Can detailed sampling and taphonomical analysis of foraminiferal assemblages offer new data for paleoecological interpretations?

REVUE DE MICROPALI~ONTOLOGIE Vol. 40, n ° 4, d6cembre 1997, pp. 313-329

CAN DETAILED SAMPLING AND TAPHONOMICAL ANALYSIS OF FORAMINIFERAL ASSEMBLAGES OFFER NEW DATA

FOR PALEOECOLOGICAL INTERPRETATIONS?

UN [~CHANTILLONNAGE DETAILLE ET UNE ANALYSE TAPHONOMIQUE D'ASSOCIATIONS DE FORAMINIFE, RES

PEUV.ENT-ILS OFFRIR DE NOUVELLES DONNEES POUR LES INTERPRETATIONS PALEOECOLOGIQUES ?

by Katar~na HOLCOVA*

ABSTRACT. - - Distinctions between the composition of foraminiferal assemblages in lithologically different superimposed beds were established in the Lower and Middle Miocene samples from the South Slovak Basin included in the Central Paratethys. These distinctions may be caused by different depositionaÁ mechanisms of the individual beds.

Foraminiferal assemblages from the beds were analysed quantitatively. A detailed taphonomical study of the oryctocenoses preceded paleoecological interpretations. Reworked, transported (in suspended load and bed load) and indigenous foraminiferal tests were recognized in assemblages. The distribution of these tests in beds was recorded. Three types of distribution were recognized: (1) only suspension-transported foraminifers occuring in both coarser and finer beds, (2) indigenous and reworked foraminiferal tests occuring with different ratios in the beds, (3) tests transported within bed load occuring in coarser beds, in finer beds they may be accompanied by reworked or indigenous tests.

The presented analysis of foraminiferal oryctocenoses from different beds supphes data on depositional environments and source areas of the sedimentary particles bearing foraminiferal tests, as well as on their transport mechanism. Analyses showed that sampling of the same lithotype in whole sections (e.g. the finest sediments) may give fragmentary or even misleading data (better preserved indigenous assemblages may occur in coarser sediments).

RI~SUME. -- Des diff6rences de composition entre les associations de foraminif~res issues de couches superpos6es de lithologie diff6rente ont 6t6 6tablies pour des 6chantillons du Miocb~ne inf6rieur et moyen de la Parat6thys Centrale (Juhoslovensk~ panva). Ces 6carts peuvent ~tre dus ~ des diff6rences dans les m6canismes de d6p6t des couches individuelles.

Les associations de foraminif~res des diff6rentes couches ont 6t6 analys6es quantitativement. Une 6tude taphonomique d6taill6e de l'o~yctoc6nose est suivie d'interpr6tations pal6o6cologiques. Des tests de foraminif~res remani6s, transport6s (en suspension ou en traction) et autochtones sont reconnus dans les associations. La distribution de ces tests dans les couches a 6t6 not6e. Trois types de distribution ont 6t6 reconnus : (1) les foraminif~res transport6s en suspension sont senls pr6sents, (2) les tests de foraminif~res autochtones et remani6s sont pr6sents dans des proportions variables, (3) les tests transport6s par traction sont pr6seuts dans les couches les plus grossi~res; dans les plus fines, ils peuvent ~tre accompagn6s de tests remani6s ou autochtones.

Ces analyses d'oryctoc6noses de foraminif~res apportent des informations sur les milieux de d6p6t, sur l'origine des particnles s6dimentaires accompagnant les foraminifbres et sur les m6canismes de transport. L'6chantillonnage d 'un seul et m~me facies dans une coupe complete (p. ex. les s6diments les plus fins) peut n 'apporter que des indications fragmentaires ou erron6es (par exemple, les associations les mieux pr6serv6es peuvent se trouver dans les s6diments les plus grossiers).

Key-words : Foraminifera - Taphonomy - Depositional environment - Miocene - Central Paratethys - Palaeoenviromnent.

Mots-cl6s : Foraminif~res - Taphonomie - Milieu de d6p6t - Miocene - Parat6thys Centrale - Pal6oenvironnement.

* Department of Paleontology, Charles University, Albertov 6, CZ-128 43, Czech Republic.

314 PALEOECOLOGICAL ANALYSIS OF FORAMINIFERAL ASSEMBLAGES

I N T R O D U C T I O N

Foraminiferal tests included in sediments provide two kinds of information about the paleoenviron- men t : (1) foraminifers need specific life habitats during their life, (2) tests of dead foraminifers are t ransformed into sedimentary particles and, as such, they can be transported and .transformed.

The starting point of this work is a paleoecological study of foraminiferal assemblages obtained from millimeter- to centimeter-thick lithologically different beds in clastic sediments (siltstone and sandstone). Paleoecological interpretations are based on a taphonomical analysis of the assemblages. It is supposed that the compared beds were deposited in a similar paleoenvironment by different depositional mechanisms. Therefore, differences in species composition, size distribution and preservation of foraminiferal tests in beds were caused by these depositional mechanisms. This work aims to show the influence of test t ransport on the composition of foraminiferal assemblages, and then on paleoenvironmental interpretations based on this composition.

In the study of clastic sediments, environmental interpretation based mainly on the grain-size distribution of sedimentary particles provides an explanation of the t ransport mechanism (e.g. Folk and Ward, 1957 ; Friedman, 1979 ; Middleton, 1976 ; McCave, 1 9 7 8 ; McLaren, 1 9 8 2 ; Visher, 1 9 6 9 ; Singer and Anderson, 1 9 8 4 ; etc.). But interpretations of grain-size distribution are equivocal in many cases. McLaren and Bowles (1985) gave two reasons for the disagreement in interpretations : the process of erosion and deposition of particles involves many variables, which cannot be measured very well; the grain-size distribution changes continuously fi'om source to final deposits by multiple t ransport or other sedimentary processes (winnowing, selective deposition, etc.), which cannot be easily recognized.

Foraminiferal tests differ from other sedimentary particles by certain characteristics. Therefore, se- dimentological models are not fully applicable on foraminiferal assemblages. The size distribution of t ransported foraminiferal tests can be different from the distribution of clasts. It can be caused by :

(1) difference in the size distribution of source deposit ( log-normal: Udden, 1914) and "source" (= indigenous) foraminiferal assemblages (polymodal, flat distribution; shape of distribution curve depends on species composition);

(2) t ransport and resedimentation of foraminiferal tests, that usually do not show as many recur-

rences as those of sedimentary particles. Therefore, foraminiferal tests document mainly the last reworked episodes of sedimentary particles;

(3) predisposition to t ransport under certain phy- sical conditions, that depends on the ratio between volume and weight of transported particles. Diver- sity of morphotypes of foraminiferal tests is mar- kedly larger than tile morphological diversity of clasts. Therefore, an accumulation of some foraminiferal morphotypes can provide detailed information about t ransport mechanisms.

In spite of this, the size range of size-sorted tests has provided a distinction between the suspended- load and bed-load t ransport (Murray, 1965 ; Loose, 1 9 7 0 ; Culver and Banner, 1 9 7 8 ; Murray et al., 1 9 8 2 ; Wang and Murray, 1983).

The interpretation of the t ransport mechanism of foraminiferal tests can be made more easily than that of inorganic sedimentary particles. The following characters can be utilized (Murray, 1 9 9 1 ) : absence of juveniles or adults, breakage and abra- sion of foraminiferal test, different modes of test preservation. A discrepancy between ecological requirements of species in the assemblages may correspond to different life habitats of source and deposition areas. Differences in stratigraphical range of some species in the assemblages may indicate a succession of reworking features.

Therefore, t ransported and resedimented tests are able to provide more information about the sediment story than a single grain-size distribution. On thc other hand, the paleoecological interpretation of a test t ransport requires the experience of a sedimentologist.

M A T E R I A L

The analysed material comes from the Miocene of the South Slovak Basin (included in the Central Paratethys) (Fig. 1). Two core-samples and two sections were studied from the "Rzehakia (Onco- phora) Beds" and 10 core-samples were selected from the Lower Badenian interval.

"Rzehak ia (Oncophora) B e d s "

The "Rzehakia (Oncophora) Beds" represent an important Upper Ottnangian (= Lower Miocene, equivalent of the middle par t of the Burdigalian : Papp et al., 1973) Paratethys horizon bearing a characteristic endemic molluscan fauna. Generally,

HOLCOVA 315

r~

y

• LOWER BADENIAN

FIG. l . - Locations of the studied cores and exposure.

Localisation des carottes et affleurement ~tudi&

the "Rzehakia Beds" were deposited in shallow brackish seas or large brachyhaline to oligohahne lagoons (Kvaliashvili, 1 9 6 2 ; ~tyrok)~, 1968) . In the southern par t of the Paratethys, these brackish basins were periodically connected with the open Lower Miocene sea. In the majority of the Parate- thys basins, the Beds represent a regressive phase of the overlying Lower Miocene (in tile Central Paratethys Eggenburgian - Lower Ottnangian) cycle of seadevel changes.

In the Pannonian Basin (the studied area - the South Slovak Basin - represents the northern par t of the Pannonian Basin), the "Oncophora (Rzeha- kia) Beds" seem to transgressively overlie the conti- nental Ottnangian sedimentation. Therefore, the Beds are proposed by some authors to be a transgressive phase of younger Karpat ian cycle of sea- level changes (e.g. Vass, 1 9 9 5 ; Hhmor, 1985) .

The lowstand character of the beds, very similar lithotypes in the whole Paratethys region and a significant influence of storm activity (tempestites, foraminiferal tests transported by storm waves) enable one to propose an isochroneity of the "Rzehakia (Oncophora) Beds" (in agreement with the opinion of Kovh~ et al., 1989). The relative transgressive or regressive position of the Beds may be caused

by tectonic control of sea-level changes (Holcovh- ~utovsk~, 1996) .

The "'Rzehakia (Oncophora) Beds" in the South Slovak Basin (Vass et al., 1979 , 1992) are represented by massive or laminated fine-grained sandstone. The massive sandstone is intensively bioturbated. The laminated sandstone contains laminae or thin beds of claystone, sihstone or coarse-grained sandstone. Samples issued from these well-indivi- duahzed siltstone and sandstone were chosen for analysis (Fig. 2 ; P1. 1, fig. 1-3).

An abundant occurrence of foraminiferal tests is a distinctive feature of the South-Slovak "'Rzehakia (Oncophora) Beds". Small, thin-walled, and well- preserved tests prevailed in the analysed samples. The abundance of these tests is high, foraminiferal numbers (= number of foraminiferal tests in 1 g of sediment) reach values of 800. Benthonic foraminiferal assemblages are dominated by outer shelf to bathyal species, e.g. Globoc~a~sidulina, Cassidulina, Cibicidoides, Trifarina, Bolivina~ Uvigerina, Episto- maria, Caucasina, Spiroloxostoma, etc. In some horizons, inner shelf assemblages dominated by Am- monia ex gr. parkinsonia-tepida occur. Planktonic foraminifers are represented by Globigerina ex gr. praebulloides BLOW, Cassigerinella boudecensis POK. and small microperforate pentacamerate species (Tenuitella plexus). In some horizons, large and well-preserved tests occur among the small thin-walled tests. The large tests included hyposaline species : Haynesina depressula (WALKER and JACOB), Monspeliensina vulpesi GLAGON and LYS and Am- monia parkinsonia-tepida group. Stenohaline, epiphytic species Elphidium div. sp., Lobatula lobatula (WALKER and JACOB), Hanzawaia boueana (d'OR- BIGNY), Asterigerinata planorbis (d'ORBIGNY) w e r e found very rarely.

Two significant cyclical changes of foraminiferal oryctocenoses were recognized for the South-Slovak "Rzehakia (Oncophora) Beds" using: (1) changes in the ratio of indigenous, suspension-transported, bedload-transported and reworked tests, and (2) changes in the abundance of indigenous tests. Using these characteristics, two cycles of sea-level changes of the 5th order may be interpreted for the South-Slovak "Rzehakia (Oncophora) Beds" (Uoleovh, 1996b) (Fig. 2).

T h e E a r l y B a d e n i a n

The Early Badenian sediments (equivalent of the Langhian) in the South Slovak Basin characterize, in a transgressive position, the Early Badenian sediments in the whole Paratethys region (e.g. R6gl


Z

~D

N -83

N-96 N-65

~ 2

~ 4 ~ s ~ 6

96 ~ 12

117'" ~ 13

MK=I TM

MK-2

- - - 20 -- 21

'~A 15

FIG. 2. - Lithological sections of the s tudied cores N-48 , N - 6 5 , N-96 , N - 8 3 , N-95 and exposures f rom sandpi t Mal~ Krti~ (MK 1, MK 2). Explana t ions : 1 - c laystone, 2 - sands tone , 3 - conglomera te , 4 - siltstone, 5 - clayey sands tone , 6 - tuffaceous sands tone , 7 - g r a d e d bedding, 8 - l amina ted sands tone , 9 - sandstone with undula t ing lamina t ion , 10 - cross-bedding, 11 - siltstone with sandstone laminae , 12 - b recc ia with volcanic mater ia l , 13 - tuffite wi th shell de t r i tus , 14 - sands tone lenses accumula t ed in t roughs of wave r ipples , 15 - b io tu rba t ions , 1 6 - 1 8 - pa l eoenv i ronmen ta l in te rpre ta t ions . ( l 6 - lacus t r ine sediments , 17 - h t to ra l , hyposal ine env i ronmen t , 18 - l i t toral , s tenohal ine env i ronmen t ) , 19 - h ia tus , 20 - b o u n d a r y be tween cycles of sea-level changes, 21 - cor re la t ion

of h ighs tand t racts . Samples a re f r a m e d and the i r depths a r e given. F o r detailed lithology of samples see Fig. 3 -5 .

Coupes l i thologiques des carot tes dtudi~es N ~ 8 , N - 6 5 , N - 9 6 , N 8 3 , N - 9 5 et des a f f l euremen t s de la sabli~re Ma ly Kr t i s ( M K 1 , M K 2 ) . L@eudes : 1 - argilol i thes, 2 - gr$s , 3 - conglom~rats , 4 - s i l ts tone, 5 - gr$s argi leux, 6 - gr~s tufJhcd, 7 - g r a n o c l a s s e m e n t , 8 - gr$s lamin~, 9 - gr~s ~t l amina t i on ondul~e, 10 - d6p~ts entrecrois~s, 11 - s i l ts tone & lamines gr~seuses, 12 - br$che ~t mater ie l volcanique , 13 - tu f f i te ~t ddbris coquill iers, 14 - lentilles gr6seuses accumul~es dans les c r e u x de rides de houle, 15 - b io turbat ions , 1 6 - 1 8 - i n t e rpre ta t ion pa l~oenv i ronnemen ta l e ( i 6 - s~diments lacustres , 1 7 - e n v i r o n n e m e n t l i t toral hypoha l in , 18 - e n v i r o n n e m e n t l i t toral s t~nohal in) , 19 - h ia tus , 2 0 - l imites en tre cycles de var ia t ions d u n i veau mar in , 21 - corre la t ion des corteges de h a u t n iveau

mar in . Les ~chanti l lons sont localisds, et l eur p r o f o n d e u r indiqu~e. Voir f i g . 3-5 p o u r la litologie d~taill~e des ~chanti l lons.

and Steininger, 1983) . The sedimentation in South Slovakia was significantly influenced by volcanic activity. The studied boreholes are situated in the marginal par t of the Early Badenian sea. Tuffaceous sandstones and sihstones with common bioturbation dominated by domichnia overlie the basal coarse volcaniclastics (Fig. 2 ; P1. 1, fig. 4-7). Well-individualized laminae to thin beds of siltstone and sandstone characterize the whole sections, what allowed more detailed sampling of the N-83 borehole.

The benthonic foraminiferal assemblages in boreholes N-95 and N-83 are dominated by epiphytic, inner shelf, stenohaline species : Pararotalia stellata (REUSS), Lobatula lobatula (WALKER and JACOB), Asterigerina planorbis (d'ORBIGNY), Glabratella pa- telliformis (d'OBBIGNY), elphidiids and miliolids. The rare occurrence of Praeorbulina and Orbulina allows biostratigraphical interpretation. The species composition of the assemblages as well as the percentage of species in assemblages are very similar

HOLCOVA 317

in the whole sections. In the nearshore area (N-48 borehole), hyposaline assemblages dominated by the Ammonia parkinsonia-tepida group and Haynesina depressula (WALKER and JACOB) occur very rarely in the middle par t of the sections.

Cychcal changes in these very similar, upper neritic foraminiferal assemblages are not very pro- minent. Cyclical changes in the foraminiferal abundance, part ly in the epifauna/infauna ratio and in the similarity, were used for the interpretation of cycles of sea-level changes. Three cycles, probably of the 4 th order, may be distinguished (Holcov~, 1996b) .

M E T H O D S

Well-individualized, superimposed thin beds, represented by coarse and fine sediment (sihstone/fine sandstone, fine sandstone/coarse sandstone, sandstone/coarse conglomerate) were washed separately using a 63 ~m (240-mesh) sieve. Weight percentage of the sand fraction (> 63 ~tm) was entered for every sample. For comparison, a par t of the whole sample containing both lithotypes was washed.

S t a n d a r d a n d q u a n t i t a t i v e analys is o f f o r a m i n i f e r a l a s s e m b l a g e s

Analysis of foraminiferal assemblages includes :

(1) determination of species occurring in assemblages (list of species for boreholes N-83 and N-95 was published in Holeov~ et al., 1996) ;

(2) quantitative analysis of assemblages. The following four quantitative data, which can be used in paleoenvironmental interpretation, were given for all analysed beds (Fig. 6 below) :

- - foraminifera1 number of Scott (= number of foraminiferal tests in 1 g dry weight of sediment) ;

- - P/B-ratio (= percentage of planktonic forami- nifcrs in foraminiferal assemblage calculated for 300-500 specimens);

- - diversity of benthonic foraminiferal assemblages calculated for 300 specimens using Simpson's formula :

N ( N - l ) D -

Ni (N~-I)

where D is diversity, N is the number of counted specimens in the assemblage and Ni is the number of specimens of the i-th species.

- - similarity of foraminiferal assemblages from superimposed beds calculated for 300 specimens using Jaccard ' s formula.

C S -

C + U

where S is similarity, C is the number of species occurring in both compared samples and U is the number of species occurring only in the first sample + number of species occurring only in the second sample.

T a p h o n o m i c a l analysis o f f o r a m i n i f e r a l o r y e t o e e n o s i s

For recognizing the influence of t ransport on foraminiferal tests, the following criteria were studied :

(1) Size distribution o f tests : from every sampled bed, 100 rounded, 50 elongate benthonic forms and 50 planktonic foraminiferal tests were chosen for the analysis from > 63 ~m (240-mesh) sieve fraction. The largest diameter of tests for rounded forms and planktonic foraminifers and the length of tests for elongate forms were measured using the VIA video measuring system. Size distributions of tests (separately for rounded forms, elongate forms and planktonic foraminifers) were summarized in histograms.

For recognizing the t ransported and autochto- nous assemblages, size sorting was deduced from histograms : narrow, unimodal histograms characterize size-sorted tests, polymodal histograms with great range of test size are typical of unsorted tests.

To determine the mode of t ransport , a range of test sizes were studied among transported tests. Small tests (rounded forms < 200 ~tm, elongate forms < 300 ~m) indicate a suspended-load transport . Adults of a majority of species absent in the oryctocenoses were t ransported within a suspended load.

Large well-sorted tests (> 300 ~m) have been t ransported within a bed load (Murray, 1 9 6 5 ; Loose, 1 9 7 0 ; Culver and Banner, 1 9 7 8 ; Murray et al., 1 9 8 2 ; Wang and Murray, 1983). Juveniles are absent in oryctocenoses t ransported within a bed load.

These results are also applicable to fossil assemblages (Holcov~, 1996a).

(2) Preservation o f tests determined by SEM examination : well-preserved and corroded/abraded tests were recognized. Significant diagenetic changes of the tests' walls were not observed.

318 PALEOECOLOG1CAL ANALYSIS OF F O R A M I N I F E R A L ASSEMBLAGES

(3) P a l e o e c o l o g i c a l i n t e r p r e t a t i o n o f s p e c i e s in assemblages were based mainly on data of Pfleger (1965) , Boltovskoy and Wright (1976) , Mur ray ( 1 9 7 3 , 1991) , Reiss and Hott inger (1984) . Diffe- rent paleoecological requirements of species in an assemblage indicate the occurrence of t r anspor ted tests.

(4) R e w o r k e d s p e c i e s can be distinguished by comparison of biostrat igraphical ranges of species in assemblages (mainly Cicha e t a l . , 1 9 8 3 ; RSgl, 1986) .

R E S U L T S

T y p e s o f d i f f e r e n t l y p o s t m o r t e m - m o d i f i e d f o r a m i n i f e r a l o r y c t o c e n o s e s

Based on the taphonomical analysis of foraminiferal oryctocenoses, six types of oryctocenoses were distinguished in the analysed material using previous resuhs (Holcov~, 1996a ) (Tab. 1 ) :

(1) Foraminiferal tests in oryctoccnoses are size- unsorted, well-preserved and exhibit different onto- genetic stages. Ecological requirements and strat igraphical ranges of species are identical. These parameters character ize indigenous or weakly t ranspor ted tests without any influence of t ranspor t on their composition and preservation.

(2) The oryctoeenosis is composed of size-sorted, small ( rounded tests < 200 ~m, elongate ones < 300 ~m), well-preserved and thin-walled tests, with juveniles being dominant . Outer shelf to bathyal species occur in assemblages. This type of oryctoccnoses was formed by t ranspor t in suspension.

(3) Tests t r anspor ted in bedload are size-sorted and essentially > 200 ~m. They are abraded , broken and dominated by robust forms. Lit toral species occur in this type of oryctocenoses.

(4) Two types of test preservat ion were observed in this oryctoccnosis : some tests are unsorted, well- preserved and belong to outer to inner shelf species ; the others are size-sorted, large, broken, abraded, and belong to euryhal ine and littoral species. The strat igraphical ranges of all species in assemblages are identical. The oryctocenosis contains indigenous or weakly t ranspor ted elements mixed with tests t ranspor ted in bed load f rom a coastal area to a more central pa r t of the basin.

TAB. 1. - Types of differently postmortem modified foraminil~ral oryctocenosis. Abbreviations: corr. = corroded, us = unsorted, sl = size-sorted, large tests (larger than 200 ~m), ss = size-sorted, small tests (< 200 ~m), hs = hyposaline environment, is = inner shelf, stenohaline, os = outer shelf, ba = bathyal, LM = Lower Miocene, LB = Lower Badenian, ident. = identical for all species in sample, u.b. = in underlying beds. For detailed explanations

see text. Divers types d'associations ~bssiles de forautinigQres d i f ~ r a n t p a r les modif icat ions pos tmor t em subies. Abr~viat ions : corr. = cor- rode, us = non classd, sl = grands tests classes selon leur taille (sup~rieure & 2 0 0 ~tm), ss = pet i ts tests classes selon leur taiUe ( inf~rieure h 200 ~m), hs = env i ronnemen t hyposal~, is = p late forme interne, s tdnohaline, os = p la t e forme ex terne , ba = ba thyva l , LM = Miocene inf~rieur, LB = B a d d n i e n inf$rieur, ident . = c o m p a r a b l e p o u r toutes les esp~ces de l '6chant i l lon , u .b . = d a n s les n i v e a u x souss jacen t s . Voir le tex te p o n r les

l@endes ddtaill~.es.

== ~ ~ ~ o z~NN'E~ • ~ ~ O~ ~ ~ ~ ~ ~ 0 ~ " ~ "~ Interpretation

_ ~ ~ of postmortem ~- ~o ~_ ~ '~ > ~ ~.° ~= ~ changes

- . . I ~ , I . . . . ,,l~or, i j . v l . d h,li, lo, lba LM ILB I x x x x ident, ident, indigenous or weakly transported

- I 2 x x x rare x x x suspension-transported

3 x x are x x x ident, bedload-transported

x x x x x x indigenous mixed 4 ident, with bedload transported

x x x x x indigenous with

5 x x x x x x suspension-t ra nsport ed x x x rare x x x and then reworked

suspension-transported i 6 x x x rar~ x I x x u .b and then reworked _

(5) The size distl~budon of tests in the oryctocenosis is polymodal with a great peak at the value of about 165 ~m. All the tests are well-preserved. Small ones are thin-walled, issued f rom outer shelf to ba thyal environments and often represented by juveniles only. Index species of the Lower Miocene were observed among them. Species with size-unsorted tests are issued f rom inner shelf environments with index species of the Lower Badenian. Both juvenile and adult specimens occur in assemblages. The oryctocenosis is composed of indigenous or little t ranspor ted , shallow marine, Lower Badenian assemblages with reworked Lower Miocene suspension- t ranspor ted tests.

(6) The oryctocenosis consisting of only Lower Miocene suspension- t ranspor ted tests reworked to Lower Badenian sediments is character ized by size- sorted, small, well-preserved or cor roded , thin-walled tests belonging mainly to juveniles. Outer shelf and ba thyal species occur in this oryctocenosis. Only the Lower Miocene index species were found, while in the underlying and overlying samples Lower Badenian index species occur.

H O L C OVA 3 1 9

TAB. 2. -- Types of distribution of foraminiferal oryctocenosis in superimposed thi~l beds characterized by different lithologies, lx - 1st postmortem transport of tests, 2x = 2nd postmortem transport of tests, in = indigenous tests, st = suspension-transported tests, bt = bedload-transported tests, rw = reworked tests, LB = Lower Badenian, LM = Lower Miocene. 1 - transport of foraminiferal tests in suspension, 2 - resedimentation of foraminiferal tests, 3 - mixing of foraminiferal assemblages by bioturbation, 4 - transport of foraminiferal tests in bedload, 5 - hyposaline environment, 6 - inner shelf, stenohaline, 7 - outer shelf, 8 - posssible misinterpretation of paleoenvirorm)ent, 9 - sandstone, 10 - siltstone, l l - elaystone, 12 - undulating lamination, 13 - graded bedding. For detailed explanations see text.

Types de distribution des associations fossiles de foraminif~res dans des lits minces superposes, caract~ris~s par des lithologies diff~rentes, lx = premier transport post-mortem des tests, 2x = 2 ~ transport post-mortem des tests, in = tests autochtones, st = tests transport~s en suspension, bt = tests transport~s par traction, rw = tests remanids, LB = Bad~nien infdrieur, LM = Miocene inf~rieur, 1 - transport en suspension des tests de foraminiJ~res, 2 - res~dimentation des tests, 3 - rr~lange des associations de foraminij~res par bioturbation, 4 - transport des tests par traction, 5 - environnement hyposal$, 6 - plateforme interne, st~nohaline, 7 - p l a t e f o r m e externe, 8 - risques d'erreur dans l~nterpr~tation du pal~oenvironnement, 9 - gr$s, 10 - siltstone, 11 - argilolithe, 12 - lamination ondul~e, l 3 - granoclassetwsnt.

Voir le texte pour les l@endes d~taill~es.

D i s t r i b u t i o n o f t y p e s o f o r y c t o c e n o s e s i n b e d c o u p l e s

F o r a m i n i f e r a l o ryc tocenos i s f r o m pa i r s of well i n d i v i d u a l i z e d th in beds of f ine ( d o m i n a t e d by s ih- s tone) a n d c o a r s e ( d o m i n a t e d by s ands tone ) sediments w e r e t a p h o n o m i c a l y a n a l y s e d a n d c lass i f ied in to six types of o ryc tocenoses f r o m Tab . 1. T h e d i s t r i b u t i o n o f o ryc tocenoses in ana ly sed samples def ines the fo l lowing types a n d sub types (Tab . 2) :

T y p e A : O n l y s u s p e n s i o n - t r a n s p o r t e d

f o r a m i n i f e r s o c c u r r i n g i n t h e s e d i m e n t

S u b t y p e A a : S u s p e n s i o n - t r a n s p o r t e d f o r a m i n i f e r s (o ryc tocenos i s 2) o c c u r in b o t h c o a r s e r a n d f ine r beds (Fig. 3) .

F o r c o m p a r i s o n wi th o t h e r a n a l y s e d samples , the exc lus ive o c c u r r e n c e of s u s p e n s i o n - t r a n s p o r t e d fo- r a m i n i f e r s is n o t e d usua l ly in t he f ines t s ed imen t s (Fig. 6) , w h a t is in a g r e e m e n t wi th t he o b s e r v a t i o n of W a n g a n d M u r r a y ( 1 9 8 3 ) . Changes in g r a in size, e x p r e s s e d by p e r c e n t a g e o f s and in s ed imen t , h a v e no i n f l u e n c e on the r a n g e of test size. T h e specif ic c o m p o s i t i o n o f assemblages is s imi l a r ( G l o b o c a s s i -

d u l i n a div. sp. , C a s s i d u l i n a l a e v i g a t a , I s l a n d i e U a

sp., B o l i v i n a a n t i q u a , C a u c a s i n a s c h i s c h k i n s k a y a e

a n d C i b i c i d o i d e s p s e u d o u n g e r i a n u s d o m i n a t e ) , w h a t can be c a u s e d by some m o r p h o l o g i c a l c h a r a c t e r i s t i c s of tests s u c h as th ickness of tes t wal l , size, a n d

C"-

] i B ~ iii!~i~ <

°11

~ ~ X X X ~

1 × ×

_:_7

N t ype of o r n a m e n t a t i o n p r e d i s p o s i n g t h e m to t r a n s - p o r t in suspens ion . T h e r e f o r e , the i ndex of s imila- r i t y f o r the assemblages is h igh ( 6 8 - 9 4 %) (Fig. 6) . Th i s t y p e of f o r a m i n i f e r a l a s semblage t r a n s p o r t e d by suspens ion a n d r e c o g n i z e d in all a n a l y s e d beds occu r s on ly in the " R z e h a k i a ( O n c o p h o r a ) B e d s " .

P a l e o e n v i r o n m e n t a l i n t e r p r e t a t i o n : T h e o u t e r she l f to u p p e r b a t h y a l s t e n o h a l i n e p a l e o e n v i r o n m e n t c a n be c o n s i d e r e d as the s o u r c e a rea . T r a n s p o r t o f

Ao

Ab

MK

1

o',

" -o

"oo

•

"o'o

, "

,o

,,

°,

.o

~

•

r.e~

.'k/.e

m..v

~.k

3¢..m

~.V.

r.t.

V..~

k.V.

mL"

k,r~

el

:-"'

"'(i

'"'"

'"'"

'""'

"*'"

"'.'

.'.'

-:

: :

! ;

....

.

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

::::

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i i i i;i;',;i

iiiiii,i,i

il;i!i;i i;

i ;i :1

BE

NTH

ON

IC F

OR

AM

INIF

ER

A-

RO

UN

DE

D F

OR

MS

IO

t3

o ~

038

~27

' 0,

36

' 'o

,=5'

~ O

N/C

FO

RA

MIN

IFE

RA

1o

MK

14

..

..

..

..

..

..

..

..

13

0~0~

0,

18

c~27

(~

3s

~5

O

,S4

MK

2 -;-~:Tf

f:-':':':'

:':"- :~

'"7"":"

o.

N-96

/305

sandstone

~.-

-

~~

_~

ii

il

B

EN

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NIC

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RA

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IFE

RA

- R

OU

ND

ED

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RM

S

. -7

i.

~~..

....

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.;..

..:.

;.

I ac

e o,1

8 a~

o.

ze

a.~

0,~

~65/

120

san

dst

on

e

/

i~48

/95

~d.~

'one

::::::::::

::::::::::

::::::::::

::::::::::

:::::~ O~o

.

..

.

:':'

:':'

":':

""""

" .

..

..

..

c~aystone

,o :

/

~i:i::+:i:::::~":-':':"~

" ~

BE

NTH

ON

IC F

OR

AM

INIF

ER

A-

ELO

NG

ATE

FO

RM

S

°o.c~

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o.:-.

, o.

~ k.

e ~

.~

SIZ

E-D

ISTR

IBU

TIO

N O

F T

ES

TS

FR

OM

SA

MP

LES

MK

11 -

MK

14

o ~

BE

NTH

ON

IC F

OR

AM

INIF

ER

A-

RO

UN

DE

D F

OR

MS

1o

PLA

NK

TON

IC F

OR

AM

INIF

ER

A

..

..

..

.

21

BE

NTH

ON

IC F

OR

AM

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ER

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ATE

FO

RM

S

t,~

24

..

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so •

SIZ

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STS

~

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M S

AM

PLE

S M

K21

- M

K 2

4

o

BE

NTH

ON

IC F

OR

AM

INIF

ER

A-

ELO

NG

ATE

FO

RM

S

PLA

NK

TON

IC F

OR

AM

INIF

ER

A

0,0~

0,

18

0,27

0,

36

0,4~

0,

54

1 j

~o

~ N

-96/

305

m -

silt

ston

e

a a

~

E:~

N

-65/

120

silts

tone

[~

N-4

8/95

m -

silt

ston

e

o 0,

0~

0,18

0,

27

0,36

0,

45

0,54

0,

0~

0,18

0,

27

0,36

0.

45

0,54

6 7

SIZ

E-D

ISTR

IBU

TIO

N O

F TE

STS

FR

OM

WH

OLE

SA

MP

LES

o

N-6

5/12

0 M

o,oe

o,te

o,

z~

o,:~

o,

,~

o,~

vert

ical

c0(

is-n

umbe

r of

spe

cim

ens

horiz

onto

l c0

(Is -

test

stz

e (u

rn)

©

©

©

©

©

k=m

;z

CI3

FIG

. 3

. -

Siz

e d

istr

ibu

tio

n

of b

enth

on

ic

rou

nd

ed,

ben

tho

nic

el

on

gat

e an

d p

lan

kto

nic

fo

ram

inif

eral

tes

ts i

n sa

mp

les

N-9

6/3

05

m

, N

-65

/12

0

m,

N-4

8/9

5

m

and

se

ctio

ns

MK

1

and

M

K 2

:

typ

e A

w

ith

su

spen

sio

n-t

ran

spo

rted

te

sts.

E

xp

lan

atio

ns

of l

ith

olo

gic

al s

chem

es :

1

- si

hst

on

e,

2 -

san

dst

on

e,

3 -

clay

sto

ne,

4

- sa

nd

sto

ne

wit

h p

lan

t an

d

shel

l d

etri

tus,

5

- sa

nd

sto

ne

wit

h l

um

ach

elle

bed

s, 6

-

7 -

dis

tin

ct l

amin

ated

str

uct

ure

, 8

- in

dis

tin

ct l

amin

ated

str

uct

ure

. L

eng

ht

of s

cale

bar

:

2 cm

. S

ub

typ

es A

a an

d A

b

are

def

ined

in

tex

t.

Dis

trib

uti

on

d

e ta

ille

de

s te

sts

de f

ora

min

iJ~

res

ben

thiq

ues

a

rro

nd

is,

ben

thiq

ues

al

long

~s

et p

lan

cto

niq

ues

, d

an

s le

s $c

hant

illo

ns

N-9

6/3

05

m

, N

-65

/12

0

m,

N-4

8/9

5

met

d

an

s le

s co

up

es

MK

1

et

MK

2

: ty

pe

A,

?t t

ests

tr

an

spo

rt6

s en

su

spen

sio

n.

L~

gen

des

de

s fi

gu

rds

lith

olog

ique

s :

I -

silt

ston

e,

2 -

grbs

, 3

- ar

gilo

lith

e,

4 -

grb

s h

d~br

is

de

pla

nte

s et

de

co

quil

les,

5

- gr

$s ?

t ba

ncs

de l

um

ach

elle

, 6

-7

- st

ruct

ure

la

min

ae

dis

tin

cte,

8

- st

ruct

ure

la

min

ae

ind

isti

nct

e.

Lo

ng

ueu

r de

la

ba

rre

d'~

chel

le

: 2

cm.

Les

so

us-

typ

es

Aa

et

Ab

so

nt

d~fi

nis

du

ns

le t

exte

.

HOLCOVA 321

benthonic foraminifers in suspension is caused by storm waves. Absence of indigenous foraminifers does not allow one to interpret a paleoenvironment in the depositional area. A hfe habitat unsuitable for the survival of foraminifers (? extremely hyposaline) is supposed.

Comparison with foraminiferal assemblages from the whole sample (including fine and coarse beds) : oryctocenoses in both beds are very similar, therefore, no significant differences between results obtained from separate beds and the whole sample were observed.

Subtype Ab : Reworked, suspension-transported foraminiferal tests (oryctocenosis 6) occur in both coarse and fine beds (Fig. 3).

This oryctocenosis was found in one Lower Ba- denian sample only. Tests are larger in coarser beds than in finer beds, differing from only suspension- transported foraminifers. Size sorting of tests probably results from their reworking. Reworked foraminifers as well as other sedimentary particles are derived from the underlying Lower Miocene sediments, because index species of the Lower Mio- cene occur here. Species composition of assemblages from separate beds and the whole sample is similar. Oryctocenoses differ in a wider range of test size for the whole sample.

Type B : Indigenous or weakly transported species accompanied by reworked foraminiferal tests

Subtype Ba : Indigenous foraminifers (oryctocenosis 1) occur in coarse beds (sandstone), indigenous and reworked ones (oryctocenosis 5) in fine beds (siltstone or fine sandstone) (Fig. 4).

This type of distribution was observed in the Lower Badenian sediments. Indigenous assemblages contain foraminifers issued from a littoral, stenohaline environment: Asterigerinata planorbis, Dis- corbis discoides, Lobatula lobatula, Eponides umbonatus, Pararotalia stellata, Elphidium div.sp., Ammonia ex gr. beccarii, Quinqueloculina div.sp., etc. Suspension-transported assemblages contain Lo- wer Miocene index species (Uvigerina graciliformis, Uvigerina bononiensis primiformis, Uvigerina par- keri breviformis). The species composition looks like that found in the "Rzehakia (Oncophora) Beds". The similarity index of the suspension-transported asemblages occurring in the Lower Badenian sediment and assemblages from the "Rzehakia (Onco- phora) Beds" (sections MK 1 and MK 2) varies from 76 to 95 %. Therefore, the first transport of tests in suspension may be considered as occurring in the "'Rzehakia beds time interval".

During the Lower Badenian, small foraminifers were reworked from the "Rzehakia (Oncophora) Beds" and deposited probably from suspension. The absence of small, thin-walled suspension-transported foraminifers in the coarsest beds is probably related to a high energ~¢ environment, unsuitable for sedimentation of these small tests.

Indigenous foraminifers are 3 to 30 times more abundant in the coarse than in the fine beds. This fact may signify a lower sediment supply during the deposition of coarse beds.

Different species in assemblages from finer and coarser beds with different paleoecological requirements and stratigraphical ranges lead to low values (45-78 %) of the similarity index (Fig. 6). Also the ranges of the diversity index and P/B-ratio for samples are wide (Fig. 6).

Comparison with foraminiferal assemblages from the whole sample (including fine and coarse beds) : (1) If foraminiferal abundance in a coarse bed is higher than the abundance in a fine bed, the size-distribution of tests from the whole sample may look like a polymodal one, and size-sorting of tests in suspension may be "hidden". In that case, assemblages may be erroneously interpreted as deep- water with transported shallow-water species and a rare occurrence of the Lower Miocene index species (sample N-83/255 m). (2) For sample with similar foraminiferal abundance in fine and coarse beds, indigenous and suspension-transported tests are recognized also in whole sample (sample N-83/235 m). (3) If foraminiferal abundance in a coarse bed is lower than in a fine bed, indigenous foraminifers occur very rarely and only the peak for suspension-transported foraminifers is visible on the size distribution curve (sample N-83/225 m). In some cases, indigenous foraminifers may not be found. This causes a misinterpretation of the paleoenvironment in the depositional area of suspension-transported foraminifers.

Subtype Bb: Indigenous or weakly transported and reworked foraminiferal tests (oryctocenosis 5) are present in both finer beds and coarser fillings of bioturbation (Fig. 4).

This type of distribution was found only in the Lower Badenian sediments among samples with Ba type of test distribution. It is supposed that foraminiferal assemblages distributed in these sediments were originally type Ba. Passage from type Ba to type Bb distribution could have been caused by bioturbation. The indexes of similarity are high (67, 77 %).

As expected, assemblages obtained from separate beds and the whole sample are similar.

Ba Bb

N-83/225

BENTHONIC FORAMINIFERA

BENTHONIC FORAMINIFERA

PLANKTONIC FORAMINIFERA

sandstone

ROUNDED

FORMS

ELONGATE FORMS

4o

=o

3°1

~t I

I~

~

N-83

/225

sa

ndst

one

o ..

..

..

..

o

'°0

/ sillstone

o,o9

0,

18

0,27

0,

36

0,45

0,

54

0,09

0,

18

0,27

0,

35

0,45

0,

54

0,09

0,

18

0,27

0,

38

0,45

0,

54

)

N-8

3/23

5 [:2

2] N

-83/

235

silts

tone

: ~ /~

20

lO

3

°~

40

] ~

20

80

1 °0

~

~ N

-83/

235

sand

ston

e

--

'-

-~

si

ltsto

ne

..

..

..

..

..

..

o~

8 o~

00

,09

0,18

0.

27

0,36

0,

45

0,54

0,

09

0.18

0,

27

0,36

0,

45

0,54

N-8

3/25

5

l/

no planktonic

fora

min

ifera

/

..

..

..

..

..

..

.

0 0~' ...............

silt

sto

ne

0,

09

o j8

0,

2~

0,38

0,

45

0,54

0,

09

o,~e

0,

27

0,35

0,

45

0,54

1Oo

~ .

..

.

/ Io°~ ~ ~

....

.. /

silts

fone

o.

o9

0.18

0,

27

0.36

0.

45

0,54

o.

og

0,18

0,

27

0.36

0,

45

0,54

~

(~

0,18

0.

27

0,36

0,

45

0.54

BE

NTH

ON

IC R

OU

ND

ED

FO

RM

S -

WH

OLE

SA

MP

LE (C

OA

RS

E +

FIN

E B

EDS)

0,1~1

N-8

3/22

5 M

"' 8

3/2

35

M

0,0g

0,

18

0,27

0,

36

0,45

0,

54

0,ca

o,18

o,21

o,~

o,,~

o,

~ I

Be

N'8

3/27

8 co

ng

lorn

e ro

l- e

san

dst

on

e

~ N

-95/

225

silts

tone

..

..

..

..

o

0,G

g 0,

18

0,27

0,

36

0,45

0,

54

0,O

g 0,

18

0,27

0,

36

0,46

0,

54

0,09

0,

18

0,27

0,

36

0,45

0,

54

30

30

20

1 10

..

..

..

..

..

..

..

.

0

0,0g

0,

18

0,27

0,

30

0,45

0,

54

o,o9

0,

18

0,27

0,

36

0,~5

0,

54 ~4

[Z

B

N-8

3/27

8 m

silt

ston

e 40

~

N-8

3/27

8 m

san

dsto

ne

30

20

lO

iP

/ o

......

0,09

0,

18

0,27

0,

36

0,45

0,

54

o,oe

o,

18

o,27

o,

a8

o,45

o,

~

ver'd

cal a

xis

- num

ber o

f spe

cim

ens

horiz

onta

l axi

s - t

est s

ize

(urn

)

FIG

. 4

. -

Siz

e d

istr

ibu

tio

n o

f b

enth

on

ic r

ou

nd

ed,

ben

tho

nic

elo

ng

ate

and

pla

nk

ton

ic f

ora

min

ifer

al t

ests

in

sam

ple

s N

-83

/22

5

m,

N-8

3/2

35

m

, N

-83

/24

5

m,

N-8

3/2

55

m

, N

-83

/27

8

m,

N-9

5/2

25

m

: t

yp

e B

wit

h i

nd

igen

ou

s o

r w

eak

ly t

ran

spo

rted

an

d r

ewo

rked

fo

ram

inif

eral

tes

ts.

Fo

r ex

pla

nat

ion

s of

lit

ho

log

ical

sch

emes

see

Fig

. 3

. L

eng

ht

of s

cale

bar

: 2

cm

. S

ub

typ

es B

a,

Bb

and

Bc

are

def

ined

in

tex

t.

Dis

trib

utio

n de

tai

lle

des

test

s de

fo

ram

ini~

res

bent

hiqu

es a

rron

dis,

be

nthi

ques

al

long

& e

t pl

anct

oniq

ues,

da

ns

les

~ch

anti

llon

s N

-83

/22

5

m,

N-8

3/2

35

m

, N

-83

/24

5

m,

N-8

3/2

55

m

, N

-83

/27

8

met

N

-95

/22

5

m :

typ

e B

, ~

test

s de

fo

ram

ini~

res

auto

chto

nes

ou f

aibl

emen

t tr

ansp

ort~

s ou

rem

ani~

s, v

oir

la F

igur

e 3

po

ur

les

l~ge

ndes

des

fig

ures

lit

holo

giqu

es.

Lon

gueu

r de

la

barr

e d'

~che

lle

: 2

cm.

Les

sou

s-ty

pes

Ba,

Bb

et B

c so

nt d

~fin

is d

ans

le t

exte

.

~9

©

©

C

mm

©

©

HOLC OVA 323

Subtype Bc: Indigenous foraminifers (oryctocenosis 1) occur in fine beds (fine sandstone), indigenous and reworked ones (oryctocenosis 5) in coarse beds (fine conglomerate) (Fig. 4).

This type occurs only in one sample f rom the base of the Lower Badenian sedimentary cycles, and can reflect specific conditions in the beginning of transgression (rapid sedimentation). Species compositions of foraminiferal assemblages belong to the Ba type, but their distribution in the laminae of sediments is reversed : reworked, suspension-transported foraminiferal tests are present in the coarse bed, while indigenous foraminifers are present in the fine bed.

The size distribution curve for the whole sample does not correspond to the described type of size sorting of tests.

Type C: Tests transported in bed load prevailing in samples (Fig. 5)

The tests t ransported in bed load are always present in coarse beds but may also occur in fine beds. The sediments including these assemblages are the coarsest of all analysed samples (Fig. 6). Species compositions of indigenous and bedload-transported assemblages are similar (index of similarity varies between 74-88 %) with prevailing littoral, stenohaline species : Asterigerinata planorbis, Discorbis discoides, Lobatula lobatula, Eponides umbonatus, Pa- rarotalia steUata, Elphidium div. sp., Ammonia ex gr. beccarii, Quinqueloculina div. sp., etc. This similarity shows that foraminiferal tests were transported in bed load only along a short distance in the same type of paleoenvironment. Tests t ransported in bed load are often abraded and rarely broken. All samples with this type of distribution come from the Lower Badenian unit.

The following subtypes of type C were distinguished (Fig. 5). All subtypes are represented only by one sample :

Subtype Ca : Tests t ransported in bed load (oryctocenosis 3) are present in coarse bed (coarse sandstone), while indigenous foraminifers or weakly t ransported ones (oryctocenosis 1) occur in fine laminae (fine sandstone).

Subtype Cb : Tests t ransported in bed load (oryctocenosis 3) are found in coarse beds (sandstone), while indigenous Lower Badenian foraminifers and reworked suspension-transported Lower Miocene foraminifers (oryctocenosis 5) occur in fine beds (siltstone). Lower values of the similarity index are due to the occurrence of different reworked species.

In the whole sample, mixing of corroded shallow-water species and well-preserved deep-water species may lead to an interpretation of a deep-water environment with bedload-transported shallow- water species.

Subtype Cc : Tests t ransported in bedload (oryctocenosis 3) are observed in coarse beds (coarse sandstone), while indigenous and bedload-transported foraminifers (oryctocenosis 4) occur in fine beds (fine sandstone).

Assemblages from the whole sample of types Ca and Cb contain indigenous and bedload-transported assemblages, and, generally, the paleoenvironmental interpretation of assemblages f rom the whole samples and from the separate beds is similar. Analysis of separate beds gives complementary information about accumulation of bedload-transported tests in coarse beds (probably lenses accumulated in troughs of wave ripples).

P o s i t i o n o f t ypes A-C in cyc le o f s ea - l eve l c h a n g e s

Cycles of sea-level changes were distinguished in analysed sections from the cyclical changes in foraminiferal assemblages (Holcov~, 1996b). The presence of types A, B and C distributions of foraminiferal tests in beds was summarized for these cycles. The presented results are based on a small number of samples from only a shallow-marine environment. The set analysed is too small to draw significant conclusions, but it can provide some useful information :

Lower Badenian samples (Fig. 7) The Lower Badenian transgressive layer is cha-

racterized by two distinctive subtypes of oryctocenosis distr ibution: (1) in the nearshore area only reworked tests occur in both beds (type Ab), (2) in the more central par t of the basin, small, suspension-transported and reworked tests occur in coarse beds (type Bc). I t may be caused by a rapid sedimentation of coarse beds which enabled the preservation of small tests. These subtypes are absent from other parts of sea-level change cycles.

Tests t ransported in bed load without reworked species (types Ca, Cc) are typical of the middle and upper parts of transgressive systems tracts.

Reworked species, deposited probably in finer beds from suspension (type Ba) appear in highstand systems tracts and characterize also lowstand systems tracts. In highstand systems tracts, the species reworked into coarser beds may be accompanied by tests t ransported in bed load (type Cb). Type Ba with indigenous or weakly t ransported tests in

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FIG. 6. - Quan t i t a t i ve charac te r i s t i cs of fo ramin i fe ra l assemblages , and percen tage of s and f rac t ion in s e d i m e n t ; sample 1 - fine bed, sample 2 - coa r se bed ; Aa, Ab, Ba , Bb, Bc, C : types of d i s t r i b u t i o n of f o r a m i n i f e r a l a s semblages in beds , for d e t a i l e d e x p l a n a t i o n s

see text.

Caract~ristiques quantitatives des associations de foraminif~res, et pourcentage de la f rac t ion sableuse dans le s~diment ; ~chantillon 1 - lit rift, ~chantillon 2 - lit grossier ; Aa, Ab, Ba, Bb, Bc, C : types de distribution des associations de foraminif~res dans les lits,

voir d~tail dans le texte.

both type of beds prevailed in both highstand and lowstand systems tracts. Bioturbated layers with mixed assemblages (type Bb) appear in lowstand systems tract, what is in agreement with the obser- vation of Fiirsich et al. (1991).

The "Rzehakia (Oncophora) Beds"

Suspension-transported foraminifers dominate in the whole sections. The analysed samples come from lowstand systems tracts and contain exclusively suspension-transported foraminiferal tests.

Applications on sampling methods

The following recommendations for sampling in lithologically variable sections can be given on the basis of differences in the composition of foraminiferal oryctocenosis in thin, lithologically different superimposed beds :

(1) In many cases an analysis of foraminiferal assemblages from different lithotypes of a studied section (especially indicative of a shallow marine environment) enables the detection of different types

326 P A L E O E C O L O G I C A L ANALYSIS OF F O R A M I N I F E R A L ASSEMBLAGES

LOWER PART OF TRANSGRESSIVE SYSTEMS TRACTS

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foraminiferal assemblages by bioturbation. ModUle de d i s t r ibu t ion des types A , B, C (vo ir d~tail dans le tex te) dans les cycles de var ia t ion d u n iveau m a r i n au Bad~n ien inf~rieur. 1 - gr~s, 2 - s i l ts tone, 3 - argilol i the, 4 - granoc las - s emen t , 5 - s ihs tone & lamina t ion ondul~e et lentille gr~seuse accumul~e dans u n c reux de r ide de houle, 6 - rempl issage gross ier d 'une t race foss i le dans un si l ts tone lamin~, 7 - res~- d imen ta t i on de tests de f o r a m i n i ~ r e s , 8 - t ranspor t p a r t rac t ion de tests de f o r a m i n i f ~ r e s , 9 - p r d s e n c e de tests de f o r n m i n i ~ r e s a u t o c h t o n e s , 10 - m ~ l a n g e d 'a s soc ia t ions de f o r a m i n i f ~ r e s p a r

b io turba t ion .

of assemblages on the basis of the degree of post- mor t em changes. The presence of t r a n s p o r t e d and r eworked tests p rov ides add i t iona l da t a abou t the bas in h i s to ry (e.g. su spens ion - t r anspo r t ed assemblages - type A - give in fo rmat ion about the cen t ra l p a r t of bas in and its d y n a m i c s ; tests t r a n s p o r t e d in bed load - type C - about marg ina l p a r t ; r eworked species - types A b and B - abou t the

occu r rence of o lder sediments and condi t ions sui~ tab le for the i r r ework ing and r e sed imen ta t ion of par t ic les) .

(2) The finest beds are genera l ly cons ide red as the more f avourab le for micropa leonto log ica l analyses and are often sampled preferent ia l ly . Our s tudy shows tha t assemblages wi thout ev ident post- mor t em changes can occur in the coarses t beds while r e w o r k e d tests a re found in the finest beds ( type Ba).

(3) Strongly b i o t u r b a t e d layers conta in mixed fo ramin i fe ra l assemblages ( type Bb) , so a de ta i l ed sampl ing of these layers p roduces mis leading da ta .

CONCLUSIONS

Var iab ih ty in the composi t ion of fo ramin i f e r a l assemblages (more exact ly oryctocenoses) f rom diffe ren t hthologies were s tudied in 12 core samples and 2 ou tc rops f rom the Ot tnangian (Middle Bur - digal ian) and Lower B a d e n i a n (Langhian) sediments of the South Slovak Basin inc luded in the Cen t ra l P a r a t e t h y s .

Based on size sor t ing of tests , the i r p r e s e r v a t i o n and the presence /absence of species with d i f ferent paleoecological r equ i remen t s and s t r a t i g raph ica l ranges in assemblages, six types of fo ramin i f e r a l oryctocenosis were d is t inguished (Tab. 1), each of them conta in ing indigenous , su spens ion - t r anspo r t ed tests , b e d l o a d - t r a n s p o r t e d and /o r r e w o r k e d tests. These types of oryctocenoses may be d i s t r i bu t ed in couples of supe r imposed l i thological ly d i f fe ren t beds . The following cases may occur :

(1) Only suspens ion - t r anspo r t ed fo ramin i fe ra l tests occur in the bo th beds. The tests be long to ner i t ic and u p p e r b a t h y a l species, and cha rac t e r i ze the source a rea by ma te r i a l t r a n s p o r t e d in suspension by s to rm waves. A coasta l , hyposa l ine envi ronmen t unsu i tab le for the surv iva l of fo ramin i fe r s is p r o p o s e d for the depos i t iona l a rea . These oryc tocenoses may occur in the whole cycle of sea-level change.

(2) Sed imen t s wi th p r e v a i l i n g u n s o r t e d , well- p r e s e r v e d , inner-shelf , indigenous or weak ly t r ans - p o r t e d tests may conta in r eworked , su spens ion - t r anspb r t ed , outer -shel f to b a t h y a l fo ra - minifers . The l a t t e r or iginate f rom the under ly ing sediments , fully e r o d e d in the ana lysed area . Re- worked tests occur in the t ransgress ive layer , while

HOLC OVA 327

in highstand and lowstand systems tracts they appear in finer beds probably deposited from suspension. Bioturbations occurring in lowstand systems tracts cause mixing of reworked and indigenous assemblages.

Size-distributions of tests from some whole samples (including coarse and fine beds) are polymodal without a peak for suspension-transported foraminifers. In that case, a deep-water paleoenvironment with transported shallow-water species and a rare occurrence of the reworked Lower Miocene foraminifers may be erroneously interpreted.

(3) The coarsest beds (in some cases lenses accumulated in troughs of wave ripples) contain littoral stenohaline foraminifers sorted by bed-load transport. Unsorted, indigenous or weakly-transported tests prevail in the finest beds. Sediments were deposited in a coastal marine stenohaline environment affected by wave action. They were observed in the middle and upper parts of transgressive systems tracts, and, together with reworked outer- shelf to bathyal foraminffers, also in highstand systems tracts.

An analysis of assemblages from the whole sample may cause a misinterpretation of a deep-water environment with an occurrence of bedload-transported shallow-water species and a rare occurrence of the Lower Miocene index species.

(4) Only reworked tests and similar assemblages in both beds were observed at the base of a transgressive systems tract.

Thus, detailed sampling of all lithotypes and a taphonomical analysis of assemblages is able to provide new paleoenvironmental information. Sam- pling of a unique lithotype (e.g. claystone) in sections may yield incomplete data.

ACKNOWLEDGMENTS

The author thanks reviewers for their comments and suggestions.

This study is a part of research project No. 201/95 supported by Charles University, Prague.

BIBLIOGRAPHY

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PLATE 1

Studied outcrops and core samples (sd = sandstone, st = siltstone).

1. Section MK 1, samples 1-4, Mal~ Krti~ sand pit, "Rzehakia (Oncophora) Beds". Massive sandstone (1) at the base, laminated sandstone with slump structure (2) above. Lami- nated sandstone (3) with thin beds of shell detritus (4) in the upper par t of the section (tempestites).

2. Section MK 2, samples 1 4 , Mal)~ Krti~ sand pit, "Rzehakia (Oncophora) Beds". Massive sandstone (1) overlain by laminated sandstone (2) with pebbles of massive sandstone (3). Cross bedding (4) is observed in the upper part .

3. Core N-96, 305 m, "Rzehakia (Oncophora) Beds". Thin bed of sihstone (st) in massive sandstone (sd). Coin diameter : 2 cm.

4. Core N-83, 235 m, Lower Badeuian. Sihstone with undulating lamination (st), a sandstone lens (sd) is accumulated in a trough of a wave ripple. Lenght of scale bar : 2 cm.

5. Core N - 8 3 , 2 7 8 m, Lower Badenian. Fine-grained sandstone with undulat ing lamination (st), conglomerate (sd) on ero- sional surface. Bioturbations occur, fillings of bioturbations were not sampled.

6. Core N - 9 5 , 2 5 5 m, Lower Badenian. Laminae to thin beds of siltstone and fine-grained sandstone (st) overlain by coarse-grained sandstone (sd).

7. Core N-95, 225 m, Lower Badenian. Coarse filling of ichnofossil (sd) in laminated siltstone (st).

Echantillons $tudi~s d'affleurements et de carottes (sd = gr~s, st = siltstone).

1. Coupe MK 1, ~chantillons 1-4, Mal~ Krti~ sand pit , ~ Bancs it Rzehakia (Oncophora) ~,. Gr$s massi f h la base (1), gr~s laminas it slump au-dessus (2). Gr$s lamin~ (3) h miuces lits de d~bris coquilliers (4) it la partie sup~rieure de la coupe (tempestites).

2. Coupe MK 2, ~chantilloas 1-4, Mal~ Krti~, ~, Bancs it Rzehakia (Oncophora) ,,. Gr$s massi f (1) surmont6 par des gr$s laminas (2) it galets de gr$s massi f (3). Des d~p6ts entrecrois~s (4) s'observent it la partie sup~rieure.

3. Carotte N-96, 305 m, ~ Bancs it Rzehakia (Oncophora) ,,. Mince lit de siltstone (st) dans du gr$s massi f (sd). Diam$tre de la piece : 2 cm.

4. Carotte N-83, 235 m, Bad~nien inf~rieur. Sihstone it lamination ondul~e (st), une lentille gr~seuse (sd) est accumul~e dans un creux de ride de houle. Longueur de la barre d'$chelle : 2 cm.

5. Carotte N-83, 278 m, Bad~nien inf~rieur. Gr$s f i n it lamination ondul~e (st), conglom~rat (sd) sur une surface d'~rosion. Presence de bioturbations, dont les remplissages n'out pas ~t~ ~chantillonn~s.

6. Carotte N-95, 255 m, Bad$nien iuf~rieur. Lamines ou minces lits de siltstone et gr$s f ins (st) surmont~s de gr$s grossiers (sd).

7. Carotte N - 9 5 , 2 2 5 m, Bad~nien inf6rieur. Remplissage grossier d'une trace fossile (sd) darts un siltstone lamin~ (st).

HOLCOVA. PLANCHE

REVUE DE MICROPALI~ONTOLOGIE, VOL. 40, N ° 4

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