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Revue de micropaléontologie 59 (2016) 409–424

Original article

Quantative analysis and paleoecology of Middle to Upper Eocene Ostracodsfrom Jebel Jebil, central Tunisia

nalyse quantitative et paléoécologie des Ostracodes de l’Éocène moyen et supérieur de Jebel Jébil,Tunisie centrale

Aïda Amami-Hamdi a,∗, Ferid Dhahri b, Dhouha Jomaa-Salmouna a, Kmar Ben Ismail-Lattrache a,Najeh Ben Chaabane a

a Department of Geology, El Manar II, University of Tunis El Manar, Faculty of Sciences of Tunis, 2092 Tunis, Tunisiab Department of Earth Sciences, Sidi Ahmed Zarroug, University of Gafsa, Faculty of Sciences of Gafsa, 2112 Gafsa, Tunisia

bstract

One hundred and seventy collected samples from Jebil section have been carefully studied for their ostracod content and referred to 41 specieselonging to 20 genera. Their vertical distribution allowed to distinguish five successive associations of ostracod assemblages; two of whichre correlated with the Early Lutetian, one with the Late Lutetian, another association with the Bartonian and the last one with the Priabonian.ommunity structure of the collected ostracod fauna has been studied; three indices have been calculated for each sample: Shannon (diversity),argalef (richness) and Equitability indexes. In the lower and the middle part of the Formation, they indicate a stable environment supporting

igh diversity ostracod communities; whereas in the upper portion the environmental conditions were unstable characterized by low diversity.he results of a multivariate statistical method, using the cluster analysis and the Detrended Correspondence Analysis of the 41 ostracod speciesnd the 170 samples, have led to conclude that the most effective environmental factor in the study area is the paleodepth and of less importancexygenation and salinity. Thus, it allowed to distinguish four palaeoenvironmental intervals within the Cherahil Formation: the first one representedy taxa that are known from the shallower parts of the shelf; the second interval includes the majority of the encountered species of inner neritichelf with normal salinity; the third one, corresponding to an outer neritic domain; and the last interval refers to a circalittoral environment, isomprised mainly of Cytherella angulata and of Soudanella laciniosa triangulata.

2016 Elsevier Masson SAS. All rights reserved.

eywords: Ostracods; Middle to Late Eocene; Central Tunisia; Community structure; Multivariate statistical analysis; Palaeoenvironmental intervals

ésumé

Cent soixante-dix échantillons prélevés de la section Jebil ont été soigneusement étudiés pour leur contenu en ostracodes ; la faune est composée

e 41 espèces appartenant à 20 genres. La distribution verticale de ces espèces a permis de distinguer cinq associations successives d’ostracodes,ont deux sont corrélées avec le Lutétien inférieur, une avec le Lutétien supérieur, une autre avec le Bartonien et la dernière avec le Priabonien.a structure communautaire de la faune à ostracodes recueillie a été étudiée, trois indices ont été calculés pour chaque échantillon : indice de

ns la partie inférieure de la Formation, ils indiquent un environnement stable

hannon Waever (diversité), de Margalef (richesse) et d’Équitabilité. Da outenant des communautés d’ostracodes à valeurs élevées de diversité ; tandis que dans la partie supérieure, les conditions environnementalesnt été instables caractérisées par une faible diversité. Les résultats de l’analyse de cluster et de l’analyse détendancée de correspondances des1 espèces d’ostracodes et des 170 échantillons ont permis de conclure que, dans la zone d’étude, le facteur environnemental déterminant est la paléo-rofondeur et de moindre importance l’oxygénation et la salinité. Ainsi, cette étude a permis de distinguer quatre intervalles paléoenvironnementauxe long de la Formation Chérahil : le premier est souligné par des taxons connus dans les parties très peu profondes de la plateforme interne ; le

∗ Corresponding author.E-mail addresses: amamiaida@yahoo.fr (A. Amami-Hamdi), feriddhahri@yahoo.fr (F. Dhahri), jomaadhouha@yahoo.fr (D. Jomaa-Salmouna),

mbenismailattrache@yahoo.fr (K. Ben Ismail-Lattrache), najeh.geo.tun@live.fr (N. Ben Chaabane).

http://dx.doi.org/10.1016/j.revmic.2016.10.001035-1598/© 2016 Elsevier Masson SAS. All rights reserved.

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10 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

econd comprend la majorité des espèces rencontrées aux environnements à salinité normale de la plateforme interne ; le troisième correspond auomaine de plateforme externe et le dernier intervalle traduit un environnement circalittoral, composé principalement de Cytherella angulata et deoudanella laciniosa triangulata.

2016 Elsevier Masson SAS. Tous droits reserves.

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ots clés : Ostracodes ; Éocène moyen à supérieur ; Tunisie centrale ; Structure

. Introduction

Several micropalaeontological (Oertli, 1976; Bismuth et al.,978; Said-Benzarti, 1978; Bismuth, 1981; Mechmeche, 1981;en Ismail-Lattrache and Bobier, 1996; Ben Ismail-Lattrache,000; Trabelsi et al., 2015) and petroleum studies (Said-Benzartind Kharbachi, 1995) have been realized on ostracods fromunisia.

However, rare are the studies that attempted a paleoecolog-cal analysis of Eocene ostracod assemblages from Tunisia. Aso other countries from North and West Africa, there exist sev-ral studies related to the paleoecology and paleogeography ofocene ostracods (Elewa et al., 1999; Elewa, 2002; Elewa, 2004;lewa, 2005; Shahin, 2005; Elewa, 2007; Shahin, 2008; Amami-amdi and Ben Ismail-Lattrache, 2013; Amami-Hamdi et al.,014). In Libya, El Waer (1992) used the ostracod morphologynd carapace nature of Eocene ostracods for paleoenvironmentaleconstructions. In West Africa, Sarr (1995 and 1999) studiedhe migration of ostracods during the Middle Eocene and theirelation with the paleoenvironmental evolution of the westernenegalian deposits; the same author (2012) illustrated a linketween changes in ostracod faunas and the paleogeographicvolution of the Senegalese basin. Elewa et al. (2001) focusedis study on the reconstruction and interpretation of the paleoen-ironmental conditions that prevailed during the deposition ofhe Middle Eocene succession of Northern Somalia by means ofstracod assemblages. In Egypt, Elewa (2004) realized a pale-ecological study of the Eocene series in the region of Cairo,ased on the quantitative analysis of ostracod assemblages.

Mixed methods integrating quantitative and qualitative dataollection and analysis were explored in recent studies (Gliozzind Grossi, 2004; Mazzini, 2004, 2005; Elewa, 2004, 2005;uasti, 2005; Van Itterbeeck, 2007, Gliozzi and Grossi, 2008;rossi and Gennari, 2008; Sarr, 2012; Amami-Hamdi and Ben

smail-Lattrache, 2013 and Amami-Hamdi et al., 2014). Theyere applied to Middle and Upper Eocene deposits, which are

ich in pelagic microfauna.We have sampled and studied in detail the Middle and Upper

ocene succession of the Jebil outcrop in order to obtain aetailed report of its ostracod assemblages.

. Stratigraphy

The Jebil section is located in central Tunisia, near the Khit◦ ′ ◦ ′

l-Oued village (18 10 N and 3 71 E); the area is covered by

he geological map of Haffouz (1:50,000 scale) (Fig. 1).The Middle and Upper Eocene marine deposits are

00 m thick and well exposed in Jebel Jebil. They presentss

unautaire ; Analyse statistique multivariée ; Intervalles paléoenvironnementaux

ntercalations of bioclastic limestone (oyster rich) and marls richn foraminifers and ostracods. These deposits correspond to theherahil Formation (Comte and Dufaure, 1973), which is sub-ivided into three units, which are as follows from base to top:he Lower Cherahil, the Siouf and the Upper Cherahil MembersFig. 2).

.1. Lower Cherahil Member

This member can be divided into three main units:

the lower unit (J1–J48) is 46 m thick and comprised of lam-inated green clays with crystallized calcite interbedded withthin argillaceous limestones and a lumachellic limestone bed;

the middle unit (J48–J88) is 40 m thick and comprised ofyellowish sandy clays, sometimes gypsiferous and slightlyphosphatic with ferruginous concretions and flint nodules.These levels are interbedded with centimetric dolomite bedsrich in nummulites;

the upper unit (J88–J122) is 35 m thick and composed oflaminated gray-green clays intercalated with fossiliferousargillaceous limestones containing ferruginous concretions.

.2. Siouf Member

It is 5 m thick and composed of lumachellic gray sandyimestones. This level is rich in large benthic foraminifera: Num-ulites gizehensis, Discocyclina roberti, Discocyclina sella,perculina sp. and Alveolina sp.

.3. Upper Cherahil Member

This member can be divided into two units:

the lower unit (J129–J149) is 20 m thick and represented bygreen laminated claystones, rich in iron oxides and gypsum,and intercalated with centimetric dolomite beds;

the upper unit (J149–J184) is 35 m thick, comprised of finegreenish sandy clays and interbedded with metric lumachelliclimestones, rich in Ostrea lamellosa. These limestones arerepresented by biomicritic grainstone texture with bryozoans,bivalves and algae.

. Materials and methods

Many authors have analyzed different aspects of the Jebilection. Ben Ismail-Lattrache (2000) has been the first totudy the planktic and benthic foraminifera, as well as the

A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424 411

Fig. 1. Geological map of the study area (after Dhahri and Boukadi, 2010).

412 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

Fig. 2. Lithostratigraphy and description of microfacies observed in the Jebil section.

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stracod fauna. Subsequent studies have covered structuralspects (Rigane et al., 1994; Rabhi, 1999; Dhahri and Boukadi,010).

One hundred and seventy samples were collected for thistudy; they were washed after treatment with diluted H2O2. Theried residues were divided into three grain-size fractions (afterhey were collected with sieves of 250, 100 and 63 �m, in mesh).hen they were dried in an oven at 50 ◦C. The picked ostra-ods and planktic foraminifers were identified with the help of

stereoscopic binocular.The Middle and Upper Eocene deposits have delivered

rich microfauna characterized by abundant ostracods andoraminifers. The preservation of the planktic foraminifers andstracods is in general good. Taxonomic analysis and speciesdentification of ostracods was completed with reference torevious works (Bassiouni 1969, 1971; Oertli, 1976; Bismuth,981; Mechmeche, 1981 and El Waer, 1992). The species abun-ance and richness were calculated and normalized to 10 gf each dried and sieved sample. An analysis of the commu-ity structure (i.e., species richness, Shannon, Margalef andquitability indexes; Dodd and Stanton, 1990) and multivari-te analysis (i.e., cluster analysis and detrended correspondencenalysis), were performed on our ostracod dataset with the helpf the PAST software-PAleontology STatistics: 1.52 v (Hammert al., 2001).

. Results

.1. Biostratigraphy

Collected from the Upper and Middle Eocene deposits of theebel Jebil, the ostracod assemblages comprise more than 41pecies belonging to 20 genera.

The zonation of these ostracods, used in this paper (Oertli,976; Bismuth et al., 1978; Mechmeche, 1981; El Waer,992), is calibrated with the coeval local planktic foraminiferaiozonal scheme (Ben Ismail-Lattrache, 2000). A correlationetween these zones with their regional and worldwide equiv-lents has been realized. From base to top, we distinguishFig. 3):

Loculicytheretta semipunctata interval zone: it constituteshe range zone of the marker species L. semipunctata, corre-ated with the Turborotalia frontosa planktonic foraminiferalone Berggren and Pearson (2005) of earliest Lutetian age.his biozone is recognized in Tunisia by Oertli (1976),ismuth et al. (1978), Mechmeche (1981), Said-Benzarti andharbachi (1995), Ben Ismail-Lattrache (2000), Amami-Hamdi

nd Ben Ismail-Lattrache (2013) and Amami-Hamdi et al.2014) within the base of the Lower Cherahil marls. It isharacterized by the abundance of Loculicytheretta harshae,untonia ramosa Bassiouni, 1969; Argilloecia ghalilae El Waer,992; Costa libyaensis El Waer, 1992; Acanthocythereis salahiiassiouni, 1969; Acanthocythereis tarabulusensis El Waer,

992; Paleocosta mokattamensis Bassiouni, 1969. In Libya andccording to El Waer (1992), this biozone is homologous to theeptaloculites harshae zone of Early Lutetian age. In Algeria,

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paléontologie 59 (2016) 409–424 413

postolescu and Magné (1956) is attributed to the same zonef this interval. In Egypt, Shama and Helal (1993) assignedhe Costa praetricostata praetricostata zone to the Earlyutetian.

Loculicytheretta semirugosa interval zone: this zone com-rises the interval between two last occurrence (LO) events, theO of L. semipunctata (Apostolescu and Magné, 1956) at thease and the LO of L. semirugosa at the top. It occurs withinhe middle part of the Lower Cherahil member. In Tunisia,ismuth et al. (1978) assigned a late Early Lower Lutetian age

o this zone, characterized by abundant ostracods, characteris-ic of the Early Lutetian: Loculicytheretta prima Bismuth andertli, 1978; Soudanella tarabulusensis El Waer, 1992; Para-

ypris eskeri Bassiouni and Morsi (2000); Paracypris buisaeorsi, 2003 and Leguminocythereis sadeki Bassiouni, 1969.

his interval zone is attributed to the Lutetian in Algeria (Apos-olescu and Magné, 1956) and to the Middle Lutetian (El Waer,992) in Libya.

Loculicytheretta minuta interval zone: this zone is cha-acterized by the extinction of both L. semirugosa at its basend the markers species at its top. It occurs within the upperart of the Lower Cherahil marls of Late Lutetian age. Thisssemblage zone is characterized by the presence of abundantstracods (Loxoconcha tarabulusensis El Waer, 1992; C. angu-ata El Waer, 1992; Bairdia samdunae El Waer, 1992 andoudanella laciniosa triangulata Apostolescu, 1961) associatedith larger benthic foraminifers such as Nummulites gizehensis

Forskal, 1775) (A and B forms) and N. discorbinus Schlotheim1820).

In central Tunisia, Mechmeche (1981) described this zone inhe Middle Eocene deposits. In Libya, El Waer (1992) assigned

Late Lutetian to this zone.Loculicytheretta cavernosa interval zone: this zone of Bar-

onian age, is restricted between two LO respectively thosef L. minuta at the base and L. cavernosa (Oertli, 1976)t the top. It occurs within the lower part of the Upperherahil marls. It is correlated with the Middle Eocene Hep-

aloculites cavernosa zone recognized by El Waer, 1992 inibya. In Egypt, this zone is correlated with the Lutetian Dig-ocythere ismaili–Uromuellerina saidi zone (Shahin et al.,008).

Loculicytheretta aff. gortanii interval zone: this zone isharacterized by the LO of both L. cavernosa at its basend the marker species at its top. The co-occurrence of theominate taxon with the Priabonian taxon Loculicytheretta tune-ana (Oertli, 1978), Propontocypris tarabulusensis El Waer,992 and Hermanites libyaensis El Waer, 1992 and with thelanktic foraminiferal marker species Turborotalia cerroazulen-is Cole, 1928 (Wade and Pearson, 2008) allows to correlatehis interval with the Priabonian. In Tunisia, Oertli (1976),ismuth et al. (1978), Mechmeche (1981), Said-Benzarti andharbachi (1995), Ben Ismail-Lattrache (2000) and Amami-amdi and Ben Ismail-Lattrache (2013) described this zone

n the Priabonian deposits. In Libya, this zone is correlatedith the Priabonian Heptaloculites aff. gortanii zone (El Waer,992).

414 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

Fig. 3. Stratigraphic distribution of ostracofauna in the Middle and Upper Eocene lithostratigraphical units of the Jebel Jebil.

A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424 415

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Fig. 4. Diagrams of the community structure indices of 41 ostracod taxa sam

.2. Paleobioecology

.2.1. Community structure analyses- diversity indicesCommunity structure analyses have been performed on the

stracod assemblages collected from the Cherahil Formation,n the Jebil section. Diversity takes into account not only theumber of species, but also the distribution of individuals inhese species. Three assemblage structure indexes were calcu-ated for each sample: Shannon (diversity), Margalef (richness)nd Equitability indexes (Fig. 4).

In the lower part of the Cherahil Formation, samples display rather medium diversity and Equitability (which may reachhe value of 1), coupled with high richness up to a maximumalue of 4 (Samples J2, J10, J56 and J59), indicating a stablenvironment able to support a mature assemblage.

Within the middle part of the Cherahil Formation (J112 to152), samples display a high diversity and richness with maxi-um values of Shannon (1.6) and Margalef indexes (up to 5 in

ample J129), coupled with a peak of Equitability around 1.6.hese parameters reflect a relatively stable environment, leading

o the establishment of several mature communities of ostracods.The top of the Upper Cherahil Member (J152 to J184), dis-

lays very low values for the Shannon and Equitability indexes,oupled with low species richness (with a Margalef indexalue below 1), indicating an unstable environment with low

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recorded from the Middle and Upper Eocene intervals of the Jebil section.

iversity communities dominated by the taxa Loculicytherettaff. gortanii.

.2.2. Multivariate analysis

.2.2.1. Cluster analysis. In order to depict the detailed pale-environmental evolution of the Middle to Upper Eoceneuccession at the Jebil section, a multivariate statistical approachas carried out based on the analysis of ostracod assemblages.luster analysis based on the similarity coefficient (Jaccard coef-cient) using the paired-group method was applied to the dataatrix. Hence, four distinct biofacies can be discerned (Fig. 5),hich are often characteristic of a specific paleoenvironment:Biofacies A: is represented by A. salahii, P. mokattamensis,

. libyaensis and Isobuntonia pseudotuberata. This ostraco-auna was encountered at the base of the Lower Cherahil

ember. This biofacies has a low P/B ratio (8%).Biofacies B: which includes species that are increasingly

bundant in the L. semipunctata and L. semirugosa zones. Theajority of these species are recognized in the Lower Cherahilember. This biofacies has a low P/B ratio (5%).Biofacies C is the most visible cluster in the dendrogram and

egroups species that are more common in the upper part of theower Cherahil Member and the lower part of the Upper Cher-hil Member, and are dominant in the L. minuta and L. cavernosaones. The P/B ratio increases to reach a maximum at 20%.

416 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

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Biofacies D is represented by species which dominate thestracod record in the Loculicytheretta aff. gortanii zone. Thisiofacies is mainly present in the top of the Upper Cherahilember. The Pelagic index is relatively high (42%). As shown

n Fig. 5, biofacies D is characterized by several reticulatedstracod fauna.

It is worth noting the coincidence of community analysesesults and cluster analysis results.

.2.2.2. Detrended Correspondence Analysis (DCA). In thetudied section, detrended correspondence analysis performedn the 170 samples was used to analyze the ostracod assem-lages. The resulting DCA species plot shows two axes (withositive values greater than 1) that account respectively 51 and6% (Fig. 6). The maximum information is provided by Axis 151%); the first two axes represent 67% of the total informationbout the correlations between variables. The graphic tests withxis 3 to 7 do not provide additional information, giving a lesslear picture of the distribution of variables. However, the graphelating the Axis 1 and Axis 2 was used to confirm the ostracodlusters distinguished by the dendrogram.

The distribution of the ostracod species of Jebil section on

he first two axis allows to distinguish four clusters according toxis 1 (the first one represents negative values: < −0.5 and the

hree other ones represent positive values: > 0.25, that match theour clusters previously recognized:

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d to 41 ostracod species. The Pelagic index is also provided.

Group I: same as Biofacies D, is represented mainly bypportunistic species of high frequency (Loculicytheretta aff.ortanii); Group II: similar as Biofacies C includes the speciesf ostracods L. minuta, L. tunetana, L. cavernosa, C. angulata,. tarabulusensis, Soudanella laciniosa triangulata, B. sam-unae, Asymmetricythere yousefi and Brachycythere omarai;roup III: the same as Biofacies B, are characterized by

he presence of species L. semipunctata, L. semirugosa, Lox-concha vetustopunctatella, Reticulina proteros, P. eskeri,. sadeki, Costa aff. bassiouni, Costa aff. saidi and A. ghalilae;roup IV: similar as Biofacies A includes C. libyaen-

is, I. pseudotuberata, P. mokattamensis and A. salahiipecies.

Species Leguminocythereis cirtaensis and Legu-inocythereis africana, occupying a position at the sameistance of Groups II and III, with low frequencies, are presentn almost all the analyzed samples.

In general, the positions of the samples in the diagram appearo be strongly influenced by the microfaunal frequency andiversity. Nevertheless for both Groups I and IV, they appearo be only characterized by low frequency of ostracods ratherhan taxonomic composition.

There are several palaeoecological data on the Eocene ostra-ods of North and West Africa (Babinot, 1973; Bismuth et al.,

978; Colin and Carbonel, 1982; Donze et al., 1982; Peypouquett al., 1983; Carbonnel and Johnson, 1989; Bassiouni and Luger,990; El Waer, 1992; Keen et al., 1994; Elewa and Ishizaki,

A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424 417

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ig. 6. Scatter plot of 41 ostracod species recovered from 170 samples coming frorrespondence Analysis taken along two Axes.

994; Elewa et al., 1998; Elewa, 1999; Elewa et al., 1999;lewa, 2004; Elewa and Morsi, 2004; Elewa, 2005; Elewa, 2007;arr, 2012; Amami-Hamdi and Ben Ismail-Lattrache, 2013 andmami-Hamdi et al., 2014), which afford a possible synecolog-

cal characterization of ostracod assemblages.Group II dominated by rather deep taxa like C. angu-

ata, B. samdunae and Soudanella laciniosa triangulata, whicheflect an outer platform domain (Bassiouni and Luger, 1990).

hile, the ostracode fauna recorded in Group III are domi-ated by taxa (Reticulina proteros and P. eskeri) known fromhe deeper parts of the shelf: outer shelf (Bassiouni and Luger,990) and reflecting reduced dissolved oxygen level (Babinot,973; Colin and Carbonel, 1982; Whatley and Coles, 1991).he ostracod assemblage of Group IV specifically proliferates

n an inner environment (Peypouquet et al., 1983). In fact,t the presence of sighted species with eye tubercle such ascanthocythereis typical of infralittoral environment of 0–150 mepth (Keen et al., 1994) where minimum oxygen zone isow and the deep ocean circulation is sufficient (Donze et al.,982), confirms this attribution. Else, the abundance of a high

rnamented form (P. mokattamensis and Costa spp.), whicholerate a high pH and Mg++/Ca++ ratio (Peypouquet et al.,980 in Carbonel, 1988), may indicate deposition at inner shelfepth.

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e Middle and Upper Eocene intervals of the Jebil section according to Detrended

Thus, the Axis 1 which accounts 51% of the total varianceould represent the ecological parameter “depth”. The interpre-ation of ostracod cluster distribution along this axis reflectsignificant sensitivity to paleodepth fluctuations. However, thexis 2 which accounts 16% of the total variance might represent

he ecological parameters salinity or oxygenation.

. Paleoecological implications

The result of quantitative analyzes (community analyses,luster analysis and DCA) of 41 species of ostracods and qual-tative analysis of the associated planktic foraminifers allowedo give important information that distinguish several palaeoen-ironmental intervals within the Cherahil Formation (Fig. 7).

Interval 1- Biofacies A–B and Group III–IV (samples1–J88); ostracod association reveals a rather medium diversitynd a high richness with the occurrence of significant speciesf middle to outer platform environment with the abundance ofnner neritic taxa with normal salinity (Whatley, 1983). How-

ver, the low P/B ratio indicates a shallow water depth. Theelationship between environmental variables and species sug-ests a preference of these species to oxygenated conditions andelatively diversified ecosystem.

418 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

Fig. 7. Paleoecological and palaeoenvironmental evolution (Paleodepth) of the Cherahil Formation in the Jebil core.

A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424 419

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Fig. 8. Distribution of the Middle and Upper Eocene Ostracoda a

Interval 2- Biofacies C and Group II (samples J96–J149); theubsequent dominance of the taxa Soudanella laciniosa triangu-ata, C. angulata and B. samdunae that seem to have inhabitedhe shallow inner shelf as well as the deep outer shelf depthsBassiouni and Luger, 1990; Whatley and Coles, 1991), togetherith high values of the diversity indexes indicates deepening

rend during deposition of interval 2 from inner to outer neritic

epths, and marks of environmental stability. These data cou-led with a relative increase of pelagic index suggest an outereritic domain with normal salinity.

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tions in Jebil section from the coastal line to the abyssal domain.

Interval 3- Biofacies D and Group I (samples J152–J184);how a very low diversity and richness indexes coupled with

very high faunal dominance characterizing an association ofpportunistic species: Loculicytheretta aff. gortanii, which tol-rate spontaneous variations of depth and dissolved oxygen inhe upper part of the section. The higher pelagic index suggestsn increase of water depth from an outer neritic to a circalittoral

nvironment, that was confirmed by the global sea trend markedn the Priabonian by Miller et al. (2005). It reflects semi pelagicithin a circalittoral environment.

420 A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424

Plate 1. Examples of typical ostracod species collected from the studied section: 1, Acanthocythereis salahii Bassiouni, 1969 × 100, lateral view of right valve, LowerLutetian (sample J10); 2: Loculicytheretta semipunctata (Apostolescu and Magné, 1956) × 150, carapace in ventral view, Lower Lutetian (sample J41); 3: Loculi-cytheretta semirugosa (Apostolescu and Magné, 1956) × 100, lateral view of right valve, Upper part of Lower Lutetian (sample J14); 4: Loculicytheretta minuta(Oertli, 1978) × 200, lateral view of right valve, Upper Lutetian (sample J122); 5, 6: Reticulina proteros Bassiouni, 1969 × 150, 5- carapace in dorsal view; 6- lateralview of left valve, Lower Lutetian (sample J58); 7: Loculicytheretta tunetana (Oertli, 1978) × 150, carapace in ventral view × 150, Bartonian (sample J145); 8:Loculicytheretta cavernosa (Apostolescu and Magné, 1956) × 150, carapace in ventral view, Upper Lutetian-Bartonian (sample J122); 9: Loculicytheretta aff. gor-tanii (Ruggieri, 1963) × 150, carapace in ventral view, Priabonian (sample J155); 10: Loculicytheretta harshae El Waer, 1992 × 100, carapace in ventral view,Lower Lutetian (sample J14); 11: Xestoleberis tarabulusensis El Waer, 1992 × 200; lateral view of right valve, Bartonian (sample J140); 12, 13: Ruggiera aff.glabella Bassiouni, 1969 × 100, 12- lateral view of right valve, 13- carapace in ventral view, Lower Lutetian (sample J1); 14: Brachycythere (Digmocythere) ismailiBassiouni 1971 × 100, carapace right side, Lower Lutetian (sample J14).

A. Amami-Hamdi et al. / Revue de micropaléontologie 59 (2016) 409–424 421

Plate 2. Examples of typical ostracod species collected from the studied section: 1: Isobuntonia pseudotuberata (Apostolescu and Magné, 1956) × 150, lateralview of left valve, Lower Lutetian (sample J10); 2: Loxoconcha vetustopunctatella Bassiouni, Bou Khary, Shama and Blondeau, 1984 × 150, lateral view ofright valve, Lutetian (sample J46); 3: Soudanella laciniosa triangulata Apostolscu, 1961 × 150, lateral view of right valve, Upper Lutetian (sample J122); 4:Acanthocythereis tarabulusensis El Waer, 1992 × 100, lateral view of left valve, Lower Lutetian (sample J2); 5, 6: Asymmetricythere yousefi Bassiouni, 1971 × 100,5- lateral view of left valve, 6- carapace in dorsal view, Middle Lutetian (sample J129); 7: Soudanella tarabulusensis El Waer, 1992 × 150, lateral view ofright valve, Lower Lutetian (sample J66); 8: Costa aff. bassiounii Cronin and Khalifa, 1979 × 100, lateral view of left valve, Lower Lutetian (sample J16); 9:Loxoconcha tarabulusensis El Waer, 1992 × 150, lateral view of right valve, Priabonian (sample J155); 10: Bairdia samdunae El Waer, 1992 × 75, lateral viewof right valve, Upper Lutetian (sample J100); 11: Parcypris eskeri Bassiouni and Morsi, 2000 × 150, lateral view of right valve, Lower Lutetian (sample J52); 12:Argilloecia ghalilae El Waer, 1992 × 100, lateral view of right valve, Lower Lutetian (sample J41); 13: Cytherella angulata El Waer, 1992 × 150, lateral view ofright valve, Upper Lutetian-Bartonian (sample J118).

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Paleoecological modelThe paleoecology of ostracods, typical of Southern Tethys,

tudied in Algeria (Faid, 1999), Libya (El Waer, 1992; Whatleynd Arias, 1993) and Egypt (Elewa and Ishizaki, 1994; Elewa,997; Elewa et al., 1998; Elewa, 1999; Elewa et al., 1999; Elewa,002; Elewa, 2004; Elewa and Morsi, 2004; Elewa, 2005 andlewa, 2007) is adopted for the reconstruction of the paleoeco-

ogical model of Tunisian ostracods.The variations of ostracod associations obtained from the

tudied section and the resultant statistical analysis (Hierarchicalnd Correspondence detrended analysis) led to the reconstruc-ion of a model showing the marine ostracod distributionepending on the depth, salinity and oxygen.

In conclusion, this paleoecological model has permitted toistinguish different paleoenvironments according to the studiedstracod associations (Fig. 8):

Association A- represented by Loculicytheretta aff. gortaniind H. libyaensis that are known from the shallower parts of thehelf: inner shelf.

Association B- includes the taxa A. salahii, A. tarabulusensis,osta aff. bassiouni and P. mokattamensis, specifically prolifer-tes in an inner neritic environment.

Association C- comprising of Reticulina proteros and. eskeri that are known from the deeper parts of the shelf: outerhelf.

Association D- dominated by Soudanella laciniosa triangu-ata, Cytherella angulata and B. samdunae that seem to havenhabited the shallow inner shelf as well as the deep outer shelfepths.

The other ostracod species which have not been reported inll the studied cross-sections are not incorporated in this model.heir distribution is sporadic and has not allowed carrying outeither a qualitative nor a quantitative study for the understand-ng of paleoenvironmental changes (Plates 1 and 2).

Accordingly, the paleoecology, based on quantitative andualitative study of the ostracod fauna, highlighted four associa-ions. The diversity indices calculated for each sample (Shannon

eaver index, Margalef and Equitability) allowed to assign annstable environment of the Middle and Upper Eocene deposits.

. Conclusion

The Middle and Upper Eocene deposits of the Jebil outcropocated in central Tunisia are subdivided from base to top intowo members: the Lower Cherahil and Upper Cherahil Mem-ers. These latter are separated by Siouf lumachellic limestones.

According to the ostracod fauna, the recognition of 41 speciesas permitted to identify five interval zones: three zones aressigned to the Lutetian: L. semipunctata zone, L. semirugosaone and L. minuta zone; one to the Bartonian: L. cavernosaone, and another to the Priabonian: Loculicytheretta aff. gor-anii zone.

In order to bring precise details for the paleoecologi-

al study, two approaches have been used; the first one isased on the distribution and the relative abundance of ostra-od species. It has permitted to recognize the modificationsnder gone by environmental parameters and to reconstruct the

B

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aleoenvironmental evolution in space and in time. The sec-nd one is based on statistical approach (cluster and detrendedorrespondence analysis), considering different environmentalariables such as paleodepth, paleosalinity and oxygenation. Itas permitted to determine the possible relationship between theistribution of the Middle and Upper Eocene ostracods and theceanographic characteristics of central Tunisia. These analysesevealed that the ostracod associations provided by the studiedaterial are characteristic of a platform environment from inner

helf to circalittoral.

isclosure of interest

The authors declare that they have no competing interest.

cknowledgments

The authors are grateful to Taniel DANELIAN (Revuee Micropaléontologie Editor-in-Chief) and to the reviewersshraf M.T. ELEWA (Minia University, Al Minya, Egypt)

nd Raphaël SARR (Cheikh Anta Diop University, Dakar) forhoughtful comments that improved the manuscript.

eferences

mami-Hamdi, A., Ben Ismail-Lattrache, K., 2013. Les ostracodes etforaminifères associés des dépôts de l’Éocène moyen et supérieur de lacoupe de Jebel Serj (Tunisie centrale). Intérêt biostratigraphique, paléoé-cologique et paléobiogéographique. Revue de Micropaléontologie 56 (4),159–174.

mami-Hamdi, A., Dhahri, F., Saïd-Benzarti, R., 2014. Middle to Upper Eoceneostracofauna of central Tunisia and Pelagian Shelf: examples of Jebel Bargouand the Gabes Gulf. Arabian Journal of Geosciences 7 (4), 1587–1603.

abinot, J.F., 1973. Ostracodes turoniens de la région de Cassis-La Bedoule(Bouches du Rhone), France: associations et affinités paléogéographiques.Geobios 6 (1), 27–48.

assiouni, M.A., 1969. Einige Buntonia und Soudanella Arten (Ostracoda Crus-taea) aus dem Eozän von Jordanien. Paläontologische Zeitschrift 43 (3/4),205–214.

assiouni, M.A., 1971. Ostracoden aus dem Eozän von Agypten Die UnterfalienBrachycytherinae und Buntoniinae. Geologisches Jahrbuch 89, 169–192.

assiouni, M.A., Luger, P., 1990. Maastrichtian to early Eocene ostracodafrom southern Egypt. Paleontology, Paleoecology, Paleobiogeography andbiostratigraphy Berliner Geowissenschaftliche Abhandlungen. Reihe (A):Geologie und Paläontologie 120, 755–928.

en Ismail-Lattrache, K., 2000. Précision sur le passage Lutétien-Bartonien dansles dépôts éocènes moyens en Tunisie Centrale et Nord-orientale. Revue deMicropaléontologie 43 (1–2), 3–16.

en Ismail-Lattrache, K., Bobier, C., 1996. Etude biostratigraphique et paléo-écologique et paléobiogéographique des séries Eocènes de Tunisie Centrale.Géologie de l’Afrique et de l’Atlantique Sud. Actes Colloques Angers 1994,563–583.

erggren, W.A., Pearson, P.N., 2005. A revised tropical and subtropical Paleo-gene planktonic foraminiferal zonation. Journal of Foraminiferal Research35, 279–298.

ismuth, H., 1981. Principaux repères microfaunistiques dans les séries nonpélagiques de l’Eocène moyen et supérieur de Tunisie. Résumé du 1ér

Congrès National des Sciences de la Terre. SEREPT, Tunis, 1 p.ismuth, H., Kelj, A.J., Oertli, H.J., Szczechura, J., 1978. The genus Loculi-

cytheretta (Ostracoda). Bulletin Centre de Recherche, d’Exploration et deProduction, Elf-Aquitaine 2 (2), 227–263.

micro

C

C

C

C

D

D

D

E

E

E

E

E

E

E

E

E

E

E

F

G

G

G

G

H

K

M

M

M

M

O

P

P

R

R

S

S

A. Amami-Hamdi et al. / Revue de

arbonel, P., 1988. Ostracods and the transition between fresh and saline waters.In: De Deckker, P., Volin, J.P., Peypouquet, J.P. (Eds.), Ostracoda in the EarthSciences. Elsevier XII, pp. 157–173.

arbonnel, G., Johnson, A., 1989. Les Ostracodes Paléogènes du Togo: tax-onomie, biostratigraphie, apports dans l’organisation et l’évolution du basin.Géobios 22, 409–443.

olin, J.P., Carbonel, P., 1982. Inventaire des ostracodes fossiles de la RéserveNaturelle Géologique de Saucats - La Brède. Bulletin de la Société Lin-néenne de Bordeaux t. 21, fasc. 1, 3–35.

omte, D., Dufaure, P., 1973. Quelques précisions sur la stratigraphie et lapaléontologie Tertiaire en Tunisie Centrale et Centro-Oriental, du Cap Bonau Mazzouna. Livre Jubilaire M. Solignac. Annale des Mines de la Géologie16, 97–115.

hahri, F., Boukadi, N., 2010. The evolution of pre-existing structures during thetectonic inversion process of the Atlas chain of Tunisia. Journal of AfricanEarth Sciences 56, 139–149.

odd, J.R., Stanton, R.J., 1990. Paleoecology. Concepts and applications. Wiley-Interscience Publication, Wiley & Sons (Edit.), New York, 502 p.

onze, P., Colin, J.P., Damotte, R., Oertli, H., Peypouquet, J.P., Said, R., 1982.Les Ostracodes du Campanien Terminal à l’Éocène inférieur de la coupede Kef, Tunisie Nord-Occidental. Bulletin du Centre de Recherche, Elf-Aquitaine 6, 273–355.

l Waer, A.A., 1992. Tertiary and Upper Cretaceous Ostracoda from NWoffshore Libya. Their Taxonomy, Biostratigraphy and Correlation with adja-cent. Earth Sciences Society Libya (Edit.), Tripoli, 445 p.

lewa, A.M.T., 1999. The use of allochthonus microfossils in determiningpalaeoenvironments: A case study using Middle Eocene ostracods from WadiEl Rayan, Fayoum, Egypt. Bulletin Faculty of Sciences Assiute University(Egypt) 28 (2), 33–52.

lewa, A.M.T., 2002. Paleobiogeography of Maastrichtian to Early EoceneOstracoda of North and West Africa and the Middle East. Micropaleontology48 (4), 391–398.

lewa, A.M.T., 2004. Quantitative analysis and palaeoecology of Eocene Ostra-coda and benthonic foraminifera from Gebel Mokattam, Cairo, Egypt.Palaeogeogr., Palaeoclimat., Palaeoecol., Elsevier, The Netherlands 211(3–4), 309–323.

lewa, A.M.T., 2005. Paleoecology and Paleogeography of Eocene OstracodFaunas from the Nile Valley between Minia and Maghagha, Upper Egypt. In:Elewa, A.M.T. (Ed.), Migration in Organisms: Climate, Geography, Ecology.Springer-Verlag Publishers, Heidelberg, Germany, pp. 25–70.

lewa, A.M.T., 2007. Predation due to changes in environment: Ostracod provin-ciality at the Paleocene-Eocene thermal maximum in North and West Africaand the Middle East. In: Elewa, A.M.T. (Ed.), Predation in Organisms -A Distinct Phenomenon. Springer–Verlag Publ, Heidelberg, Germany, pp.7–26.

lewa, A.M.T., Bassiouni, M.A., Luger, P., 1999. Multivariate data analysisas a tool for reconstructing paleoenvironments: The Maastrichtian to EarlyEocene Ostracoda of southern Egypt. Bulletin Faculty of Sciences MiniaUniversity (Egypt) 12 (2), 1–20.

lewa, A.M.T., Ishizaki, K., 1994. Ostracodes from Eocene rocks of the ElSheikh Fadl-Ras Gharib stretch, the Eastern Desert, Egypt (Biostratigraphyand paleoenvironments). Earth Science (Chikyu Kagaku, Tokyo) 48 (2),143–157.

lewa, A.M.T., Luger, P., Bassiouni, M.A., 2001. Middle Eocene Ostracoda fromNorthern Somalia (paleoenvironmental appraisal). Revue de Micropaléon-tologie 44 (1), 279–289.

lewa, A.M.T., Morsi, A.A., 2004. Palaeobiotope analysis and palaeoenvi-ronmental reconstruction of the Paleocene-early Eocene ostracodes fromeast-central Sinai, Egypt. In: Beaudoin, A.B., Head, M.J. (Eds.), The Paly-nology and Micropalaeontology of Boundaries. The Geological Society,London, pp. 293–308.

lewa, A.M.T., Omar, A.A., Dakrory, A.M., 1998. Biostratigraphical and pale-oenvironmental studies on some Eocene ostracodes and foraminifers fromthe Fayoum depression, Western Desert, Egypt. Egyptian Journal of Geology

42 (2), 439–469.

aid, N., 1999. Ostracodes de l’Eocènes inférieur moyen de l’Atlas saharien(Algérie) : Interprétation environnementale et paléogéographique. Géobios32 (3), 459–481.

S

paléontologie 59 (2016) 409–424 423

liozzi, E., Grossi, F., 2004. Ostracode assemblages and palaeoenvironmentalevolution of the Latest Messinian lago-mare event at Perticara (Montefeltro,Northern Apennines, Italy). Revista Espanola de Micropaleontología 36 (1),157–169.

liozzi, E., Grossi, F., 2008. Late Messinian lago-mare ostracod palaeoecology:A correspondence analysis approach. Palaeogeography, Palaeoclimatology,Palaeoecology 264, 288–295.

rossi, F., Gennari, R., 2008. Palaeoenvironmental reconstruction across themessinian/zanclean boundary by means of ostracods and foraminifers: theMontepetra borehole (Northern Apennine, Italy). Atti del museo civico distoria naturale di Trieste 53, 67–88.

uasti, E., 2005. Early Paleogene environmental turnover in the Southern Tethysas recorded by foraminiferal and organic-walled dinoflagellate cysts assem-blages. Berichte aus dem Fachbereich Geowissenschaften der UniversitätBremen 241, 1–203.

ammer, Ø., Harper, D.A.T., Ryan, P.D., 2001. PAST: Paleontological Statisticssoftware package for education and data analysis. Palaeontologia Electronica4 (1), 9 p.

een, M.C., Al Sheikhly, S.S.J., El Sogher, A., Gammudi, A.M., 1994. Ter-tiary ostracods of North Africa and the Middle East. In: Simmons, E.D.(Ed.), Micropaleontology and Hydrocarbon Exploration in the Middle East.Chapman & Hall, London, pp. 371–388.

azzini, I., 2004. Quaternary benthic Ostracoda from the Tasman Sea: dis-tribution patterns within circumpolar deep-waters. Bollettino della SocietàPaleontologica Italiana 43, 217–224.

azzini, I., 2005. Taxonomy, biogeography and ecology of Quaternary benthicOstracoda (Crustacea) from circumpolar deepwater of the Emerald Basin(Southern Ocean) and the S Tasman Rise (Tasman Sea). SenckenbergianaMaritima 35, 1–119.

echmeche, R., 1981. La Formation Souar (Éocène moyen et supérieur) dansle secteur Maktar-Siliana, Bou-Arada (Tunisie du Centre-Nord): Etudelithostratigraphique, biostratigraphique et paléontologique. Université Lyon(Thèse 3e cycle), 165 p.

iller, K.G., Kominz, M.A., Browning, J.V., Wright, J.D., Mountain, G.S.,Katz, M.E., Sugarman, P.J., Cramer, B.S., Christie-Blick, N., Pekar, S.F.,2005. The Phanerozoic record of global sea-level change. Science 312,1293–1298.

ertli, H.J., 1976. The evolution of Loculicytheretta in the Eocene. Abhandlun-gen und Verhandlungen der Naturwissenschaftlichen Vereins in Hamburg.NF 18/19 (Supplement), 153–160.

eypouquet, J.P., Carbonel, P., Taieb, M., Tiercelin, J.J., Perinet, G., 1983. Theostracodes and evolution of the past hydrologic environment in the HadarFormation (the Afar depression, Ethiopia). In: Maddocks, R.F. (Ed.), Appli-cations of Ostracoda. Proceedings of the 8th International Symposium onOstracoda. University of Houston, pp. 277–285.

eypouquet, J.P., Ducasse, O., Gayet, J., Pratviel, L., 1980. Agradationet dégradation» des tests d’ostracodes. Intérêt pour la connaissance del’évolution paléohydrologique des domaines margino-littoraux carbonatés ,Congrès : « Cristallisation-Déformation-Dissolution des carbonates », Bor-deaux, pp. 357–369.

abhi, M., 1999. Contribution à l’étude stratigraphique et analyse de l’évolutiongéodynamique de l’axe Nord-Sud et des structures avoisinantes (TunisieCentrale). Université de Tunis II, Faculté des Sciences, Tunis, 206 p.

igane, A., Gourmelen, C., Broquet, P., Truillet, R., 1994. Originalité desphénomènes tectoniques syn-sédimentaires fini-yprésiens en Tunisie centro-septentrionale (région de Kairouan). Bulletin de la Société géologique deFrance 165 (1), 27–35.

aid-Benzarti, R., 1978. Etude stratigraphique et micropaléontologique du pas-sage Crétacé-Tertiaire du Synclinal d’Ellès (Région Siliana-Sers) TunisieCentrale. Thèse de doctorat, 3e Cycle, Université Pierre et Marie Curie,Paris VI, 275 p.

aid-Benzarti, R., Kharbachi, S., 1995. Eocene Ostracode and foraminiferalayering in Ashtart Field-Ostracoda and Biostratigraphy. 12th InternationalSymposium on Ostracoda, Prague 1994, 193–202.

arr, R., 1995. Étude biostratigraphique et paléoenvironnementale des sériesd’âge Crétacé terminal à Eocène moyen du Sénégal occidental. Systématiqueet migration des Ostracodes. Thèse de doctorat (inédite), Université Dakar,335 p (unpublished).

4 micro

S

S

S

S

S

T

V

W

W

W

24 A. Amami-Hamdi et al. / Revue de

arr, R., 1999. Le Paléogène de la région de Mbour-Joal (Sénégal occidental):biostratigraphie, étude systématique des ostracodes, paléoenvironnement.Revue de Paléobiologie, Genève 18 (1), 1–29.

arr, R., 2012. Biozonation et paléoenvironnement des ostracodes du Paléogènedu Sénégal occidental (Afrique de l’Ouest). Revue de Paléobiologie 31 (1),145–158.

hahin, A., 2005. Maastrichtian to Middle Eocene ostracodes from Sinai, Egypt:systematics, biostratigraphy and paleobiogeography. Revue de Paléobiologie24, 749–779.

hahin, A., El Halaby, O., El Baz, S., 2008. Middle Eocene ostracodes of the Qat-tamiya area, northwest Eastern Desert, Egypt: Systematics, biostratigraphyand paleobiogeography. Revue de Paléobiologie 27 (1), 123–157.

hama, K., Helal, S., 1993. Stratigraphy of the Eocene sediments at Shabrawet

area, Suez Canal Environs, Egypt. Egyptian Journal of Geology 37 (2),275–298.

rabelsi, K., Sames, B., Salmouna, A., Piovesan, E.K., Ben Rouina, S.,Houla, Y., Touir, J., Soussi, M., 2015. Ostracods from the marginal

W

paléontologie 59 (2016) 409–424

coastal Lower Cretaceous (Aptian) of the Central Tunisian Atlas (NorthAfrica): paleoenvironment, biostratigraphy and paleobiogeography. Revuede Micropaléontologie 59, 309–331.

an Itterbeeck, J., 2007. Danian/Selandian boundary stratigraphy, paleoenviron-ment and Ostracoda from Sidi Nasseur, Tunisia. Marine Micropaleontology62, 211–234.

ade, B.S., Pearson, P.N., 2008. Planktonic foraminiferal turnover, diversityfluctuations and geochemical signals across the Eocene/Oligocene boundaryin Tanzania. Marine Micropaleontology 68, 244–255.

hatley, R.C., 1983. The application of Ostracoda to paleoenvironmental anal-ysis. In: Maddocks, R.F. (Ed.), Applications of Ostracoda. University ofHouston Geoscience, Houston, pp. 51–77.

hatley, R., Arias, F.C., 1993. Paleogene Ostracoda from the Tripoli basin

Libya. Revista Espanola de Micropaleontologia 25 (2), 125–154.

hatley, R.C., Coles, G.P., 1991. Global change and the biostratigraphy of NorthAtlantic Cainozoic deep water ostracoda. Journal of Micropaleontology 9,119–132.