Carnets Geol. 14 (6)  

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[Introduction] [The isotope C7 segment] [Division of the segment C7 in the Prebetic Domain, Spain]
[Intra-Furcata Negative Excursion (IFNE): Definition]
[Probable expressions of the "IFNE" in the Old World] [(...) in the New World]
[Conclusions] [Bibliographic references] and ... [Appendix]

A negative carbon isotope excursion
within the Dufrenoyia furcata Zone:
proposal for a new episode
for chemostratigraphic correlation in the Aptian

Fernando Nuñez-Useche

Posgrado en Ciencias de la Tierra, Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, D.F. (Mexico)

Josep Anton Moreno-Bedmar

Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, D.F. (Mexico)

Miguel Company

Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada Avenida Fuentenueva s/n, 18002 Granada (Spain)

Ricardo Barragán

Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, D.F. (Mexico)

Manuscript online since May 8, 2014
[Editor: Michel Moullade; copy editor: Bruno Granier; language editor: Phil Salvador]

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In this work we discuss a proposed updated division of the C7 isotope segment of Menegatti et al. (1998). The new standard division of the segment C7 is based on a revision of published Barremian-Aptian carbon isotope curves from stratigraphic sections of the Prebetic Domain in Spain. It includes four distinct isotopic subunits labeled C7a to C7d, with a characteristic negative carbon isotope excursion at the base of the segment and which correlates with the Dufrenoyia furcata ammonite Zone. The negative excursion is recognized on a regional extent, and the term Intra-Furcata Negative Excursion (IFNE) is proposed to identify it. We provide possible sites correlatable with the IFNE in both the Old and New worlds, which suggest its potential use as an even global chemostratigraphic marker for the Aptian record.


Aptian; C7 segment; negative carbon isotope excursion; Dufrenoyia furcata Zone.


Núñez-Useche F., Moreno-Bedmar J.A., Company M. & Barragán R. (2014).- A negative carbon isotope excursion within the Dufrenoyia furcata Zone: proposal for a new episode for chemo-stratigraphic correlation in the Aptian.- Carnets de Géologie [Notebooks on Geology], Brest, vol. 14, nº 6, p. 129-137.


Une excursion négative de la courbe isotopique du carbone au sein de la Zone à Dufrenoyia furcata : proposition pour un nouvel épisode permettant la corrélation chimiostratigraphique dans l'Aptien.- Dans ce travail nous proposons une mise à jour de la subdivision du segment isotopique C7 de Menegatti et al. (1998). Ce nouveau standard est fondé sur une révision des courbes isotopiques du carbone publiées pour le Barrémo-Aptien à partir de coupes stratigraphiques du domaine prébétique en Espagne. Le segment C7 inclut quatre sous-unités isotopiques distinctes répertoriées C7a à C7d et est caractérisé à sa base par une excursion isotopique négative qui est corrélée avec la Zone d'ammonites à Dufrenoyia furcata. Cette excursion négative est reconnue à l'échelon régional, et le terme Excursion Négative Intra-Furcata (ENIF) est proposé pour sa dénomination. Nous proposons d'autres sites, à la fois dans l'Ancien et le Nouveau Monde, qui paraissent révéler cette ENIF, ce qui suggère ses potentialités comme marqueur chimiostratigraphique global pour l'Aptien.


Aptien ; segment C7 ; excursion négative des isotopes du carbone ; Zone à Dufrenoyia furcata.


The carbon isotope segments of Menegatti et al. (1998) describe long-term trends linked to different disturbances in the global carbon cycle during the Late Barremian-Aptian interval. They derived from high-resolution studies of carbon isotope stratigraphy from sections at the western and eastern margins of the Alpine Tethys. From C1 to C8, each segment is characterized by a distinctive pattern of variation in the inorganic (δ13Ccarb) and organic carbon (δ13Corg) isotope curve. Their recognition in several paleogeographic domains worldwide has provided evidence of their reliability as a well-established standard pattern for the carbon isotope curve and attests to their use as a valuable tool for correlations between different stratigraphic sections (Bralower et al., 1999; Gea et al., 2003; Renard et al., 2005; Li et al., 2008; Méhay et al., 2009; Millán et al., 2009; Bover-Arnal et al., 2010; Najarro et al., 2011; Moreno-Bedmar et al., 2012). Among the different isotope segments, greatest emphasis has been given to segments C3 to C6 because they characterized the most prominent shift in the C-isotope curve during the early Aptian, the Oceanic Anoxic Event 1a (OAE 1a, Selli event, ~120 Ma) (Schlanger & Jenkyns, 1976; Jenkyns, 1980, 1999; Arthur et al., 1990). So far the other segments have received less attention, but conspicuous fluctuations within their temporal pattern also have the potential to be used as chemostratigraphic markers. Characterizing in detail these minor but significant episodes allow us to improve the chemostratigraphic and chronologic resolution of the original segments (Menegatti et al., 1998).

In this paper we focus on segment C7 (Menegatti et al., 1998), and we attempt to identify particular characteristics of useful minor isotopic trends that can be recognized in different stratigraphic sections. We propose a new division of segment C7 into discrete sub-units based on similar isochronous behavior of δ13C values within this segment, as provided in different published European sections. We also provide evidence to demonstrate that the most significant sub-unit within C7 is characterized by a negative δ13C shift that we propose should be considered as a new and important element of correlation for the lower Aptian record. We also aim to motivate future research that may further reveal the minor isotopic shift discussed in this study in order to increase its known record and verify its potential as a tool for spatio-temporal correlations.

The isotope C7 segment

The C7 isotope segment (Menegatti et al., 1998) the longest of all segments, corresponds to the maximum positive δ13C excursion of the lower Aptian record, and is known as the Cismon event (Weissert & Lini, 1991; Weissert et al., 1998). Based on the planktonic foraminifera biozones used by Menegatti et al. (1998) from Cismon core reference section in Italy (Fig. 1 ), C7 spans from the upper part of the Globigerinelloides blowi through the entire Leupoldina cabri Zone (Fig. 2.A ). However, at the same section, Erba et al. (1999) constrained this segment mostly to the Leupoldina cabri Zone and stated that its uppermost part falls within the Globigerinelloides ferreolensis Zone (Fig. 2.B ). Despite the overall high δ13C values that originally defined segment C7 (Menegatti et al., 1998), the actual pattern includes minor, relatively abrupt negative to positive excursions. Numerous investigations have addressed the issue of these minor carbon isotopic variations and divided segment C7 into discrete sub-segments or zones that emphasize the value of these isotopic trends as suitable correlation patterns. In this respect, a detailed δ13Ccarb analysis in sections from the Vocontian Basin, Southeast France (Herrle et al., 2004) allowed the splitting of segment C7 into three units labeled Ap7, Ap8 and Ap9 at Serre Chaitieu section (Fig. 1 ). Furthermore, since Ap7 consisted of a prominent positive δ13Ccarb excursion that included distinct lower magnitude variations, Herrle et al. (2004) also subdivided unit Ap7 into four sub-units (Fig. 2.D ). According to this scheme, sub-unit Ap7b is located within the uppermost part of the planktonic foraminifera L. cabri Zone and encloses the lowest δ13C values in the lower part of segment C7.

Fig. 1
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Figure 1: Map showing location of stratigraphic sections mentioned in this contribution in a paleogeografical reconstruction at 120 Ma (Blakey, 2010; © Ron Blakey, Colorado Plateau Geosystems). 1-Cismon core section, Italy (Menegatti et al., 1998; Erba et al., 1999); 2-Serre Chaitieu section, Vocontian Basin, France (Herrle et al., 2004), 3- Cassis-La Bédoule section, France (Moullade et al., 1998), 4-Prebetic Domain sections, Spain (Moreno-Bedmar et al., 2012, this study); 5- Djebel Serdj section, Tunisia (Held et al., 2008), 6-Igaratza section, Basque-Cantabrian Basin, Spain (Millán et al., 2009), 7-Santa Rosa section, Mexico (Li et al., 2008), 8-Permanente Quarry section, USA (Robinson et al., 2008), 9- Curití section, Colombia (Gaona-Narvaez et al., 2013).

Subsequently, DeBond et al. (2012) studied the Aptian δ13C signal at Ocean Drilling Program Site 765C, Leg 123, off the northwestern margin of Australia. They found differences with the scheme proposed by Menegatti et al. (1998), especially with respect to the values in the segment C7. They divided the segment C7 of site 765C into two zones which also found on a composite section with better sampling resolution and conformed with δ13Ccarb data from the Cismon core section (Erba et al., 1999) and the Vocontian Basin (Herrle et al., 2004) (Fig. 2.C ). In this section, Zone C7a represents increasing values and correlates with the lower Aptian highest positive δ13C excursion of Menegatti et al. (1998). This zone is equivalent to the lower and middle part of the C7 segment of Erba et al. (1999), which is the upper part of the C6 segment of Herrle et al. (2004). Zone C7b of the composite section is equivalent to a period of high δ13C variation not clearly distinct in the Cismon core section, and corresponds to the uppermost part of the C7 segment of Erba et al. (1999) and to the unit Ap7 of Herrle et al. (2004). The latter correlation reduced the upper extent of Herrle's segment C7 and made it more coherent with the original age-calibration of the segments defined by Menegatti et al. (1998) (see in Fig. 2 ). Based on the pattern of δ13C values of Herrle et al. (2004) and ammonite biostratigraphy data analysis, Moreno-Bedmar et al. (2012) even proposed that only sub-units Ap7a to Ap7c defined by Herrle et al. (2004) correspond to segment C7.

The main issue with these proposed subdivisions for segment C7 (Herrle et al., 2004; DeBond et al., 2012) is that they are based in each case only on the carbon isotopic record of a single section, and the sub-units cannot be clearly recognized in other stratigraphic sections; therefore, their potential as chemostratigraphic tools remains unproven and may only have a local value.

Fig. 2
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Figure 2: The C7 isotope segment of Menegatti et al. (1998) and Erba et al. (1999) and the subsequent divisions of Herrle et al. (2004) and DeBond et al. (2012). Dashed lines are used for correlation. Scale bar in A, B and D indicates distance interval in meters (m), whereas in C represents time interval in million years (Myr).

Division of the segment C7 in the Prebetic Domain, Spain

The present study uses δ13Ccarb values within segment C7 from different published stratigraphic sections of the Prebetic Domain in Spain, including the L'Alcoraia, Racó Ample and Cau sections (Moreno-Bedmar et al., 2012) (Figs. 1 and 3 ). Carbon isotope determinations were carried out with reproducibility better than 0.03‰. All these sections have been calibrated by means of ammonite biostratigraphy (Moreno-Bedmar et al., 2012), and the Cau section has also been correlated with planktonic foraminifera zonation (Gea et al., 2003).

Since segment C7 shows a similar pattern in all these sections, we divided it into four distinct isotopic trends labeled C7a to C7d, from bottom to top (Fig. 3 ). While sub-unit C7a is represented by somewhat variable but overall constant values, the sub-unit C7b consists of a conspicuous negative excursion followed by a positive shift (sub-unit C7c). Finally, uniform to slightly increasing values characterize sub-unit C7d. These sub-units are identified in sections from the Prebetic Domain but are not clearly correlatable with the sub-units defined by Herrle et al. (2004) or DeBond et al. (2012).

All the sections shown in Moreno-Bedmar et al. (2012) include the well-defined negative excursion of sub-unit C7b, which corresponds to the lowest carbon isotope data within segment C7. This negative shift has an amplitude of about 0.7‰ in the L'Alcoraia section, 1.2‰ in the Racó Ample section and close to 1‰ in the Cau section (Fig. 3 ). This sub-unit occurs within the middle to upper part of the Leupoldina cabri Zone. A more consistent biostratigraphic position for this δ13C sub-unit is achieved if it is correlated with established Mediterranean ammonite zones. As shown in Figure 3 , the negative inflection equivalent to subunit C7b consistently occurs in the Dufrenoyia furcata Zone. Taking into account the subzones of the Dufrenoyia furcata Zone showed in Moreno-Bedmar et al. (2012) for the Cau and Racó Ample sections, it seems that the lower part of the zone is condensed and consequently this sub-unit is located about the middle part of the zone. The fact that this negative carbon isotope excursion is defined by a single point is significant. This may be a result low sedimentation rate in an outer-ramp environment where these sections were deposited (Castro, 1998; Gea, 2004; Castro et al., 2008). Since this negative inflection is not linked to a significant lithologic change nor is it coeval with an oxygen isotope shift (see Appendix 1), it can be considered as a primary carbon isotope signal. Diagenetic overprinting can be also excluded, given the presence of this negative carbon isotope excursion, with a similar value and biostratigraphic position, in geographically distant stratigraphic sections.

Intra-Furcata Negative Excursion (IFNE): Definition

The δ13Ccarb values of segment C7 of the three sections from the Prebetic Domain (Fig. 3 ) reveal that the negative carbon isotope excursion represented by sub-unit C7b appears in the same chemo- and bio-stratigraphic position and displays a similar drop in carbon isotope values at each location. Hence, this excursion appears to represent a constant chemostratigraphic marker with regional significance. This characteristic carbon isotope trend is here named the Intra-Furcata Negative Excursion (IFNE), which is defined as a negative carbon isotope excursion with the lowest values within segment C7, and can be correlated with the middle part of the Dufrenoyia furcata ammonite Zone (Fig. 3 ). Regarding planktonic foraminifera biozones, the IFNE can be recognized within the middle to the upper part of the Leupoldina cabri Zone. However, considering inconsistency regarding the definition of the base of this planktonic foraminifera biozone (Bolli, 1959; Premoli Silva & Verga, 2004), such correlation for the IFNE is less accurate.

Fig. 3
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Figure 3: Carbon-isotope stratigraphy of sections in the Prebetic Domain: Cau, Racó Ample and L'Alcoraia sections. Proposed sub-units for dividing the segment C7 are shown. Sections are correlated (dashed line) using the negative carbon isotope excursion represented by the sub-unit C7b (IFNE). For all sections scale bar is 10 m.

Probable expressions of the "IFNE" in the Old World

Although more studies are needed, it is likely that the IFNE appears elsewhere beyond the Prebetic Domain (Fig. 4.A ) because a comparable negative variation also occurs in other stratigraphic sections in Old World. The Cassis-La Bédoule Stratotype section in southeast France (Moullade et al., 1998) is such an example, as a negative shift in the δ13Ccarb curve (~1.2‰) is recorded within the planktonic foraminifera L. cabri Zone, and is correlatable with the Dufrenoyia furcata Zone (e.g., Ropolo et al., 2006; Moreno-Bedmar et al., 2012) (Fig. 4.B ). In the Vocontian Basin, a negative carbon isotope excursion similar to IFNE has been documented by Herrle et al. (2004) (Ap7b=~1.5‰). This correlation is very reliable because Ap7b has been related to the Niveau Blanc (Herrle et al., 2004), which is a significant reference level observed in most sections of the Vocontian Basin, and its upper part has been associated with the lower part of the Dufrenoyia furcata Zone (Dutour, 2005). This biochronologic correlation is also in agreement with the reconstructed carbon isotope segments of Menegatti et al. (1998) in the Vocontian Basin, as shown in Figure IX of Moreno-Bedmar et al. (2012) (Fig. 4.C ). Another comparable negative carbon isotope shift that may be equivalent to the IFNE is reported in the Aptian outcrops of the Djebel Serdj area, north-central Tunisia (Held et al., 2008). It consists of a δ13Ccarb negative variation of ~2.5‰ within the L. cabri Zone (Fig. 4.D ).

In the Basque-Cantabrian Basin (Spain), at Igaratza section, Millán et al. (2009) documented a pronounced negative δ13Ccarb spike predating the Aparein level and within the Dufrenoyia furcata Zone. Since according to Millán et al. (2009) this negative carbon isotope excursion overlies the segment C8 and records a variation of about ~4.1‰, we consider that this does not correspond to the IFNE. Instead, it is more likely that the carbon isotope drop of ~1‰ to the middle part of the segment C7 correlates with the IFNE (Fig. 4.E ). A firm correlation is not possible due to the fact that this drop is included in the Deshayesites deshayesi - Dufrenoyia furcata transition Zone. All mentioned sections in this chapter are located in Figure 1 .

Fig. 4
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Figure 4: Different stratigraphic sections in the Old World which exhibit a negative carbon isotope excursion similar to the IFNE. Cau section of the Prebetic Domain is shown for comparison. Dashed line correlates the stratigraphic sections using IFNE as a characteristic chemostratigraphic marker. Ammonite biozones plotted for the Cassis-La Bédoule (Moullade et al., 1998) and the Serre Chaitieu (Vocontian Basin) sections (Herrle et al., 2004) correspond to the interpretation of Moreno-Bedmar et al. (2012). Planktonic foraminifera zones of the Djebel Serdj section are also depicted (Held et al., 2008). The segment C7 of the Vocontian Basin is also in agreement with Moreno-Bedmar et al. (2012). The Igaratza section [reference section of the Aparein level of Millán et al. (2009)] is shown for comparison with the IFNE.

Probable expressions of the "IFNE" in the New World

A cursory review of the literature reveals that fewer published data are available for the New World regarding the Aptian interval; however, carbon isotope data from some sites show isotopic trends that could correspond to the IFNE. The δ13Corg curve of the Santa Rosa section in northeastern Mexico displays a negative carbon isotope excursion of ~2.0‰ toward the base of segment C7 in the La Peña Formation, within the L. cabri planktonic foraminifera Zone (Li et al., 2008). Since ammonite data are not available for the Santa Rosa section, we cannot determine whether or not this carbon isotopic drop is related to the Mexican ammonite zone equivalent to the European Dufrenoyia furcata Zone. In the USA, a decrease of 0.4‰ in carbon isotope composition of organic matter is reported at the base of the segment C7 of the La Calera limestone exposed at the Permanente Quarry in California (Robinson et al., 2008). A lack of biostratigraphic data along with the carbon isotope data prevents us from further constraining the age of this negative excursion. In Colombia, the δ13Corg curve of the Curití section shows a pronounced negative inflection in the lowermost part of the segment C7 that reaches ~2.0‰ (Gaona-Narvaez et al., 2013) and is also compatible with the IFNE. All mentioned sections in this chapter are located in Figure 1 .


A review of the δ13Ccarb curve in three different stratigraphic sections of the Prebetic Domain in Spain reveals a consistent pattern that allows us to propose a quadripartite division of the segment C7 of Menegatti et al. (1998). We divided segment C7 into distinct isotopic trends labeled, from bottom to top, C7a, C7b, C7c and C7d. The most conspicuous of these subdivisions corresponds to sub-unit 7b and consists of a negative carbon isotope excursion, with the lowest values within the lower middle part of segment C7. Since its record is chronologically linked to the Dufrenoyia furcata Zone, this isotope trend is here named the Intra-Furcata Negative Excursion (IFNE).

The chemostratigraphic record of the IFNE does not seem to be limited to the Prebetic Domain in Spain. We provide several plausible sites in both the Old and New worlds where a comparable negative carbon isotope excursion may be equivalent to the IFNE. Although additional research is needed, we wish to highlight the possible use of the IFNE as a new chemostratigraphic marker that has the potential to provide a more robust chronologic framework for the lower Aptian record.


The authors are grateful to Drs Karl Föllmi, Florentin Maurrasse and Peter Skelton for the careful review and the helpful comments and suggestions that significantly improved the original manuscript. Special thanks also are due to Michel Moullade and Bruno Granier for their constructive editing. We are very grateful to the Language Editor, Phil Salvador, for his corrections which allowed significant improvements to the manuscript.

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Carbon and Oxygen isotope data from stratigraphic sections in the Prebetic Domain

Cau section Raco Ample section L'Alcoraia section
Sample δ13Ccarb
Sample δ13Ccarb
Sample δ13Ccarb
54 3.10 -1.78 46 2.63 -2.29 212 3.01 -1.50
53 3.05 -2.16 45 2.66 -2.14 210 2.99 -2.03
51 3.41 -2.07 44 2.78 -2.35 209 2.92 -1.77
50 3.70 -1.67 43 2.64 -1.99 208 3.38 -2.24
49 3.57 -1.92 42 2.46 -2.06 207 2.98 -1.74
48 3.55 -2.04 41 3.82 -2.32 206 3.08 -1.55
47 3.61 -2.15 40 2.70 -2.50 205 3.01 -1.65
46b 3.88 -1.66 39 3.17 -2.27 204 3.68 -1.10
46a 3.58 -1.72 38 3.13 -2.02 203 3.38 -1.52
46 3.78 -2.02 37 3.47 -2.32 202 3.17 -1.69
44* 3.04 -1.97 36 3.43 -2.45 201 3.74 -1.44
43 4.04 -1.67 35 3.39 -2.52 200 3.78 -1.47
42 3.54 -2.52 34 3.24 -2.41 199 3.30 -2.12
41 4.07 -1.22 33 3.57 -2.46 198 3.85 -1.29
39 3.88 -2.02 32 3.100 -2.36 197 3.76 -1.92
38 3.78 -2.08 31 3.96 -2.35 196 4.23 -1.42
37 3.96 -1.95 30 4.03 -2.27 195 3.76 -1.92
35 4.04 -1.49 29 3.81 -2.47 194 4.36 -1.41
33 3.71 -2.09 28 3.97 -2.25 193 4.44 -1.57
32 3.77 -1.96 27 3.44 -2.61 191 4.13 -2.07
31 3.84 -1.96 26 3.74 -2.56 190 4.02 -2.34
30 3.99 -1.85 24 3.93 -2.41 189 4.43 -1.85
29a 3.100 -2.01 23 4.02 -2.39 188 4.36 -1.65
29 3.59 -1.97 22 3.64 -2.46 187 4.11 -1.75
28 3.69 -1.69 21 3.93 -2.08 186 3.71 -2.50
27 3.52 -1.85 20 3.89 -2.25 185 4.08 -2.06
26 3.61 -1.92 19a* 2.82 -2.76 184 3.77 -2.31
25 2.97 -1.98 19 4.00 -2.06 183 3.97 -2.32
23 2.48 -2.05 18 3.96 -2.24 182* 3.07 -1.44
16 4.00 -2.43 181 3.84 -2.09
Reproducibility ± 0.03  ±0.03 15 3.83 -2.56
14 3.75 -2.32 Reproducibility ± 0.01 ± 0.06
*IFNE 13 2.91 -2.73
11a 3.10 -2.27
11 2.62 -2.25
Reproducibility ± 0.02 ± 0.05