High-resolution ??13C stratigraphy through the early Aptian ``Livello Selli'' of the Alpine Tethys

Abstract

Very similar high-resolution delta13Ccarb and delta13Corg curves are reported for the early Aptian ``Livello Selli'' (LS, oceanic anoxic subevent 1a) at two pelagic successions of the Alpine Tethys: ``Roter Sattel'' (Swiss Préalpes), deposited along the northwest margin, and ``Cismon'' (southern Alps of northern Italy), deposited along the southeast margin. The delta13Ccarb and delta13Corg curves are both divided into eight segments, six of which occur within the early Aptian Globigerinelloides blowi foraminiferal zone, indicating significant subzonal resolution. Most of the LS coincides with a chemostratigraphically defined ``Selli event'': a period of constant isotopic values (mean values of delta13Ccarb and delta13Corg ~+2.60/00 and -250/00 respectively) lasting 500 kyr to 1 Myr, rather than of positive excursion as previously supposed. This uniformity may reflect an equilibrium between Corg burial and increased recycling rates of 12C and nutrient-rich intermediate water resulting from the intensification of oceanic thermohaline circulation.

Full text

PALEOCEANOGRAPHY, VOL. 13, NO. 5, PAGES 530-545, OCTOBER 1998
High-resolution 13C stratigraphy through the early Aptian
"Livello Selli" of the Alpine Tethys
Alessio P. Menegatti and Helmut Weissea
Department of Earth Sciences, EidgenOssische Technische Hochschule, Z0rich, Switzerland
Robert S. Brown, 1 Richard V. Tyson and Paul Farrimond
Newcastle Research Group, University of Newcastle-upon-Tyne, Newcastle, England, United Kingdom
Andr6 Strasser and Michele Caron
Institut de G6ologie, Fribourg, Switzerland
Abstract. Very similar high-resolution fi13Ccarb and fi13Corg curves are reported for the early Aptian "Livello Selli" (LS,
oceanic anoxic subevent 1 a) at two pelagic successions of the Alpine Tethys: "Roter Sattel" (Swiss Pr6alpes), deposited
along the northwest margin, and "Cismon" (southern Alps of northern Italy), deposited along the southeast margin. The
fi13Ccarb and fi13Corg curves are both divided into eight segments, six of which occur within the early Aptian
Globigerinelloides blowi foraminiferal zone, indicating significant subzonal resolution. Most of the LS coincides with a
chemostratigraphically defined "Selli event": a period of constant isotopic values (mean values of fi13Ccarb and fi13Corg
=+2.6%o and -25%o respectively) lasting 500 kyr to 1 Myr, rather than of positive excursion as previously supposed. This
uniformity may reflect an equilibrium between Corg burial and increased recycling rates of 12C and nutrient-rich interme-
diate water resulting from the intensification of oceanic thermohaline circulation.
1. Introduction
During the last 20 years, carbon isotope geochemistry has
been applied as an increasingly valuable tool in the stratigraphy
of pelagic successions [e.g., Scholle and Arthur, 1980; Renard,
1986; Schtanger et at., 1987; Lini et at., 1992] as well as, more
recently, their shallow-water equivalents [e.g., denkyns, 1995;
Vahrenkamp, 1996; Ferreri et at., 1997]. The long-term varia-
tions in isotopic composition of carbonate and organic carbon
(1513Ccarb and/513Corg) revealed by these studies have been inter-
preted as evidence of perturbations of the global carbon cycle
[e.g., Arthur et at., 1985; Weisseft et at., 1985; Shackleton, 1987;
Schidtowski, 1987; Lini et at., 1992]. Long-term (>100 kyr) shifts
of the/513C signal with amplitudes >+1.5%o are believed to re-
flect global fluctuations in Ccarb and C org burial [e.g., Berger and
Vincent, 1986; Schidtowski, 1987; Weisseft, 1989; Kump, 1991;
Weisseft and Mohr, 1996; Weisseft et at., 1998]. Positive excur-
sions in the marine carbonate 1513C record tend to coincide with
widespread to quasi-global episodes of "black shale" deposition,
the resulting organic carbon burial accelerating the transfer of the
light 12C isotope from the oceans to the sedimentary carbon
reservoir [Weisseft et al., 1979; Schotle and Arthur, 1980;
Schidtowki, 1987; Schlanger et at., 1987; Arthur and Sageman,
1994; Bratower et at., 1994].
1Now at Robertson Research International, Tyn-y-coed Site, Llanrhos,
Llandudno, North Wales, United Kingdom.
Copyright 1998 by the American Geophysical Union.
Paper number 9SPA01793.
0883-8305/98/98PA-01793 $12.00
One of the best described global carbon isotope events occurs
in the lower Aptian (Lower Cretaceous, = 123 Ma). The associ-
ated episode of organic-rich sediment deposition corresponds to
part of the Barremian-Albian "oceanic anoxic event 1" (OAE 1)
of Schtanger and Jenkyns [1976] and Jenkyns [1980] and, more
specifically, to the "oceanic anoxic subevent la" (OAE la) of
Arthur et el. [1990]. Black shales of early Aptian age are
widespread in the marine shelf and continental margin succes-
sions of Europe [e.g., Tyson end Funnell, 1987]; the correspond-
ing horizon in the Umbro-Marchean Apennines of central Italy
has been named the "Livello Selli" (LS) [Wezel, 1985; Coccioni
et el., 1987, 1989]. The stratigraphic equivalent in other areas of
Italy has also been termed the "Livello Selli equivalente"
[Coccioni et el., 1987; Bersezio, 1994]. In the southern Alps of
northern Italy the LS is associated with a large positive shift in
the •13Ccarb curve of up to +39/oo [Weissert et al., 1985; Lini,
1994]. Similar positive carbon isotope excursions have also been
identified in other correlative Tethyan sections: the Vocontian
Trough [ Weissert end Brdhdret, 1991; R. Brown, unpublished
data, 1997], the Umbro-Marchean Basin [Hedji, 1991; Erbecher
et el., 1996], the Abruzzi-Campania Platform of southern Italy
[Ferreri et el., 1997], the Helvetic Alps [FOllmi et el., 1994;], the
Swiss and French Pr6alpes [Dupesquier et el., 1989; Heble,
1997], and the western Carpathians [Lintnerov3 et el., 1997].
Furthermore, an apparently synchronous carbon isotope event oc-
curs in the North Atlantic [Arthur et el., 1979; Ldtolle et el.,
1979; Cleuser et el., 1988], in the Mexican Sierra Madre
Oriental [Scholle end Arthur, 1980], the Crimean Basin [Fouke
end Schleger, 1996], northwest Greece [GrOtsch et el., 1996], the
Middle East [Vehrenkemp, 1996], and the Pacific Ocean
[Jenkyns, 1995].
530

MENEGATTI ET AL.: THE •13C STRATIGRAPHY IN THE "LIVELLO SELLI" 531
Early Apttan Alpine Tethys
-•25 øN • • ½•: i::•i ...... --.œ" ..:/•' .---•...-,,?: '•Søuthern Alps
.:• PU L IA ":'•:':'•'•'•'•';•':•:•:•:•'•" '"':" ;• A
-•.•.•.Z..••.• • ...........
Piemont
(• Cismon
.......... • Helvetic• (• Roter Sattel
200 Km
Oceanic crust Continental crust
,,.5øE .,./Hypothetical submarine
fault scarps
17o E I 12OE• - •
•6ON (•
Figure 1. Schematic paleoceanographic reconstruction of the early Apttan western Tethys and palcolocation of the Cismon and
Roter Sattel sections (modified after Weissert and Bernoulli [1985] and Stampfit, 1993; paleolatitude from Hauck [1997]). The
map coordinates of the Roter Sattel section are: 585'88-159'44/585'98-159'30 (topographic map of Switzerland 1:25'000, foil
1226: "Boltigen"). The location of the Cismon section is 17 km of the main road "Strada Statale 50 del Monte Grappa" in the
valley of the Cismon River (coordinates: 46ø03•N, 11 ø45'E, "Carta Geologica d' Italia" 1:100'000, foil "Feltre").
In this study we present high-resolution •513C curves through
the LS interval in two Tethyan sections: one located on the for-
mer eastern margin (Cismon section, southern Alps of northern
Italy) and the other on the former western margin of the Alpine
Tethys Ocean (Roter Sattel section, Pr6alpes M6dianes
Romandes of western Switzerland). Our data from these sections
show that positive shifts in the •13Ccarb and •513Corg records oc-
curred at the onset and at the end, but not during, most of the de-
position of the LS. Hence a revision of the hitherto proposed in-
terpretation of positive carbon isotope excursions [e.g., Scholle
and Arthur, 1980; Berger and Vincent, 1986] is required to ex-
plain these observations.
2. Geological Setting
The Roter Sattel section is located in the Swiss Pr6alpes
Medianes Romandes (Figure 1). It was deposited on the western
continental margin of the Tethys Ocean [Python-Dupasquier,
1990; Borel, 1995] in a marginal basin located on the
Brian9onnais Swell [Stampfii and Marthalet, 1990; Stampfii,
1993]. The section has been described in detail by Page [1969]
and Python-Dupasquier [ 1990] and dated by means of planktonic
foraminifera [Python-Dupasquier, 1990; M. Caron et al., unpub-
lished data, 1997]. The Cismon section is located in the Venetian
Alps (northern Italy), 15 km west of Feltre, in the Valley of the
Cismon River. It was deposited in part of the Belluno Basin,
which was situated on the eastern continental margin of the
Tethys Ocean (Figure 1) [ Charmell et al., 1979]. The section has
been described by Charmell et al. [1979], Weisseft et al. [1985],
and Erba [1994] and has been dated using planktonic
foraminifera [Erba, 1994], calcareous nannofossils [Bralower,
1987; Bralower et al., 1994; Erba, 1994, 1996], and magne-
tostratigraphy [ Channell et al., 1979]. Some carbon isotope data
have been published previously by Weissert et al. [1985],
Weissert [ 1989], and Weisseft and Lini [1991 ].
During most of the Early Cretaceous, white to grey pelagic
limestone (carbonate content up to 95 wt% and total organic car-
bon (TOC) content <_0.3 wt%) consisting mostly of calcareous
nannofossils was deposited in alternation with --1-2 cm thin
marly horizons in both study areas; this sequence is known
locally as the "Calcaires Plaquett6s" formation at Roter Sattel
[Python-Dupasquier, 1990] and the "Calcare di Soccher" or
"Maiolica" formation at Cismon [Channell et al., 1979]. These
limestones are overlain by an Aptian-Albian marly hemipelagic
facies referred to as the "Intyamon" Formation in the west
[Python-Dupasquier, 1990] and the "Scaglia Variegata" forma-
tion in the east [Erba, 1994]. This hemipelagic facies is com-
posed of alternating marlstone or marly limestone (carbonate
content 10-85 wt% and TOC content 0.2-1.0 wt%), consisting
mostly of planktonic foraminifera and calcareous nannofossils,
and marly or siliceous limestone of green-grey, light grey, red, or
black color, enriched in radiolarians. Analogous marlstones and
limestones have been described from the Apennines, where they
are known as Scisti a Fucoidi [e.g., Cresta et al., 1989]. The
green-grey hemipelagic facies shows strong bioturbation, identi-
fied in the "Scisti a Fucoidi" as Chondrites, Planolites, and
Zoophycos [Erba et al. , 1989].
The base of the hemipelagic facies is characterized by a 2-5 m

532 MENEGATTI ET AL.: THE •5•3C STRATIGRAPHY IN THE "LIVELLO SELLI"
thick, darkly colored interval of relatively organic-rich sediments
referred to as the Livello Selli [Coccioni et al., 1987; Erba, 1988]
(Figures 4 and 5). The LS consists of a cyclic alternation of black
bioturbated marlstone or marly limestone (carbonate content of
10-40 wt% and a TOC content of 1-8 wt%) with black, laminated
siliceous and marly limestone or green-grey marly limestone
(carbonate content --60 wt% and a TOC content 0.2-1 wt%). The
noncarbonate mineralogy consists mainly of biogenic quartz
(from radiolarians). The mineralogy of the nonbiogenic fraction
consists of quartz, clay minerals (chlorite, illite, and il-
lite/smectite mixed layers), pyrite, a small amount of feldspars,
and, in the Roter Sattel section, --1% by volume phosphoritic
grains (Figures 4 and 5).
The LS occurs within the middle to upper part of the
Globigerinelloides blowi planktonic foraminifer zone [ Channell
et al. , 1979; Python-Dupasquier, 1990; Erba, 1994] of Deshayesi
ammonite zone age. Cyclostratigraphical studies in different sec-
tions of the southern Alps and Apennines allow the duration of
the LS at Cismon to be estimated as between 500 kyr and 1 Myr
[Herbert, 1992; Erba, 1996]; this is in reasonable agreement with
estimates of the duration of the equivalent OAE la strata in other
areas [e.g., Sliter, 1989; Brdhdret, 1994; Bralower et al., 1994].
The onset of the LS is estimated to occur =300 kyr after the end
of the reverse magnetostratigraphic Subchron M0 [Channell et
al., 1979; Erba, 1994, 1996].
In the Roter Sattel section the sediments indicate a higher
thermal overprint than at Cismon due to the more intense burial
diagenesis [Borel, 1995] and the buildup of the nappe pile during
the Alpine orogenesis [Starnpfii and Marthalet, 1990]. This is
indicated by (1) a stronger tectonically induced cleavage of the
marly facies, (2) the presence of numerous calcitic veins indicat-
ing dissolution and reprecipitation of CaCO3 [e.g., Matter et al.,
1975], (3) the higher thermal maturity of the organic matter sug-
gested by a mean Tmax of 440øC that is up to 17øC higher than at
Cismon despite a similar range in hydrogen index [Brown et al.,
1996; Brown et al., also manuscript in preparation, 1998], and (4)
the presence of highly ordered diagenetic illite-smectite mixed
layer minerals (IS-ISII) in contrast to randomly ordered illite-
smectite in the Cismon section [ Menegatti and Niiesch, 1997].
carbon and oxygen isotopes was performed on the bulk CaCO3
fraction. Carbonate powder was extracted with a dental drill in
order to avoid any contamination by diagenetic calcite veins. X
ray diffraction (XRD) was used to establish that dolomite was
not present. We did not ash the samples at 375øC in order to
remove organic matter (e.g., as used by denkyns and Clayton
[1986] and Lini et al. [ 1992]); however, a comparison between
ashed and nonashed samples with a TOC content <8 wt%
revealed no significant difference in the isotopic values, and a
comparison of the isotopic composition of dark burrow fills and
lighter colored matrices did not show any differences in •513Ccarb
(although the •i18Ocarb of the burrow fill material is --0.3%o more
negative). The powder samples were reacted with 100% H3PO 4
at 90øC [McCrea, 1950], and the carbon and oxygen isotope
composition of the liberated CO2 gas was measured with a
Fisons Isocarb device coupled with a prism dual inlet mass
spectrometer (EidgenOssische Technische Hochschule (ETH))
calibrated against the international standard National Bureau of
Standards (NBS) 19. The isotopic compositions of carbon and
oxygen are expressed in the standard d notation in per mill
relative to the Vienna Peedee belemnite (VPDB) international
isotope standard [Coplen, 1994], the working standard was MS-2
(Carrara Marble, •i 13Ccarb = +2.109/oo and 15180 = - 1.82%o). The
reproducibility of the apparatus was of _+0.05%o for carbon and
+0.10%o for oxygen isotope ratios. For organic carbon isotope
analysis, --5 g of powdered sample was treated with 1 M HC1
acid (heated to 70øC) for 24-36 hours to remove any carbonate
minerals. The samples were filtered through precombusted glass
fibre filters (Whatmann GF/C) and washed with three volumes of
Milli-Q TM deionized distilled water. The 1513Corg values were
obtained from CO2 on combustion [ Craig, 1953] within a Europa
Scientific automated nitrogen carbon mass spectrometer
(Newcastle; reproducibility: +0.36%o) and calibrated against an
internal laboratory standard (•513Corg = -25.34%o VPDB) or
within a Carlo Erba NCS2500 CE Instruments elemental
analyzer (ETH; reproducibility: +0.25%o; see Figures 2 to 5)
calibrating against the laboratory standard Atropina (•513Corg =
-28.74%o VPDB). Repeated measurements of the same sample
with the two different organic carbon isotope analyzers gave
identical results.
3. Sampling and Methods
The two sections were sampled for isotope investigations at a
high resolution. Within the LS, samples were taken at intervals
equivalent to = 15-20 kyr, according to the time scale established
by Herbert [ 1992].
For the determination of the amount of carbonate (wt%), total
organic carbon (wt%), and •513Corg the procedure was as follows:
(1) the rock samples were cleaned of any surface contamination
and then broken into fragments of--5-10 mm. (2) The fragments
were rinsed in methanol, dried, and then crushed to a fine
powder with a Tema rotary disc mill. (3) For total carbon
analysis, --50-80 mg of powder were analyzed using a Leco CS-
244 carbon-sulfur analyzer (precision: _+0.03 C%). (4) The TOC
values were obtained using --100 mg of powder after dissolution
of carbonate minerals with 2 M HC1. (5) The difference between
total carbon and organic carbon values was used to calculate the
carbonate content of the samples.
Because it was not possible to separate single macro, micro-
fossils, or nannofossils from the carbonate matrix, the analysis of
4. Results
The carbonate carbon isotope curves can be split into eight
segments (C1-C8; Figures 2 and 3). In both sections the mean
•513Ccarb values in the upper Barremian limestones (+2.0-2.89/oo,
C1) progressively fall to +1.6-2.0%o in the more marly lower
Aptian hemipelagic facies (C2), reaching a minimum (the lowest
values measured in this study) of +1.2-1.4%o in a thin (<2 m)
relatively organic-rich interval immediately underlying the LS
(C3). The •513Ccarb values then show an abrupt step-like positive
shift (C4) at the lower boundary of the LS. Subsequently, the
•513Ccarb values remain unvaried within the range +2.6-+2.89/oo
for much of the rest of the LS (C5); however, toward the top of
the LS interval, there is another abrupt step-like increase to
+3.6%o (C6). This event precedes the maximum of the early
Aptian positive 1513Ccarb excursion (the "Cismon Event" in the
sense of Weisseft and Lini, [1991] and Weisseft et al., [1998]),
during which •513Ccarb values of +4.59/oo characterize the entire
Leupoldina cabri zone (C7). The subsequent drop in 1513Ccarb

MENEGATTI ET AL.' THE •13C STRATIGRAPHY IN THE "LIVELLO SELLI" 533
s•e•e•
euoz
le•e•!u!me•o4
UO!leW•oj
eBelS NVlS'IV
ß 1oe.•,•el 'Pi9 ! J q • o "7 !•olq'O
N 0 I• V & i N I
k13ddn N V i ld V

534 MENEGATTI ET AL.: THE bl3C STRATIGRAPHY IN THE "LIVELLO SELLI"
ouoz
I leJojlUlLUeJo_-I I $,suelBB e,q '•1 l'"l'p,•)t !$ q to o '7 !• o lq '•)
UO!)eLUJO-i I VSSOa VllOVOS l ¾1¾031•¾A V lOVO$ VOllOIVbN
' e6elS d V, ..... a 3 • o • • .............................

MENEGATTI ET AL.: THE 813C STRATIGRAPHY IN THE "LIVELLO SELLI" 535
ii iiii i i
............
....
O- •-.•.;.• .•...• ,, -:•"• -•; ,• :• .... ';"• '•:-,•'"• } ::-•• .................
• .... •:: -*- .... . ..... .... :.• - ......................
• .......... • •....• .......................................
__
, -- -s:.:. - .................... • ...........
-•3 • •X_-__•; --•.;.:•••'•:"•..•::':•7::•.'•--'::::;• '•'-- .. ':,T'• ............... • ........
' : ............. _• ........... EZ3?%C.?,;:;;;; •::; ...... o ........
_,,•j ::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
J"• J-:::::::::'L'L':: ::::::'Z::': ===============================
t ......................... %7%•".,•:.•' ........ •,:•'• ..... '•-r •-*: •- ....................
- . .......................... :;;•-:,•;•:..:-:•::?•; ............... ';:;•7%•ff:-::½':•;:•::-'•-'..%?:.. '::.i • ..............
-27.2 • ...... • .... I- • .... • ....
• .......................... •jZ:x•.:::.•::2:.::':•;X•;.'•':,-x;;;.'d;x•:;L ....... ;f;.,.• •. ;: .................
.•,.•; :::::::::::::::::::::::::-"*:•Z;:S:/;;:,*dZ•;;;;::/..*::;';;'•;•:.:::• -_ .... :::::::::::::::::::
• • ':':•'-'?•"':•'•::4Z:"•:':: ?•:..;;:E:::.•::•:;f•;•::::.;•:::; ....
• -........T • ...... ::,:•;:•:•::;.t•::;::%½:,•.::•'•:•-••;:ig•:-'•:•-,•::'-?'-• :'%•.•';X:'•::',% .........................
• .................. ",?:f:::?;...,x:;•E;•./: t :•..-*:•D:::...... ':;/•:.- :•; .........................
½' ?' ..... :•-•.%2.T-:x?-':z:%•:.•:":.• .........................
•- • .... _ ........................
;'.'.-' ." -';'.. :: ..... ....•._-".a.'-'--•: .:-'-'-'--•
• ............................ ;•:•;
• ............................ %.LT"E ...... %,.:X ':::•'•:• %?•':•' - ........... ;• .........................
o '•...:Ec::4,..
• ............................ :•,•;,,7•:;•:.,..:.•....•/½•:.%•:•73;%,:•?,,•f$... ........... •.•. :;?; .................
w ............................ •-•::•:•::;•-•;;--• :-:-?•e::•
-• '*'*'
• .... •..• ............. -:-:?•;,r:::•.:•;•:..•d:,.•..'•?.•---4?;:$:,:•--.•:,::• .........
..................... %a;,::;,%'T'"B?;•;;
...................... .... ..... '* ....
• ..............
•'; ......................... •'•'½' ";"•"•*;'*•*:"'•"-•;"• ....... ;' •' ..,•;;,,•:• -i ........................
0 .......................... jJ ....... • __ _
o ' '"' "•'••'•••:' "'"'"•" '"":;•••:':••-'
• .......................... -½? ;:' ::a ":;:: Z:* ........ • .... • .....
- E/•--•:;•::- ...... '" '% ..... ;:'e";:;i ::::;' ,;:.::.•::•i •:;:• :;;;•:" '" ::•.:" '"":
. ...... ..... ?..:,,...,.
::½7;;.'"':::•F :**•: ..... :;....';., ½:'.".•-':• ::8 .•::::::::::•:....::• ..•
sJelelN
euoz I•qeo '3 I /• o I q 'E)
uoBeu•Jod N 0 • V A I N I
e6e•S N V !1 d V
i , ,, ,, ,,11 ,,,,,, ,,,,,,,,,,,,,,,,,,,,,,,, ii ii , , , ,
.,.., o
c• ,
.,..,
.• >

536 MENEGATTI ET AL.: THE (•13C STRATIGRAPHY IN THE "LIVELLO SELLI"
values (C8) differs between the two sections: in the Roter Sattel
section the values fall progressively to --+2.6%o in the upper
Aptian Globigerinelloides algerianus zone, whereas at Cismon
they abruptly fall to +2.3%o by the base of the Globigerinelloides
J•rreolensis zone (but note this is based on only one sample). The
presence of a late Aptjan-early Albian disconformity in both
sections [Weisseft et al., 1985; Python-Dupasquier, 1990; Hable,
1997] eliminates the record of a second major latest AptJan posi-
tive isotope excursion documented in some Tethyan sections of
the southern Alps [Lini, 1994], the Apennines [Erbacher, 1994],
the Vocontian Trough [Weisseft and Brdhdret, 1991], the
Helvetic Realm [FOllmi et al., 1994], and the Pacific Ocean
[denkyns, 1995] in Greece [ GrOtsch et al., 1996] and the Middle
East [ Vahrenkarnp, 1996].
The structure of the •513Ccarb and •513Corg curves (Figures 4
and 5) is generally very similar, but there are some differences.
In the upper part of segment C3 the •13Ccarb values exhibit a
minor 0.2-0.4%o increase, whereas the •513Corg values are still
generally falling; this divergence is expressed as a peak in the
A•S13C value (Figures 4 and 5), which is the relative isotopic
difference between carbonate and organic matter [e.g., Hayes et
al., 1989]. A similar "lag" in the •13Corg has been previously
observed in the Valanginian [Cotilion and Rio, 1984; Lini et al.,
1992]. However, the •513Corg signal in segment C2 is rather noisy
at Cismon, and the progressive increase in A•513C seen over the
same interval (C2-C3) at Roter Sattel is mainly due to the steeper
gradient of change in •13Corg compared to •13Ccarb Indeed,
because •513Ccarb is SO uniform through segments C3, C5, and
C7, the A•S13C curve generally mirrors that for •513Corg
Although the isotopic values are rather uniform through most of
the LS (C5), in the thicker section at Cismon it is clear that the
•5•3Corg values do not stabilize as quickly as those for •13Ccarb,
showing a progressive enrichment rather than a discrete step
(Figure 5). Also, at Cismon the A•5•3C curve shows a clear (1%o)
change in the upper (more frequently organic-rich) third of
segment C5 due to a slight increase in •513Ccarb and a slight
decrease in •13Corg which precedes the larger change in segment
C6; this feature also appears to be present in the upper half of C5
at Roter Sattel. It is evident that C6 is much more strongly
expressed in the •513Corg curve, especially at Cismon, and the
•13Ccarb curve is almost a straight line from the upper part of C5
through to lower half of C7; furthermore, at Roter Sattel the C6
change in •13Corg seems to clearly precede that in •13Ccarb
(Figure 4).
The results of bulk and biomarker organic geochemistry and
kerogen microscopy studies of these and other Tethyan LS
sections (R. Brown et al., manuscript in preparation, 1998) will
be presented elsewhere and are only briefly summarized below.
These studies were undertaken to evaluate the extent to which the
•13Corg curves may be influenced by changing marine/terrestrial
ratios. This is made difficult by the very low TOC values outside
the LS (means of 0.4 wt% or less) which make most methods of
organic matter analysis impracticable or unreliable. However, it
is possible to evaluate the influence of organic matter type within
the LS, especially its most organic matter-rich upper part (the
"black member") which shows the largest •13Corg range
(<4.5%o). For the hydrogen index (HI) range 0-300 (over 90% of
the data), there is a positive correlation with TOC (r 2 = 0.8) and a
negative correlation with •13Corg values (r 2 = 0.4-0.6), but none
of these parameters shows a significant correlation with the ma-
rine amorphous organic matter (AOM) to the terrestrial phyto-
clast ratio determined from transmitted light microscopy or with
biomarker data (R. Brown et al., manuscript in preparation,
1998). It is also noteworthy that the individual samples with peak
TOC values within segment C5 do not exhibit different •5•3Corg
values such as might be expected if these contained significantly
different terrestrial/marine ratios [Dean et al., 1986; Tyson,
1995].
We believe the above trends indicate that much of the varia-
tion in HI is dependent on the preservation of marine AOM
[Tyson, 1995], which dominates the LS palynofacies
assemblages (>75%), and that any variation in the
marine/terrestrial ratio is not a significant control on this part of
the •13Corg curve. The strong correlation with the • 13Ccarb curve
(r 2 = 0.9) and its uniformity in all the studied Tethyan LS
sections also suggest that the •13Corg curve is not controlled by
marine/terrestrial mixing in this interval. Because of the distal
hemipelagic nature of the sections, terrestrial inputs are likely to
be at low and relatively constant background levels and strongly
diluted wherever dysoxic-anoxic conditions permit preservation
of marine AOM; however, one would expect the more refractory
terrestrial material to become selectively concentrated under the
oxic conditions within the white pelagic limestones below and
above the LS. An overall difference between the dysoxic-anoxic
LS and the adjacent oxic beds might therefore reflect partly
marine/terrestrial ratios (the stratigraphic interval that
incorporates TOC values > 1 wt% has •513Corg values all <-24%o),
but it is very unlikely that they can explain the fine structure of
the •13Corg curve. It should also be noted that other studies have
shown that OAE or similar isotopic signals can be preserved
even within more oxic organic-poor intervals dominated by
terrestrial organic matter [e.g., Holser et al., 1986; Magaritz et
al., 1992; Hasegawa, 1997].
A comparison between the •13Ccarb and •5 •80 curves (Figures
2, 3, and 6) indicates no significant covariance between these pa-
rameters. In contrast to the •513C values, the oxygen isotope val-
ues show a more scattered evolution through both sections.
Nevertheless, the •5180 values reveal similar relative trends in the
G. blowi and lower L. cabri zones of both sections (below and
above the LS), although at Roter Sattel the absolute values are
generally 2-3%o more negative (Figure 6). The •5180 values mea-
sured below the LS vary between -4.4%o and -2.6%o at Roter
Sattel and -2.6%o and -0.7%o at Cismon, becoming increasingly
negative up-section (trend O 1 on Figures 2 and 3), which may re-
flect a warming trend. The LS is characterized by a lower ampli-
tude of variation and divergent trends: at Roter Sattel the •5180
values continue to fall, whereas at Cismon they show a gradual
shift toward positive values. The end of the LS coincides with a
short-term drop to more negative values in both sections
followed by a general long-term trend to more positive •5180
values (trend 02 on Figures 2 and 3) through the positive •5•3C
excursion (C4-C7). The O1 and 02 trends are also apparent in
the pre- and post-Livello Selli strata in the Umbro-Marchean data
of Marconi et al. [ 1994].
5. Discussion
$.1. Isotopic Signatures and Diagenesis
Numerous authors have demonstrated that •513C variations,
such as those described here, do not represent diagenetic artefacts
but preserve original oceanographic and environmental signals

MENEGATTI ET AL.' THE (513C STRATIGRAPHY IN THE "LIVELLO SELLI" 537

538 MENEGATTI ET AL.: THE •13C STRATIGRAPHY IN THE "LIVELLO SELLI"
o Ci•mon .....
0 - ß Roter Sattel ¸ ¸ ¸
o
,• ¸¸ •
ø o oo,o %
• 0 0 ¸ 0o • 0
o
o 8 o oo
o .o• • o
i i i i i i
1 1 5 2 25 3 35 4 4,5
Ccaco (
[i•re 6. The 8•Cc•SO plot of the b•lk c•bo•te m•ix. Note
ß e 8•Cc•-si•l,
[e.g., Scholle and Arthur, 1980; Weisseft and Lini, 1991; Lini et
al., 1992; Cotfield et al., 1991; denkyns et al., 1994; denkyns,
1995, 1996; Ferreri et al., 1997]. Several observations support
the hypothesis that the 1513C "plateau" (C5) in the LS is not a dia-
genetic artefact: (1) there is no covariance between 1513Ccarb and
1518Ocarb (Figures 2, 3, and 6), as has been attributed to overprint-
ing during early [e.g., denkyns, 1974] or burial diagenesis [e.g.,
denkyns and Clayton, 1986; denkyns, 1996]; (2) the uniform •13C
values in segment (25 occur in both the carbonate and organic
matter records (Figures 3 and 4); (3) the relatively high carbon-
ate/TOC ratio (>7:1) in the LS [Scholle and Arthur, 1980] and
the lack of an inverse relationship between TOC and •13Ccarb
[denkyns and Clayton, 1986] argue against a diagenetic effect
[Irwin et al., 1977; Raiswell and Berner, 1987]; (4) The LS is too
thick for postdepositional homogenization by bioturbation, and
levels of mixing are likely to have been minimal in the black
shale facies; (5) local early or burial diagenetic influences can be
excluded because the structure of the •5 •3C curves is the same in
both sections despite different depositional environments
[Python-Dupasquier, 1990; Weissert and Lini, 1991 ], different
burial histories [Bosellini, 1973; Borel, 1995], and different sedi-
mentation rates.
While diagenesis did not apparently influence the structure of
the •513C curve, contrasting burial diagenetic conditions did result
in different •5180 values because in the water-calcite system the
fractionation of oxygen [Bottinga, 1968; Erarich et al., 1970] is
more temperature sensitive than the fractionation of carbon
[Erarich et al., 1970; Hudson, 1977]. The sediments at Roter
Sattel show •5 •80 values that are clearly more negative than at
Cismon (Figures 2, 3, and 6), suggesting a greater overprinting
by burial diagenesis [e.g., McKenzie et al., 1978; Marshall, 1981;
Weissert, 1989], as indicated by further mineralogical and geo-
chemical evidence. This may also have caused the overall 0.5%o-
1.0%o difference in •513C values between the two sections.
5.2. Palaeoceanography of the Live!!o Se!!i
While some authors have attributed the origin of deep water
Aptian-Albian black shales to a combination of low productivity
and enhanced preservation under stagnant dysoxic-anoxic condi-
tions [e.g., Bralower and Thierstein, 1987; Pratt and King, 1986;
Premoli Silva et al., 1989], others have proposed that OAE 1
primarily reflects an episode of increased primary productivity
and increased upwelling rates [e.g., Weissert et al., 1985; Leckie,
1989; Weissert, 1989; Erbacher et al., 1996]. The best (but still
inferential) evidence for enhanced productivity during OAE l a
comes from the marked changes in oceanic nannofloral assem-
blages [ Coccioni et al., 1992; Bralower et al., 1993, 1994; Erba,
1994], which begin before the black shales, and also radiolarian
assemblages [Erbacher, 1994; Lambert and De Wever, 1996;
Erbacher et al., 1996; Erbacher and Thurow, 1997].
There are a number of possible factors that could contribute to
enhanced nutrient supply and increased palaeoproductivity. It is
widely accepted that the volcanically and tectonically induced
increase in atmospheric CO2 levels [e.g., Larson, 1991a, b;
Tarduno et al., 1991] resulted in global warming during early
Aptian time [e.g., Barron and Washington, 1985; Barron and
Peterson, 1990; Caldeira and Rampino, 1991; Herman and
Spicer, 1996]. Computer models suggest that this would have
favored an intensification of the oceanic thermohaline circulation
mainly due to increased salinity contrasts in the Early Cretaceous
ocean [Hay, 1995; Hay and Wold, 1997; see also Manabe and
Bryan, 1985; Sarmiento et al., 1988; Gdrard and Dols, 1990;
Herbert and Sarmiento , 1991; Rind and Chandler, 1991; Huber
et al., 1995; Schmidt and Mysak, 1996]. Such a change would, in
turn, have promoted intensified nutrient recycling from the deep
and intermediate water column and thus enhanced productivity
[e.g., Parrish and Curtis, 1982]. In addition, the intensified
"greenhouse" conditions may have accelerated the hydrological
cycle [e.g., Schmidt and Mysak, 1996] resulting in increased rain-
fall and continental weathering and hence in altered nutrient and
sediment fluxes from the continents to oceans [e.g., Berner et al.,
1983; Manabe and Bryan, 1985; Weissert, 1990; Fdillmi et al.,
1994; FOllmi, 1995]. In the studied sections, enhanced (CO2)atm
levels may be reflected in the low values of 1513Ccarb and •13Corg
(C1-C3, Figures 2-5) and in the corresp.onding increase of A•513C
preceding the onset of the LS (D 1, Figures 4 and 5) [e.g., popp et
al., 1989; Rau et al., 1989]. Furthermore, an indication of warm-
ing of the surface ocean in the late Barremian to early Aptian is
given by the general trend of •5180 toward more negative values
(O1, Figures 2 and 3) [e.g., Savin, 1977]. Any increase in pro-
ductivity will have favored radiolarians and organic-walled phy-
toplankton taxa [e.g., Leckie, 1989; Bralower et al., 1994; Erba,
1994; Erbacher et al., 1996]; coupled with the high (CO2)a q lev-
els and the periodic shallowing of the calcite compensation depth
[Thierstein, 1979]; this shift resulted in lower sediment carbonate
contents and thus decreased burial of Ccarb. The higher TOC
contents of oceanic OAE l a sediments thus probably reflect a
combination of higher organic matter fluxes, lower carbonate
autodilution, low siliciclastic sediment dilution, and enhanced
preservation under dysoxic-anoxic conditions [cf. Tyson, 1995,
see also Arthur et al., 1984, 1990; Sarmiento et al., 1988;
Pedersen and Calvert, 1990].
The high-productivity model contrasts with model calculations

MENEGATTI ET AL.: THE •13C STRATIGRAPHY IN THE "LIVELLO SELLI" 539
showing that at the low-sedimentation (dilution) rates observed
and with the carbon preservation factors apparently associated
with laminated sediments [Bralower and Thierstein, 1987],
primary productivity would not need to be particularly high in
order to explain the observed range of TOC values observed in
the black shales [Tyson, 1995]. The productivity may have been
higher but not high.
5.3. Livello Se!li in the Context of the •13C Excursion
In previous studies the coincidence of the Livello Selli and its
equivalents with the onset of the positive Aptian 1513C excursion
was taken as evidence of a direct link with episodes of increased
organic carbon burial and black shale formation [e.g., Berger and
Vincent, 1986; Weisseft, 1989; Weisseft and Lini, 1991]. Our
new high-resolution carbon isotope records through the LS indi-
cate that positive shifts in the carbon isotope curve occur at the
onset of (C4), near the end of (C6), and after the end of (C7),
rather than during, deposition of most of the LS. Bralower et al.
[1994, p. 357] previously realized that the fact that the main
Aptian positive isotopic shift (C7) occurs after the LS poses a
challenge to the earlier interpretations; our observation of the
uniformity of the 1513Ccarb signal at values of--2.6%o (for several
100 kyr) emphasizes further the incompatibility with any
mechanism that assumes 15 •3C is driven simply by increased
carbon burial during widespread anoxia and black shale deposi-
tion. Indeed, from the carbon isotope data it appears that the LS
may reflect a peculiar paleoceanographic mode marked by a
stable marine carbon isotope budget. We believe there are several
possible scenarios which may explain the isotopic uniformity
seen during segment C5 of our curves.
5.3.1. Scenario 1. Assuming enhanced primary productivity
during deposition of the LS, the extraction of •2C into the sedi-
mentary carbon sink would have to have been balanced by an
accelerated flux of isotopically light carbon into the surface
water reservoir [Bralower et al., 1994]. The duration of the LS
interval implies that mass and isotopic steady state conditions
were established during the LS episode [Kurnp, 1991 ]. Several
different sources of •2C probably coexisted:
1. The first source is intensified recycling and upwelling of
intermediate water enriched in •2C-rich carbon. This hypothesis
would be in agreement with the circulation models cited previ-
ously. The constant •513C values due to enhanced recycling rates
of intermediate deep water would result in the reduction of the
bathymetric 15•3C gradient, but isotopic data from deep dwelling
organisms from lower Aptian sections are not available to test
this implication. However, late Paleocene [Corfield, 1994] and
Miocene carbon isotope records [Jacobs et al., 1996] show a--1
Myr period of convergence in the 15•3C of planktonic and benthic
foraminifera during the interval of constant 1513C values preced-
ing positive excursions. In the Miocene example the stabilization
and homogenization of the isotopic gradient coincides with the
deposition of phosphoritic sediments, suggesting increased up-
welling rates. According to Kump [1991], a decrease in the
bathymetric •513C gradient can be related to either a decreased
flux of organic matter which is oxidized in the water column
and/or an increased flux of carbonate to the deep ocean or by
changing the proportion between downward and upward flux of
13C depleted carbon. The high organic carbon and low carbonate
contents in the LS suggest the latter scenario as the most likely.
The described scenario may have acted over a longer time span
of 500 kyr to 1 Myr assuming a constant elevated input of nutri-
ents from the continent and may be coupled with the enhanced
river ine flux of isotopically light carbon.
2. The second source is the enhanced riverine flux of isotopi-
cally light carbon from continents to oceans at times of intensi-
fied "reenhouse weathering of carbonate rocks and organic
matter [e.g., Berner et al., 1983; Weisseft, 1990, FOllmi et al.,
1994; Hay, 1995]. According to Kurnp [1991], changes of
riverine flux affect the carbon isotope signal for periods longer
than the residence time of carbon in the oceans.
3. The third source is the build-up of isotopically light dis-
solved carbonate [e.g., Mackenzie, 1975] due to the decreased
fixation of carbon in C carb during the LS [e.g., Opdyke, 1997]
caused by unfavorable ecological conditions affecting calcareous
organisms in pelagic, shelf, and platform environments [Erba,
1994; Bralower et al., 1994; Fdillmi et al., 1994; Weisseft et al.,
1998] or a combination of increased (CO2)atm levels and trans-
gression leading to the periodic shallowing of the carbonate com-
pensation depth (CCD). It is likely that perturbed partitioning
between organic and carbonate carbon burial has acted over
several 100 kyr [ Weisseft et al., 1998].
4. The fourth source is an increased flux of isotopically light
CO 2 into the marine carbon reservoir at times of persistently high
volcanic and tectonic activity [e.g., Barron and Washington,
1985; Barron and Peterson, 1990]. However, although the rapid
changes of the carbon isotope pattern could be attributed to en-
hanced volcanic activity, higher atmospheric CO2 concentrations
should lead to more negative •13Corg values [e.g., Mizutani and
Wada, 1982; Dean et al., 1986; Rau et al., 1989; Bralower et al.,
1994].
5. The fifth source is the upwelling of •2C-rich HCO 3- derived
from bacterial sulfate reduction [Kernpe and Kazrnierczak, 1994]
would act during the deposition of the LS under anoxic condi-
tions, but its quantification is difficult unless accurate sediment
accumulation rates can be estimated.
5.3.2. Scenario 2. Assuming enhanced primary productivity,
isotopic balancing of enhanced •2C extraction from surface water
by temporarily increased oxidation of older terrestrial organic
matter buried on land cannot be excluded. This reaction, favored
by increased weathering and precipitation rates [e.g., Berner et
al., 1983] and increasing 02 levels in the atmosphere [e.g.,
Karhu and Holland, 1996], would result in higher levels of 12C
in the atmosphere and dissolved inorganic carbon (DIC) of ocean
and river water [e.g., Arthur, 1982; Kurnp, 1991]. Beveridge and
Shackleton [ 1994] demonstrated that the anthropogenic oxidation
of fossil fuels and the consequent increase of •2C in atmospheric
CO2 have resulted in a measurable decrease of 15•3C in plank-
tonic foraminifera. However, this has occurred at a very much
faster rate than that which would be associated with natural
weathering processes.
5.3.3. Scenario 3. A decrease of primary production and a
decelerated "biological carbon pump" resulted in the deposition
of the LS. It is likely, on the basis of the variations in TOC
(Figures 4-5), that changes in the flux of organic carbon and in
the efficiency of the biological carbon pump [Berger and
Vincent, 1986] occurred during deposition of the LS. The corre-
lation between the darker more laminated horizons and high
TOC contents with better preserved marine organic matter are

540 MENEGATTI ET AL.: THE 8•3C STRATIGRAPHY IN THE "LIVELLO SELLI"

MENEGATTI ET AL.: THE •513C STRATIGRAPHY IN THE "LIVELLO SELLI" 541
perhaps suggestive that oxygen levels and preservation were a
more important control on carbon burial than was productivity;
however, productivity (carbon flux) determines the oxygen
demand and is thus a major control on dissolved oxygen levels.
Summarizing, the carbon isotope data throughout the LS do
not provide conclusive evidence of either higher or lower
primary production modes but show that whatever
paleoceanographic mode was dominant, it had no impact on the
marine carbon isotope budget. The scenarios describing
enhanced recycling of 12C due to the intensification of the
thermohaline circulation in intermediate watermasses (scenario
la), coupled with changed riverine flux (scenario ld), appear as
the most likely. They are in best agreement with the
paleoclimatic and paleoceanographic patterns described for the
LS and for the Early Cretaceous. The constant 1513C values
through the LS appear to document a stable high-temperature
oceanic circulation mode which would have been characteristic
for Early Cretaceous greenhouse episodes, resulting in the
equilibrium between the export of 12C-rich carbon from the
oceanic photic zone into the sedimentary reservoir and the import
of •2C-rich carbon into the surface ocean by intensified recycling
of intermediate water. In this context the black shales of the
Livello Selli would represent the sedimentary expression of en-
hanced nutrient recycling and episodically enhanced TOC preser-
vation factors caused by a peculiar Livello Selli circulation
mode.
5.4. Comparisons With Mesozoic/ and Tertiary •13C
Excursions
Our study has documented two additional characteristic fea-
tures of the early Aptian 1513C curve: (1) the trend to more nega-
tive 1513C values prior to the positive excursion at the onset of the
LS (C3) and (2) the step-like character of the 1513C curve result-
ing from the stabilization of the values during the Selli event
(C5). Our survey of the literature confirms that negative trends
prior to positive excursions are rather common (Table l a). In
Cretaceous and Cenozoic sediments the systematic record of the
trend to more negative values preceding positive carbon isotope
excursions may confirm the hypothesis of intensified volcanic
activity and enhanced CO 2 emissions as the principal trigger of
global perturbations of the carbon cycle [e.g., Arthur, 1982; Lini,
1994]. Finally, temporary stabilizations or significant kinks in the
1513C gradient during other major positive excursions also appear
to be common (Table 1 b), regardless of whether or not they are
associated with black shale episodes.
5.5. Stratigraphic Significance
The LS is a lithostratigraphic unit recognized on the basis of
lithological criteria, primarily the lower carbonate content and
the darker, more radiolarian- and organic-rich character of the
sediments [ Coccioni et al., 1987]. However, our data show that it
is now possible to make a more objective definition of a Selli
event based upon the stable carbon isotope curves. As the i513C
signal is not primarily driven by local oceanography, a
chemostratigraphically defined Selli event should be a more
definitive tool for high-resolution correlations than lithology-
based units whose expression is known to vary geographically
depending upon palaeobathymetry and the extent of redeposition,
etc. [Coccioni et al., 1987, 1989; Bersezio, 1994]. We therefore
propose that a Selli event be chemostratigraphically defined as
the interval including the first and second major positive 1513C
shifts (segments C4 and C6) and a main central segment (C5)
corresponding to the period of temporary uniformity of 1513C
(•13Ccarb +2.6-2.8%o) that precedes the maximum early Aptian
positive excursion (the Cismon event, segment C7). Such a
definition makes the Selli event almost synonymous with the LS
at Cismon, but it corresponds to only half of the LS at Roter
Sattel. No organic carbon-rich beds (> 1% TOC) occur above the
top of this Selli event, but a few organic-rich beds, and the
carbonate minimum (<40 wt%), occur below it (within segments
C2 and C3). However, there are no suitably distinct isotopic
features which can be used to define the event in such a way that
these beds are included. If it is assumed that these isotopically
defined boundaries are time parallel, then the sedimentation rate
of this Selli event (C5) was =2.7 times faster at Cismon than at
Roter Sattel (about 4 m versus 1.5 m), perhaps partly explaining
their different organic contents.
As the stratigraphic gradients in 15•3C are determined against
sediment thickness rather than time, intervals of apparent uni-
formity potentially reflect periods of more rapid sedimentation
rates; however, we view this as unlikely because of the similarity
of the •13C curves from other regions. Similar 1513C curves are
seen in the bulk carbonate [Erbacher et al., 1996; also Marconi
et al., 1994] and organic matter [Erbacher, 1994] data from the
Mame a Fucoidi of the Umbro-Marchean region, as well as in the
carbonates of the Abruzzo-Campania Platform where black
shales are not developed [Ferreri et al., 1997]. Furthermore,
similar curves are also observed in the North Atlantic [Arthur et
al., 1979] and in shallow water sequences from northwest
Greece, the Arabian Shelf [Vahrenkamp, 1996], and the Pacific
guyot [ Jenkyns, 1995].
6. Summary and Conclusions
The structure of the high-resolution •13Ccarb and •13Corg
curves through the early Aptian Livello Selli (LS; equivalent to
OAE la) is essentially identical at two different sections (Roter
Sattel and Cismon) from the western and eastern margins of the
Alpine Tethys. This rules out diagenetic artifacts or local facies
controls.
The •13Ccarb and 1513Corg curves can both be divided into
eight segments at each locality; six of these segments are from
the lower Aptian G. blowi zone, indicating significant subzonal
resolution (>15-20 kyr). Some of these segments can be identi-
fied in previously published early Aptian 15 •3C records from
other areas.
The •13Ccarb and 1513Corg curves can be used to define a
chemostratigraphic Selli event as the stable interval (segment C5)
that occurs between the first and second abrupt step-like positive
shifts that precede the main early Aptian positive excursion
(Cismon event). Thus defined this interval includes the main part
of the lithostratigraphically defined LS at the study localities.
The cyclic organic-rich and organic-poor sediments of the LS
were thus largely deposited during a period (500 kyr to 1 Myr) of
unchanging carbon-isotope values, rather than during an interval
of positive excursion (as was previously inferred from earlier
low-resolution studies).

542 MENEGATTI ET AL.: THE •13C STRATIGRAPHY 1N THE "LIVELLO SELLI"
The isotopic uniformity during this chemostratigraphically
defined Selli event probably reflects an equilibrium between Corg
burial, increased recycling rates of 12C-rich intermediate water,
and intensified flux of isotopically light weathering-derived
riverinc DIC. The equilibrium represents the consequence of an
extreme but stable mode of intensified deep and intermediate
water circulation of early Aptian low to intermediate latitude
oceans. The new mode of circulation was triggered by global
warming at the time of elevated atmospheric CO 2 levels, which
favored warm temperatures and extreme salinity contrasts in the
Aptian ocean at a time of accelerated hydrological cycling. The
low •5180 values measured in the LS could confirm warmer
ocean temperatures. The black shale circulation mode expressed
in the Livello Selli did not contribute to major changes in the
marine carbon isotope budget. The steep positive shift observed
in the •513C curve above the LS indicates a major destabilization
of carbon partitioning in the Aptian ocean not linked with the
deposition of the LS.
We have identified that initial negative •5 13C shifts and
periods of stabilization during the greatest •5•3C gradient are a
common feature of Mesozoic and Cenozoic positive •513C
excursions regardless of whether or not they are associated with
black shale deposition. This observation suggests the hypothesis
of a peculiar response of the oceanic circulation mode to a
volcanically induced perturbation of climate and provides further
constraints in modeling the origin of •5 •3C variations.
Acknowledgments. We thank Stefano Bernasconi and Uli Wortmann
(ETH-Ztlrich) for stimulating discussion, as well as Hilary Paul (Stable
Isotope Laboratory, ETH-Ztlrich)and Clive Heatherington (Biomedical unil•
University of Newcastle) for technical support on carbonate carbon isotope
and organic carbon isotope analyses, respectively. Constructive reviews by
M. Arthur, T. Herbert and M. Leckie helped to improve the manuscript.
Financial support from ETH-Grant No. 0-20-863-94 (A.M.) is gratefully
acknowledged. R.S.B., P.F. and R.V.T. thank the State of Guernsey for a
studentship (for R.S.B.).
References
Arthur, M. A., The carbon cycle-controls on at-
mospheric CO 2 and climate in the geologic
past, in Climate in Earth History, Stud.
Geophys., vol. 5, ppo 5-67, AGU,
Washington, D. Co, 1982.
Arthur, M. A., and B. B. Sageman, Marine
black shales: Depositional mechanisms and
environments of ancient deposits, Annu.
Rev. Earth Planet. Sci. , 22, 499-551, 1994.
Arthur, M. A., P. A. Scholle, and P. Husson,
Stable isotopes of oxygen and carbon in car-
bonates from Sites 398 and 116 of DSDP,
Initial. Rep. Deep Sea Drill. Proj., 47/2,
477-492, 1979.
Arthur, M. A., W. E. Dean, and D. A. V. Stow,
Models for the deposition of Mesozoic-
Cenozoic fine-grained organic-carbon-rich
sediments in the deep sea, in Fine-Grained
Sediments: Processes and Products, edited
by D. A. V. Stow, and D. J. W. Piper, Geol.
Soc. London Spec. Publ., 15, 527-562, 1984.
Arthur, M. A., W. E. Dean, and S. O.
Schlanger, Variations in the global carbon
cycle during the Cretaceous related to
climate, volcanism, and changes in
atmospheric CO 2, in The Carbon Cycle and
Atmospheric CO:: Natural Variations
Arcbean to Present, Geopbys. Monogr. Set.,
vol. 32, edited by E. T. Sundquist and W.
E. Broecker, pp. 504-529, AGU,
Washington, D.C., 1985.
Arthur, M. A., W. E. Dean, and L. M. Pratt,
Geochemical and climatic effects of in-
creased marine organic carbon burial at the
Cenomanian/Turonian boundary, Nature,
335, 714-716, 1988.
Arthur, M. A., H. C. Jenkyns, H.-J. Brumsack,
and S. O. Schlanger, Stratigraphy, geochem-
istry, and paleoceanography of organic-car-
bon rich Cretaceous sequences, in
Cretaceous Resources, Events and Rhythms,
edited by R. N. Ginsburg and B. Beaudoin,
pp. 75-119, Kluwer Acad., Norwell, Mass.,
1990.
Barron, E. J., and W. H. Peterson, Mid-
Cretaceous ocean circulation: Results from
model sensitivity studies,
Paleoceanography, 5, 319-338, 1990.
Barron, E. J., and W. M. Washington, Warm
Cretaceous climates: High atmospheric CO 2
as a plausible mechanism, in The Carbon
Cycle and Atmospheric COy Natural
Variations Archcan to Present, Geophys.
Monogr. Set., vol. 32, edited by E. T. S.
Sundquist and W. E. Broecker, pp. 546-553,
AGU, Washington, D.C., 1985.
Bartolini, A., P.O. Baumgartner, and J.
Hunziker, Middle and Late Jurassic carbon
stable isotope stratigraphy and radiolarite
sedimentation of the Umbria-Marche Basin
(central Italy), Eclogae Geol. Helv. , 89, 811 -
844, 1996.
Berger, W. H., and E. Vincent, Deep sea car-
bonates: Reading the carbon isotope signal,
Geol. Rundschau, 75, 249-269, 1986.
Berner, R. A., A. C. Lasaga, and R. M. Garrels,
The carbonate-silicate geochemical cycle
and its effect on atmospheric carbon dioxide
over the past 100 million years, Am. J. Sci.,
283, 641-683, 1983.
Bersezio, R., Stratigraphic framework and sedi-
mentary features of the Lower Aptian
"Livello Selli" in the Lombardy Basin
(Southern Alps, Northern Italy), Riv. Ital.
Palaeontol. Strat., 99,569-590, 1994.
Beveridge, N. A. S., and N.J. Shackleton,
Carbon isotopes in recent planktonic
foraminifera: A record of anthropogenic
CO 2 invasion of the surface ocean, Earth
Planet. Sci. Lett., 126, 259-273, 1994.
Borel, G., Pr6alpes m6dianes romantics:
Courbes de subsidence et implications g6o-
dynamiques, Bull. Soc. Vaudoise Sci. Nat.,
83, 293-315, 1995.
Bosellini, A., Modello geodinamico e paleotet-
tonico delle Alpi Meridionali durante il
Giurassico-Cretacico. Sue possibili appli-
cazioni agli Appennini, paper presented at
Moderne Vedute sulla Geologia dell'Appen-
nino, Accad. Naz. Lincei, 370, 163-213,
1973.
Bottinga, Y., Calculation of fractionation fac-
tors for carbon and oxygen isotope
exchange in the system calcite-carbon
dioxide-water, J. Phys. Chem., 72, 800-808,
1968.
Bralower, T. J., Valanginian to Aptian calcare-
ous nannofossil stratigraphy and correlation
with upper M-sequence magnetic anomalies,
Mar. Micropaleontol. , 11,293-310, 1987.
Bralower, T. J., and H. R. Thierstein, Organic
carbon and metal accumulation rates in
Holocene and mid-Cretaceous sediments:
Palaeoceanographic significance, in Marine
Petroleum Source Rocks, edited by J.
Brooks and A. J. Fleet, Spec. Publ. Geol.
Soc. London, 26, 345-369, 1987.
Bralower, T. J., W. V. Sliter, M. A. Arthur, R.
M. Leckie, D. J. Allard, and S. O.
Schlanger, Dysoxic/anoxic episodes in the
Aptian-Albian (Early Cretaceous), in The
Mesozoic Pacific: Geology, Tectonics, and
Volcanism, Geophys. Monogr. Set., vol.
77, edited by M. S. Pringle et al., pp. 5-37,
AGU, Washington, D.C., 1993.
Bralower, T. J., M. A. Arthur, R. M. Leckie, W.
V. Sliter, D. J. Allard, and S. O. Schlanger,
Timing and paleoceanography of oceanic
dysoxiadanoxia in the late Barremian to
early AptJan, Palaios, 9, 335-369, 1994.
Br6h6ret, J.-G., The mid-Cretaceous organic-
rich sediments from the Vocontian Zone of
the French Southeast Basin, in Hydrocarbon
and Petroleum Geology of France, edited by
A. Mascle, Spec. Publ. Eur. Assoc. Petrol.
Geol., 4,295-320 1994.
Brown, R., P. Farrimond, R. V. Tyson, A. P.
Menegatti, and H. Weissert, A molecular
and isotopic geochemical study of the
Aptian Oceanic Anoxic Event on the west-
ern Tethyan margins, paper presented at the
Research Conference: Carbonates and
Global Change: An Interdisciplinary
Approach, Soc. for Sediment. Geol./Int.
Assoc. Sediment., Wildhaus, Switzerland,
June 22-27, 1996.
Caldeira, K., and M. R. Rampino, The mid-
Cretaceous super plume, carbon dioxide,
and global warming, Geophys. Res. Lett.,
18, 987-990, 1991.
Channell, J. E. T., W. Lowrie, and F. Medizza,
Middle and Early Cretaceous magnetic
stratigraphy from the Cismon section, north-

MENEGATTI ET AL.' THE 813C STRATIGRAPHY IN THE "LIVELLO SELLI" 543
em Italy, Earth Planet. Sct. Letr, 42, 153-
166, 1979.
Clauser, S., M. Renard, and G. Richebois,
Variation in trace element contents and iso-
topic compositions of Lower Cretaceous
carbonates from the Galicia margin (ODP
Leg 103): Reconstruction of the pale-
ochemistry of the Early Cretaceous Ocean,
Proc. Ocean Drill. Program Sci. Results,
103, 489-504, 1988.
Coccioni, R., O. Nesci, M. Tramontana, C. F.
Wezel, and E. Moretti, Descrizione di un
livello guida "Radiolaritico-Bituminoso-
Ittiolitico" alia base delle Marne a Fucoidi
nell' Appennino Umbro-Marchigiano, Boll.
Soc. Geol. Ital. 106, 183-192, 1987.
Coccioni, R., R. Franchi, O. Nesci, C. F. Wezel,
F. Battistini, and P. Pallecchi, Stratigraphy
and mineralogy of the Selli level (early
Aptian) at the base of the Marne a Fucoidi
in the Umbrian-Marchean Apennines (Italy),
in Cretaceous of Western Tethys, 3 r d
International Cretaceous Symposium, edited
by J Weidmann, pp. 563-584,
Schwe•zerbart'sche, Stuttgart, Germany,
1989.
Coccioni, R., E. Erba, and I. Premoli-Silva,
Barremian-Aptian calcareous plankton bios-
tratigraphy from the Gorgo Cerbara section
(Marche, central Italy) and implications for
plankton evolution, Cretaceous Res., 13,
517-537, 1992.
Coplen, T. B., Reporting of stable hydrogen,
carbon, and oxygen isotopic abundances,
Pure Appl. Chem., 66, 273-276, 1994.
Corfield, R. M., Paleocene oceans and climate:
An isotopic perspective, Earth Sci. Rev., 3 7,
225-252, 1994.
Corfield, R. M., and J. E. Cartlidge, Whole-
rock oxygen and carbon isotope stratigraphy
of the Paleogene and Cretaceous/Tertiary
boundary in ODP Hole 807C, Proc. Ocean
Drill. Program Sct. Results, 130, 259-268,
1993.
Corfield, R. M., J. E. Cartlidge, I. Premoli-
Silva, and R. A. Housley, Oxygen and car-
bon isotope stratigraphy of the Palaeogene
and Cretaceous limestones in the
Bottaccione Gorge and the Contessa
Highway sections, Umbria, Italy, Terra
Nova, 3, 414-422, 1991.
Cotilion, P., and M. Rio,' Cyclic sedimentation
in the Cretaceous of DSDP Sites 535 and
540 (Gulf of Mexico), 534 (central Atlantic)
and the Vocontian Basin (France), Initial
Rep. Deep Sea Drill. Pro,/., 77, 339-376,
1984.
Craig, H., The geochemistry of the stable car-
bon isotopes, Geochim. Cosmochim. Acta, 3,
53-92, 1953.
Cresta, S., S. Monechi, and G. Parisi,
Stratigrafia del Mesozoico e Cenozoico nell'
area Umbro-Marchigiana (Mesozoic-
Cenozoic Stratigraphy in the Umbria-
Marche Area), Mem. Desc. Della Carta
Geol. d'Italia, vol. 39, pp. 1-185, Ist.
Poligrafico e Zecca dello Stato, Rome,
1989.
Dean, W. E., M. A. Arthur, and G. E. Claypool,
Depletion of •3C in Cretaceous marine or-
ganic matter: Source, diagenetic, or environ-
mental signal? Mar. Geol., 70, 119-157,
1986.
Dupasquier, C., B. Ligouis, and M. Caron, The
organic matter of "mid Cretaceous" deposits
of the Median Prealps, in Cretaceous of
Western Tethys, 3rd International
Cretaceous Symposium, edited by J.
Weidmann, pp. 607-635,
Schweizerbart'sche, Stuttgart, Germany,
1989.
Emrich, K., E. H. Ehalt, and J. C. Vogel,
Carbon isotope fractionation during the pre-
cipitation of calcium carbonate, Earth
Planet. Sci. Lett., 8, 363-371, 1970.
Erba, E., Aptian-Albian calcareous nannofossil
biostratigraphy of the Scisti a Fucoidi cored
at Piobbico (central Italy), Riv. Ital.
Paleontol. Strat., 94, 249-284, 1988.
Erba, E., Nannofossils and superplumes: The
early Aptian "nannoconid crisis",
Paleoceanography, 9, 483-501, 1994.
Erba, E., The Aptian stage, Bull. Inst. R. Sct.
Nat. Belg., Sci. Terre, 66, 31-43, 1996.
Erba, E., R. Coccioni, and I. Premoli Silva, The
"Scisti a Fucoidi" in the Umbria-Marche
area: The Apecchiese road section, in
Strattgrafia del Mesozoico e Cenozotco nel-
l'area Umbro-Marchtgiana (Mesozotc-
Cenozoic Stratigraphy in the Umbria-
Marche area), Mem. Desc. Della Carta
Geol. d'Itaha, vol. 39, edited by S. Cresta et
al., 99. 146-164, Ist. Poligrafico e Zecca
dello Stato, Rome, 1989.
Erbacher, J., Entwicklung und
Palaozeanographie m it telkretazischer
Radiolarien der westlichen Tethys (Italien)
und des Nordatlantiks, Tiibinger
MikropaMontol. Mitt., 12, pp. 88, 19•94.
Erbacher, J., and J. Thurow, Influence of
oceanic anoxic events on the evolution of
mid-Cretaceous radiolaria in the North
Atlantic and western Tethys, Mar.
Micropaleontol. , 30, 139-158, 1997.
Erbacher, J., J. Thurow, and R. Littke,
Evolution patterns of radiolaria and organic
matter variations: A new approach to iden-
tify sea-level changes in mid-Cretaceous
pelagic environments, Geology, 24, 499-
502, 1996.
Ferreri, V., H. Weissert, B. D' Argenio, and F.
P. Buonocunto, Carbon-isotope stratigra-
phy.' A tool for basin to carbonate platform
correlation, Terra Nova, 9, 57-61, 1997.
FOllmi, K. B., 160 m.y. record of marine sedi-
mentary phosphorous burial' Coupling of
climate and continental weathering under
greenhouse and icehouse conditions,
Geology, 23, 859-862, 1995.
FOllmi, K. B., H. Weisseft, M. Bisping, and H.
P. Funk, Phosphogenesis, carbon-isotope
stratigraphy and carbonate-platform evolu-
tion along the Lower Cretaceous northern
Tethyan margin, Geol. Soc. Am. Bull., 106,
729-746, 1994.
Fouke, B. W., and W. Schlager, Mid-
Cretaceous Carbon-isotope stratigraphy: A
facies-breaking record of global environ-
mental change in Russia, Ukraine, and Italy,
paper presented at the Research Conference:
Carbonates and Global change' An
Interdisciplinary Approach, Soc. for
Sediment. Geol./ Int. Assoc. Sediment.,
Wildhaus, Switzerland, June 22-27, 1996.
Gerard, J.-C., and V. Dols, The warm
Cretaceous climate: Role of the long-term
carbon cycle, Geophys. Res. Lett., 17, 1561-
1564, 1990.
GrOtsch, J., I. M. Billing, and E. J. Oswald,
Carbon iso tope records in Lower Cretaceous
shallow water carbonates: Stratigraphic and
palaeoceanographic implications, paper pre-
sented at the Research Conference:
Carbonates and Global change: An
Interdisciplinary Approach, Soc. for
Sediment. Geol./ Int. Assoc. Sediment.,
Wildhaus, Switzerland, June 22-27, 1996.
Hable, R., Biostratigraphie, Sedimentologie und
palaozeanographische Entwicklung der
Pr•alpes M•dianes des Chablais (Haute
Savoie) im Zeitabschnitt vom Apt bis Unter-
Eozan, Ph.D. dissertation, Univ. de
Fribourg, Fribourg, Switzerland, 1997.
Hadji, S. Stratigraphie isotopique des carbon-
ates pelagiques (Jurassique superieur-
Cretace in ferieur) du Bassin d' Ombrie-
Marches (Italie), Ph.D. dissertation, Univ.
Pierre et Marie Curie, Paris, France. 1991.
Hasegawa, T., Cenomanian-Turonian carbon
isotope events recorded in terrestrial organic
matter from northern Japan, Palaeogeogr.
Palaeoclimatol. Palaeoecol. , 130, 251-273,
1997.
Hauck, J., Palaomagnetische Untersuchungen
an ausgewahlten Profilen der Kreide in der
Rhenodanubischen Flysch-Zone, Ph.D. dis-
sertation, Univ. Ludwig-Maximilians,
Munich, Germany, 1997.
Hay, W. W., Cretaceous paleoceanography,
Geol. Carpathica, 46, 257-266, 1995.
Hay, W. W., and C. N. Wold, The effect of
changes of the mean salinity on ocean circu-
lation, Miner. Slovaca, 29, 243-244, 1997.
Hayes, J. M., B. N. Popp, R. Takigiku, and M.
W. Johnson, An isotopic study of biogeo-
chemical relationships between carbonates
and organic carbon in the Greenhorn
Formation, Geochim. Cosmochim. Acta, 53,
2961-2972, 1989.
Herbert, T. D., Paleomagnetic calibration of
Milankovitch cyclicity in Lower Cretaceous
sediments, Earth Planet. Sci. Lett., 112, 15-
28, 1992.
Herbert, To D., and J. L. Sarmiento, Ocean nu-
trient distribution and oxygenation: Limits
on the formation of warm saline bottom wa-
ter over the past 91 m.y., Geology, 19, 702-
705, 1991.
Herman, A. B., and, R. A. Spicer,
Palaeobotanical evidence for a warm
Cretaceous Arctic Ocean, Nature, 380, 330-
333, 1996.
Holser, W. T., M. Magaritz, and Jo Wright,
Chemical and isotopic variations in the
world ocean during Phanerozoic time, in
Global Bio-events, edited by O. Walliser,
pp. 63-74, Springer, New York, 1986o
Huber, B. T., D. A. Hodell, and C. P. Hamilton,
Middle-Late Cretaceous climate of the
southern high latitudes: Stable isotopic evi-
dence for minimal equator-to-pole thermal
gradients, Bull., Geol. Soc. Am., 107, 1164-
1191, 1995.
Hudson, J. D., Stable isotopes and limestone
lithification, d. Geol. Soc. London, 133, 637-
660, 1977.
Irwin, H., C. Curtis, and M. Coleman, Isotopic
evidence for source of diagenetic carbonates
formed during burial of organic-rich sedi-
ments, Nature, 269, 209-213, 1977.
Jacobs, E., H. Weissert, G. Shields, and P.
Stille, The Monterey event in the

544 MENEGATTI ET AL.: THE •13C STRATIGRAPHY IN THE "LIVELLO SELLI"
Mediterranean: A record from shelf sedi-
ments of Malta, Paleoceanography, 11,
717-728, 1996.
Jenkyns, H. C., Origin of red nodular
limestones (Ammonitico Rosso,
Knollenkalke) in the Mediterranean
Jurassic: A diagenetic model, in Pelagic
Sediments on Land and Under the Sea,
Spec. Publ. Int. Assoc. Sedimentol., vol. 1,
edited by K .J. Hsti and H. C. Jenkyns, pp.
49-271, Blackwell, Cambridge, Mass.,
1974.
Jenkyns, H. C., Cretaceous anoxic events: From
continents to oceans, d. Geol. Soc. London,
137, 171-188, 1980.
Jenkyns, H. C., Carbon-isotope stratigraphy and
paleoceanographic significance of the
Lower Cretaceous shallow-water carbonates
of resolution Guyot, Mid-Pacific mountains,
Proc. Ocean Drill. Program Sci. Results,
143, 99-104, 1995.
Jenkyns, Ho C., Relative sea-level change and
carbon isotopes: Data from the Upper
Jurassic (Oxfordtan) bf central and Southem
Europe, Terra Nova, 8, 75-85, 1996.
Jenkyns, H. C., and C. J. Clayton, Black shales
and carbon isotopes in pelagic sediments
from the Tethyan Lower Jurassic,
Sedimentology, 33, 87-106, 1986.
Jenkyns, H. C., A. S. Gale, and R. M. Corfield,
Carbon and oxygen-isotope stratigraphy of
the English Chalk and Italian Scaglia and its
palaeoclimatic significance, Geol. Mag.,
131, 1-34, 1994.
Karhu, J. A., and H. D. Holland, Carbon iso-
topes and the rise of atmospheric oxygen,
Geology, 24, 867-870, 1996.
Kempe, S., and J. Kazmierczak, The role of al-
kalinity in the evolution of ocean chemistry,
organization of living systems, and biocalci-
fication processes, Bull. Inst. Oc•anogr., 13,
61-117, 1994.
Kump, L. R., Interpreting carbon isotope excur-
sions: Strangelove oceans, Geology, 19,
299-302, 1991.
Lambert, E., and P. De Wever, •v•nements bi-
ologiques chez les radiolaires au cours des
phases k•noxiques du Cr•tac•, Rev.
Micropaleontol., 39,283-292, 1996.
Larson, R. L., Latest pulse of Earth: Evidence
for a mid-Cretaceous superplume, Geology,
19, 547-550, 1991a.
Larson, R. L., Geological consequences of su-
perplumes, Geology, 19, 963-966, 1991 b.
Leckie, R.M., A paleoceanographic model for
the early evolutionary history of planktonic
foraminifera, Palaeogeogr. Palaeoclimatol.
Palaeoecol., 73, 107-138, 1989
L•tolle, R., C. Vergnaud-Grazzini, and C.
Pierre, Oxygen and carbon isotopes from
bulk carbonates and foraminiferal shells at
DSDP Sites 400 and 406, Initial Rep. Deep
Sea Drill. Proj., 48, 741-755, 1979.
Lint, A., Early Cretaceous carbon isotope
stratigraphy of the Maiolica Formation,
Southern Alps (northern Italy and southern
Switzerland): Stratigraphic and paleoenvi-
tonmental significance, Ph.D. disserta tion,
259 pp, Eidg. Techn. Hochsch., Ziirich,
Switzerland, 1994.
Lint, A., H. Weisseft, and E. Erba, The
Valanginian carbon isotope event: A first
episode of greenhouse climate conditions
during the Cretaceous, Terra Nova, 4, 374-
384, 1992.
Lintnerovh, O., J. Michailik, D. Rehakovh, M.
Peterchkovh, E. Halasovh, and J. Hladikovh,
Sedimentary and isotopic record of the
Apttan anoxic "Selli" event in the Pieniny
Klippen Belt, Slovakia, Miner. Slovaca, 29,
315-316, 1997.
Mackenzie, F. T., Sedimentary cycling and the
evolution of seawater, in Chem ical
Oceanography, vol. 1, 2nd ed., edited by J.
P. Riley and G. Skirrow, pp. 309-364,
Academic, San Diego, Calif., 1975.
Magaritz, M., Krishnamurthy, R. V. and W.
Holser, Parallel trends in organic and inor-
ganic carbon isotopes across the Permian-
Triassic boundary, Am. d. Sci., 292, 727-
739, 1992.
Manabe, S., and K. Bryan, CO 2-induced change
in a coupled ocean-atmosphere model and
its paleoclimatic implication, d. Geophys.
Res., 90, 11689-11707, 1985.
Marconi, M., F. C. Wezel, and A. Longinelli, A
stable isotope study of a calcareous-black
shale series from the Barremian-Aptian of
the northern Apennines, Umbro-Marchean
succession, Italy, Miner. Petrogr. Acta, 37,
211-218, 1994.
Marshall, Jo D., Stable isotope evidence for the
environment of lithification of some
Tethyan limestones, Neues dahrb. Geol.
Palaontol. Monatsh., 4, 211-224, 1981o
Matter, A., R. G. Douglas, and K. Perch-
Nielsen, Fossil preservation, geochemistry
and diagenesis of pelagic carbonates from
Shatsky Rise, northwest Pacific, Initial Rep.
Deep Sea Drill. Proj., 32, 891-921,1975.
McCrea, J. M., The isotopic chemistry of car-
bonates and a paleotemperature scale, 3;.
Chem. Phys., 18, 849-857, 1950.
McKenzie, J. A., D. Bernoulli, and R. E.
Garrison, Lithification of pelagic-
hemipelagic sediments at DSDP Site 372:
Oxygen isotope alteration with diagenesis,
Initial Rep. Deep Sea Drill. Proj., 42A, 473-
478, 1978.
Menegatti, A. P., and R. Ntiesch, Influence of
organic matter on smectite illite transforma-
tion in carbonates, paper presented at the
11th International Clay Conference, Clay
Minerals Society, Ottawa, Ont. Can., June
15-21, 1997.
Mizutani, H., and E. Wada, Effect of high
atmospheric CO 2 on/5 •3C of algae, Origin
L•fe, 12, 377-390, 1982.
Ogg, J. G, A. H. F. Robertson, and L. F. Jansa,
Jurassic sedimentation history of Site 534
(western North Atlantic) and of the Atlantic-
Tethys Seaway, Initial Rep. Deep Sea Drill.
Proj., 76, 829-884, 1983.
Opdyke, B. N., Apticore Project-Cismon Core:
A high-resolution stable isotope record
through the middle Apttan carbon isotope
excursion, a chemostratigraphic type
section, Eos Trans., AGU, 78, Fall Meet.
Suppl., F 371, 1997.
Page, C., Observations g6ologiques sur les
Pr6alpes au NW des Gastlosen orientales,
Bull. Soc. Frib. Sci. Nat., 58, 83-177, 1969.
Parrish, J. T., and R. L. Curtis, Atmospheric
circulation, upwelling and organic-rich
rocks in the Mesozoic and Cenozoic eras,
Palaeogeogr. Palaeoclimatol. Palaeoecol.,
40, 31-66, 1982.
Patton, J. W., P. W. Choquette, G. K. Guennel,
A. J. Kaltenback, and A. Moore, Organic
geochemistry and sedimentology of Lower
to mid-Cretaceous deep-sea carbonates,
Sites 535 and 540, Leg 77, Initial Rep. Deep
Sea Drill. Proj., 77, 417-443,1984.
Pedersen, T. F., and S. E. Calvert, Anoxia vs.
Productivity: What controls the formation of
or ganic-carbon-rich sediments and sedimen-
tary rocks?,AAPG Bull. 74, 454-466, 1990.
Popp, N. B., R. T akigiku, J. M. Hayes, J. W.
Louda, and E. W. Baker, The post-Paleozoic
chronology and mechanism of •3C depletion
in primary or ganic matter, Am. •. Sci., 289,
436-454, 1989.
Pratt, L. M., Isotopic studies of organic matter
and carbonate in rocks of the Greenhorn ma-
rine cycle, in Fine-Grained Deposits and
Biofacies of Cretaceous Western Interior
Seaway: Evidence of Cyclic Sedimentary
Processes, edited by L. M. Pratt et al., Soc.
Econ. Paleontol. Mineral., Tulsa, Field Trip
Guidebook, 4, 38-48, 1985.
Pratt, Lo M., and J. D. King, Variable marine
productiv ity and high eolian input recorded
by rhythmic black shales in mid-Cretaceous
pelagic deposits from central Italy,
Paleoceanography, 1,507-522, 1986.
Premoli-Silva, I., E. Erba, and M. E. Tomaghi,
Paleoenvironmental signals and changes in
surface fertility in mid Cretaceous Corg-rich
facies of the Fucoid Marls (central Italy),
G•obios M•m. , 11,225-236, 1989.
Python-Dupasquier, C., La Formation de l'
Intyarnon ("Cr•tac• Moyen") des Pr•alpes
M•dianes Romandes, Ph.D. dissertation,
197 pp., Univ. de Fribourg, Fribourg,
Switzerland, 1990.
Ratswell, R., and R. A. Berner, Organic carbon
losses during burial and thermal maturation
of normal marine shales, Geology, 15, 853-
856, 198T
Rau, G. H., T. Takahashi, and D. J. Des Marais,
Latitudinal variations in plankton
Implications for CO 2 and productivity in
past oceans, Nature, 341, 516-518, 1989.
Renard, M., Pelagic carbonate stratigraphy (Sr,
Mg, 180, •3C) ' Mar. Micropaleontol., 1 O,
117-164, 1986.
Rind, D., and M. Chandler, Increased ocean
heat transport and warmer climate,
Geophys. Res., 96, 7437-7461, 1991.
Sarmiento, J. L., T. Herbert, and J. R.
Toggweiler, Causes of anoxia in the world
ocean, Global Biogeochem. Cycles, 2, 115-
128, 1988.
Savin, S., The history of the Earth's surface
temperature during the past 100 million
years, Annu. Rev. Earth Planet. Sci., 5, 319-
355, 1977.
Schidlowski, M., Application of stable carbon
isotopes to early biochemical evolution on
earth, Annu. Rev. Earth Planet. Sci., 15, 47-
72, 1987.
Schlanger, S. O., and H. C. Jenkyns, Cretaceous
anoxic events: Causes and consequences,
Geol. Mijnbouw, 55, 179-184, 1976.
Schlanger, S. O., M. A. Arthur, H. C. Jenkyns,
and P. A. Scholle, The Cenomanian-
Turonian oceanic anoxic event, I.,
Stratigraphy and distribution of organic car-
bon-rich beds and the marine/5 •3C excur-
sion, in Marine Petroleum Source Rocks,
Spec. Publ. Geol. Soc. London, vol. 26,

MENEGATTI ET AL.: THE 813C STRATIGRAPHY IN THE "LIVELLO SELLI" 545
edited by J Brooks and A. J. Fleet,
Blackwell, Cambridge, Mass., pp. 371-399,
1987
Schmidt, G. A., and L. A. Mysak, Can
increased poleward oceanic heat flux
explmn the warm Cretaceous climate?,
Paleoceanography, 11,579-593, 1996.
Schmitz, B., S. D. Charisi, E. I. Thompson, and
R. P. Speijer, Barium. SiO 2 (excess), and
P205 as proxies of biological productivity in
the Middle East during the Paleocene and
the latest Paleocene benthic extinction
event, Terra Nova, 9, 95-99, 1997.
Scholle, P., and M. A. Arthur, Carbon isotopic
fluctuations in pelagic limestones: Potential
stratigraphic and petroleum exploration tool,
AAPG Bull., 64, 67-87, 1980.
Shackleton, N.J., The carbon isotope record of
the Cenozoic: History of organic carbon
burial and of oxygen in the ocean and atmo-
sphere, •n Martne Petroleum Source Rocks,
Geol. Soc. Spec. Publ. London, vol. 26, pp.
423-434, edited by J. Brooks and A. Fleet,
Blackwell, Cambridge, Mass., 1987.
Shackleton, N.J., and M. A. Hall, Carbon iso-
tope data from Leg 74 sediments, Initial
Rep. Deep Sea Drill. Proj., 74, 613-619,
1984.
Shackleton, N.J., M. A. Hall, and U. Bleil,
Carbon isotope stratigraphy Site 577, in: R.
G. Heath, L. H. Buckle, et al., Intttal Rep.
Deep Sea Drtll. Proj., 86, 503-512, 1985.
Sliter, W. A., Aptian anoxia in the Pacific
Basin, Geology, 17, 909-910, 1989.
Stampill, G. M., Le Brianqonnais, terrain exo-
tique dans les Alpes?, Eclogae Geol. Helv.,
86, 1-45, 1993.
Stampfii, G. M., and M. Martbaler, Divergent
and convergent margins in the northwestern
alps confrontation to actualistic models,
Geodln. Acta, 4, 159-184, 1990.
Tarduno, J. A., W. V. Sliter, L. Kroenke, M.
Leckie, H. Mayer, J. J. Mahoney, R.
Musgrave, M. Storey, and E. L. Winterer,
Rapid formation of Ontorig-Java Plateau by
Aptian mantle plume volcanism, Science,
254, 399-403, 1991.
Thierstein, H. R., Paleoceanographic implica-
tions of organic carbon and carbonate distri-
butions in Mesozoic deep-sea sediments, in
Deep Drilling i;: the Atlanttc Ocean.'
Continental Margtns and
Paleoenvlronment, Maurice Ewing Ser., vol.
3, edited by M. Talwani, W. Hay and W. B.
F. Ryan, pp. 249-274, AGU, Washington D.
C., 1979.
Tyson, R. V., Sedtmentary Organtc Matter:
Organtc Factes and Palynofactes, 615 pp.,
Chapman and Hall, New York, 1995.
Tyson, R. V., and B. M. Funnell, European
Cretaceous shorelines, stage by stage,
Palaeogeogr. Palaeochmatol. Palaeoecol.,
59, 69-91, 1987.
Vahrenkamp, V. C., Carbon isotope
stratigraphy of the Upper Kharaib and
Shuaiba formations: Implications for the
Early Cretaceous evolution of the Arabian
Gulf region, AAPG Bull., 80, 647-662,
1996.
Weissert, H., C-isotope stratigraphy, a monitor
of paleoenvironmental change: A case study
from the Early Cretaceous, Surv. Geophys.,
10, 1-61, 1989.
Weissert, H., Siliciclastics in the Early
Cretaceous Tethys and North Atlantic
Oceans: Documents of periodic Greenhouse
climate conditions, Mem. Soc. Geol. ltal.,
44, 59-69, 1990.
Weissert, H., and D. Bernoulli, A transform
margin in the Mesozoic Tethys: Evidence
from the Swiss Alps, Geol. Rundschau, 74,
665-679, 1985.
Weissert, H., and J. Breheret, A carbonate car-
bon-isotope record from Aptian-Albian
sediments of the Vocontian Trough, Bull.
Soc. Gdol. France, 162, 1133-1140, 1991.
Weissert, H., and A. Lini, Ice Age interludes
during the time of Cretaceous greenhouse
climate?, in Controversies in Modern
Geology, edited by D. W. Mailer et al., pp.
173-191, Academic, San Diego, Calif.,
1991.
Weissert, H., and H. Mohr, Late Jurassic cli-
mate and its impact on carbon cycling,
Palaeogeogr. Palaeoclimatol. Palaeoecol.,
122, 27-43, 1996.
Weissert, H., J. A. McKenzie, and P. Hochuli,
Cyclic anoxic events in the Early
Cretaceous Tethys Ocean, Geology, 7, 147-
151, 1979.
Weissert, H., J. A. Mc Kenzie, and J. E. T.
Channell, Natural variations in the carbon
cycle during the Early Cretaceous, in The
Carbon Cycle and Atmospheric C02:
Natural Variations Arcbean to Present,
Geophys. Monogr. Ser., vol. 32, edited by E.
T. Sundquist and W. E. Broecker, pp. 531-
545, AGU, Washington, D.C., 1985.
Weissert, H., A. Lini, K. B. FOllmi, and O.
Kuhn, Correlation of Early Cretaceous car-
bon isotope stratigraphy and platform
drowning events: A possible link?,
Palaeogeogr. Palaeoclimatol. Palaeoecol.,
137, 189-203, 1998.
Wezel, F. C., Facies anossiche ed episodi
geotettonici globali, G. Geol., Ser. 3a., 47,
281-286, 1985.
R. S. Brown, P. Farfimond, and R. V. Tyson,
Newcastle Research Group, University of
Newcastle-upon-Tyne, The Drummond
Building, NE1 7RU, Newcastle, England,
United Kingdom. (e-mail: R. V.
Tyson(•newcastle. ac.uk;
paul.farrimond•ncl.ac.uk)
M. Caron and A. Strasser, Institut de
G6ologie, Universit6 de Fribourg, P6rolles, 1700
Fribourg, Switzerland. (e-mail:
andreas.strasser@unifr.ch;
michele.caron•unifr.ch)
A. P. Menegatti and H. Weissert,
Geologisches Institut, Eidgen•ssische
Technische Hochschule Ztirich, Sonneggstr. 5,
8092 Ztirich, Switzerland (e-mail:
alessio•clay.igt.baum.ethz.ch;
helmi@erdw.ethz.ch)
(Received December 10, 1997;
revised May 14, 1998;
accepted May 19, 1998.)