological interpretation. Revue de Micropal., 16(2), 147-157, 5 figs.

WRIGHT, C.A. & MURRAY, J.W. 1972 - Comparisons of .M:>dern and Paleogene Foraminiferid distributions and their environmental implications. Mem. Bur. Rech. Geol. Min., 79, 87-96, 5 figs. -3i-

Quantitative distribution and paleoecology

of benthonic foraminifera in the Eocene

Brussels Sands Formation at Diegem (Belgium)

H.J.F. HOOYBERGHS ·-34-

CONTENTS.

l. Abstract. 2. Introduction. 3. Lithological description of the Brussels Sands Formation at Diegem. 4. Quantitative distribution of benthonic foraminifera. 5. Triangular plot of suborders. 6. Similarities. 7. D i\&sity index or Fisher a index. 8. Dominance index. 9. Percentage dominance. 10. Paleoecological significance of the occurring taxa. 11. Conclusions. 12. References. -35-

ZAVENTEM

Fig. 1: Location map. -36-

15 . . . •. • . . . • . . .• • .• • .• •fll . ••• . .• • • • •

• •e•4)CD• ~ .CI) •• •• 13 •. ·e · . ·a:JJ • !" . . · CD • • • • • • . . . . 12 . Q . ,a, ;:::;:; . • .• .CD . • . . cp •(I) e • • • . . 0 .m . . 11 • ,..-y • • • • ,...... • • (I). • • • "d) SJ> • c». a> 4S) • • • • • 0. ..0. .. C'll •• 10 • (11 • fD • • a~.. . . • • • ttf/...... ~0. .a,.. • (D. • • 9 • • • • c:l> • • tD • • • • 4). • ~ • dJ BRUSSELS • tJ:) • • • • • • • • • '(a:) • •••• (I) • • ...... FORMATION 8 ., • 'U#. • (!) • • . .-•• • CD ,(I) CD • • ·o• • . • 5;:)·o.• .t:J;IJ • 6 • C2. J::::j "tD "4) •• a>•• LiJ~ White spots 5 - ·. : cg". ".c:Pa» r-"'\.. t:d~. •\...... • . a» . :---....J.& . . • .C!P •. •. •. Cl>. • . eel). [J Fine sand ~. . • • •• 4 • • •CD • CD • CD• cD ... cD _: ch ... to

0 0 0 (!) lllo D 0 0 Oa:>O ID • • (I) • • "cb I<:)I Sandstone 3 en . • "'·. •. ru Bivalvia 2 ""...... • . 4). • . (p .

Fig. 2 : Development of the Brussels Sands Formation at Diegem . -37-

& VI ... i!... .§ ~ ~ :§ ~ 'Su ~ ·~ ~ ~ e 0 ~ VI :g ·~ ~ .!;! ·~ I! VI e ~ .!;! VI i 2 .i;! ] "' :::. ~ :s .Q ~ 8 ~ ... ·- ~ ~ u ~ ~ ii a 1 ~ 01 .s .~ .i i 31: i ~ c: " .!;! ~ a I S! ~ ·~ ... ~ .S! i 0 ... 13 0 0 1! 0 ~ 0 .:::.e VI VI ~ .s "' "' .s i ~"' :§ .~ .~ c: ~ § ·~ :ij ~ ~ ~ ~ ~ :. .!;! ] :::. .S! .a: .!:! 2 2c: :Q !:! .a ~ ~ c: -~ ~ ... ~ .Q ~ 'S ·- .9- §! 1.:) ;3 ct' ~ tu ! 3 1...1 5 13 1...1 3 d ~ ~ .3 15 2 8 28 " ' 31. ' 3 14 ' 1 9 26 13 3 " 3 13 6 1 11 23 12 3 " 3 12 8 9 1 12 " 1.() 8 1 ~ , 1 7 13 12 2' 59 2 ....0 3 - 10 5 9 17 7 1 51 7 2 1 ~ Q: 9 2 ' 24 22 2 47 ' 2 e 8 3 12 7 11 ' 57 6 7 2 , 1 9 , 9 7 5 55 2 6 7 , (/) 1 16 53 , 3 ~ 6 5 3 (/) " ' 5 2 3 8 , 10 13 3 55 5 ~ Q: 9 1 9 15 2 51 1 , 2 , , QJ ' ' ' , 12 ~ 8 1 3 2 9 , 9 58 , , 2 3 6 " 13 57 , 3 , 2 11 , 16 1(} ', 55

Tab#• 7 : Distribution of bf!lllhonic forammlf«a in thf} Bruss.ls Sands Formation at Di.g.m. ~ ~ BRUSSeLS FORMATION

"' - ~ ~ ~ ~ ~ ~ ~ ~ 5 : ~ ~ ~ ~ ~ Q i u u ...... w ...... 0 ...... u-.....-ui..Trrou .... Guttulina tactea [ Pyrulii!O thoumi Trifarii!O WtiCOXei!SIS §- ~------u - "'iiiiiiiiJ Elphidium subl!tXIOsum ~ () ~rrTI-uu··uuo·rro .... Eponides schreibef'si ~ Cibicides proprius proprtus ~:;,, i'i' ouuoououUUUUUUTI a0' 3 5' Cibicides westi a~ oooouuuouuuuooo s· I .... 0 = u 0 0 0 = - ...... w u u u I Oyroidii!O octacamerata w l 00 I ~ Hanzawaia baUeanum l ~;) a- w ~ w ~ L.. g...... ------.....~ Cibicides lobatullus !a Cibicides proprius acutimorgo § --rru-aL:J-uwu-u .....u -.;;.;1-L..l u Guttulina pulchella ~ Lagena hexagona = .... = u Guttulii!O irregularis 1 8alivi110 anglica NofltOII affine Cancrls auriculus primitivus -39-

1. ABSTRACT.

The benthonic foraminiferal populations in the Eocene Brussels Sands Formation have been studied in a temporary outcrop at Diegem. Countings to 100 individuals per sample have been made. By successive use of quantitative distribution, triangular plots of suborders, similarities, Fisher a index, dominance index, percentage dominance and paleoecological significance of the occurring taxa, it has been possible to interpret the faunal assemblage paleoecologically.

2. INTRODUCTION.

During excavations along the railway Brussels - Leuven at Diegem (fig.1, location map), the Brussels Sands Formation was temporarily exposed. The samples have been treated with H 0 and sieved 2 2 on a 0.074mm sieve. In each residue, countings to 100 individuals of benthonic foraminifera have been made. For a full systematic description of the occurring taxa, we refer to KAASSCHIETER (1961).

3. LITHOLOGICAL DESCRIPTION OF THE BRUSSELS SANDS FORMATION AT DIEGEM.

Fig.2 shows the developement of the Brussels Sands in the lo­ cality studied. In the lower part of the section, these sands are yellowish with many small white spots. Bivalvia have been observed at the base of the interval. Sandstone concretions occur at discontinuous beds at levels 7 and 8. Higher up, the Brussels Sands become more green due to a higher glauconite percentage. Spots of white sand still occur in the higher part of the section. Between levels 9 and 12 different scattered sandstone concretions have been observed.

4. QUANTITATIVE DISTRIBUTION OF BENTHONIC FORAMINIFERA.

Tables l and 2 show the relative frequenties of the occurring taxa. The populations in this interval are rather homogeneous. -40-

M/L/OLINA

ROTALIINA TEXTULARIINA

Fig. 3 : Triangular plot of suborders in the Brussel Sands at Diegem . -40- 1

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1 0% 50% 100%

Fig. 4: Similarities. -41-

70 II J v II ,/ r;J vv II I 1/ 65 v I / v I II 1/ v~vV/; I II II 60 V; I v I Vv 1 ~ I '/; I I I 55 I VV I I / v I /! //; / 50 I I I I / VI I I / / ~ J II v II v 45 I ! 'I "V; / 1/ j II ~I; v v /'t' /; ~ I :Y/ / / ~ v v I v v v v I ,'/ ,,. I I / / V$ ~ v / v I / / // v ,. ~ / v / ~ / / / / / / / v ~ l/ v 25 ~ / v v v v v~--' v v v v v / / 1--' / 20 ~ v v / v :,...... / v v-~--" 15 v v / --- ~ _..!.------10 - ~ - --- -1- - 5 fo- - - --

0 100 500 1000 5000 10000 , Number of individuals ' Fig.S: Diversity index or Fisher oc index. -42-

Hanzawaia (34-59%) 1s the dominating genus. However, its frequency decreases slightly in the upper part of the section. The Cibieides species are also important. The frequency of C. westi varies from 7 to 22% and C. proprius aeutimargo reaches 0-8% in the assemblages. C. proprius proprius (7-28%) becomes more frequent especially at the top of the interval. A few other hyalin calcareous benthonic foraminifera are fairly constant components of the associations : Guttulina laetea (2-8%) and Elphidium subnodosum.

5. TRIANGULAR PLOT OF SUBORDERS.

Since no ~liolina or Textulariina occur in the section studied, the triangular plot of suborders lies on the Rotalia corner (fig.3). According to the interpretation of the different ecological fields by MURRAY (1973), the following environments are possible : hypersaline marshes and lagoons, hyposaline lagoons, normal marshes and shelf sea of normal salinity.

6. SIMILARITIES. (SANDERS, 1960).

Fig. 4 represents the similarity index between successive samples. This index varies between 77 and 96%. These high values underline the homogeneity of the different populations.

7. DIVERSITY INDEX OR FISHER a INDEX. (FISHER, CORBETT & WILLIAMS, 1943).

In fig. 5, the number of species is plotted against the number of individuals. The diversity index or Fisher a index varies between 1.5 and 4. According to the interpretation of the different environments corresponding to the various a values by WRIGHT & MURRAY (1972) and MURRAY (1973), -43-

15

11.

13

12

11

10

9

8

7

6

5

I.

3

2

1 0 5 10

Fig. 6 : Dominance index. -44-

15

14

13

12

11

10

9

8

7

6

5

.4

3

2

1 0% 50% 100%

Fig. 1: Percentage dominance. -45-

the following environments are possible : hyposaline and nearshore shelf seas, hypersaline lagoons and marshes, hyposaline lagoon and marshes and normal marine marsh.

8. DOMINANCE INDEX. (WRIGHT, 1972).

Fig. 6 represents the number of species in 80% of the populations. The dominance index is fairly constant and varies from 3 to 5. These low values indicate a rather shallow sea or marginal environment in ~ich the sedimentation took place.

9. PERCENTAGE DOMINANCE. (WALTON, 1964).

The percentagesof the most abundant species in the different samples are given in fig. 7. In the lower part of the section, these percentages are fairly constant. They vary between 51 and 58. These high values indicate a rather shallow environment. From sample 9 to sample 15, the percentagffibecome more variable. They vary from 34 in sample 15 to 59 in sample 11. The generally lower values in the uppermost part of the section probably suggests a slight deepening of the sea.

10. PALEOECOLOGICAL SIGNIFIANCE OF THE OCCURRING TAXA.

Information on the (paleo-) ecologicalsignificance of the occurring taxa is found in e.g. PHLEGER (1960), BANDY (1960, 1964), WALTON (1964), WRIGHT & MURRAY (1972), MURRAY (1973), WRIGHT (1972-1973), MURRAY & WRIGHT (1974), BOLTOVSKOY & WRIGHT ·(1976) and GERITS, HOOYBERGHS & VOETS (1981).

Hanzawaia~ the most abundant genus prefers a shelf environment. Cibicides is currently most abundant on shelves of temporate seas, where it is attached on all types of substrates such as vegetation. Elphidium occurs most frequently on a shallow inner shelf in oxygen-rich waters with a lot of algae. -46-

Guttulina is a typical inner shelf genus and Gyroidina is found especially on a normal marine shelf.

The absence of ~liolina suggests a low salinity. Quinqueloeulina and Triloeulina do not suffer salinities below 30%.

11. CONCLUSIONS.

In this locality, the Brussels Sands were deposited on a shallow inner shelf. Later, the sea depth probably increased slightly. The water was oxygen-rich and the revival of algae was favoured. The salinity of the temperate waters was rather low (below 30%). -47-

12. REFERENCES.

BANDY, O.L. 1960 General correlation of foraminiferal structure with environment. Int. Geol. Congress, Report 21, Sess. Nordon 1960, XXII, 7-19, 9 figs. 1964 General correlation of foraminiferal structure with environment. In "Approaches to Paleoecology", IMBRIE & NEWELL, 75-95.

BOLTOVSKOY, E. & WRIGHT, R. 1976 Recent Foraminifera. 515 p.

FISHER, R.A. ; CORBETT, A.S. & WILLIAMS,' C.B. 1943 The relation between the number o£ species and the number of individuals in a random sample of an animal population. Journ. Animal Ecol., vol.l2, 42-58, 8 figs., 9 tab.

GERITS, M. ; HOOYBERGHS, H. & VOETS, R. 1981 Quantitative distribution and paleoecology of benthonic forami­ nifera recorded from some Eocene deposits in Belgium. Prof. Paper, 1981/3, nr.l82, 53 p., 6 figs., 19 tab.

KAASSCHIETER, J.P.H. 1961 Foraminifera of the Eocene of Belgium. Mem. Inst. r. Sci. Nat. Belg., 147, 271 p., 8 tab., 16 figs., 16 pls.

MURRAY, J.W. 1973 Distribution and ecology of living benthic foraminiferids. 274 p., 102 figs.

MURRAY, J.W. & WRIGHT, C.A. 1974 Palaeogene foraminiferida and paleoecology, Hampshire and Paris Basins and the English Channel. Spec. Papers in Paleont., 14, 129 p., 47 figs., 20 pls. -48-

PHLEGER, F.B. 1960 Ecology and distribution of Recent foraminifera. 297 p., 79 figs., 11 pls.

SANDERS, H. L. 1960 Benthic studies in Buzzands Bay. II. The structure of the soft-bothom community. Limnol. Oceanogr., 5(2), 138-151.

WALTON, W.R. 1964 Recent Foraminiferal Ecology and Paleoecology. In "Approaches to Paleoecology", IMBRIE & NEWELL, 151-237, 29 figs.

WRIGHT, C.A. 1972 Foraminiferids from the London Clay at Lower Swanwick and their paleoecological interpretation. Proc. Geol. Assoc., 83(3), 337-347, 4 figs. 1972 The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proc. Geol. Assoc., 83(4), 413-420. 1973 Foraminiferids from the Lutetian at Ronquerolles (Val-d'Oise) and their paleoecological interpretation. Revue de Micropal., 16(2), 147-157, 5 figs.

WRIGHT, C.A. & MURRAY, J.W. 1972 Comparisons of modern and paleogene foraminiferid distribution and their environmental implications. Mem. B.R.G.M., 79, 87-96, 5 figs. -49-

Quantitative distribution and paleoecology of benthonic foraminifera in the Eocene Lede

Formation at Balegem (Belgium)

H.J.F. HOOYBERGHS -so-

CONTENTS.

1. Abstract. 2. Introduction 3. Lithological description of the Lede Sands at Balegem. 4. Quantitative distribution of benthonic foraminifera. 5. Triangular plot of suborders. 6. Similarities. 7. Diversity index or Fisher a index. 8. Dominance index. 9. Percentage dominance. 10. Paleoecological interpretation of the taxa. 11. Conclusions. 12. References. -51-

~3 ..... - t(Of tr•l"

0 5 10Km

' ' ' ' ' ', \ ' \ .... \ \ ston\ \ \ \ \ 0 1Km \ \ \

Fig. 1 : Location map. -52-

Asse Formation 1.4 :. : •: .:. :. : .:. •..... ·.. : . :...... 13

.:. :. : . : . : . : . :. i )·),.. : ••••.•.. ·(J·ll· . : . : . : . : .(j . : . : . :. : . :· . :-:.fJ·>. . . . :-:. .!):· . . . . .

Lede Formation II.••• •., •••• • Nummulites

M) Bivalvia

Clay I I ~ I I Calcareous ·I· I· I· l·l· I ·1· . s.:~ndstone 2 :-:-:-:-:-:-:·:-·.-:·:-: ffi8 · i ."1: I·· .I: I·· .I :T·· . Sand 1 ~~-~-~~;-~~~~~~~... ~o_ .. :".~ ------D •••••••••••• •· ••••••••• 0 ...... r···~-t Gravel rm ...... Panisel Formation •• ••• ......

Fig.2: Outcrop of the Lede Formation at Balegem. -53-

1. ABSTRACT.

The benthonic foraminifera in the Eocene Lede Sands Formation have been studied in a quarry at Balegem. Quantitative countings of up to 100 individuals per sample are made. Successive use of quantitative distributions, triangular plots of suborders, similarities, Fisher a index, dominance index, percentage dominance and paleoecological significance of the occurring taxa, allowed us to interpret the fa~nal association paleoecologically.

2. INTRODUCTION.

The Lede Sands Formation is exposed in a quarry at Balegem (fig. 1, location map). The outcrop was sampled in 1982. The samples were washed on a 0.074 rom sieve after treatment with H o • In each dried 2 2 residue, countings to 100 individuals of benthonic foraminifera have been made. For a full systematic description of the occurring benthonic taxa, we refer to KASSCHIETER (1961).

3. LITHOLOGICAL DESCRIPTION OF THE LEDE SANDS FORMATION AT BALEGEM.

In the Balegem quarry, the Lede sands cover the glauconitic sands of the Panisel Formation (fig.2). At the base of the Lede Sands, a thin gravel layer occurs which yields many reworked fish teeth. The lower part of the Lede Sands is white in colour and four calcareous sandstone beds are observed, two of which are rich in Bivalvia. Level 5 contains many Nummulites. The middle part of the section was not exposed when it was sampled. Higher up (levels 6-12) Bivalvia occur scattered in the Lede Sands or more concentrated in levels 6 and 12. In the uppermost part, the Lede Sands become yellow in colour (levels 13 and 14), but here they are completely decalcified. The Lede Sands are covered by the Cassel Clay Member of the Asse Formation. -54-

e ¥l ·~ ~ '5 Ill ·- Ill :::;, ·r ~ 5 ·~ -Q. ·~ j ~ 'tJ .s ... Ill Ill 41 - .2 ~ .... .2 a ~ Qi .2 :::;, e ~ .g 41 2 ....: ~ ~ ·~ .2 2 - u :::;, c:i .s·- e a 8 :> 2 ~ ~ c:i ~ .Q ·- .... :g c:i c: Ill b .~ ~ u ~ 41 "' .. -J ... ·2' a ~ 41 .....t t '5 ~ .s 01 Q. "' ... 0 ·- ~ .t ~ .Q u ~ -Ill u a ~ c: :::;, .!;! ·a 0 Ill ~ .s 0 c: a a a ~ ·- e ~ ~ ... .~ c: .s 0 ~ .:::! a Qj ·-:::;, ~ ·~ .~ .~ ~ .s .!:!' .!;! c: ~ c: ~ ~ -u ~ ::J ·- :> ~ .Q 0 0' ... V) .... ~ - - .....'5 '5 ~ .~ e ~ ·-... ·-·~ ...... -.2 .Q e .s c: ~ ::J ·- ·- Ill -a. .E 0 ::J 41 ~ i ~ -- (..) 1-:::: C) (!)- (!) (!) <5 t3- c3-

12 1 8 6 28 5 4 4 <: 11 2 8 13 3 31 5 3 3 a TO 7 12 7 31 5 6 h: 9 5 5 7 25 I. 15 5 3 2 ~ 8 2 2 5 1 10 2 20 8 5 Q: 7 2 3 6 3 6 14 6 2 2 4 6 3 3 19 fr 5 7 1 1 1 4 2 2 24 6 26 2 4 I. 1 3 I. 34 7 21 3 2 2 lu C) 3 13 8 3 I. 2 2 2 26 2 16 lU 2 7 3 4 I. 3 27 3 17 6 2 2 -J 3 1 6 2 7 2 2 39 6 3 17 5 2

Table 1. ~ o- ., SAMPLES :-- LED£ FORMATION I I _/""' TAXA ~· .... too...... , ' ~ ~ VI ~ Cb

.... - "v ~ til a, ...... CIO 10 5 - i\) - - - "v Bulimina parisiensis "v - Cibicides carinatus - Articulina terquemi "v - - CIO til - Nonion scaphum - - Spiraloculina canaliculata - Reussella terquemi Nanion graniferum I - \J1 0\ - Hanzawaia boueanum I ~ o- I'D- !"' LED£ FORMATION

~ ~ ~ ~ ~ ~ ~ ~ 5 ~ ~

u D uo D LO.T------.:;d--..- ~ Textularia agglutinans

Dentalina inarnata Gtobulina gibba ~--""'""' ......

U---uL...J-~------~ ..... Globulina gravida ~- ...... ~ ------...... --- Guttu/ina irregularis I U1 Guttulina tactea -..! 0 o ""'""'w o u w u u-0 u ...... I

~ ~------...-..-. Guttulina problema Dot ina orbignyana

~------...... L-.1 Buliminella sp. cf. 8. pulchra Bolivina crenulota m w ""'""'0 ~ - ----o - ..... t::J ....., ....., 0 m. Asterigerina sp.

Rotalia audauini

~DO -~ouwu £/phidium taeve

D ...... -----~...... ------...-...... ,.. Bifarina selseyensis ~ o- -11) FORMATION SAMPLES ~ LED£ TAXA

'I ~ ~ 5 ...... 1\1 " "' 0) - - "' ""' Cibicides tenellus

0TI uu-~-LI u-DurrffiJ

o------u·-~--~- D D 0 D Nonionello wemmelensis wo wwooooouo Lomorckino cristelloroides I Quinqueloculino /udwigi V1 00 w uoo= wo I

\:-J -I...,;;,J" ...... --·--~-- --- ______,. Lenticulino sp. ------~------~ Bolivina anglico w------c:r-=------c.J Cancris subconicus uu=.rr~uuo Cibicides lobotulus Cibicides proprius propr'fUs ooc::~o...... , DODO ~o u-u---~ Cibicides proprius var. acutimargo

=------~-~...... ------= Spiroloculino costigero var. nuda ...... LJ Pyrulina thouini Glondulino loevigoto Triferino murolis Q;1 o- -~ FORMATION !\.1 LED£

... t.J ~ u, 0) 'I Cb (() 0 ... - "' "'- Lagena striata Reussella I imbata = uuuoouu Miliolacea Quinqueloculina bicarinata uuu c::lc::lo Quinqueloculina carinata Quinqueloculina juteana Quinqueloculina seminula I ==o 1.1'1 uu 1.0 u u I uuuo== Triloculina angularis

uur::;::J Triloculina trigonula = = c:J t:::J Bulimina parifiensis Cibicides carinatus . Articulina terquemi a==uu = Non ion scaphum Spiroloculina canaliculata Reussella terquemi Nanion graniferum Hanzawa1a boueanum -60-

4. QUANTITATIVE DISTRIBUTION OF THE BENTHONIC FORAMINIFERA.

Tables l and 2 show the relative abundance of the benthonic forami­ nifera in the Lede Sands at Balegem. It is possible to distinguish three different faunules in this section. We shall discuss here the relative frequencies of the different taxa in the three faunules.

Faunule 1 (levels 1-5).

Rotalia audouini is the most abundant species in this faunule : 24 to 39%. Cibicides tenellus also reaches relative high frequencies : 16- 26%. The agglutinated Textularia agglutinans is a significant component of the associations 3-13%. Different hyalin calcareous taxa occur in this interval in smaller quantities : Globulina gPavida (1-6%), Guttulina iPPegularis (1-4%), Guttulina lactea (2-7%), Bolivina cPenulata (l-4%), and Elphidium laeve (2-7%). Some other hyalin calcareous species appear in part of the interval : Nonionella wemmelensis (0-5%), Lamarckina cPistellaPoides (0-6%), CancPis subconicus (0-3%), Cibicides lobatulus (0-10%), Cibicides pPopPius pPopPius (0-6%), Cibicides pPopPius acuti­ maPgo (0-4%) and Buliminella cf. B. pulchPa (0-2%).

Faunule 2 (levels 6-7).

The frequencies of Rotalia audouini (6%) and Cibicides tenellus (3%) diminish distinctly in these samples. The sudden appearance of

different ~liolids : Quinqueloculina ludWigi (14-19%), SpiPoloculina costigePa var. nuda (0-l%), broken ~liolacea (10-11%), Quinqueloculina bicaPinata (1%), Quinqueloculina caPinata (5-9%), Quinquelocutina juleana (0-3%), Quinqueloculina seminula (6-13%), TPilocutina angutaPis (10-17%) and TPiloculina tPigonuZa (7-8%) is noteworthy. Cibicides tobatutus (2-10%) and LamaPckina cPistellaPoides (3-6%) still occur significantly. Several hyalin calcareous taxa disappear completely or occur in small quantities : Guttulina iPPegulaPis (2%), Guttulina lactea (3-4%), Cibicides pPopPius pPopPius (0-1%),and Cibicides pPopPius -61-·

Miliolina

Rotaliina Textulari ina

Fig. 3: Triangular plot of suborders in faunule 1.

Miliolina

Rotaliina Textu/ari ina

Fig. 4: Triangular plot of suborders in faunule 2. -62-

Miliolina

Rotaliina Textulariina

Fig. 5: Triangular plot of suborders in faunule 3. -63-

aautimargo (0-1%). Nonion saaphum first appears (0-2%). The agglutinated Textularia agglutinans occurs but sporadic (0-2%).

Faunule 3.

Faunule 3 is characterized by new high frequencies of Rotatia audouini (8-25%) and Cibiaides teneZZus (15-31%) and by the presence of different ~Ziotids, mostly less abundant than in faunule 2 : Quinque­ ZoauZina Zudwigi (o-5%), SpiroZoauZina aostigera var. nuda (0-2%), broken

~Ziotaaea (2-11%), Quinquetoautina aarinata (0-4%), Quinquetoautina semi­ nuta (1-9%), Tritoautina angutaris (0-6%) and Tritoautina trigonuta (0-2%). The agglutinated Textularia aggtutinans occurs in restricted quantities (o-2%). EZphidium Zaeve is again distinctly present in faunule 3 (4-7%). Also Guttutina Zaatea (2-8%) and Lamarakina aristeZZaroides (3-8%) commonly occur (2-8%). Some other hyalin calcareous foraminifera are represented in small quantities : Gtobutina gibba (0-2%), Bolivina arenutata (0-5%), Nania­ netta wemmeZensis (Q-5%), Cibiaides Zobatutus (3-5%) and Cibiaides proprius proprius (0-5%). The more significant appearance of Asterigerina sp. in part of the interval (0-7%) and of Nonion saaphum (1-8%) is of note.

5. TRIANGULAR PLOT OF SUBORDERS.

The three suborders of benthonic foraminifera, Textutariina,

~ZioZina and Rotaliina, can be plotted on a triangular diagram. MURRAY (1973) marks out the fields for the different possible environment in this diagram.

The triangular plots of suborders ~n the three faunules are show in figs. 3,4 and 5. In faunule 1, the values lie in the vicinity of the RotaZia corner, on or near the Rotaliina - Textutariina line. The possible environ­ ments for these plots are : hypersaline marshes or lagoons, normal marine marshes, shelf seas and hyposaline lagoons. -64-

12

11

10

9

8

7

6

5 ' 3

2

1 0% 50% 100%

Fig. 6 : Similarity between the successive samples. -65-

70 I I v / v / ljj I 1/ I 65 / I v j I 1/ vv 1/; I I / 60 ,, v l/ I/ 1/ II v II 1/ 1/ v;; I v II 55 1/ 1/ 1/1/ ij v v I/ I/ II v / r; V; /_ / 50 I 1/ !/ J v v v / I I ~IJ ~ !J II VV; /_ v 45 v 1.1 1/ / v v J v v-"' 1/ / /; ~ ~ J r/ / I v I / v v I; I II ///;; ~ I J / "V v v' / vv y / / / / W; j: / / vv v ... 7 / ~~~ / y / / v / v v v 25 ~ v v v 1-- v v v ~---~--- v v v v / / v 20 ~ v v v v 1-- / v ....- -~- 15 v v - 7 v l_..-----1-- I- v ~ 10 p -- -1- 1--J--: .---- ~ ~ 1--- 5 - -- 0 100 500 1000 5000 10000 Number of individuals

Fig. 7: Fisher ~ index in faunule 1. -66-

70 17 r; 1/ v II iljj / II 65 1/ I/ !/ v II 1/ v 1/ 7/; I 1/ II 60 v 7 v I y II :; I /; I I II 55 I I l / I I / y /:; I 11 I I /; I / 50 I I I v / v 17 v / I vr; v I v '/ / v 45 I v v ll/ I I/ v vlt' V IIP'/ / /; ~ ~ v J / v / I vI II v __."' / V'~ VI/;; 1; I / I/ 'V / / /y / I '/ / v /; / v ,V/ "' ~ / -1 // / ~ / / 7 / / v v / 25 ~ ,.. / / v v/ ~... ) ..... v v v / v __..... v 20 ~ v v v ...... / v -~ 15 v v - v / - _... -- v ~ ---- 10 - L...---"' -- __, --- ...., --1- --1 5 ------0 100 500 1000 5000 10000 Number of individ.ua/s

Fig. 8: Fisher 0<:: index in faunule 2. -67-

70 v I v I I Vjj v I I 65 1/ I I v I I I I I II I I I 60 1/ v I/ II v 1/ 1/1/ 'i; I v ~y 55 i/ 1/ VIJ v I/ v I/ v v / I / I / 50 V; II / / I 1/ v / ~lj / v I V; /v 45 I I II / I 1,; v I / /; ·~ ~ I I v/ / )/ / vv v / v / II/;; 1; I I / / / v v / vv v / / ~ J; / / / / v / / / / v / v v/ 1/ v 25 ~ v v v ~ v v v ~---~-- v v v v / v ./ 20 ·~ 7 v / v y ~---~-- / r..--~--' _... 1-- 15 / v ~ / l--- ~ ~ 10 ~ ...... ------1--I-f- 1---I- - 5 - - -- 0 100 500 1000 5000 10000 Number of individuals

Fig. 9: Fisher ~ index in faunule 3. -68-

The points for faunule 2 fall on or near the Rotaliina - ~liolina line, much closer to the ~liolina corner. These populations occur in hypersaline lagoons and marshes or normal marine lagoons. In faunule 3, the values also lie on or near the Rotaliina - Milio­ lina line, but closer to the Rotaliina corner. These associations survive in hypersaline lagoons or marshes, normal marine lagoons, hyposaline lagoons or on the continental shelf.

6. SIMILARITIES. (SANDERS,l960).

Fig. 6 gives the similarities between the successive samples. In faunule 1, the similarity index varies between 61 and 84%. Espe­ cially in the upper part of this interval, the populations ressemble each other well, less so 1n the lower part. The transition from faunule 1 to faunule 2 is marked by a distinct . decrease of the similarity index (25%), which indicates an important change in the composition of the populations. The similarity index between the two samples 1n faunule 2 is fairly high (72%). The associations in these samples differ only slightly. A new decrease of the similarity index is noted at the transition from faunule 2 to faunule 3 (56%) and even more (53%) between samples 8 and

9, which is explained by the relatively high frequencies of ~liolids in sample 9, in which Cibicides tenellus however occurs already more abundant. Higher up in faunule 3, the similarity index increases to maximum 84%. The smaller value in the uppermost part (73%) is explained by the occurrence of more Miliolids in sample 12.

7. DIVERSITY INDEX OR FISHER a INDEX. (FISHER, CORBETT & WILLIAMS, 1943).

The relationship between the number of individuals and the number of species in the populations of the three faunules is given in figs. 7,8 and 9. In faunule I, the Fisher a index varies between 5.5 and 9.5. In faunule 2, the values lie between 6.2 and 7.2. The Fisher a index is slightly higher in faunule 3 : between 6.8 and 11.2. -69-

12

11

10

9

8

7

6

5

4

3

2

1 0 10 20 number of species in 80% of the populations.

Fig. 10: Dominance index -70-

12

11

10

9

8

7

6

5

4

3

2

1 0% 25% 50%

Fig. 11 : Percentage dominance -71-

According to the interpretation of the different fields correspon­ ding to the various a values by WRIGHT & MURRAY (1972) and MURRAY (1973), we conclude that the possible environments for the three faunules are : hypersaline or normal marine lagoons and shelf seas of normal salinity.

8. DOMINANCE INDEX. (WRIGHT, 1972).

Fig. 10 gives the number of species in 80% of the total popula­ tion. The dominance index is fairly constant in the different samples. It varies mostly between 8 and II. Only in the lowermost sample, the index is lower : 6. The environment during deposition of the Lede Sands was moderately stahl~. It is impossible to distinguish different faunules on the base of the dominance index.

9. PERCENTAGE DOMINANCE. (WALTON, 1964).

Fig. 11 shows the percentages of the most abundant species in the different samples. In faunule I, these percentages vary betwenn 24 and 39. The highest value is noted in the lowermost sample (39), which corresponds to the trangres­ sion level of the Lede sea. In faunule 2, the percentage dominance is lower (17-19), indicating a deepening of the sea in a second impulse in the transgression. The percentage dominance increases again in faunule 3 to maximum 31%. After a slight deepening of the sea in a second transgressive phase, the sea starts to regress slowly.

10. PALEOECOLOGICAL INTERPRETATION OF THE TAXA.

Information on the (paleo-) ecological significance of the occurring taxa is faund in e.g. PHLEGER (1960), BANDY (1960, 1964), WALTON (1964), WRIGHT & MURRAY (1972), MURRAY (1973), WRIGHT (1972-1973); MURRAY & WRIGHT (1974), BOLTOVSKOY & WRIGHT (1976) and GERITS, HOOYBERGHS & VOETS (1981). -72-

Faunule 1.

Rotalia3 . which occurs frequently, prefers shallow waters with a lot of algae and seagrass. Cibicides is a common inner shelf genus, living in a wide variety of temperature and salinities. It is attached to all types of substrates •. Cibicides occurs from arctic to tropical areas, but is currently most abundant in temperate seas. Cibicides lobatulus prefers most frequently a transition zone between a protected bay and the open ocean. Elphidium occurs in greatest abundance in shallow, oxygen-rich water, in tidal marshes and lagoons or nearshore. Cancris is a subtropical genus living most frequently on a normal marine shelf. Globulina and Guttulina are inner shelf taxa in temperate to tropical seas. The agglutinated Textularia occurs preferabely on normal marine shelfs, in arctic to tropical conditions. Small, not striated species of Bolivina prefer a marginal to shelf environ­ ment. The absence of ~liolids can be explained by low salinities. Espe­ cially Quinqueloculina does not tolerate salinities below 30%. The presence of planktonic foraminifera (HOOYBERGHS, in press) however indicates an opening to the ocean.

Faunule 2.

The sudden appearance of ~liolids indicates an icreasing salinity in the second impulse of the transgression, which starts between samples 5 and 6. The deepening of the sea explains the low frequency of Rotalia. Cibicides tenellus does not tolerate here well the increasing salinity. Onl¥ a few hyalin calcareous genera as Guttulina and Lamarckina survive. Also the agglutinated Textularia disappears nearly completely.

The presence of several broken ~liolacea is caused by a more turbulent water.

Faunule 3.

The occurrence of Asterigerina indicates a more stable s~linity. -73-

Rotalia audouini and Cibicides tenellus occur more frequently again. Also Elphidium and Nonionella reappear in this shallow water. The fre­ quency of Miliolids decreases slightly with increasing depth but they occur quickly more frequently again during the regression of the sea. The frequencies of Guttulina (G. lqctea) and Cibicides lobatulus are less influenced by the changing environments.

11. CONCLUSIONS.

In this locality, the transgression of the Lede sea first led to a hyposaline marginal deposit or lagoon. Although there was a connection with the open ocean. The water was oxygen-rich and contained much algae or seagrass. The temperature was fairly high. The sedimentation took place in a subtropical- tropical environment. The salinity increased to normal or hypersaline values during a second impulse in the transgression. The sea remained however rather shallow. The second transgression was only of short duration. A regression of the sea followed quickly. The existence of two impulses in the transgression of the Lede sea has also been proved by GERITS, HOOYBERGHS & VOETS (1981). --74-

. 12. REFERENCES.

BANDY, O.L. 1960 Gener.al correlation of foraminiferal structure with environment. Int. Geol. Congress, Report 21, Sess. Nordon 1960, p.XXII, 7-19, 9 figs. 1964 General correlation of foraminiferal structure with environment. In "Approaches to Paleoecology", IMBRIE & NEWELL, 7S-9S.

BOLTOVSKOY, E. & WRIGHT, R. 1976 Recent Foraminifera. SIS p.

FISHER, R.A.; CORBET~ A.S. & WILLIAMS, C.B. 1943 The relation between the number of species and the number of individuals in a random sample of an animal populations. Journ. Animal Ecol., 12, 42-S8, 8 figs., 9 tab.

GERITS, M.; HOOYBERGHS, H. & VOETS, R. 1981 Quantitative distribution and paleoecology of benthonic foraminifera recorded from some Eocene deposits in Belgium. Prof. Paper, 1981/3, nr. 182, 53 p., 6 figs., 19 tab.

HOOYBERGHS, H. in press : Planktonic foraminifera from the Lede Sands Formation at Balegem. Tert. Research.

KAASSCHIETER, J.P.H. 1961 Foraminifera of the Eocene of Belgium. Mem. Inst. r. Sci. Nat. Belg., 147, 271 p.; 16 figs., 16 pls., 8 tab.

MURRAY, J.W. 1973 Distribution and ecology of living benthic foraminiferids. 274 p., 102 figs. -75·-

MURRAY, J.W. & WRIGHT, C.A. 1974 Paleogene foraminiferida and paleoecology Hampshire and Paris Basins and the English Channel. Spec. Papers in Pal., nr. 14, 129 p., 47 text-figs., 20 pl.

PHLEGER, F.B. 1960 Ecology and distribution of Recent foraminifera 297 p., 79 figs., II pl.

SANDERS, H.L. 1960 Benthic studies in Buzzands Bay. II. The structure of the soft-bottom community. Limnol. Oceanogr., 52, 138-151.

WALTON, W. R. 1964 Recent Foraminiferal Ecology and Paleoecology. In " Approaches to Palroecology", IMBRIE & NEWELL, 151-237, 29 figs.

WRIGHT., C. A. 1972 Foraminiferids from the London Clay at Lower Swanwick and their paleoecological interpretation. Proc. Geol. Assoc., 83(3), 337-347, 4 figs. 1972 The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proc. Geol. Assoc., 83(4), 413-420. 1973 Foraminiferids from the Lutetian at Ronquerolles (Val-d'Oise) and their paleoecological interpretation. Revue de Micropal., 16(2), 147-157, 5 figs.

WRIGHT, C.A. & MURRAY, J.W. 1972 Comparisons of Modern and Paleogene Foraminiferid distributions and their environmental implications. Mem. B.R.G.M., 79, 87-96, 5 figs. -76-

Quantitative distribution and paleoecology

of benthonic foraminifera 1n the Wemmel

Sands Member of the Asse Formation (Eocene)

at Strombeek-Bever (Belgium)

H.J.F. HOOYBERGHS -77-

CONTENTS.

I. Abstract. 2. Introduction. 3. Lithological description of the Wemmel Sands at Strombeek-Bever. 4. Quantitative distribution of the benthonic foraminifera. 5. Triangular plot of suborders. 6. Similarities. 7. Diversity index or Fisher a index. 8. Dominance index. 9. Percentage dominance. 10. Paleoecological significance of the occurring taxa. 11. Conclusions. -78-

0 SKm.

"t:SGENT

BRUSSELS

Fig.1 : Location map. -79-

58 IIBANDE NOIRE" -·-·-·-·-··-··-··-··----- 12 ;::::. : :-:-::::::::::::: :: •. ·:: .7. ·::: ·:·: :.ittttl!tti::.e·(t.·.·:. 11 ... .. •.. • • .. • • •• • J. ••••. ~.~.~.~.~. :..:.. :¢:~ ••• •• ·.c:>: ...... : () Bivalvia 10 :~:· .. !?.· ::i=? .....: ·.·.·.-:-:o.:...:..-:-:-:: ·E.·.·.·.·..:...: ".9.·... :.: •••• ••••...... Nummulites 9 ·~::::::::·.-:.

••• 1111 :.:... . :·: . .-:···. . . ·:.:.:·e.:-: ...... Sand 8 .:• • .• :-·:::.:.:::.·::.• • • .. • • • • • 0 •• ·:. ::: ...... Clay 7 ·:.·.·.·:::.·:::.·.·:~ "!! ~ '! .• •• .. • ... ! ~ ~ .• ...... oo White Patches ·:s~;·:·:·.!.~~.. :-:(·):z 6 :-:- .. ::; ~ ..... : .. ·: ...... () ...... Glauconite ...... @ : .:·.··:·.··:·()··:·e:· concentrations 5 ...... ·-····-··· ~ Brown Colour (Fe) -=-----·-...:_-.....:... ::e :..:..: ·... .•: ;•: .·•..... ~ ..·:::: .:.._...... -=-- -=-·-=-.:...

1 • ABSTRACT.

The benthonic foraminiferal populations in the Wemmel Sands Hember of the Asse Formation have been studied in a temporary outcrop at Strombeek-Bever. Quantitative countings of up to 100 individuals per sample are made. Successive use of quantitative distribution, triangular plot of suborders, similarities, Fishera index, dominance index, percen­ tage dominance and paleoecological significance of the occurring taxa allowed us to interpret the faunal assemblages paleoecologically.

2. INTRODUCTION.

During excavations on the highway around Brussels, the Wemmel Sands were temporarily exposed in 1982 (fig.l, location map). The samples were treated with H and sieved on a 0.074 mm sieve. In each dried 2o2 residue, countings of up to 100 individuals were made. For a full syste­ matic description of the occurring taxa, we refer to KAASSCHIETER (1961).

3. LITHOLOGICAL DESCRIPTION OF THE WEMMEL SANDS AT STROMBEEK-BEVER.

In the lower part of the outcrop (fig.2), the Wemmel Sands are homogeneous, brown to green-yellow and glauconitic. Although few Bivalvia are disposed throughout these sands, in several areas of about lOcm diameter there are Bivalvia concentrations. Higher up, the Wemmel Sands become slightly clayey. Nummulites occur frequently in the middle part of the section. The sands show a cross-lamination at levels five and six. They become grey in colour and fragments of Bivalvia occur scattered in the sediment. The amount of glauconite increases upwards. In the upper part of the section, patches of white sand are observed and one level (ll) is rich in small concentrations of limestone nodules. At the top of the section, there is a dark-brown clayey, very glauconitic band, which is the "Bande Noire'! o:;t o-.,- WEMMEL SANDS ...... 01 Clc> c.o .. "' l.w "' U! '-I C3 - C) (I)-· ~ Textularia agglutinans ...... , - o--· .... Spiroloculina bicarmata c: - - .... "' .... l.w 0 Sptroloculma costigera var. nuda :::,-· "' Quinquelocultna cartnata 0 - "' - - --...... o- Quinqueloculina JUieana ...... ~.... - "' - - Quinqueloculina ludwigia 5 Quinqueloculina seminula :::, - - t=)• "' Dental tna elegans a- - - ...... c.o .... Bolivina cookei Q! 3 Buliminella cf. B. pulchra I :;· "' I 00 -. .... ;:;;- - "' l.w "' "' Bulimina parisiensis Q! .... - 1\J - Trifarina muralis :;· "' - Discorbis pansiensis :::,- ., l.w l.w 0 U! 01 Cancris subconicus - "' "' - - - Siphonma lamarcktna ~ - - "' - 3 3 ~ ~ ~ ~ ~ l.w "' - "' l.w Astengerina bertoniana ~ <5 P\j 01 - Bifarina selseyensis ~ ... Eponides schreibersi :::, - - ~ U! l.w ~ l.w t:l l.w ~ l.w P\j U! - Epontdes toulmini "' Planulina burlinglonensis U! - - l.w - I Cibictdes dutemplei "' "' - - ICibicides sp. ct. C. mauricensis ~ 5 .... - ..... c.o Clc> '-I .... ~ Cibic1des proprius acutimargo --82··

.2

1Jt ._; Ill g ::J 2 .2 ~ q; !!! g E ~ ::J 0 ~Q. j ~ § Ill .2 Q; 0 .g ~ Ill 0 Ill !!! u c: ::J Ill E 0 0 0 2' ::J ~ E 0 .2 .2 c: .c:: "5 .2 :l> \.: ti. 2 ~ :it ~ 0 .Q 8 s ::J Ill Ill .... 8 ::J ::;, ~ ~ 0 u f3 g. ~ ~ Ill u ~ ·~ E c: :12 0 Ill .Q 0 ~ "5 ~ .~ ~ c: 0 0 0. Ill 01 .9 Ill .!!! ..... 0 !! 0 u ~ E .... :£: !? ~ a...... 0 t ~ !! 0 0 .2 E II) 0 ·~ 0 0 .... g 0 E :t Ill ~ 0 0 !! ::;, 0 Q; .>! ~ ~ s c: c: "5 s s c: c: ~ ~ -o s s \.: :-Q ~ ~ ~ 0 0 ·'2 \.: g. 0 "5 Qj ~ ~ ~ u Q .... "5 .~ .~ 3i Ill .c. .Q "5 '- .c:: ·~ ~ c: ~ .... !::: s Q. .... '- 0 :§ .Q c c c: .... ~ ...Ill 0 .Q 0 :12 Ill ::J 0 0 0 ljj {3 c: (J G (J ~ ~ -J <5 !.:> Ql Ql ~ ~ t7} a ~ ~ i¥; G ~ {3

11 6 13 6 2 12 3 11 2 3

10 18 11 5 4 6 15 4 3 3 2 ~ 9 11 I. 10 2 18 2 3 2 3 <: 8 17 5 11. 2 I. 6 3 5 2 2 ~ 7 12 11 15 2 2 I. 2 4 2 7 2 6 18 10 3 I. 7 3 2 5 2 3 3 2 6 Qj 5 9 23 2 5 3 2 I. 9 5 2 2 ~ 3 7 11. 2 6 ~ 2 7 2 20 3 2 13 3 9 7 2

Table 1: Distribution of benthonic foraminifera in the Wemmel Sands. -83-

...0 c:0 ~ ;:: 0 ~ u Ill iii Ill S{ 0 0 c: c: i0 \:: E f01 ta_, E .!:! .E! 0 i ~ ~ g ~ c:0 ;:: ~ ~ "& iJ ~ 01 ...... E! 5: jj ;:) ~ ~ G

11 12 2 10 3 2 2 ~ 9 15 1 <: 8 7 V) 7 6 ~ 5 t. ~ 3 ~ 2 1

Tabl~ 1: Distribution of b~nthonic foraminif~ra in th~ Wemm~l S.:mds. ji;i b- WEMMEL SANDS 1'1)- ~ ~ ~ ~ ~ ~ ~ ~ c ""' - ~ ii;'" w----...... Textulona aggtutmons ..... ~· -----~------~------Sptrolocuhno btcannota 1'1) Sptroloculma cosftgera var. nuda ~ ~ w 0

~ Qumqueloculmo JUieono C"') ...... ,.IIIO:OOJ....,...... ,. ~------m Qumqueloculmo ludwtgto ff ~ ------...... ------Qumqueloculma semmula 0 ..... Dentalina elegans b- ~~ ----~----~--~rr~ Bolivma cookei ~ ..... g Bulimme/la ct. 8. pulchra = I r;· -o Buftmmo paristensts 00 ...... t g ~ ..... LO:J ...... ---- ...... Trifarma murolts a; Discorbis partstensts 3 Cancr1s subcantcus ::;· o .... wo-=-oooo o ~ ii! ------~--- Siphonma tomorckmo ::;· Asfengerino bertomono s 1'1)

~ 3 3 !t

~

~

Bilarina se/seyens1s o--lJ-u----~ Q;l o- W£MM£L SANDS SAMPLES -11> IV ~ ~ ~ ~ ~ ~ ~ ~ c TAXA ------~-- Eponides schreiberst ~a; .... Eponides toutmint ULJU ~ U D U m ~· DO ~ ':;' ~ c: = Ptanulina burlmgtonensts ~ ...... Cibicides dutemplet C"') u~ w=-

~· ~ '*"""J ...,. m Cibicides sp. ct. C. mauncensts g_ Cibicides propnus acutimargo uu-----uoo .....D ~ Ctbicides propnus proprtus g- ooooooooooo . ;:;· c(; U"l 0' 0 LOOJ m m Ctbtcides sulzensts I ii'! Ctbicides tenellus tenellus 3 5' oooo~oooooo ~ iil Nonion a ff me 5' oowmmoooooo ~ ~LO;;i ...... L:OOJ LlfliiJOIIImO&::J Nontonella wemme/ensis ~ 3 mm mwom Lenticul ma sp. 3 Guttulina lactea ~ ---m------u-~D """"0 D ~ D Guffu/ina problema ~ - mmo... -o-woo ODDBolivina anglica ~ b- WEMMEL SANDS I'D- ~ 1.11 O'J "-) Clo 10 c "' - "' " - ~ =-=co ;::::a c::::l cu Bolivma carinata Q;' .... Reusefla limbata ~· 5::1' s::::::l 1::1 c t:J = c= Astengenna sp. ;:- ..... Sptroplectammtna carmata var. cieperdita It) ouoCJoCJ ~ Ooitna morginata ~ t') Elphidium subnodosum m· = oouc = Globulma gibba 0 ...... Pyru/tna thoumt m Karrerielta siphonella i CJ t::l - g- oum"""'CJCl Elphidium loeve ;::;· Cibicides lobatulus I 00 Anomaltna ocuta (j' u-oo-- "'I ~ 3 Gtandulino loevtgoto :;· Uviger1na fortnoso ~ =-uCJu ~ :;· Sptrop/ectammtno corinoto Trifortno wilcoxensis ~ I'D Cibicides pygmeus

~ 3 --··~-- 3 ~

~

~ -87-

4. QUANTITATIVE DISTRIBUTION OF THE BENTHONIC FORAMINIFERA.

The relative abundance of the occurring taxa is given in tables 1 and 2. In the interval studied, we can distinguish two different faunules.

Faunule 1. (levels 1-5)

In this faunule, Asterigerina bartoniana dominates the populations. The frequencies however vary considerably (13-66%). Cibicides tenellus is another important component of the associations, with variable frequencies (5-23%). Some other Cibicides species also occur commonly C. proprius proprius (7-13%) and C; proprius acutimargo (1-10%). The frequency of Eponides toulmini changes very much (3-23%). Different hyalin calcareous species as Nonion affine (1-7%), Nonionella wemmelensis (1-2%), Bolivina anglica (1-6%), Bolivina carinata (1-5%) and Cancris subconicus (1-4%) occur regularly but less frequently. Bifarina selseyensis (0-12%) is represented especially in the lower part of the section. The presence of different Quinqueloculina species in the lower­ most sample is of note. At the top of the interval, Spiroplectanunina carinata var. deperdita appears distinctly (0-3%).

Faunule 2. (levels 6-11)

The importance of Asterigerina bartoniana diminishes distinctly (0-3%). The maximum frequency of Cibicides tenellus is also lower than in faunule (5-13%). Different other hyalin calcareous taxa become more important in (part of) this second interval : Cancris subconieus (0-11%), Nonion affine (3-15%), Nonionella wemmelensis (0-4%), Bolivina anglica (0-18%) and Cibieides proprius proprius (6-18%). Bolivina carinata (0-4%), Cibicides proprius aeutimargo (0-9%) and Eponides toulmini (1-12%) still occur regularly. Some new hyalin calcareous species appear fairly regularly : Lenticulina sp. (D-2%), Guttulina lactea (2-12%), Globulina gibba (0-5%), Elphidium -88-

MILIOLINA

ROTALIINA TEXTULAR/1 NA

Fig. 3: Triangular plot of suborders in faunule 1.

MILIOLINA

ROTALIINA TEXTULARIINA

Fig. 4 : Triangular plot of suborders in faunule 2. -89-

11

10

9

8

7

6

5

4

3

2

1 0% 50% 100%

Rg. 5: Similarities. -90·-

l-aeve (I-7%), AnomaUna acuta (l-6%), Uvigerina farinosa (0-15%), BuUinina parisiensis (0-4%) and Bol-vvina eookei (0-9%).

The presence of agglutinated species as Ka~eriel-Za siphoneZZ-a (0-3%) and Spiropl-ectammina carinata var. deperdita is noteworthy.

5. TRIANGULAR PLOT OF SUBORDERS.

TextuZariina, Mil-iol-ina and Rotal-iina represent the three suborders of benthonic foraminifera. We can plot them on a triangular diagram. The ecological interpretation of the different fields for the various possible environment is worked out by MURRAY (1973). Figs.3 and 4 show the triangular plot of suborders in the two faunules. In both faunules, the points lie in the vicinity of the Rotaliina corner. The populations contain only a few TextuZariina and MiUoUna. They can occur in the following possible ecological conditions : hypersaline marshes and lagoons, normal marine marshes, hyposaline marshes and lagoons, and on the continental shelf.

6. SHHLARITIES. (SANDERS, 1960)

The similarities between successive samples are represented in fig.S. In faunule I, the similarities varie between 50 and 69%. The lower values are explained by the distinct change in frequency of some taxa. The transition from faunule I to faunule 2 is marked by a very low similarity (36%), due to a sudden renewal in the associations of benthonic foraminifera. The similarity increases to 73% in faunule·2. The populations differ only slightly in the lower part of this faunule. Higher up, the values decrease again to 53%, which is caused by a generally more abundant but variable occurrence of some taxa.

7. DIVERSITY INDEX OR FISHER a INDEX. (FISHER, CORBETT & WILLIAMS, 1943)

Figs.6 and 7 represent the relationship between the number of individuals -91-

70 !/ II v v 'J / J 65 /11 ~ I II v I v / ' I 1/~ 7;; J 60 I I l v I vII I I I I i/ ~v;/ I 55 I I I I I I v I ,; ,_'\ I vII /v} I // rJ.-"' 50 ~ 7 I I I / v / r1 ~ v 1/ I I r; I ,V; / v 45 v v / II v J ,r/ 1// /~, vI / v ~ v / i/ J v / ,)"' I / VI/;; 1; I I v f/v v"' / / / I v / // / ); / / v v ..... WI / '/ / ;// / 7 / / v / 25 ~ / v / / v ...... / v / ·~ v v ~ v 20 / / v / / i~ / ...... __. 15 / v 7 / _..... / _..... ------10 -- __.....--....- - _..:... ------5 ---

0 100 500 1000 5000 10000 Number of individuals

Fig. 6: Fisher oc index in faunule 1. -92-

70 I I I ll ljj I vI I 65 I v v I v I !/ /v//; I 60 I I VII v i/ I/ i/ 1/ II /I/ "'i:v I I 55 1/ I/ 1/ 1/ IJV v II l/ v v v vVJ / 50 I I v I I v 1/ 17 v / v/ v [/I/ J I ~lj vI vv '/ / 45 / 17 ll' v v v / v v v y/ / / z~ ~ / v I v v i.-' 1/ '/ I& ~ I I ,/ "V / v v / / / I v v r" 1!/1; j; / v vv / / v v/ / v v v / v/ v vv v 25 rd v / vi-- v v ~v v ~ v ~y v 20 ~ / / v v v v v / -~--- 15 v 1-' v v v ~ v 1------10 - 1-- l.---- - f---- ~ 1-- - 5 1------

0 100 500 1000 5000 10000 Number of individuals

Fig. 7: Fisher !X index in faunule 2. -93-

11

10

9

8

7

6

5

4

3

2

1 0 50

Fig. 8: Dominance index. -94-

11

10

9

8

7

6

5

4

3

2

1 0% 50% 100%

Fig. 9: Percentage dominance. -95-

and the number of species in the associations of the two faunules. In faunule 1, the a index varies between 4,8 and 13. The a values lie between 7 and 11 in faunule 2. . The interpretation of the differe~t ~cological fields corresponding to the -~~ various a value~ is worked out by WRIGHT & MURRAY (1971). The possible environments for faunule I are : shelf seas_of normal marine salinity or, for the lowes;--value, a hyposaline and ne~t~hore shelf sea. The populations in faunule 2 prefer a shelf sea of normal salinity.

8. DOMINANCE INDEX. (WRIGHT, 1972)

Fig.8 shows the number of species 1n 80% of the total population. The dominance index in faunule 1 varies between 3 and 13. The distinctly different values are probably due to an unstable environment in which the sedimentation took place. In faunule 2, the dominance index is generally higher and less variable. It changes between 9 and 12. During a second impulse in the transgression, the sea bottom became more stable. The deepening of the sea took place gradually.

9. PERCENTAGE DOMINANCE. (WALTON, 1964)

The percentages of the most abundant species 1n the different samples are represented in fig.9. Faunule l shows distinctly changing frequencies. They vary from 13 to 66. Again, this can be explained by an unstable sedimentation environment. The values for faunule 2 are less variable. Here they lie between 13 and 18. A second impulse in the transgression led to a more stable continental shelf.

10. PALEOECOLOGICAL SIGNIFICANCE OF THE OCCURRING TAXA.

Benthonic foraminifera occur in specific ecological conditions. Information on the (paleo-) ecological significance of the occurr1ng taxa is faund in: PHLEGER (1960), BANDY (1960,1964), WALTON (1964), -96-

WRIGHT & MURRAY (1972), MURRAY (1973), WRIGHT (1972-1973), MURRAY & WRIGHT (1974), BOLTOVSKOY & WRIGHT (1976) and GERITS, HOOYBERGHS & VOETS (1981).

Faunule 1.

The dominant genus AstePigerina is a typical inner shelf genus, where it occurs under conditions of stable salinity in a normal marine environment with tr~pical-subtropical temperature. Cibicides is currently most abundant in temperate seas. It is attached on all types of substrates such as algae or seagrass vegetation. The presence of several Quinqueloculina's in the lowermost part of the section indicates a nearshore environment with a salinity higher than 30%. Cancris occurs on the shelf of normal marine seas in a subtropical climate.

Bifarina survives o~ an inner shelf. As the sea depth increases, BifaPina selseyensis disappears in the upper levels. Eponides prefers a continental shelf of a normal marine sea with cold to temperate waters. Nonion occurs on the shelf of normal to hyposaline seas in different temperature conditions, but with oxygen-rich waters. Nonionella is a normal marine shelf genus in temperate to tropical seas. Small smooth species of Bolivina prefer an inner shelf environment with normal salinity (32-36%). The appearance of Spiroplectammina in the upper part of the interval indicates a deepening of the sea.

Faunule 2.

Several taxa from faunule 1 still occur and often even higher frequencies. Individuals of Canaris, Eponides, Cibicides, Nonion, Nonionella and Bolivina (B. anglica) still survive in this environment. Asterigerina however disappeared ne~rly completely. The appearance of some new taxa however indicates an increasing depth. Striate Bolivina's (B. cookei) prefer a central to outer shelf milieu. The occurrence of Karreriella, Spiroplectammina, Lenticulina and Uvigerina -97-

also suggests a greater depth of the sea in normal marine conditions. GuttuZina and GZobuZina prefer a shelf of a normal sea in a temperate to tropical climate. Bulimina lives in a wide depth range, from nearshore to bathyal, in a normal marine environment. EZphidium normally dominates at an inner shelf depth with rather high salinities (35-50%) and in a oxygen-rich water,

11. CONCLUSIONS.

The nearshore facies at the beginning of the Wemmel transgression passed to an inner shelf environment. The normal salinity was fairly constant and the sedimentation took place in a subtropical- tropical climate. The sea bottom however was rather unstable. The water was oxygen­ rich and algae or seagrass were favoured. A second impulse in the transgression was accompanied by strong currents , which explains the cross bedding. The sea bottom became more stable with increasing depth. The sediments were. finally deposited in a central to outer shelf environment in a subtropical to tropical climate. The salinity of thewater remained normal (33-37%). -98-

12. REFERENCES.

BANDY, O.L. 1960 General correlation of foraminiferal structure with environment. Int. Geol. Congress, Report 21, Sess. Nordon 1960, XXII,7-l9, 9 figs. 1964 General correlation of foraminiferal structure with environment. In "Approaches to Paleoecology" IMBRIE & NEWELL, 75-95.

BOLTOVSKOY, E. & WRIGHT, R. 1976 Recent Foraminifera. 515 p.

FISHER, R.A. ; CORBETT, A.S. & WILLIAMS, C.B. 1943 The relation between the number of species and the number of

individuals in a ra~dom sample of an animal population. JouLn. Animal. Ecol., 12, 42-58, 8 figs., 9 tab.

GERITS, M ; HOOYBERGHS, H. & VOETS, R. 1981 Quantitative distribution and paleoecology of benthonic foramini- · fera recorded from some Eocene deposits in Belgium. Prof. Paper, 1981/3, nr.l82, 53 p., 6 figs., 19 tab.

KAASSCHIETER, J.P.H. 1961 Foraminifera of the Eocene of Belgium.

Mem. Inst. r. Sci. Nat. Bel~., 147, 271 p., 8 tab., 16 figs., 16 pls.

MURRAY, J.W. 1973 Distribution and ecology of living benthic foraminiferids. 274 p., 102 figs. -99-

MURRAY, J.W. & WRIGHT, C.A. 1974 Palaeogene foraminiferida and paleoecology, Hampshire and Paris Basins and the English Channel. Spec. ·Papers in Paleont., nr.14, 129 p., 47 text-figs., 20 pls.

PHLEGER, F.B. 1960 Ecology and distribution of Recent foraminifera. 297 p., 79 figs., 1lpls.

SANDERS, H.L. 1960 Benthic studies in Buzzands Bay. II. The structure of the soft-bothom community. Limnol. Oceanogr., vo1.5(2), 138-151.

WALTON, W.R. 1964 Recent Foraminiferal Ecology and Paleoecology. In "Approaches to Paleoecology" IMBRIE & NEWELL, 151-237, 29 figs.

WRIGHT, C.A. 1972 Foraminiferids from the London Clay at Lower Swanwick and their

paleoecological interpretatio~. Proc. Geol. Assoc., 83(3), 337-347, 4 figs. 1972 The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proc. Geol. Assoc., 83(4), 413-420. 1973 Foraminiferids from the Lutetian at Ronquerolles (Val-d'Oise) and their paleoecological interpretation. Revue de Micropal., 16(2), 147-157, 5 figs.

WRIGHT, C.A. & MURRAY, J.W. 1972 Comparisons of modern and palaeogene foraminiferid distribution and their environmental implications. Mem. Bur. Rech. Geol. Min., 79, 87-96, 5 figs. -100-

Quantitative distribution and paleoecology of benthonic foraminifera in the Asse and

Kallo Formation at Assenede (Belgium).

H.J.F., HOOYBERGHS ·-101·-

CONTENTS.

1. Abstract. 2. Introduction. 3. Lithological description of the section studied. 4. Distribution of benthonic foraminifera in the Assenede well. 5. Triangular plot of suborders. 6. Similarities. 7. Diversity index or Fisher a index. 8. Dominance index. 9. Percentage dominance. 10. Paleoecological significance of the occurring taxa. 11. Conclusions. 12. Acknowledgements. 13. References. -102-

LOG LITHOLOGICAL UNITS

SANDS 53 MEMBER K A OJ L L 0

F 0 R M A B Sandstone

r 1=:-il Clayey sand .I 0 [J Fine silty sand

N cloy CASSEL ~Sandy

CLAY Cloy MEMBER ~Gravel

jclPI Bivalvia

Nummulites WEMMEL ~ SANDS MEMBER IV vI Biofurbotions

PANISEL FORMATION

Fig. 1 : L ithologicol subdivision in the Assenede well. -103-

1. ABSTRACT.

The bent.honic foraminiferal populations in the Eocene Asse Formation and Kallo Formation have been studied in a borehole at Assenede. Quantita­ tive countings of up to 100 individuals per sample have been made. To interpret the faunal assemblages paleoecologically, we successively used the following methods : quantitative distributions,triangular plot of suborders, similarities, Fisher a index; dominance index, percentage domi-:· nance and paleoecological significance of the occurring taxa.

2. INTRODUCTION.

The Asse Formation and the Kallo Formation have been sampled in a well at Assenede. The well description is held in the archives of the Belgian Geological Survey (K.B. Zelzate 25E-123Id - codenr. DB.43002-14.2, Peilput 101, Assenede). The samples were washed on a 0.0074mm sieve. Since different samples yielded only a small number of benthonic foraminifera, we were obliged to use the CCL method to concentrate the foraminifera. Countings of up to maximum 4 100 individuals have been made in the different samples •. For a full syste­ matic description of the taxa, we refer to KAASSCHIETER (1961).

3. LITHOLOGICAL DESCRIPTION OF THE SECTION STUDIED.

Two lithological units have been sampled in the Assenede well the Asse Formation and the Kallo Formation (Fig.l.). l) Asse Formation. (KAASSCHIETER, 1961)

A thin petrified gravel bed occurs at the base of the Wemmel Sands

Member which is develop~d between 86,.50 and 8la48m • Higher up, the deposit contains fine, slightly clayey, silty grey-green sands. BivaZvia and NummuZites have been observed in both the lower and the upper part of the Wemmel Sands. Especially the upper part is distinctly glauco- -104-

'

e>0 .~ "' ~ .!Q 12 :2> ~ ~ ~ & ~ e 0 :! c. "';:: 0 ~ ~ a .!! ·~ ~ g ~ ~ g 0 .a ~ 1:1 I l! ::J :; 0 i ~ ~ (/) ::J £ 0 ~ ~ :;: I -~ a ~ ::J .\:! s t I 15 -~ 2 ~ Ill j j l:l lU 8: ~ :; 0. ,g ~ e ~u 0 5 0. l: Q. ( ) .~ I 01 0 !? K ~ § .~ tA ~ a ~ i "' t 0 2 0 0 0 0 0 0 0 e e "' I ~ ~ -~ :t § ~ c c: 0 0! ~ I i .~ 41: s s -0! a -~ s s 2 ,g ~ :0 c c: ~ J -~ ~ a :;: ~ ~ -~ l !;! ~ .§ ~ ~ :a ,g ~ ~ :2 :2 :; .2 .\;! Q Q I 2 -~ 0 ~ ~ .2 ,13 Q § § e i ~ :§ :§ (!) fj j (3 "" ~ i3 ~ ~ ~ ~ ! Gi iii 0 0 I

11.90 5 2 1 1 2 3 36 7 11 2 $3 32,1.0 1 1 1 2 I. 37 2 13 I. 1 32.90 3 8 4 2 2 2 3 3 36 13 2 2 36.1.0 3 , 1 2 1 37,1.5- 37.50 1 2 1 3 2" , 38.30-38.1.0 1 2 I, 2 I, 1 'J 39,1.0 1 1 1 1 ~30-~1.0 1 1 1.1,50-1.1,60 1 , 1 1.2.65-1.2./ll 1 1 1.3,60 1.7.60 t , , .2 52.30-51,1.0 1 3 1 4 7 58.35-58.1.5 2 2 3 1 6 2 6 illl2 60.60 60.15 1 1 1 s., 62,55-62.65 1 , 1 ~~-6!l70 1 ~ Ba25-8ll30 12 2 10 2 1 19 3 5 I 1 1 : ~ ~ Ba90-BQ95 I, 1 7 I, 2 8 2 I, 3 6 1 3 ~a 81,15-81.20 6 3 7 1 1 , 2 I, 7 5 , 1 2 2 I, I, , 81.90 9 1 2 12 1 3 3 5 ' 2 ' 3 2 , .2 I, 1 82.30- 82.1.0 5 2 3 2 5 6 ' 7 6 82.65-82.70 10 2 , 9 9 1 , 10 1 3 , 1 &95 35 3 1 2 7 1 , 1 3 1 3 6 2 , 5 (/) ~ 83.30-83..&0 22 1 8 19 2 3 2 3 2 7 7 , 4 ~ 8l80 8l85 15 , 15 1 1 6 13 2 , 6 3 84.35-84.1.0 10 1 1 1 2 , 3 , 1 I, , lAJ :t 81..-'5 20 2 21 I 3 I 1 11 2 2 IJ 6 2 , ~ 81..50 11 4 3 2 3 2 3 2 3 I, 3 2 , 2 6 15 :1t 85.60-85.65 12 '5 17 1 7 8 2 12 10 2 4 , 7 , I B5.90-86 10 3 'I 3 13 7 ~ 8 2· 5 3 2 , 3 ] , ,. 1 , 1 86.50 12 ' 3 5 3 ' I 1 2 2 I 5

T

2 0 \! f l ~ g g 2 0 2 i 0 2 .!:! ~ ~ ~ :1 ~ .\! 2 ~ ~ .~ 0 l '!! .E Ill § ~ !S 1 ~ ~ .2 E .Q i \! .2"' 0 2 Ill IIi .!2 '!! s ~ g ! ~ !: 8 ~ ~ .~.. .§ ~ .2 i ~ .~ 1 ~ ""'u e l Ill 0 l i Q. ~ ~ ~ § .e I 1i Q ~ a ~ I u ~ i § ~ ~ .~ ~ .~ 0 i ~ ~ i .s .2 ·C

31.90 2 1 1 8 1 1 1 2 SJ 12.1.0 7 3 11. 12.90 1 3 1 2 36.1.0 , 37.1.5- 37.50 1 f 38.30-38.1.0 aJ 39.1.0 ~30-I.QI.O 1.1.50-1.1.60 1.2.65-1.2.80 1 1 1.3.60 1.7.60 1 , .2 52.30-52.1.0 2 58.35-5445 11 1 3 , 3 a2 60.60 60.75 , Sf 62.55-62.65 ~~-&!70 .... Ba25-81l30 2 13 3 2 5 4 9 4 ~).. ' ~ '!:( 81l90-Bil95 4 1 3 , 7 8 , 3 1 6 4 2 , 6 , 4 (Jd 81.15- 81,20 14 2 4 s 4 2 , , 2 3 3 2 81.90 , l 3 2 2 , , , , 2 , 7 2 82.30-82.1.0 2 , 3 2 2 2 3 2 , 5 , 24 82.65- 82.10 3 9 s 4 2 1 2 2 , 8 2 2 2 , 6 1 I 3 , 3 , , 6 , 4 2 (/) 82.95 ~ 83.30-83.1.0 1 , 2 2 7 2 • ~ 83.80 83.85 , 1 2 2 5 7 3 1 6 , 3 84,35-81..40 1 5 1 4 1 , 1 d 84.1.5 1 2 , , 2 12 ~ 81..50 2 , 2 , , 2 3 1 , 2 1 ~ 85.60-85.65 1 4 1 3 2 , 1 1 , , 2 85.90-86 3 2 2 , 6 3 2 2 86.50 I

Table1 : O.u.antit.ative distribution of benthonic for-aminifera. -106-

CJ ~ '5 .Q ~ ~ ~ g 2 -~ CJ -~ 2 ~ ~ ~ !; 2 ~ ~ .... 2 § ...CJ ~·~ :Q g, 0:: l ~ £ "t:l 2 2 ... I CJ CJ c: Ci 0 CJ -~ ~ 0 I! .8 t3 ~ ;;: a0 '"' '5 ~ 0 I 0 0 ~ ~ it ~ 0 ..c:i 1 e ! 5: :t -.; ~ -~ E i .!i! 2 ~ ~ i .f ~ 2 -~ :I;! 2 8' :::1 ... i0 ~ '{ 0 .'{ i'{ --1 1..1 ~ l ~ ~ i !' J 31.90 11 1 100 s3 32.40 9 100 32.90 11 1 100 . 36.40 13 37.45- 37.50 , tZ 38.30-38.1.0 3 11 a3 39.1.0 ' 1.0.30-4Q40 2 41.50-41.60 3 42.65- 42.80 1 5 1.3.60 1 1 47.60 1 6 s2 52.30-52.40 1 13 58.35-58.45 a2 "' 6Q60 6Q75 ' s., 61.55-62.65 3, ~~!lSS- 6a/O ...... 80,25- Ba30 100 1.4j)o. ~ oq Ba90-Ba95 98 ~d 81.15-81.20 ' 3 100 81.90 , , 2 1 , 89 82.30-82.40 2 2 100 82.65- 82./0 99 82.95 1 100 II) ~ 83.30-83.40 3 , 100 ~ 83.80 8385 1 100 81..35-84,40 41 ~ :t 81..1.5 100 a 84.50 87 ~ 85.60-85.65 TOO 85.90-86 96 86.50 48

Table 1 : Qu.Jntitative distribution of benthonic forclminifer

31,90 32.1.0 32.90

82.Xl-82,1.0 82.65-82.70 82.95 83.30-83.1.0 83.80-83,85

Tabl• 1 : Relative abund;mce of benthonic foraminifera. ~ CASSE'LI BASSEVEI..!E 0' WEMM£L SANDS - CLAY SANDS SJ SAMPLES "v*" I i .. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ TAXA Q, ~ ~ ~ ~ ~ ~ ~ ~ ~ 8 ~ ~ ~ ~ .... ~ ~ ~ s ~ s ~ ~ ~ ~· Cibicides proprius acutimargo 0, u-= u----- LJ m ...... -- ...... LJ 0 LJ Q- § Cibicides proprius proprius 2-

~ 0 ...... Q- ....~ I :;,. Cibicides tenet/us ~1]-~D ...... -0 g uo= =o OJ ;;· I Nonien affiM 0' ouwoo=--=ooooooo ~ 3 0 c:J Nonion scaphum 5' 0 woo oo ~ cr-u=ou --uu Nonionella lllff!mtnelensis ~ ~------~a------~=r- Hanzawaia bou«Jna ...... ----~·------~ Globcfl ina gravida Eponides schreibersi wTILJDDD'""""'O""""w'""'" o= Quinqueloculina ludwigi ...... ---- == = Bulimina parisiensis ~-~ Gyroidina octocamerota c::r--u-- D <=" Lamarckina cristellaroides ~ CASS£L BASSEVELD£ 0' WE:MMEL SANDS •- CLAY SANDS SJ SAMPLES ~ Qa ~ ~ ~ ~ ~ .- ~ CD ~ c.., fR ~ .~ ~ 8: ~ ! ~ ~ I ~ I I I I I ~ ~ tg ~ .- ~ VI ~ Qa ~ ~ TAXA as I ~ ~ ~ ~ ~ .- a ~ s ~ ~ ~ s (!f s ~ ~ ~ -~· 11:::1 Q, CJII:::II II:::ICJ Bolivina carinata o­ c: uo ~ Bolivina cnmulata

0:::::0 c:::J r::::::J Reusella terquemi ~ 0 illl:llli s:::::m ===-lllll:l:l c:::::::&i Uvigerina farinasa ...... -o- Trifarina muralis o- uoc::::~ Clu u ~ I CJC c o:::::ou Discorbis quadrata -5 uoc -0 ;::, \0 r;· w 0 c:::J c:::a £ponides toulmini I 0' c. 11:1! Alabamina wolterstorffi ~ uuo 3 r::::J Karreriella siphonella :;· """" W"""'CJWCJ uo ~ :"1· 1:::::1 11::111 £::11 t:::J r::::J Quinquetoculint;J carinata Qf """" Lagena striata O:::::OI::::Iu 0:::::0 11:::1 Cibicides dutemplt!H ...... 0 w t::l CJQ Cibicids pyr;;rntrus Spiroloculina fricarinafa wr. belgica Quinqueloculina seminula Dentalina elegans Lenticulina sp. 0 0 """'DO Cancris subconicus ~ CASSE'L BASSEVE!DE. 0' W£MM£L SANDS ..- CLAY SANDS SJ SAMPt.E:S Cia ""' ~ e .e ~·~ ~ ~ 81 ~ ~ ~ ~ ~ ~ ~ 1:e e: I ~ ~ :-. ~ I I I I I ~ .- ~ ~ VI a, ~ Q, I ~ ~ ~ 1:e ~ ~ ~ s TAXA .e :-. .- ~ 8l ~ at 0 ~ s ~ ~ ~ -~- Q, Cibicides carinatus 0' CJ Spiroplectammina carinata var. deperdita § ==uo oucu= ~ Spirolocuf ina canaliculata ~ Triloculina trigonula 0 ..... m Cancris auriculus primifivus == I::J I::J var. b- Anomafina ocufa ~-.. Entosolenia orbignyana I ::t­ I::J t::J u .CJ u u .... o u :::, 0 r;· == r=:a 1::::1 CJ r::::ll Buliminella cf. B. pulchra I Trifarina wilcoxensis 0' u Q! U~""D 3 ::;· ~ Angulogerina abbreviata var. fubulifera Quinqueloculina bicarinato ~· Glandulina laevigata Quinqueloculina costata Articul ina flandrica Anomalina acufa onomalinoides uuu • Bolivina cCJOkei Astt!N'igerina sp. Reuse/fa limbata -111-

niferous and bioturbated, The clay percentage increases upwards.

The Wemmel Sands are covered by a very glauconiferous clayey level ~1.48 and-77.80m) which is also bioturbated and which yields Bivalvia and Nurrorrulites. It <;onstitutes the basal layer of the Cassel Clay Member of the Asse Formation (DELATTRE et al. , 1973) •

2. Kallo Formation. (GULINCK, 1969)

The Kallo Formation represents a marine cyclic sedimentation with alternating clay layers. ans silty sands. The different beds have been numbered by GULINCK (1969) as a , S-I' a , s , a , and s • 1 2 2 3 3

s glauconiferous, micaceous sands with Nummulites and Bivalvia 3 and. slightly bioturbated. Those sands are know as the Basse­ velde Sands Member.

a3 clay bed of which especially the upper part becomes very sandy and micaceous. It is bioturbated at the top. Pyrite has been observed in this part. s gray-green to dark gray clayey fine sands. 2 a gray-green silty clay with pyrite. 2 s gray-green silty and clayey sands. 1 a gray-green clay with pyrite. This can be correlated with the 1 Cassel Clay Member of the Asse Formation.

4. DISTRIBUTION OF BENTHONIC FORAMINIFERA IN THE ASSENEDE WELL.

Table 1 shows the quantitative distribution of benthonic foramini­ fera to a maximum of 100 individuals. The r~lative abundance of the benthonic foraminifera in samples with 100 individuals is given in table 2. In this table, we can distinguish three different faunules which corresponds respec­ tively to the Wemmel Sands, the Cassel Clay and the Bassevelde Sands.

I) Faunule 1 (Wemmel Sands).

The agglutinated Textularia agglutinans becomes a very important -112-

component of the populations. Its frequency varies between 5 and 35%. A few other agglutinated species occur in part of this interval : KaTre­ rietla siphonetla (0-3%) and Spiropleetammina earinata var. deperdita (0-8%). Different porcelaneous species appear in at least part of the section : Quin­ quetoeutina ludwigi (1-7%), Triloeulina angularis (0-3%), Quinqueloeulina earinata (0-2%), QuinqueZoeulina seminulum (0-2%), Spiroloeulina eanali­ eutata (0-8%) and Triloeulina trigonula (0-4%). The populations contain several hyalin calcareous foraminifera. An important genus is Cibieides : Cibieides·. proprius proprius (2-12%), Cibieides proprius aeutimargo (0-6%), Cibieides tene.llus (0-10%), Cibieides dutenplei (0-5%) and Cibieides pygmeus (0-7%). Some other taxa become frequent in part of the interval : Globulina gibba (0-8%), Guttulina laetea (0-21%), Bolivina angliea (0-15%), Elphidium Zaeve (0-13%), Bifarina selseyensis (0-8%), Nonion affine (1-13%), Nonion seaphum (0-8%), Nonionella w~mmelensis (0-7%), Trifarina muratis (0-6%), Caneris subeonieus (0-12%), Entosolenia orbignyana (0-6%) and Trifarina wiZeoxensis (0-24%). Other hyalin calcareous species occurs regularly but less frequently : Ro­ tatia audouini (0-3%), Bulimina parisiensis (0-2%), Lamarekina eristellaroides (0-4%), Botivina earinata (D-3%), Bolivina erenulata (0-4%), Reusella terquemi (0-2%), Uvigerina farinosa (0-1%), Diseorbis quadrata (0-5%), Eponides touZmini (0-4%), Alabamina wolterstorfi (0-2%), Caneris aurieuZus var. primitivus (0-2%) and BuZininella sp. cf. B. pulehra (0-1%).

2) Faunule 2 (Cassel Clay).

This faunule is characterized by the sudden frequent appearrance of AZabamina wolterstorfi (7-11%). Agglutinated species still occur commonly : Textularia agglutinans (4-12%), Karreriella siphonella (0-8%) and Spiropleetammina earinata var. deperdita (0-9%). Cibieides is well represented in the populations : Cibieides proprius aeutimargo (0-2%), Cibieides tenellus (0-4%), Cibieides pygmeus (3-5%) and especially Cibieides proprius proprius (2-19%), which becomes abundant at the top of this interval. ·-113-

M/LIOLINA

• • • • • •• ROTALIINA TEXTU LARIINA

Fig. 2 : Triangular plot of suborders in faunule 1.

MILIOLINA

ROTALIINA TEXTULARIINA

Fig. 3 : Triangular plot of suborders in faunule 2. -·114--

MILIOLINA

ROTALIINA T£XTULARIINA

Fig. 4 : Triangular plot of suborders in faunule 3. -115-

The porcelaneous taxa are represented by Quinqueloaulina ludwigi (1-3%), Quinqueloaulina aarinata (0-2%), Spiroloaulina triaarinata var. belgiaa (0-1%) and Spiroloaulina aanaliaulata (0-2%). Several hyalin calcareous species occur regularly in this interval : Guttulina laatea (2-7%), Bolivina angliaa (4-10%), Nonion affine (3-7%), Nonionella wemmelensis (1-6%), Disaorbis quadrata (2-4%), Canaris subaoni­ aus (1-6%) and Entosolenia orbignyana (3-6%). Some other hyalin calcareous individuals appear in part of the Cassel Clay Rotalia audouini (0-2%), Elphidium laeve (0-1%), Nonion saaphum (0-5%), Bolivina aarinata (0-14%), Uvigerina farinosa (0-4%), Trifarina muralis (0-5%), Eponides toulmini (0-2%), Buliminella sp. cf. B pulahra (0-3%) and Trifarina wilaoxensis (0-4%).

3) Faunule 3 (Bassevelde Sands).

Faunule 3 shows the appearrance of several Bolivina aookei specimens (9-12%). A few other taxa occur more frequently than before. Especially the frequency of Cibiaides proprius proprius (36-37%) increases distinctly. Nonion affine (11-13%) and Spiropleatammina aarinata var. deperdita (l-14%) become important components of the assemblages. Elphidium laeve (0-2%) is replaced by Elphidium subnodosum (2-3%). The agglutinated Textularia agglutinans occurs less frequently (0-5%). Porce­ laneous taxa become less characteristic elements. The frequency of Quinque­ loaulina ludwigi varies from 0 to 4%. A few hyalin calcareous species are significantly present in(part of) the interval : Globulina gibba (0-8%), Guttulina Laatea (1-4%), Guttulina problema (0-2%), Cibiaides proprius aautimargo (3-4%), Cibiaides tenellus (0-7%), Cibiaides pygmeus (3-8%), Gyroidina.. :oatoaamerata (0-2%) and Canaris subaoniaus (0-3%).

5. TRIANGULAR PLOT OF SUBORDERS.

The three suborders of benthonic foraminifera are plotted in the triangular diagrams shown in figs;2,3 and 4. MURRAY (1973) marks out the fields for the different possible env,tonments. -116-

31.90

3240 BASSEVELDE SANDS

32,90

80.25-80.30

80,90-80.95 CASSEL CLAY

81.15- 81,20

82,30 _82.40

82,65_82,70

82,95

83,30_83,40 WEMMEL SANDS

83,80_83,85

84,45

85,60-85,65

85.90-86 0% 50% 100%

Fig. 5: Similarity index between the successive samples. -117-

70 I v I Vj vI v 65 v I v I vv v v I v;; v / 60 VI v v v v I vVI V;i; / I 55 1/ / vvv v v ll vv I 50 I I '/ VI I vv v v v 1/ I v v I j v v V; / / 1.5 ~ v v v ~ vv v v v /; ~ vv / v v/ / vv v v v II v vv v v ~ j / / v V/d ~ v v v VII y vv v v !Jf/; ~ L ll v L_ "' v ,..v ,_./"' v v v v/ v 25 ~ v v ~ v I-' v !--"" v v :,...... / y v~-' v 20 .~ / v v ~ / ~ y v v v :.- 15 ,..- ~ ,....-- / v ~ / 1-" i-- 10 _...... f-:" ~- ~ i- ---- ~ r- --- 5 - - 0 100 500 1000 5000 10000 Number of individuals

Fig.6: Fisher 01- index in faunule 1. -118-

70 v v v iJ vp iJ 65 I / I I I I I / lj/; ~ I v iJ 60 I I IV I 1/ l! I/ v II 1/ ~v 'i'; J I/ 55 1/ 1/ 1/1/ 1/ I/ v II J r; v ll 50 I r; v~ I / / 1.1 17 v v / I I 1/ !/ v V; / v/ 45 ~ / v 1/ !/ ~,.Y v v / ./ /; r; I v v/ / v v ~ / I / vI / v v,.,.. 1-./ I//;; ~ J iJ v / / / / I / / v If///; / / / / I-' ~ / .// / v v / / / ~/ 1/ 25 ~ v 17 v ~ v v v ~---~--- v I/ _.. v / v 20 ~ v v ,..... y v I/ 1-- / v v 1- 15 v ~ / v / v ~ ~ v _.... 1-- ~---~ 10 ~ 1-- I- ~ ~ -· ~ - ---- ~ 5 -- -- 0 100 500 1000 5000 10.000 Number of individuals

Fig. 7: Fisher cc: index in faunule 2. -119--

70 l I v I I II/ I I 65 ~ J I I v I lj/; I I 1/ I I I 60 J 'lv I I I II I v 55 v lj/ J I I I / / I v I / I / / I V /; I / 50 I v v I '/ vI v v[.l / / I I I v I I; / v 45 ~ v v I ll [.I [.I v I / I/[.I ll // /; ~ ~ I v / v v v v v / 1." vI v v ~v v//;; ~ I / / v v [.1 v v/ vv / ~ ~ / v v / I-' / vv v v v v / v / 1."1-"v 25 ~ / v v v ~~f-' / / v v v ,..,..... !---"' 20 ~ v v v / /~ 15 v/ v v~--" 1-f--" v v v l-----~ - v 1- 10 !-""' - r- l------I-I- f-.---f..-- r-- f.- 5 - - ~

0 100 500 1000 5000 10.000 Number of individuals

Fig.B: Fisher (X index in faunule 3. -120-

According to this interpretation, the following environments are possible for the different faunules. Faunule 1 can occur in hypersaline or normal marine marshes, hyposaline lagoons or on the continental shelf. Faunule 2 can survive in hypersaline or normal marine marshes, hyposaline or hypersaline lagoons and on the continental shelf. Faunule 3 is typical for hypersaline marshes and lagoons, normal marine marshes, hyposaline marshes and lagoons and the continental shelf.

6. SIMILARITIES (SANDERS, 1960).

The similarity between the successive samples in the section studied is given in fig.5. Within the Wemmel Sands, this index varies between 29 and 61. The lower values are explained by the aberration in the frequencies of taxa as Guttulina Zaetea, Bolivina angliea, Nonion affine and Cancris subconicus in sample 83.80-83.85. This association could be described as a subfaunule within the Wemmel Sands. The transition from the Wemmel Sands to the Cassel Clay is marked by a low similarity index (34%). Within the Cassel Clay, the values vary between 48 and 55%. The generally low similarity index in the Wemmel Sands and Cassel Clay reflects the rather different populations within this units. A low similarity index of 34% marks the transition from the Cassel Clay to the Bassevelde Sands. Within the Bassevelde Sands, the similarity index is distinctly higher than in the previous deposits (71-75%), which indicates more homogeneous populations in this member.

7. DIVERSITY INDEX OR FISHERa INDEX (FISHER, CORBETT & WILLIAMS, 1943).

The relationship between the number of individuals and the number of species in the populations of the three faunules is represented in figs. 6, 7 and 8. According to the interpretations of the different environments corresponding to the various a values by WRIGHT & MURRAY (1972) and MURRAY (1973), the following conditions for the three faunules are possible. -121-

ll.l 31.90 Cl ~ll) ~~ 32,1,0 ~:""{ (J)(/'j ~ 32,90

80,25 _80,30

,..,J ~).. ll)..q: 8Q90_80,95 ..q:(j 0 81,15- 81,20

82,30_82,1,0

82.65_82,70

ll) 82,95 ~ (}j 83,30_83,1,0 ttl 83.80_83,85 ~ ~ 81,,45

85,60-85,65

85,90_ 86 -----1- I 0 10 20

Fig. 9 : Dominance. index. -122-

------lll 31.90 Cl ~V) ::::.;Cl 32,40 t.u~ ~~ '<;( en 32,90

80,25-80.30

. V)}..~ V)'<;( 80,90-80.95 tid 81.15-81,20

82,30_82,40

82,65 _82,70

V) 82,95 ~ ~ 83,30-83,40 ~ ~ 83,80-83,85 ~ 84,45

85,60-85,65

85.90-86 I 0 50

Fig. 10: Percentage dominance. -123-

In faunule I, the Fisher a index varies between 7.5 and 13. Faunule 2 gives a values between 7 and 14, These populations survive in shelf seas of normal salinity or in normal marine lagoons. The diversity index is distinctly lower in faunule 3. It varies between 4 and 6.5. These associations occur in shelf seas of normal salinity or in hyposaline and nearshore shelf seas, in normal marine lagoons, in hyposaline and hypersaline lagoons and in hypersaline marshes.

8. DOMINANCE INDEX (WRIGHT, 1972).

Fig.9 represents the number of species in 80% of the populations.

Within the Wemmel Sands~ the dominance index varies between 7 and 15. Espe­ cially in sample 84.45, the index is rather low (7). The stability of the sea bottom probably changed during the deposition of the Wemmel Sands. An important increase of the dominance index in sample 81.15- 81.20 (18) markes the transition to the Cassel Clay. The index however decreases quickly higher up in;this unit (13). Roughly speaking, the values become higher in the Cassel Clay than in the Wemmel Sands. The Cassel Clay was deposited in a more stable environment. The dominance index is lowest in the Bassevelde Sands (5-9), which should suggest a more marginal environ­ ment.

9. PERCENTAGE DOMINANCE (WALTON, 1964).

The percentages of the most abundant species in the different samples are given in fig.IO. In the Wemmel Sands, these percentages vary distinctly. The values lie between 10 and 35. It suggest an environment with changing stability of the sea bottom. The percentage dominance becomes lower in the Cassel Clay. Here, the values vary between 8 and 19. The sea bottom became-more stable during deposition of this Cassel Clay. The Bassevelde Sands are characterized by high and more constant values of the percentage dominance (36-37). These high values could indicate -124-

a deposition in a shallower sea, in which however this deposition took place under stable conditions.

10. PALEOECOLOGICAL SIGNIFIC&~CE OF THE OCCURRING TAXA.

Different authors supply us information on the (paleo-) ecological significance of the occurring taxa : PHLEGER (1960), BANDY (1960, 1964), WALTON (1964), WRIGHT & MURRAY (1972), MURRAY (1973), WRIGHT (1972-1973), MURRAY & WRIGHT (1974), BOLTOVSKOY & WRIGHT (1976) and GERITS, HOOYBERGHS & VOETS (1981).

1) Wemmel Sands.

The agglutinated Textularia, which lives on the continental shelf or in the upper bathyal zone, is well represented in the Wemmel Sands. Other agglutinated genera with more complex morphological features as Spiropleatammina and Karreriella (siphonate aperture) prefer greater depths in the sea (outer shelf to upper bathyal zone). KaTTeriella occurs most abundantly on a muddy sediment. The porcelaneous Quinqueloaulina is widespread in shallow shelf conditions with a salinity higher than 30%. Triloaulina can survive at greather depths in temperature to tropical waters of at least normal marine seas. Several hyalin calcareous genera occur in this interval. Guttulina and Globulina occur most frequently on a inner shelf. Globulina prefers temperate to tropical waters in normal marine seas. Small smooth species of Bolivina (B. angliaa and B. arenulata) are found in rather shallow shelf conditions. Rotalia occurs most frequently in a nearshore environment. The greatest abundance of Elphidium is observed on a shallow inner shelf with oxygen-rich waters in which algae are favourable. Bifarina is a typical inner shelf genus. Cibiaiaes is currently most abundant in temperate, normal marine seas, where it lives on the shelf or in the bathyal zone in a wide range of salinity. It is attached to all types of substrates. -125-

Nonion prefers an inner shelf zone in hyposaline to normal marine seas with cold to tropical temperatures and with oxygen-rich waters. Nonionella is an inner shelf to bathyal genus in temperate to tropical seas. Bulimina occurs.most frequently on muddy sediment in a nearshore to bathyal environment with salinities between 32 and 36%. Uvigerina and Trifa.Pina also like a muddy sediment in normal marine seas in an outer shelf to upper bathyal environment. Disoorbis prefers a shallow sea with subtropical to tropical temperature and with a lot of seagrass and algae. Cancris is found in the central shelf zone of subtropical normal marine seas. Buliminella prefers a muddy sediment in a temperate, normal marine shelf to bathyal environment.

2) Cassel Clay.

Several taxa from the Wemmel Sands still occur in the Cassel Clay. The appearance of Alabamina however, indicates an increasing depth. This genus prefers an outer shelf to upper bathyal environment. The increase of Karreriella also suggest a greather depth of the sea. Quinqueloculina occurs less frequently in this conditions and Elphidium completely disappeared.

3) Bassevelde Sands.

Genera as Textula.Pia, Spiropleatammina, Guttulina, Cibicides and Nonion also occurs in the Bass:evelde Sands. The most important renewal in the populations is the occurrence of striate Bolivina's (B. cookei). This suggest a considerable depth of the sea in which the deposition took place. Nevertheless, Elphidium reappears in the assemblages, which indicates the presence of oxygen-rich waters and algae.

11. CONCLUSIONS.

The trangression of the Wemmel sea led to a deposition of fine sands in an inner, later Ln a central shelf environment. The sea bottom -126-

however was rather unstable. The salinity of the water was at least normal (33%). The temperature increased to subtropical values. The sea water was oxygen-rich and algae were favourable. The sea depth ii1creased to an outer shelf environment during the deposition of the Cassel Clay. The sea bottom became more stable in this time. We get little information on the environment of deposition of the middle part of the Kalla Formation, which is explained by the small number of benthonic foraminifera in this part o~ the formation. The occurrence of several MilioZina in sample 58.35 - 58.45 (a ) however suggest nearshore 2 conditions or a temporary regression of the sea at this time. The upper part of the Kalla Formation, or the Bassevelde Sands, was deposited on a stable shelf with oxygen-rich waters. Although the dominance index and the percentage dominance suggest more marginal conditions, the presence of Bolivina cookei reflects a rather deep sea.

12. ACKNOWLEDGEMENTS.

The author is grateful to Dr. P. LAGA (Belgische Geologische Dienst) fot the permission to study the samples from the Assenede Well. -127-

13. REFERENCES.

BANDY, O.L. 1960 General correlation of foraminiferal structure with environment. Int. Geol. Congress, Report 21, Sess. Nordon 1960, XXII, 7-19, 9 figs. 1964 General correlation of foraminiferal structure with environment. In "Approaches to paleoecology", IMBRIE & NEWELL, 75-95.

BOLTOVSKOY, E. & WRIGHT, R. 1976 Recent Foraminifera. 515 p.

DELATTRE, C. ; MERIAUX, E. & WATERLOT, M.

1973 Region du Nord Flandres, Artois, Boulonnais, Picardie Guide Geol. Regionaux. Masson & le Paris. 1-175.

FISHER, R.A. ; CORBETT, A.S. & WILLIAMS, C.B. 1943 The relation between the number of species and the number of individuals in a random sample of an animal population. Journ. Animal. Ecol., 12, 42-58, 8 figs., 9 tab.

GERITS, M. ; HOOYBERGHS, H. & VOETS, R. 1981 Quantitative distribution and paleoecology of benthonic foramini­ fera recorded from some Eocene deposits in Belgium. Prof. Paper, 1981/3, nr. 182, 53 p., 6 figs., 19 tab.

GULINCK, M. 1969 Coupe resumee des terrains traverses au sondage de Kallo et profil geologique NS passant par Woensdrecht - Kallo - Halle. In "Le Sandage de Kallo" (Au nord-ouest d'Anvers). Mem. Expl. Cartes, Geol. et Min. Belg., 11, 1-7, 2 figs.

KAASSCHIETER, J.P.H. 1961 Foraminifera of the Eocene of Belgium. Mem. Inst. r. Sc. Nat. Belg., 147, 271 p., 8 tab., 16 figs., 16 pls. -128-

MURRAY, J. W. 1973 Distibution and ecology of living benthic foraminiferids. 274 p.·, 102 figs.

MURRAY, J.W. & WRIGHT, C.A. 1974 Palaeogene foraminiferida and paleoecology, Hampshire and Paris Basins and the English Channel. Spec. Papers in Paleontology, nr.4, 129 p., 47 text-figs., 2 pls.

PHLEGER, F.R. 1960 Ecology and distribution of Recent Foraminifera. 297 p., 79 figs., 11 pls.

SANDERS, H.L. 1960 Benthic studies in Buzzands Bay. II. The structure of the soft-bottom community. Limnol. Oceanogr., 5(2), 138-151.

WALTON, W.R. 1964 Recent Foraminiferal Ecology and Paleoecology. In "Approaches to Paleoecology", IMBRIE & NEWELL, 151-237, 29 figs.

WRIGHT, C.A. 1972 Foraminiferids from the London Clay at Lower Swanwick and their

paleoecolog~cal interpretation. Proc. Geol. Assoc., 83(3), 337-347, 4 figs. 1973 Foraminiferids from the Lutetian at Ronquerolles (Val-d'Oise) and their palaeoecological interpretation. Revue de Micropal., 16(2), 147-157, 5 figs.

WRIGHT, C.A. & MURRAY, J.W. 1972 Comparisons of modern and palaeogene foraminiferid distributions and their environmental implications. Mem. B.R.G.M., 79, 87-96, 5 figs.