Benthic foraminiferal evidence for the formation of the Holocene mud-belt and bathymetrical...

Marine Micropaleontology 57 (2005) 25–49

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Benthic foraminiferal evidence for the formation of the Holocene

mud-belt and bathymetrical evolution in the central Adriatic Sea

Caterina Morigi a,*, Frans J. Jorissen b, Simona Fraticelli a, Benjamin P. Horton c,

Mirko Principi a, Anna Sabbatini a, Lucilla Capotondi d,

Pietro V. Curzi e, Alessandra Negri a

aDipartimento di Scienze del Mare, Universita Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, ItaliabLaboratoire des Bio-Indicateurs Actuels et Fossiles, UPRES EA 2644, Universite d’Angers, 2 Boulevard Lavoisier, 49045 Angers,

and Laboratoire d’Etude des Bio-Indicateurs Marins, Port Joinville, Ile d’Yeu, FrancecDepartment of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104-6316, USA

dISMAR–CNR, Via Gobetti 101, Bologna, ItaliaeDip. di Scienze della Terra e Geol.-Ambientali, Universita di Bologna, Via Zamboni 67, Bologna, Italia

Received 24 July 2004; received in revised form 13 June 2005; accepted 14 June 2005

Abstract

Detailed analyses of modern and fossil benthic foraminiferal assemblages collected in the central Adriatic Sea are used as

tools to reconstruct the environmental changes that occurred between the Last Deglaciation and the Present (last 14 Kyrs); in

particular we focus on the timing and formation of the mud-belt. The modern benthic foraminiferal assemblages display a

parallel zonation to the Italian coast controlled by the interaction between food/oxygen availability and water depth. Cluster

analysis of 4 sediment cores separates the fossil foraminiferal assemblages in 6 groups: Cluster A is dominated by three

Ammonia species; Cluster B consists of Ammonia papillosa, Nonionella turgida, Elphidium advenum and Elphidium decipiens;

Cluster C is composed of two taxa, Hyalinea balthica and Trifarina angulosa; Cluster D is dominated by 5 species, Cibicides

lobatulus, Buccella granulata, Reussella spinulosa, Textularia agglutinans and Elphidium crispum; Cluster E contains

Bulimina spp., Gavelinopsis praegeri, Bolivina spp., Cassidulina neocarinata and Asterigerinata mamilla; and Cluster F is

dominated by Bulimina marginata, Valvulineria bradyana, Globocassidulina subglobosa and Melonis padanum. The cluster

analysis and contemporary distribution patterns of these taxa are used together with ecological preferences of the most frequent

species to reconstruct the spatial and temporal distribution of the different biofacies in the past. This reveals information about

Holocene palaeoenvironmental changes that are related to water depth fluctuations and the installment of the coast-parallel

mud-belt. The benthic assemblage records the transition from a infralitoral environment (Biofacies I) to deeper marine condition

(Biofacies III). After that the sea level reached about the modern level (Biofacies IV) the benthic foraminiferal community

0377-8398/$ - s

doi:10.1016/j.m

* Correspondi

E-mail addre

ee front matter D 2005 Elsevier B.V. All rights reserved.

armicro.2005.06.001

ng author. Tel.: +39 071 2204287.

ss: [email protected] (C. Morigi).

C. Morigi et al. / Marine Micropaleontology 57 (2005) 25–4926

evidences the development of the mud-belt and the subsequent transformation of the ecological niches linked to the trophic

evolution of the environment.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Benthic foraminifera; Adriatic Sea; Mud-belt; Sea level; Holocene

1. Introduction

Many of the world’s coastal areas are extremely

vulnerable, and are strongly menaced by future sea

level rise. The Adriatic Sea is one of the areas where

sea level rise could create important damages at the

coast and at the human activities. In spite of the fact

that an accurate knowledge of the sea level history is

important for environmental studies, the literature

dealing with the Holocene sea level history of the

Adriatic Sea is still scarce (Lambeck et al., 2004).

Although the transgressive deposits of the last sea-

level cycle in the Adriatic Sea are well investigated

from a sedimentological point of view (Pigorini,

1968; Van Straaten, 1970; Brambati et al., 1983;

Ciabatti et al., 1987; Curzi and Tomadin, 1987; Trin-

cardi et al., 1994; Correggiari et al., 2001; Cattaneo et

al., 2003), there are few studies about the relation

between high stand deposits and benthic microfauna

(Asioli, 1996; Asioli et al., 2001).

Some of the best records of sea-level change have

been derived from intertidal microfossil assemblages

(diatoms, foraminifera and pollen) contained in a

range of post-glacial Holocene sedimentary deposits

(Scott and Medioli, 1980; Horton et al., 2003; Horton

and Edwards, 2005). During the past 50 years, these

indicators have been used extensively to provide

reconstructions of Holocene Relative Sea Level

(RSL) change for the UK, Europe and elsewhere,

and have been the primary source of data for devel-

oping and testing models of RSL (e.g. Lambeck et al.,

2002; Peltier, 2002). However, the potential applica-

tion of benthic foraminifera from open marine envir-

onments is poorly understood. In open marine

environments, the bathymetrical zonation of benthic

foraminifera appears not to be tightly constrained, but

to vary as a function of the organic flux to the ocean

floor (e.g. De Rijk et al., 2000; Morigi et al., 2001).

In shallow marine areas, on the contrary, several

studies report a consistent bathymetric distribution

of benthic foraminifera (e.g. Jorissen, 1988; Asioli

and Borsetti, 1989; De Stigter et al., 1998). Jorissen

(1987, 1988) studied in detail the geographical dis-

tribution of the benthic foraminifera in Recent sedi-

ment samples of the Adriatic Sea. He found that

benthic assemblages show a zonation parallel to the

Italian coast. At greater distance from the Po delta,

this bathymetrical species zonation becomes clearer.

The runoff of the Po delta is indeed responsible for

strong environmental changes over short distances.

This influence is evident in the upper part of the

water column, but also on the sea floor, where it

strongly affects the distribution of the benthic fora-

minifera. River runoff causes the input of suspended

clay, organic detritus and dissolved nutrients into the

marine system. This can provoke strong primary

production events, leading to eutrophic conditions

in the water column and on the sea floor. As a

consequence of the stratification of the water column

in summer (Giordani and Angiolini, 1983; Tahey et

al., 1995) the bottom environment may seasonally

become oxygen depleted. The quantity and quality

of the changes in the Recent foraminiferal association

clearly reflect the impact of these phenomena.

Several studies (Parker, 1958; Jorissen, 1988; De

Stigter et al., 1998) investigated the relationship

between water depth and the composition of benthic

foraminiferal assemblages, and determined a bathy-

metrical species succession. Some studies (Carney,

1989; De Rijk et al., 2000), argued that the bathy-

metrical changes of benthic fauna are not directly

indicative of a specific water depth but are mainly

related to a certain level of organic flux exported

from the photic zone. In the Adriatic Sea, Jorissen

(1987) showed a slight southward deepening of the

depth zones of taxa inhabiting the mud-belt, in

response to a deepening of the central part of the

mud-belt, where maximum percentages of organic

matter are found due to focussing of the fine-

grained material.

In this paper we want to use the Holocene

sediment record, and more precisely the benthic

C. Morigi et al. / Marine Micropaleontology 57 (2005) 25–49 27

foraminiferal microfossils to reconstruct the Adriatic

Sea level history. The aim of our study is to

reconstruct palaeoenvironmental changes in this epi-

continental sea, as documented by the fluctuation

of the foraminiferal assemblage, and particularly, to

document the evolution of the mud-belt deposited

after the time of maximum marine transgression.

The study of this high stand deposit is important

because it allows a detailed reconstruction of envi-

ronmental variability in the recent geological past

and because it may serve as an analogue to recent

and future situations. This is achieved by the anal-

ysis of the modern benthic foraminiferal communi-

ty in the Conero area, and the planktonic and

benthic foraminiferal assemblages of four gravity

cores taken in the central western part of the

Adriatic Sea.

2. Study area

The Adriatic Sea is an elongated NW/SE oriented

basin, located in the central Mediterranean Sea. The

bathymetric features allow a threefold subdivision. Its

northern section is very shallow and gently sloping

with an average water depth of about 35 m. In the

central part, water depth moderately increases off San

Benedetto del Tronto, where a shelf-break delimits

the 270 m deep Middle Adriatic Depression (MDA)

(Ciabatti et al., 1987) or Jabuka pit. The southern

Adriatic Sea, which extends to the S of Gargano–

Lagosta line, reaches a maximum depth of 1250 m.

Finally, the basin is limited by a sill, the Otranto strait,

with a water depth of about 800 m.

There are three principal water masses in the

Adriatic Sea: the Adriatic Surface Water (AdSW),

the Levantine Intermediate Water (LIW) and the

Adriatic Deep Water (AdDW; each sub-basin has

its own characteristic deep water) (Orlic et al.,

1992; Artegiani et al., 1997). The general circulation

is cyclonic with a flow towards the northwest along

the eastern side and a return flow towards the

southeast along the western side (Fig. 1). The cir-

culation in the three sub-basins is often dominated

by local cyclonic gyres that vary in intensity accord-

ing to the season. The sub-gyre of the southern

Adriatic tends to persist throughout the year. The

sub-gyre of the middle Adriatic is more pronounced

in summer and autumn. In the north, during the

autumn, a cyclonic gyre is evident in front of the

Po river mouth (Russo and Artegiani, 1996). A

secondary western-descending current is connected

to bathymetric variations and/or to the input of

coastal fresh water. This circulation consists of two

stable branches, which turn from E to W at the

latitude of Gargano (Drina cell) and Conero (Ner-

etva cell) (Mosetti, 1984). In connection with these

circulatory features a long shore current is directed

from S to N along the eastern coast and from N to S

along the western coast. A transverse line of con-

vergence (zone of sinking waters) separates these

two opposite surface currents. Because of the pres-

ence of important annual river discharge (e.g. Po

river) in the western part of the Adriatic Sea, and

the southward direction of the coastal current com-

ing from the northern basin, the western coastal

areas are nutrient enriched, whereas the eastern

part of the basin is rather oligotrophic (Artegiani

et al., 1997; Zavatarelli et al., 1998).

The circulation pattern described above clearly

affects the thickness and the distribution of the

modern sediment cover. South of the Po delta, a

prograding coastal/deltaic system correlates with a

muddy offshore wedge that extends continuously

along the western Adriatic coast (Trincardi et al.,

1994). This modern sedimentary system shows a

number of shore-parallel depocenters of clay-rich

sediments (less than 1% sand content), which can

reach about 40 m of thickness in its southern part

(Curzi and Tomadin, 1987; Cattaneo et al., 1997;

Van Straaten, 1970). These transgressive deposits

span from about 14.0 Kyr BP in the southern part

to 5.0 Kyr BP in the north (Asioli, 1996; Trincardi

et al., 1996). A transgressive surface separates ma-

rine and deposits typically condensed to a thin lag

veneer of shelly and muddy sediments (about 30–40

cm with maxima of over 150 cm) (Correggiari et

al., 1992; Cattaneo and Trincardi, 1999). These

sediments correspond to the becozone rfQ of Asioli

(1996), which is dominated by a benthic fauna

typical of intertidal environments. Recent works in

the southern part of the mud-belt dated the begin-

ning of the formation of the high stand system track

to 5.5 Kyr BP (Trincardi et al., 1996; Cattaneo and

Trincardi, 1999). This muddy sedimentary structure

is delimited to the west by the modern littoral

37.0

38.0

34.035.0 36.0

16 17

2021

12o 13o 14o 15o

43o

44o

45o

0 50 100

km

Ravenna

RELICT SANDS

CORE

SALINITY ‰

SURFACE CURRENTSIsopach in meters of thethickness of the mud-belt

25

20

25

1015 5

ITALIA

Ancona

Fig. 1. Principal circulation and currents in the Adriatic Sea (from Mosetti, 1984 and Curzi et al., 1988 modified). The thickness of the Holocene

mud-belt is indicated in meters, considering a sound speed of 1600 m/s. The position of the 4 cores is shown.


deposits and to the east by Pleistocene relict sands

that crop out offshore.

Table 1

Details of the sediment cores: locations, depth and length

Cores Latitude N Longitude E Water

depth (m)

Length

(cm)

AD87-20 438 43V 58W 148 07V 10W 78.8 216

AD87-21 438 40V 23W 148 00V 43W 77.3 360

AD87-16 438 45V 24W 138 54V 57W 75.5 283

AD87-17 438 49V 07W 148 01V 61W 76.5 214

3. Materials and methods

The analysis of fossils sediments is based on 4

gravity cores (AD 87:16, 17, 20, 21) collected in the

central Adriatic Sea during oceanographic cruise AD

87 (Fig. 1), at 75 to 80 m water depth. Details of the

cores are reported in Table 1. The lithological de-

scription of the cores is summarised in Fig. 2. Two

main lithological units can be recognised in all the

cores. The lower unit is characterised by firm sed-

iment almost devoid of foraminifera. The upper unit

consists of blue clays rich in micro- and macrofos-

sils. These two intervals are separated by an ero-

sional surface, marked by a concentration of shell

debris and reworked benthic foraminifera. For the

micropaleontological studies, 1 cm thick samples

have been taken every 10 cm. Preparation of fossil

samples followed a standard technique. All samples

were dried at 50 8C for 72 h and weighted. Then

they were re-hydrated with distilled water and

washed over a 63 Am sieve. Quantitative and qual-

SC

CS

CS

S

CS

SC

CS

SC

CS

SC

CS

SC

SSC

C

C

SC

SC

CS

SC

SL

LS

CS

SC

SC

SC

CS

CS

CS

SC

Ad 87-16

50

Ad 87-20 Ad 87-17Ad 87-21

100

150

250

80%

300

cm

200

350

Clay

Silty clay

Clayey silt

Sandy silt

Sand Silt Clay

Shelly debris

Shell

Disappearance ofH. balthica

erosional surface

Silty sand

SiltSilt

C

SC

LS

CS

SSC

SL

S

CS

SSC

00

Clay %0 80%0 90%080%

Clay % Clay % Clay %

SL

CS

Fig. 2. Lithology and clay content (%) of the studied cores. Based on the proportions of sand-, silt- and clay-sized particles, the bottom

sediments were classified according to Shepard’s diagram (based on unpublished work of Principi, 1997).


itative analyses of planktonic and benthic foraminif-

era have been performed. Samples containing abun-

dant microfauna have been split in aliquots

containing at least 300 specimens, which were sub-

sequently picked, identified and counted. Planktonic

versus benthic foraminifera ratio (P /P+B) has been

used as a first qualitative approximation of paleo-

bathymetry (according to Grimsdale and Van Mor-

khoven, 1955). R-mode cluster analysis has been

performed on the benthic assemblages found in the

cores, and we used the 24 species, that showed a

relative abundance in the assemblage, higher than

5% in at least one sample (Table 2). This is a

mathematical technique which clusters variables

based on their similarity or dissimilarity (Davis,

1986). In our case we use it in order to define the

Table 2

Percentages of the 24 more important taxa in the sediment cores

Sample

(cm)

A.

beccarii

A.

papillosa

A.

perlucida

A.

tepida

A.

mamilla

Bolivina

spp.

B.

granulata

B.

marginata

Bulimina

spp.

C.

neocarinata

C.

lobatulus

E.

advenum

Core AD87-21

3–5 1 0 0 0 1 2 0 5 12 0 0 0

10–12 0 0 0 0 3 7 1 8 9 1 0 1

20–22 2 0 0 0 2 4 1 13 6 2 0 1

30–32 1 0 0 0 5 6 2 10 10 1 0 2

40–42 1 0 0 0 2 4 3 3 12 1 0 0

50–52 0 0 0 0 9 3 2 0 8 1 0 2

60–62 0 0 0 0 5 2 3 0 17 1 0 1

70–72 0 0 0 0 3 4 1 0 16 1 0 0

80–82 0 0 0 0 8 4 1 0 17 2 0 3

90–92 0 0 0 0 6 5 1 1 13 4 0 1

100–102 0 0 0 0 5 7 0 0 16 9 0 1

110–112 0 0 0 0 5 9 0 3 19 9 0 2

118–120 0 0 0 0 3 7 1 0 16 8 0 2

120–122 0 0 0 0 3 9 1 2 21 9 0 3

130–132 1 0 0 0 2 15 1 1 18 2 0 3

140–142 1 0 0 0 0 2 2 1 23 0 1 2

150–152 1 0 0 0 2 2 1 1 24 0 0 4

160–162 1 0 0 0 3 2 1 1 15 1 0 5

170–172 3 1 0 0 1 1 2 1 7 0 0 6

180–182 5 0 0 0 4 1 3 1 4 0 0 7

190–192 5 1 1 1 4 1 4 5 1 0 0 6

200–202 6 4 1 3 2 0 1 1 0 0 0 4

210–212 9 5 2 8 4 0 1 0 0 0 0 7

220–222 6 1 26 38 1 0 0 0 1 0 0 3

230–232 8 0 26 38 0 0 0 0 1 0 0 2

238–240 9 0 19 30 1 0 0 0 1 0 0 3

Core AD87-20

8–10 0 0 0 0 5 4 2 4 20 5 0 2

18–20 0 0 0 0 6 4 3 4 16 5 0 2

28–30 1 0 0 0 6 4 1 1 21 5 0 2

38–40 1 0 0 0 7 5 2 1 16 7 0 2

48–50 1 0 0 0 3 6 3 1 16 11 0 2

58–60 2 1 0 0 1 6 1 0 16 4 0 4

66–68 4 1 0 1 3 2 1 1 11 0 0 5

78–80 11 1 0 3 5 2 3 1 10 1 0 1

104–106 15 0 0 0 5 2 6 0 2 0 5 2

Core AD87-17

5–7 1 0 0 0 3 3 2 1 20 1 0 0

15–17 2 0 0 0 1 1 3 1 15 3 0 1

25–27 1 0 0 0 2 2 4 2 16 2 0 0

34–36 1 0 0 0 5 5 3 2 15 4 0 2

44–46 1 0 0 0 5 3 2 0 17 6 0 2

54–56 1 0 0 0 3 6 1 0 15 4 0 2

74–76 5 0 0 0 0 0 5 0 14 0 0 0

Core AD87-16

7–9 1 0 0 0 0 5 1 1 12 0 0 1

20–22 4 0 0 0 2 5 5 2 6 0 0 0


E.

crispum

E.

decipiens

G.

praegeri

G.

oblonga

H.

balthica

M.

padanum

N.

turgida

P.

granosum

R.

spinulosa

T.

sagittula

T.

angulosa

V.

bradyana

Other

species

Total

4 11 2 6 0 8 2 4 3 9 0 1 26 100

3 17 6 2 0 3 3 8 2 5 0 2 20 100

2 11 5 4 0 3 3 7 3 6 0 5 23 100

2 13 3 2 0 4 3 7 3 9 0 1 19 100

3 15 2 3 0 8 3 8 3 11 0 1 19 100

2 16 2 4 0 3 7 10 4 11 0 0 17 100

4 12 2 5 0 1 4 6 4 10 1 0 22 100

4 15 4 3 0 3 4 9 4 9 0 0 19 100

4 11 4 2 0 2 2 5 4 8 0 0 23 100

5 14 4 1 0 1 3 5 2 7 0 0 27 100

2 9 4 0 0 3 2 10 3 7 0 0 22 100

4 11 4 1 1 0 1 5 3 5 0 0 20 100

2 15 3 2 1 1 1 5 6 11 0 0 16 100

2 11 4 1 1 1 1 5 1 7 0 0 17 100

2 9 4 3 2 1 2 7 3 7 0 0 18 100

1 13 2 8 2 0 1 7 3 8 0 0 23 100

5 7 5 2 6 0 3 5 1 7 1 0 24 100

2 11 4 3 6 1 3 7 2 5 1 0 27 100

2 11 2 2 6 2 6 7 1 13 1 0 26 100

2 20 1 0 1 1 7 4 5 14 0 0 18 100

6 17 1 0 0 0 10 6 13 8 0 0 10 100

4 14 0 0 0 0 13 7 7 14 0 0 17 100

3 11 1 0 0 0 8 7 4 9 1 0 20 100

1 7 1 0 0 0 1 7 1 1 0 0 7 100

0 10 1 0 0 0 1 6 0 2 0 0 5 100

2 13 0 0 0 0 1 6 0 4 0 0 9 100

2 8 6 5 0 2 1 5 2 3 0 0 24 100

1 7 6 3 0 1 3 7 3 4 0 0 22 100

2 7 4 4 0 1 1 9 3 6 0 0 23 100

2 5 5 4 1 1 2 8 2 6 0 0 22 100

2 6 3 4 0 0 1 6 3 8 1 0 24 100

3 8 1 6 1 1 0 7 5 8 1 0 25 100

4 8 2 5 3 0 1 7 3 12 1 0 24 100

2 7 1 4 3 0 1 8 5 12 1 0 17 100

2 7 0 0 0 0 4 7 6 12 0 2 21 100

3 6 4 3 0 0 2 5 5 7 0 0 34 100

9 7 5 3 0 1 1 8 6 10 0 0 23 100

7 7 2 5 0 1 2 8 3 15 0 0 20 100

2 10 3 3 0 0 2 9 2 7 0 0 22 100

5 3 2 3 0 1 1 9 3 14 0 0 23 100

3 7 2 2 1 0 1 9 5 10 1 0 26 100

5 10 0 2 0 0 2 10 5 14 0 0 28 100

4 12 4 8 0 3 1 11 1 8 0 0 27 100

6 7 3 6 0 5 4 3 1 10 0 0 30 100

(continued on next page


)

Sample

(cm)

A.

beccarii

A.

papillosa

A.

perlucida

A.

tepida

A.

mamilla

Bolivina

spp.

B.

granulata

B.

marginata

Bulimina

spp.

C.

neocarinata

C.

lobatulus

E.

advenum

Core AD87-16

32–34 3 0 0 0 1 4 6 6 7 0 0 0

40–42 3 0 0 0 2 4 5 1 7 0 0 0

43–45 1 0 0 0 1 7 7 3 6 0 1 0

53–55 1 0 0 0 2 4 8 0 8 0 0 0

63–65 1 0 0 0 5 6 3 0 11 0 0 0

73–75 1 0 0 0 4 4 2 2 16 2 0 1

83–85 1 0 0 0 6 12 1 1 17 2 0 0

93–95 0 0 0 0 3 11 1 1 17 6 0 1

103–105 1 0 0 0 3 5 2 1 18 4 0 1

113–115 1 1 0 0 2 2 2 1 18 1 0 1

123–125 1 0 0 0 2 2 1 1 17 0 0 2

133–135 7 0 0 0 2 2 2 0 16 1 0 3

143–145 8 1 0 0 1 1 3 0 5 0 1 4

153–155 14 1 0 2 2 0 2 2 1 0 0 1

163–165 17 0 0 0 2 0 2 1 1 0 0 3

Table 2 (continued)

Table 3

Bathymetrical range and weighted mean water depth (MWD) in

meters of each species according to the formula explained in the text

Cluster Taxon Water depth

range (m)

MWD

(m)

Cluster A Ammonia perlucida b20 10

Ammonia tepida b20 10

Ammonia beccarii 0–40 29

Cluster B Ammonia papillosa 21

Nonionella turgida 0–60 37

Elphidium advenum 0–25 25

Elphidium decipiens 20–80 40

Cluster C Hyalinea balthica N80 200

Trifarina angulosa N80 200

Cluster D Cibicides lobatulus 50–80 70

Buccella granulata 0–20 35

Reussella spinulosa 0–80 52

Textularia agglutinans 0–80 50

Elphidium crispum 0–80 33

Cluster E Bulimina spp. 20–60 46

Gavelinopsis praegeri 80 71

Bolivina spp. N60 66

Cassidulina neocarinata N70 200

Asterigerinata mamilla N70 200

Protelphidium granosum 20–80 33

Cluster F Bulimina marginata 40–80 60

Valvulineria bradyana 40–80 60

Globocassidulina subglobosa N60 200

Melonis padanum N60 200


various benthic foraminiferal groups, with different

ecological requirements.

We re-analysed existing data of the literature (Jor-

issen, 1987) in order to have more insight into the

bathymetrical distribution of the 24 dominant species

of the analysed cores and to depict the bathymetrical

distribution of the most frequent benthic foraminiferal

taxa in the central Adriatic mud-belt. Among the sites

studied by Jorissen (1987), we chose those stations

positioned on the mud-belt in the central area of the

Adriatic Sea, with water depths between 13 to 80 m.

The data of Jorissen (1988) are based only on the

N150 Am size fraction, and not on the N63 Am frac-

tion that was used for our study. Although the study of

the larger size fraction does not represent many smal-

ler species, it does correctly represent the bathymetri-

cal range of the larger species, on which our

bathymetrical reconstructions are based.

Finally, a paleo-bathymetric reconstruction was

performed based on the Recent bathymetrical distri-

bution of the 24 benthic foraminiferal species consid-

ered for the cluster analysis. For each species we

calculated the weighted mean water depth (MWD),

on the bases of the distribution of the recent dataset,

according to the following formula:

MWD ¼X

PxTWDxð Þ.X

Px x ¼ 1; i

where Px is the percentage of the species in each of

the i samples and WDx is the water depth of each of

the i samples.

For the species which have only part of the bathy-

metrical range in the studied depth interval (20–80

m), we attributed arbitrarily values (see Table 3) on

E.

crispum

E.

decipiens

G.

praegeri

G.

oblonga

H.

balthica

M.

padanum

N.

turgida

P.

granosum

R.

spinulosa

T.

sagittula

T.

angulosa

V.

bradyana

Other

species

Total

3 5 2 3 0 4 7 4 3 6 0 0 34 100

6 6 3 2 0 3 6 4 2 5 0 0 40 100

5 8 2 4 0 2 5 3 3 7 0 0 34 100

6 4 2 5 0 2 9 5 4 5 0 0 34 100

6 8 6 4 0 2 3 6 4 8 0 0 28 100

2 10 7 2 0 0 2 7 5 8 0 0 24 100

3 8 5 0 0 0 2 5 1 6 0 0 29 100

4 6 5 0 0 1 1 7 3 8 0 0 27 100

7 3 2 1 1 0 0 9 4 12 0 0 25 100

6 7 3 1 2 0 1 6 7 15 0 0 24 100

3 7 4 1 7 0 2 5 4 13 5 0 22 100

6 6 0 0 3 1 2 7 5 16 1 0 20 100

7 13 0 0 1 0 4 9 7 23 1 0 10 100

6 14 1 0 0 1 7 7 6 18 1 0 14 100

1 15 0 0 0 0 8 5 4 17 0 0 25 100


the bases of their depth distribution as described by

Jorissen (1988).

In order to calculate the estimated paleo water-

depth (EWD) of each sediment sample of the cores,

we followed an opposite strategy, and multiplied for

each species found in the sample the weighted mean

water depth determinated before, with its percentage:

EWD ¼X

PxTMWDxð Þ.X

Px x ¼ 1; i

50

100

150

200

Dep

th (

cm)

Number

Ad 87-21 Ad 87-16P/

2500 10 20 30 40 50 0 10 20 30 40 50

00 10%5 10%50

Fig. 3. Number of benthic foraminiferal species identified and number

foraminifera referred as P / (P+B) ratio in the cores.

4. Results

4.1. Faunal and cluster analysis of the gravity cores

Approximately 70 benthic foraminifera species be-

longing to 50 genera (see taxonomic list) and 11

planktonic foraminifera species have been identified

in the 63 samples studied (Table 2). The number of

benthic specimens counted varied from 286 to 667.

Ad 87-17Ad 87-20

of species

(P+B)

0 10 20 30 40 500 10 20 30 40 50

0 10%50 10%5

of planktonic foraminifera versus number of benthic+planktonic


The number of species ranges from 18 to 41 (Fig. 3),

with the highest values in the upper part of the cores.

Planktonic foraminifera are only present in the

upper part of the cores and always in low numbers.

The planktonic foraminifera assemblages principally

consist of Globigerina bulloides, Globigerinoides

ruber (white and pink variety), Globigerinoides trilo-

bus and Orbulina universa. The P-B index (P /P+B),

reported in Fig. 3, shows the highest values in cores

21 and 16.

From the cluster analysis we obtained a dendro-

gram (Fig. 4) that shows 6 clusters of benthic forami-

nifera if a cut-off level of 0.25 is used. Only the taxon

Protelphidium granosum shows a very low correla-

tion with all the other species and can not be related to

any of the clusters.

The frequencies of the taxa belonging to these

clusters have been summed and have been plotted

A. perlucida

A. beccarii

A. papillosa

N. turgida

E. advenum

E. decipiens

H. balthicaT. angulosa

C. lobatulus

B. granulata

T. agglutinans

R. spinulosa

E. crispum

G. praegeri

Bulimina spp.

Bolivina spp.

C. carinata

A. mamilla

P. granosum

B. marginata

V. bradyana

G. oblonga

M. padanum

1 0.9 0.8 0.7

A. tepidaCluster A

Cluster B

Cluster C

Cluster D

Cluster E

Cluster F

Fig. 4. Dendrogram resulting from a R-mode cluster analysis on the basi

the cores.

for each core (Fig. 5). In the following paragraphs

we describe the cluster content, their bathymetrical

distribution in the recent data, and their behaviour in

the studied cores.

A. Cluster A is exclusively composed of Ammonia

species: A. beccarii, A. tepida and A. perlucida.

Cluster A shows a sharp peak in the lower part

of all cores. In particular, in core 21 this cluster

accounts for 80% of the total assemblages. In

core 16 and 20, the maximum value is about

20%. Finally, in core 17 cluster A has a lower

maximum percentage (about 6%), but still

shows a peak in the lower part of the core.

B. Cluster B consists of 4 species: Ammonia papil-

losa, Nonionella turgida, Elphidium advenum

and Elphidium decipiens. In core 21 cluster B

shows a fluctuating trend with maximum values

0.6 0.5 0.4 0.3 0.2 0.1 0

s of the relative frequencies of the 21 most frequent taxa found in

0 20% 0 30% 0 10% 0 50% 0 50% 0 20%0

50

100

150

200

Dep

th (

cm)

Ad 87-16

0 80% 0 40% 0 10% 0 50% 0 60% 0 30%0

50

100

150

200

Dep

th (

cm)

250

Biofac

iesCluster B Cluster C Cluster D Cluster E Cluster F

Ad 87-21

Cluster A

II

VI

V

IV

III

I

pT

Litho

logy

V

IV

II

pT

VI

III

0

20

40

60

80

0

20

40

60

80Dep

th (

cm)

120

100

0 20% 0 30% 0 10% 0 50% 0 50% 0 20%

Ad 87-17

Dep

th (

cm)

Biofac

ies

Litho

logy

IV

pT

II

V

IV

pT

II

V

III

Cluster A Cluster B Cluster C Cluster D Cluster E Cluster F

0 20% 0 30% 0 10% 0 50% 0 50% 0 20%

Ad 87-20

Fig. 5. Downcore distribution of the cumulative percentages of the 6 clusters in the studied cores. Lithology and biofacies are indicated for each

core.



between 210 and 180 cm. In core 16, cluster B

is more abundant from the bottom to 140 cm

and shows a minimum at 105 cm. Values in the

upper part of the core are constant around 10%.

Cores 20 and 17 show no trend, with fluctuat-

ing percentages between 6% and 14%. In par-

ticular, a strong minimum is observed in core

17 at 45 cm.

C. Only two taxa, Hyalinea balthica and Trifarina

angulosa, are grouped in cluster C. This cluster

shows very low values in all the cores, with one

sharp peak from 170 to 140 cm in core 21, and

from 140 to 110 cm in core 16. A peak is also

Cluste

Nonionella turgida

0

20

40

60

80

0 10 20 30 40 50%Elphidium a

0

20

40

60

80

0 5 10

Ammonia

0

40

60

80

0 10 20

20

Wat

er d

epth

(m

eter

s)

0

20

40

60

80

0 20 30 30%

Wat

er d

epth

(m

eter

s)

Ammonia beccarii

Clustea

Fig. 6. a–b — Distribution of the recent benthic foraminiferal fauna in 41

grouped into clusters as explained in the text. Cluster C is not shown, since

sediment samples. Also the graph of Ammonia papillosa (Cluster C) and

species are not present in the Recent sediment samples selected for this s

present in the other two cores, but with lower

percentages (less than 5%).

D. Cluster D contains 5 species, Cibicides loba-

tulus, Buccella granulata, Reussella spinulosa,

Textularia agglutinans and Elphidium crispum.

In core 21 cluster D shows a similar tendency

as cluster B. The same trend is present in core

16, with the highest values between 150 to

100 cm. In core 20 this cluster shows a de-

creasing trend from the bottom to the top of

the core. Finally, in core 17 there is no an

evident trend with fluctuating percentages be-

tween 17% to 30%.

r B

Ammonia perlucida

0

20

40

60

80

0 10 20 30%

Elphidium decipiens

0

20

40

60

80

0 5 10 15 20%dvenum

15 20%

tepida30 40 50%

r A

stations of the Central Adriatic Sea (Jorissen, 1987). The species are

Hyalinea balthica and Trifarina angulosa are not present in Recent

Asterigerinata mamilla (Cluster E) are not included because these

tudy.


E. Cluster E consists of 5 taxa, Bulimina spp.,

Gavelinopsis praegeri, Bolivina spp., Cassidu-

lina neocarinata and Asterigerinata mamilla.

Core 21 shows very low values in the lower

part of the core, then the percentages quickly

increase from 210 cm on, until a maximum

between 130 and 100 cm (more than 50%). In

Cibicides lobatulus

0

20

40

60

80

0 5 10%

Buccella granulata

0

20

40

60

80

0 5 10%

Reussella s

0

20

40

60

80

0 5

Gavelinopsis praegeri

0

20

40

60

80

0 5 10%0

20

40

60

80

0

Valvulineria bradyana

0 10 200

20

40

60

80

30%0

20

40

60

80

0

Bulimina marginata

0

20

40

60

80

0 10 20 30 40 50%

Bulimina spp.

0

20

40

60

80

0 10 20 30 40 50%

Wat

er d

epth

(m

eter

s)

Cluster F

Wat

er d

epth

(m

eter

s)

Cluster D

Cluster E

Wat

er d

epth

(m

eter

s)

b

Fig. 6 (conti

core 16 a similar trend can be observed. In core

20, however, cluster E shows an increasing trend

from the bottom to the top of the core, ranging

from 15% to 45%. Finally, in core 17 cluster E

shows an increasing trend from the base to 30

cm (from 20% to more than 40%), and a slight

decrease in the upper part of the core.

pinulosa

10%

Textularia agglutinans

0

20

40

60

80

0 5 10 15 20%

Elphidium crispum

0

20

40

60

80

0 5 10%

Brizalina catanensis

5 10%

Cassidulina neocarinata

0

20

40

60

80

0 5 10%

Globocassidulina oblonga

5 10%

Melonis padanum

0

20

40

60

80

0 10 20%

nued).


F. Cluster F consists of Bulimina marginata, Val-

vulineria bradyana, Globocassidulina subglo-

bosa and Melonis padanum. The relative

abundances of Cluster F are consistent among

cores; values are low in the first part of the

cores, and steadily increase towards the top,

with the exception of core 17 that shows a

decreasing trend in the upper 20 cm.

4.2. Modern benthic foraminiferal community in the

Conero area

We selected 41 stations from the paper of Jorissen

(1987) (water depth 13 to 80 m) and we considered 24

taxa for each sample. Fig. 6a–b show the percentages

of these species in the samples plotted as a function of

water depth. The distribution of many species shows a

strong relationship with water depth. For example,

Ammonia perlucida, Ammonia tepida and Elphidium

advenum are mainly limited to shallow water depths,

30 m or less. Bulimina marginata shows its maximum

percentage between 40–60 m water depth, whereas

Valvulineria bradyana appears deeper than 30 m

water depth. The other species of Bulimina, grouped

together as Bulimina spp., have a maximum frequency

at deeper sites, around 70 m water depth. Asteriger-

inata mamilla, Bolivina spp., Cassidulina neocari-

nata, Cibicides lobatulus, Gavelinopsis praegeri,

Globocassidulina oblonga and Melonis padanum

are present only in the deepest stations (N60 m), albeit

in low percentages. Some species (Buccella granu-

lata, Elphidium crispum, Elphidium decipiens, Non-

ionella turgida, Protelphidium granosum, Reussella

spinulosa, Textularia agglutinans) do not show a

clear relation with water depth, suggesting that other

environmental parameters have a stronger influence

on their bathymetrical distribution. Ammonia papil-

losa, Asterigerinata mamilla, Hyalinea balthica and

Trifarina angulosa, that are present in core material,

have not been observed in Recent samples. Jorissen

(1987) shows an upper distribution limit of 80 m for

Hyalinea balthica and of 90 m for Trifarina angulosa.

For this reason they are not shown in Fig. 3.

4.3. Chronology of the cores

The sedimentological analyses of the cores clearly

indicate the boundary between alluvial plain and

marine deposits, corresponding to the transgressive

surface (Fig. 2). In cores collected in the western

inner shelf of the central Adriatic basin (RF95-13,

water depth 77 m; RF 95-14, water depth 72 m;

Cattaneo and Trincardi, 1999; Cattaneo et al., 1997;

Asioli et al., 2001) this surface has an age ranging

between 11 to 10 Kyr BP. According to the same

authors, the base of the mud sediments corresponds

to the high system track and is dated at 5.5 Kyr BP.

Asioli (1996) observed the disappearance of H.

balthica coinciding to this change in sedimentolog-

ical features (onset of the mud-belt formation). In

our cores, the disappearance of H. balthica generally

corresponds to a sedimentological change to more

muddy sediments (Fig. 2). Only in core 16 disap-

pearances is situated in the middle of a clayey silt

interval. However, the percentage of clay increases

from 26% at 113 cm to 33% at 93 cm.

The faunas found in the topmost samples of the

studied cores are very similar to the Recent fauna.

Surface samples of cores 21 and 16 consist of V.

bradyana, Bulimina spp. and E. decipiens, a fauna

that according to Jorissen (1987) corresponds to the

central part of the mud-belt. Cassidulina neocarinata

and Bulimina spp., which characterise the outer part

of the modern mud-belt, dominate the benthic micro-

fauna of the top of the cores 17 and 20. Although no

non-fossilising agglutinant foraminifera were found,

these similarities suggest that the top of our cores is

representative of the Recent situation.

5. Discussion

We distinguish seven biofacies (the six clusters

plus a pre-Holocene assemblage) in the 4 gravity

cores. The stratigraphic boundaries are based on

both appearance and disappearance of the foraminif-

eral species and/or the fluctuations in their abundance.

The limits of the biofacies are reported in Table 4. The

results of the cluster analysis that resulted in a subdi-

vision with six faunal associations also allow to rec-

ognise six different benthic environments, inhabited

by typical species groups. In this way the species that

compose the different clusters allow us to obtain

further details about environmental parameters, such

as water depth, organic matter input, turbulence, etc.

Furthermore we consider a separate biofacies (Biofa-

Table 4

Boundaries of the biofacies in the four cores

Biofacies Core 21

(cm)

Core 16

(cm)

Core 20

(cm)

Core 17

(cm)

VI 0–45 0–45 – –

V 45–85 45–65 0–20 0–47

IV 85–135 65–110 20–68 47–70

III 135–175 110–145 68–82 –

II 175–215 145–165 82–106 70–80

I 215–240 – – –

pT 240–bottom 165–bottom 106–bottom 80–bottom


cies pT) corresponding to the lower stratigraphic unit.

This includes the alluvial plain deposits and is char-

acterised by the absence of foraminifera and the pres-

ence of terrestrial gastropods. The topmost part of this

biofacies shows an erosional surface, characterised by

the presence of shell debris, and the appearance of few

shallow marine benthic foraminifera.

In core 21, the high abundance of cluster A (Am-

monia species forming about 80% of the total associ-

ation) (Fig. 6a) at the bottom of the transgressive

surface suggests a rather shallow depth. Jorissen

(1987) found that in the Adriatic Sea, A. beccarii

dominates the coastal shallow-water stations (depth

shallower than 20 m). Furthermore, some authors

(Scott et al., 1976; Murray, 1991; Debenay et al.,

1998; Serandrei-Barbero et al., 1999; Horton, 1999;

Horton et al., 2005) found rich populations of A.

beccarii and A. tepida in estuaries and lagoons of

southern California, Brazil, Venice lagoon, UK, Aus-

tralia, Indonesia, respectively, where salinity ranges

between 15x and 68x. In core 21, beside the pres-

ence of A. beccarii, the assemblages also show abun-

dant A. tepida and A. perlucida, whereas in cores 16,

17 and 20 A. beccarii dominates the assemblages.

According to Jorissen (1987) A. tepida (referred to

as A. parkinsoniana) also lives in very shallow water

(10 and 20 m water depth) and tolerates lower salinity.

It appears closely related to the Po runoff system. This

suggests that the interval dominated by cluster A,

corresponding to Biofacies I, reflects shallow and

restricted water environments that may be affected

by salinity variations due to the nearby presence of

river runoff. A very low number of species charac-

terises the oligotipic association, reflecting the insta-

bility of the system. This biofacies is not present in

core 20, 17 and 16.

A second interval (Biofacies II) shows increasing

percentages of A. papillosa, N. turgida (cluster B) and

epiphytic taxa (cluster D) such as C. lobatulus, B.

granulata, R. spinulosa, and E. crispum (Kitazato,

1988; Langer, 1988). Ammonia papillosa, character-

istic of sandy substrate and strong hydrodynamic

energy (Tomadin et al., 1984), shows a clear peak at

the base of this interval. Upward, this species, as well

as epiphytic taxa, are gradually replaced by N. tur-

gida. This succession of events suggests a decrease of

hydrodynamic energy, probably caused by an increase

of water depth. The gradual disappearance of the

epiphytic species and the subsequent increase of

mud-dwelling taxa, such as N. turgida (Barmawidjaja

et al., 1992), imply that the vegetation cover gradually

disappeared, and clay input becomes more important.

This sequence of events, observed in core 21, suggests

a change in the hydrodynamic system. An increasing

value of the number of species from the bottom to the

top of this interval testifies a larger stability of the

benthic ecosystem. The first appearance of planktonic

foraminifera and the corresponding low values of the

P / (P+B) ratio, suggest a water depth deeper than 30

m (Van der Zwaan et al., 1990).

Next, a third assemblage occurs (Biofacies III),

with maximum abundances of Hyalinea balthica and

Trifarina angulosa (cluster C). Also Bulimina spp.

achieves its highest percentage whereas the epiphytic

species strongly decrease. Living specimens of H.

balthica are found in the Tyrrhenian Sea, at a

depth of 56–110 m (Bergamin and Di Bella, 1997),

but also occur at bathyal depths (800–900 m water

depth) (Schmiedl et al., 2000), indicating that other

parameters than water depth control the appearance

of this species. This taxon shows its maximum abun-

dance in samples with the highest diversity, indicat-

ing little ecological stress (Bergamin and Di Bella,

1997; Schmiedl et al., 2000). Hyalinea balthica and

T. angulosa are very abundant at high latitudes, in

cold water (9–13 8C) and in muddy sand substrate

(Murray, 1991). Jorissen (1988) noted that in modern

samples these two taxa are not present in the mud-

belt area, but they are characteristic of the upper-

slope of the Adriatic Sea (water depth 100–200 m).

The number of species reaches relatively high values,

confirming the favourable environmental conditions

at the sea floor. Moreover, the P / (P+B) ratio reaches

high values, testifying that the conditions of the


water column permit the life of some planktonic

foraminifera (Globigerina bulloides, Globigerinoides

ruber, Orbulina universa, Turborotalita quinque-

loba), albeit in small number. This biofacies is not

present in core 17.

The fourth benthic assemblage (Biofacies IV) is

characterised by a low number of species. C. neocar-

inata, Bolivina spp. and Bulimina spp. (cluster E)

dominate. These taxa are typical of an area with

high organic flux to the sea floor. C. neocarinata

has a low dead / living ratio in upwelling areas of

Cap Blanc, which implies an opportunistic life strat-

egy (Jorissen and Wittling, 1999). According to this

study, after the deposition of fresh phytodetritus at the

seafloor, this taxon increases in density to take advan-

tage of the short-term food availability. The composi-

tion of this assemblage implies an unstable

environment, where seasonal pulses of organic matter

sustain the benthic microfauna (Jorissen and Wittling,

1999; Morigi et al., 2001). In the Adriatic Sea, De

Stigter et al. (1998), described Cassidulina laevigata

(as Cassidulina neocarinata) in the outer shelf area as

a superior competitor for food in oxygen-rich surface

microhabitats. Furthermore, oxygen concentrations

may have fluctuated during this interval, since organic

pulses could provoke seasonal dysoxia. Thus, the high

percentages of Bolivina genera could be related to

relative prolonged periods of dysoxia at the sea bot-

tom (Bernhard and Sen Gupta, 1999), periodically

following the strong input of organic matter to the

sea floor.

The fifth interval (Biofacies V) shows a higher

number of species. This interval shows a strong dim-

inution of the percentage of C. neocarinata and the re-

occurrence of B. marginata. The interval is marked by

a slight increase in the percentages of taxa typical of

clusters B and D, in particular of N. turgida and

epiphytic species. N. turgida is a mud-dwelling epi-

faunal taxon, abundantly found in eutrophic shallow

areas of the north Adriatic Sea (Barmawidjaja et al.,

1992; Morigi et al., 1998; Duijnstee et al., 2004),

according to other studies (e.g. Corliss and Emerson,

1990) it belongs to infauna. This species seems to

survive in dysoxic habitats and also under anoxic

conditions for considerable periods of time (Moodley

et al., 1998; Bernhard and Sen Gupta, 1999). Today,

this benthic assemblage occurs in the central part of

the mud-belt, where strongly stressed conditions (an-

oxic situation in the summer season) have been

recorded (Jorissen, 1988; Duijnstee et al., 2004).

Finally, Biofacies VI, which is dominated by Val-

vulineria bradyana, is found in the upper part of cores

21 and 16. This zone records a sharp increase in

percentages of B. marginata and M. padanum, togeth-

er with a decrease of B. granulata, N. turgida and A.

mamilla. According to several studies (e.g. Jorissen et

al., 1992; Hohenegger et al., 1993) based on ecolog-

ical observation on living benthic foraminifer associa-

tions, M. padanum and B. marginata appear to have

an intermediate deep infaunal microhabitat, and usu-

ally indicate a high, continuous flux of organic matter

to the seafloor. In strongly dysoxic sediments, how-

ever, these taxa could move to superficial sediments,

and take over the niches of less resistant taxa (Van der

Zwaan and Jorissen, 1991). Jorissen (1987) describes

a minimum water depth of 40 m for V. bradyana, in

combination with stressed conditions. This biofacies

could eventually reflect a human impact on the marine

environment, such as increased organic matter input

associated with industrial development, but could

simply reflect a progradational phenomenon. Clay

input and organic carbon flux increase in a very

significant way because the sedimentological system

shows an eastward progradational shift.

A tentative paleo-bathymetric reconstruction has

been made using a weighted mean of the benthic

foraminifera relative abundances and the mean of the

bathymetric distribution obtained considering their

modern distribution. The water depth curve obtained

for core 21 is presented in Fig. 7, together with the

planktonic /benthic ratio. The water depth curve

shows in the first part after the marine transgression

(Biofacies I) a shallow environment (0–40 m water

depth) with fauna on a vegetated, sandy substrate,

followed by a rapid deepening phase (Biofacies II —

40–60 m water depth) where sediments become finer

but vegetation is still present. Subsequently, after the

increasing trend a stationary level is reached (65 m

water depth), corresponding to the environment that

we find today outside (seaward) of the mud-belt

(Biofacies III). The maximum sea level is reached

in the middle of Biofacies IV (more than 80 m water

depth) and finally sea level remains more or less

stable in the upper part of the core corresponding to

Biofacies V and VI. The planktonic /benthic ratio,

although it does not provide a quantitative estimate

P/(P+B)

AD87-16

V

IV

pT

VI

110

cm

AD87-20

V

pT

IV68 c

m

AD87-17

V

pT

IV

70 c

m

AD87-21

VI

V

IV

pT

135

cm

Pre-Transgressive deposit

Mud-belt

Circalitoral deposit

0% 10% 20%

0 40 60 80 10020

50

100

150

200

250(cm)

0

Paleodepth (m)

II

III

II

II

II

III

I

III

Fig. 7. Scheme of the distribution of biofacies in the four cores and reconstructed bathymetrical evolution. Numbers indicate the successive

biofacies. The thickness of mud-belt deposits is given for every core.


of the water depth, it confirms the general trend of

this bathymetrical evolution. The qualitative estimate

made with the P / (P+B) ratio is in according with

the paleodepth reconstruction obtained with the ben-

thic foraminifera. Only in the Biofacies IV the two

curves present an opposite trend, P / (P+B) ratio

indicates a shallowing phase, whereas the benthic

curve shows a maximum sea level. As discussed

above Biofacies IV is characterised by the presence

of opportunistic taxa and infaunal taxa adapted to

dysoxic period. In both cases, pulsed organic flux to

the sea floor followed by periods of dysoxia at the

sea bottom could provoke an increase in the popu-

lation size of benthic foraminifera (Verhallen, 1987).

The strong increase of number of benthic foraminif-

era in comparison to the relatively low number of

planktonic foraminifera could explain this decreasing

trend in the P / (P+B) ratio.

The mud-belt starts to develop when the maxi-

mum water depth is reached. Its development leads

to a temporal succession of ecological niches for the

benthic community, reflected by compositional

changes of the microfaunal assemblages. The evolu-

tion of the mud-belt shows different phases: initial

phase characterised by silty sediments and favourable

environmental conditions, both for planktonic and

benthic foraminiferal microfauna (Biofacies III).

This is followed by a phase of instability inferred

from the presence of opportunistic benthic taxa (Bio-

facies IV). This biofacies is probably influenced by

pulses of organic matter periodically arriving at the

sea bottom. At this stage the benthic ecosystem starts

to be under the influence of Po-derived food input,

causing a first stage of ecosystem eutrophication. A

significant change is represented by Biofacies V,

indicating an increase of organic matter and clay

input to still higher values. This biofacies indicates

that the center of the mud-belt is shifting eastward

towards deeper water. However, only in Biofacies VI,

the core sites became located in the centre of the

eutrophicated area, with maximal abundances of the

Valvulineria assemblage. These changes, caused by


the ongoing seaward shift of the clay depocenter over

time, caused a continuous increase of the organic

matter input to the sea floor, and probably also

provoked increasingly dysoxic conditions in the ben-

thic ecosystem. This phase corresponds to the Recent

configuration of the mud-belt, with the 60–80 m

depth zone inhabited by mud-dwelling taxa resistant

to seasonal dysoxia occurring together with taxa

requiring a high organic carbon flux.

Summarising, two main stages can be recognised

in the development of the Holocene outer shelf sedi-

mentation system. In the first stage represented by our

Biofacies I to III, the succession of the benthic faunas

is mainly controlled by the ongoing sea level rise, and

represents a bathymetrical succession of foraminiferal

assemblages. In the second stage, represented by Bio-

facies IV to VI, on the contrary sea level was more or

less stable, and the benthic foraminiferal faunas are

controlled by organic matter input (ultimately result-

ing from Po discharge) and related dysoxia. The

succession of three biofacies is caused by a progres-

sive deepening of the organic matter depocenter, prob-

ably as a result a progressively changing surface

current pattern.

6. Conclusions

This detailed microfossil study presents informa-

tion on Holocene paleoenvironmental changes related

to water depth fluctuations and changes in sedimen-

tation pattern. The benthic foraminiferal assemblages

change in relation to the Holocene sea level rise,

recording the transition from alluvial plain deposits

to fully marine environments. The integrated analysis

of the four cores reveals the succession of events that

have formed the mud-belt. A lagoon or restricted

marine environment is recorded in the southern site,

as soon as the transgression arrived at this latitude.

The rapid increase of water depth created the sharp

succession of events. The gradual disappearance of

the epiphytic taxa due to the input of fine-grained

Plate I. All scale bars=100 Am. 1 — Ammonia tepida, a: apertural view, b

ventral view, b: apertural view (Ad87-21/230–232 cm); 3 — Ammonia bec

Ammonia papillosa, a: ventral view, b: lateral view (Ad87-21/210–212 cm)

40–42 cm); 6 — Asterigerinata mamilla, a: ventral view, b: dorsal view

dorsal view (Ad87-21/190–192 cm) (See page 19).

sediments is followed by a Hyalinea–Trifarina assem-

blage, which testifies a rise to maximum sea-level,

comparable, or even slightly higher than today. Sub-

sequently, a mud-dwelling assemblage colonised the

sea bottom. The Recent benthic community of the

outer part of the mud-belt (cores 21 and 16) is char-

acterised by an adaptation to more stressed conditions

due to higher concentration of organic matter that co-

varies with decrease of oxygen availability. The ben-

thic communities of surficial sediments of cores 20

and 17, on the contrary, seem to represent a transi-

tional environment from the outer part of the mud-belt

to normal open marine sediments.

Acknowledgments

The authors wish to express their gratitude the

reviewers, Robin Edwards and Gerhard Schmiedl,

and the Editor, Andreas Mackensen, for their help

and advice. The authors are indebted with Paolo

Ferrieri for assistance during SEM images acquisition.

Appendix A. Faunal list

Foraminifera species observed in this study. Iden-

tification and naming of the taxa are based on Jorissen

(1987). Plate and figure numbers refer to taxa illus-

trated in this paper.

Ammonia beccarii (Linne) = Nautilus beccarii

Linne, 1758 (Plate I — Fig. 3 a–b).0

Ammonia inflata (Seguenza) = Rosalina inflata

Seguenza, 1862.

Ammonia papillosa (d’Orbigny) = Rotalia papil-

losa d’Orbigny, 1850 (Plate I — Fig. 4 a–b).

Ammonia perlucida (Heron-Allen and Earland) =

Rotalia perlucida Heron-Allen and Earland, 1913

(Plate I — Fig. 2 a–b).

Ammonia tepida (Cushman) = Rotalia beccarii

(Linne) var. tepida Cushman, 1926 (Plate I — Fig.

1 a–b).

: ventral view (Ad87-21/230–232 cm); 2 — Ammonia perlucida, a:

carii, a: ventral view, b: apertural view (Ad87-20/104–106 cm); 4 —

; 5 —Melonis padanum, a: lateral view, b: apertural view (Ad87-21/

(Ad87-20/38–40 cm); 7 — Nonionella turgida, a: ventral view, b:


Amphicoryna scalaris (Batsch) = Nautilus scalaris

Batsch, 1791.

Asterigerinata mamilla (Williamson) = Rotalina

mamilla Williamson, 1858 (Plate I — Fig. 6 a–b).

Bigenerina nodosaria d’Orbigny, 1826 (Plate III

— Fig. 22). Bolivina spp. All species of the genus

Bolivina d’Orbigny, 1839 are included (Plate II — Fig.

14 a–b).

Brizalina catanensis (Seguenza) = Bolivina cata-

nensis Seguenza, 1862.

Buccella granulata (Cushman) = Eponides frigi-

dus (Cushman) var. granulata di Napoli, 1952 (Plate

II — Fig. 8 a–c).

Bulimina marginata d’Orbigny, 1826 (Plate III —

Fig. 18 a–b).

Bulimina spp. All elongate species without under-

cut of the genus Bulimina d’Orbigny, 1826 are in-

cluded (Plate II — Fig. 13 a–b).

Cancris oblongus (d’Orbigny) = Valvulina

oblonga d’Orbigny, 1839.

Cancris spp. All species of the genus Cancris

Montfort, 1808 are included.

Cassidulina neocarinata Thalmann, 1950 (Plate

III — Fig. 15 a–c).

Cibicides lobatulus (Walker and Jacob) = Nautilus

lobatulus Walker and Jacob, 1798.

Cibicidoides pachyderma (Rzehak) = Truncatulina

pachyderma Rzehak, 1886.

Cornuspira spp. All species of the genus Cornus-

pira Schultze, 1854 are included.

Coryphostoma sp. All species belonging to the

genus Coryphostoma Loeblich and Tappan, 1962 are

included.

Dentalina spp. All species of the genus Dentalina

Schultze, 1854 are included.

Eggerella bradyi (Cushman) = Verneulina bradyi

Cushman, 1911.

Elphidium advenum (Cushman) = Polystomella

advena Cushman, 1922.

Elphidium crispum (Linne) = Nautilus crispus

Linne, 1758 (Plate II — Fig. 9 a–c).

Elphidium decipiens (Costa) = Polystomella deci-

piens Costa, 1856 (Plate II — Fig. 11 a–b).

Plate II. All scale bars=100 Am. 8 — Buccella granulata, a: ventral v

Elphidium crispum, a: lateral view, b: apertural view (Ad87-21/90–92 cm

11 — Elphidium decipiens, a: lateral view, b: apertural view (Ad87-21/1

view (Ad87-21/170–172 cm); 13 — Bulimina sp., lateral view (Ad87-21/

(Ad87-16/83–85 cm) (See page 20).

Epistomella spp. All species of the genus Episto-

minella Husezima and Maruhasi, 1944 are included.

Fissurina spp. All species of the genus Fissurina

Reuss, 1850 are included.

Florilus spp. All species of the genus Florilus

Montfort, 1808 are included.

Fursenkoina squammosa (d’Orbigny) = Virgulina

squammosa d’Orbigny, 1826.

Gavelinopsis praegeri (Heron-Allen and Ear-

land) = Discorbina praegeri Heron-Allen and Ear-

land, 1913.

Globobulimina affinis (d’Orbigny) = Bulimina affi-

nis d’Orbigny, 1839.

Globocassidulina oblonga (Reuss) = Cassidulina

oblonga Reuss, 1850.

Guttulina spp. All species of the genus Guttulina

d’Orbigny, 1839 are included.

Hanzawaia spp. All species of the genus Hanza-

waia Asano, 1944 are included.

Hyalinea balthica (Schroeter) = Nautilus balthicus

Schroeter, 1783 (Plate II — Fig. 12 a–b).

Lagena clavata (d’Orbigny) = Oolina clavata

d’Orbigny, 1846.

Lagena striata (d’Orbigny) = Oolina striata d’Or-

bigny, 1839.

Lenticulina spp. All species of the genus Lenticu-

lina Lamarck, 1804 are included.

Marginulina spp. All species of the genus Margin-

ulina d’Orbigny, 1826 are included.

Melonis padanum (Perconig) = Nonion padanum

Perconig, 1952 (Plate I — Fig. 5 a–b).

Nonionella turgida (Williamson) = Rotalina tur-

gida Williamson, 1858 (Plate I — Fig. 7 a–b).

Oolina squamosa (Montagu) = Vermiculum squa-

mosum Montagu, 1803.

Pleurostomella alternans Shwager, 1866.

Protelphidium granosum (d’Orbigny) = Nonionina

granosa d’Orbigny, 1846.

Pseudoclavulina crustata Cushman, 1936.

Pyrgo depressa (d’Orbigny) = Biloculina depressa

d’Orbigny, 1826.

Pyrgo oblonga (d’Orbigny) = Biloculina oblonga

d’Orbigny, 1839.

iew, b: apertural view, c: dorsal view (Ad87-16/53–55 cm); 9 —

); 10 — Trifarina angulosa, lateral view (Ad87-21/160–162 cm);

80–182 cm); 12 — Hyalinea balthica, a: lateral view, b: apertural

140–142 cm); 14 — Bolivina sp., a: lateral view, b: apertural view


Pyrgo spp. All species of the genus Pyrgo De-

france, 1824 are included. (Plate III — Fig. 20 a–b).

Quinqueloculina padana Perconig, 1954.

Quinqueloculina seminulum (Linne) = Serpula

seminulum Linne, 1758.

Quinqueloculina spp. All species, except Q.

padana and Q. seminulum, of the genus Quinquelo-

culina d’Orbigny, 1826 are included. (Plate III — Fig.

19 a–c).

Reussella spinulosa (Reuss) = Verneuilina spinu-

losa Reuss, 1850.

Sigmoilina spp. All species of the genus Sigmoi-

lina Schlumberger, 1887 are included.

Sigmoilinita tenuis (Czjzek) = Quinqueoculina ten-

uis Czjzek, 1848.

Sigmoilopsis schlumbergeri (Silvestri) = Sigmoi-

lina schlumbergeri Silvestri, 1904.

Spiroloculina depressa d’Orbigny, 1826.

Spiroloculina excavata d’Orbigny, 1846.

Stainforthia complanata (Egger) = Virgulina

schreibersiana Czjzek var. complanata Egger, 1893.

Textularia agglutinans D’Orbigny, 1839.

Trifarina angulosa (Williamson) = Uvigerina

angulosa Williamson, 1858 (Plate II — Fig. 10).

Triloculina austriaca d’Orbigny, 1846.

Triloculina spp. All species of the genus Trilocu-

lina d’Orbigny, 1826 are included.

Triloculina tricarinata d’Orbigny, 1826.

Uvigerina mediterranea Hofker, 1932.

Uvigerina peregrina Cushman, 1923 (Plate III —

Fig. 21).

Valvulineria bradyana (Fornasini) = Discorbina

bradyana Fornasini, 1900 (Plate III — Fig. 17 a–b).

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