GeolCarp_Vol50_No1_91

GEOLOGICA CARPATHICA, 50, 1, BRATISLAVA, FEBRUARY 1999

91–96

C-ISOTOPE STRATIGRAPHY, A CALIBRATION TOOL BETWEEN

AMMONITE- AND MAGNETOSTRATIGRAPHY:

THE VALANGINIAN-HAUTERIVIAN TRANSITION

SUSANNE HENNIG

, HELMUT WEISSERT

and LUC BULOT

Geological Institute, ETH Zürich, CH-8092 Zürich, Switzerland; *helmi@erdw.ethz.ch

Centre de Sédimentologie et Paléontologie, Université de Provence, Centre Saint-Charles,

Place Victor Hugo, F-13331 Marseille Cedex 03, France

(Manuscript received February 25, 1998; accepted in revised form September 1, 1998)

Abstract:

Detailed carbon isotope stratigraphy was calibrated with standard ammonite stratigraphy for two Valanginian

to Lower Hauterivian sections in Southern France, La Charce in the Vocontian Basin and Pont de Carajuan on the
Provence platform margin. The excellent correspondence of ammonite zonation and carbon isotope composition between
the two sections allowed us to create a composite C-isotope curve. The Valanginian carbon isotope excursion starts
with a positive

C-shift of ca. +1.3 ‰ in the upper Campylotoxus Zone.

C-values culminate in the Verrucosum

Zone and decrease from the upper Verrucosum Zone to the Hauterivian Loryi Zone where they reach pre-excursion
values again. Correlation of the Valanginian to Lower Hauterivian standard ammonite zonation of Southern France
(N. Tethys) with other bio- and chronostratigraphies, such as the South Alpine nannofossil- and magnetostratigraphy
(S. Tethys) is significantly improved by the link via carbon isotope stratigraphy.

Key words:

Lower Cretaceous, Tethys, Southern France, Valanginian-Hauterivian transition, carbon isotope excursion,

ammonite stratigraphy.

Valanginian-Early Hauterivian ammonite stratigraphy and
magnetostratigraphy.

The studied sections

Two sections, La Charce and Pont de Carajuan, both located

in Southern France (Drôme and Alpes de Haute Provence)
have been used for this C-isotope study (Fig. 1). The
ammonite-rich section La Charce in the basinal part of the
Vocontian domain is described in Bulot et al. (1992). It is now
used as the stratotype for the Upper Valanginian to Lower
Hauterivian ammonite zonation (Mutterlose et al. 1996). Its
lithology consists of hemipelagic, fossiliferous, cyclic marl-
limestone alternations (Fig. 2). The Lower Valanginian and the
Lower Hauterivian parts of the section are more calcareous
than the Upper Valanginian interval, where marls
predominate. The section used for C-isotope stratigraphy
covers the Late Valanginian and Early Hauterivian
(Verrucosum Zone–Loryi Zone, Fig. 2).

The section Pont de Carajuan has been studied previously by

various authors (Ferry & Rubino 1989; Walter 1991; Arnaud &
Bulot 1992). It is located within the “réserve géologique de
Haute Provence”, in the Verdon Valley near Castellane. The
section is paleogeographically situated at the transition of the
Provence platform to the Vocontian domain. The sequence
consists of fossiliferous shallow water limestones and marls.
The studied section starts in the upper Campylotoxus Zone
with the “Karakaschiceras Beds”, ammonite and bivalve-
bearing marly limestones. These limestones are overlain by a
thick, marly sequence, the “Marnes à Toxaster”, containing

Introduction

Over the last decades C-isotope stratigraphy has been
established as a powerful tool in stratigraphy (e.g. Scholle &
Arthur 1980; Renard 1986; Weissert & Lini 1991; Weissert et
al. 1998). If combined with biostratigraphy and magneto-
stratigraphy it can contribute to a higher resolution of the
sedimentary record and it may serve as a correlation tool in
basin-shelf studies. In addition, the use of C-isotope
stratigraphy may help to solve correlation problems between
biostratigraphy and magnetostratigraphy and it may also
provide a link between biostratigraphies considered as
uncorrelatable. In this study we establish a link between the
Valanginian-Hauterivian C-isotope stratigraphy of the
southern Tethyan margin (Lini et al. 1992; Lini 1994) and the
hypostratotype ammonite stratigraphy recently revised for the
Valanginian northern Tethyan margin (Busnardo & Thieuloy
1979; Bulot et al. 1992; Bulot et al. 1996). We analysed bulk
samples from the hemipelagic section La Charce (Vocontian
Trough, S. France) which was chosen as the boundary
stratotype for the Valanginian-Hauterivian boundary
(Thieuloy 1977; Bulot et al. 1992; Mutterlose et al. 1996). In
order to test the correlation potential of C-isotope
stratigraphy, we also measured bulk carbonate samples from
the outer platform sequence Pont de Carajuan, located in the
Provence region (S. France), (Ferry & Rubino 1989; Walter
1991; Arnaud & Bulot 1992). We compared this new C-
isotope stratigraphy with the magnetostratigraphically calibr-
ated C-isotope curve for the Valanginian-Hauterivian (Lini et
al. 1992; Channell et al. 1993). The comparison allows us to
propose a new, isotopically calibrated correlation between

92 HENNIG, WEISSERT and BULOT

mainly Toxaster, bivalves, brachiopods and some ammonites,
and getting marlier and more fossiliferous towards the top. The
“Petite Lumachelle” represents a calcarenitic interruption
within these marls. The “Grande Lumachelle” lies on top of the
“Marnes à Toxaster” and consists of bioclastic Alectryonia-
limestones alternating with marls containing Alectryonia,
bivalves, serpulids, brachiopods, bryozoans and crinoids. The
“Grande Lumachelle” represents the peak of a shallowing
upward trend and is dated to the Verrucosum Zone (Arnaud &
Bulot 1992). After an outcrop gap, calcareous marls with
limestone beds and thin-bedded white nodular limestones with
numerous, large ammonites mark the transition to the
Hauterivian. Blue marls with few fossils form the top of the
studied Pont de Carajuan section. The detailed ammonite
stratigraphy for the Pont de Carajuan section is published in
Arnaud & Bulot (1992).

Methods

On the basis of positive experience with other pelagic,

hemipelagic and shallow water sediments of Early Cretaceous
age (Lini 1994; Jenkyns 1995; Ferreri et al. 1997), bulk sam-
ples were used for this C-isotope study. The samples from the

section La Charce were drilled at the University of Grenoble
from the ammonite bearing rocks collected for ammonite
stratigraphy at the recommended boundary stratotype (Bulot et
al. 1992; Bulot & Thieuloy 1993). The samples from the sec-
tion Pont de Carajuan were prepared at ETH Zürich.

The powdered samples were reacted with 100 % H

C, or 50

C. The carbon and oxygen isotope composition

of the gas liberated was analysed at ETH Zürich with a VG
Isocarb device coupled with a Prism inlet mass spectrometer,
or with a VG 903 mass spectrometer. The isotope data are ex-
pressed in per mill (‰) deviation relative to the Cretaceous
Pee Dee Belemnite (PDB) standard (McCrea 1950; Craig
1957). The working standard used in the Zürich laboratory is
MS2 (Carrara Marble,

C = 2.10 ‰;

O = –1.82 ‰). The

reproducibility of replicate analyses was ±0.1 ‰ for both car-
bon and oxygen isotope ratios.

The carbonate content was analysed on some of the same

samples of the Pont de Carajuan section. The analysis were
effected on a Coulometer 5011 (Laborlux S. A.) at EAWAG,
Dübendorf. The standard for calibration was pure Na

reproduction error was ±1 % CaCO

Data

The oxygen isotope data were used as indicators of diage-

netic overprint. At la Charce, the

O-values fluctuate

around –1 ± 0.2 ‰ throughout the section. The values indicate
that burial diagenetic overprint is minor and that potential
alteration by meteoric waters may be neglected. The

C-

values range between +1.0 ‰ and +2.6 ‰ (Fig. 2). The

C-

curve starts with values of about +2.0 ‰. More positive values
of up to +2.6 ‰ were measured at 25 m, in the lower part of
the ammonite horizon V3. Within the upper part of ammonite
horizon V3, and part of ammonite horizon T1,

C-values

decrease by 1 ‰ to +1.6 ‰. The curve fluctuates around
+1.7 ‰ for the rest of the Trinodosum-Zone, then it decreases
to lower values varying between 1.1 ‰ and 1.6 ‰ in the
Callidiscus and Radiatus- zones. A small positive shift marks
the transition from the Radiatus to the Loryi- zones. In the
uppermost part of the section the measured

C-values

decrease to ca. +1.0 ‰.

The outer platform section Pont de Carajuan is marked by

less stable

O-values varying between –4 ‰ and –1.2 ‰.

Carbonate concretions with pyrite have a maximal deviation
of –0.4 ‰ in

C corresponding to a shift of –1 ‰ in

All data of the section together, however, show no covariance
of

C-values with

O-values. Nor is there any correlation

of the carbonate content ranging from 60 % to 95 % with

O. The negative shift of

O to non-marine values is

most probably due to meteoric diagenesis and had little or no
effect on the

C-values (see also James & Choquette 1990).

Therefore, the established

C-curves with values ranging

from +1 ‰ to +3 ‰ probably preserve an original paleoceano-
graphic pattern (Fig. 2). This observation is in agreement with
earlier studies made in neritic carbonate sequences (e.g. Jen-
kyns 1995).

The measured curve starts with values of +1.4 ‰ interrupt-

ed by a small but remarkable negative excursion to +1.1 ‰

Fig. 1.

Geographical and paleogeographical situation of the

sections. Paleogeography after Dercourt et. al. (1986).

Transform fault

Flysch

Conglomerate

Sandstone

Clay, shale

Pelagic limestone

Emerged land

Shallow water–intermediate–deep sea

Volcanism

Fault

Oceanic subduction

Thrust
Active spreading ridge

J Jura
H Helvetics
VL Valais

B Briançonnais
LAa Lower Austroalpine

MAa Middle Austroalpine

UAa Upper Austroalpine
L Lombard

TR Tridentin

1: La Charce,

2: Pont de Carajuan

3: Capriolo

Platform limestone

Radiolarite

C-ISOTOPE STRATIGRAPHY, A CALIBRATION TOOL BETWEEN AMMONITE - AND MAGNETOSTRATIGRAPHY 93

Fig. 2.

Correlation of carbon isotope stratigraphy with ammonite biozonation in the Pont de Carajuan and La Charce sections. Carajuan am-

monite zonation amended after Arnaud & Bulot (1992). La Charce ammonite zonation from Bulot et al. (1992). Lower shaded area: p ositive
carbon isotope shift of +1.3 ‰ in the Pont de Carajuan section. Upper shaded area: rapid decrease of carbon isotope values by c a. 1 ‰ in the
Pont de Carajuan and La Charce sections.

within ammonite horizon Ct3 (Fig. 2). Within Ct4 the

C-

values steadily increase by +1.3 ‰ and they reach a first peak
at the top of the Campylotoxus Zone (+2.4 ‰). The C-isotope
curve is marked by a second peak (+2.5 ‰) in the ammonite
horizon V1, and a third, most positive peak (+2.6 ‰) in the
lower part of V3. The rapid decrease of

C-values within V3

to +1.6 ‰ is interrupted by an outcrop gap between 65 m and
69 m. In the uppermost, Lower Hauterivian part of the section
the

C-values vary between +1 ‰ and +1.5 ‰, with a small

positive peak at the boundary of the Radiatus to the Loryi-Zone.

Discussion

Both the Pont de Carajuan and the La Charce sections are ac-

curately dated with ammonites (Arnaud & Bulot 1992; Bulot et
al. 1992). The C-isotope curve established at the two localities
La Charce and Pont de Carajuan shows a remarkable pattern
which can be described as follows (Fig. 3):

(1) A minor negative

C-event within the campylotoxus

ammonite horizon (Ct3) marks the base of the Valanginian C-
isotope excursion. The positive shift of +1.3 ‰ to the first

94 HENNIG, WEISSERT and BULOT

Fig. 3.

Correlation of the Southern Tethyan margin (Lombardian Basin) carbon isotope stratigraphy (Lini 1994) with the Northern

Tethyan margin (Provence) carbon isotope stratigraphy. Lower shaded area: positive carbon isotope shift of +1.3 ‰ in the Capriolo and
Pont de Carajuan sections. Upper shaded area: rapid decrease of carbon isotope values by ca. 1 ‰ in the Capriolo, Pont de Carajuan and
La Charce sections.

maximum in the

C-record falls within the upper part of the

Campylotoxus Zone. The first maximum is measured in the
upper part of the Inostranzewi Subzone (Ct4).

(2) An interval of very positive

C-values of up to +2.6 ‰

extends from the uppermost Campylotoxus to the lower to
middle Verrucosum zones. The second positive peak (+2.5 ‰)
occurs within the verrucosum horizon (V1) and the highest
peak is measured at the base of the peregrinus horizon (V3).

(3)The

C-values decrease rapidly by 1 ‰ within the up-

per Verrucosum and lower Trinodosum zones. Then, they de-
crease irregularly and finally reach pre-excursion values in the
Loryi Zone.

(4) A minor positive peak is measured at the boundary be-

tween the Radiatus and the Loryi zones.

The Pont de Carajuan section apparently contains the entire

Valanginian-Hauterivian C-isotope event, while the La
Charce section covers only the upper part of it. In the
overlapping part, however, the

C-stratigraphy of the two

sections coincides precisely with the ammonite zonation.
This C-isotope curve can therefore be regarded as an ammo-
nite-calibrated standard for stratigraphic correlations.

In a further step we correlate the La Charce-Pont de Cara-

juan curve with the southern Alpine

C-record (Fig. 3) (Lini

et al. 1992; Channell et al. 1993; Lini 1994). In the Southern
Alps, (e.g. Capriolo section, Lombardian Basin) the Valangin-
ian

C-excursion was dated with calcareous nannoplankton

and with magnetostratigraphy. The excursion falls within the
C. oblongata and the C. bollii nannofossil zones. Paleomag-

netic data document a beginning of the

C-event within

magnetozone CM12. Peak values are reached in CM11. Be-
tween CM10N and CM8 the

C-curve returns to pre-excur-

sion conditions.

C-isotope stratigraphy allows us to link the new Valangin-

ian-Hauterivian ammonite stratigraphy with magnetostratigra-
phy and with southern Alpine nannofossil zonation. Our data
indicate that:

(1) The beginning of the

C-excursion occurs within the

campylotoxus

horizon Ct3 of the Campylotoxus Zone.

Therefore, the ammonite horizon Ct3 falls within magneto-
zone CM12.

(2) The Inostranzewi Subzone (Ct4) containing the positive

shift can be correlated with the upper CM12 and lowermost
CM11.

(3) Peak values of the verrucosum (V1) and pronecostatum

(V2) horizons entirely lie within CM11.

(4) The decreasing

C-values marking the end of the Val-

anginian

C-excursion allow us to place the uppermost Ver-

rucosum zone horizon peregrinus (V3) into magnetozone
CM10N. The Trinodosum, Callidiscus, Radiatus and the
basal part of the Loryi zones coincide with magnetozones
CM10N–CM9.

The correlation of the Southern French composite

C-

stratigraphy with the reference

C-stratigraphy in the

Southern Alps offers the opportunity to link ammonite stratig-
raphy with magnetostratigraphy. The new correlation differs
by about one magnetozone from earlier published correlations.

C-ISOTOPE STRATIGRAPHY, A CALIBRATION TOOL BETWEEN AMMONITE - AND MAGNETOSTRATIGRAPHY 95

Channell et al. (1995) placed the top of the Campylotoxus
Zone into CM12A. With our new correlation we place the
boundary between Campylotoxus and Verrucosum Zone into
CM11. Channell et al. (1995) correlated the Verrucosum Zone
into CM12A–CM11A. Our data document that the Verruco-
sum Zone falls within CM11, and possibly the lower part of
CM10N. Channell et al. (1995) and Mutterlose et al. (1996)
place the Radiatus Zone into CM11–CM10N. In our correla-
tions we can place the Radiatus Zone into CM10 to CM9. The
base of the Radiatus Zone is proposed as the stage boundary
between the Valanginian and the Hauterivian (Busnardo &
Thieuloy 1979; Bulot & Thieuloy 1993; Mutterlose et al.
1996). According to our correlation, this boundary falls into
the normally magnetized zone of CM10, while Channell et al.
(1995) and Mutterlose et al. (1996) placed it into CM11. The
lower Loryi Zone is shifted from a CM10N position (Channell
et al. 1995; Mutterlose et al. 1996) into CM9.

Conclusions

We established a

C-stratigraphy for the Late Valanginian

to Early Hauterivian in a hemipelagic (La Charce) and in an
outer carbonate platform section (Pont de Carajuan) in South-
ern France. Both sections are accurately dated with ammonite
stratigraphy and the section La Charce has been proposed as
the boundary stratotype for the Valanginian-Hauterivian tran-
sition (Mutterlose et al. 1996). The C-isotope record seems to
preserve an original paleoceanographic isotope signal. This al-
lows us to use the

C-curves as a stratigraphic tool to estab-

lish a composite Southern French curve covering a time span
between the Campylotoxus Zone (Valanginian) and the Loryi
Zone (Hauterivian).

Based on our study of the Valanginian-Hauterivian

transition we conclude that C-isotope stratigraphy will provide
extremely useful information for stratigraphy which will result
in a significant improvement of the stratigraphic timescale.

Acknowledgements:

This project was supported by the

Swiss Science Foundation. We thank Dr. Stefano Bernasconi
for his support in the Isotope Laboratory of ETH Zurich, and
Hanspeter Funk for his constructive comments on an earlier
version of the manuscript.

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