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Geol. Mag. 141 (4), 2004, pp. 401–416. c
2004 Cambridge University Press 401
DOI: 10.1017/S0016756804009409 Printed in the United Kingdom
Organic-carbon deposition in the Cretaceous of the Ionian Basin,
NW Greece: the Paquier Event (OAE 1b) revisited
HARILAOS TSIKOS*†, VASILIOS KARAKITSIOS‡, YVONNE VAN BREUGEL§,
BEN WALSWORTH-BELL¶, LUCA BOMBARDIERE, MARIA ROSE PETRIZZO¶,
JAAP S. SINNINGHE DAMST ´
E§, STEFAN SCHOUTEN§, ELISABETTA ERBA¶,
ISABELLA PREMOLI SILVA¶, PAUL FARRIMOND, RICHARD V. TYSON
& HUGH C. JENKYNS*
*Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK
‡Department of Geology, University of Athens, Panepistimiopolis 15784, Athens, Greece
§Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research (NIOZ),
1790 AB Den Burg, The Netherlands
¶Department of Earth Sciences ‘Ardito Desio’, University of Milan, Via L. Mangiagalli 34, 20133 Milano, Italy
NRG, School of Civil Engineering & Geosciences, Drummond Building, University of Newcastle,
Newcastle upon Tyne NE1 7RU, UK
(Received 11 August 2003; accepted 20 January 2004)
Abstract – We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for
the Vigla Shale Member of the Ionian Zone in NW Greece, in order to characterize organic carbon-rich
strata that potentially record the impact of Cretaceous Oceanic Anoxic Events (OAEs). In a section
exposed near Gotzikas (NW Epirus), we sampled a number of decimetre-thick, organic carbon-rich
units enclosed within marly, locally silicified, Vigla Limestone (Berriasian–Turonian). All these units
are characterized by largely comparable bulk geochemical characteristics, indicating a common marine
origin and low thermal maturity. However, the stratigraphically highest of these black shales is further
distinguished by its much higher total organic-carbon (TOC) content (28.9 wt%) and Hydrogen Index
(HI) (529), and much enriched δ13Corg value (−22.1‰). Planktonic foraminiferal and calcareous
nannofossil biostratigraphy indicate a lower to middle Albian age for the strata immediately above,
and a lower Aptian age for the strata below, the uppermost black shale. In terms of molecular organic
geochemistry, the latter black shale is also relatively enriched in specific isoprenoidal compounds
(especially monocyclic isoprenoids), whose isotopic values are as high as −15‰, indicating a
substantial archaeal contribution to the organic matter. The striking similarities between the molecular
signatures of the uppermost Vigla black shale and coeval organic-rich strata from SE France and the
North Atlantic (ODP Site 1049C) indicate that this level constitutes a record of the Paquier Event
(OAE 1b).
Keywords: Cretaceous, Albian, stratigraphy, isotopes, carbon.
1. Introduction
The western Hellenides constitute part of the southern
passive continental margin of the early Mesozoic to
mid-Cenozoic Tethyan Ocean. Within this domain, a
number of argillaceous–siliceous and organic carbon-
rich units are associated with pelagic carbonate series
(Bernoulli & Jenkyns, 1974; Chiotis, 1983; Jenkyns,
1988; Baudin & Lachkar, 1990; Karakitsios, 1995;
Karakitsios & Rigakis, 1996; Rigakis & Karakitsios,
1998; Neumann & Zacher, 2004). Some of these
organic-rich sediments may be causally linked to
widespread Oceanic Anoxic Events (OAEs), as ori-
ginally defined by Schlanger & Jenkyns (1976) for the
Mesozoic. OAEs define periods during which much
†Author for correspondence: h.tsikos@abdn.ac.uk; present
address: Department of Geology & Petroleum Geology, University
of Aberdeen, Aberdeen AB24 3UE, UK.
of the world’s oceans became severely depleted in
oxygen and widespread deposition of organic carbon-
rich shales took place (Jenkyns, 1980). The driving
mechanism of OAEs is still the subject of much con-
troversy and suggested possibilities include, amongst
others, increased primary production, expansion of the
oxygen-minimum zone, water-column stratification,
large-scale volcanism, and/or episodic release of gas
hydrates, either singly or in combination (Jenkyns,
1999, 2003; Larson & Erba, 1999; Jones & Jenkyns,
2001). In many cases there is organic geochemical
evidence for sulphate reduction in the higher levels
of the water column during the most intense phases
of OAEs (Sinninghe Damst´
e&K¨
oster, 1998; Kuypers
et al. 2002b; Pancost et al. 2004).
The organic-rich intervals cropping out in the
Ionian Zone in northwestern Greece are contained
withinthe Albian–Cenomanian ViglaShale Member or
402 H. TSIKOS AND OTHERS
‘Upper Siliceous Zone’ of the Vigla Limestone Form-
ation (IGRS-IFP, 1966; Karakitsios, 1995; Rigakis &
Karakitsios, 1998). Although certain lithological and
organic geochemical aspects of such horizons in the
Vigla Shale Member have already been reported
(e.g. Rigakis & Karakitsios, 1998), no combined
stratigraphic and geochemical studies in the context of
Oceanic Anoxic Events have hitherto been undertaken.
In this paper, we present new chemostratigraphic,
biostratigraphic and organic geochemical data from a
section of the Vigla Shale Member in the Gotzikas area
in NW Epirus, Greece. These results provide insights
into the palaeoenvironmental setting of the Vigla
sediments, and facilitate comparisons and correlation
with analogous organic-rich sequences deposited in the
Tethys and Atlantic oceans.
2. Regional geological framework
The Ionian Zone of northwestern Greece (Epirus
region) constitutes part of the most external zones
of the Hellenides (Paxos Zone, Ionian Zone, Gavrovo
Zone; Fig. 1a). These zones correspond to the Hellenic
domain of the southern passive continental margin
associated with early Mesozoic opening and late
Mesozoic–early Cenozoic closure of the Neotethyan
Ocean (Laubscher & Bernoulli, 1977; Karakitsios,
1992, 1995). The rocks of the Ionian Zone range from
Triassic evaporites and associated breccias through
a varied series of Jurassic through upper Eocene
carbonates and lesser cherts and shales, followed by
Oligocene flysch (Fig. 2).
During the early Lias, the present part of north-
western Greece was covered by an extensive carbonate
platform (Bernoulli & Renz, 1970; Karakitsios, 1992,
1995). The contemporaneous, shallow-water Pan-
tokrator limestones (Aubouin, 1959; IGRS-IFP, 1966;
Karakitsios,1990,1992)representthepre-riftsequence
of the Ionian Basin. These limestones overlie early
to middle Triassic evaporites, probably related to
the initial rifting of the Neotethyan Ocean, through
Foustapidima Limestones of Ladinian–Rhaetian
age (Renz, 1955; Pomoni-Papaioannou & Tsaila-
Monopolis, 1983; Dragastan, Papanikos & Papanikos,
1985; Karakitsios & Tsaila-Monopolis, 1990).
During the Pliensbachian, extensional stresses as-
sociated with the opening of the Neotethyan Ocean
brought about the formation of the Ionian Basin
(Karakitsios, 1992, 1995). Although production of
platform carbonates persisted through the entire Jur-
assic period in the adjacent Paxos (pre-Apulian) and
Gavrovo-Tripolitza zones, the Ionian Basin became
an area of more persistent syn-sedimentary faulting
and subsidence. A syn-rift sequence began with
deposition of the Siniais Limestones and their lateral
equivalent, the Louros Limestones (Karakitsios &
Tsaila-Monopolis, 1988; Dommergues et al. 2002).
These formations record regional subsidence, which
was followed by internal syn-rift differentiation of the
Ionian Basin into smaller palaeogeographic units. The
latter are recorded by the prismatic syn-sedimentary
wedges of the syn-rift formations, and include the
Louros Limestones, the Ammonitico Rosso or Lower
Posidonia Beds, the ‘Limestones with Filaments’ and
the Upper Posidonia Beds (Karakitsios, Danelian & De
Wever, 1988; Karakitsios, 1995; see Fig. 2).
The early Berriasian was defined by a break-up
marked by an unconformity at the base of the pelagic
Vigla Limestone Formation; in this post-rift period
sedimentation was relatively uniform across the whole
Ionian Basin (Karakitsios, 1990; Karakitsios & Koletti,
1992). The post-rift sequence (Vigla Limestones and
overlying Alpine formations) largely obscures the syn-
rift structures and, in some cases, directly overlies the
Pantokrator limestone pre-rift sequence (Karakitsios,
1992, 1995). This palaeogeographic configuration
continued with minor off- and onlap movements
along the basin margin until the late Eocene, when
orogenic movements and flysch sedimentation began.
The permanence of differential subsidence during the
deposition of the post-rift sequence, shown by the
strong variation in thickness of these formations,
is probably due to the halokinetic movements of
the Ionian Zone evaporitic base (IGRS-IFP, 1966;
Karakitsios, 1990, 1992). The particular geometry of
the restricted sub-basins that were formed during the
syn-rift and post-rift period of the Ionian Zone may
have favoured increased organic matter burial during
the early Toarcian, late Callovian–Tithonian (Posidonia
Beds) and Aptian–Cenomanian (Vigla Shale Member)
(Karakitsios, 1995; Rigakis & Karakitsios, 1998).
Some of these intervals, in fact, appear to record global
rather than local events, as is the case with the early
Toarcian (Jenkyns, 1988; Jenkyns etal. 2002) and early
Aptian (Danelian et al. 2004).
3. The Gotzikas Section
The Vigla Limestone Formation (Berriasian–Turonian)
consists of thinly bedded, white to grey micritic
packstone, rhythmically alternating with chert layers
and containing rare intercalations of shale. The
Vigla Shale Member constitutes part of the Vigla
Limestone Formation (Fig. 2) and corresponds to the
‘Upper Siliceous Zone’ of IGRS-IFP (1966). Since
the attribution of the ‘Upper Siliceous Zone’ to the
Albian–Cenomanian by IGRS-IFP (1966), very few
detailed biostratigraphic studies have been carried out
(e.g. Skourtsis-Coroneou, Solakius & Constantinidis,
1995). The Vigla Shale Member comprises limestone
and chert beds interbedded with dark, greenish-grey
shale, and is generally seen in the upper part of the
Vigla Limestone Formation.
We examined rock outcrops of the Vigla Limestone
Formation in the Gotzikas valley, south of Tsamantas
village in NW Epirus, close to the border with Albania
Organic carbon-rich strata and Cretaceous OAEs 403
1 km
20 km
50 km
a
c
b
N
N
N
ALBANIA
GREECE
KERKYRA
EPIRUS
IONIAN SEA
S
S
ALBANIA
TSAMANDAS
ALBANIA
IONIAN ZONE
PINDOS ZONE
PAXOS ZONE
GAVROVO ZONE
IOANNINA
Quaternary Ionian flysch
(Oligocene) Eocene -
Paleocene Senonian Vigla Formation
(Berriasian-Turonian)
dip
fault
Gotzikas outcrop section
40o20o
Figure 1. (a) The zones of NW Hellenides; (b) location of the study area; (c) simplified geological map of the study area (modified
after IGRS-IFP, 1966).
(Fig.1b,c). Here, the ViglaShale Member is developed
in the core of an anticline with its axis verging ap-
proximately along an E–W direction. Stratigraphically
downwards, the sequence comprises Oligocene flysch,
Eocene to Senonian limestones and the upper part of
the Vigla Limestone Formation. Approximately 100 m
of the Vigla Limestone Formation are seen, whereas
the expected formation thickness in this area is 600 m
(IGRS-IFP, 1966).
The upper c. 50 m of the Vigla Limestone in the
Gotzikas section typically consists of a rhythmically
alternating, thinly bedded limestone/black chert suc-
cession. Towards the lower 15–20 m of this interval,
the limestone becomes more massive, pinkish-grey in
colour and increasingly silicified. Within this lower
portion we encountered a first, isolated black-shale
horizon of a thickness of c. 15 cm. Silicified Vigla
Limestonecontinuesstratigraphicallylowerforanother
404 H. TSIKOS AND OTHERS
Pelites/sandstones
Cherty limestones
with clastic material
Pelagic limestones
with clastic material
Pelagic cherty
limestones
Cherty beds with
green & red clay
Pelagic limestones, marls
& siliceous argillites
Pelagic limestones with
thin-shelled bivalves
Pelagic limestones
with small ammonites
& brachiopods
Pelagic, red, nodular
limestones with ammonites
(ammonitico rosso)
Pelagic limestones
Platform carbonates
Platy black limestones
Gypsum and salt
Dolomites
breccia section of pelagic bivalve
(filament) ammonite brachiopod
LITHOLOGYPERIOD-EPOCH-AGE FORMATIONS
PALEOGENECRETACEOUSJURASSICTRIASSIC
KIMMERIDGIAN
TITHONIAN
BERRIASIAN
OXFORDIAN
CALLOVIAN
BATHONIAN
BAJOCIAN
AALENIAN
TOARCIAN
PLIENSBACHIAN
SINEMURIAN
HETTANGIAN
NORIAN
CARNIAN
LADINIAN
ANISIAN
SCYTHIAN
VALANGINIAN
HAUTERIVIAN
BARREMIAN
APTIAN
ALBIAN
CENOMANIAN
TURONIAN
CONIACIAN
SANTONIAN
CAMPANIAN
DANIAN
SELANDIAN
YPRESIAN
LUTETIAN
BARTONIAN
PRIABONIAN
RUPELIAN
CHATTIAN FLYSCH
MICROBRECCIOUS LIMESTONES
FOUSTAPIDIMA LIMESTONES
EVAPORITES
VIGLA LIMESTONES
VIGLA SHALE MEMBER
MAASTRICHTIAN
RHAETIAN
EARLY EARLY
LIASSIC LIASSIC MALM NEOCONIAN SENONIAN EO-
CENE OLIGO-
CENE
PALEO
PRERIFT SYNRIFT
HIATUSES
POSTRIFT
EARLYMIDDLE MIDDLELATE LATE LATE
LIMESTONES WITH
FILAMENTS
AMMONITICO ROSSO
LOUROS
LIMESTONES
PANTOKRATOR
LIMESTONES
SINIAIS
LIMESTONES
POSIDONIA BEDS
Figure 2. Representative stratigraphic column of the Ionian Zone (after Karakitsios, 1995).
Organic carbon-rich strata and Cretaceous OAEs 405
8–10 m below this black shale. The series then appears
to pass downwards to the Vigla Shale Member proper,
although lack of exposure over the upper part of this
shale-bearing section has hindered acquisition of a
continuous lithological record.
In the lowermost c. 15 m of the examined outcrop,
20 individual organic-rich, marly horizons were seen,
ranging in thickness from 10 to 40 cm. These layers are
generally dark grey to black in colour, well laminated
and free of evidence for bioturbation. They are
interbedded with reddish-grey, 20–50 cm thick (marly)
limestone beds, silicified in places and containing
common intercalations of dark chert layers (5–10 cm
thick).
4. Methods
4.a. Sampling
We collectedhand-specimens approximatelyevery 2 m
throughtheupperc.50 moftheViglaLimestone Form-
ation, including one sample from the stratigraphically
uppermost black shale. Sampling on a decimetric to
sub-decimetric scale was carried out for the lowermost
c. 15 m of section (Vigla Shale Member proper), with a
totalof 25 samples being collectedfrom the20organic-
rich intervals themselves. All samples were powdered
after careful screening to avoid contamination from
weathering surfaces, local intense silicification or
secondary carbonate veining.
4.b. Bulk organic geochemistry and C, O isotope
determinations
Powdered samples were analysed for TOC and total
carbonate contents, as well as bulk organic carbon
and/or carbonate isotope ratios at the Departments
of Earth Sciences and Archaeology, University of
Oxford (Table 1). Duplicate TOC analyses were
obtained for all organic carbon-rich samples, using a
Strohlein Coulomat 702 device (for more details on
thistechnique,seeJenkyns,1988).Rock-Evalpyrolysis
data(S0, S1, S2 and Tmaxvalues) for thesame samples
were quantified using a LECO THA 200 Thermolytic
Analyser at the University of Newcastle (Table 2). The
standard deviations of duplicate analyses for S2 and
Tmax, expressed as percentages of the average value,
are ±5% and ±4% respectively.
For determinations of bulk organic carbon-isotope
compositions,allTOC-richsamples wereacidifiedwith
diluteHCl at ambient temperature to removecarbonate.
Approximately 5–10 mg of the dried carbonate-free
residues were weighed in tinfoil cups and placed in
a Europa Scientific Limited CN biological sample
converter connected to a 20–20 stable-isotope gas-
ratio mass spectrometer. Carbon-isotope ratios were
measured against a laboratory nylon standard, with
aδ13C value of −26.1 ±0.2‰. Analytical results
are presented in the usual δnotation, in ‰devi-
ation from the VPDB (Vienna Pee Dee Belemnite)
standard.
Carbonate (C, O) isotope ratios for all collected
samples were determined on CO2gas yielded after
reaction withorthophosphoric acid at 90 ◦C,usingaVG
Isocarb device and Prism mass spectrometer. Normal
corrections were applied and the results are reported
using the δnotation v. VPDB. Calibration to VPDB
was performed via our laboratory standard calibrated
against NBS19 and Cambridge Carrara marble. Re-
producibility of replicate analyses of standards was
generally better than 0.1‰for both carbon- and
oxygen-isotope ratios.
4.c. Palynofacies analysis
Kerogen assemblages of ten selected organic-rich
samples (including the sample representing the upper-
most black shale) were isolated using non-oxidative
palynological maceration with hydrochloric and hy-
drofluoric acids. The organic residues were then
filtered via a 10 µm nylon mesh. Palynofacies analysis
was undertaken at the University of Newcastle and
involved the microscopic identification of opaque
phytoclasts (black, oxidized woody debris), semi-
opaque phytoclasts (brown, partially oxidized woody
particles), translucent phytoclasts (fresh, non-oxidized
woody debris), sporomorphs (land plant spores and
pollen), marine algae (mainly dinoflagellate cysts)
and amorphous organic matter (AOM) in transmitted
white light (Table 3). Their percentages (based on
particle number) were evaluated by counting at least
300 particles in each slide. The kerogen assemblages
were also analysed in incident blue-light microscopy,
using a blue light 450–490 nm excitation filter. The
fluorescence intensity of AOM particles, which was
used to evaluate the preservational state of kerogen,
and consequently to infer the redox status of the
depositional environment, was assessed using a six-
point fluorescence scale (after Tuweni & Tyson, 1994;
Tyson, 1995).
4.d. Compound-specific isotope methods
Rock powders of the ten organic-rich samples selected
for palynofacies analyses were also solvent-extracted
with a mixture of dichloromethane/methanol (9:1, v/v),
using an automated solvent extractor (ASE). The total
lipid extracts were subsequently separated by column
chromatography into apolar and total polar fractions,
and the apolar fractions were further separated into
saturated and unsaturated fractions. Compositional
information for all saturated apolar fractions was
obtained using standard gas chromatography (GC)
andgaschromatography–massspectrometry (GC–MS)
techniques.δ13C measurements on selected compounds
were performed after silicalite-adduction, to remove
406 H. TSIKOS AND OTHERS
Table 1. Bulk-rock geochemical and isotopic data of the Vigla Formation, NW Greece
TOC CaCO3δ13CTOC δ13Ccarb δ18 Ocarb Depth∗
Sample wt% wt% ‰‰‰m Lithology
C1 2.69 −1.89 55 Limestone-chert interbeds
C2 2.70 −2.04 54 ”
C4 2.99 −1.87 53 ”
C6 2.53 −2.09 52 ”
C8 2.40 −2.11 51 ”
C10 2.42 −2.05 50 ”
C12 2.37 −2.07 49 ”
C14 2.31 −2.05 47.5 ”
C15 2.55 −1.94 46.5 ”
C16 2.29 −2.10 45.5 ”
C17 2.25 −2.14 44.5 ”
C18 2.38 −1.99 43.5 ”
C19 2.39 −2.01 42.5 ”
C20 2.48 −1.72 41.5 ”
C21 2.64 −1.63 40.5 ”
C22 3.07 −1.81 39.5 ”
C23 3.04 −1.89 38.5 ”
C24 2.30 −1.94 36.5 ”
C25 2.14 −1.81 34.5 ”
C26 2.81 −1.87 32.5 ”
C27 2.74 −1.74 30.5 ”
C28 2.76 −1.67 28.5 ”
C29 2.63 −1.77 26.5 ”
C30 2.78 −1.55 24.5 ”
C31 2.81 −1.49 22.5 ”
C32 2.61 −1.44 20.5 Cherty limestone
C33 2.81 −1.27 18.5 ”
C34 2.62 −0.78 16.5 ”
C35†28.87 23.25 −22.14 2.92 −1.32 14.8 Black shale
C36 2.97 −1.42 14.7 Cherty limestone
C37 3.79 −0.70 14.65 ”
C39 3.39 −0.72 7.65 ”
C40 2.07 −0.75 5.65 Marly limestone
C41 2.33 76.67 −26.61 2.23 −1.21 1.15 Organic C-rich shale
Observation gap* (taken also as ‘zero’ base line)
V1 1.94 −0.96 −0.1 Marly limestone
V2 1.88 −0.98 −0.2 ”
V3 2.10 −1.12 −0.3 ”
V4a 2.16 −1.12 −0.36 ”
V4b 2.23 −0.99 −0.42 ”
V4c 2.05 −1.28 −0.48 ”
V4d 2.19 −1.11 −0.54 ”
V4e 1.81 −1.75 −0.6 ”
V7 1.95 −1.34 −0.9 ”
V8 1.80 −1.75 −1.02 ”
V9 1.97 −1.24 −1.2 Light pink limestone
V11 2.18 −1.46 −1.4 ”
V12a 1.58 76.58 −24.86 2.67 −1.43 −1.43 Organic C-rich shale
V12b 2.35 −1.83 −1.52 Light pink limestone
V12c 2.08 77.92 −25.84 2.58 −1.77 −1.55 Organic C-rich shale
V13 2.50 81.17 −25.75 2.61 −1.60 −1.6 ”
V14 2.34 −1.52 −1.65 Light pink limestone
V16 1.57 −2.31 −1.9 ”
V18 1.92 −1.59 −2”
V19 2.05 −1.01 −2.1 ”
V20 1.88 −1.18 −2.3 ”
V21 2.06 −1.11 −2.5 ”
V22 2.20 −1.19 −2.6 Marly limestone
V23a 1.41 91.33 −26.43 2.19 −1.16 −2.67 Organic C-rich shale
V23b 2.34 83.96 −26.25 2.24 −1.50 −2.75 ”
V24 1.94 −1.42 −2.9 Light pink limestone
V25a 2.41 −1.33 −3”
V25b 2.18 −1.19 −3.05 ”
V26 3.35 61.67 −26.83 2.48 −1.53 −3.1 Organic C-rich shale
V27 2.34 −1.27 −3.3 ”
V28 2.18 −1.49 −3.55 Light pink limestone
V29a 2.77 74.62 −26.10 2.64 −1.54 −3.65 Organic C-rich shale
V29b 2.15 84.67 −26.20 2.57 −1.67 −3.8 ”
V29c 2.64 81.50 −25.97 2.70 −1.45 −3.9 ”
V30 2.57 −1.46 −4 Light pink limestone
Organic carbon-rich strata and Cretaceous OAEs 407
Table 1. Continued.
TOC CaCO3δ13CTOC δ13Ccarb δ18 Ocarb Depth∗
Sample wt% wt% ‰‰‰m Lithology
V32 2.08 −0.96 −4.1 ”
V33 2.03 −0.78 −4.62 ”
V34a 2.15 −1.00 −4.74 ”
V34b 2.09 −1.03 −4.79 ”
V35a 2.07 −1.44 −4.99 ”
V35b 1.97 −1.31 −5.14 ”
V38 1.88 79.58 −26.91 2.20 −1.97 −5.34 ”
V39 1.08 74.42 −26.79 2.17 −1.45 −5.41 ”
V41a 2.15 75.75 −27.88 2.05 −1.61 −5.61 Organic C-rich shale
V41b 3.19 72.92 −27.59 2.15 −1.52 −5.69 ”
V42 2.00 −1.24 −5.79 Light pink limestone
V43a 2.03 −1.20 −6.04 Marly limestone
V43b 1.98 −0.94 −6.19 ”
V45 2.57 54.08 −26.67 2.35 −1.50 −6.44 Organic C-rich shale
V46 2.05 −1.07 −6.79 Marly limestone
V47 4.42 67.83 −26.84 2.28 −1.55 −7.29 Organic C-rich shale
V48 1.54 83.42 −27.22 2.10 −1.01 −7.79 ”
V49 2.39 80.08 −26.86 2.34 −1.44 −8.24 ”
V50 3.61 53.35 −26.75 2.29 −1.34 −8.64 ”
V51 2.32 −0.76 −8.7 Cherty/marly limestone
V52 2.32 −0.89 −9.5 ”
V54 2.43 81.30 −25.96 2.62 −1.31 −10.05 Organic C-rich shale
V55 2.39 −1.03 −10.65 Cherty/marly limestone
V56 1.77 20.00 −26.37 2.35 −2.66 −10.72 Organic C-rich shale
V57 2.39 −0.68 −11.22 Cherty/marly limestone
V58 0.27 41.00 −26.52 2.46 −2.00 −11.52 Marly limestone
V59 2.53 −1.44 −12.32 Cherty/marly limestone
V60 2.29 84.50 −26.20 2.74 −1.37 −12.47 Organic C-rich shale
V61 2.58 −0.96 −12.97 Cherty/marly limestone
V62 6.33 59.92 −26.20 2.77 −1.30 −12.99 Organic C-rich shale
V63 2.48 −0.96 −13.17 Cherty/marly limestone
V64 2.77 81.12 −25.63 2.49 −1.14 −13.22 Organic C-rich shale
TOC: total organic carbon; carb: total carbonate (as calcite); †: uppermost black shale.
* Observation gap estimated to represent no more than 4–5 m stratigraphic thickness.
Table 2. Summary of bulk organic geochemical data for all 25 TOC-rich samples collected from the Vigla section
in the Gotzikas locality
TOC cf-TOC* HI Tmax
(wt%) (wt%) (mg/g) S2 (◦C)
Mean (n =24,excl. UBS) 2.6 10.9 321 8.7 417
Range (excl. UBS) 1.1–6.3 2.2–16.3 171–450 2.4–29.1 402–425
UBS 28.9 37.6 529 152.7 420
* carbonate-free total organic carbon content; UBS – uppermost black shale.
Table 3. Summary of palynofacies data for ten TOC-rich samples selected from the Gotzikas section, including the uppermost black
shale (UBS)
Opaque Semi-opaque Translucent Marine
phytoclasts phytoclasts phytoclasts Sporomorphs AOM algae Fluorescence
(%) (%) (%) (%) (%) (%) scale
Mean (excl. UBS) 41.2 4.1 6.6 0.4 29.7 17.9 3.8
Range (excl. UBS) 31.5–51.3 1.4–5.7 1.9–14.1 0.0–0.7 18.0–37.2 13.8–26.1 3–5
UBS 33.2 2.8 4.4 0.0 56.3 3.2 5
Percentages expressed relative to the total population of particulate organic matter; AOM=Amorphous Organic Matter.
the abundant n-alkanes which may otherwise interfere
with some of these compounds. Analyses were per-
formed using a Thermofinnigan Delta C isotope-ratio
monitoring gas chromatographer–mass spectrometer
(irm-GC–MS) at the Royal Netherlands Institute for
Sea Research (NIOZ). All compound-specific carbon-
isotope measurements were carried out at least in
duplicate, and the mean δ13C values for each sample
are presented in the usual δnotation with respect to the
VPDB standard (Table 4).
408 H. TSIKOS AND OTHERS
Table 4. Compound-specific δ13C data (in per mil v. VPDB) for the same ten organic carbon-rich Vigla samples as in Table 3
Monocyclic
Sample Norpristane Pristane Phytane C29-sterane C30-hopane isoprenoid C31-hopane
C35 −17.9 −20.5 −18.1 −27.8 −24.7 −15.0 −25.4
C41 nd −32.1 −32.0 −30.3 −27.7 −29.8
V13 −30.9 −32.2 −32.8 −29.9 −26.3 −29.1
V23b −32.2 −33.2 −33.0 −30.0 −27.1 −29.0
V29b −30.6 −32.2 −32.5 −29.4 −26.1 −29.2
V38 −32.1 −32.7 −33.0 −29.6 −27.1 −29.8
V41b −32.9 −32.9 −33.4 −29.7 −28.1 −29.7
V47 −31.4 −32.4 −32.2 −30.2 −27.3 −29.3
V54 −30.3 −31.4 −31.5 −28.6 −28.7 −28.9
V60 −31.5 −31.8 −31.3 −28.3 −28.1 −28.4
Data from all nine samples below the uppermost black shale (UBS. sample C35) represent duplicate means; values for the uppermost
black shale sample are means of triplicate analyses: nd – not determined.
4.e. Biostratigraphic analyses
Calcareous nannofossil biostratigraphy was generated
from 36 samples across the Gotzikas section, using
standard smear slides (Bown & Young, 1998) and thin-
sections. Planktonic foraminiferal biostratigraphy was
based on the study of 63 thin-sections. All analyses
were conducted at the Department of Earth Sciences
‘Ardito Desio’, University of Milan.
5. Results
5.a. Biostratigraphy
The distribution of biostratigraphically useful cal-
careous nannofossils and planktonic foraminifera
across the Gotzikas section, and resulting age determ-
inations, are summarized in Figure 3. Generally, a com-
bination of poor preservation, low abundance and low
diversity results in the absence of diagnostic taxa and
thus hinders formulation of a complete biostratigraphic
record through the entire section (Fig. 3). However,
the interval −12 to −0.1 m (26.8 to 14.9 m below
the uppermost black shale) may be assigned to the
lower Aptian, based on the presence of the nannofossils
Assipetra infracretacea larsonii,Hayesites irregularis
and Rucinolithus terebrodentarius youngii (Larson
et al. 1993; Tremolada & Erba, 2002), and the absence
of nannofossils and planktonic foraminifera diagnostic
of the upper Aptian.
Inaddition, the interval 22.5to 32.5 m (7.7to 17.7 m
above the uppermost black shale) may be assigned to
the middle Albian, based on the first occurrence of the
nannofossil Quadrum eneabrachium and the presence
of the planktonic foraminifer Biticinella breggiensis
(Varol, 1992; Premoli Silva & Sliter, 1995). The
overlying interval 36.5 to 38.5 m (21.7 to 23.7 m
above the uppermost black shale) is uppermost Albian,
based on the presence of the planktonic foraminifera
Rotalipora appenninica and Planomalina buxtorfi, the
presenceofthenannofossil Eiffellithusturriseiffeliiand
the last occurrence of the nannofossil H. irregularis
(Roth, 1978; Larson et al. 1993; Premoli Silva &
Sliter, 1995). The first occurrence of the planktonic
foraminifer Rotalipora cushmani at 44.5 m (29.7 m
above the uppermost black shale) indicates the middle
Cenomanian (Premoli Silva & Sliter, 1995).
5.b. Chemostratigraphy
Carbon- and oxygen-isotope profiles through the
studied section are presented in Figure 4. Carbonate-
carbon δ13C values (δ13Ccarb) show little stratigraphic
variation, generally ranging between 2 and 2.5‰over
the lower 15 m (Vigla Shale Member), and between 2.5
and 3.0‰in the upper 40 to 50 m (Vigla Limestone
proper). Similarly, δ18O values show a narrow range
of c.−1to−2‰across essentially the entire section,
although data exhibit significant scatter on a smaller
scale.
With respect to the organic-rich samples, total
carbonate is the main component in all samples below
the uppermost black shale, with values generally
around 75–80 wt% (as CaCO3). TOC data for the
same samples vary over the relatively narrow range
of 1.1 to 6.3 wt%. However, the uppermost black
shale shows a substantially reduced amount of bulk
carbonate (23.3 wt%, as CaCO3) and particularly high
TOC content (28.9 wt%). In terms of bulk organic
carbon δ13C data (δ13Corg), the same black shale is
also relatively enriched in 13C with a δ13Corg value
of −22.1‰. This contrasts with the δ13Corg values
observed in all remaining samples lower in the section,
which range between −28 and −25‰. It should be
noted that δ13Ccarb values from both the uppermost
black shale itself and from adjacent carbonate samples
are also high, relative to average values from the
remaining section (Fig. 4). It is debatable, however,
whether these represent a primary isotopic signal or
are the result of later diagenetic overprinting.
It is also noteworthy that there is no evidence for a
negative carbonate isotope spike below the uppermost
black shale in the Gotzikas section, as has been
documented from immediately below both the lower
Organic carbon-rich strata and Cretaceous OAEs 409
Zone (Roth 1978)
Age
(Premoli Silva &
Sliter 1995)
Age
54.00
50.00
47.50
46.50
45.50
R. cushmani 44.50
40.50
H. irregularis P. buxtorfi 38.50
NC10 L Alb P. buxtorfi, R. appenninica 36.50
E. turriseiffelii B. breggiensis 32.50
30.50
B. breggiensis 28.50
26.50
Q. eneabrachium 22.50
14.80
R.t. youngii -0.10
-0.20
-0.48
-1.40
-2.00
-2.90
-3.30
-4.62
-4.79
-4.99
Key -5.79
-6.79
Present -8.70
-10.35
Range -11.22
-12.02
R. appenninica
B. breggiensis
R.t. youngii
R. appenninica
R. cushmani
P. buxtorfi
E. turriseiffelii
H. irregularis
A.i. larsonii
Calcareous nannofossils
Events
Q. eneabrachium
Not zoned
Thickness (m)
?NC10
L Alb - Cen
NC9
M - L Alb
R. cushmani
NC6
E Apt
Not zoned
Planktonic foraminifera
B. breggiensis
M Alb
L Alb
Events
M Cen
UBS UBS
?
?
Zone
Figure3. Summary ofbiostratigraphic information for the Gotzikassection,basedon observeddistributionsof calcareous nannofossils
and planktonic foraminifera. Whilst 36 samples were investigated for nannofossils and 63 for planktonic foraminifera, only those
samples yielding age-diagnostic taxa are represented here. (UBS – uppermost black shale).
Albian Paquier Level (or OAE1b; for more details, see
Section 6) in the Vocontian Basin of SE France and
from a core in the Atlantic (Herrle, 2002). It is possible,
however, that the critical level may have been lost to
erosion, may not be exposed, or may have been missed
due to the low sampling resolution over the interval in
question.
5.c. Bulk organic geochemistry and palynofacies
Bulk organic geochemical and palynofacies data are
summarizedinTables2and 3, respectively. All samples
are very similar in terms of their organic facies
characteristics, with the exception of the uppermost
black shale. The mean Hydrogen Index (HI =mg S2/g
TOC) is 321 (or 468 when computed from the linear
regression of S2 v. TOC) and the HI values (ranging
from 171 to 450) are broadly proportional to both the
TOC and carbonate-free TOC contents. The uppermost
black shale which, as mentioned earlier, is typified by a
muchhigherTOCcontent(28.9 wt%), also hasahigher
HI value of 529. Using the plot of S2 v. TOC (after
Langford & Blanc-Valleron, 1990), all samples are
characterized as Type II kerogen (Fig. 5). The average
Tmax value of 417◦C indicates that the samples are
thermally immature, that is, stratigraphically above the
oil window.
Ternary plots are routinely used in palynofacies
analysis to investigate proximal-distal trends and
redox conditions. The composition of the kerogen
assemblagesfor the tenselected samples is summarized
in the ternary diagram of AOM (Amorphous Organic
Matter) v. phytoclasts v. palynomorphs (sporomorphs
and marine algae) of Figure 6 (after Tyson, 1989,
1995). Palynofacies are dominated by small opaque
phytoclasts, AOM and dinoflagellate cysts. This sug-
gests a marine depositional environment quite distant
from sources of fresh continental organic matter. The
fluorescence of AOM is moderate to good (points 3 to
5 on the Fluorescence Scale), suggestive of dysoxic to
anoxic conditions. The uppermost black shale sample
exhibits the highest fluorescence and percentage of
AOM (point 5 and 56%, respectively), indicating better
preservational conditions.
410 H. TSIKOS AND OTHERS
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
10
20
30
40
50
60
metres
-28 -27 -26 -25 -24 -23 -22
KEY: Black shale
Chert
Silicified marly limestone
Marly limestone
Bedded, cherty limestone
Pink-grey limestone
VIGLA LIMESTONE
VIGLA SHALE MEMBER
C
org
(per mil VPDB)
13
δ
UBS
Aptian Albian
Cen
?
?
?
?
C
carb
(per mil VPDB)
13
δ
1.5 2 2.5 3 3.5 4
-2.5 -2 -1.5 -1 -0.5-3
O
carb
(per mil VPDB)
18
δ
Figure 4. Lithostratigraphic log and bulk stable (C, O) isotope profiles through the Vigla section in the Gotzikas area. The uppermost
black shale (UBS) is highlighted. Note the different scales used for the portions of the section above and below the observation gap
(field observations indicate that this gap represents no more than 4–5 m of poorly exposed section).
5.d. Compound-specific isotope results
GC-MS data from the saturated apolar fractions of the
same ten samples selected for palynofacies analyses
show essentially identical composition, except for the
sample representing the uppermost black shale. The
components include mixtures of acyclic isoprenoids,
n-alkanes, steroids and hopanoids (Fig. 7a, b) and to
a much lesser extent alkylated thiophenes and naph-
thalenes. In contrast, the uppermost black shale con-
tains relatively higher amounts of acyclic isoprenoids
(especially norpristane) and, in addition to the afore-
mentioned compounds, substantially elevated relative
concentrations of monocyclic isoprenoids (Fig. 7a), the
precisemolecularstructuresofwhichare still unknown.
Also, despite very low concentrations and strong co-
elution effects, two other unusual isoprenoidal com-
pounds, namely TME (2,6,15,19-tetramethylicosane)
and PME (2,6,10,15,19-pentamethylicosane), were
also detected in the uppermost black shale (Fig. 7a),
on the basis of their corresponding mass spectra and
characteristic retention times (Vink et al. 1998). All
such isoprenoids have also been reported from the
lower Albian, Niveau Paquier black shales from the
Organic carbon-rich strata and Cretaceous OAEs 411
0 5 10 15 20 25 30 35
0
20
40
60
80
100
120
140
160
180
UBS
S2
TOC (wt %)
Type I
Type III
Type II
Figure 5. Binary plot of TOC v. S2 for all 25 TOC-rich
samples from the Gotzikas section (kerogen type subdivisions
afterLangford & Blanc-Valleron,1990). UBS – uppermost black
shale.
0 102030405060708090100
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
0
UBS
Phy
AOM Pal
Figure 6. Ternary ‘APP’ plot (after Tyson, 1989, 1995) for
ten selected TOC-rich samples, including the uppermost black
shale (UBS). AOM – amorphous organic matter; Phy – total
phytoclasts; Pal – palynomorphs (sporomorphs and marine
algae).The size ofthe symbols isproportionalto the fluorescence
scale values (ranging from 3 to 5).
Vocontian Basin, SE France, as well as coeval organic
carbon-rich sediments from ODP Site 1049C in the
North Atlantic (Vink et al. 1998;Kuyperset al.2002a),
and are regarded as originating from marine archaea.
Compound-specific isotope data for selected organic
compounds present in the saturated apolar fractions of
the ten extracted samples are presented in Table 4.
The nine samples stratigraphically below the up-
permost black shale show essentially constant δ13C
compositions for pristane (−33 to −31‰), phytane
(−34 to −30‰), norpristane (−34 to −30‰), steroids
(e.g. C29-sterane: −31 to −28‰) and hopanoids (e.g.
C30-hopane: −29 to −26‰;C
31-hopane (S+R): −30 to
−28‰). The uppermost black shale sample, however,
displays isoprenoid δ13C values (pristane: −20.5‰;
phytane: −18.5‰; norpristane: −17.9‰) that are
substantially higher than those seen in the underlying
TOC-richsamples. Furthermore, δ13Cvaluesfor mono-
cyclic isoprenoids are also very high (up to −15‰
for monocyclic isoprenoid I; see also Fig. 7). These
results contrast with the carbon isotope compositions
of largely algal- and bacterial-derived biomarkers such
as steranes and hopanes (Table 4), which exhibit only
relatively small stratigraphic change, on the order of
2to4‰.
6. Discussion
It is known that at least two major Oceanic Anoxic
Events (OAEs), that is, the early Aptian Selli event
or OAE1a (e.g. Menegatti et al. 1998) and the
Cenomanian–Turonian Bonarelli event or OAE2 (e.g.
Arthur, Dean & Pratt, 1988; Tsikos et al. in press),
represent episodes of global perturbation in both the
marine inorganic and the marine/terrestrial organic
carbon reservoirs, due to excess burial of organic
matter. Such perturbations are commonly manifested
in the form of positive isotopic excursions in both
inorganic and organic carbon, by up to 2.5 and 6‰
respectively. At least a further three anoxic events of
mostly (supra)regional geographical distribution have
also been identified in the middle to upper Cretaceous
(e.g. Leckie, Bralower & Cashman, 2002). Among
these is the early Albian Paquier Event (or as variously
termed, OAE 1b), a relatively short-lived (30–45 kyr)
event of increased organic-carbon burial, that has been
documented from the broader Tethys-Atlantic region
(e.g. Br´
eh´
eret, 1985, 1997; Erbacher et al. 2001;
Kuypers et al. 2001, 2002a; Herrle, 2002; Herrle
et al. 2003a,b).
Planktonic foraminiferal and calcareous nannofossil
stratigraphy across the Gotzikas section, in combina-
tion with the c.4.5
‰isotopic shift seen in the bulk
δ13Corg record upwards in the section, provide a first
indication that the uppermost part of the Vigla Shale
Member examined herein (the uppermost black shale)
may represent the lithological expression of the early
Albian Paquier event. Direct evidence in this regard
is provided by the compound-specific geochemical
data (see Table 4, Fig. 8). Recent studies of the
molecular organic geochemistry of lower Albian black
shales from the Vocontian Basin, SE France (Niveau
Paquier)andODPSite1049C,North Atlantic (Kuypers
et al. 2001, 2002a), have shown that the Paquier
Event is characterized by significant contributions of
marine organic matter predominantly derived from
chemoautotrophic archaea. This characteristic is firmly
supported by the high δ13C values (−18 to −16‰)
observed in archaeal-derived isoprenoidal biomarkers,
relative to biomarkers of more typical algal derivation
(typically in the range −28 to −32‰), and thus
distinguishes the Paquier Event from other Cretaceous
OAEs.
412 H. TSIKOS AND OTHERS
(a) UBS
Retention time
(b) pre-UBS
Relative intensity
i.s.
C isoprenoid
16
C isoprenoid
17
Norpristane
Pristane
Phytane
Monocyclic isoprenoid I
123
45
67
8911
Norpristane Pristane
Phytane
20Methyl-5 ,14 -Pregnane
αβ,17β
5 ,14 -Pregnane
α β,17β
1012
1314
15 16
17
Monocyclic isoprenoid II
1
16
17
15
14
13
12
11
10
9
7
22
6
19
23
4
18
n-alkanes
PME
TME
21
20
(20S) 24-Ethyl-5 -Cholestane
α
(20R) 24-Ethyl-4 -methyl-5 -Cholestaneαα
(20S) 24-Ethyl-4 -methyl-5 -Cholestaneαα
Norhopane
C -Hopane
30
(22S) + (22R) 17 , 21 (H)-Hopane
αβ
(20R) + (20S) 5 ,14 ,17 -Sterane
αββ
(20R) + (20S) 24-Methyl-5 ,14 ,17 -Steraneαβ β
(20R) + (20S) 24-Ethyl-5 ,14 ,17 -Steraneαβ β
17 , 21 (H)-Homohopaneβα
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
5 -Cholestaneβ
5 -Cholestaneα
17α-Trisnorhopane
(20S) 24-Methyl-5 -Cholestane
(20S) 24-Methyl-5 -Cholestane
(20R) 24-Methyl-5 -Cholestane
(20S) 24-Ethyl-5 -Cholestane
(20R) 24-Ethyl-5 -Cholestane
(20S) 24-Methyl-4 -methyl-5 -Cholestaneαα
Norhopane
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
(20R) + (20S) 13 ,17 -Diacholestane
βα
(20R) + (20S) 24-Ethyl-13 ,17 -Diacholestane
βα
α
β
α
α
β
Figure 7. Total ion currents of the saturated apolar fractions for (a) the uppermost black shale (UBS) and (b) for one sample
stratigraphically lower (V29b), indicating major compounds/compound groups present. Note the relative predominance of acyclic and
monocyclic isoprenoids in the uppermost black shale (i.s. – internal standard).
The carbon-isotope profiles of Figure 8 illustrate
striking similarities between the uppermost black shale
and the Paquier black shale from ODP site 1049C
(Kuypers et al. 2002a). The c.4.5
‰isotopic shift
in bulk δ13Corg values between the uppermost black
shale and underlying organic-rich units in the Gotzikas
section can therefore be largely attributed to a change
in the source of the organic matter, from predominantly
marinealgaltoonewheremarine archaea became much
more dominant. Respective isotopic shifts of at least
10‰in acyclic isoprenoids appear to reflect such a
mixedsource (algaland archaeal),whereas values of up
to −15‰for monocyclic isoprenoids would indicate
an almost exclusively archaeal derivation (Fig. 8). On
the other hand, compounds of specifically algal origin
(e.g. steranes) show little stratigraphic change in their
δ13C values (up to 4 per mil; see Fig. 8), as well as
in their relative abundance. It is therefore unlikely that
the isotopic shift seen in the upper part of the bulk
δ13Corg profile was caused exclusively by changes in
isotopic fractionation of the primary algal biomass
alone, and/or changes in the isotopic composition of
dissolved inorganic carbon.
Estimations of the relative contribution of primary
archaeal and algal sources to the uppermost black shale
can only be tentative. Mass-balance calculations using
the entire c. 4.5 shift in bulk δ13Corg and end-member
values of c.−26‰for algae (based on the −30‰of
algal steranes corrected for the isotopic depletion of
lipids in algae: Schouten et al. 1998) and −15‰for
archaea(basedon the archaeal monocyclic isoprenoids)
would lead to an estimate of an archaeal contribution
Organic carbon-rich strata and Cretaceous OAEs 413
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
10
20
30
metres
-35 -30 -25 -20 -15
TOC
Pristane
Phytane
Sterane
Monocyclic isoprenoid
Hopane
UBS
C (per mil VPDB)
13
δ
Black shale
Limestone (marly)
Limestone (cherty)
KEY:
-30 -25 -20 -15
C (per mil VPDB)
13
δ
dm
Bicyclic biphytane
Tricyclic biphytane
algal+archaeal
algal/bacterial
archaeal
VIGLA FM,
GREECE
Paquier Event (OAE1b)
ODP 1049C,
N. ATLANTIC
Figure 8. Carbon-isotope profiles for TOC, pristane, phytane, steranes, hopanes and archaeal isoprenoids, through the Vigla Shale
Member of the Gotzikas section (this study) and ODP site 1049C from the North Atlantic (Kuypers et al. 2002a). TOC-rich intervals
corresponding to the Paquier event (OAE1b) are highlighted. (UBS – uppermost black shale).
of c. 40%. This figure compares particularly well
with that reported by Kuypers et al. (2002a)for
the black shale of the Niveau Paquier in SE France.
However, corresponding isotopic shifts of c.1.5
‰in
bulk carbonate and 2–4‰in algal/bacterial biomarkers
(steranes and hopanes) over the same stratigraphic
interval, imply that approximately one third of the
overallisotopic shift inthe bulkorganiccarbon isotopic
record may, in fact, be related to a respective change
in the isotopic composition of the dissolved inorganic
carbonreservoir.Therefore, the foregoingestimationof
a primary archaeal contribution of c. 40% would only
be a maximum one and should be reduced accordingly.
The recognition of a black shale attributable to the
Paquier Event in the uppermost part of the Vigla
Shale Member of the Ionian Basin also provides
further insight into the chronostratigraphic extent of
this interval. Traditionally, the upper portion of the
Vigla Shale Member has been thought to span the
late Cenomanian/early Turonian, though little biostrati-
graphic evidence has been presented to date in support
of this (IGRS-IFP, 1966). Recent biostratigraphic and
chemostratigraphic studies (Danelian et al. 2004) have
demonstrated that the lower part of the Vigla Shale
Member records the Selli Event/OAE1a (early Aptian).
The present study complements this work, by setting
a minimum age for the upper part of the Vigla Shale
Member as Aptian to middle Albian.
7. Conclusions
The present study constitutes the first documentation
of sediments deposited during the Paquier Event
(OAE 1b) from the Ionian Basin of western Greece
and complements similar recent work in older strata
from the same area (Danelian et al. 2004). It also
provides a new, revised minimum age constraint for the
uppermost portion of the Vigla Shale Member which,
untilprovenotherwise, appears to be considerablyolder
thanpreviouslyassumed (thatis, earlyAptian to middle
Albian rather than Cenomanian/Turonian).
Our results also reinforce the notion that the Paquier
Event constitutes a distinct episode in the Cretaceous
geological record, whereby carbon-isotope anomalies
of several per mil can be accounted for by variation
in the source(s) of organic matter (that is, archaeal v.
algal) in the marine realm. The Paquier equivalent in
the Vigla section is in fact the third occurrence world-
wide displaying these particular organic geochemical
characteristics at the molecular level. Given that these
horizons are geochemically so unusual they can be
considered as time-equivalent, recording a specific
biological event in the marine realm. By reference to
the Niveuau Paquier in France and its equivalent in
the Atlantic, the uppermost black shale in the Vigla
section exposed near Gotzikas can hence be referred
to the Leymeriella tardefurcata ammonite zone, the
414 H. TSIKOS AND OTHERS
Hedbergella planispira planktonic foraminiferal zone
and the NC8B nannofossil zone of the early Albian
(Br´
eh´
eret, 1997; Herrle, 2002).
Acknowledgements. This work was supported by the
European Community’s Improving Human Potential Pro-
gram through the project ‘C/T-Net – Rapid global change
during the Cenomanian/Turonian oceanic anoxic event:
examination of a natural climatic experiment in Earth
history’, under contract HPRN-CT-1999-00055, C/T-Net.
Theassistanceand contributions of J.Cartlidge,T.O’Connell
and S. Wyatt (TOC and bulk stable isotope analyses,
Oxford), D. Sansom (drafting, Oxford), and M. Baas and
W. I. C. Rijpstra (molecular analyses, NIOZ) are gratefully
acknowledged. M. M. M. Kuypers (Max Planck Institute for
Marine Microbiology, Bremen, Germany) is also thanked for
providing selected data from ODP site 1049C from the North
Atlantic, for the isotopic comparisons shown in Figure 8.
Reviews by A. Y. Huc and H. Weissert greatly improved an
earlier version of this manuscript.
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