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ABSTRACT
The Alano section has been presented at the
International Subcommission on Paleogene
Stratigraphy (ISPS) as a potential candidate
for defi ning the global boundary stratotype
section and point (GSSP) of the late Eocene
Priabonian Stage. The section is located in
the Venetian Southern Alps of the Veneto re-
gion (NE Italy), which is the type area of the
Priabonian, being exposed along the banks of
the Calcino torrent, near the village of Alano
di Piave. It consists of ~120–130 m of bathyal
gray marls interrupted in the lower part by
an 8-m-thick package of laminated dark to
black marlstones. Intercalated in the sec-
tion, there are eight prominent marker beds,
six of which are crystal tuff layers, whereas
the other two are bioclastic rudites. These
distinctive layers are useful for regional cor-
relation and for an easy recognition of the
various intervals of the section. The section
is easily accessible, crops out continuously, is
unaffected by any structural deformation,
is rich in calcareous plankton, and contains
an expanded record of the critical interval for
defi ning the GSSP of the Priabonian. In order
to further check the stratigraphic complete-
ness of the section and constrain in time the
critical interval for defi ning the Priabonian
Stage, we performed a high-resolution study
of integrated calcareous plankton biostratig-
raphy and a detailed magnetostratigraphic
analysis. Here, we present the results of these
studies to open a discussion on the criteria for
driving the “golden spike” that should defi ne
the middle Eocene–late Eocene boundary.
INTRODUCTION
Chronostratigraphy, the subdivision and
classi fi ca tion of Earth’s geologic record on the
base of time (Hedberg, 1976), represents the
most widely used “common language” of com-
munication in the earth sciences. The develop-
ment of a standard global chronostratigraphic
scale (GCS), based on rigorous agreement upon
stratigraphic principles, terminology, and clas-
sifi catory procedure, is one of the long-standing
objectives of the Inter national Commission on
Stratigraphy (ICS).
A fundamental step toward this goal is the
elaboration of a standard series and stage divi-
sion of each system, together with precise defi ni-
tion of boundaries between them (Bassett, 1985).
With regard to the latter effort, the principle has
become fi rmly accepted that the base of each
division be defi ned at a unique point in a rock
sequence, representing a unique point in time, to
serve as standard against which other sequences
can be correlated by the different available time
correlation tools. The standard section and point
of the defi nition are referred to as the global
boundary stratotype section and point (GSSP) of
the designated stratigraphic boundary.
During the last decades, signifi cant progress
has been made in establishing the standard GCS,
which, integrated with other tools for “geologic
time telling,” was synthesized in 2004 in an up-
dated geologic time scale (GTS04; Gradstein
et al., 2004). In the GTS04, the Paleogene Sys-
tem, that is the Paleocene, Eocene, and Oligo-
cene Series, remains in a state of major fl ux
(Berggren and Pearson, 2005; Hilgen, 2008)
for multiple reasons: (1) existing age models of
the geologic time scale (in pre-Oligocene times)
are not yet well established, (2) in some inter-
vals, the biomagnetostratigraphic framework
is confused because it is based on a limited
database, and (3) only the GSSPs of the basal
stages of the series (i.e., Danian, Ypresian, and
Rupelian) have been defi ned to date (Premoli
Silva and Jenkins, 1993; Molina et al., 2006c;
Aubry et al., 2007). As a result, the practice of
recognizing intraseries stages and subdivisions
is highly contradictory. For example, as reported
in Figure 1, the recognition of the base of the
Priabonian, i.e., the middle Eocene–late Eocene
boundary, varies by more than 1.5 m.y. among
various authors. In order to rapidly overcome
the current situation, the International Subcom-
mission on Paleogene Stratigraphy (ISPS) has
promoted working groups for defi ning all the
Paleogene stages, and proposals are expected
soon for all of them (Hilgen, 2008). Within this
activity of the ISPS, we were asked to explore
the possibility of defi ning the Priabonian Stage
in the Veneto region, NE Italy, where a classi-
cal record of early Paleogene stratigraphy is
preserved that has served as reference for intro-
ducing the Priabonian Stage for over a century
(Munier Chalmas and de Lapparent, 1893). All
the sections indicated by Munier Chalmas and
de Lapparent, located in the Lessini Mountains
and Berici Hills (western Veneto; Fig. 2), and
in particular, the stratotype section near the vil-
lage of Priabona, in the eastern Lessini Moun-
tains (Roveda, 1961; Hardenbol, 1968; Fig. 2),
were deposited in shallow-water sediments
that are diffi cult to precisely frame in time and,
hence, are unsuitable for usefully defi ning a
chronostratigraphic unit. Therefore, at the Eo-
cene Colloquium held in Paris in 1968 (Cita,
1969), several parastratotypes sections were
proposed, among which the deep-water section
of Possagno (Treviso Province; Fig. 2), where
For permission to copy, contact editing@geosociety.org
© 2011 Geological Society of America
841
GSA Bulletin; May/June 2011; v. 123; no. 5/6; p. 841–872; doi: 10.1130/B30158.1; 18 fi gures; 2 plates; 4 tables.
†E-mail: claudia.agnini@unipd.it
Integrated biomagnetostratigraphy of the Alano section (NE Italy):
A proposal for defi ning the middle-late Eocene boundary
Claudia Agnini1,2, Eliana Fornaciari1, Luca Giusberti1, Paolo Grandesso1, Luca Lanci3,4, Valeria Luciani5,
Giovanni Muttoni4,6, Heiko Pälike7, Domenico Rio1, David J.A. Spofforth7, and Cristina Stefani1
1Dipartimento di Geoscienze, Università di Padova, Via G. Gradenigo, I-35131 Padova, Italy
2Istituto di Geoscienze e Georisorse, CNR-Padova c/o Dipartimento di Geoscienze, Università di Padova, Via G. Gradenigo,
I-35131 Padova, Italy
3Facoltà di Scienze Ambientali, Università di Urbino, Loc. Crocicchia, 61029 Urbino, Italy
4Alpine Laboratory of Paleomagnetism (ALP), Via Madonna dei Boschi 76, I-12016 Peveragno (CN), Italy
5Dipartimento di Scienze della Terra—Polo Scientifi co Tecnologico, Università di Ferrara, Via G. Saragat, 1, I-44100, Ferrara, Italy
6Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, I-20133 Milano, Italy
7National Oceanography Centre, University of Southampton Waterfront Campus, European Way, SO14 3ZH Southampton, UK
Agnini et al.
842 Geological Society of America Bulletin, May/June 2011
2n
G. seminvoluta
G. index
Berggren and
Pearson, 2005
M. crassatus
O. beckmanni
G. nuttalli
M. aragonensis
G. kugleri
ADDITIONAL
BIOHORIZONS
G. seminvoluta
T. cunialensis
Cr. erbae AB
C. inflata FO
1n
1r
1n
3n
2r
2n
1r
2n
1n
1r
34
35
36
37
38
39
40
41
42
43
44
45
AGE
(Ma)
S. furcatolithoides
S. obtusus
Cr. erbae AE
C. reticulatum
E. obruta LCO
CP13b
NP15 NP16 NP17 NP
18
CP13c CP14a CP14b CP
15a CP15b CP16a
NP19-NP20 NP21 Martini, 1971
Okada and
Bukry, 1980
BKSA This work and Fornaciari et al. (2010)
E11
-
E10
(P12)
E9
(P11)
E12
(P13)
E13
(P15
pars)
E14
(P15
pars)
E15
(P16
pars)
E16
(P16
pars)
POLARITY
CHRON
I. recurvus
C. oamaruensis
R. umbilicus
C. solitus
C. grandis
D. saipanensis
C. gigas
B. gladius
S. pseudoradians
standard
biohorizon
E8
BARTONIAN PRIABONIAN
BKSA95
PLANKTIC
FORAMINIFERA
CALCAREOUS
NANNOFOSSILS
CHRONO
STRATIGRAPHY
CK95
LUTETIAN
BARTONIAN
LUTETIAN
GTS04
PRIABONIAN
UMBRIA-
MARCHE
BARTONIAN PRIABONIAN
D. bisectus LCO
MECO
(Bohaty & Zachos, 2003)
C 19r event
(Edgar et al., 2007)
PALEOCLIMATE
Temporary reversal
(Sexton et a., 2006)
stable and cool conditions
LUTETIAN
RUPE
LIAN
Late Eocene
warming event
(Bohaty and Zachos, 2003)
Cooling event
(Tripati et al., 2005)
Cooling event
(Villa et al., 2008)
Cooling event
(Villa et al., 2008)
Cooling event
(Vonhof et al., 2000)
Cooling trend
(Sexton et al., 2006)
Cooling trend
(Sexton et al., 2006)
Cooling trend
(Zachos et al., 2001)
long-term trend
warm ing event
cooling event
Oi-1 event
(Miller et al., 1991)
Cooling trend
(Sexton et al., 200 6)
20 40 60 80
CaCO
3 preservation
intervals
(Tripati et al., 2005)
SBZ 20
(N. retiatus, H. gracilis)
SBZ 19
(N. fabianii, D. prattii minor)
SBZ 18
(N. biedai, N. cyrenaicus)
SBZ 17
(Al. elongata, Al. fusiformis,
N. brognarti, N. perforatus)
“strati di Roncà”
early Bartonian
SBZ 16
(N.aturicus, Al. gigantea,
D. pulchra balatonica)
late Lutetian
SBZ 14
(Al. munieri, As. spira spira)
SBZ 15
(N. millecaput, N. crassus)
SBZ 13
(N. laevigatus, Al. stipes As. parva)
middle Lutetian
“strati di S. Giovanni Ilarione”
early Lutetian
SHALLOW BENTHIC
FORAMINIFERA SEA LEVEL
Miller et al., 2005
RUPE
LIAN
RUPE
LIAN
m
SBZ 21
C20r
C20n
C19r
C19n
C18r
C18r
C18n C17n
C16r
C16n
C15r
C15n
C13r
C13n
(N. vascus, N. fichteli)
SBZ
(Serra-Kiel, 1998)
STANDARD
BIOHORIZONS
CW
I. recurvus LCO
Figure 1. Time frame of the middle to late Eocene. The chronology is based on the geomagnetic polarity time scale (GPTS) of Cande and Kent (1995). Planktic foraminiferal
zones are from Berggren and Pearson (2005). Calcareous nannofossil standard zones are those of Martini (1971) and Okada and Bukry (1980); several additional calcareous
nannofossil biohorizons are also reported. Age estimations of calcareous plankton bioevents are after Berggren et al. (1995; BKSA95), Fornaciari et al. (2010), and this work.
The chonostratigraphies used are those previously proposed by Berggren et al. (1995; BKSA95) and more recently by Gradstein et al. (2004; GTS04). On the right, the main
paleoclimatic events and/or long-term trends are presented together with enhanced preservation interval of CaCO3 (Lyle et al., 2005; Tripati et al., 2005) and the sea-level
curve of Miller et al. (2005).
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 843
B
D
ALANO
section
SR 348
C
A
ALANO
DI PIAVE
PEDEROBBA
QUERO
SCHIEVENIN
PIAVE RIVER
Tomba Mt.
Pallon Mt.
Peurna Mt.
Sassumà Mt.
Santo Mt.
Tomatico Mt.
SEREN DEL
GRAPPA
Fontana
secca Mt.
syncline
anticline
fault
village
mount
1km
N
C
Cemetery
LOMBARDIAN BASIN
?
PERIADRIATIC LINEAMENT
11°55′4.87″E
45°54′51.10″N
100 km
D
Venezia
Figure 2. Geographic and geological context of the Alano section. (A) Paleogeographic reconstruction of the main
paleogeographic elements of the southern Alps during the Paleogene (adapted from Bosellini and Papazzoni, 2003).
(B) Simplifi ed geological scheme of the Southern Alps (adapted from Doglioni and Bosellini, 1987). (C) Simplifi ed
geological sketch of the study area. (D) Location map of the study area with indication of the Alano section. The best
access to the section (dashed line) is also reported.
Agnini et al.
844 Geological Society of America Bulletin, May/June 2011
calcareous plankton are abundant and facies
are suitable for long-distance correlations, was
particularly promising. The section was inten-
sively studied in the seventies (Bolli, 1975).
Unfortunately, the transition from the Middle to
the Upper Eocene is poorly outcropping, and no
meaningful proposal of the GSSP of the Pria-
bonian could be made. However, detailed geo-
logical mapping executed close to the village
of Alano di Piave, some 8 km NE of Possagno
(Treviso Province; Fig. 2), indicated that the
transition from the Middle to Upper Eocene was
present there in a deep-water, expanded succes-
sion that spectacularly outcrops with absolute
continuity (Fig. 3). This section, in the follow-
ing termed the Alano section, which has been
orally presented at the ISPS since 2004 (the an-
nual reports are available at the Web site http://
wzar.unizar.es/isps/priabonian2004.htm), is fi rst
described in this paper, wherein:
(1) we provide a detailed lithologic descrip-
tion and report a high-resolution integrated
calcareous plankton biostratigraphy and mag-
neto stratigraphy carried out in the section;
(2) we present an improved biomagnetostrati-
graphic framework of the middle to late Eocene
transition based on the results obtained from the
Alano section and data collected specifi cally
for this work on the calcareous nannofossils at
Ocean Drilling Program (ODP) Site 1052, in the
western North Atlantic, a reference section for
the time interval of interest here;
(3) we show that the Alano section is com-
plete, straddling the critical interval for defi ning
the middle Eocene–late Eocene boundary, and it
is well and widely correlatable worldwide;
(4) we propose a specifi c lithologic level in
the Alano section as the GSSP of the Priabonian,
discussing the rationale for the proposal in terms
of historical appropriateness and global correla-
tion; and
(5) we discuss the work that still is lacking for
making the geologic time scale at the transition
from the middle to late Eocene more reliable.
ALANO DI PIAVE SECTION
In the following, we provide general geo-
graphic and geologic information on the
Alano section, with a special emphasis in its
lithostratigraphy.
Location and Outcropping Conditions
The Alano section is located in the southern
part of the Belluno Province, Veneto region,
in NE Italy, ~8 km NNE from the well-known
deep-water Possagno section and ~50 km
NE from the Priabona section, the historical
strato type of the late Eocene Priabonian Stage
(Fig. 2). Its latitude is 45°54′51.10″N, and its
longitude is 11°55′4.87″E (WGS84).
The study section is exposed for ~500 m along
the banks of Calcino Creek, between the small
villages of Colmirano and Campo, ~1 km NE of
the Alano di Piave village (Fig. 2). In correspon-
dence to the section outcrop, Calcino Creek has
deeply eroded the Quaternary deposits (Figs. 3
and 4), exposing the marly substratum in banks
2 m up to 6 m high, along which the succession
outcrops with total continuity (Fig. 5).
The lithology is mainly represented by gray-
ish hemipelagic marls with intercalated numer-
ous millimeter-thick sandy-silty layers and 8- to
>6-cm-thick sandy-silty layers that represent
useful marker beds. Six of these thicker lay-
ers are crystal tuff layers and have been named
from the bottom to the top after famous Vene-
tian painters: Mantegna, Giorgione, Tiziano,
Tiepolo, Tintoretto, and Canaletto beds (Fig. 6);
the other two marker beds are biocalcarenite-
rudite beds and have been named Palladio and
Canova after famous Venetian artists (Fig. 6).
The general bedding strike is 130–140°N and
the dip is ~20°–25°. The section is unaffected
by any structural deformation. The numerous
thin sandy layers can be traced laterally and in-
dicate that no, not even small, fault is present in
the section. Actually, tectonic deformation in the
Southern Alps was less severe than elsewhere in
the Alps and Apennines (Channell and Medizza,
1981), thus making this region ideally suited for
studying the early Paleogene deep-water record
in on-land sections (Giusberti et al., 2007). In
addition, the marls outcropping in the Alano
section seem to have not been deeply buried,
as testifi ed by the good preservation of micro-
fossils and the scarce maturity of the organic
matter (Spofforth et al., 2010).
The section measured for the present work is
~105 m thick (Fig. 6). Above the study interval,
there are at least 15 m of continuously outcrop-
ping marls, followed downstream only by spot-
ted outcrops.
Access to the Section
The Alano di Piave village is easily reached
by regional road SR 348 and provincial road
SP10 (Fig. 2D). The best way to access the
section is to pass the small Colmirano village
and reach the soccer fi eld reported in Figure
2D. From the parking lot of the soccer fi eld to
the base of the section, there is an easy walk of
some 300–400 m in a plain grass fi eld (Fig. 2D).
Regional Geologic Context
The Veneto region is part of the eastern
Southern Alps (NE Italy; Fig. 2), a major struc-
tural element of the Alpine chain interpreted as
a south-verging fold-and-thrust belt (Doglioni
and Bosellini, 1987) resulting from the poly-
phasic deformation of the southern passive
continental margin of the Mesozoic Tethyan
Ocean (Bernoulli, 1972). This continental mar-
gin is interpreted either as a part of a promon-
tory of the Africa continent (Channell et al.,
1979; D’Argenio et al., 1980) or an independent
micro continent (Adria; e.g., Dercourt et al.,
1986). During the Middle–Late Triassic, this
area was characterized by extensive shallow-
water carbonate platforms (e.g., Dolomia prin-
cipale; Costa et al., 1996) that were broken up
during the Early Jurassic because of regional
rifting that resulted in the separation between
Europe and Africa. In particular, this process
led to the drowning of the entire Southern Alps,
where several NNE-SSW–trending “lows” and
“highs” began to develop. From east to west,
these are the Friuli Platform, the Belluno Basin ,
the Trento Platform (or Trento Plateau), and
the Lombardian Basin (Bernoulli and Jenkyns,
1974; Bernoulli et al., 1979; Winterer and Bose-
llini, 1981; Fig. 2A). As the rifting process came
to an end, widespread, rather uniform pelagic
sedimentation (Rosso Ammonitico Veronese,
Biancone, Scaglia Rossa; Costa et al., 1996)
began throughout the Southern Alps, spanning
from the Middle Jurassic to the early Eocene
(Bosellini, 1989; Channell et al., 1992). This
widespread pelagic sedimentation was termi-
nated in the early Eocene, when a major paleo-
geographic reorganization of the Southern Alps,
tied to the complex collision between Europe
and the African promontory (or Adria micro-
plate; Doglioni and Bosellini, 1987), occurred.
The former Trento Plateau was uplifted and
block-faulted, and signifi cant basic to ultrabasic
volcanic activity characterized the area in be-
tween the Garda Lake and the Brenta River since
the Paleocene (e.g., Beccaluva et al., 2007). An
articulated and complex paleogeography devel-
oped that resulted in rapid changes of facies,
from continental to deep marine deposits. In
the western part of the Veneto region, carbonate
shallow-water sedimentation resumed with the
formation of an articulated carbonate platform
referred to as Lessini Shelf (Bosellini, 1989; Fig.
2A). This platform represents, albeit reduced in
size, the renewed Trento Platform (Bosellini,
1989; Fig. 2). In the eastern part of the region,
where the Jurassic Belluno Basin was set, deep-
water sediments persisted up to early Eocene
time. These pelagic and hemipelagic sediments
attributable to the Scaglia Rossa (Dallanave
et al., 2009) were capped by a turbiditic succes-
sion, locally up to 1000 m thick, referred to as
the Flysch di Belluno (Stefani and Grandesso,
1991; Costa et al., 1996; Stefani et al., 2007),
which represents the foredeep deposits linked to
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 845
0 500 1000 m
bedding attitude
overturned bedding attitude
45°
27°
11°55′5″E
45°54′51″N
Alluvial, slope and landslide post-Last Glacial
Maximum (LGM) deposits – Holocene
Fluvioglacial and glacial syn-LGM deposits
Upper Pleistocene
Fluvial pre-LGM deposits
Middle Pleistocene
Marna di Possagno and “Marna scagliosa di Alano” –
Upper-Middle Eocene – Massive blue-gray clayey
marls; scaly olive-gray marls with bioclastic and
volcaniclastic layers.
Belluno flysch – Lower Eocene – Alternation
of yellowish graded biocalcirudites/calcarenites
or scattered laminated ochreous sandstones
and gray marls.
Scaglia rossa – Lower Eocene-Upper Cretaceous p.p. –
(pro parte) Gray and reddish marls alternating with red brown
or greenish limestones; pink or red cherty calcilutites,
with thin clayey interbeds in the lower part.
Biancone p.p. – Cretaceous p.p. – Whitish or light gray
thin-bedded calcilutites,with gray cherty lenses and
gray green-dark gray clay-marly intercalations,
common in the upper part; black shales at the top.
27°
65°
50°
65°
70°
50°
50°
65°
50° 20°
75°
50° 35°
55°
80°
40°
45°
45°
30°
70°
50°
40°
35°
27°
25°
25°
30°
25°
35°
20°
70°
65°
25°
20°
30°
20°
A
B
Figure 3. Geologic map of the study area. A legend with a detailed description of lithostratigraphic units is also reported in the lower part
of the fi gure (see text for discussion).
Agnini et al.
846 Geological Society of America Bulletin, May/June 2011
the erosion of the Dinaric chain; these sediments
become younger southwestward (Grandesso,
1976) due to the migration of the Dinaric thrusts
system (e.g., Doglioni and Bosellini, 1987). Be-
tween the Belluno Basin and the Lessini Shelf, a
transition area developed, where a hemipelagic
sedimentation, referable to Scaglia Rossa sensu
latu persisted up to the early–middle Eocene.
These deep-water deposits were later capped by
slope to outer-shelf marlstones and claystones,
referred to in the literature as Scaglia Cinerea
(see following) and Marna di Possagno from the
middle to late Eocene (Cita, 1975; Trevisani,
1997), that show a clear regressive trend eventu-
ally leading, in the advanced Priabonian, to the
deposition of inner-shelf mud and sand (upper
part of the Marna di Possagno) and shelf car-
bonates (Calcare di Santa Giustina). Both the
Alano and Possagno sections are located in this
transitional area.
Local Geologic Context
In order to frame the Alano section in its geo-
logic context, we provide a geological map of
the area (Fig. 3). The section is located in the
core of a wide fold that is W-E oriented and
composed of Upper Jurassic–Eocene deep-
water units (e.g., Biancone, Scaglia Rossa; Figs.
3 and 4). This fold is referred to as the Alano-
Segusino syncline and is located between the
Tomba Mountain anticline to the south and
the Grappa Mountain–Tomatico Mountain anti-
cline to the north, and it is bounded to the west by
the Schievenin line (Fig. 2C).
Lithostratigraphic Assignment
Despite the fact that the Paleogene of the
Veneto region has been investigated for a
long time, the lithostratigraphic assignment
of the succession outcropping at Alano is
not straightforward. The marly sediments at
Alano are virtually identical to those observed
in the upper part of the Carcoselle segment
of the classical Possagno section (middle Eo-
cene), where they have been referred to as
Scaglia Cinerea (Agnini et al., 2006). How-
ever, Scaglia Cinerea is one of the traditional
Italian lithostratigraphic units fi rst described
in the Umbria-Marche area by Bonarelli at the
end of nineteenth century (Bonarelli, 1891)
and later ascribed to late Eocene–Miocene age
(Canavari, 1894; Selli, 1954; Coccioni et al.,
1988). In addition, this term was improperly
used for describing a Paleocene lithostrati-
graphic unit outcropping in eastern part of the
Belluno Basin (Di Napoli Alliata et al., 1970).
The ambiguous signifi cance of this term cre-
ates confusion and uncertainty and should be
abandoned in the Veneto region. The litho-
logic assignment of the Alano section still
remains problematic, because at Alano , the
succession shows a carbonate content higher
than 20%, thus preventing a possible asso-
ciation with Marna di Possagno, which is de-
fi ned by CaCO3 values never exceeding 20%
(Cita, 1975).
Because none of the existing formational
units available can be properly applied to the
succession outcropping at Alano, we have de-
cided to provisionally and informally intro-
duce the term “Marna Scagliosa di Alano” for
referring to the entire succession of the Alano
section. However, it is noteworthy that at the
Possagno section, similar sediments, interposed
between Scaglia Rossa and Marna di Possagno ,
have been previously referred to as Scaglia
Cinerea . On this basis, we thus stress the strong
need for a systematic revision of the regional
Paleogene lithostratigraphy to overcome the
current situation.
Detailed Lithologic Description
We logged the lithology of the Alano sec-
tion at very high resolution with observation at
the centimeter scale. A simplifi ed columnar log
of the section is reported in Figure 5, together
with the CaCO3 contents (%) determined by the
EUROPA Scientifi c GEO 20–20 isotope mass
spectrometer (Spofforth et al., 2010). The rather
monotonous mudstone facies is interrupted by
a distinctive ~8-m-thick package of often lami-
nated dark to black, organic-rich clayey marls in
the lower part of the section. A repetitive charac-
teristic feature throughout the section is also the
presence of sandy-silty layers, six of which are
more prominent, being thicker than 6 cm.
Crystal Tuff Layers
In order to avoid repetitions in describing
the sandy-silty layers, in the following text,
we provide a general overview of the simi-
lar petro graphic characters while referring to
Table 1 for a detailed description of each layer.
These beds are dark gray–black in color, and a
millimeter- to centimeter-thick greenish plas-
tic clay is sometimes present at the top. There
is no evidence of current activity, while the
bed thickness is slightly laterally variable.
Quite abundant, small (4–10 mm in diameter),
horizontal to subvertical, cyclindrical burrows
sometimes fi lled with greenish clays, suggest
a quick depositional mechanism. The optical
analyses reveal that these layers are almost ex-
clusively made of angular crystal-shape twinned
or zoned feldspars, quartz grains, biotite fl akes,
vitric or microlithic volcanic rock fragments,
scarce heavy minerals, and sporadic bioclasts.
All data, which include mineralogical composi-
tion, grain size, lack of cementation, common
vertical burrowing, and the lack of current activ-
ity, point to a common volcanic source for these
type of layers, which are suspected to be tephra
layers, i.e., linked to fallout deposits. Due to
prevailing types of grains, they are classifi ed as
crystal tuffs (Schmid, 1981). The scattered bio-
clastic content is linked to common bioturbation
traces or to normal water-column deposition.
X-ray analyses on the clay intervals show great
abundance of Illite-Smectite clay (IS) material
(Tateo, 2009, personal commun.).
Lithozone Description
Field observations integrated with carbonate
values allow the subdivision of the section into
four lithozones:
Lithozone A (0–17 m level). The marly fa-
cies of the basal lithozone up to 13.4 m level
is the more calcareous interval in the section.
Carbonate content ranges from 57% to 21%,
with average values of 45%. In the interval,
M. Bastia T. Calcino T. Formisel T. Ornic
NW SE
500
300
100 masl
reverse fault
AB
Colmirano
Quaternary continental deposits Scaglia rossa
Lower Eocene – Upper Cretaceous p.p.
Marna di Possagno – “Marna scagliosa diAlano”
Upper Middle Eocene
Biancone p.p.
Cretaceous p.p.
Figure 4. Geologic cross section showing the stratigraphic and structural relationships of
rock units present in the study area.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 847
crystal tuff layer > 6 cm thick
bioclastic layer > 6 cm thick
σ σ
V V V
V V V
V V V
V V V
V V V
σ σ σ
σ σ σ
Lithology
Polarity/Chron
C17r
C18r
C17n.1r
C17n.2r
C16r
?
C18n.1r
C18n.2n
C18n.1n
C17n.1n
C17n.1n
NP18
NP17
CP14b CP Nannozone
NP Nannozone
Berggren et al. (1995)
P13 P14 P15
P12
Okada and Bukry (1980)
Martini (1971)
P Foramszone
20
10
30
40
50
70
60
80
90
100
Thickness (m)
0
C17n.2n
NP19-20
E10-11 E12 E13 Berggren and Pearson (2005)
E Foramszone
C17n.3n
E14
CP14a
NP16
CP15a CP15b
Tintoretto
Tiepolo
Canaletto
Canova
Palladio
Giorgione
Mantegna
V V V Tiziano
4020 8060
4020 8060
CaCO3 (%)
v v
prominent layer of variable composition
dark marlstone locally clay rich and laminated
light gray marlstone CaCO3 (%)
Lithozone
A
B
C
D
Figure 5. Lithologic column of the Alano section. The main volcaniclastic/bioclastic beds are positioned in the log and named after
famous Venetian artists. CaCO3 content throughout the section is presented in the central part of the section (after Spofforth
et al., 2010). The total carbonate content allows the subdivision of the section into four lithozones reported on right side.
Agnini et al.
848 Geological Society of America Bulletin, May/June 2011
we recognized several millimeter-thick lay-
ers and two major crystal tuff layers that have
been named Mantegna and Giorgione (Figs. 5
and 6; Table 1).
Lithozone B (17–25.5 m level). A promi-
nent package of dark to black, more clayey
lithologies interrupts the monotonous lithol-
ogy of the section. This interval is easily rec-
ognized in the fi eld and is reminiscent of the
classical Cretaceous black shales widely out-
cropping in the Southern Alps. The base of
the interval is sharp with a marked contrast in
color that is caused by an increase in organic
carbon content, from the background values of
~0.1% to 3% (Spofforth et al., 2010). The stra-
tigraphy within the package is structured: it
is interrupted at 18.90 m level by a 2-m-thick
interval of marls similar to those present in the
underlying and overlying intervals. The car-
bonate content reaches the lowest values in the
section (around 22%) and mimics the triparti-
tion observed in the lithology, even if the de-
crease of the carbonate contents starts below
the base of the interval at 13.4 m level (Figs.
5 and 6). This peculiar lithozone corresponds
largely to a global major climatic perturba-
tion, the so-called middle Eocene climatic op-
timum (MECO) as detailed in Spofforth et al.
(2010) see also Bohaty and Zachos, [2003]
and Bohaty et al. [2009] for an overview). Up-
ward, two prominent bioclastic arenitic/ruditic
layers, the fi rst one located in lithozone B and
the second one lying in lithozone C (Fig. 5),
are observed in the lower-middle part of the
section. The faunal associations and sedimen-
tological characters of both strata point to
resedimentation processes of shallow-water
clasts from the nearby Lessini Shelf.
Lithozone C (25.5–59.95 m level). The
middle-upper part of the section, starting from
25.5 m level up to the top, cannot be differ-
entiated in the fi eld, but the carbonate content
undergoes a major change at 59.95 m level,
where a decrease, used for separating the two
lithozones C and D, is observed (Fig. 5). Spe-
cifi cally, from 25 to 59.95 m level, the total car-
bonate content curve shows wide oscillations
ranging from 31% to 56%, with an average
value of 46%. Lithozone C is characterized by
the absence of thick volcaniclastic layers that
are present both in lithozone A and the overly-
ing lithozone D. The only marker bed observed
in this interval is represented by the bioclastic
Canova bed (Fig. 5), which can be classifi ed as
a bioclastic rudstone (Table 1).
Lithozone D (59.95 m level to section top).
From ~60 m level up to the section top, total
carbonate contents range from 29% to 51%,
with an average value of 41%. In lithozone D,
four prominent crystal tuff layers are present, in
ascending order, they are the Tiziano Bed, the
Tiepolo Bed, the Tintoretto Bed, and the Cana-
letto Bed (Fig. 6). The Tiziano Bed is the most
prominent, being 16 cm thick (Table 1).
Paleontological Content
The hemipelagic marls of Alano section
contain abundant calcareous nannofossils,
planktic foraminifera, and common benthic
forami nif era, and rare ostracods. Palinomorphs
are abundant as well (Brinkhuis, 2009, per-
sonal commun.). Scattered bryozoans have
been found in the upper part of lithozone D
(e.g., Batopora spp.; Braga, 2009, personal
1 m 1 m
1 m 1 m
1 m 1 m
BA
1 m 1 m
1 m 1 m
1 m 1 m
DC
FE
Figure 6. Alano section. (A) View of the lower part of the Alano section (lithozone A).
(B) Detail of lithozone A with indication of the crystal tuff layer Giorgione. (C) Basal por-
tion of the sapropelic interval, the lithological expression in the study area of the middle
Eocene climatic optimum (lithozone B). (D) The upper part of the sapropelic interval
with indication of the prominent bioclastic layer Palladio (lithozones B and C). (E) Close-
up view of the critical interval showing the prominent crystal tuff layer Tiziano (basal
lithozone D). (F) Upper part of the sampled section with indication of the crystal tuff layer
Canaletto (lithozone D).
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 849
commun.). The macrofossils are conspicuously
absent, as expected in deep-water sediments
like those cropping out in the Alano section.
In our detailed fi eld work, we found just two
badly preserved bivalves in lithozone C and
scattered plant debris throughout the section.
Ichno fossils are commonly present through-
out the section and are mainly represented by
Zoophycos in the gray marls and Chondrites in
the black interval during the middle Eocene cli-
matic optimum.
DATA AND RESULTS
We fi rst present benthic foraminiferal assem-
blages data and planktic/benthic (P/B) ratios
that were used to infer the paleodepth of the
Alano succession and thus better constrain the
depositional setting throughout the section. Suc-
cessively, we illustrate the magnetostratigraphy
and calcareous plankton biostratigraphy of the
Alano section in an attempt to establish an ac-
curate chronology.
Benthic Foraminifera and Paleodepth
at Alano
Samples used for studying benthic and plank-
tic foraminiferal assemblages were prepared
following standard methods. Briefl y, the indu-
rate marlstones were disaggregated with hydro-
gen peroxide at concentrations varying from
10% to 30%. When necessary, samples were ad-
ditionally treated using Neo-desogen, a surface-
tension–active chemical product of the Ciba
Geigy Company. Finally, to break up clumps of
residue, some samples were placed in a gentle
ultrasonic bath.
Paleobathymetric estimates of the section
were based both on P/B ratio and presence of
index taxa. The P/B ratio is expressed as 100 ×
P/(P + B), i.e., the percentage of planktic fora-
minifera in the total foraminiferal assemblages,
using >63 μm size fraction. The presence of
benthic foraminiferal paleobathymetric index
taxa (e.g., Van Morkhoven et al., 1986) was
evaluated within 23 samples throughout the
entire section, scanning residues splits of both
>63 and >125 μm size fractions. Bathymetric
divisions follow van Morkhoven et al. (1986)
and Berggren and Miller (1989): upper bathyal
200–600 m, middle bathyal 600–1000 m, and
lower bathyal 1000–2000 m.
The small benthic foraminiferal assemblages
at Alano are highly diverse and dominated by
calcareous taxa, indicating deposition well
above the calcite compensation depth. The
most common calcareous taxa are bolivinoids
(Bolivinoides crenulata latu sensu and Bolivina
antegressa group), uniserial taxa, lenticulinids,
Osangularia pteromphalia, Globocassidulina
subglobosa, Oridorsalis umbonatus, Cibici-
doides spp., Anomalinoides spissiformis, and
gyroidi nids (namely Gyroidinoides girardanus).
Representatives of the triserial morphogroups
such as Bulimina and Uvigerina consistently
occur in some samples, especially from the
sapropelic interval. Miliolids, which include
mainly Spiroloculina sp., are generally rare.
The agglutinated foraminiferal assemblages are
mostly represented by clavulinids, Ammodiscus,
Karrerulina, Karrierella, vulvulinids, and Plec-
tina dalmatina. Resedimented small benthic
shallow-water taxa, e.g., asterigerinids, Schlos-
serina asterites, Sphaerogypsina globula, and
Thalmannita sp., were solely observed in the
marls just above bioclastic macroforaminifera-
bearing layers (e.g., Canova bed).
The P/B ratio shows values >95% at the base
of the section, decreasing up to ~90% at 76 m
level, whereas in the remaining 30 m, it fl uctu-
ates around 85% (Fig. 7). Percentages >90% are
consistent with deposition at bathyal and greater
depths (e.g., Gibson, 1989; van der Zwaan et al.,
1990). However, it must be noted that P/B values
<90%, recorded from 81 to 105 m, are probably
affected by a general up-section decrease in the
planktic foraminiferal preservation state. In order
to better constrain the paleo depth of the Alano
section, the distributions of frequently occur-
ring, cosmopolitan benthic taxa useful to infer
paleobathymetric position are reported in Fig-
ure 7. The paleodepth ranges used here are those
of Tjalsma and Lohmann (1983), van Mork-
hoven et al. (1986), Berggren and Miller (1989),
Müller-Merz and Oberhänsli (1991), Bignot
(1998), and Barbieri et al. (2003). Throughout
the investigated section, many taxa occur with
an upper bathyal upper depth limit or are com-
mon at bathyal depths, e.g., Bolivina antegressa
group, Osangularia pteromphalia, Rectuvigerina
mexicana, Cibicidoides eocaenus, C. hettneri,
C. micrus, Bulimina tuxpamensis, Hanzawaia
ammophila, Anomalinoides capitatus, A. spissi-
formis, and A. alazanensis (e.g., Van Morkhoven
et al., 1986; Holbourn and Henderson, 2002;
Barbieri et al., 2003). Bolivinoides crenulata
TABLE 1. PETROGRAPHIC CHARACTERIZATION OF CRYSTAL TUFF AND BIOCLASTIC BEDS
Bed name
thickness (cm) Field observations Optical analyses
Rock
classifi cation
Mantegna
(11 cm)
Uncemented sand, with
biotite fl akes at the base
Sand consisting of more than 80% of
feldspars, quartz, biotite, volcanic lithics, and
heavy minerals, with scattered planktonic
foraminifera and small calcite spars
Crystal tuff
Giorgione
(4–5 cm)
Slightly cemented sand with
horizontal burrowing
Sand consisting of almost 70% feldspars,
quartz, biotite, and heavy minerals, with
scattered planktonic foraminifera and small
calcite spars
Crystal tuff
Palladio
(12–16 cm)
Normal graded bioclastic
horizontal lamination
arenite with sparse green
grains. Quite frequent
large (up to 8 cm) pelitic
intraclasts at the base;
common bioturbation
Carbonate rock with clastic texture; at the
base, fl oatstone with pelitic intraclasts and
scattered debris of corallinacean algae,
echinodermata, bryozoa, and nummuliths,
rapidly grading to a bioclastic packstone
Bioclastic-
intraclastic
rudstone-
packstone
Canova
(3–6 cm)
Bioclastic rudite with large
forams with closed-sutured
contacts
Carbonate rock with clastic texture; the grains
are biosomes and clasts of nummuliths,
discocyclinids, debris of bryozoans,
corallinacean algae, molluscs,
and echinodermata. Green particles are
present both as individual grains and as
infi ll of foraminifera tests. Sutured and
concave-convex contacts between grains
and mechanical fractured bioclasts
Bioclastic
rudstone
Tiziano
(14–16 cm)
Sandy-silty bed: at the base,
horizontal burrowing,
sometimes crossing the
entire bed. At the top a
centimeter-thick green
pelitic plastic interval
Uncemented sand to silt made of transparent
zoned and twinned feldspar crystals, vitric
fragments, quartz, and biotite and green
particles. Scattered heavy minerals, calcite
gouges, and foraminifera texts
Crystal tuff
Tintoretto
(10–12 cm)
Very fi ne-grained sands,
with horizontal burrowing
at the base
Slightly cemented sand consisting of almost
80% feldspars, quartz, biotite, and volcanic
lithics
Crystal tuff
Tiepolo
(11 cm)
Coarse-grained silt, with
concentrations of large
biotite fl akes in parallel
laminae; horizontal
burrowing at the base
Sand consisting of almost 70% feldspars,
quartz, biotite fl akes, and heavy minerals,
with scattered bioclastic debris
Crystal tuff
Canaletto
(6 cm)
Medium- to fi ne-grained
sands with cross lamination
and abundant biotite; on
the top, 2-mm-thick interval
of large (up to 3 mm in
diameter) biotite fl akes
Sand made of about 80% crystal-shape
feldspars, quartz, biotite, volcanic lithics,
and scattered heavy minerals
Crystal tuff
Agnini et al.
850 Geological Society of America Bulletin, May/June 2011
latu sensu, the most common and continuously
present taxon at Alano, has a wide bathymetric
distribution (e.g., Sztrákos, 2005; Nomura and
Takata, 2005; Ortiz and Thomas, 2006; Molina
et al., 2006a; Alegret et al., 2008). Nuttallides
truempyi is present, up to 83.6 m level, and the
Bulimina impendens-trinitatensis group is pres-
ent up to the top of the section. These two taxa
are described commonly as having an upper
depth limit around 5–700 m (e.g., van Mork-
hoven et al., 1986; Barbieri et al., 2003; Molina et
al., 2006b), which further constrains the deposi-
tion of the Alano section to at least upper-middle
bathyal depths. In their bathymetric zonation
of the Possagno section (7 km south of Alano),
Grünig and Herb (1980) used the disappearance
of N. truempyi to separate their deeper assem-
blage 1 (nearly 1000 m for the uppermost part)
from the shallower assemblage 2 (between 1000
and 600 m). The presence of specimens of Cibici-
doides grimsdalei, a cosmopolitan and easily rec-
ognizable taxon for which an upper depth limit
within the lower bathyal zone has been reported
(van Morkhoven et al., 1986; Bignot, 1998; Bar-
bieri et al., 2003; Katz et al., 2003), suggests for
the lower two-thirds of the measured section,
deposition occurred close to the lower-middle
bathyal boundary. It must be noted, however,
that C. grimsdalei has been recently reported by
some authors (Mancin and Pirini, 2002; Ortiz and
Thomas, 2006; Živkovic and Glumac, 2007) in
supposed upper-middle bathyal sediments. Sum-
marizing the aforementioned considerations, we
can hypothesize a bathymetric evolution for the
Alano section from a full middle bathyal depo-
sitional depth (lower two-thirds of the section,
Selected benthic foraminifera
P/(P+B)*100
Middle bathyal Upper-middle bathyal boundary
BB4 BB5
ZONE 1 ZONE 2
Berggren and Miller (1989)
Grünig and Herb (1980)
Inferred paleodepth
Bulimina impendens-trinitatensis group
Cibicidoides grimsdalei
Anomalinoides capitatus
Globocassidulina subglobosa
Hanzawaia ammophila
Oridorsalis umbonatus
Osangularia pteromphalia
Rectuvigerina mexicana
Cibicidoides truncanus
Nuttallides truempyi
Bolivina antegressa group
Bolivinoides crenulata
Cibicidoides micrus
Cibicidoides eocaenus
V V V
V V V
V V V
V V V
V V V
σ σ σ
σ σ σ
Lithology
NP18
NP17
P13 P14 P15
P12
20
10
30
40
50
70
60
80
90
100
0
NP19-20
E10-11 E12 E13 E14
NP16
Tintoretto
Tiepolo
Canaletto
Canova
Palladio
Giorgione
Mantegna
V V V
Tiziano
σ σ σ
Martini (1971)
BKSA95
Berggren and Pearson (2005)
Thickness (m)
ALANO SECTION
80 90 100
Figure 7. The P/(P + B) (%) (=
planktic to planktic and benthic
ratio) and stratigraphic distri-
bution of selected small benthic
foraminifera plotted against
lithology and calcareous plank-
ton biostratigraphy (NP—Mar-
tini, 1971; P—Berggren et al.
1995; E—Berggren and Pear-
son, 2005). Benthic foraminif-
era biozonation (Berggren and
Miller, 1989) and inferred paleo-
depth of the Alano section are
reported on the right side.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 851
600–1000 m paleodepth) up to an upper-middle
bathyal boundary depth (~600 m paleodepth) for
the remaining one-third of the section.
In terms of benthic foraminiferal biozonation,
the exit of Cibicidoides truncanus (C. parki
auctorum), recorded between 81 and 83.6 m,
marks the BB4/BB5 boundary of the Berggren
and Miller (1989) bathyal biozonation (Fig. 7).
In addition, the highest occurrence (HO) of
N. truempyi, an important benthic foraminiferal
event that has been proposed by Berggren and
Miller (1989) for defi ning the AB7/AB8 bound-
ary of their abyssal biozonation in the same in-
terval, is also recorded. The exit of this species
is a strongly diachronous event: in the abyssal
settings, it roughly approximates the Eocene-
Oligocene boundary, whereas in bathyal set-
tings, it disappears earlier in the late Eocene or
within the middle to late Eocene transition (e.g.,
Barbieri et al., 2003; Coccioni and Galeotti ,
2003). At Alano, the HOs of both C. truncanus
and N. truempyi occur much earlier than in the
deeper Umbria-Marche Basin, where the two
events are spaced further apart (Coccioni and
Galeotti, 2003), as in the southern Tethyan
Nahal Nizzana section (Barbieri et al., 2003).
Paleomagnetism
Paleomagnetic samples were drilled and
oriented in the fi eld at an average sampling in-
terval of ~0.6 m, giving a total of 159 standard
~11 cm3 specimens for analysis (Figs. 8A–8B),
conducted at the Alpine Laboratory of Paleo-
magnetism (ALP). The intensity of the natural
remanent magnetization (NRM), measured on a
2G DC-SQUID cryogenic magnetometer located
in a magnetically shielded room, ranged between
0.03 and 24 mA/m (mean of 2.7 ± 8 mA/m),
with a single sample reaching 89 mA/m; higher
values were prevalently associated with volcani-
clastic-rich intervals (Fig. 8C). All samples were
thermally demagnetized from room temperature
to 400–600 °C. The component structure of the
NRM was monitored after each demagnetization
step by means of vector end-point demagnetiza-
tion diagrams (Zijderveld, 1967). Magnetic com-
ponents were calculated by standard least-square
analysis (Kirschvink, 1980) on linear portions of
the demagnetization paths and plotted on equal-
area projections. Fisher (1953) statistics were ap-
plied to calculate overall mean directions.
After removal of spurious initial magnetiza-
tions, the presence of a bipolar characteristic (Ch)
component trending to the origin of the demagne-
tization axes was observed in 65% of the samples
on average between ~200 and ~400 °C. Above
~400 °C, the Ch component usually became
unstable, and the origin of the demagnetization
axes was rarely approached at ~550–575 °C, sug-
gesting the presence of (titano)magnetite as main
carrier of the magnetic remanence (Fig. 9A).
The Ch component, characterized by maximum
angular deviation values usually below 10° (Fig.
8D), was oriented either northwest and shallow
down or southeast and shallow up in geographic
(in situ) coordinates, and it becomes steeper after
correction for homoclinal bedding tilt (azimuth
of dip/dip = 130–140°E/20–25°) (Figs. 9A–9B).
These populations depart from antipodality by
~11°, which we attribute to residual contamina-
tion from spurious lower-temperature compo-
nents. The effect of the contaminating bias on the
mean direction can be minimized by inverting all
directions to common polarity, which resulted
in a tilt-corrected mean direction of declination
(Dec.) = 351°, inclination (Inc.) = 39.5° (N = 104,
k = 12, α95 = 4°; Table 2).
We compare the mean paleomagnetic pole
(paleo pole) from Alano (65.4°N, 211.7°E;
Table 2), calculated from the characteristic
component mean direction in tilt-corrected co-
ordinates, to the Late Cretaceous–Cenozoic
(80–0 Ma) synthetic apparent polar wander
(APW) path in African coordinates of Besse
and Courtillot (2002). The Alano paleopole (A.
obs in Fig. 9C) falls at lower latitudes with re-
spect to the 40 Ma African paleopole (77.3°N,
191.6°E, A95 = 7.2°). This is because the charac-
teristic component mean inclination from Alano
(39.5° ± 4°) is ~13° shallower compared to the
inclination expected at the site from the 40 Ma
African paleopole (53° ± 5°). Syn- and/or post-
depositional compaction can produce an incli-
nation fl attening of the magnetic remanence in
sediments (e.g., Tauxe, 2005); hence ,we used the
elongation/inclination (E/I) method of Tauxe and
Kent (2004) to detect and correct for the shallow
bias of paleomagnetic directions (see also Krijgs-
man and Tauxe, 2004; Kent and Tauxe, 2005).
We unfl attened the Alano characteristic direc-
tions by applying fl attening (f) values ranging
from 1 to 0.3, and for each unfl attening step, we
evaluated the E/I value of the directional data
set (Fig. 9D, heavy line with ticks). The E/I pair
consistent with those expected from a statistical
geomagnetic fi eld model (TK03.GAD, Tauxe
and Kent, 2004; Fig. 9D, dashed line) was at-
tained at f = 0.57. The analysis was repeated
5000 times by means of bootstrap technique
(examples of bootstrapped curves are plotted as
light curves in Fig. 9D). In Figure 9E, we show
a cumulative distribution of all inclinations de-
rived from the bootsrapped crossing points. We
obtained a corrected mean inclination (and asso-
ciated 95% confi dence interval) of Incc = 53°
(42°–69°), which is virtually identical to the in-
clination expected from the coeval 40 Ma Afri-
can paleopole (Ince = 53° ± 5°), and indicates a
mean paleolatitude for Alano of ~34°N.
The unfl attened mean characteristic direc-
tion of the Alano section (Dec. = 351.2°, Inc. =
53°) yielded a corrected paleopole (A. corr in
Fig. 9C; 75.9°N, 223.5°E) that falls on the early
Cenozoic portion of the African APW path and
is only moderately rotated counterclockwise
by 9° ± 8° with respect to the 40 Ma African
paleopole. We can therefore consider this part
of the Southern Alps as tectonically coherent
with Africa since at least the Eocene, in sub-
stantial agreement with previous fi ndings from
the nearby Paleocene–Eocene Possagno sec-
tion (Agnini et al., 2006) as well as from sites
of Permian–Mesozoic age from elsewhere in
the Southern Alps, e.g., the Dolomites (e.g.,
Muttoni et al., 2003, and references therein).
A virtual geomagnetic pole (VGP) was
calculated for each characteristic component
direction in tilt-corrected coordinates. The
latitude of the sample characteristic magnetiza-
tion VGP relative to the mean paleomagnetic
(north) pole axis was used for interpreting po-
larity stratigraphy (Lowrie and Alvarez, 1977;
Kent et al., 1995). VGP relative latitudes ap-
proaching +90°N or –90°N are interpreted as
recording normal or reverse polarity, respec-
tively (Fig. 8E). For polarity magnetozone
identifi cation, we adopted the nomenclature
used by Kent et al. (1995). We assigned integers
in ascending numerical order from the base of
the section to polarity intervals as defi ned by
successive pairs of predominantly normal and
predominantly reversed magnetozones. Each
ordinal number is prefi xed by the acronym for
the source of the magnetostratigraphy (i.e., “A”
for Alano), and has a suffi x for the dominant
polarity (“n” is normal, “r” is reversed) of each
constituent magnetozone. An overall sequence
of 13 polarity magnetozones, labeled from A1r
to A4r(?), has been established starting from the
section base (Fig. 8F); of these magnetozones,
one is poorly defi ned by only intermediate VGP
latitudes (A1n.1r), and two are defi ned by only
one sample (A2n.2r, A4r).
Planktic Foraminifera
For the planktic foraminifera study, 264
samples were prepared using standard meth-
ods (see benthic foraminifera and paleodepth
at Alano). All samples were washed through a
38-µm-mesh sieve in order to avoid the loss of
the very small specimens; the fi nest fraction was
separated from the 63 µm residue. Foraminifera
are continuously present, abundant, and diverse
throughout the section, except for some levels
from the sapropelitic interval. The preservation
varies from moderate to good, and micro fossil
assemblages are generally well recogniz-
able even if recrystallization of tests commonly
Agnini et al.
852 Geological Society of America Bulletin, May/June 2011
VVV
VVV
VVV
VVV
VVV
VVV
sss
sss
20
10
30
40
50
70
60
80
90
100
0
0102030
01020
89
24
NRM (mA/m) MAD (°)
–90 –45 0 45 90
VGP Lat. (°)
Paleomag.
samples
Lithology
Thickness (m)
A1r
A1n.2n
A1n.1r(?)
A1n.1n
A2r
A2n.3n
A2n.2r(?)
A2n.2n
A2n.1r
A2n.1n
A3r
A3n
A4r(?)
Polarity
ABCDEF
Figure 8. Stratigraphic syn-
thesis of the Alano section with
(A) lithology, (B) stratigraphic
position of samples for paleo-
magnetic analysis, (C) natural
remanent magnetization (NRM)
intensity, (D) mean angular de-
viation (MAD) of the character-
istic magnetic component, and
(E) virtual geomagnetic pole
(VGP) latitude used for polarity
interpretation (F); black is
normal polarity; white reverse
polarity.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 853
A
B
E
D
C
sample 150W,U p
575 °C
550 °C
300 °C
100 °C
NRM NRM
400 °C
500 °C
550–
600 °C
NN
IN SITU
sample 640 W,Up W,Up sample 1150
N
550 °C
300 °C
100 °C
NRM
NRM
100 °C
300 °C
500 °C
sample 2870 W,U p
N
IN SITU
GAD
TILT CORRECTED
Figure 9. (A) Vector end-point demagnetization diagrams of Alano samples. Closed symbols are projections onto the horizontal plane, and
open symbols are projections onto the vertical plane in geographic (in situ) coordinates. Demagnetization temperatures are expressed in °C.
NRM—natural remanent magnetization. (B) Equal-area projections before (in situ) and after bedding tilt correction of the characteristic
component directions from Alano (Table 2). Closed symbols are projections onto the lower hemisphere, and open symbols are projections
onto the upper hemisphere. The geocentric axial dipole (GAD) is indicated by the solid star. (C) The paleopole from Alano calculated from
the mean characteristic component in tilt-corrected coordinates (A.obs; Table 2) falls at lower latitudes compared to the reference Late
Cretaceous–Cenozoic (80–0 Ma) synthetic apparent polar wander (APW) path in African coordinates of Besse and Courtillot (2002) (solid
line with A95 error circles), probably because of anomalously shallow paleomagnetic inclinations recorded in the Alano sediments. After
inclination shallowing correction, obtained by using the elongation/inclination (E/I) method of Tauxe and Kent (2004), the corrected paleo-
pole (A.corr; Table 2) is in latitudinal agreement and only moderately rotated counterclockwise by 9° ± 8° with respect to the broadly coeval
40 Ma African paleopole. The Alano sampling site is also indicated together with the poles–site colatitude great circle (dashed line). (D) Plot
of elongation versus inclination for the TK03.GAD (Tauxe and Kent 2003. Geomagnetic Axial Dipole) model (dashed line) and for the Alano
data (line with ticks) for different fl attening (f) values from 1 to 0.3. The ticks indicate the direction of elongation, horizontal being E-W
and vertical being N-S. Also shown are the results from 20 (out of a total of 5000) bootstrapped data sets. The crossing points represent
the inclination/elongation pair most consistent with the TK03.GAD model. (E) Histogram of crossing points from 5000 bootstrapped data
sets. The most frequent inclination (Incc = 53°; 95% confi dence interval = 42°–69°) is in good agreement with the inclination expected at
Alano from the 40 Ma synthetic pole of Besse and Courtillot (2002) (Ince = 53° ± 5°). The mean inclination of the raw data in tilt-corrected
coordinates (Inco = 39.539.5° ± 4°) is also indicated. See text for discussion.
Agnini et al.
854 Geological Society of America Bulletin, May/June 2011
occurs . Taxonomic criteria adopted in this study
are after Pearson et al. (2006). Illustrations of
selected signifi cant species, including zonal
markers, are provided in Plate 11.
The biostratigraphic classifi cation of the
late Middle Eocene and late Eocene is in a
state of fl ux. An extensive review is available
in the revised tropical to subtropical Paleogene
planktonic foraminiferal zonation by Berg-
gren and Pearson (2005), to which we refer
(Fig. 1), though the biozonal scheme proposed
in Berggren et al. (1995) is reported as well.
We have also taken into account the scheme
of Toumarkine and Bolli (1970), later updated
in Toumarkine and Luterbacher (1985), based
on the evolution of the Turborotalia cerroazu-
lensis plexus, and specifi cally developed for
midlatitude areas, with specifi c reference to
sections located in the Veneto region. In the
scheme of Berggren and Pearson (2005), we
have combined zones E10 and E11, altogether
equivalent to the long zone P12 in the scheme
of Berggren et al. (1995), because at Alano, the
highest consistent occurrence Gumbelitriodes
nuttalli is recorded at 57.52 m level, after the
HO of Orbulinoides beckmanni (Fig. 10). In-
deed, rare and small specimens of G. nuttallii
(Plate 1; Fig. 10) are present up to 75.61 m
level, within zone E14.
In this study, we carried out planktic forami-
niferal analysis for the >63 µm size fraction.
Samples were fi rst studied qualitatively to check
for presence-absence of index species. Quanti-
tative analysis was performed for establishing
the distribution patterns of the zonal markers,
including key species of middle Eocene–late
Eocene transition (e.g., morozovellids, acarini-
nids). The sample spacing is on average 40 cm,
except in critical intervals, for instance, near the
middle to late Eocene transition, where the sam-
pling spacing is ~20 cm (roughly 8000 k.y.).
At Alano, the assemblage composition is
distinctive of subtropical-temperate latitudes
and shows variations in the relative abundance
of different taxa throughout the section. Sub-
botinids and globigerinathekids are among the
more frequent and common groups. The large
acarininids are abundant in the lower part of the
section, but they neatly decrease concomitantly
with the sapropel-like interval corresponding to
the middle Eocene climatic optimum (Fig. 10).
Consistent with previous records from other NE
Italian sections (Toumarkine and Luterbacher,
1985; Luciani and Lucchi Garavello, 1986), the
middle–late Eocene genus Hantkenina displays
an uneven distribution and, where present, con-
stitutes a minor component of the assemblages.
Biostratigraphic classifi cation of the Alano
section, based on standard and additional bio-
horizons, is commented as follows:
(1) The basal part of the section, up to 14.40 m
level, can be confi dently assigned to the upper
part of the combined zone E10/E11 (P12 in the
zonal scheme of Berggren et al., 1995), because
of the absence of Morozovella aragonensis and
O. beckmanni. A noteworthy feature of this in-
terval is the occurrence, from 13.20 m level, of
rare and discontinuous specimens of T. cerro-
azulensis (Fig. 10). This is the lowest occur-
rence so far documented for this species, which
is normally reported within E13 or higher up
(e.g., Nocchi et al., 1986; Coccioni et al., 1988;
Gonzalvo and Molina, 1992; Berggren et al.,
1995; Berggren and Pearson, 2005). However,
it should be observed that the species is rare
and unevenly distributed up to 26.10 m level,
becoming relatively common and continuously
distributed from 46.52 m level (Fig. 10).
(2) The 5.1-m-thick interval from 14.40 to
19.50 m levels is assigned to zone E12 (or P13)
based on the total range distribution of Orbu-
linoides beckmanni. According to Edgar et al.
(2007), the origination, subsequent evolutionary
development, and extinction of this short-lived
species was intimately linked to environmental
changes associated with the middle Eocene cli-
matic optimum warming event. The recognition
of the O. beckmanni lowest occurrence (LO) can
however be affected by some degree of subjec-
tivity, because the species derives from Globi-
gerinatheka euganea, and transitional forms of
problematic assignment with sec ondary aper-
tures along the inner spire occur from 12.80 m
level. Pearson et al. (2006) proposed that
O. beckmanni has a greater number of apertures
than G. euganea, without specifying their exact
number. On the other side, Berggren and Pear-
son (2005) recommended a relatively broad tax-
onomical concept for O. beckmanni in order to
permit a consistent identifi cation of the base of
E12 zone, but they did not provide details on the
nature of the broad taxonomical concept to be
applied. In this work, we have decide to assign
to O. beckmanni forms having, beside numerous
secondary apertures, a more compact, almost
spherical test with less depressed sutures, almost
indistinguishable, in the earlier chambers of the
last whorl (Plate 1). It is interesting to note that
in the Alano section, the total range distribution
of O. beckmanni appears to be virtually con-
fi ned to the middle Eocene climatic optimum
interval, in agreement with Edgar et al. (2007).
However, the identifi cation of the O. beck manni
HO is diffi cult to precisely recognize because of
its scarce abundance and the moderate preserva-
tion state of planktic foraminiferal assemblages
within the sapropel-like interval.
Within zone E12, we observed the fi rst speci-
mens ascribable to Turborotalia cocoaensis that
in the past was considered restricted to the late
Eocene (e.g., Toumarkine and Bolli, 1970). At
Alano, typical T. cocoaensis, distinguishable
from its ancestor T. cerroazulensis by an acute
profi le of the fi nal chamber (Plate 1), fi
rst occurs
as low as 15.60 m level, even if the specimens
recorded at this level are very few. Nevertheless,
the occurrence and abundance of the species are
highly variable throughout the section, alternat-
ing intervals of extreme scarcity in abundance
with others of relatively common and continu-
ous presence. This feature is likely controlled by
as-yet unidentifi ed environmental factors.
(3) The 38.02-m-thick interval from 19.5 m
level and 57.52 m level, where the HO of the
genus Morozovelloides is observed, is attributed
to zone E13. The top of this zone represents one
of the major faunal changes in the evolutionary
history of planktic foraminifera in the Cenozoic
and has implications for defi ning the middle
Eocene–late Eocene boundary (see following).
Specifi cally, these prominent changes in plank-
tic foraminiferal assemblages include the fi nal
extinction of large muricate planktic forami nif-
era (large Acarinina and Morozovelloides) that
1Plates 1 and 2 are on a separate sheet accompany-
ing this issue.
TABLE 2. CHARACTERISTIC COMPONENT DIRECTIONS AND PALEOMAGNETIC POLE FROM THE ALANO SECTION
In situ detcerrocDAG.30KTdetcerroctliT
Nkα95 Dec. Inc. kα95 Dec. Inc. Plat Plong dp/dm Inc.c Err.Inc Plat.c Plong.c
104 12 4.2 344.1 20.5 12 4.2 351.2 39.5 65.4 211.7 3/5 53.0 42-69 75.9 223.5
Note: Site latitude, longitude—45.92°N, 11.87°E. N—number of samples; k—Fisher precision parameter of the mean paleomagnetic direction; α95—Fisher angle
(°) of half cone of 95% confi dence about the mean paleomagnetic direction; Dec. and Inc.—declination (°) and inclination (°) in geographic (in situ) coordinates or
bedding (tilt-corrected) coordinates of the mean paleomagnetic direction; Plat and Plong—latitude (°N) and longitude (°E) of the mean paleomagnetic pole in bedding
(tilt-corrected) coordinates (pole A.obs); dp/dm—error (°) about the mean paleomagnetic pole; Inc.c—TK03.GAD corrected mean inclination (°); Err.Inc—error band of
the TK03.GAD corrected mean inclination (°); Plat.c and Plong.c—latitude (°N) and longitude (°E) of the TK03.GAD corrected mean paleomagnetic pole (A.corr). The
declination and inclination predicted at Alano from the Besse and Courtillot (2002) 40 Ma synthetic pole (in S. Africa coordinates) is 0.3°E, 52.6° (±5.2°).TK03—Tauxe and
Kent 2003; GAD—Geomagnetic Axial Dipole.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 855
dominate low- and mid latitude assemblages
in the early and middle Eocene. Therefore, we
detailed the faunal patterns observed in this in-
terval as sketched in Figure 10. In the Alano sec-
tion, the extinction of distinctive muricate group
occurred in three steps involving, respectively,
the “large” (~>250 µm) Acarinina (i.e., A. rohri,
A. pretopilensis, A. topilensis, A. bullbrooki,
A. primitiva, A. collactea), the genus Morozo-
velloides (i.e., M. crassatus, M. coronatus), and
fi nally the “small” (~<200 µm) Acarinina (i.e.,
A. medizzai, A. echinata).
The extinction level of large Acarinina bear-
ing well-developed muricae occurs at 57.32 m
level and is immediately followed (20 cm
above, some 8000 k.y.) by the disappearance
of M. crassatus and M. coronatus. It is worth
pointing out, however, that muricate forms, par-
ticularly large Acarinina, display a signifi cant
decline in abundance well below the horizon of
their highest occurrence, precisely within zone
V V V
V V V
V V V
V V V
V V V
σ σ σ
σ σ σ
Lithology
Polarity/Chron
C17r
C18r
C17n.1r
C17n.2r
C16r
?
C18n.1r
C18n.2n
C18n.1n
C17n.1n
C17n.1n
20
10
30
40
50
70
60
80
90
100
Thickness (m)
0
C17n.2n
E10-11 E12 E13
C17n.3n
E14
V V V
large acarininids
small acarininids
O. beckmanni
P. capdevilensis
G. semiinvoluta
040
010
01
010
05
05
G. nuttallii
05
T. cocoaensis
%%
%
%
%
%
%
Morozovelloides
05
%
T. cerroazulensis
010
%
P13 P14P12 P15
Berggren et al. (1995)
P Foramszone (m)
Berggren and Pearson (2005)
E Foramszone (m)
ALANO SECTION
Figure 10. Planktic foraminifera data and resulting biostratigraphic classifi cation of the Alano section according to the zonal schemes of
Berggren et al. (1995) and Berggren and Pearson (2005). The relative abundance of each taxon is reported in terms of percentage with
respect to the entire assemblage. Positions of the biohorizons are reported in Table 3.
Agnini et al.
856 Geological Society of America Bulletin, May/June 2011
E12, in correspondence to the middle Eocene
climatic optimum event. Even if these forms are
not frequent close to their extinction level, their
disappearance constitutes a signifi cant, easily
recognizable event.
(4) The upper 47 m of the investigated section,
above the 57.52 m level, are assigned to zone
E14 because Globigerinatheka semiinvoluta is
present, although discontinuously, up to the top
of the section (Fig. 10). This species fi rst appears
at 68.37 m level, i.e., 10.85 m above the HO of
Morozovelloides. The presence of a signifi cant
gap between the LO of G. semiinvoluta and the
HO of Morozovelloides, i.e., the disappearance
of large muricate forms, has also been found by
several other workers (e.g., Benjamini, 1980;
Nocchi et al., 1986; Pearson and Chaisson, 1997;
Norris et al., 1998). In particular, this datum is in
agreement with data from the Cordillera Betica
sections (Spain; Gonzalvo and Molina, 1996).
However, in some areas (western North Atlan-
tic Ocean Drilling Program [ODP] Site 1052;
Wade, 2004, Umbria-Marche sections; Nocchi
et al., 1986), the LO of G. semiinvoluta oc-
curs just above the HO of large acarininids and
M. crassatus.
Within zone E14, we observed the HOs of the
small acarininids (<200 µm), A. medizzai and
A. echinata, that overlap with the range of Glo-
bigerinatheka semiinvoluta, up to 80.41 m level
(Fig. 10). These species represent a minor but
characteristic component of the planktic forami-
nif eral fauna, evenly distributed up to their
highest occurrence. The persistence of small
acarininids into the Upper Eocene, contrary to
the large forms, was noted as well in high lati-
tudes at ODP Sites 702 and 703 (South Atlan-
tic) by Nocchi et al. (1991), at Sites 738 and
744 (Kerguelen Plateau) by Huber (1991), and
at Site 1052 (western North Atlantic) by Wade
(2004). The acarininid lineage thus extends after
the major biotic turnover in the latest middle Eo-
cene. Data so far available suggest however that
the extinction of this group was not a synchro-
nous event. Further investigation is needed to
verify possible regional use of this event.
Calcareous Nannofossils
We studied calcareous nannofossils assem-
blages in 303 samples that were prepared from
unprocessed material as smear slides and exam-
ined under a light microscope at 1250× magni-
fi cation. Samples immediately across the main
useful biostratigraphic biohorizons were ana-
lyzed every 20 cm. Outside these critical inter-
vals, samples were studied every ~60–120 cm.
First, all samples were examined with qualitative
methods to evaluate the abundance and state of
preservation of calcareous nannofossil assem-
blages. We applied the following counting meth-
ods to check the presence or absence and esti mate
the abundance of index species: (1) counting spe-
cies versus total assemblage, taking into account
at least 500 nannofossils (Thierstein et al., 1977),
(2) counting a prefi xed number of taxonomically
related forms, i.e., 50–100 sphenoliths (Rio et al.,
1990); and (3) counting the number of rare but
biostratigraphically useful species, that is species
of genus Chiasmolithus and Istmo lithus, in an
area of ~9 mm2 (three vertical traverses; Backman
and Shackleton, 1983). The last, time-consuming
counting method was used for checking the
presence-absence of key index species that are
particularly rare in the Alano section (Chiasmo-
lithus grandis, Chiasmolithus oamaru ensis, and
Istmolithus recurvus). Taxonomic concepts used
follow Perch-Nielsen (1985) and Fornaciari et al.
(2010). Index species are illustrated in Plate 2
(see footnote 1).
For the purposes of this work, we have made
an effort to establish in the section the standard
zonations of Martini (1971; Nannoplankton
Paleogene [NP] zones) and Okada and Bukry
(1980; Coccolith Paleogene [CP] zones; Fig. 1).
However, these zones are of problematic recog-
nition, and therefore we will strongly rely in our
correlation on a set of additional biohorizons
that have been proposed in the literature over
the years (e.g., Perch-Nielsen, 1985; Fornaciari
et al., 2010).
Generally, the calcareous nannofossil assem-
blages are rich, well preserved, and diversi-
fi ed throughout the section. To illustrate the
makeup of the calcareous nannofossil assem-
blages at Alano, we present Figure 11, where
0100
ALANO SECTION
Cribrocentrum spp.
Dictyococcites spp.
Coccolithus spp.
Cyclicargolithus spp.
Reticulofenestra spp. Others
Lanternithus spp.
Z. bijugatus
Sphenolithus spp.
Discoaster spp.
Ericsonia spp.
10
20
30
40
50
60
70
80
0
Chiasmolithus spp.
reworking
0303
%%%
Position
(m)
Figure 11. Cumulative percentage curve of selected calcareous
nannofossil taxonomic groups in the Alano section. The relative
abundance (%) of Chiasmolithus spp. and reworked forms are also
reported on right side.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 857
the quantitative distribution of selected taxo-
nomic groups is reported. The assemblages are
strongly dominated by placoliths, among which
Cribrocentrum and Dictyococcites are promi-
nent (together up to ~70% of the total assem-
blage). Discoasterids and chiasmoliths (Fig. 1),
which provide important datums in the standard
zonations of Martini (1971) and Okada and
Bukry (1980), are exceedingly rare at Alano, as
they are normally in low to middle latitude areas
(Perch-Nielsen, 1985; Wei and Wise, 1989).
In Figure 12, we report the quantitative distri-
bution patterns of index species from the Alano
section that allow us to defi ne the following
types of biohorizons: lowest rare occurrence
(LRO), lowest occurrence (LO), lowest com-
mon occurrence (LCO), highest common occur-
rence (HCO), highest rare occurrence (HRO),
highest occurrence (HO), acme beginning (AB)
and acme end (AE).
A biostratigraphic classifi cation of the Alano
section, based on standard and additional calcar-
eous nannofossil biohorizons, is provided next.
The positions and calibrations of used bioevents
are reported in Table 3:
(1) The basal part of the section up to 44.73 m
level is assigned to zones NP16/CP14a (Fig. 12)
because of the rare occurrence of Chiasmo lithus
solitus and the scarce/common presence of
Cribrocentrum reticulatum and Reticulofenes-
tra umbilicus (see Fig. 1).
(2) The interval from 44.73 m level, where the
HO of C. solitus was observed, to 62.85 m level,
V V V
V V V
V V V
V V V
V V V
V V V
σ σ σ
σ σ σ
Lithology
Polarity/Chron
C17r
C18r
C17n.1r
C17n.2r
C16r
?
C18n.1r
C18n.2n
C18n.1n
C17n.1n
C17n.1n
NP18
NP17
CP14b CP15a
20
10
30
40
50
70
60
80
90
100
Thickness (m)
0
C17n.2n
NP19-20
C17n.3n
CP14a
NP16
CP15b
2
%
0
%
0600 6
0703
04
03
0
%
0
% within
Sphenolithus
N/9mm2
S. furcatolithoides
S. obtusus
R. umbilicus
D. bisectus
D. scrippsae gr.
7
9
9-15
7
AE
AB LRO
HO
HO
LCO LCO
LO
HO
HCO
HCO
HO
LRO
C. erbae
050
C. oamaruensis
N/9mm2
C. grandis
N/9mm2
I. recurvus
1
0
%
1
C.grandis
C. solitu
s
% within Sphenolithus %%
20
no data
no data
ALANO SECTION
NP Nannozone
Martini (1971)
CP Nannozone
Okada and Bukry (1980)
Figure 12. Quantitative distribution patterns of selected calcareous nannofossils and resulting biostratigraphic classifi cation of the Alano
section according to the zonal scheme of Martini (1971) and Okada and Bukry (1980). Additional biohorizons shown by Fornaciari et al.
(2010) as useful for correlations are evidenced. The position of the biohorizons is reported in Table 3. LRO—Lowest Rare Occurrence;
LO—Lowest Occurrence; LCO—Lowest Common Occurrence; HCO—Highest Common Occurrence; HO—Highest Occurrence; AB—
Acme Beginning; AE—Acme End.
Agnini et al.
858 Geological Society of America Bulletin, May/June 2011
in correspondence with the LRO of Chiasmo-
lithus oamaruensis, is assigned to zone NP17.
It should be observed that the recognition of
the top of this zone has been diffi cult at Alano
because C. oamaruensis is exceedingly rare and
exhibits a discontinuous abundance pattern, es-
pecially in the lower part of its range. However,
a single specimen ascribable to C. oamaruensis
was observed and used for recognizing the top
of zone NP17. Okada and Bukry (1980) de-
fi ned the top of their zone CP14b on the basis
of the HO of Chiasmolithus grandis, which in
the Alano section occurs at 66.47 m level. This
event is also not easily detectable because of
the scarcity of this species at Alano as in other
Italian sections (Monechi and Thierstein, 1985;
Fornaciari et al., 2010).
(3) In a short interval, between 78.11 and
79.91 m levels, we observed the occurrence of
rare specimens of Istmolithus recurvus, which
is termed I. recurvus spike. The LO of this
taxon defi nes the bottoms of zones NP19–20/
CP15b (Fig. 1). Therefore, the upper 26.38 m
of the section are to be assigned (Fig. 12) to
zone NP19–20/CP15b. It should be pointed
out that the fi rst occurrence of I. recurvus at
Alano, just above the HO of C. grandis and
LO of C. oamaruensis, is much earlier than
generally assumed in the literature (Berggren
et al., 1995), but it is consistent with data from
the South and North Atlantic and central west-
ern Tethys (Backman, 1987; Villa et al., 2008;
Fornaciari et al., 2010).
The recognition at Alano, as well as in other
Tethyan sections, of all the aforementioned late
middle Eocene and late Eocene standard zones
is sometimes tricky because they are based on
index species that are exceedingly rare and dis-
continuous. Nevertheless, we will show later
herein that the observed positions of the “stan-
dard” biohorizons in the Alano section are fairly
consistent with magnetochronologic evaluations
from Blake Nose (Fig. 13; ODP Site 1052; For-
naciari et al., 2010), but they are poorly reliable
if compared to the biochronology proposed in
Berggren et al. (1995). The low abundances
and scattered occurrence of index species make
these biohorizons have little practical utility
for reliable biostratigraphic correlations. For
these reasons, previous authors have proposed
the use of alternative biohorizons (e.g., Perch-
Nielsen,1985; Lyle et al., 2002), and we have
undertaken a project with the specifi c purpose
of improving resolution and reliability of cal-
careous nannofossil biostratigraphy in the late
middle Eocene (Bartonian) and late Eocene
(Priabonian) interval (Fornaciari et al., 2010). In
particular, at Alano, there are at least fi ve bioho-
rizons that are based on the quantitative distri-
bution patterns of species common in Tethyan
sections, which thus provide confi dent long-
distance correlation tools. They are in ascending
stratigraphic order:
(1) The HO of Sphenolithus furcatolithoides,
at 6.30 m level; this well-defi ned and easily
recognizable biohorizon was fi rst proposed by
Perch-Nielsen (1985) as an alternative event to
the HO of Chiasmolithus solitus (Fig. 12). Al-
though the HO of S. furcatolithoides has been
observed well below the HO of C. solitus, it
is found to maintain the same relative position
with respect to other additional events (Fig. 14).
(2) The LCO of Dictyococcites bisectus,
at 9.5 m level; this biohorizon, observed just
3.20 m above the HO of S. furcatolithoides, was
reported by Perch-Nielsen (1985) up to the upper
part of zone NP16, consistent with our fi ndings;
the species is deeply affected by taxonomic
ambi guities (e.g., Wei and Wise, 1989) that in
our opinion could be overcome if a biometric
defi nition were adopted assigning only forms
larger than 10 µm to D. bisectus (Bralower and
Mutter lose, 1995). These large forms appear in
Alano and in other Tethyan sections abruptly
and provide a neat event (Fornaciari et al., 2010),
although specimens of D. bisectus have been re-
ported from ODP Site 1052 and Agost section
also at lower stratigraphic levels (e.g., Mita,
2001; Larrasoaña et al., 2008), and this species
is widely considered to be biogeographically
controlled (e.g., Perch-Nielsen, 1985; Wei and
Wise, 1989). On this basis, it is thus possible to
assume that the appearance at Alano is the fi rst
common and continuous occurrence of the spe-
cies, possibly environmentally controlled. This
interpretation is reinforced by the fact that in co-
incidence with the abrupt entrance of D. bisec-
tus, a sharp increase in Dictyococcites scrippsae
is also observed (Fig. 12).
(3) The HO of Sphenolithus obtusus, at
49.58 m level; this easily recognizable species
has been reported by Perch-Nielsen (1985) as
having a restricted distribution range in zones
NP16–18, but it has never been formally utilized
before. At Alano, the form is well distributed,
showing a neat appearance and a neat extinc-
tion; by comparison with other sections, we
consider that its HO is a reliable biohorizon.
TABLE 3. CALCAREOUS PLANKTON BIOHORIZONS AT THE ALANO SECTION AND ODP SITE 1052
59KCegApotnorhcotevitalernoitatoNnoitisoPnozirohoiB
Alano Site 1052 Alano Site 1052 Alano Site 1052 Multisite
)aM(ega)aM(ega)aM(ega)dcmr(htpeD)m(noitisoP
1 I. recurvus 63*
787.63–891.0n1.n71C–98.55–)N(OL
2 A. medizzai–A. echinata HO (F) 80.41 – C17n.1n 0.765 – 37.272 – –
3 I. recurvus spike end (N) 79.91 72.415 C17n.1n 0.784 C17n.1n 0.795 37.288 37.298 * –
4 I. recurvus spike beginning (N) 78.11 81.285 C17n.1n 0.853 C17n.1r 0.885 37.347 37.589 * –
5 C. erbae –*714.73944.73439.0n1.n71C279.0n1.n71C72.6710.57)N(EA
6 G. semiinvoluta LO (F) 68.37 91.67 C17n.2n 0.250 C17n.3n 0.160 37.665 38.000 † 38.4
7 P. capdevilensis HO(F) 68.37 38.32 C17n.2n 0.250 C16n.2n 0.793 37.665 36.240 † –
8 C. grandis 1.73*527.73427.73694.0n2.n71C294.0n2.n71C17.4874.66)N(OH
9 C. erbae –*128.73338.73198.0n2.n71C939.0n2.n71C526
.7869.26)N(BA
10 C. oamaruensis LRO (N) 62.85 86.5 C17n.2n 0.953 C17n.2n 0.722 37.837 37.780 * 37
11 M. crassatus–M. coronatus HO (F) 57.52 92.37 C17.3n 0.394 C17n.3n 0.264 37.996 38.020 † 38.1
12 Large acarininids HO (F) 57.32 92.77 C17.3n 0.418 C17n.3n 0.324 38.001 38.030 † 38.5–37.5
13 S. obtusus –*904.83352.83449.0r71C844.0r71C21.70195.94)N(OH
14 C. solitus 4.04*893.83094.83019.0r71C750
.0n1.n81C67.60137.44)N(OH
15 O. beckmanni HO (F) 19.5 135.69 C18n.2n 0.582 C18n.2n 0.615 39.922 39.980 † 40.1
16 T. cocoaensis ––722.04–r81C–6.51)F(OL
17 O. beckmanni 5.04–352.04–r81C–4.41)F(OL
18 T. cerroazulensis LO (F) 13.2 – C18r – 40.366 – –
19 D. bisectus 83*453.04095.04
r81Cr81C49.3415.9)N(OCL
20 S. furcatolithoides HO (N) 6.3 144.54 C18r C18r 40.780 40.384 * –
Note: (F)—foraminifera; (N)—calcareous nannofossils. CK95—Cande and Kent, 1995; LO—Lowest Occurrence; LCO—Lowest Common Occurrence; HO—Highest
Occurrence; AB—Acme Beginning; AE—Acme End.
*From this work and after Fornaciari et al, 2010.
†After Wade (2004).
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 859
(4) The AB of Cribrocentrum erbae, at
62.96 m level; although this new species (For-
naciari et al., 2010; Plate 2) occurs virtually
throughout the entire section with rare/scarce
and sometimes discontinuous abundances, it
shows a neat increase in abundance, up to 40%,
within zone NP18. At Alano, the peculiar abun-
dance pattern of C. erbae is used to identify an
acme event defi ned as the interval characterized
by percentages of C. erbae greater than 4%–5%.
This biohorizon has also been tested at ODP
Site 1052, where it maintains the same ranking
and spacing, virtually coinciding with the LO of
C. oamaruensis (Fig. 14).
(5) The AE of Cribrocentrum erbae, at 75.01 m
level; this biohorizon marks the return of C. erbae
to background abundances. The AE of C. erbae
is more diffi cult to defi ne because it shows a
more gradual pattern, but the abundances of
C. erbae during the acme are substantially more
copious from that characterizing the rest of the
section. Surprisingly, a comparison between
the Alano section and ODP Site 1052 points
out that the AB and AE of C. erbae have to be
Depth (rmcd)
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
Pälike et al.
(2001)
CP14a CP15b
Polarity/Chron
C17r
C18r
C17n.1r
C17n.2r
C18n.2n
C18n.1n
C17n.1n
C17n.2n
C17n.3n
C16n.2n
C16n.1n
C16r
NP16 NP17 NP19-20NP18
CP14b CP15a CP Nannozone
Okada and Bukry (1980)
NP Nannozone
Martini (1971)
R. umbilicus
020
I. recurvus
S. obtusus
C. oamaruensis
C. grandis
S. furcatolithoides
HO
C. solitus gr.
C. erbae
AE
AB
05
030
030
030
050
LCO?
LCO
LCO
D. scrippsae D. bisectus
LO
HO
LO
LRO HO
HO
65
50–70
%
% within Sphenolithus
020
%
050
% within Sphenolithus
05
%
N/9mm
2
05
%
N/9mm
2
N/9mm
2
N/9mm
2
LRO
ODP Site 1052
Hiatus
Figure 13. Quantitative distribution patterns of selected calcareous nannofossils and resulting biostratigraphic classifi cation of the Alano
Ocean Drilling Program (ODP) Site 1052 according to the zonal scheme of Martini (1971) and Okada and Bukry (1980). Additional bio-
horizons shown by Fornaciari et al. (2010) as useful for correlations are evidenced. The position of the biohorizons is reported in Table 3.
LRO—Lowest Rare Occurrence; LO—Lowest Occurrence; LCO—Lowest Common Occurrence; HCO—Highest Common Occurrence;
HO—Highest Occurrence; AB—Acme Beginning; AE—Acme End; rmcd—revised metres composite depth.
Agnini et al.
860 Geological Society of America Bulletin, May/June 2011
considered as promising biostratigraphic tools
for correlations over wide areas (Fig. 14; Forna-
ciari et al., 2010).
Interpreting Magnetostratigraphy by
Correlation with ODP Site 1052
The calibration of calcareous plankton bio-
horizons to the geomagnetic polarity time scale
(GPTS; Cande and Kent, 1995) at the transition
from the middle to late Eocene is controversial
(see Berggren et al., 1995; Table 3). For exam-
ple, the HO of morozovellids and large acarini-
nids, probably the most critical biohorizon in
the interval, has been associated with the top
of chron C18n in the Apennines (Nocchi et al.,
1986; Premoli Silva et al., 1988), while in the
oceans, it has been often associated with chron
C17n (Berggren et al., 1995), with a discrepancy
of some 1.0 m.y. There has been a dearth of
good low- and midlatitude sections for establish-
ing a reliable calcareous plankton magnetobio-
chronol ogy until the recovery in ODP Leg 171
of expanded and well-preserved successions in
the subtropical western North Atlantic. In par-
ticular, a succession that can be considered a
reference deep-sea section for the middle Eo-
cene to late Eocene transition is that recovered
at ODP Site 1052 in the Blake Nose, in which
magnetostratigraphy (Ogg and Bardot, 2001),
cyclostratigraphy (Pälike et al., 2001), and high-
resolution planktic foraminifera biostratigraphy
(Wade, 2004) have been carried out.
In order to obtain an improved and sound
correlation between the Alano section and ODP
Site 1052 reference section, we decided to
conduct a high-resolution study of the calcare-
ous nannofossils at this site, using a consistent
counting methodology and taxonomy. The
results of this study are presented in detail in
Fornaciari et al. (2010). Here, we report (Fig.
13) the distribution patterns of the same index
species that have been monitored at Alano,
and in particular, the distributions of the index
species not used in the standard zonations, the
stratigraphic range of which is poorly known. In
Figure 14, we report the correlations of calcar-
eous plankton biohorizons between Alano and
ODP Site 1052 based on data of Wade (2004)
and our own data. The correlation shows that
10 biohorizons maintain the same ranking and
spacing and occur in the same position with
respect to the magnetic polarities. This correla-
tion suggests a straight forward interpretation of
magnetostratigraphic data from the Alano sec-
tion in terms of the standard GPTS, as indicated
by Figure 14 and summarized in Table 3. Spe-
cifi cally, Alano magnetozone A1r corresponds
to magnetochron C18r, A1n.2n to C18n.2n,
A1n.1n to C18n.1n, A2n.3n to C17n.3n, A2n.2n
to C17n.2n, and A2n.1n to C17n.1n (Figs. 8 and
14). Based on the correlation inferred between
the Alano section and ODP Site 1052 (Fig. 14),
A4r is considered to be equivalent of C16r, and,
as a consequence, the short magnetozone A3r at
Alano is apparently missing in the geomagnetic
polarity time scale of Cande and Kent (1995)
time scale. In particular, the basal part of the
section correlates with the upper part of chron
C18r, while the single sample with a reversed
polarity at the top of the section should correlate
to the base of chron C16r.
Chronology and Sediment
Accumulation Rates
The chronology of the middle–late Eocene
GPTS is in a state of fl ux (see Berggren and
Pearson, 2005, p. 284), and using the various
available calibrations (Cande and Kent, 1995;
Pälike et al., 2001; Ogg and Smith, 2004), the
chronology of the Alano section varies, as do the
calcareous plankton biochronology and sedi-
ment accumulation rates.
30
40
50
70
60
80
90
O. beckmanni HO
Morozovelloides HO
large acarininids HO
C18n
1r
2n
1n
C17n
3n
C17r
1r
2n
2r
C16n
2n
1r
1n
C16r
C18r
20
10 S. furcatolithoides HO
D. bisectus LCO
Pälike et al., 2001
150
140
130
120
110
100
90
80
70
60
50
40
17r
17n.2n
17n.1n
C18r
16r
16n.2n
Cande & Kent, 1995
17n.3n
18n.1n
18n.2n
C18r
17n.1r
16r
17n.1n
18n.1n
17r
17n.3n
17n.2n
?
18n.1r
17n.1n
17n.2r
I. recurvus LCO
O. beckmanni LO
18n.2n
Position
(m)
ALANO
section
GPTS
rmcd
(m)
ODP Site 1052
Age
(Ma)
36
37
38
39
40
S. obtusus HO
C. erbae AE
C. grandis HO
I. recurvus spike C. oamaruensis LO
G. semiinvoluta LO
C. erbae AB
C. solitus LO
Figure 14. Calcareous plankton correlation between the Alano section and Ocean Drilling
Program (ODP) Site 1052 (western North Atlantic) and resulting interpretation of the mag-
netostratigraphy of the Alano section. The geomagnetic polarity time scale of Cande and
Kent (1995) is plotted on the left side.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 861
In Figure 15, we constructed an age-depth
plot and derived sediment accumulation rates
by means of magnetostratigraphic correlation
to the geomagnetic polarity time scale of Cande
and Kent (1995), taking into account the avail-
able biostratigraphic constraints. The Alano
magnetostratigraphy straddles magnetochrons
C18r–C16r with an average sediment accumula-
tion rate of ~2.4 cm/k.y. (not corrected for com-
paction) throughout the entire section (Fig. 15).
The extrapolated age of the base of the section
is 41.15 Ma, assuming for chron C18r the mean
accumulation rate estimated during chron C18n,
and the age of the top of the section is 36.48 Ma
according to the geomagnetic polarity time scale
of Cande and Kent (1995), thus extending over
a 4.40 m.y. time interval. Adopting the chronol-
ogy of Ogg and Smith (2004), the section would
extend from 40.09 Ma to 36.40 Ma, spanning a
time interval of 3.70 m.y., and if we use the time
scale of Pälike et al. (2001), with the same as-
sumptions, the bottom and the top of the section
are at 40.82 and 36.26 Ma, respectively, cover-
ing a time interval of 4.56 m.y.
Calcareous Plankton Biochronology
Though the early Paleogene time scale is far
away from being established defi nitively, the
integrated calcareous plankton and magneto-
stratigraphic data reported in Figure 14 suggest
that at least 10 biohorizons should be consid-
ered synchronous between the Alano section
and ODP Site 1052. These datums thus provide
a precise framework and a precious correlation
tool that can be used to approximate the base of
the Priabonian Stage.
In Table 3, we synthesize the calcareous
plankton biochronology obtained in these two
successions, but a more comprehensive and de-
tailed discussion on the calcareous nannofossil
biochronology can be found in Fornaciari et al.
(2010). Here, we will only concentrate on bio-
chronologic data concerning the chronostratig-
raphy of the middle and late Eocene.
In particular, high-resolution studies on
planktic foraminifera and calcareous nanno-
fossil biohorizons reported in this study improve
our capability of correlation over wide areas by
enhancing and strengthening the biomagneto-
stratigraphic scheme available to date.
Planktic Foraminifera Biochronology
Over the last decades, several planktic
forami nifera biohorizons have been used to
subdivide the middle Eocene–late Eocene tran-
sition; a brief discussion summarizes the three
main bioevents next.
The Extinction of Muricate Morozovellids
and Large Acarininids. The most important
single point in the considered interval is the
calibration of the extinction of morozovellids
and large acarininids. The calibration of the
fi nal exit of morozavellids in Umbria-Marche
sections has been associated with the top of
chron C18n (Nocchi et al., 1986), while Wade
(2004) associated this event with the middle
part of chron C17n.3n in the NW Atlantic
ocean. Our data are in perfect agreement with
age estimation from Blake Nose, suggesting
that the event as recorded in the Apennines
might have been affected by tectonic distur-
bances (Jovane et al., 2007a).
The First Appearance of Globigerinatheca
semiinvoluta. The FAD of Globigerinatheca
semiinvoluta has been used as a primary crite-
rion for defi ning the base of zone P15 of Berg-
gren et al. (1995). The LO of G. semiinvoluta
has been observed within chron C17n.2n
(37.66 Ma) at Alano and is younger than previ-
ously indicated by Berggren et al. (1995), who
placed the LO of the species close to the base
of chron C17r (38.4 Ma), thus being older than
the HO of Morozovelloides (38.1 Ma). Our data
strongly suggest that the LO of G. semiinvoluta
is likely a diachronous event, as already noted
by Berggren et al. (1995) and Berggren and
Pearson (2005), and thus is not suitable to be
used for correlations over wide areas.
The Final Exit of Small Acarininids. At
Alano , the extinction of small acarininids occurs
within chron C17n.1n (37.27 Ma) and is older
with respect to data from Wade (2004), who re-
ported the presence of small acarininids at least
up to 34.59 Ma in chron C16n. This discrepancy
indicates a possible diachroneity of this event
and suggests caution in considering even a pos-
sible regional use for this biohorizon.
This overview clearly shows that the ex-
tinction of muricate morozovellids and large
acarini nids could be considered a valuable cor-
relation tool over wide areas, except for the
Umbria-Marche region, where the presence of a
major fault has likely produced an incorrect age
estimation for this event.
Calcareous Nannofossil Biochronology
Previous literature has proposed that the
Bartonian-Priabonian boundary is defi ned at
the base of calcareous nannofossil zone NP18,
37 38 39 40
0
20
40
60
80
100
V V V
V V V
V V V
V V V
V V V
V V V
σ
σ
σ
σ
σ
σ
Thickness T (m )
Age = M0+M1*T+M2*T
2
M0 = 41.156
M1 = –0.067829
M2 = 0.00023018
R = 0.99684
T = Thickness (m)
Age CK95 (Ma)
C18
n.3n
n.2n
n.1n
n.2n
n.1n
r
r
C17
A1r
A1n.2n
A1n.1r(?)
A1n.1n
A2r
A2n.3n
A2n.2r(?)
A2n.2n
A2n.1r
A2n.1n
A3r
A3n
A4r(?)
C16
r
Figure 15. Age-depth plot and
derived sediment accumula-
tion rate function for the Alano
section obtained by magneto-
stratigraphic correlation to
the geomagnetic polarity time
scale of Cande and Kent (1995)
(CK95).
Agnini et al.
862 Geological Society of America Bulletin, May/June 2011
where the LO of C. oamaruensis occurred (see
Berggren et al. (1985, 1995). According to
these authors, the LO of C. oamaruensis oc-
curs at 37.00 Ma in chron C17n.1n, and as a
consequence, the base of the Priabonian Stage
correlates with chron C17n.1n, with an age of
36.9 Ma (Berggren et al., 1995).
The placement of the Bartonian-Priabonian
Stage in chron C17n.1n has been commonly
used without any criticisms at least in the last
two decades. However, the recognition of fi rst
specimens of C. oamaruensis, at least in the
lower part of chron C17n.2n, both in the Alano
section (37.84 Ma) and at ODP Site 1052
(37.78 Ma), in turn implies, adopting the defi ni-
tion of Berggren et al. (1995), that the base of
the Priabonian Stage now correlates with chron
C17n.2n, not with chron 17n.1n. Unfortunately,
the LO of C. oamaruensis as well as the HO of
C. grandis have a low degree of reproducibil-
ity in many areas because of their scarce abun-
dances. Nonetheless, the integration of these
poor reference datums with the AB and AE
of C. erbae, at 37.833 Ma and 37.449 Ma, re-
spectively, provides alternative biostratigraphic
correlation tools that also better constrain this
interval.
The Middle Eocene Climatic
Optimum Interval
Though the focus of this paragraph is on
the middle to late Eocene transition, we would
just note that from the biostratigraphic point of
view, another interesting interval in the Alano
section is that between 6.3 m level (40.60 Ma)
and 22.70 m level (39.66 Ma) (Fig. 16). Several
biohorizons, which include the LOs of Spheno-
lithus predistentus, Dictyococcites scrippsae,
D. bisectus, and S. obtusus and HOs of S. fur-
catolithoides and S. spiniger, have been found to
occur close to the middle Eocene climatic opti-
mum event. Calibrations of these additional cal-
careous nannofossil biohorizons (Table 3) and
of planktic foraminifera recorded in the same
interval, for instance the LO and HO of O. beck-
manni, provide a fi ne integrated biochronologic
framework.
CHRONOSTRATIGRAPHIC
POTENTIAL OF THE ALANO SECTION:
PROPOSING THE DEFINITION OF
THE PRIABONIAN
The chronology discussed herein indicates
that the Alano section straddles the middle
Eocene–late Eocene boundary, whatever prac-
tice is followed for its recognition (Fig. 1). The
section meets all the requirements for serving as
the global stratotype section and point (GSSP)
of the chronostratigraphic unit (Remane et al.,
1996). Hence, the Alano section is here pro-
posed as a candidate GSSP for defi ning the Pria-
bonian, the accepted stage/age corresponding to
the entire Upper/late Eocene (Luterbacher et al.,
2004). According to the practice recommended
by ICS (Hedberg, 1976; Cowie et al., 1986;
Salvador, 1994; Remane et al., 1996), the Pria-
bonian Stage is formally defi ned by the GSSP
of its base, which serves also as the defi nition
of the top of the underlying Bartonian Stage and
middle Eocene–late Eocene boundary. Within
this practice, the chronostratigraphic units are
defi ned solely by the GSSPs of their bases.
However, recently, Hilgen et al. (2004) recom-
mended that the practice of unit stratotype for
standard chronostratigraphic units should be re-
covered. In the following, we detail our proposal
of defi nition of the Priabonian Stage that is to be
submitted to the ICS.
Rationales in Choosing the GSSP
The chronostratigraphic principles and prac-
tice recommended by the ICS have been largely
infl uenced by Hollis Hedberg and are summa-
rized in Hedberg (1976), Cowie et al. (1986),
Salvador (1994), and Remane et al. (1996).
They have received a wide consensus, but they
are not, however, universally accepted (e.g., see
discussions in Walsh, 2005a, 2005b, 2005c)
and, when accepted, not uniformly applied. We,
therefore, feel the need to make clear the ratio-
nales underlying our proposal of defi nition of
the Priabonian Stage.
First, contrary to some recent views (see
Walsh, 2004), we consider, in agreement with
Hedberg (1976, p. 71), the stages (and the equiv-
alent ages) to be “one of the smallest units in
the standard chronostratigraphic hierarchy that
in prospect may be recognized worldwide.”
Hence, the most important single criterion that
needs to be met by our proposal is its amenabil-
ity to worldwide correlation. There is an almost
unanimous consensus that a modern defi ni-
tion of global chronostratigraphic units should
be defi ned in points of geologic time where a
wealth of correlation tools is available so that
the boundaries of the stage can be recognized in
the different stratigraphic records. In addition,
we consider that, for an elemental need of stabil-
ity of the stratigraphic nomenclature, the mod-
ern defi nition of the global chronostratigraphic
units should be historically appropriate. The
historical appropriateness of redefi ned chrono-
stratigraphic units has been widely discussed
in the last years, and we refer to Walsh (2005a,
2005b, 2005c) for an extensive review.
In other words, in making our proposal,
the rationales driving our choice of a specifi c
point in the section will be such that: (1) the
Priabonian should be recognized worldwide,
(2) the historical stratotype sections of the Pria-
bonian and Bartonian should remain largely
Priabonian and Bartonian in age, and (3) the
most followed practice in the recognition of
the Priabonian, i.e., of the middle–late Eocene
boundary, should be respected as much as pos-
sible; the latter is the most diffi cult task, and
we are aware that it is impossible to completely
fulfi ll this latter requirement, as well as to ob-
tain a general consensus.
In the following, we fi rst address the histori-
cal appropriateness issue by briefl y reviewing
(1) the status of the Priabonian and Bartonian
Stages (and the middle–late Eocene boundary)
with reference to the classical sections upon
which they are based, including the historical
stratotypes, and (2) the practice followed in
recognizing the middle–late Eocene boundary
in the different biogeographic areas and strati-
graphic settings. The potential of global correla-
tion, a major point of dispute, will be discussed
after having proposed the position in the section
of the GSSP that is the “golden spike.”
The Middle–Late Eocene Boundary:
An Historical Overview
The history of the chronostratigraphic sub-
division of the middle and late Eocene is ex-
tremely complex and is not reviewed here.
Complete information is available in the litera-
ture to which we refer the reader (e.g., Berggren
et al., 1995; Luterbacher et al., 2004). In the
International Chronostratigraphic Scale by ICS,
the upper part of the Middle Eocene is repre-
sented by the Bartonian Stage, while the Upper
Eocene is represented by the Priabonian Stage
(Luterbacher et al., 2004; Fig. 1).
As argued by Berggren et al. (1985, 1995),
the problem with the placement of the Middle–
Upper Eocene boundary, i.e., the base of the
Priabonian, has been intimately linked with
the diffi culties in correlating the classical NW
Europe Eocene sections, mainly located in the
Paris and London Basins, with those cropping
out in the Veneto region of the Mediterranean
area (Munier-Chalmas and de Lapparent, 1893).
Actually, for a long time, they have been consid-
ered time equivalent, and have been used for in-
dicating the late Eocene (e.g., Berggren, 1971).
The Bartonian Stage
Though the stage was fi rst introduced with
reference to rocks in the Paris Basin, its name
was derived from the Barton Clay in the Hamp-
shire Basin of England (Mayer-Eymar, 1857),
and it is best known today from spectacular
exposures, serving as a “unit stratotype” for the
Bartonian, on the Isle of Wight (Fluegeman ,
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 863
PLANKTIC
FORAMINIFERA
CALCAREOUS
NANNOFOSSILS
T. cerroazulensis LO
V V V
V V V
V V V
V V V
V V V
σ σ σ
σ σ σ
Lithology
O. beckmanni
D. bisectus LCO
large acarininids HO
Morozovelloides HO G. semiinvoluta LO
P. capdevilensis HO
S. furcatolithoides HO
C. solitus HO C. oamaruensis LRO
C. oamaruensis LO
I. recurvus spike
S. obtusus
C. erbae Acme
additional calcareous plankton biohorizon
C. solitus HCO
Polarity/Chron
C17r
C18r
C17n.1r
C17n.2r
C16r
?
C18n.1r
C18n.2n
C18n.1n
C17n.1n
C17n.1n
NP18
NP17
CP14b CP Nannozone
NP Nannozone
Berggren et al.(1995)
P13 P14 P15
P12
Okada and Bukry (1980)
Martini (1971)
P Foramszone
20
10
30
40
50
70
60
80
90
100
Thickness (m)
0
C17n.2n
NP19-20
E10-11 E12 E13
Berggren and Pearson(2005)
E Foramszone
C17n.3n
E14
CP14a
NP16
CP15a CP15b
Tintoretto
Tiepolo
Canaletto
Canova
Palladio
Giorgione
Mantegna
BARTONIAN-
PRIABONIAN
BOUNDARY
C. grandis HO
A. medizzai -
A.echinata HO
D. scrippsae LCO
MECO
S. spiniger HCO
V V V
Tiziano
S. predistentus
T. cocoaensis LO
standard calcareous plankton biohorizon
Figure 16. Summary of the biomagnetostratigraphic results obtained in the Alano section. The position of the middle Eocene climatic
opti mum (MECO) as evidenced by Spofforth et al. (2008, 2010) is indicated in the lower part of the section. The shaded light-gray band
between 57.32 and 68.37 m highlights the critical interval for defi ning the base of the Priabonian Stage. LRO—Lowest Rare Occurrence;
LO—Lowest Occurrence; LCO—Lowest Common Occurrence; HCO—Highest Common Occurrence; HO—Highest Occurrence.
Agnini et al.
864 Geological Society of America Bulletin, May/June 2011
2004). On the base of data reported in Aubry
(1986), Berggren et al. (1995) assigned the
Bartonian Stage to nannofossil zones NP16
and NP17, and questionably to a part of zone
NP18. Specifi cally, Aubry reported the presence
of Sphenolithus furcatolithoides as restricted to
the Lower Barton Beds (Fig. 15 in Aubry, 1986),
whereas Sphenolithus obtusus was observed just
in lower part of the Middle Barton Beds. The
calcareous nannofossil magnetobiochronology
established in this paper (Table 3) suggests that
the Lower Barton Beds should be older than the
mid-late chron C18r, where S. furcatoli thoides
becomes extinct (Fig. 1) and lie within the early
NP16 zone, and that the Middle Barton Beds,
containing S. obtusus, should correlate with
chron C18n and upper NP16 to lowermost NP17
zones. To our knowledge, no data are available
for time constraining the Upper Barton Beds
and, hence, the top of the Bartonian as defi ned
in its type area.
The Priabonian Stage
The Priabonian Stage, named after the village
of Priabona in the eastern Lessini Mountains
(NE Italy), was proposed by Munier-Chalmas
and de Lapparent (1893, p. 479) on the basis of
several localities in the Lessini Shelf, in order
to overcome problems in correlating the NW
Europe and Mediterranean middle–late Eocene
marine stratigraphic records. Hardenbol (1968)
formally proposed, among the different sections
indicated by Munier-Chalmas and de Lapparent
(1893), to choose as the stratotype section of
the Priabonian that at Priabona (Fig. 2). This
proposal was accepted at the Eocene Collo-
quium held in Paris in 1968, where, however,
fi ve parastratotype sections were also proposed;
these were the Granella and Ghenderle (or Val
Bressana) sections in the Lessini Mountains, the
Brendola and Mossano sections in the Berici
Hills, and the Possagno section in the Veneto
pre-Alps (Cita, 1969; Fig. 17).
The sections in the Lessini Mountains (Pri-
abona, Granella, and Ghenderle) were located in
the inner part of Lessini Shelf, close to emerging
lands. Their content in calcareous plankton is
very poor, and their precise time framing is very
diffi cult (e.g., Verhallen and Romein, 1983).
The sections in the Berici Hills (Brendola and
Mossano) were as well located in the Lessini
Shelf, in more distal conditions, and have scarce
content in calcareous plankton (Luciani et al.,
2002). Finally, the deep-water Possagno section,
located at the transition from the Lessini Shelf
to the Belluno Basin, is the only one, among
those proposed as parastratotype of the Pria-
bonian, that can be framed in time accurately
(Bolli, 1975; Agnini et al., 2006). To follow, we
will concentrate on three of these parastratotype
sections, the Priabona, Mossano, and Possagno
sections, adding some remarks also on the pe-
lagic Contessa Highway section (central Italy),
which has been proposed by Luterbacher et al.
(2004) as a candidate section for defi ning the
Priabonian.
Traditional Criteria Used in Locating the
Base of the Priabonian (Upper Eocene)
In the shallow-water sections, the master
paleontologic guiding criterion used for recog-
nizing the Priabonian has been the fi rst appear-
ance of Nummulites fabianii. This biohorizon
defi nes the base of the shallow benthic forami-
nifera zone SBZ19 (Serra-Kiel et al., 1998)
and has been utilized in the Priabona and Mos-
sano section (Hottinger, 1977; Parisi et al.,
1988; Bassi and Loriga Broglio, 1999; Bassi
et al., 2000) as well as in all other Tethyan
shallow-water successions (e.g., Strougo, 1992;
Serra-Kiel et al., 1998).
In the deep-water sections, the base of the
Priabonian (Upper Eocene) has been tradition-
ally associated with the extinction of the large
muricate globorotalids, which virtually coin-
cide with the base of zone E14 (Berggren and
Pearson, 2005; Fig. 1), and with the lowest ap-
pearance of C. oamaruensis, which defi nes the
base zone NP18 (Martini, 1971). These two
bio horizons have been observed both in the
Tethyan domain (Alano, Possagno, and Con-
tessa Highway sections; Jovane et al., 2007a;
this study) and in and NW Atlantic ODP Site
1052 (Wade, 2004; this study).
It is noteworthy that the LO of N. fabianii,
that is the base of zone SBZ 19, was considered
as correlative with the base NP18 (Serra-Kiel
et al., 1998), although this correlation is not
warranted by sound data to our knowledge.
Time Frame of the Base of the Priabonian
at Priabona
The time frame of the Priabona section is par-
ticularly diffi cult because of the shallow-water
transgressive nature of the succession (Setiawan,
1983). Probably the most reliable time frame of
the section was established by Brinkhuis (1994)
by means of a dinofl agellate cyst biostratigraphy
from previously magnetostratigraphically well-
calibrated pelagic sequences from central Italy.
Brinkhuis concluded that the Priabona section
belongs to Melitasphaeridium pseudorecur-
vatum cone, correlative with chron C15–C16
and zones NP19–20 and P16 (Brinkhuis and
Biffi , 1993; Brinkhuis, 1994). This interpreta-
tion is supported by the evidence at Priabona
where I. recurvus has been detected virtually
from the base of the section with good continu-
ity (Ver hallen and Romein, 1983), and this form
becomes well established in the Mediterranean
sections only in advanced chron C16n time
(Coccioni et al., 1988; Fornaciari et al., 2010).
Hence, we concur with Brinkhuis (1994) that the
historical Priabonian stratotype starts indeed in
advanced Priabonian time, if all the current prac-
tices for its recognition are considered (Fig. 1).
Time Frame of the Base of the Priabonian
at Mossano
The Mossano section has been intensively
studied because of its rich paleontologic con-
tents (for a comprehensive review, see Bassi
et al., 2000). The Bartonian-Priabonian bound-
ary, i.e., the LO of N. fabianii, has been placed
in coincidence with a major facies change from
shallow-water carbonate facies (Calcare num-
mulitico Auctorum) to deeper-water terrigenous
facies (Marna di Priabona). The Priabonian at
Mossano is more than 100 m thick (Ungaro,
1969), although useful fairly detailed data have
been collected only in the basal most part by Lu-
ciani et al. (2002), who studied the calcareous
plankton across the transition between the two
formations. Specifi cally, they observed the total
lack of calcareous plankton in the upper part
of Calcare nummulitico and documented poor
planktic foraminifera and calcareous nanno-
fossils assemblages in 10 samples from the
basal ~11 m of the Marne di Priabona, where
signifi cant datums are the occurrences of Glo-
bigerinatheca semiinvoluta (in the lower 6 m of
the Marne di Priabona), I. recurvus (in a single
sample at 8 m above the base of the Marna di
Priabona), and Turborotalia cunialensis (in two
samples at 9 and 10 m above the base of the
Marna di Priabona). The presence of the latter
form, appearing in chron C15r time (Berggren
et al., 1995), strongly suggests, as for the type
Priabonian at Priabona, an advanced Priabonian
age with reference to the conventional criteria
used for its recognition (Figs. 1 and 17). The oc-
currence of I. recurvus at ~8 m from the base
would reinforce this interpretation. However,
detailed interpretation of the Mossano data is
diffi cult. Specifi cally, it is diffi cult to interpret
the short spacing (just 3 m) between the HO
of G. semiinvoluta and the LO of T. cunialen-
sis, because these two biohorizons would be
separated by some 0.6 m.y. on the basis of the
available biochronology (Fig. 1). Three options
are possible: (1) the current distribution models
of the two species are not completely known,
(2) the sediment accumulation rate is exceed-
ingly (and unreasonably) low for shelf sedi-
ments, or (3) there is a hiatus within the short
interval considered. Whatever the interpretation
is, it can be conservatively stated that the basal
sediments at Mossano are younger than the late
chron C17n.2n to which we have calibrated
the LO of G. semiinvoluta at Alano (Fig. 10;
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 865
0
100
150
200
250
300
Position
(m)
Catanzariti (unpublished)
Cita (1975)
Proto Decima et al. (1975)
240
230
220
210
290
280
270
260
190
180
170
160
140
130
120
110
50
40
30
20
10
90
80
70
60
30
40
50
70
60
80
90
large acarininids HO
C18n
1r
2n
1n
C17n
3n
C17r
1r
2n
2r
C16n
2n
1r
1n
C16r
C18r
20
10 S. furcatolithoides HO
D. bisectus LCO
C18r
17n.1r
16r
17n.1n
18n.1n
17r
17n.3n
17n.2n
?
18n.1r
17n.1n
17n.2r
I. recurvus LCO
18n.2n
Brinkhuis (1994)
Setiawan (1983)
Verhallen and Romein (1983)
R. umbilicus LO
Lowrie et al. (1982)
Luciani et al. (2002)
18r
18n.2n
19r
Jovane et al. (2007a)
20n
20r
19n
16n
18n.1n
Monechi and Thierstein (1985)
17n
140
130
120
110
100
150
160
Coccioni et al. (1988)
Lowrie and Lanci (1994)
Jovane et al. (2007b)
0
10
20
30
40
50
60
70
80
Position
(m)
100
0
C16n.1n
C15r
C15n
C13r
C13n
20
10
0
Position
(m)
C16n.2n
Ungaro (1969)
10
0
Position
(m)
Conglomerato
del Boro
conglomerate
nodular, relatively
brittle limestone
nodular limestone
slightly nodular limestone
unbedded limestone
bedded limestone
bedded limestone with
discontinuous clayey layers
silty marl
silty marl with nodules
not exposed
POSSAGNO
section
NP18/NP19/NP20
Position
(m)
ALANO
section
GPTS
(CK95)
Age
(Ma)
36
37
38
39
40
PRIABONA
section
MOSSANO
section
CONTESSA
HIGHWAY
section
Position
(m)
NP17/NP18
NP16NP15
MASSIGNANO
section
NP16/NP17
NP15
NP19/NP20/NP21
NP19/20 NP21
DEEP-WATER SECTIONS
SHALLOW WATER
SECTIONS
NP18NP16 NP19/NP20
NP17
G. semiinvoluta LO
I. recurvus spike
S. obtusus HO
Figure 17. Stratigraphic correlation between the deep-water sections of Alano, Possagno, Contessa
Highway, and Massignano and the shallow-water successions of Mossano and Priabona.
Agnini et al.
866 Geological Society of America Bulletin, May/June 2011
Table 3). However, probably, the most impor-
tant output of this discussion is that the LO of
N. fabianii, i.e., the base of zone SBZ19, is to be
correlated with a time younger, probably much
younger, than the late chron C17n.2n.
Correlation among Alano, Possagno, and
Contessa Highway Sections
In Figure 17, we show the correlation of the
Alano section with the classical deep-water sec-
tions of Possagno and Contessa Highway. The
correlation with Possagno is straightforward,
even if the available data for Possagno have
been collected in low resolution. The correla-
tion to the Contessa Highway section is more
problematic, because the position of the ex-
tinction of large acarininids, one of the most
distinctive biohorizons in late Eocene planktic
foraminifera, is located in chron C17n.3n in
the Alano section, whereas it was interpreted
to lie in chron C18n.1n in the Contessa High-
way section (Jovane et al., 2007a; Fig. 17).
The apparent inconsistency between these data
is likely explained by the presence of a major
previously undescribed fault. We agree with
Jovane et al. (2007a) that this signifi cant fault
zone has removed a portion of the record, but in
our interpretation, the missing interval is much
more important than indicated by these authors,
covering at least the entire C18n.1n, and thus
suggesting that the HO of large acarininids falls
in chron C17n.3n, now in accordance with data
from the Alano section and ODP Site 1052.
Current Practice in Recognizing the
Base of the Priabonian (Middle–Upper
Eocene Boundary)
We can confi dently state that, in the past 30 yr,
the most infl uential authors in determining the
practices in Cenozoic chronostratigraphic as-
signments have been William Berggren and
coworkers, in particular, with their compila-
tions of 1985 and 1995. Marine and continental
stratigraphers have, sometimes uncritically, fol-
lowed the proposals of Berggren and coworkers,
which have become an unoffi cial standard in
the absence of a formally defi ned International
Chronostratigraphic Scale. Concerning the Pria-
bonian, Berggren et al. (1985), after carefully
reviewing the status of the Bartonian-Priabonian
boundary in the literature, and considering both
the time frame of historical sections and the
correlation tools available at that time, placed
the Bartonian-Priabonian boundary, i.e., the
middle–late Eocene boundary, at NP17/NP18
zonal boundary, correlated with the younger part
of chron C17n (Fig. 5 in Berggren et al., 1985).
Berggren et al. (1995) confi rmed this placement
of the boundary, assigning a revised estimated
age of 37.0 Ma to the LO of C. oamaruensis,
that is, the base of zone NP18 (Fig. 2 in Berg-
gren et al., 1995). Actually, data on the calcare-
ous plankton biostratigraphy and biochronology
available in Berggren et al. (1985, 1995) were
contradictory and poorly constrained (see Tables
9 and 15 in Berggren et al., 1995), as shown by
Wade (2004) and in the present work (Table 3).
Surprisingly, Berggren et al. (1985, 1995)
did not attach a major importance to the extinc-
tion of large muricate globorotalids, which they
calibrated to late chron C18n, and associated
the base of the Priabonian with chron C17n.1n,
to which they calibrated the LO of C. oamaru-
ensis (Fig. 2 in Berggren et al., 1995). Hence,
they privileged the latter two poor biostrati-
graphic datums and underplayed an event that
we consider to be reliable. However, the pro-
posal of Berggren and coworkers has become
widely accepted, and it can be safely stated
that the most widespread practice for locating
the base of the Priabonian has been to equate the
Middle–Upper Eocene boundary with the base
of zone NP18 lying in late chron C17n.1n (e.g.,
Serra-Kiel et al., 1998). As a matter of fact, even
planktic foraminifera specialists (e.g., Wade,
2004; Berggren and Pearson, 2005) have placed
the Middle–Upper Eocene boundary above the
extinction of large muricate planktic foraminif-
era. Actually, in the present work (Table 3), we
have shown that our LO of C. oamaruensis, al-
though scarcely reproducible, is much closer to
extinction of large planktic spinose foraminifera
than reported by Berggren et al. (1995), and this
fi nding is of considerable importance for pro-
posing the GSSP of the Priabonian put forward
in the following section.
Proposal of the GSSP of the Priabonian
In synthesis, the previous discussion shows
that these are the paleontologic criteria that have
been widely used for recognizing the base of the
Priabonian in the marine stratigraphic records:
(1) the LO of Nummulites fabianii, i.e., the
base of zone SBZ19, applied in shallow-water
facies (e.g., Serra-Kiel et al., 1998);
(2) the HO of large muricate planktic forami-
nifera, correlating with the base of zone E14
(e.g., Mancin and Pirini, 2002); and
(3) the base of zone NP18, i.e., the LO of
C. oamaruensis (i.e., Berggren et al., 1985, 1995).
In the deep-water Alano section, the LO of
N. fabianii is not recorded, while events defi n-
ing the other two criteria are clearly detected
and occur in the lower chron C17n, in a ~6–7 m
interval, corresponding to ~0.16 m.y. (Fig. 18).
This is the critical interval to consider for driving
the “golden spike,” if we wish to guarantee both
correlatability and historical appropriateness.
The most widespread practice in proposing
GSSPs has been and still is to locate the “golden
spike” exactly in the lithologic level where a
specifi c, arguably widely correlatable, biostrati-
graphic or magnetostratigraphic event occurs.
Within this practice, there would be three viable
options at Alano for defi ning the base of the
Pria bonian (see Figs. 16 and 18):
(1) the HO of large muricate globorotalids
foraminifera at 57.32 m level, which is here
considered a reliable and widely traceable event
(see previous discussion); this choice would be
probably the best preferred by planktic forami-
nifera specialists;
(2) the base of zone NP18, at 62.85 m level,
which we have shown to be defi ned by a poor
biohorizon (LO of C. oamaruensis), but which
appears to be a commonly followed practice in
the last years and would be probably the best
preferred by calcareous nannoplankton spe-
cialists; or
(3) the polarity reversal at the base of chron
C17n, which would allow a correlation with
continental records, and would be probably the
best preferred choice by magnetostratigraphic
specialists.
However, we disagree this practice and con-
cur with Berggren et al. (1985, p. 1409) that:
“...proper stratigraphic procedure requires that
paleontologic criteria, although defi nitive for
regional correlation (i.e., recognition) beyond
the stratotype region, should not be part of the
defi nition itself... (Hedberg, 1976).”
Therefore, in order to preserve harmony
within the stratigraphic community, we pre-
fer to propose as the GSSP a lithologic level
easily recognized in the fi eld around which
signifi cant changes occur that allow its ap-
proximated correlation in the different strati-
graphic rec ords worldwide. Such an approach,
beyond having the advantage of making the
GSSP easily recognizable in the fi eld, serves
also to make it clear that chronostratigraphy
is not biostratigraphy and/or magnetostratig-
raphy, and that long distance and different
facies (marine and continental) correlations
are essentially geochronologic in nature (Van
Couvering and Berggren, 1977). It is to say,
time, and not a particular biostratigraphic or
magnetostratigraphic feature, is used for rec-
ognizing with approximation a chronostrati-
graphic boundary. Therefore, what is crucially
important is to know the exact age of the litho-
logic point that defi nes a boundary. Ideally, as
it has been done for the late Neogene, a GSSP
should be defi ned in orbitally tuned sections,
i.e., framed in an astrochronology with an ac-
curacy that is not attainable with other tools.
Such a chronology is not yet available in the
Alano section, even if the cyclicity apparently
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 867
present in geochemical and lithologic proper-
ties is presently under study.
Within this strictly Hedbergian conceptual
frame, we propose to the ICS that the base of
the Priabonian should be defi ned at the base
of the Tiziano bed at 63.57 m level in the
Alano section. In Figure 18, we report
the chronology of the Tiziano bed with refer-
ence to the geomagnetic polarity times scale
available models, none of which is probably
defi nitive. The proposed defi nition allows
the recognition of the Priabonian worldwide
with a good approximation. The defi nition we
propose is historically appropriate and rea-
sonably respectful of the most recent strati-
graphic practices; in fact:
(1) the Priabonian, as defi ned in its strato-
type at Priabona and recognized in the classical
Veneto region, is comprehended in the proposed
defi nition;
(2) classical middle Eocene taxa like the large
muricate planktic foraminifera remain in the
middle Eocene;
(3) Istomolithus recurvus, an unquestionable
late Eocene calcareous nannofossil taxon, re-
mains in the late Eocene; and
(4) Nummulites fabianii, an unquestionable
Late Eocene large foraminiferal taxon, remains
in the late Eocene.
A major drawback of the proposed defi nition is
represented by the fact that we do not know with
accuracy the chronology of the large foraminifera
evolution at the transition from the middle to the
late Eocene, and there is a chance that large ben-
thic foraminifera traditionally considered middle
Eocene could result in the late Eocene moving
within the proposed defi nition. However, looking
at the stratigraphic information available in the
critical interval for defi ning the Priabonian, we
do not see alternative to the proposed defi nition.
Global Correlation
The GSSP is the only place where we actually
know (by defi nition) that time and rocks coincide
within our classifi cation (Holland, 1984, p.149).
Elsewhere from the type section, a chrono-
stratigraphic boundary can only be approxi-
mated by using and cross-checking the different
available correlation tools. In the following, we
discuss the correlatability potentials of the pro-
posed GSSP of the Priabonian at Alano.
Magnetostratigraphy
The chron C17r–chron C17n boundary is lo-
cated 10.95 m below the proposed GSSP and
serves as good approximation of the base of the
Priabonian in continental and marine settings.
Within the current age models of the geomag-
netic polarity time scale, the approximation
range from 309 to 250 ka depends on the model
considered (Fig. 18).
Marine Biostratigraphy
It is beyond our scope to review all the marine
fossil groups that may provide tools for recog-
nizing the base of the Priabonian in the differ-
ent depositional settings and biogeographic
regions. In Figure 18 (and Table 4), we compare
the age of the Tiziano bed, that is the base of
the Priabonian, with the biochronology of cal-
careous plankton, the most powerful correlation
tool available in marine sediments. The extinc-
tion of the large muricate planktic foraminifera
would approximate the base of the Priabonian
within 200 k.y. The well-consolidated practice
of recognizing the Priabonian by the means of
its original defi nition, i.e., the LO of C. oamaru-
ensis, should be used with caution. Instead,
C17r
50
70
60
80
TIZIANO BED
Δ
38.0
37.6
37.8
(37.814)
37.9
37.7
38.1
V
Δ
(38.001)
(37.996)
(37.837)
(37.833)
C. oamaruensis LRO (62.85 m)
Morozovelloides HO (57.52 m)
large acarininids HO (57.32 m)
G. semiinvoluta LO (68.37 m)
(37.833)
CK95
37.7
37.3
37.5
(37.521)
37.6
37.4
37.8
V
Δ
(38.677)
(37.673)
(37.539)
(37.537)
(37.396)
GTS04
C. erbae AB
(62.96 m)
37.7
37.5
37.9
(37.588)
37.6
37.4
37.8
V
Δ (37.778)
(37.773)
(37.608)
(37.605)
(37.454)
Pälike et al.
C17n.3n C17n.2n
2r 1r C17n.1n
V
(2001)
(Ma) (Ma)
(Ma)
Chron Lithology
Position (m)
Chron C17n.3n base (52.62 m)
(38.113)
38.2
(37.771)
(37.897)
Figure 18. Close-up of the critical interval for defi ning the base of the Priabonian. Biomagnetostratigraphic events considered as useful for
approximating the middle–late Eocene boundary, that is the base of the Tiziano bed, are plotted against magnetostratigraphy and lithology.
Age estimations for the Tiziano bed as well as for biomagnetostratigraphic events are calculated using different time scales (geomagnetic
polarity time scale of Cande and Kent [1995]; GTS04; Pälike et al., 2001) and are reported on the right side. LO—Lowest Occurrence;
LCO—Lowest Common Occurrence; HO—Highest Occurrence.
Agnini et al.
868 Geological Society of America Bulletin, May/June 2011
we are confi dent that the acme beginning of
C. erbae , at 61 cm below the base of the Tiziano
bed, recorded in many sections in Italy and in
the Atlantic Ocean (see Fornaciari et al., 2010),
represents an easy to recognize event and accu-
rate approximation (within less than 20 k.y.; Fig.
18; Table 4) of the base of the Priabonian.
Required Future Work
The proposed defi nition of the GSSP of the
Priabonian will serve to overcome the present
unacceptable state of uncertainty and contradic-
tions in recognizing the middle Eocene–late Eo-
cene boundary. However, further work is needed
to better constrain in time the absolute age of the
proposed GSSP. In particular, we are working
on the radioisotopic dating of the Tiziano bed
and the orbital tuning of the Alano section in
order to assess a better age of the GSSP.
Other work that is needed is a better tie be-
tween the large benthic foraminifera biostratig-
raphy and the geomagnetic polarity time scale
in order to provide a better correlation potential
between shallow- and deep-water successions.
Toward a Unit Stratotype of the Priabonian
Within the current rules of the ICS, the top
of the Priabonian, equivalent to the base of
the Rupelian and to the Eocene-Oligocene
boundary, is defi ned by the GSSP approved
at Massignano, in the Marche region (North-
ern Apennines, Italy). If our proposal at Alano
will be accepted, the Priabonian Stage may be
formally and unequivocally defi ned according
to the approved rules of the ICS. However, we
concur with Hilgen et al. (2004) that a stage is a
kind of stratigraphic unit that is best represented
by succession of strata rather than by two single
points in the stratigraphic record. It is proposed
here that if the orbital tuning at Alano is suc-
cessful, the unit stratotype of the Priabonian
could be represented by the composite section
constituted by the Alano and Massignano sec-
tions. As shown in Figure 17, these two sections
together seem to represent the entire interval of
time that we have proposed as representing the
Priabonian.
CONCLUSIONS
The major output of this paper is the proposal
to the ICS of designating the base of a promi-
nent crystal tuff layer (Tiziano bed) in the Alano
section, NE Italy, as the GSSP of the Priabonian
Stage, the standard chronostratigraphic unit of
the Upper Eocene. The section, described for
the fi rst time in this paper, is continuously and
spectacularly outcropping, well accessible, un-
affected by structural deformation, rich in well-
preserved planktic foraminifera and calcareous
nannofossils, and contains six prominent crystal
tuff layers, some of which seem amenable to
isotopic dating.
A second output of our study is a much im-
proved chronostratigraphic framework for the
middle–late Eocene transition, which has been
controversial in the literature. The high-resolu-
tion and solid biomagnetostratigraphic frame-
work established at Alano has been compared
with the data already available (Wade, 2004) or
was acquired specifi cally for this work in the
deep-sea ODP Site 1052, straddling the middle–
late Eocene. We have shown that the extinction
of large muricate planktic foraminifera, a major
step in the evolution of this group during the
Cenozoic (e.g., Berggren, 1969), occurred in
mid–chron C17n.3n and was probably a syn-
chronous event over wide areas. Concomitant
with this event, major changes are observed in
the calcareous nannofossil assemblages, the
most important of which is the acme beginning
of the distinctive Cribrocentrum erbae. We have
revised the biostratigraphic reliability and bio-
chronology of calcareous plankton, pointing out
that the LO of C. oamaruensis and the HO of
C. grandis must be used with extreme caution
for accurate correlations, the LO of I. recurvus
is much older than in previous age estimates
(e.g., Berggren et al., 1995), and the biochronol-
ogy of the LO of T. cerroazulensis group likely
needs to be signifi cantly changed with respect
to calibration reported in Berggren et al. (1995).
We have discussed the correlation potential
of the proposed Priabonian GSSP at Alano. The
extinction of muricate planktic foraminifera and
the acme beginning of C. erbae are thought to
be useful tools for approximating the base of the
Priabonian in the marine stratigraphic records
over large areas and depositional settings. The
base of chron C17n is useful for correlation with
continental records. Most probably, the fi rst ap-
pearance of Nummulites fabianii would remain
a useful criterion for recognizing the Priabonian
in shallow-water marine settings, even if an im-
proved correlation between the large forami nif-
era biostratigraphy to the geomagnetic polarity
time scale is in order.
If the proposed GSSP will be accepted,
the Priabonian, the top of which is defi ned at
Massignano (Premoli Silva and Jenkins, 1993),
would have a duration of ~4.1 m.y., compared
to the estimated duration of 3.5 m.y. of Berg-
gren et al. (1995) and 3.3 m.y. of Ogg and
Smith (2004).
Work is continuing on the Alano section in an
attempt to establish an orbital tuning of the pro-
posed GSSP and isotopic dating of the Tiziano
bed, both of which would allow a much better
time frame for the base of the Priabonian and
improve the time scale of the late Eocene. How-
ever, the data available and presented in this
paper are considered adequate for formalizing
the GSSP of the Priabonian at the base of the
Tiziano bed in Alano section, thus contributing
to the task of ratifying GSSPs and stabilizing
the International Chronostratigraphic Scale ex-
pected within the next International Geologic
Congress in 2012.
ACKNOWLEDGMENTS
We would like to thank Eustoquio Molina,
Simonetta Monechi, and the GSA Bulletin science
editor, Christian Koeberl, for their reviews. This re-
search was mostly funded by MIUR-PRIN grant
2007W9B2WE_004 to D. Rio (within a National
Research Project coordinated by I. Premoli Silva).
Additional funding was provided to P. Grandesso and
TABLE 4. EVENTS DURING THE BARTONIAN-PRIABONIAN TRANSITION
Position Position†Notation relative to chron top CK95 Age* GTS04 Age* Pälike et al. (2001) Age*
)ak()aM()ak()aM()ak()aM()m()m(tnevE
C. erbae AE 75.01 11.44 C17n.1n 0.972 37.449 365 37.342 179 37.396 191
G. semiinvoluta LO 68.37 4.8 C17n.2n 0.250 37.665 149 37.396 125 37.454 134
Tiziano bed (base) 63.57 0 C17n.2n 0.861 37.814 0 37.521 0 37.588 0
C. erbae AB 62.96 –0.61 C17n.2n 0.939 37.833 –19 37.537 –16 37.605 –17
C. oamaruensis LRO 62.85 –0.72 C17n.2n 0.953 37.837 –22 37.539 –19 37.608 –20
Morozovelloides HO 57.52 –6.05 C17n.3n 0.394 37.996 –182 37.673 –153 37.773 –185
Large acarininids HO 57.32 –6.25 C17n.3n 0.418 38.001 –187 37.677 –157 37.778 –190
Chron C17n.3n base 52.62 –10.95 C17n.3n 1.000 38.113 –299 37.771 –250 37.897 –309
Note: CK95—Cande and Kent, 1995; GTS04—Geological Time Scale 2004; LO—Lowest Occurrence; AB—Acme Beginning; LRO—Lowest Rare Occurrence; HO—
Highest Occurrence. Age is calculated relative to the base of the Tiziano bed.
*Age (ka) relative to the Tiziano bed.
†Position (m) relative to the Tiziano bed.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Geological Society of America Bulletin, May/June 2011 869
C. Stefani by the University of Padova, to L. Lanci
by Urbino University, to G. Muttoni by the Univer-
sity of Milano, to D.J.A. Spofforth by a Natural
Environment Research Council studentship (NER/
S/A/2005/13474), and to H. Pälike by Particle Physics
and Astronomy Research Council - Science and Tech-
nology Facilities Council grant PP/D002176/1.
The research project was promoted and coor-
dinated by D. Rio, who supervised the organiza-
tion and wrote the general parts of the manuscript;
P. Grandesso, C. Stefani, C. Agnini, L. Giusberti, and
D. Rio described the section and regional geology;
D. Spofforth and H. Pälike produced the geochemical
data; L. Giusberti studied benthic foraminifera and in-
terpreted paleodepth; G. Muttoni and L. Lanci studied
paleomagnetism; V. Luciani studied planktic forami-
nifera; and E. Fornaciari and C. Agnini examined cal-
careous nannofossils.
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MANUSCRIPT RECEIVED 22 AUGUST 2009
REVISED MANUSCRIPT RECEIVED 22 OCTOBER 2009
MANUSCRIPT ACCEPTED 29 OCTOBER 2009
Printed in the USA
Plate I. 1–23: Planktonic foraminiferal scanning electron micrograph (SEM) images of selected zonal markers from the middle–late Eocene
Alano section (northern Italy). “Large acarininids”: 1, 2—Acarinina topilensis. Sample COL 345 b (1. ventral view; 2. spiral view). 3, 4—
Acarinina rohri (3. sample COL 40a, spiral view; 4. sample COL 600a, spiral view). “Small acarininids”: 5, 6—Acarinina medizzai. Sample
COL 2799c (5. ventral view; 6. spiral view). 7, 8—Acarinina echinata. Sample COL 4845c (7. ventral view; 8. ventral view). 9—Morozo-
velloides coro natus. Sample COL 2496c, ventral view. 10—Morozovelloides crassatus. Sample COL 732c, ventral view. 11–15—Turborotalia
cocoaensis (11, 12, 13—sample COL 520a [horizon of lowest occurrence of the species], profi le; 14. sample COL 600 a, ventral view; 15—
sample COL 1285b, profi le). 16, 17—Globigerinatheka semiinvoluta, sample COL 4605c. 18, 19—Sample COL 440a, Orbulinoides beckmannii.
20–23—Guembelitroides nuttallii (20. sample COL 240a, spiral side; 21. sample COL 3701c, spiral side; 22. sample COL 492c, ventral side;
23—sample COL 3281c, lateral side). Scale bar = 100 µm.
Integrated biomagnetostratigraphy of the Alano section (NE Italy): A proposal for defi ning the middle-late Eocene boundary
Agnini et al.
Plates I and II.
Supplement to: Geological Society of America Bulletin, v. 123; no. 5/6; doi: 10.1130/B30158.S1
© Copyright 2011 Geological Society of America
1234
5678
910 11 12
13 14 15 16
Plate II. Microphotographs of selected calcareous nannofossil taxa from the middle–late Eocene Alano section (north-
ern Italy). 1, 2—Isthmolithus recurvus. Sample COL 4645c (1. parallel light; 2. crossed nicols). 3—Chiasmolithus
oamaurensis. Sample COL 5225c. Crossed nicols. 4—Chiasmolithus grandis. Sample COL 40a. Crossed nicols. 5, 6—
Cribrocentrum erbae (5. sample COL 3521c, crossed nicols; 6. sample 171B-1052B-10H-2w, 130 cm, crossed nicols).
7—Cribrocentrum reticulatum. Sample COL 10b. Crossed nicols. 8—Chiasmolithus solitus. Sample COL 40a. Crossed
nicols. 9–11—Sphenolithus obtusus. Sample COL 1285b (9. crossed nicols 0
°
; 10. crossed nicols 45
°
; 11. crossed nicols
20
°
). 12—Reticulofenestra umbilicus. Sample COL 40a. Crossed nicols. 13—Dictyococcites bisectus. Sample COL 40a.
Crossed nicols. 14—Dictyococcites scrippsae. Sample COL 40a. Crossed nicols. 15, 16—Sphenolithus furcatolithoides.
Sample COL 0 (15. crossed nicols 0
°
; 16. crossed nicols 45
°
).
