Facies (2008) 54:25–43

DOI 10.1007/s10347-007-0123-3

ORIGINAL ARTICLE

Evolution of shallow benthic communities during the Late Paleocene–earliest Eocene transition in the Northern Tethys (SW Slovenia)

J. Zamagni · M. Mutti · A. Konir

Received: 9 January 2007 / Accepted: 22 August 2007 / Published online: 6 November 2007© Springer-Verlag 2007

Abstract A paleoecological and sedimentological studywas carried out on shallow-water carbonates of the KrasPlateau (SW Slovenia) with the goal of reconstructingpaleoenvironmental conditions and evolution of foraminif-eral communities on the northwestern Adriatic CarbonatePlatform (AdCP) during the Late Paleocene–earliestEocene. Three facies have been recognized and summa-rized in a carbonate ramp model. Within these facies, sixforaminiferal assemblages, representing diVerent ramp sub-environments, have been deWned: during the Late Paleo-cene sedimentation took place in a protected innermostramp with (1) smaller miliolids- and (2) small benthicforaminifera-dominated assemblages thriving on partlyvegetated, soft substrates. In the Uppermost Paleocene, sed-imentation primarily occurred along a mid ramp. The uppermid-ramp was sporadically inXuenced by storms/currentsand occupied by (3) Assilina-dominated assemblage occur-ring on a soft sandy substrate. The deeper mid-ramp wascharacterized by (4) ‘bioconstructors’- and (5) ortho-phragminids-dominated assemblages, colonizing biotopeswith substrates of diVerent nature. During the earliestEocene, deposition occurred in an inner-ramp setting with(6) alveolinids-nummulitids assemblage thriving on muddyand sandy substrate, partly covered or close to seagrassbeds. The Late Paleocene–earliest Eocene environmentalconditions, coupled with the long-term evolution of largerbenthic foraminifera (LBF), seem to have favored this

low-light dependent group as common sediment contribu-tors. By comparing the evolution of the shallow-water biotafrom the Adriatic area with data from the Pyrenees andEgypt, a general latitudinal trend can be recognized. How-ever, on a smaller geographical scale, local conditions arelikely to have played a pivotal role in promoting the evolu-tion of biota characterized by suites of unique features.

Keywords Shallow-water carbonates · Larger benthic foraminifera · Paleoecology · Facies analysis · SW Slovenia · Late Paleocene–earliest Eocene

Introduction

A distinct period of extreme global warming occurred closeto the boundary between the Paleocene and Eocene,approximately 55.5 Ma ago (e.g., Zachos et al. 2001). Thisevent, termed the Paleocene–Eocene Thermal Maximum(PETM), coincided with a time of generally warm, “green-house” climate conditions representing a short-lived eventin global warm temperatures. The PETM was characterizedby a globally quasi-uniform 5–8°C warming in less than10 ka (e.g., Röhl et al. 2000). The biotic responses to thisevent in the oceans were largely investigated. These studiesdocumented heterogeneity in nature and severity ofresponses, including radiations, extinctions, and migrations(e.g., deep benthic foraminifera extinction, Pak and Miller1992; planktonic foraminifera and calcareous nannofossildiversiWcations, e.g., Thomas 1998; Kelly et al. 2005; Bra-lower 2002). Conversely, how and to which extent shallow-water ecosystems reacted to these paleoenvironmentalchanges has been almost neglected.

Larger benthic foraminifera (LBF) were the mostcommon constituents of Upper Paleocene–Lower Eocene

J. Zamagni (&) · M. MuttiInstitute of Geosciences, University of Potsdam, Karl Liebknecht Str. 24, 14476 Golm, Potsdam, Germanye-mail: zamagni@geo.uni-potsdam.de

A. KonirIvan Rakovec Institute of Paleontology ZRC SAZU, Novi trg 2, 1000 Ljubljana, Slovenia

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26 Facies (2008) 54:25–43

shallow-water carbonates. Especially Eocene LBF wereused extensively as a tool for reconstructing paleoenviron-ments due to their great diversity and abundance in the pho-tic zone of tropical and subtropical settings. In the late earlyEocene–middle Eocene, LBF experienced their highestdiversiWcation marking the climax of the Eocene globalcommunity maturation (GCM) cycle (see Hottinger 1997,1998). In the frame of this general reorganization after thecrisis at the Cretaceous-Paleocene boundary, a Wrst turn-over occurred during the Thanetian (Hottinger 1998) with adiversiWcation of LBF at the genus level. Starting from theEocene a speciWc diversiWcation of a restricted number ofsuccessful genera occurred. This second event is placedbetween the top of Thanetian and the base of Ilerdian (Hott-inger 1998) marking the Paleocene–Eocene boundary. Atthis time, LBF modiWed their life strategy and the speciWcdiversiWcation was mainly linked to the development ofadult dimorphism and a large shell size (Hottinger 1998).

In recent studies from northern Spain (Orue-Etxebarriaet al. 2001; Pujalte et al. 2003; Baceta et al. 2005; Rasseret al. 2005; Scheibner et al. 2007) and Egypt (Scheibneret al. 2005) the LBF evolution was correlated to the PETMclimatic changes. These authors proposed a synchronicityand a causal relation between the environmental changes(i.e., warmer sea temperatures and changes in the trophicregimes) and the general turnover in the LBF communitiesat the P–E transition. Scheibner et al. (2007) analyzed andcompared the shallow-water benthic communities fromSpain and Egypt, especially their evolution during the Tha-netian and the Ilerdian. They suggested that a latitudinaleVect determined diVerences in the biotic composition, withthe PETM and the long-term warming during the EarlyEocene aVecting the low-latitude southern Tethys (Egypt)more severely than the mid-latitude Atlantic realm (Pyre-nees).

Paleontological and biostratigraphical studies on carbon-ate platform successions from SW Slovenia documented agreat diversity of shallow-water benthic foraminifera dur-ing the Late Paleocene–Early Eocene (e.g., Drobne 1977;1979; Drobne et al. 1988). Within this frame, the study ofthe Slovenian (northern Tethys) sedimentary successions isof great interest in order to verify the latitudinal eVects onshallow-water benthic communities. In fact, during theEarly Paleogene, the Adriatic and the Pyrenean carbonateplatforms were located approximately at the same paleolat-itudes (around 35°N).

Here we present data on two continuously exposed shal-low-water carbonate successions from the Kras region (SWSlovenia). The study of these successions allows us to trackdown the evolution of the LBF assemblages across the P–Etransition by documenting their major features during thepre-climax phase of the Eocene. A carbonate ramp faciesmodel is reconstructed by combining the depth gradient

with the nature of the substrate. Based on our Wndings, wedescribe three phases of evolution for the Slovenian succes-sions. These phases have diVerent features relative to thosedescribed for Spain and Egypt by Scheibner et al. (2007).We suggest that local eVects (i.e., paleogeography anddiVerences in depositional settings) are the main sources forthe diVerences in the evolution of shallow-water biotabetween the results from Spain and Egypt and our Wndingsin SW Slovenia.

Geologic setting and stratigraphy

The studied carbonate successions crop out in the southernpart of the Kras (Karst) Plateau in SW Slovenia (Fig. 1).Structurally, the Kras Plateau corresponds to the KomenThrust Unit of the NW External Dinarides fold-and-thrustbelt (Placer 1981). The latest Cretaceous to Early Paleo-gene paleogeography of the NW External Dinarides and theDinaric foreland (Istrian Peninsula) was characterized by avast subaerially exposed central area of the Adriatic Car-bonate Platform (AdCP) and signiWcantly reduced extent ofshallow-water carbonate depositional environments on themarginal parts of the formerly extensive Mesozoic carbon-ate platform (VlahoviT et al. 2005). Towards the north/northeast, a deep-water basin was contiguous to a south-westward-verging advancing orogenic wedge (Otonibar2007 and references therein).

The uppermost Cretaceous and Early Paleogene shallow-water carbonate successions represent a terminal, synoro-genic megasequence of the AdCP. The megasequence,together with the overlying siliciclastic successions, exhibitsa typical stratigraphic pattern of underWlled foreland basins(Sinclair 1997). This pattern comprises three units, superim-posed during basin migration (Konir and Otonibar 2001),

Fig. 1 SimpliWed geological map of SW Slovenia and NE Croatiashowing location of the study area and the stratigraphic sections.Adapted from Konir (2003). KZ Kozina section, CB Bebulovicasection

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Facies (2008) 54:25–43 27

which reXect deposition during major tectonic events whenthe AdCP was subaerially exposed, subsequently re-estab-lished, then drowned, and Wnally buried by prograding deep-water clastics (Xysch). A generalized stratigraphic columnof the Upper Cretaceous, Paleocene, and Eocene deposits inthe Kras region is shown in Fig. 2. The lower unit (the KrasGroup; Konir 2003) overlies the forebulge unconformity andcomprises three formations: (1) Liburnian Formation (UpperMaastrichtian to Lower Paleocene) characterized byrestricted, marginal marine, paralic and palustrine carbon-ates; (2) Trstelj Formation (Upper Paleocene) composed offoraminiferal and coralgal limestones deposited in shallow-water environments; and (3) Alveolina-Nummulites Lime-stone (Lower Eocene) dominated by accumulations of largerbenthic foraminifera. The total thickness of the Kras Groupranges from several tens of meters to more than 450 m. Themiddle unit (transitional beds; Lower Eocene) consists of upto 50 m of pelagic and hemipelagic limestones and marls.The upper unit (Flysch; Lower Eocene) is composed of asuccession (>1,000 m thick) of sandstone-dominated turbi-dites, marls, mudstones, and resedimented carbonates (deb-rites and calciturbidites). All three of the units occurdiachronously along the regional proWle, corresponding tothe platform and basin migration from NE towards SW. Thislasted from the Campanian/Maastrichtian to the MiddleEocene (Bignot 1972; Drobne 1977; Cousin 1981; Konirand Otonibar 2001). Age assignments noted above corre-spond to overall time-spans of the lithostratigraphic units inthe Kras region (see Drobne 1977; Jurkovnek et al. 1996).

Relatively consistent NE-SW regional stratigraphictrends (Konir and Otonibar 2001; Otonibar 2007) indicatethat the platform and basin stratigraphies were largely con-trolled by the Xexural deformation and/or tilting of the fore-land. Local variations in stratigraphy, especially ofcarbonates onlapping the forebulge unconformity and ofplatform-to-basin successions, most likely resulted fromnon-Xexural deformations, e.g., reactivation of antecedentpre-orogenic structures.

A reliable reconstruction of the architecture and size ofthe early Paleogene carbonate platform in the studied areais diYcult because of the complex thrust-nappe structure ofNW Dinarides and the intensive post-orogenic tectonicdeformation. However, the platform geometry inferredfrom regional facies relationships (Drobne 1977; Jurkovneket al. 1996, 1997) corresponds to a carbonate ramp deposi-tional system characterized by roughly parallel NW-SE-trending facies belts. This is in agreement with the paleo-transport patterns recorded in the siliciclastic turbidites ofthe Xysch foredeep successions in the NW Dinarides (Ore-hek 1991; BabiT and ZupaniT 1996), which have predomi-nantly NW and SE-oriented axial paleocurrent directions,whereas a general paleotransport pattern in resedimentedcarbonates shows that carbonate debris derived from south-southwestern source areas (Turnnek and Konir 2004; BabiTand ZupaniT 1996). Vertical facies successions of Paleo-cene and Lower Eocene shallow-marine carbonates (TrsteljFormation and Alveolina-Nummulites Limestone) gener-ally exhibit a retrogradational (backstepping) pattern. ThisreXects a deepening trend and Wnal drowning of the carbon-ate ramp by pelagic and hemipelagic deposits (Konir 1997).

The Late Paleocene–Early Eocene width of the carbon-ate ramp and the foredeep basin can only be inferred from arough palinspastic restoration (Placer 1981) based on acombination of published maps and structural mapping ofSW Slovenia. The width of the Early Paleogene shallow-water carbonate depositional area probably did not exceed50 km, whilst the maximum width of the contemporaneousforedeep basin, estimated from the north-easternmost out-crops of Upper Paleocene Xysch, supposedly deposited ininner foredeep settings, was probably less than 100 km. It isimportant to note, however, that the position of the front ofthe orogenic wedge during the Early Paleogene cannot beprecisely established. Indeed, the Periadriatic Fault cuts thenappe structure of western Slovenia from its “root zone” onthe NNE side (Otonibar 2007 and references therein).

Materials and methods

Two continuously outcropping stratigraphic sections(Bebulovica and Kozina) were studied at road cuts alongthe highway between Ljubljana and Koper (Figs. 1, 3).

Fig. 2 Generalized stratigraphic column of the uppermost Creta-ceous-Eocene succession in the Kras region, SW Slovenia (Konir2003) and the studied interval

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28 Facies (2008) 54:25–43

The Bebulovica section is located 4 km northwest of thetown of Divaba. The section is »200 m thick and covers thecomplete Trstelj Formation and the lower part of the Alveo-lina-Nummulites Limestone. The basal part of the sectionincludes the contact with the underlying Liburnian Forma-tion.

The Kozina section is located near the town of Kozina,about 12 km southwest of the Bebulovica section. The sec-tion (100 m thick) comprises the upper part of the TrsteljFormation and the lower part of the Alveolina-NummulitesLimestone. The lower part of the Trstelj Formation and thecontact with the Liburnian Formation are not exposed.

The sections have been logged, sampled, and describedwith respect to the sedimentary structures, textures andbiotic components, with special attention to the distribu-tion of foraminifera. Textural and compositional charac-teristics of the investigated lithologies were based ontransmitted-light microscopy of 350 thin sections. Thetextural descriptions follow Dunham (1962) and Embryand Klovan (1971) classiWcations. The shallow benthiczones of Serra-Kiel et al. (1998) have been adopted for thepresent study.

The paleoenvironmental distribution of foraminiferalassemblages and depositional conditions have been recon-structed, combining comparison with Recent counterpartsand with the distribution of fossils forms from knownfacies models. Since many of the early Paleogene LBFbecame extinct at the Eocene–Oligocene boundary, thecomparisons between distribution of fossil and livingforaminifera have been conducted mainly consideringsimilarities in the foraminiferal shell structures betweenextant and extinct forms. Hence, the ecology of livingLBF has been applied for paleobathymetric interpretationat a qualitative level. Since the depth signal producedby foraminiferal is strictly dependent on the age of thestudied association (Hottinger 1997), only Late Paleo-cene–Early Eocene foraminiferal occurrences have beenconsidered for paleoecological interpretation. Additionalecological considerations on some of the main bioticcomponents (calcareous algae and scleractinian corals)have been used to implement paleoenvironmental recon-struction.

Facies and foraminiferal assemblages: description and interpretation

Based on Weld observations, fossil contents, textural andsedimentological features, both successions have been sub-divided into three facies (Fig. 3, Table 1): Foraminiferallimestones (F), corresponding to the lower part of theTrstelj Formation (SBZ3, Early Thanetian); the Foralgallimestones (FA), covering the upper part of the Trstelj

Formation (SBZ4, Late Thanetian); and the Bio-Peloidallimestones (BP), which corresponds to the lower part of theAlveolina-Nummulites Limestones (SBZ5–SBZ8, Early toLate Ilerdian). Each facies is characterized by distinct fora-miniferal assemblages (Table 1). In particular, two forami-niferal assemblages dominated by small benthicforaminifera have been described from the facies F, threeforaminiferal assemblages in the facies FA dominated byAssilina, orthophragminids, and encrusting foraminifera,respectively, and one assemblage dominated by alveolinidsand nummulitids in the facies BP.

Foraminiferal limestones (F)

Facies description

The facies occurs at the base of the two studied sectionswith a thickness of 30 m in the Kozina and 65 m in theBebulovica, (Fig. 3). In the Kozina section, the basal con-tact with the Liburnian Formation is not exposed, therefore30 m should be considered a minimum thickness. Thesedark limestones consist of a heterogeneous group of alter-nating lithologies dominated by thick-bedded packstones,wackestones, and rare grainstones. Wackestones with milli-metric-sized fenestral porosity are occasionally present.The biota consists of abundant and diversiWed benthicforaminifera (mainly miliolids associated with small rotali-ids, conical agglutinated foraminifera and lituolids) andsubordinate calcareous green algae (dasycladaleans). Mis-cellanea and small Ranikothalia are rarely present. Locallysmall dendritic-ramose coral colonies (mainly Dendrophyl-lia and Oculina) are scattered in the sediments to formsmall patches of baZestone. Additional biogenic compo-nents are ostracods, echinoids, gastropods and bryozoans.Micritized foraminifera and fecal pellets are abundant.Reworked Microcodium occurs in the basal parts of grain-stone/packstone beds or in situ in packstones, representingsubaerial exposure surfaces in poorly developed shoalingsequences.

Among benthic foraminifera, the most valuable for bio-stratigraphical purpose are Coskinon rajkae, Fallotellaalavensis, Cribrobulimina carniolica, Haymanella pale-ocenica and Miscellanea juliettae, the occurrence of whichindicates Early Thanetian age (SBZ3) for the Foraminiferallimestones.

Fig. 3 Stratigraphic columns of the Kozina and Bebulovica sectionswith distribution of the foraminiferal assemblages (1–6) and facies (F,FA, BP). 1 Smaller miliolids-dominated assemblage; 2 small benthicforaminifera dominated assemblage; 3 Assilina-dominated assem-blage; 4 ‘bioconstructors’-dominated assemblage; 5 orthophragmi-nids-dominated assemblage; 6 alveolinids-nummulitids assemblage.SBZ shallow benthic zones (Serra-Kiel et al.1998)

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Facies (2008) 54:25–43 29

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30 Facies (2008) 54:25–43

Tab

le1

Rel

atio

nshi

p am

ong

faci

es, f

oram

inif

eral

ass

embl

ages

, tex

tura

l and

sed

imen

tolo

gica

l fea

ture

s an

d m

ajor

com

pone

nts

Ben

thic

for

amin

ifer

a an

d ot

her

biot

a ar

e lis

ted

in o

rder

of

decr

easi

ng a

bund

ance

FA

for

amin

ifer

al a

ssem

blag

es, K

Z K

ozin

a se

ctio

n, C

B B

ebul

ovic

a se

ctio

n

Fac

ies

Tex

ture

sS

edim

enta

ry

stru

ctur

esT

apho

nom

ic a

nd

earl

y di

agen

etic

fe

atur

es

FAB

enth

ic f

oram

inif

era

Oth

er b

iota

Occ

urre

nces

Inte

rpre

ted

sett

ing

FW

acke

ston

es

to p

acks

tone

sT

hick

bed

ded

Bio

turb

atio

n m

icri

tisa

tion

1M

iliol

ids,

dis

corb

ids

Das

ycla

dale

ans,

ost

raco

des

KZ

, CB

Inne

rmos

t ram

p w

ith

rest

rict

ed

cond

ition

s

Pac

ksto

nes,

ra

rely

gr

ains

tone

s

2M

iliol

ids,

agg

lutin

ated

for

amin

ifer

a,

rota

liids

, Mis

cell

anea

, sm

all R

anik

otha

lia

dasy

clad

alea

ns, e

chin

oids

, bry

ozoa

nsK

Z, C

BIn

nerm

ost r

amp

FA

Pac

ksto

nes

to r

udst

ones

Poo

rly

bedd

edM

icri

tisat

ion

Enc

rust

atio

n B

ioer

osio

n

3A

ssil

ina,

laca

zini

ds, s

mal

l/ov

ate

Dis

cocy

clin

a,

smal

l/ova

te N

umm

ulit

es, M

isce

llan

ea,

acer

vulin

ids,

Had

doni

a, s

mal

l rot

alii

ds,

mili

olid

s, te

xtul

ariid

s

Pey

sson

neli

acea

ns, c

oral

linac

eans

(m

elob

esio

ids,

spo

roli

thac

eans

, D

isti

chop

lax

bise

rial

is),

sc

lera

ctin

ian

cora

ls, e

chin

oids

, br

yozo

ans,

ost

reid

s

KZ

, CB

Upp

er m

id r

amp

Bou

ndst

ones

to

Xoa

tsto

nes

Mas

sive

4A

cerv

ulin

ids,

Had

doni

a, P

lano

rbul

ina,

M

inia

cina

, Plo

cops

ilin

a, D

isco

cycl

ina,

sm

all r

otal

iids

Scl

erac

tinia

n co

rals

, enc

rust

ing

red

alga

e, m

icro

bial

cru

sts,

bry

ozoa

ns,

biva

lves

, ost

raco

des,

pla

nkto

nic

fora

min

ifer

a

KZ

, CB

Dee

per

mid

ram

p

Wac

kest

one

to p

acks

tone

sP

oorl

y be

dded

to

mas

sive

5Fl

atte

ned

orth

ophr

agm

inid

s, A

ssil

ina,

ace

rvul

inid

s,

Had

doni

a, s

mal

l rot

aliid

sC

oral

linac

eans

, pey

sson

nelia

cean

s,

bryo

zoan

s, e

chin

oids

, cri

noid

s, b

ival

ves

CB

Dee

per

mid

ram

p

BP

Pac

ksto

nes

Poo

rly

bedd

ed

wit

h w

ave

bedd

ing

surf

aces

Mic

ritis

atio

n E

ncru

stat

ion

Bio

turb

atio

n B

ioer

osio

n

6A

lveo

lina

, Ass

ilin

a, N

umm

ulit

es, s

oriti

ds

(Orb

itol

ites

, Ope

rtor

bito

lite

s),

smal

l Dis

cocy

clin

a, a

cerv

ulin

ids,

Had

doni

a,

lituo

lids,

agg

lutin

ated

for

amin

ifer

a (T

hom

asel

la la

byri

nthi

ca, V

ania

ana

toli

ca),

m

iliol

ids,

sm

all r

otal

iids

Das

ycla

dale

ans,

ech

inoi

ds, b

ryoz

oans

, ga

stro

pods

, biv

alve

s, o

stra

code

sK

Z, C

BIn

ner

ram

p

123

Facies (2008) 54:25–43 31

Foraminiferal assemblages

This facies is characterized by two foraminiferal assemblages(Fig. 3, Table 1): smaller miliolids-dominated assemblageand small benthic foraminifera-dominated assemblage.

Assemblage 1: Smaller miliolids-dominated assemblage

This assemblage occurs in Wne-grained packstones towackestones representing an oligotypic community domi-nated by small miliolids and discorbids (Fig. 4a). Dasycla-daleans and ostracods are associated to foraminifera.

Recent miliolids are euryhaline forms living in shallow,restricted/lagoonal environments with low turbulence thriv-ing on soft substrates. They were observed to proliferatealso within seagrasses as epifaunal benthos (Davies 1970)and as epiphytes on vegetated sediments (Brasier 1975a).When present in great abundance they may indicate nutri-ent-enriched conditions and/or extreme salinities (Geel2000).

Therefore, the low diversity of this foraminiferal assem-blage might be indicative of a shallow, locally restrictedenvironment, most likely characterized by enhanced nutri-ents, and development of algal meadows.

Assemblage 2: Small benthic foraminifera-dominated assemblage

This assemblage usually occurs in Wne-grained, bioturbatedpackstones, and very rare grainstones. It is composed ofmiliolids (e.g., Idalina, Periloculina), small rotaliids (e.g.,Kathina, Smoutina), agglutinated foraminifera (Coskinonrajkae, Fallotella alavensis), lituolids (Haymanella pale-ocenica), Miscellanea (Fig. 4c), the latter locally commonin the Bebulovica section as well as very rare and smallRanikothalia. Foraminifera of this assemblage are associ-ated with peloids, dasycladaleans (Fig. 4b) and subordinateechinoid remains, bryozoans, gastropods and isolatedcorals.

This assemblage has a high diversity of small, r-strate-gist foraminifera. It is worth remembering that the r-strat-egy (where r is the intrinsic growth rate of the population)applies to small-sized organisms, with a high rate of fecun-dity, short generation times, and rapid growth of popula-tions. These traits are advantageous in unstable and/orunpredictable environments where resources have to beexploited in the quickest possible manner as soon as theybecome available. On the other hand, K-strategists (whereK indicates the carrying capacity of the environment) havelarge body sizes, long life-spans and produce fewer, butnurtured oVspring. These organisms usually colonize tem-porally stable environments and their population sizes arevery near to the carrying capacity to stretch limiting sources

by the mechanism of nutrient recycling (like symbionticrelationship in LBF; Hottinger 1983).

Small rotaliids and agglutinated foraminifera are gener-ally considered to be shallow-water dwellers living inlagoonal and open marine waters (e.g., Geel 2000; Ghose1977). Rotaliids have been found on seagrass leaves ineastern Shark Bay (Davies 1970). The development of ven-tral ornamentation characterizes Paleocene rotaliids (i.e.,Kathina). Hottinger (2006) proposed that they use theseventral structures to maintain a proper position on soft, Wne-grained substrate. Miscellanea is a common component inthe shallow-water biota of the Thanetian. Based on theobservation of Periadriatic platforms, Pignatti (1994) sug-gested that small forms of Miscellanea are reef dwellers,while larger forms should be typical of deeper waters, asso-ciated with nummulitids and Discocyclina. In our surveys,Miscellanea has always a small size and is associated withsmall rotaliids in Wne-grained packstones with relativelyabundant carbonate mud.

Thanetian foraminiferal assemblages from Turkey, dom-inated by small rotaliids and miscellanids, have been inter-preted by Özgen-Erdem et al. (2005) as thriving in lagoonalopen environments. Accordi et al. (1998) described a simi-lar Thanetian association from Greece with abundant smallbenthic foraminifera associated with dasycladaleans asdeposited in a shallow protected subtidal setting with algalmeadows. The relatively high diversity of foraminiferalassemblage 2 might also be related to the existence of sea-grass beds. Brasier (1975b) concluded that ancient seagrassassemblages might be expected to show increased diversitycompared to adjacent biofacies due to the higher nutrientlevels within and adjacent to seagrass beds.

Summarizing, the small benthic foraminifera-dominatedassemblage likely represents a community thriving on soft,sandy to muddy, locally vegetated substrate, in a low-energy, very shallow subtidal setting.

Facies interpretation

The Early Thanetian deposits of the Wrst facies are domi-nated by mud-supported lithologies. Evidence for periodi-cal subaerial exposure is indicated by the occurrence oflevels enriched in Microcodium. Reworked Microcodiumand in situ colonies in almost unalterated limestones indi-cate early stages of soil formation during periodical subaer-ial exposure (Konir 2004). The facies was probablydeposited in a very shallow protected environment with alateral gradient in degree of restriction as testiWed by thepresence of thin strata dominated by oligotypic fauna(smaller miliolids-dominated assemblage). The commonoccurrence of bivalves, gastropods and echinoids associ-ated with a diversiWed community of benthic foraminiferalikely suggests the presence of some algal or seagrass

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cover. The relatively high percentage of dasycladaleanssupports this hypothesis. Moreover, fecal pellets, locallyforming linear accumulations, suggest the occurrence ofsedentary organisms (e.g., annelids). They usually burrowclose to the seagrass roots and deposit fecal pellets in thetunnel that they dig (e.g., Beavington-Penney et al. 2004).The presence of seagrass beds could have favored the highdiversity of small benthic foraminifera in this facies.

Foralgal limestones (FA)

Facies description

The facies occurs in the middle part of the studied succes-sions and has a thickness of 15 m in the Kozina section and75 m in the Bebulovica section (Fig. 3, Table 1). The bulkof this facies consists of massive, white coral-microbialitemud mounds (Zamagni et al. 2006) alternating with poorlystratiWed bioclastic packstones (dominated by Assilina spp.)and massive wackestones (with Xattened orthophragminidsand small rotaliids). Miliolines, represented by lacazinidsand small miliolids, are usually scarce throughout thisfacies. The diversity and abundances of larger benthicforaminifera are generally low and rarely exceeds the 10%of the rock volume.

Associated with larger foraminifera are mainly calcare-ous red algae. The algal assemblage is dominated by coral-linaceans (mainly melobesioids such as Mesophyllum andLithothamnion), Sporolithon, Distichoplax biserialis (usu-ally as small fragments) and peyssonneliaceans (Poly-strata alba). Calcareous red algae form crusts (associatedwith bryozoans and encrusting foraminifera) and smallaggregates (rhodoliths) with sediments or other organismslike bryozoans as nuclei. In more muddy lithologies, thealgae form thin, irregularly distributed crusts. Scleractin-ian corals occur throughout the facies with diversity andabundance changing in diVerent lithotypes. In packstonesand wackestones they are present as rubbles and small col-onies with domal-bulbous or laminar-tabular encrustingmorphologies. The diversity is low with Actinacis andGoniopora as common genera, frequently found encrusting

bivalves. In the coral-microbialite mud mounds the coralcommunity is quite diverse and dominated by small colo-nies of ramose-dendritic and encrusting morphotypes com-monly associated with microbialitic crusts and encrustingforaminifera. Algae are reduced to thin crusts occasionallycoating corals.

Macrofauna in this facies is mainly represented by echi-noid remains, bryozoans and bivalves (mainly ostreids).Rare planktonic foraminifera are also present.

Bioerosion is a common feature aVecting all the com-ponents and producing abundant sandy to silty debris(common coral, algal, and foraminiferal fragments) andmud. Macroborings aVecting foralgal encrustations,coral-microbialites and single components (mainly bival-ves and foraminifera) are a common feature throughoutthis facies. Micritization is pervasive: foraminifera oftenshow destructive micritic envelopes (see Perry 1999).Rare biofabrics, such as tubular tempestite, can also beobserved (Tedesco and Wanless 1991). No wave-pro-duced fabrics are identiWed so far and the amount of car-bonate mud is high. Only occasionally beds occurenriched in abraded and fragmented grains, where foram-inifera are preferentially orientated parallel to bedding.The packing degree is usually medium to low withmicrite partially Wlling the inter-skeletal voids betweenthe foraminiferal tests.

The most important biostratigraphic markers in FA lime-stones are represented by the nummulitids Assilina yvettae,Assilina azilensis, the miliolines Lacazina blumenthali,Glomalveolina dachalensis and Glomalveolina levi.Among calcareous algae, the most valuable biostratigraphi-cal indicator is Distichoplax biserialis. This fossil contentindicates SBZ4 (Late Thanetian).

Foraminiferal assemblages

The FA limestones are characterized by three, alternatingassemblages of benthic foraminifera (Fig. 3, Table 1).Nummulitids (Assilina-dominated assemblage), encrustingforaminifera (‘bioconstructors’-dominated assemblage) andorthophragminids (orthophragminids-dominated assem-blage) are dominant.

Assemblage 3: Assilina-dominated assemblage

The Assilina-dominated assemblage consists of commonXattened Assilina (Assilina yvettae and Assilina azilensis)(Fig. 4d, e), associated with small rotaliids, rare Miscella-nea spp., rare small miliolids, lacazinids (Lacazina sp. andPseudolacazina sp.), alveolinids (Glomalveolina spp.), rareRanikothalia sp. and very rare robust/lenticular Discocy-clina. Haddonia and acervulinids are present, locallyencrusting larger foraminifera (Fig. 4e). Associated with

Fig. 4 Photomicrographs of Thanetian foraminiferal assemblagesfrom innermost ramp facies (F) and mid-ramp facies (FA). a Assem-blage 1: fenestral packstone/wackestone with dasycladalean algae (D)and almost completely micritized miliolids. b Assemblage 2: pack-stone with dasycladaleans (D), miliolids (M) and agglutinated forami-nifera (A, Cribrobulimina carniolica). c Assemblage 2: Wne-grainedpackstone with Miscellanea (Mi), echinoid fragments and micritizedforaminifera. d Assemblage 3: bioclastic packstone with Assilina (Ass)and lacazinids (L). e Assemblage 3: bioclastic packstone with Assilina(Ass), note acervulinid (Ac) encrusting Assilina. f, g Assemblage 4:boundstone with acervulinids (Ac) and haddonids (H) associated withred algae and microbial crusts (Mc) encrusting corals. h Assemblage 5:Wne bioclastic wackestone with orthophragminids (Di)

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foraminifera are calcareous red algae and isolated coral col-onies. This assemblage occurs in poorly stratiWed pack-stones with abundant skeletal debris and carbonate mud.

Nowadays, Assilina thrives in the lower photic zone onsoft, muddy sediments, with Assilina ammonoides beingone of the few larger benthic foraminifera able to tolerate acertain degree of eutrophication (e.g., Lacadive Islands;Langer and Hottinger 2000). Fossil, the large, Xat form ofAssilina, were interpreted as living in the deeper parts ofthe photic zone (e.g., Oman; Racey 1994) but also as shal-low-water dwellers in turbid fore- and back-reef environ-ments (e.g., Early Eocene forms from the South Pyreneanforeland; Gilham and Bristow 1998; Ghose 1977). Thepaleoecology of the other larger foraminifera found in theassemblage is here only tentatively inferred because extantcounterparts do not exist. Lacazinids represented a wide-spread group of miliolines during the Early Paleogene; theywere completely replaced by the ecologically vicariantalveolinids during the Early Eocene (Drobne and Hottinger2004). Their occurrence in this assemblage likely indicatesa preference for a soft substrate.

Data on the Central Western Tethys foraminiferal asso-ciations (e.g., Turkey; Özgen-Erdem et al. 2005; Greece;Accordi et al. 1998) show the simultaneous occurrence ofAssilina along with small rotaliids and Discocyclina. Suchan assemblage once again indicates preference for a softsubstrate (both muddy and sandy) in low water energy andclose to the lower photic zone. Scheibner et al. (2007)described a similar assemblage in an inner platform of thePyrenean realm.

Summarizing, the Assilina-dominated assemblage waslikely developed on a soft sandy substrate composed offoraminifera and other bioclastic fragments, in the shallowpart of the mid-ramp. The Xattened shape of Assilina sug-gests reduced-light conditions.

Assemblage 4: ‘Bioconstructors’-dominated assemblage

The ‘bioconstructors’-dominated assemblage is composedof a diverse community of encrusting foraminifera, mainlyacervulinids, associated with textulariids (Placopsilina andHaddonia, Fig. 4f, g), Planorbulina and Miniacina. Otherforaminifera are less frequent and are represented by small-Xattened Discocyclina and small rotaliids. Rare planktonicforaminifera are observed. Encrusting foraminifera are asso-ciated with scleractinian corals, microbial crusts, encrustingalgae and branching bryozoans to form complex encrusta-tions. Together with algae and/or bryozoans, encrustingforaminifera form thin crusts or aggregates and play a pri-mary role in the bioconstructions of coral-microbialite mudmounds and acervulinid Xoatstones/boundstones.

At present, the distribution of encrusting foraminifera isprimarily controlled by light intensity, water energy and

competition for space (e.g., Perrin 1992). Modern acervuli-nids occur commonly from shallow water down to 130 m,with a cryptic habitat in very shallow settings (e.g., Gulf ofAqaba; Reiss and Hottinger 1984). Perrin (1992) describedacervulinids as adapted to low-light conditions where com-petition with other encrusting organisms as calcareousalgae is reduced. This would allow foraminifera to spreadlaterally, enhancing their role as primary builders. Duringthe Early Eocene the acervulinid Solenomeris has been ableto build monospeciWc reefs substituting corals as the mainreef builder in relatively deep-water settings of the Tethyanrealm (Plaziat and Perrin 1992). The encrusting textulariidHaddonia and Placopsilina genera are widespread in thisassociation occurring with in situ specimens. Modern Had-donia from the Somali coast and Java (Matteucci 1996)thrive in low-light, low-energy environments, being highlysusceptible to detachment and destruction by high waterenergy. The association of encrusting foraminifera withfew, Xattened Discocyclina and small rotaliids points to theexistence of limiting conditions like low light intensity andrelatively high nutrients, which favor extensive microbialcrusts development. This scenario would explain the lowabundance and diversity of the LBF.

In conclusion, the ‘bioconstructors’-dominated assem-blage represent a benthic community adapted to live in alow-energy environment (deep mid-ramp setting), on pri-mary soft, muddy substrate and secondary hard biogeneticsubstrate (corals and microbial crusts), likely characterizedby enhanced nutrient level and reduced-light intensity.

Assemblage 5: Orthophragminids-dominated assemblage

This foraminiferal assemblage only occurs in the Bebulov-ica section, usually in massive Wne-grained wackestones. Itis dominated by Xattened orthophragminids, which consti-tute most part of a scarce and low-diverse community.Orthophragminids are usually represented by few speci-mens, associated with rare fragmented Assilina and smallrotaliids (Fig. 4h). Calcareous red algae are a commoncomponent associated with foraminifera.

The paleoecological interpretation of this assemblage isdiYcult because orthophragminids became extinct at theEocene–Oligocene boundary. Therefore, a direct compari-son to phylogenetically close extant taxa is not possible.Based on the morpho-functional characteristics, ortho-phragminids are considered homeomorph to Cycloclypeus(e.g., 0osoviT et al. 2004). Today, most of the speciesbelonging to this genus colonize the deep environments,down to the lower limit of the photic zone (Langer andHottinger 2000). Fossil orthophragminids have beendescribed from a diverse array of environments within thephotic zone including shallow back- and fore-reef/shoalenvironments (e.g., Anketell and Mriheel 2000; Ghose

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1977) to deeper, outer ramp environments (e.g. Gilham andBristow 1998). Their test morphologies were proposed as afeature to diVerentiate inner-ramp environments above theFWWB (ovate form) from mid- to outer-ramp areas (Xat-tened forms; e.g., Eocene from Tunisia; Loucks et al.1998). In our assemblage, orthophragminids have quite Xattests and lateral chamberlets with a low shape. They occurin a micritic matrix together with thin, delicate algal andforalgal crusts. These features indicate deposition in asomehow deep, low-energy setting with reduced-light con-ditions.

Therefore, the orthophragminids-assemblage thrived in adeep mid-ramp setting characterized by a soft muddy sub-strate.

Facies interpretation

The facies FA is characterized by foraminiferal assem-blages and sedimentological features, which indicate achange in depositional conditions with respect to the under-lying Foraminiferal limestones (F). The boundary betweenfacies F and FA is marked by an increase in the amount ofmicrite, an increase in diversity (but only moderately inabundance) of larger foraminifera and the common occur-rence in the FA of encrusters (mainly foraminifera associ-ated with red calcareous algae, corals, and microbialcrusts). The high amount of micrite and the absence ofwave-related sedimentary structures likely reXect deposi-tion in a relatively low-energy environment.

The diversity of larger foraminifera in this facies indi-cates the existence of ecological niches with diVerent fea-tures. However, their moderate abundance, especially inthe more muddy lithologies, might be due to limiting eco-logical conditions likely low light intensity and/or rela-tively high nutrient levels. Considering the calcareous redalgae assemblage, corallines are dominant, represented byMelobesioideae, Sporolithaceae and Peyssonneliaceae. Inmore bioclastic lithologies they occur as small rhodolithsand subordinate thick crusts, commonly associated withAssilina. When the mud content is higher, they form thin,irregular crusts and occur together with small ortho-phragminids and small rotaliids. Nowadays, sporolitha-ceae and melobesioideae occur in carbonate environmentsof subtropical and tropical areas occupying deep-waterhabitats with variable nutrient conditions (Aguirre et al.2000). Peyssonneliaceans show a broad latitudinal distri-bution ranging from the tropics to the poles in waters ofnormal marine salinity at depths of few meters, althoughthey were observed down to depths of 120 m (Bassi1997).

Therefore, this facies is interpreted as deposited belowthe FWWB, in a mid-ramp setting. The presence of abradedand fragmented bioclasts, occurring in speciWc beds, points

to occasional reworking by storms and/or bottom currents.In this mid-ramp, the upper part was dominated by LBF(mainly Assilina) commonly associated with calcareous redalgae and small coral colonies and rubbles. The deepermid-ramp, close to the lower limit of the photic zone, hadfew LBF (mainly Xattened orthophragminids) and encrust-ing biota forming coral-microbialite mud mounds andwackestones with thin foralgal crusts. The occurrence ofthese thin delicate crusts, the presence of a diversiWed com-munity of encrusting foraminifera, and the morphologicalfeatures of corals occurring as dendritic-ramose andencrusting colonies suggest reduced-light conditions (Bassi2005; Bosellini and Papazzoni 2003). Moreover, possiblehigh nutrient values could have favored the growth ofmicrobial crusts (Zamagni et al. 2006) associated withencrusting foraminifera.

Bio-Peloidal limestones (BP)

Facies description

This facies occurs in the uppermost part of the studied sec-tions with a thickness of 55 m (Fig. 3, Table 1). It is repre-sented by poorly stratiWed, dark grey packstones with arelatively high amount of carbonate mud, dominated bylarger foraminifera and other skeletal remains mixed withvariable percentage of fecal pellets and micritic grains(mainly micritized bioclasts) acting as a matrix to largerbioclasts (e.g., alveolinids). The most abundant largerforaminifera are represented by the alveolinids, nummulit-ids, and subordinate soritids associated with other benthicforaminifera (mainly small rotaliids and miliolids), encrust-ing foraminifera, and rare small, robust/ovate ortho-phragminids. The associated macrofauna is composed ofabundant echinoid fragments and rare complete skeletonswith spines clustered around their tests, common bryozoansand few molluscs (mainly gastropods). Calcareous algaeare rare, mostly represented by dasycladaleans and veryrare small fragments of red algae.

Micritization and bioerosion strongly aVect the bioclastsin this assemblage producing a bimodal grain-size distribu-tion with abundant mud and sand-size fragments (mainlyforaminifera and echinoids). Foraminifera are usuallyabraded and aVected by micritization, especially nummulit-ids and small rotaliids with development of thin destructivemicritic coatings. Constructive micrite envelopes with noclear evidence of microborings are locally developed onforaminiferal outer walls. Alveolinid shells are frequentlyencrusted by acervulinids and/or thin constructive coatingsand are aVected by macroborings (Fig. 5d). Peloids are thesecond most abundant component in this facies. Theymostly represent micritized bioclasts and fecal pellets,which form elongated clusters.

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The appearance of Alveolina spp. (A. aramaea aramaea)at the base of PB limestones indicates Ilerdian age (SBZ5)for this facies, ranging until SBZ8 (middle Ilerdian).

Foraminiferal assemblages

One foraminiferal assemblage was identiWed in this facies,the alveolinids-nummulitids assemblage (ass. 6).

Assemblage 6: Alveolinids–Nummulitids assemblage

The most abundant larger foraminifera in this assemblageare represented by Alveolina, Assilina, Nummulites and sub-ordinate soritids (Fig. 5). Other common foraminifera aresmall rotaliids (e.g. Smoutina sp., Kathina sp.), encrustingforaminifera (acervulinids and Haddonia), miliolines (smallmiliolids, lacazinids), agglutinated foraminifera (Vania,Thomasella), and rare small and robust Discocyclina sp. The

alveolinids–nummulitids assemblage is dominated by alve-olinid in the lower portion of the facies and Nummulites,occurring throughout the facies but with variable concentra-tion. To a general extent, they are more abundant in theupper part of the successions. Nummulites are ‘robust’,ovate, macrospheric forms whereas B-forms are rarely pres-ent. Assilina is present throughout the facies with few, smallspecimens. Soritids are concentrated in beds and are repre-sented by Orbitolites (Fig. 5b) and Opertorbitolites.Encrusting foraminifera occur with acervulinids, whichencrust and bond larger foraminifera or as scattered frag-ment with circular and hooked shapes (Fig. 5c). Haddonia isalso present, encrusting foraminiferal shells.

Living and fossil alveolinids are shown to occur in avariety of shallow-marine settings with distributions inde-pendent of the substrate. Living forms, such as Borelis sp.and Alveolinella quoyi, proliferate to depths less than 35 m(Langer and Hottinger 2000). In Papua New Guinea,

Fig. 5 Photomicrographs of Ilerdian foraminiferal assemblages of theinner ramp Bio-Peloidal facies (BP). a Assemblage 6: packstone withAlveolina (Alv). b Assemblage 6: packstone with Orbitolites (Orb). c

Assemblage 6: packstone with Alveolina (Alv), echinoid fragments andhooked-shape acervulinids (Ac). d Assemblage 6: packstone with Al-veolina (Alv) and Nummulites (N), note bioerosion of the alveolinids

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Alveolinella quoyi has been observed to live as epibiont onboth algal-covered hard substrates in protected, shallow (3–5 m) environments, or on stable substrates covered withorganic detritus in 20–30 m of water (Severin and Lipps1989). Alveolinids have been described from the Eocene ofOman, associated with Nummulites and Assilina as livingon protected, inner ramp setting with sparsely vegetatedsand substrates close to seagrass beds (Beavington-Penneyet al. 2006). Extant Nummulites have never been describedas seagrass dwellers. However, the occurrence in this fora-miniferal assemblage of robust/ovate, A-form-dominatedpopulation with rare or absent B-forms suggests a shallow-marine environment aVected by limiting conditions, such asslightly elevated nutrient levels, favoring the developmentof a community of ‘r-selection’ strategists (Beavington-Penney and Racey 2004; Hohenegger 1999). Since Orbito-lites and Opertorbitolites are extinct since the Late Eocene,ecological considerations must be based on living homeo-morphs. Based on structural similarities (e.g., Ghose 1977),a general agreement exists to consider living larger soritidssuch as Marginopora, Sorites and Amphisorus as the clos-est genera to Orbitolites. Living soritids are commonlydescribed as epiphytes thriving in shallow lagoonal envi-ronments, although none appear to be restricted to seagrassleaves. Amphisorus and Marginopora have been observedin the NW PaciWc (Hohenegger 2004) to settle on roundedboulders and unstructured carbonate rocks, where theystrongly attach with organic glue to numerous Wne algalWlaments (Langer 1993). Today, the closest analogue ofPaleogene Haddonia and acervulinids represent importantstabilizing encrusters of tropical bioclastic bottom with awide depth range of distribution (e.g. 40–90 m in the Gulfof Elat; Hottinger 1983). Modern analogue of PaleogeneHaddonia heissigi have been found to live in low intertidaland subtidal environments on bioclastic sand forming thesubstrate for seagrass covers (e.g. Southern Somalia; Mat-teucci 1996).

A similar foraminiferal assemblage from Greece havebeen interpreted by Accordi et al. (1998) as deposited at theboundary between inner and mid ramp, representingstabilized sandy shoals in a protected coastal embayment.Similarly, Beavington-Penney et al. (2006) described aforaminiferal community from Oman dominated by Alveo-lina likely thriving on the patchily vegetated muddy sandsof a protected lagoon or embayment. Özgen-Erdem et al.(2005) interpreted alveolinids, nummulitids, orbitolitidsdominated assemblage from Turkey as deposited in alagoonal environment. In Spain (Scheibner et al. 2007) andin France (Rasser et al. 2005) Alveolina-dominated assem-blages have been considered as thriving in inner platform,inXuenced by silicoclastic input.

To summarize, foraminifera of the assemblage 6 thrivedin a protected inner ramp, likely a lagoon or embayment,

characterized by muddy and sandy substrate, mainly repre-sented by foraminiferal test and echinoids fragments andcarbonate mud. The substrate was probably sparsely vege-tated by seagrass and/or stabilized by algal Wlms as indi-cated by the occurrence of the ephiphytic Orbitolites andOpertorbitolites.

Facies interpretation

Based on their biotic components and sedimentological fea-tures, facies of the Ilerdian BP limestones have been inter-preted as deposits of an inner ramp setting. The commonoccurrence of carbonate mud and absence of structuresindicative of high-energy events support this interpretation.However, in the Weld no evidence of shoals or bioconstruc-tions that would allow the development of a protectedlagoon has been found. The protection could have derivedfrom an embayed nature of the depositional setting as wellas from the existence of seagrass or algal cover. The occur-rence of constructive micrite envelopes on larger foraminif-era indicates the presence of a vegetated substrate; in factsuch structures have been described from modern seagrassbeds (Perry 1999). The patchy distribution of encrustingepiphytes (Orbitolites and Opertorbitolites) and dasyclada-leans indicate the existence of algal meadows. Their distri-bution in speciWc beds could be the result of storm-inducedwinnowing from close seagrass with consequent transportof seagrass leaves and respective encrusters or alternativelydue to a low seagrass cover. However, large distribution ofepiphytic foraminifera was described from Istrian EoceneAlveolina-Nummulites Limestone (Drobne 1977, 1979).Moreover, the biofabrics and poorly developed bedding infacies BP most probably reXect intensive bioturbation andabundant remains of infaunal echinoids support this inter-pretation. Widespread bioerosion and micritized bioclastsindicate a low sedimentation rate likely coupled withenhanced nutrient conditions (Hallock 1988).

Discussion and paleoenvironmental interpretation

The distribution of the studied benthic assemblages in theshallow-water carbonates from SW Slovenia have beencontrolled mostly by a combination of depth gradient andsubstrate nature. Based on sedimentological and paleonto-logical data a generalized facies model and foraminiferalassemblage distribution has been reconstructed (Fig. 6).

The facies model presented here shows a depth gradientfrom the inner ramp to the mid ramp with distribution offoraminifera and other important components (scleractiniancorals and calcareous algae) reXecting the presence ofdiVerent depositional biotopes depending mainly on thenature of the substrate. In fact, substrate nature and water

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depth are key parameters in controlling biosystems inhab-ited by diVerent genera or species of larger foraminifera(Hottinger 1983).

In the Thanetian, the studied successions exhibit a deep-ening trend with Foraminiferal limestones (facies F) depos-ited in a protected, locally restricted, patchily vegetatedinnermost ramp. In this setting the two foraminiferalassemblages (assemblages 1 and 2) are dominated byagglutinated foraminifera, small rotaliines and miliolineswith local enrichment of Miscellanea and small Ranikotha-lia. The presence of beds with oligotypic fauna (smallermiliolids-dominated assemblage) indicates locallyrestricted conditions. The Foralgal limestones (facies FA)are interpreted as deposited in a mid-ramp setting. Thethree foraminiferal assemblages that characterize thisfacies, alternate with one another suggesting close deposi-tional depths. However, some major ecological and compo-sitional gradients can be identiWed between the Assilina-dominated assemblage (assemblage 3) on one side and the‘bioconstructors’-dominated assemblage (assemblage 4)/

orthophragminids-dominated assemblage (assemblage 5)on the other side. These gradients are expressed by: (1) anincrease in encrusting biota (foraminifera, calcareous redalgae and microbialite crusts); (2) decrease in abundancesand diversity of larger foraminifera; (3) increase in carbon-ate mud; and (4) decrease in coarse bioclasts. These fea-tures indicate a decrease in the hydrodynamic energy withAssilina-dominated assemblage thriving in storm/currentinXuenced environments, just below the FWWB, passing tothe orthophragminids and the ‘bioconstructors’-dominatedassemblages colonizing a deeper, lower energy settingalong the mid ramp. Additionally, the substrate natureshows a diVerentiation as consequence of changing waterenergy. The Assilina-dominated assemblage thrived onsandy, unstable substrates; the orthophragminids-domi-nated assemblage lived on muddy substrates, and the‘bioconstructors’-dominated assemblage Xourished onsecondary hard biogenic substrate represented by coral-microbial encrustations. Deposition of the Ilerdian Bioclas-tic-Peloidal limestones (facies BP) marks a shallowing

Fig. 6 Schematic reconstruction of late Paleocene–earliest Eocene foraminiferal assemblage distributions in respect to depth, substrate nature,along a ramp transect

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trend with deposition on a protected inner ramp withmuddy and sandy substrates, partly covered or close to sea-grass beds. Alveolina, Nummulites and locally Orbitolites(assemblage 6) thrived in this setting.

The quality of the paleo-depth signal is the highest whena foraminiferal community reaches its greatest diversiWca-tion. The consequence of higher diversiWcation is therestriction of each group to speciWc niches (Hottinger1997). In fact, paleoenvironmental models of foraminiferaldistribution during the Early Paleogene are mainly based onEocene assemblages (e.g., Arni 1965; Luterbacher 1984),since that was the time of higher diversiWcation. Thesemodels usually involve “bank” of larger foraminifera (espe-cially made up of Nummulites and Alveolina), which formssigniWcant relief on the sea Xoor producing a range oflinked sub-environments within the photic zone. In thepresent study we focus on a pre-Eocene climax, when thediversiWcation of foraminifera was still quite low.

This model diVers from the Eocene ones mainly for theabsence of foraminiferal shoals and banks, which have beennot found in the studied area.

Light intensity

Changes in the foraminiferal test composition, shape, anddimensions express environmental changes nonlinearlycorrelated with water depth gradients, most likely lightintensity and water energy (Hottinger 1983). Thanetianassemblages are characterized by a taxonomic transitionfrom small imperforate porcelaneous and robust lamellar-perforate hyaline forms in the lower facies (Facies F) tolarger, Xatter hyaline forms (including orthophragminidsand Assilina) and encrusting foraminifera in the facies FA.Such a shift suggests a decrease of light intensity. In fact,LBF typical of shallow waters produce ovate tests withthick wall, like lamellar-perforate foraminifera, and/or por-celaneous, imperforate wall structures. These featuresallow preventing photoinhibition of symbiontic algaewithin the test in high intensity light conditions. On theother hand, the shift to Xattened, hyaline foraminifera areusually found at increasing water depths where the lightintensity is strongly reduced (e.g., Hohenegger 1999). Anincrease in light intensity in shallower-water settings mostlikely characterizes the deposition of the Ilerdian facies BP,as attested by the presence of large porcelaneous forms(lacazinids, alveolinids and Orbitolites) associated in vari-able proportions with lenticular/ovate hyaline forms (smallNummulites and Assilina).

Water energy

All of the facies analyzed in the present study have a lowenergy index. Carbonate mud is generally abundant and

cements are reduced to syntaxial overgrowth on echinoidfragments. Such low-energy conditions would explain thelack of hard substrates. These evidences combined with theabsence of high-energy structures in the inner-ramp faciesF and PB, indicate deposition of Bebulovica and Kozinasuccessions in a protected environment, like an embay-ment, as a local feature characterizing the studied part ofthe AdCP during the late Paleocene—early Eocene. Alter-natively or additionally, sedimentological and composi-tional evidence suggests the existence of a vegetationcover, which could explain the low energy index.

Nutrients

The protected nature of the depositional setting, possiblyaVected by tectonically conWned physiography of the NWDinaric foreland basin during the Early Paleogene, wouldexplain the development of high nutrient content in an oth-erwise oligotrophic region as the Central Tethys (Hottinger1990). In the studied sections, both facies and foraminiferalassemblages show evidence of an elevated trophic regime.In particular, the facies F, deposited in shallow subtidal set-ting, hosts foraminiferal assemblages dominated by smallmiliolids and rotaliids, usually micritized. Miliolids andsmall rotaliines commonly replace larger symbiont-bearingrotaliines when trophic resources increase (Hallock andGlenn 1986). Additionally, bioeroders, such as endolithicalgae and fungi, clionid sponges, boring bivalves and echi-noids, may Xourish in moderately oligotrophic to mesotro-phic settings, with highly eVective micritization processes(Hallock 1988; Peterhänsel and Pratt 2001).

LBF became common in the facies FA. These are mainlylarge, Xat rotaliines with moderate diversity and abundance,mainly associated with echinoids, encrusting foraminiferaand encrusting calcareous red algae. The common occur-rence of encrusting biota in assemblages 4 and 5 suggestsenhanced trophic levels (i.e., mesotrophic conditions), withcompetition for the substrate as the main limiting factor(Mutti and Hallock 2003). The presence of scleractiniancorals as small encrusting colonies, rubbles and/or coloniesencrusted by microbialite to form mud mounds support thisinterpretation. Indeed, bioerosion may reduce or halt reefdevelopment as a consequence of an excess of nutrients.These nutriWcation processes would in turn account for thecyanobacterial and algal blooms (Hallock 2005), as sug-gested by the development of microbialites overgrowingcorals in the mid-ramp setting. This pattern could be inter-preted as the result of occasional storms creating bottomcurrents responsible for transportation and redistribution ofnutrients in deeper waters (e.g., Bassi 2005).

Facies BP also shows evidence of enhanced nutrient lev-els, possibly due to the proximity of seagrass beds. Porcela-neous foraminifera (alveolinids, Orbitolites) and robust,

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small hyaline foraminifera (Nummulites) strongly aVectedby micro- and macro-bioerosion are dominant in this facies.Additionally, abundance of detritivores (echinoids) andsuspensivores (bryozoans) agrees with this interpretation.

Mechanisms for changes in nutrient supply

High nutrient concentration is a limiting factor in the Xour-ishing of symbiont-bearing foraminifera that are consideredforms highly adapted to stable, oligotrophic, nutrient-deW-cient conditions of tropical and subtropical settings (e.g.,Hallock 1985). Nevertheless, studies performed on shal-low-water carbonate sediments in SE Asia (e.g., Wilsonand Vecsei 2005) demonstrated that low light-dependantorganisms, like LBF, can form abundant and extensivefacies in humid tropical settings aVected by local upwellingand/or intense run oV. During the late Paleocene–earlyEocene, sedimentation along the AdCP took place in thesubtropical climate zone. The hot humid climate of thisarea during the Early Paleogene is indicated by the wide-spread occurrence of bauxites in Istria (Durn et al. 2003).These bauxites are associated with a regional paleokarsticunconformity and occur in an apparent stratigraphic gap ofabout 30–50 Ma between the lower to Upper Cretaceousand Lower to Middle Eocene carbonate deposits. The EarlyEocene age of the paralic/palustrine Liburnian depositsoverlying the bauxite-Wlled karst relief in northern Istria(Drobne 1977) indicates hot and humid climatic conditions,contemporaneous to the deposition of the studied UpperPaleocene/lowermost Eocene carbonates. In fact, these con-ditions are fundamental for ferrallitic weathering and baux-ite formation.

The deposition of facies FA and BP coincided with theincursion of the warmest period of the Cenozoic (Zachoset al. 2001). This thermal perturbation should not have haddirect eVects on distribution of larger foraminifera. Extantsymbiont-bearing foraminifera are usually distributedwithin the 25°C summer isotherms, with selected largerforaminifera (i.e., alveolinids and nummulitids) toleratingtemperature around 30°C and more (Langer and Hottinger2000). However, high temperature could have also pro-moted secondary eVects such as the intensiWcation of tropi-cal cyclones/storms (Huber 2006) and/or of the weatheringprocesses. Increased nutrient input by rivers is consistentwith results from general circulation models predicting anintensiWed hydrological cycle at elevated greenhouse gasconcentrations (Pierrehumbert 2002; Huber et al. 2003;Caballero and Langen 2005), like during the PETM. Theseprocesses could have modulated nutrient delivery to theshallow-water realm coupled with bottom currents respon-sible for transportation of nutrients along the coastal sur-face water and the ramp.

Facies changes across the Paleocene–Eocene boundary

The studied successions in the northwestern AdCP show acertain diVerentiation in facies and foraminiferal assem-blages from the Paleocene to the Eocene. Small benthicforaminifera dominate the Upper Paleocene (SBZ3) facies.Corals are almost entirely absent except for rare and smallpatches. LBF become common in the benthic communitiesof the Uppermost Paleocene (SBZ4), with Assilina andorthophragminids being the most abundant forms oftenassociated with red calcareous algae and corals. TheEocene is still dominated by diVerent groups of LBF. Thedominance of larger benthic foraminifera in the wholeTethyan realm during the latest Paleocene to earliestEocene is a well-known phenomenon. However, a majordiVerence emerges by comparing the distribution of theshallow-water biota presented in this study with thosedescribed for North Spain and Egypt by Scheibner et al.(2007). The authors proposed a three-stage evolution forshallow-water carbonates from Spain relatively similar tothat identiWed in Egypt (Scheibner et al. 2005). They foundpersistent corals in the Pyrenees throughout the entireperiod under study. This does not hold for Egypt, wherecoralgal associations disappeared in the Uppermost Paleo-cene. At this time LBF became common in both regions,with Assilina dominant in the Pyrenees (Assilina beds, Bac-eta et al. 2005), Ranikothalia and Miscellanea formingshoals in Egypt (Scheibner et al. 2003). Scheibner et al.(2007) interpreted this evolution in terms of temperaturegradients, with extreme values developed during the PETMand the long-term Eocene warming, aVecting in a strongerway the low-latitude communities. Instead, the middle-latitude assemblages suVered a less intense eVect withforaminifera experiencing only changes in morphotypes.Thus, the two middle-latitude carbonate platforms (AdCPand Pyrenees) were more similar to each other that each ofthem was to Egypt. Similarly to what observed in Spain,during the latest Paleocene–earliest Eocene the LBF of thenorthwestern AdCP adapted to diVerent depths, but no dra-matic changes occurred in the assemblage composition.Similarities between these areas suggest the existence of alatitudinal eVect on the evolution of shallow-water benthiccommunities. However, during the Late Paleocene, theshallow-water biota of the AdCP was dominated by Assilina,orthophragminids and coral-microbialite mud-mounds.This represents an unusual association if compared to otherTethyan localities. Moreover, the Early Eocene biota showstransitional features compared to Egypt and Spain, withLBF still dominant and with corals and red algae beingcompletely absent.

These dissimilarities could be, at least partially,explained in terms of diVerences in the local conditions

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exerting a strong control in the development of the shallow-water carbonate assemblages.

Conclusions

During the late Paleocene–earliest Eocene the sedimenta-tion in the northwestern AdCP (SW Slovenia) took placealong a shallow-water carbonate ramp depositional sys-tem. This carbonate system was dominated by foraminif-eral and foralgal deposits during the Thanetian.Agglutinated foraminifera, small rotaliids and miliolidsdominated the lower Thanetian innermost ramp assem-blages. Assilina, Discocyclina, lacazinids and encrustingforaminifera associated with red algae and corals charac-terized the upper Thanetian communities colonizing themiddle-ramp setting. During the Ilerdian Alveolina, Num-mulites and Orbitolites thrived in a protected and vege-tated inner ramp.

In the studied sections the predominance of mud-sup-ported lithologies, packstones with relatively abundant car-bonate mud and the lack of wave-related fabrics indicatethat deposition occurred along a protected carbonate ramp.The widespread microbial activity, indicated by strongmicritization and growth of microbial mud mounds, hasbeen interpreted as the consequence of increased concentra-tion of nutrients. The intense weathering in the humid, hotclimate of the late Paleocene–early Eocene most probablyplayed an important role delivering nutrients to the basin.These environmental conditions promoted the developmentof speciWc low-light dependent communities, with LBF(Alveolina, Nummulites, Assilina and orthophragminids)showing tolerance to enhanced nutrients levels.

The hypothesized ecological changes in the shallow-water realms of the AdCP at the Paleocene–Eocene transi-tion were most probably linked to drastic climatic changescoupled with the peculiar paleogeography of the area.Overall, when comparing the studied LBF assemblages tothose from other mid-latitude (Atlantic realm, Pyrenees)and low-latitude areas (southern Tethys, Egypt), the exis-tence of a latitudinal gradient in the benthic communitycomposition is evident. The present study demonstrates,however, that on a more geographically restricted scale,local conditions were predominant in controlling the devel-opment and evolution of shallow-water biota.

Acknowledgments This work is partially supported by the GermanScience Foundation (DFG project MU1680/5-1). Jessica Zamagni re-ceived a graduate grant from the Graduate School of the University ofPotsdam as well as a postgraduate grant from the International Asso-ciation of Sedimentologists, which are gratefully acknowledged.Paolo Ballato, Davide Bassi, Giovanna Della Porta, Valerio Ketmaierand Christian Scheibner are thanked for critical reading of variousversions of this paper. We wish to thank Christine Fischer (Potsdam)

for preparation of thin sections. Alenka Eva Brne is gratefullyacknowledged for the valuable help in the Weld. Daniel Melnick isthanked for valuable improvement of English.

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