GeolCarp_Vol69_No2_117

GEOLOGICA CARPATHICA

, APRIL 2018, 69, 2, 117–127

doi: 10.1515/geoca-2018-0007

www.geologicacarpathica.com

Carbon cycle history through the Middle Jurassic

(Aalenian – Bathonian) of the Mecsek Mountains,

Southern Hungary

GREGORY D. PRICE



, ISTVÁN FŐZY

and ANDRÁS GALÁCZ

School of Geography, Earth & Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, United Kingdom;



g.price@plymouth.ac.uk

Department of Palaeontology and Geology, Hungarian Natural History Museum, POB 137, Budapest, H-1431 Hungary; fozy.istvan@nhmus.hu

Department of Palaeontology,

Eötvös Loránd University, Pázmány P. sétány 1/C, Budapest, H-1117 Hungary; galacz@ludens.elte.hu

(Manuscript received June 9, 2017; accepted in revised form January 16, 2018)

Abstract: A carbonate carbon isotope curve from the Aalenian–Bathonian interval is presented from the Óbánya valley,

of the Mecsek Mountains, Hungary. This interval is certainly less well constrained and studied than other Jurassic time

slices. The Óbánya valley lies in the eastern part of the Mecsek Mountains, between Óbánya and Kisújbánya and provides

exposures of an Aalenian to Lower Cretaceous sequence. It is not strongly affected by tectonics, as compared to other

sections of eastern Mecsek of the same age. In parts, a rich fossil assemblage has been collected, with Bathonian

ammonites being especially valuable at this locality. The pelagic Middle Jurassic is represented by the Komló Calcareous

Marl Formation and thin-bedded limestones of the Óbánya Limestone Formation. These are overlain by Upper Jurassic

siliceous limestones and radiolarites of the Fonyászó Limestone Formation. Our new data indicate a series of carbon

isotope anomalies within the late Aalenian and early-middle Bajocian. In particular, analysis of the Komló Calcareous

Marl Formation reveals a negative carbon isotope excursion followed by positive values that occurs near the base of the

section (across the Aalenian–Bajocian boundary). The origin of this carbon-isotope anomaly is interpreted to lie in

significant changes to carbon fluxes potentially stemming from reduced run off, lowering the fertility of surface waters

which in turn leads to lessened primary production and a negative δ

C shift. These data are comparable with carbonate

carbon isotope records from other Tethyan margin sediments. Our integrated biostratigraphy and carbon isotope

stratigraphy enable us to improve stratigraphic correlation and age determination of the examined strata. Therefore, this

study of the Komló Calcareous Marl Formation confirms that the existing carbon isotope curves serve as a global standard

for Aalenian–Bathonian δ

C variation.

Keywords: Carbon, isotope stratigraphy, Aalenian, Bajocian, Óbánya, Mecsek, Hungary.

Introduction

The δ

C curve of the Aalenian–Kimmeridgian interval shows

a series of major Jurassic isotope events within the Aalenian,

early-middle Bajocian, Callovian and middle Oxfordian

(Hoffman et al. 1991; Bill et al. 1995; Jenkyns 1996; Weissert

& Mohr 1996; Bartolini et al. 1999; Rey & Delgado 2002;

O’Dogherty et al. 2006; Sandoval et al. 2008; Nunn et al.

2009; Price et al. 2016) recorded in both southern and northern

Tethyan margin sediments. The potential of these δ

C records

for regional and global correlation of ancient marine sedi-

ments is evident. Some of these excursions (e.g., during the

Oxfordian) are intrinsically coupled with climatic changes and

have been extensively studied in many parts of the world (e.g.,

Bill et al. 1995; Jenkyns 1996). With respect to the Middle

Jurassic interval (e.g., the Aalenian–Bathonian) it is the carbon

isotope curves of Bartolini et al. (1999) and Sandoval et al.

(2008) that often serve as a global standard (e.g., Ogg &

Hinnov 2012). Major carbon-cycle perturbations in the Middle

Jurassic are also recognised in terrestrial organic matter (fossil

wood) (Hesselbo et al. 2003). Although the excursions of

the Middle Jurassic have received only modest attention, they

occur on more than one continent and may thus serve for

global correlation of strata (e.g., Wetzel et al. 2013; Hönig &

John 2015; Dzyuba et al. 2017). The goal of this study is to

examine Aalenian–Bathonian carbon isotope stratigraphy from

Hungary for comparison. A further aim of this study is to

examine linkages between the δ

C record of past global biotic

and climatic change.

Geological setting

The Lower Jurassic of the Mecsek Mountains of Hungary

(Fig. 1) is characterized by coal bearing continental and

shallow marine siliciclastic sediments (Haas et al. 1999).

From Late Sinemurian times onwards, deposition consisted of

deeper marine hemipelagic facies with mixed siliciclastic–

carbonate lithologies (the Hosszúhetény and Komló Calca-

reous Marl formations, Raucsik & Merényi 2000). The site of

this hemipelagic marly and calcareous marly sedimentation

was most probably on or distally beyond the northern outer

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shelf of the Tethys Ocean (Fig. 2), whilst shallower conditions

occurred towards the western margins (Enay et al. 1993).

Although the precise age of the Komló Calcareous Marl

Formation is uncertain, an Aalenian to Bajocian age is indi-

cated (Forgó et al. 1966, Fig. 3). Overlying the Komló

Calcareous Marl Formation, in the Mecsek, is the pelagic

Bathonian–Callovian Óbánya Limestone Formation consisting

of thin-bedded limestones and marls (Galácz 1994). The Upper

Jurassic is represented by a siliceous limestone and radiolarite

(the Fonyászó Limestone) as well as thin-bedded limestone

(the Kisújbánya and Márévár limestones).

The Óbánya valley (Fig. 1) lies in the eastern part of the

Mecsek Mountains, between Óbánya and Kisújbánya and

provides exposures of the Komló Calcareous Marl Formation.

The succession is not strongly affected by tectonics, as com-

pared to other sections of eastern Mecsek of the same age

(Velledits et al. 1986). The exposed Aalenian and Bajocian

sediments (the Komló Calcareous Marl Formation) can be

seen as alternating limestone beds (0.2–0.5 m) and laminated

beds consisting of dark grey, spotted, bituminous, micaceous

marls (Fig. 4). The laminated beds become harder upwards

with increasing carbonate content (from 36 to 55 %; Velledits

et al. 1986). Aside from some bivalve and plant imprints

within the lower part of the succession, an ammonite (Ludwigia

sp.) has been found indicating an Aalenian age (Velledits et al.

1986). The total thickness of the Aalenian has been estimated

by Velledits et al. (1986) to be ~75 m although only the top

~25 m was exposed. Fossils from the middle part of the

succession include the ammonites Dorsetensia (at ~105 m)

and Stephanoceras (indicative of the Humphriesianum Zone),

bivalve moulds together with carbonized plant fragments

(Velledits et al. 1986). Age diagnostic ammonites (e.g., Lepto

sphinctes, Adabofoloceras of the Niortense Zone) are recorded

within the upper part of the Komló Calcareous Marl (Velledits

et al. 1986). The total thickness of sediments of Bajocian

age is ~170 m. The Komló Calcareous Marl is overlain by

a red calcareous marl and nodular limestone (Fig. 4) rich

in age diagnostic ammonites (e.g., Parkinsonia, Morphoceras

and Procerites) and pelagic microfossils (Galácz 1994).

This 20 m thick formation (the Óbánya Limestone For mation)

is of Bathonian age (Galácz 1994) and was

deposited in a pelagic environment. During this

time major flooding events also occur elsewhere

in northern Europe, with a peak trans gression

at the Bajocian–Bathonian boundary (Hallam

2001).

Materials and methods

For this study, 273 bulk carbonate samples were

derived from the outcrop of the Óbánya valley

(from 46°13’17” N, 18°24’15” E to 46°12’47” N,

18°23’20” E). Samples were taken from both

marl and limestone lithologies (Fig. 5). The ave-

rage spacing of samples was ~0.3 m. Subsamples

(250 to 400 micrograms) avoiding macrofossils

and sparry calcite veins, were then analysed for

stable isotopes using a GV Instruments Isoprime

Mass Spectrometer with a Gilson Multiflow

carbonate auto-sampler at Plymouth University.

Isotopic results were calibrated against the

NBS-19 international standard. Reproducibility

for both δ

O and δ

C was better than ± 0.1 ‰,

based upon duplicate sample analyses.

Results

The isotope results are presented in Figures 6

and 7. As isotopic analyses were undertaken from

both marl and limestone lithologies a comparison

of the isotopic composition of the two lithologies

can be made. For the limestone (n = 181) the

mean δ

C value is 1.0 ‰ and −3.5 ‰ for δ

For the marl (n = 92) the mean δ

C value is less

Fig. 1. A — Map showing the location of the Óbánya valley within Hungary.

Grey inset box shows location of the Mecsek Mountains. B — Distribution

of Mesozoic volcanic and sedimentary units within the Mecsek Mountains from

Galácz (1994).

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positive, 0.4 ‰ and −4.3 ‰ for δ

O. The greater number of

limestone vs. marl samples analysed reflects the generally

better exposure of the limestones and poorer quality of the

marl outcrops. It is for this reason that the carbon isotope

curve (Fig. 7) is plotted though the limestone data only. Using

Student’s T-Test the isotopic difference between limestones

and marls is also significant (at p < 0.05). These data are also

consistent with stable isotope data from Raucsik (1997)

who also isotopically analysed both limestone and marlstone

carbonate samples from the Komló Calcareous Marl Formation

(Fig. 6).

With respect to the carbon isotope stratigraphy (derived

from the limestone data) a number of features of the curve

are of particular note. Firstly, there is a negative excursion

followed by positive values occurring near the base of the

section (across the Aalenian–Bajocian boundary). The carbon-

isotope values then become more positive, reaching the most

positive values seen (at about 100 m height in Fig. 7). Although

showing a good deal of scatter, values remain fairly positive,

until towards the top of the Komló Calcareous Marl Formation

where there is a drop in

C values (at 166 m). Carbon isotope

values then increase again, where they reach a maximum

(of 2.4 ‰), within the Bathonian. The carbon isotope data

derived from the marls also follow this trend.

The wide range of oxygen isotopes and the low values,

possibly points to a diagenetic overprint. Although a tempera-

ture control on oxygen isotopes cannot be excluded (see below),

deep burial diagenesis and precipitation of calcite cement,

commonly results in depleted in δ

O values (Hudson 1977;

Weissert 1989: Hönig & John 2015). The preservation of δ

values or trends during carbonate diagenesis is, however, quite

typical, and is likely due to the buffering effect of carbonate

carbon on the diagenetic system, as this is the largest carbon

reservoir (e.g., Scholle & Arthur 1980; Weissert 1989). Hence,

with respect to the oxygen isotope data, a diagenetic overprint

affecting the samples analysed and results is likely. Although

showing some scatter, oxygen isotope values remain fairly

negative at the base of the section (the Aalenian) and become

increasingly more positive upsection. The most positive

oxygen isotope values are identified in the Bathonian (the Óbánya

Limestone Formation).

Discussion

Limestone–marl alternations

The conspicuous limestone–marl alternations of the Komló

Calcareous Marl Formation are likely to be caused by temporal

variations in environmental parameters. It is generally

accepted that the cause of the cyclical alternation of limestone

beds and marls represents a direct response to changes in envi-

ronmental conditions, such as productivity cycles (e.g.,

Wendler et al. 2002); dilution, i.e. changes in the influx of

terrigenous non-carbonate material (e.g., Raucsik 1997;

Weedon & Jenkyns 1999) or changes in input of carbonate

mud from adjacent shallow-water carbonate factories (e.g.,

Pittet & Strasser 1998). Based on stable isotope data, Raucsik

(1997) suggested that the higher δ

C of the limestones was

associated with higher productivity, whilst terrigenous dilution

may have formed the limestone-marlstone alternation. Given

that the data presented here are consistent with the data of

Raucsik (1997), in that the limestones typically record more

positive δ

C values (Fig. 6), the same conclusion could be

reached. A similar pattern could also be related to relatively

short term changes in the export of neritic carbonate mud,

as the δ

C of neritic muds, derived from relatively shallow

waters, tend to show more positive values than carbonate ooze

produced by planktonic organisms (e.g., Swart & Eberli 2005).

Indeed, Bajocian shallow-water carbonate factories on the

southern Tethyan shelf (Leinfelder et al. 2002) are likely to

show relatively positive carbon isotope values, although are

somewhat distal to the study site of hemipelagic sedimen-

tation on northern outer shelf of the Tethys Ocean (Fig. 2).

The Bajocian was a time of widespread oolite formation along

the Northern (and southern) Tethys margin (Wetzel et al. 2013).

Isotope values from these Northern Tethyan oolites (Wetzel et

al. 2013) do not show particularly positive values expected

for aragonite oolites. Indeed textures indicate that these oolites

were calcitic (Wetzel et al. 2013) (i.e. a calcite sea sensu

Sandberg 1983) and therefore this region exporting aragonite

during this time appears unlikely. Of note is that the oxygen

isotope data for the marls are more negative than the data

derived from the limestones (Fig. 6), a pattern consistent with

carbonate ooze produced in relatively warm surface waters.

Bodin et al. (2016), have also suggested lithological, rather

than oceanographic controls on δ

C trends (e.g., during

the earliest Toarcian of Morocco), whereby neritic δ

micrite

signatures show more positive values than carbonate ooze

produced by planktonic organisms. Changes in carbon isotope

values in marine carbonate successions have also been

attributed to changes in organic matter remineralization and

subaerial exposure around hardgrounds and subsequent carbo-

nate precipitation from meteorically influenced fluids (e.g.,

Immenhauser et al. 2002; Hönig & John 2015). Evidence for

subaerial exposure (e.g., signs of palaeokarst) was not observed

in the Óbánya valley.

Climatic and eustatic influences on carbon cycle changes

The negative excursion followed by positive values that

occurs near the base of the section (across the Aalenian–

Bajocian boundary), observed in this study, appears to cor-

relate with a major carbon cycle perturbation recognized

elsewhere (Fig. 8) as a widespread phenomenon on the basis

of its carbon–isotope expression in both oceanic (Bartolini et

al. 1996; O’Dogherty et al. 2006; Suchéras-Marx et al. 2012;

Hönig & John 2015) and terrestrial reservoirs (Hesselbo et al.

2003). It cannot be excluded that an earlier negative excursion

followed by positive values occurring in the Aalenian

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Concavum Zone at Agua Larga (O’Dogherty et al. 2006;

Sandoval et al. 2008), is correlatable with the lowermost

negative excursion. However, this possibility is not favoured

as no sizable negative shift is located above, in the Bajocian

part of the sucession. Carbon isotopes reach their most posi-

tive values, within the Óbánya succession, during the Early to

mid-Bajocian, before declining across the Bajocian–Bathonian

boundary. This same trend, is seen, for example in the

Terminilletto section, Apennines, Italy (Bartolini et al. 1999)

and the Betic Cordillera of southern Spain (O’Dogherty et al.

2006). Although there are evident differences in facies between

these sections, due to deposition under differing conditions

across the Tethys Ocean, the δ

C signatures are similar.

The carbon-isotope trends are therefore likely to represent at

least supraregional perturbations in the carbon cycle. Hence,

wide scale mechanisms need to be considered to account for

the observed trends.

Gradual negative carbon isotope excursions in the geolo-

gical record have, for example, been explained by reduced

primary production (e.g., Weissert & Channell 1989) whereby,

increasingly oligotrophic conditions, caused by reduced run

off and nutrient fluxes to the oceans, lower the fertility of

surface waters which in turn leads to lessened primary produc-

tion and a negative δ

C shift. Such a mechanism for δ

decreases has been associated with regressive conditions in

the latest Jurassic Tethyan seaway (e.g., Weissert & Channell

1989; Tremolada et al. 2006). During the Aalenian–Bajocian

boundary interval δ

C decreases have also been correlated

with regressive intervals (Sandoval et al. 2008). O’Dogherty

et al. (2006) also point out the coincidence between carbon

cycle perturbations and major changes in marine biota. For

example the latest Toarcian–Early Aalenian is marked by the

coexistence of very low radiolarian content, high proportions

of the nannofossil Schizosphaerella spp., and moderate pro-

portions of C. crassus, indicative of oligotrophic to meso-

trophic palaeoceanographic conditions (Aguado et al. 2008).

Although, there is no evidence of a regressive Aalenian–

Bajocian boundary interval at Óbánya, a significant regressive

event in Europe took place in Late Aalenian times (e.g.,

Hardenbol et al. 1998; Haq & Al-Qahtani 2005) followed by

Early Bajocian transgression and deepening (Hallam 2001).

As noted by Hallam (2001), Underhill & Partington (1993)

demonstrated that the Aalenian eustatic sea-level fall in the

Jurassic was in fact a phenomenon of regional tectonics.

Within Europe the effects of an Early Bajocian transgression

can be recognised widely, for example, in Morocco (Bodin et

al. 2017), north eastern Spain (e.g., Aurell et al. 2003) and in

the Jura Mountains of southern France (e.g., Razin et al. 1996).

Major perturbations in the carbon cycle have also been asso-

ciated with pulses of magmatism (e.g., Pálfy et al. 2001;

Wignall 2001; Hesselbo et al. 2003). However, the carbon

isotope excursion reported here and any association with

a large pulse of magmatism is not clearly demonstrated. For

example, radiometric data from the Karoo basalts indicates

that the main volume of the Karoo Large Igneous Province

(LIP) was emplaced between 181 and 184 Ma (i.e. during the

Fig. 5. A — Photomicrograph of the limestone lithology (from the

Komló Calcareous Marl Formation) dominated by calcite micro-

spar (sample OB115, scale bar 1 mm). Small patches of coarser

sparry calcite may have formed as a cement during diagenesis

within primary porosity or by neomorphism of aragonite.

B — Photomicrograph of marl lithology (from the Komló

Calcareous Marl Formation) showing abundant small sparry

bioclasts, including crinoids within a micritic and organic rich

matrix (sample OB546, scale bar 0.2 mm). C — Photomicrograph

of the Óbánya Limestone Formation showing abundant sparry

small bioclast fragments within a muddy matrix (sample OB125,

scale bar 0.2 mm).

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Late Pliensbachian to Early Toarcian) with limited late

stage basaltic activity at 176 Ma (e.g., Jourdan et al. 2008).

Younger episodic magmatic activity, associated with the

break- up of Gondwana following the formation of the Karoo

LIP, is reported from Patagonia and the Antarctic Peninsula

(Pankhurst et al. 2000). Aalenian–Bathonian volcanism is also

reported from the Crimea (Meijers et al. 2010), the Caucasus

region (Odin et al. 1993) and Mexico (Rubio-Cisneros &

Lawton 2011). Interestingly, the Aalenian–Early Bajocian

interval also overlaps with the birth of the Pacific Plate and

a major pulse of subduction related magmatism (Bartolini &

Larson 2001; Koppers et al. 2003). Evidence for the impact of

this magmatic activity can be assessed through

Sr /

Sr data.

The Aalenian–Early Bajocian seawater

Sr /

Sr curve shows,

however, a flat segment alluding to the limited impact of

this magmatic activity. This contrasts with the relatively rapid

fall in the seawater

Sr /

Sr ratio seen through the Late

Bathonian and Early Callovian (Wierzbowski et al. 2012).

Hence it appears likely that the volcanogenic CO

associated

with these events certainly represents a potential source for

light carbon, although possibly not of sufficient magnitude

and sufficiently light to achieve the observed isotopic change.

Alternatively, an injection of isotopically light carbon into

the ocean and atmosphere from a remote source, such as

methane from clathrates, wetlands, or thermal metamorphism

organic rich sediments (e.g., McElwain et al. 2005; Bachan et

al. 2012) has been considered as means to explain negative

carbon isotope excursions. Similar events have been consi-

dered to have been a result of more regional events caused by

recycling of isotopically light carbon from the

lower water column (e.g., McArthur et al. 2008).

However, that the Aalenian–Bajocian boundary

event is observed in both marine (Fig. 8) and

terrestrial settings (e.g., Hesselbo et al. 2003) has

been considered to be an indication that the

observed isotopic signals may have recorded

a global (rather than regional) perturbation of

the carbon cycle. As noted above, changes in

the export of neritic carbonate mud (e.g., Swart &

Eberli 2005) could also conceivably result in

a negative isotope excursion in the geological

record (e.g., Bodin et al. 2016; Ait-Itto et al.

2017). Hence a shift in the δ

micrite

signature is

possible without any relation to variations in

the global carbon isotope trend (Bodin et al. 2016,

2017). For this latter mechanism to be consi-

dered, sustained changes in the export of neritic

mud are required to reach the study site and affect

carbonate factories across Tethys. Furthermore,

the negative excursion occurring in both oceanic

and terrestrial reservoirs, provides an additional

challenge for this to be a viable mechanism.

In contrast to the Aalenian–Bajocian boundary

interval, more positive δ

C values (Fig. 8) in the

Early Bajocian Tethyan seaway could have been

linked to warmer climates and rising sea levels,

increased runoff and nutrient fluxes to the oceans, increasing

the fertility of surface waters (e.g., Sandoval et al. 2008;

Suchéras-Marx et al. 2012). For example Suchéras-Marx et al.

(2012) show that calcareous nannofossil fluxes increase mar-

kedly (mainly related to the rise of Watznaueria genus) from

the upper part of the Aalenian to the Early Bajocian, coinci-

ding with a positive shift in carbon isotope compositions of

bulk carbonate. High levels of CO

in the atmosphere could

have also accelerated the transfer of nutrients from the conti-

nents to the oceans, through increasing weathering. Indeed, as

noted above, significant injections of CO

have been asso-

ciated with major pulses of subduction-related magmatism,

linked to the opening of the Pacific Ocean and the breakup of

Pangaea (e.g., Bartolini & Larson 2001). Equally, the evolu-

tion of Tethyan seawater temperatures during the Middle

Jurassic period inferred from the oxygen isotopic composition

of belemnite rostra, bivalve shells and from fish teeth (see

Brigaud et al. 2009; Price 2010) reveal warmth during the

Early Bajocian and cooling from late Bajocian times through

into the Bathonian. Also, the oxygen isotope data of this study

(Fig. 7) broadly replicate this trend, whereby more negative

values are seen in the lower part of the succession and more

positive values are observed in the upper part of the section

and within the Bathonian. Such a pattern of warming and

cooling is consistent with an Early Bajocian transgression

noted above.

Increasing δ

C values in the Bajocian Tethyan seaway have

also been linked to elevated productivity, as shown by radio-

larian assemblages (Bartolini et al. 1999). O’Dogherty et al.

Fig. 6. Cross plot of δ

O and δ

C data from the Aalenian–Bajocian interval,

Óbánya valley, of the Mecsek Mountains, Hungary. Data from Raucsik (1997) is

also shown.

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rather than any marked decreases in carbonate.

It is the Late Jurassic that sees biosiliceous

sedi mentation in the Óbánya valley (Velledits

et al. 1986).

Conclusions

Our study of the Komló Calcareous Marl

Formation of the Mecsek Mountains of

Hungary reveals a negative carbon isotope

excursion followed by positive values that

occurs near the base of the section (across the

Aalenian–Bajocian boundary). The origin of

this carbon-isotope anomaly is interpreted to lie

in significant changes to carbon fluxes stem-

ming from changes in primary production

linked to increasingly oligotrophic conditions,

caused for example, by reduced run off and

nutrient fluxes to the oceans, lowering the fer-

tility of surface waters which in turn leads to

lessened primary production and a negative δ

shift (e.g., O’Dogherty et al. 2006; Sandoval et

al. 2008). That the Aalenian–Bajocian boun-

dary carbon isotope event is observed in both

marine and terrestrial settings (e.g., Hesselbo et

al. 2003) indicates that the observed isotopic

signals record global (rather than regional) per-

turbation of the carbon cycle. Changes in the

export of neritic carbonate mud could also con-

ceivably result in a negative isotope excursion,

but this mechanism required sustained changes

affecting carbonate factories across Tethys.

Furthermore, the negative excursion occurring

in both oceanic and terrestrial reservoirs, chal-

lenges this as a viable mechanism. In view of

the gradual isotopic changes inferred from

these Tethyan carbonates, an explanation in

terms of the rapid dissociation of gas hydrates

also appears unlikely. This study of the Komló

Calcareous Marl Formation further confirms

that the carbon isotope curves of Bartolini et al.

(1999) and Sandoval et al. (2008), do indeed

serve as a global standard for Aalenian–

Bathonian δ

C variation.

Acknowledgments: This work has received

support from the SYNTHESYS Project

(http://www.synthesys.info/), financed by Euro-

pean Community Research Infrastructure

Action under the FP6 Structuring the European

Research Area Program. We thank Béla Raucsik

for assistance with fieldwork. The manu script

was considerably improved by constructive

reviews by Helmut Weissert and an anonymous

reviewer.

Fig. 8.

Carbon

isotope

stratigraphies of the

Aalenian–Bathonian interval from Óbánya compared with Southern Spain (from O'Dogherty et al. 2006), Cabo

Mondego, Portugal (from

Suchéras-Marx et

al. 2012); Chaudon Norante, SE France (from Suchéras-Marx et al. 2013);

adi Naqab, United

Arab Emirates (Hönig & John 2015) and the Umbria-Marche Basin, Italy(from Bartolini et al. 1999).

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