Three successive phases of platform demise during the early Aptian and their association with the...

Palaeogeography, Palaeoclimatology, Palaeoecology 418 (2015) 101–125

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Three successive phases of platform demise during the early Aptian andtheir association with the oceanic anoxic Selli episode (Ardèche, France)

A. Pictet a,⁎, G. Delanoy b, T. Adatte a, J.E. Spangenberg a, C. Baudouin c, P. Boselli c, M. Boselli c,P. Kindler d, K.B. Föllmi a

a Institute of Earth Sciences, Bâtiment Géopolis, 1015 Lausanne, Switzerlandb Département des Sciences de la Terre, Université de Nice-Sophia Antipolis, 28 Avenue Valrose, 06100 Nice, Francec Centre d'Etudes Méditerranéennes, Mairie, 04170 St André les Alpes, Franced Département de Géologie et Paléontologie, Maraîchers A, Bureau 407, 13, rue des Maraîchers, 1211 Genève 4, Switzerland

⁎ Corresponding author.E-mail addresses: [email protected] (A. Pictet), Ge

(G. Delanoy), [email protected] (C. Baudouin), [email protected] (P. Kindler).

http://dx.doi.org/10.1016/j.palaeo.2014.11.0080031-0182/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t
a r t i c l e i n f o
Article history:Received 28 May 2014Received in revised form 5 November 2014Accepted 12 November 2014Available online 20 November 2014

Keywords:Early AptianSE FranceArdècheChabert FormationDrowningSelli episode

A stratigraphic and depositionalmodel, constrainedby biostratigraphy, geochemistry, total phosphorus contents,and bulk-rock mineralogy, is proposed for lower Aptian sediments from the Languedoc platform in Ardèche, SEFrance. The upper lower Aptian is documented by the Chabert Formation (upper Deshayesites forbesi Zone toupper Dufrenoyia dufrenoyi Subzone), deposited on a discontinuity surface on top of the Urgonian platform, re-cording a first emersion phase and consecutive drowning event. The Chabert Formation starts with the marlyViolette Member, which passes into crinoidal limestone of the Rocherenard Member. The top of this memberis associated with a second discontinuity, recording a further drowning phase, which is followed by the deposi-tion of the glauconitic and partly phosphatic Picourel Member (upper Deshayesites grandis to upper Dufrenoyiadufrenoyi Subzone). A third erosive phase is documented by a phosphatic conglomerate (upper Dufrenoyiafurcata Zone), which represents a lag deposit derived from underlying sediments. The formation of this conglom-erate was associated with a substantial emersion phase. This emersion was followed by a drowning eventreworking the phosphatic conglomerate into the base of the upper Aptian black marls (Frayol Formation). Thecarbon-isotope record shows a negative excursionwhich coincideswith the onset of the early Aptian oceanic an-oxic Selli episode (OAE 1a) in the middle/upper part of the Deshayesites forbesi Zone. Emersion phases were animportant factor implied in the formation of the sequence boundaries, which were transformed into drowningunconformities during subsequent phases of significant transgressions. These phases were associated with theinstallation of higher trophic levels, transforming or impeding carbonate production. The first drowning phasepreceded the onset of the Selli episode, suggesting that rapid sea-level change and associated environmentalchange were already an important element of the early Aptian before the major phase of environmental changeduring the Selli episode.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

During the late Barremian and earliest Aptian (late EarlyCretaceous), the northern Tethyan inner shelf was occupied by a largephotozoan carbonate factory, which led to the formation of the so-called Urgonian platform. Profound palaeoceanographic and climaticchange occurred during the early Aptian, including rapid eustaticvariations (Arnaud-Vanneau, 1980; Arnaud and Arnaud-Vanneau,1989, 1990; Haq, 2014), coastal upwelling and the appearance of amar-ginal geostrophic current (Delamette, 1986, 1989), rise in atmosphericCO2 (Shaffer et al., 2009), increase in continental biogeochemical

[email protected]@wanadoo.fr (P. Boselli),

weathering and corresponding siliciclastic (Weissert, 1990) and phos-phorus output (Föllmi et al., 1994, 2006), rise in organic-carbon burial(Arthur et al., 1985; Weissert and Lini, 1991) and positive excursionsin the δ13C record (Weissert, 1989). These changes coincided with:(I) the disappearance of the carbonate platforms in three successivesteps and; (II) the installation of a dense succession of global anoxic ep-isodes, prevailing during the Aptian.

The detailed pattern of progressive platform demise and the exactages of the main phases during the early Aptian are still poorly under-stood for several reasons. Firstly, the sea-level record preserved indrowning unconformities is often complex andmultiphased, and not al-ways optimally interpretable due to condensation and erosion process-es (e.g., Godet, 2013). An important and not always well-establishedcomponent is the effect of emersion phases prior to drowning. Theseemersions were the consequence of sea-level fluctuations for whichtheir correlation is not in all cases established due to the lack of age-

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102 A. Pictet et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 418 (2015) 101–125

diagnostic fossils. Bottom currents, shifting onto the shelf duringtransgressions, were equally responsible for sediment-reworking pro-cesses including erosion and winnowing, creating large variations insediment-accumulation rates and multiple unconformities.

A second point is the lack of detailed studies on the heterozoansediments covering the Urgonian Formation (Chabert Formation inLanguedoc, Upper Orbitolina beds in Vercors and Chartreuse, GrüntenMember in the Helvetic Alps)widely known from the northern Tethyanmargin. These sediments are currently often confoundedwith other for-mations, partly of other ages, because of the lack of characteristic fossilsor disagreements on ammonite and foraminifera determinations. Thestudy of these sediments is of special interest, in that they do not onlydocument the environmental changes and successive drowning eventsto which the Urgonian platformwas submitted during the early Aptian,but also because they document the evolution of the shallow-waterplatform during the Selli episode, the firstmajor oceanic anoxic episode(OAE 1 a) of the Early Cretaceous (Arthur et al., 1990; Föllmi andGainon, 2008; Föllmi, 2012).

A detailed study of the sedimentology, sequence stratigraphy, bio-stratigraphy and geochemistry of the Chabert Formation from the for-mer Languedoc platform, Ardèche, SE France (Fig. 1a), allows us to(I) propose a detailed model for the evolution of the lower Aptianplatform sediments attached to the southern margin of the Europeancontinent; (II) better understand the palaeoecological setting, and;(III) precisely date this formation including its different drowning un-conformities and to demonstrate their synchronicity with comparablesuccessions in other regions.

2. Geological and palaeogeographical settings

The Ardèche plateau is located on the southeastern edge of theMassif Central (Fig. 1b). The latter is separated by the Dauphiné Alpsfrom the Rhodanian graben, which forms the base of the Rhône Valley.The Cretaceous rocks of the Ardèche plateau are separated from thecrystalline rocks of the Massif Central by the Cevennes fault system

Fig. 1. a.Geographical map of the studied area and the sections. ‘1’Michelet (geographical coord‘3’ Picourel (N 44°21′26/E 04°22′19); ‘4’ Bourg-St.-Andéol (see section description); ‘5’ ChabertN 44°32′27/E 04°39′22); b. Geological map from the studied area modified after Contensuzas

passing through Largentière, Aubenas, Privas and LaVoulte to the north-west, and by theAlès graben to the south. Currently, the entire sedimen-tary succession of the Ardèche plateau is tilted towards the southeast,towards the Rhône Valley. The Ardèche plateau is covered by Aptianand Albian patches of glauconitic marl and sandy limestone. In mostareas of the plateau, these occurrences are only preserved inside col-lapsed structures against normal faults or in basal segments of syncli-nals, the remainder having been removed by subsequent erosion.

The Urgonian sediments of the Ardèche plateau are part of a chain ofshallow-carbonate platforms, which developed around the VocontianBasin on the northwestern margin of the Tethys Ocean, including theJura, Dauphiné, and Helvetic platforms to the north and northeast, theLanguedoc platform to the west, and the Provence platform to thesouthwest during Barremian early Aptian times (Fig. 2a).

This study focuses on the Languedoc platform, which is representedmore in detail in Fig. 2b. The platform developed on top of Valanginianto Hauterivian, and locally Barremian hemipelagic marl and limestonein the Ardèche and Gard (Renaud, 1978; Cotillon et al., 1979), with theprogressive installation of oolitic shoals, coral reefs and rudist muds dur-ing Barremian and earliest Aptian (Maillard, 1965; Contensuzas, 1980).Eastward progradation in the form of bioclastic fans, represented inFig. 2a–b, took place in the direction of the Vocontian Basin during theearly and late Barremian (Ferry, 1978). To the north, the Villeneuve deBerg to Le Teil area is characterized by a deep and narrow sea, whichwas directly connected with the Vocontian Basin (Fig. 2a–b; Cotillonet al., 1979), and where hemipelagic sediments were deposited, repre-sented by the Lafarge Formation (Fig. 3). The deposition of the sedimentsof the Urgonian and Lafarge Formations ended abruptly during the mid-dle early Aptian D. forbesi Zone. These lithological units are overlain by asuccession of marl (VioletteMember), crinoidal limestone (RocherenardMember), and glauconitic marly limestone (Picourel Member), whichare all part of the Chabert Formation, and which represent an externalplatform, open marine facies (Fig. 3). These heterozoan carbonates aresurmounted by deep outer-shelf black marls from the Frayol Formation(Fig. 3).

onates: Latitude N 44°25′37/Longitude E 04°25′50); ‘2’Mezelet (N 44°23′33/E 04°24′10);(N 44°30′39/E 04°39′03 to N 44°30′54/E 04°38′54); ‘6’ Pélican (N 44°32′14/E 04°39′10 to(1980).

Fig. 2. a. Palaeogeographical map of the Vocontian Basin during the early Aptian, modified after Bert et al. (2011) and adapted for the early Aptian according to Masse and Fenerci-Masse(2011); b. Palaeogeographical map focused on the Vivarais area with the described sections indicated by stars and white frames with the locality names. (For interpretation of the refer-ences to colour in this figure legend, the reader is referred to the web version of this article.)

103A. Pictet et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 418 (2015) 101–125

3. Methods

Aptian sediments which outcrop on the Languedoc platform wereinvestigated by traditional fieldwork consisting of cartography, detailedlogging, macroscopical sedimentological and palaeontological descrip-tions, and sampling of key sections. The sections were analysed for

Fig. 3. Stratigraphic cross section of the Barremian Aptian platform from Languedoc showing thBarremian early Aptian, and its drowning during early Aptian. Lateral variations of facies (e.g. UD3 are represented.

their microfacies (thin sections), sequence stratigraphy, sedimentology,and ammonite biostratigraphy. A particular aspect is the documentationof depositional geometries, discontinuity surfaces and their large-scalecorrelation.

All samples were sawn to avoid altered parts and calcites veins, andmilled with an agate crusher. They were systematically analysed for

e installation of the platform during the early Barremian, its progradation during the latergonian Formation to Lafarge Formation) and the threemain regional discontinuities D1 to


their geochemistry (stable carbon and oxygen isotopes, total phospho-rus content) and mineralogy (bulk rock).

The microfacies classification used here to describe the eustatic var-iation as regressive and transgressive cycles are based on the classifica-tion by Arnaud-Vanneau (1980, 2005). It comprises 11 microfaciestypes ranging from F0 to F11 along the rimmed-platform transectgoing from the basin to the beach. Microfacies types higher than F9are not recognized in the studied sections. An additional microfaciestype – FT (transgressive facies) – is used to define transgressive surfacesaccording to Blanc-Alétru (1995).

Ammonites stratigraphy is based on the zonal schemeof the Tethyanregion proposed by the 4th and the 5th International Meeting of theIUGS Lower Cretaceous “Kilian Group” in Reboulet et al. (2011, 2014),and in addition on the contributions by Ropolo et al. (2006, 2008b) onthe stratotype from La Bédoule. The ammonites were determined ac-cording to the criteria of Casey (1959, 1960, 1961b, 1962, 1980),Dutour (2005), Ropolo et al. (2006, 2008 a–b), Moreno-Bedmar et al.(2009, 2010, 2012a), and Moreno-Bedmar (2010).

Stable carbon and oxygen isotope analyses on aliquots of powderedbulk-rock rock sampleswere performed using a Thermo Fisher Scientif-ic Gas Bench II carbonate preparation device connected to a Delta PlusXL isotope ratio mass spectrometer. The CO2 extraction was done by re-action with anhydrous phosphoric acid at 70 °C. The stable carbon andoxygen isotope ratios are reported in the delta (δ) notation as the permil (‰) deviation relative to the Vienna Pee Dee belemnite standard(VPDB). The standardization of the δ13C and δ18O values relative to theinternational VPDB scale was done by calibrating the reference gasesand working with IAEA standards. Analytical uncertainty (2 sigma),monitored by replicate analyses of the international calcite standardNBS-19 and the Carrara Marble laboratory standards was not greaterthan ±0.1‰ for δ13C and ±0.2‰ for δ18O.

Total phosphorus (P) contentwasmeasured on powdered bulk-rocksamples treated according to the ascorbic acid method of Eaton et al.(1995). 100 mg of powdered sample was treated with 0.5 ml MgNO3,then placed in the oven to 100 °C for a half hour, and then to 500 °C inanother oven for two hours and a half. After cooling, 10 ml 1 M HCLwas added. The samples were then passed to the stirrer for 16 h. Afterthat, the samples were filtered. 0.3ml of each sample was subsequentlyplaced in an analytical tube. 2.72 ml of ultrapure water was added. Sixstandards (1 μM, 2.5 μM, 5 μM, 10 μM, 15 μMand 20 μM)were preparedusing the same methodology. 0.1 ml of mixing reagent (SEDEX), and0.1 ml of ascorbic acid were added to each sample and standard. Thetotal phosphorus content was measured on a Perking Elmer UV/VisSpectrophotometer Lambda 10. The tubes were analysed at a wave-length of 810 nm, starting with the blank, then the samples, and finallythe standards.

The bulk-rock mineralogy was analysed by X-ray diffraction on anARL Thermo X'tra based on procedures described by Adatte et al.(1996). This method is used for the semi-quantification of the whole-rockmineralogy, obtained byX-ray diffraction patterns of randompow-der samples using external standards with a precision of 5–10% forphyllosilicates and 5% for grain minerals. We determined a detritalindex (DI), calculated by dividing the sum of quartz, phyllosilicate,K-feldspar, and Na-plagioclase contents by calcite, to observe changesin detrital influx (e.g., Adatte et al., 2002; Mort et al., 2008;Westermann et al., 2010; Bomou et al., 2013). Lower detrital indexvalues correspond to less delivery of terrigenousmaterial from continen-tal sources and/or increased dilution due to greater carbonate input.

4. Results

4.1. Lithology and microfacies

Six sectionswere logged and sampled on a centimetre tometre scalefor geochemical, mineralogical and microfacies analyses. Macrofaunaincluding oysters, other bivalves, gastropods, serpulids, sponges,

echinoderms, nautilids and ammonites were collected bed-by-bed forpalaeoecological reconstructions and biostratigraphic age control. Sec-tions are described here from more proximal to more distal parts ofthe platform along a transect across the Languedoc platform, and illus-trated in Fig. 4, together with major discontinuities, indicated on thelogs by full lines numbered D1 to D3. The occurrence and stratigraphicdistribution of ammonites is reported on the right side of the logs,where biozone or subzone boundaries are indicated by dotted lines. Asequential interpretation is given on the left side of the logs, wherekey surfaces (Vail et al., 1987) are numbered and connected as sequenceboundaries (SB) by full lines, transgressive surfaces (TS) by dash–dotlines, and maximum flooding surfaces (MFS) by dashed lines.Parasequences are also reported on the left side of the logs, togetherwith parasequence boundaries (PSB), and maximum flooding surfaces(PMFS). The sections will be described more in detail in a future publi-cation dedicated to the formal definition of the new lithostratigraphicunits (Fig. 3).

4.1.1. Michelet sectionTheMichelet section is situated between the Michelet Farm and the

small Cessas hamlet, located in the Ibie Valley, 5 km to the north ofVallon-pont-d'Arc. It was described for the first time by Duée andPaquet (1960), and later by Busnardo et al. (1977). This locality repre-sents the most internal platform outcrop considered here, underlinedby the presence of rudist communities in the Urgonian Formation,which is abruptly overlain by the Chabert and Frayol Formations.

The Michelet section (Fig. 4) starts with a rudist limestone (N10 m;only the last metre is represented on the lithological log in Fig. 4;wackestone: microfacies F8 to F9) forming the upper part of the upperUrgonian Member (see Arnaud and Arnaud-Vanneau (1990) for thedefinition of the Urgonian Formation and its members), whichends with a karstified surface (Fig. 5a) called Discontinuity 1 (D1).This surface is well exposed and contains the rudists Agriopleura andMonopleura, in life position, which are completely dissolved (Fig. 5b).Their internal moulds and other cavities are filled in by reddishmicrobreccia (Fig. 5c), yellowmicrite, and glauconitic sand. The surfaceshows also abundant bioperforations and is covered by a ferruginousand phosphatic crust, which corresponds to the base of the followingformation. The 1.75 to 6 m thick Chabert Formation, is composed of alowermarly subunit (VioletteMember); a middlemore calcareous sub-unit (Rocherenard Member); and an upper glauconitic limestone bed(Picourel Member). The Violette Member starts with a limestone bed(0.1 to 1 m thick; packstone: microfacies FT), gradually passing into asandy glauconitic marlstone (0.3 to 1.5 m; microfacies F1 to F0),which contains siliceous sponges in the lower part and planktonic fora-minifera in the upper part. The Rocherenard Member starts with a veryirregular, nodular limestone bed, rich in bivalves and ammonites(0.15m; packstone:microfacies F3), which is topped by a sandy glauco-nitic marlstone (0.3 to 2 m; microfacies F1 to F3). A yellowmarly sand-stone (0.5 to 1 m;microfacies F2 to F3) follows, which ends by a poorlyvisible discontinuity D2. The section continues with the Picourel Mem-ber consisting of a glauconitic limestone bed (1 m; microfacies F4),which is topped by the discontinuity D3, representing an erosional sur-face. Bioclasts and fossils inside this bed are recrystallized in drusicsparite. The uppermost unit examined in this section, the Frayol Forma-tion, overlays the eroded bed, and is composed of an approximately 1mthick, glauconite-rich, marly sandstone bed (microfacies FT). This sand-stone bed includes at its base a conglomerate, which contains numerousreworked and partially phosphatized fossils including the belemniteNeohibolites aptiensis.

4.1.2. Mezelet sectionTheMezelet outcrop is located on the northern bank of the Ardèche,

at the entrance of the gorge, downstream of Vallon-Pont-d'Arc. The sec-tionwas first described by Clavel et al. (2013). The outcrop is affected byseveral faults and landslides cutting the section into several

Fig. 4. Transect across the Languedoc platform from the internal to external part with, on the left side of the sections, the sequences, the sequence stratigraphic interpretations, and one-metre scales. Major discontinuities are indicated by full lines onthe logs and numbered as D1 to D3. The occurrence and stratigraphic distribution of ammonites is reported on the right side of the logs, and boundaries between biozones or subzones are indicated by dotted lines. Red ammonites are ammonitescollected by Clavel et al. (2013), and green ones by Sornay (1962). A sequence-stratigraphic interpretation is also given on the left side of the logswith sequence boundaries (SB) in full lines, transgressive surfaces (TS) in dash–dot lines, andmaximumflooding surfaces (MFS) in dashed lines. In addition, parasequences are also indicated on the left side, including their parasequence surface boundaries (PSB), andmaximum flooding surfaces (PMFS). (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of this article.)

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Fig. 6. The top interval of the upper UrgonianMember as exposed in the outcrop of Mezelet. The 2–3m thick interval, below thewhite dashed line is composed of a packstone/grainstone(microfacies F8), comprising large rudists (Requienia and Toucasia). The uppermost 1.5 m, above the dashed line is composed of a rudist wackestone including the rudists Agriopleura andMonopleura in life position (microfacies F9). The top of the Urgonian limestone is eroded (discontinuity D1), as indicated by the full line. This surface shows three different generations ofinfills in epikarts, visible on the slabbed surface of a sample from the discontinuity (left box near the top of the photo). Thefirst infill is a palustrine to continentalmicrit including gypsum,spores, pollen, and rhizoliths (n°1). The second infill consists of a reddishmicrobreccia with occasional root structures (n°2). The third infilling is composed of marine bioclastic limestoneormore commonly of glauconitic sandy andmarly limestone from the overlaying Chabert Formation (n°4), well visible on the photo, on top of discontinuity D1. The uppermost 3m of theUrgonian limestone are bioturbated and the burrows (likely Thalassinoides) are infilled by glauconitic sand as shown in the two boxes on the right side of the photo. (For interpretation ofthe references to colour in this figure legend, the reader is referred to the web version of this article.)


compartments. The section begins at the first corner of the departmen-tal road 290 by the upper Urgonian Member and continues along thefreshly rebuilt path up the Mezelet hill, where the Chabert Formationis exposed.

The Mezelet section (Fig. 4) starts with a compact grey rudist lime-stone of the upper Urgonian Member (3 m; packstone/grainstone;microfacies F8), comprising large rudists (Requienia and Toucasia),which is topped by a rudist wackestone including the rudistsAgriopleura and Monopleura in life position (above the dashed line;1.5 m;microfacies F9). The top of the Urgonian presents a discontinuityD1, which is marked by corrosion and karstification (Fig. 6), and in-cludes cavities filled with various sediment types (Fig. 6): voidsresulting from the dissolution of the limestonematrix and included fos-sils were the subject of at least three successive sediment infills, com-posed of (1) reddish microbreccia (Fig. 5c); (2) micrite with rhizoliths(Fig. 5d–e), gypsum (Fig. 5f), and spores and pollen (Fig. 5g);(3) bioclastic grainstone with miliolids, or (4) glauconitic sand(Fig. 5h–i). The Urgonian top surface also shows numerous burrowsand bioperforations (Fig. 5h) and is covered by ferruginous and phos-phatic crusts (Fig. 5i) forming the base of the Violette Member (ChabertFormation). The bored surface and its associated crust are overlain by aglauconitic marlstone (4 m thick, packstone; microfacies F1 to F3),which starts with a basal sandy nodular limestone bed (0.3 m thick;microfacies FT). A small group of crinoidal limestone beds (0.3 m;

Fig. 5. a.Discontinuity D1 separating the upper UrgonianMember from the Chabert Formation,in live position are completely dissolved and filled in by a reddish microbreccia, yellow micriteyellowmicrite with ostracodes, spores and pollens. e. Rhizolith in Urgonian limestone, filled bycontaining numerous spores and pollen, indicated bywhite arrows.h. Bioperforation in theUrgthic foraminifera. i. Phosphatic crust between the Urgonian limestone and the glauconitic sand.the web version of this article.)

microfacies F3 to F4; lower part of the RocherenardMember) is interca-lated in themiddle of thismarl. The top of themarl gradually passes intoa very heterogeneous echinodermal and bryozoan-rich rudstone (2 m;microfacies F4 to F5; upper part of the Rocherenard Member).

4.1.3. Picourel sectionThe Picourel section is located in the extreme south of the Ardèche,

near the Gard department. The outcrop is situated between the twobranches of the bifurcation of the roads D217 and N579 in the directionof Labastide-de-Virac and Vagnas from Vallon-Pont-d'Arc. The sectionwas first described by Clavel et al. (2013).

The Picourel section (Fig. 4) starts with a cross-stratified bioclasticlimestone (Fig. 7a), which represents the upper part of the upperUrgonianMember (N4 m; the last metre is represented on the litholog-ical log in Fig. 4;microfacies F5), andwhich sharply ends up by anundu-lating surface.

This discontinuity surface (D1) is surmounted by 19.5 m of yellowmarl and limestone composing the Chabert Formation. The VioletteMember (11 m; microfacies F0 to F1) consists of a blue–grey marlstoneand more calcareous sandy beds, which passes progressively through aseries of intercalated nodular beds (microfacies F2 to F3), into thecrinoidal limestone of the Rocherenard Member (8.5 m; microfaciesF4). This crinoidal limestone is topped by a discontinuity surface (D2),which is irregular and bioturbated, and which is covered by nodules of

in theMichelet section.b. Closeup of the discontinuity D1, which is karstified. Rudist shells, and glauconitic sand. c. Reddish microbreccia in a karstic fissure. d. Rhizoliths infilled bysparite. f.Micrite with gypsum, indicated bywhite arrows. g. Closeup of the yellowmicriteonian limestone (indicated by a dashed red line), filled by glauconitic sand containing ben-(For interpretation of the references to colour in this figure legend, the reader is referred to

Fig. 8. Encrusting organisms on ammonites from the phosphatic conglomerate at the base of the Frayol Formation a. Oysters and serpulids. b. Serpulids. c. Lithocodium-like fossils.


the subjacent lithology. This discontinuity is overlain by sediments ofthe Picourel Member, which are composed of decimetrical nodular,glauconite-rich and phosphatic sandy limestone and marl beds(1.5 m; microfacies FT). This unit delivered a phosphatized ammonitefauna, in addition to nautilids, bivalves, and sea urchins. The PicourelMember ends by a discontinuity (D3), and is covered by black marl(12.5 m; microfacies F2 to F3), which is part of the Frayol Formation.

4.1.4. Bourg-St.-Andéol sectionThe Chabert Formation is widely exposed along the streams around

Bourg-St-Andéol allowing to compile a complete synthetic section(Fig. 4). The presence of Aptian marl to the west and north of Bourg-Saint-Andéol was already indicated by Carez (1883), Roman (1950),and Pascal et al. (1989).

The Urgonian Formation outcrops in the Font Beaume quarry, whereit is composed of cross-stratified white oo-biosparite (N20 m; only thelast metre is represented on the lithological log in Fig. 4; microfaciesF5 to F6), topped by an irregular discontinuity surface (D1).

On top of the Urgonian Formation follows the marly-calcareousChabert Formation (30 m), which starts with the Violette Member(13 m; Pictet et al., 2009) composed of blue marl (microfacies F0 toF2) followed by alternating limestone–marl beds (microfacies F3 toF4). One of these beds (see Fig. 4, at +7.6 m) includes a bumpy andhighly bioturbated surface, containing numerous serpulids, which isoverlain by sediments rich in echinoids, bivalves, shark teeth, andlarge ammonites (Fig. 7b). The succession continues with the crinoidallimestone composing the Rocherenard Member (15.5 m; microfaciesF4), which are overlain by black marl of the Frayol Formation (5 m;microfacies F0 to F3).

4.1.5. Chabert sectionThe Chabert Formation outcrops in continuity along and near the

road ascending to the Chabert farm. The presence of lower Aptian sedi-ments north of Saint-Alban was already pointed out by Sornay (1958,1960). The section was re-examined by Contensuzas (1980), Busnardoand Clavel in Pascal et al. (1989), and Clavel et al. (2013).

The section (Fig. 4) starts with a hemipelagic limestone from theLafarge Formation (N30m; only the last 5m are represented on the lith-ological log; wackestone;microfacies F1), a lateral, deeper-water equiv-alent of the Urgonian Formation, which is well known in the L'Hommed'Arme quarry (Kilian and Reboul, 1915). The uppermost bed (0.2 m;wackestone; microfacies F1) terminates with an erosional surface D1,which is highly bioturbated. On top of this surface (Fig. 7c) follows thethick marly Violette Member (27.2 m) starting by a thinning-upwardmarl–limestone alternation (2 m; microfacies F1 to F3; Fig. 7d), whichprogressively evolves into a monotonous grey clay and marlstone rich

Fig. 7. a. Cross-stratified bioclastic limestone from the upper UrgonianMember, Picourel sectionChabert Formation,Malaubert section. cHighly bioturbatedfirmground at the top of the Lafargeof the Chabert Formation, Chabert section. e.Monotonous grey clay and marlstone rich in carbsection. f. Thickening-upward crinoidal limestone bars from the upper part of the Chabert Fofrom theupper part of theChabert Formation (HST‴), Pélican section.h.Phosphatic conglomeratei. Blackmarl from the Frayol Formation, along the Frayol river, Pélican section. (For interpretationthis article.)

in carbonate nodules (25.2 m; microfacies F0 to F2; Fig. 7e). The marlgradually passes into the crinoidal limestone of the Rocherenard Mem-ber (28.5 m thick) which is composed by three important, thickening-upward, crinoidal limestone bars (7, 14, and 7.5 m; packstone;microfacies F2 to F4; Fig. 7f). The upper one is separated from the twoothers by a thick marlstone interval (7.5 m; microfacies F0 to F1). TheChabert Formation ends with an erosional surface (D2-3).

The amalgamated discontinuity D2-3 is covered by blackmarl of theFrayol Formation (3m visible; microfacies F0) which starts with a glau-conite and phosphatic nodular conglomerate (0.2 m; microfacies FT)containing numerous phosphatized, fragmented fossils.

4.1.6. Pélican sectionLower Aptian sediments are well developed in the region of Le Teil.

They were described by Sornay (1967) from the southwest of the city,close to the Hotel pass, near the Pélican area. He observed the whitehemipelagic limestone of the Lafarge Formation unconformably over-lain by the Chabert Formation. Sornay (1967) described from the north-east of the Hotel pass also a thin green sandy and highly fossiliferous,calcareous level, separating the Chabert Formation from the overlyingblack marl of the Frayol Formation, which he attributed to the earlylate Aptian.More generally, a broader zone of Aptian sediments, studiedby Arnaudon (1936) and Contensuzas (1980), crop out from Pélican tothe west and to Mélas to the north, as part of the northern flanc of alarge anticline dipping underneath Le Teil (Fig. 4).

The hemipelagic limestone of the Lafarge Formation (less than200 m thick) forms a between 2.3 and 5 km long zone immediatelysouth of the Pélican. The top of this limestone is composed of an alterna-tion of massive, thickening-upward, limestone and marly interbeds(wackestone; microfacies F1). The last bed terminates by a highly bio-turbated bumpy terminal surface (D1). This firmground D1 is coveredby the Chabert Formation (64 m thick), which outcrops in the 200 to400 m wide area separating the Lafarge Formation from the Pélicanroad. The lower part of the Chabert Formation, is represented by athickmarly lower subunit (31m), composedof greymarlstone (VioletteMember; microfacies F0 to F1) containing planktonic foraminifera andpyritized ammonites. A gradual transition leads to the RocherenardMember (34 m thick), which is composed of three thickening-upwardcrinoidal limestone bars (6, 3.5, and 11.5 m; microfacies F1 to F4).They are separated by two marly intervals (4.5, and 7.5 m; microfaciesF0 to F3). The top of the uppermost bar (Fig. 7g), visible on the side ofthe small Pélican bridge, endswith an erosional surface (D2-3). This dis-continuity D2-3 is overlain by the black marl of the Frayol Formationwhich starts by a phosphatic conglomerate (0.2 m; microfacies FT;Fig. 7h). The conglomerate contains numerous phosphate clasts andfossils, encrusted by oysters (Fig. 8a), serpulids (Fig. 8a–b), and by

. b. Crinoidal limestone with large ammonites from themarly unit in the lower part of theFormation, Chabert section.d. Thinning-upwardmarl–limestone alternation from the baseonate nodules from the Violette Member (lower part of the Chabert Formation), Chabertrmation (HST′ and HST″), Chabert section. g. Thickening-upward crinoidal limestone barfrom the base of the Frayol Formation, containingnumerous phosphatized clasts and fossils.of the references to colour in this figure legend, the reader is referred to the web version of


Lithocodium-like organisms (Fig. 8c). The conglomerate is capped by athin brachiopod-rich layer and covered by black marl of the Frayol For-mation (only the first 3 m are logged; microfacies F0; Fig. 7i), whichcomposes the hills immediately to the north of this road. The belemniteNeohibolites is very abundant in this marl.

4.2. Palaeontology and age model

Fossils including foraminifera, serpulids, bivalves, echinoids, cepha-lopods, and vertebrate remainswere collected bed-by-bed. Several hun-dreds of ammonites, including 18 ammonite genera and 36 species,were identified in the sections studied here.

The association of the youngest representatives of the genusProcheloniceras with representatives of Deshayesites weissi withinthe top interval of the Lafarge Formation (Kilian and Reboul, 1915),allows to attribute the top of the Lafarge Formation and its neriticequivalent, the upper Urgonian Member, to the Deshayesites forbesiammonite Zone (Ropolo et al., 2008b). The lower part of the VioletteMember (Chabert Formation) also delivered Procheloniceras (Fig. 9a),which indicates the D. forbesi Zone (Ropolo et al., 2006, 2008b;Moreno-Bedmar, 2007; Moreno-Bedmar et al., 2010). The upper partof the Violette Member and the lower half of the Rocherenard Member(Chabert Formation) are attributed to the Roloboceras hambrovi Sub-zone, based on the presence of R. hambrovi (Fig. 9b–c). The uppermostpart of the Rocherenard Member dates from the Deshayesites deshayesiZone (based on the carbon-isotope record: the lower part of the C7 seg-ment, see below), and falls largely within the Deshayesites grandis Sub-zone due to the presence of D. grandis (Fig. 9d). The Picourel Memberforming the uppermost part of the Chabert Formation is dated fromthe D. grandis to D. dufrenoyi Subzone on the presence of Chelonicerascrassum (Fig. 9e), D. grandis (Fig. 9f, g), Cheloniceras minimum (Fig. 9i)Dufrenoyia furcata (Fig. 9j), Dufrenoyia praedufrenoyi (Fig. 9k),Dufrenoyia dufrenoyi (Fig. 9l), and Cheloniceras meyendorffi (Fig. 9h).The lag deposit at the base of the Frayol Formation includes a mixof fragmented ammonites reworked from the Picourel Member, suchas Cheloniceras (Fig. 9h, i), Epicheloniceras (Fig. 9m), Deshayesites(Fig. 9g) and Dufrenoyia (Fig. 9j, k, l), all indicating the presence of apolyzonal conglomerate ranging from the upper D. grandis Subzone tothe upper D. dufrenoyi Subzone. The formation of this polyzonal con-glomerate is dated from the upperD. dufrenoyi Subzone by the discoveryof the non-phosphatized index fossil together with primitiveEpicheloniceras forms (Fig. 9m). The contemporaneous existence of thelast Dufrenoyiawith the first representatives of Epicheloniceras is an im-portant observation already pointed out by Atrops and Dutour (2002),Dauphin (2002), and Moreno-Bedmar et al. (2013). The remainder ofthe Frayol Formation is reported to the Epicheloniceras martini Zone bythe presence of typical representatives of the index species (Sornay,1962; Clavel et al., 2013).

Fig. 9. Examples of the ammonites used for dating: a.— Procheloniceras sp. SPATH, 1923, coll.marly subunit, Michelet [+1.2m], early Aptian,D. forbesi Zone, 12.65 cm. b.— Roloboceras hambsubunit, Chabert, early Aptian,D. forbesi Zone, R. hambrovi Subzone, 17.6 cm. c.— Roloboceras halimestone subunit (hst′), Bourg-St.-Andéol [+13 m], early Aptian, D. forbesi Zone, R. hambrovi Sences de Lyon FSL 89019, from theupper part of the crinoidal limestone subunit, Chabert, early Acoll. Pictet MHNGGEPI 82462, from the Picourel Member, Michelet [+4.6m], early Aptian,D. dMHNG GEPI 82463, from the Picourel Member, Michelet [+4.6 m], early Aptian, D. deshayesi ZGEPI 82464, from the phosphatic conglomerate, base of the Frayol Formation, Pélican [+63.8 m8.14 cm. h.— Chelonicerasmeyendorffi (d'Orbigny, 1845), coll. Pictet MHNG GEPI 82465, from thD. furcata Zone, D. dufrenoyi Subzone, reworked in the late D. furcata Zone, 2.28 cm. i.— Chelonierate, base of the Frayol Formation, Pélican [+63.8m], early Aptian,D. deshayesi Zone,D. grandi1836), coll. Pictet MHNGGEPI 82467, from the phosphatic conglomerate, base of the Frayol FormlateD. furcataZone, 3.17 cm.k.—Dufrenoyia praedufrenoyiCASEY, 1961, coll. PictetMHNGGEPIearly Aptian, D. furcata Zone, D. dufrenoyi Subzone, D. praedufrenoyi Horizon, reworked in the laGEPI 82469, from the phosphatic conglomerate, base of the Frayol Formation, Pélican [+63.8 m4.42 cm.m.— early representative of EpichelonicerasCASEY, 1954, coll. PictetMHNGGEPI 82470Aptian, D. furcata Zone, D. dufrenoyi Subzone, reworked into the late D. furcata Zone, 2.73 cm.

4.3. Bulk-rock mineralogy

A total of 56 samples from three sections (Michelet, Bourg-St.-Andéol,and Chabert) were analysed along a proximal–distal transect across theplatform (Fig. 10). Calcite (47.34 to 90.82%), quartz (2.66 to 27.94%),phyllosilicates (0 to 28.34%), and non-quantified minerals (0.49 to19.34%), are dominant. K-feldspar, plagioclase, and iron compounds arealso present, but in smaller quantities (0 to 6.38%). Calcite content de-creases strongly from the Urgonian to the Chabert Formations and fromthe Chabert to the Frayol Formations, which confirms the field observa-tions. The detrital index (DI) allows the recognition of seven peaks,which are used as correlation tool (dotted lines) and in the sequencestratigraphic interpretations.

Within the Chabert Formation, the calcite content is quite stable acrossthe sections except where detrital index (DI) values are higher (Fig. 10),corresponding to higher phyllosilicate and quartz contents. Phyllosilicatesare abundant in the marl from the Violette Member and inside thecrinoidal limestone from the Rocherenard Member, and show a progres-sive depletion towards the top of the Chabert Formation (Fig. 10). Thefirst and well-defined maximum (DI 1) in the detrital index is observedinside the Violette Member at +9.8 m in the Chabert section, andat +1.4 m in the Michelet section. A second well-expressed maximum(DI 2) is detected at +17.6 m (Chabert), at +8.2 m (Bourg), andat +1.6 m (Michelet). A third maximum (DI 3) is observed in theRocherenard Member at +30 m (Chabert), and at +12 m (Bourg), and– less well expressed – also at +1.5 m (Michelet). A fourth maximum(DI 4) is situated inside the important marly interval between the secondand the third crinoidal limestone bar, and is discernible at +36.7 m(Chabert), at +18.5 m (Bourg), and at +3 m (Michelet). Within theupper part (third bar) of the Rocherenard Member, a further maximum(DI 5) is expressed at +45.7 m (Chabert; GC AP120), at +24.9 m(Bourg; GC AP60), and at +3.4 m (Michelet, GC AP12). A penultimatemaximum (DI 6) near the boundary of the Rocherenard and PicourelMembers, is visible at +28.5 m in the Bourg section (GC AP53),at +4.2 m in the Michelet section, while it is amalgamated with the fol-lowing maximum DI 7 at +56 m in the Chabert section (GC AP130), ontop of the Chabert Formation. Maximum DI 7 is also visible in the Bourgsection (GC AP50) at +30 m, and in the Michelet section at +5.1 m(GC AP22), which belongs to the base of the Frayol Formation.

Quartz contents, which are the main component of the DI, are anti-correlated with calcite contents (Fig. 10), and are higher in the crinoidallimestone (Rocherenard Member) than in the marl (Violette Member).K-feldspar, plagioclase, and iron compounds show no correlation orsimilar distribution between the analysed sections.

4.4. Geochemistry

A total of 129 bulk-rock samples were analysed from the Michelet,Picourel, Bourg-St-Andéol, and Chabert sections representing a

Pictet Muséum d'Histoire Naturelle de Genève (MHNG) GEPI 82460, from the base of therovi (FORBES, 1845), coll. SornayMHNParis, from the lower part of the crinoidal limestonembrovi (FORBES, 1845), coll. PictetMHNGGEPI 82461, from the lower part of the crinoidalubzone, 20.6 cm. d.— Deshayesites cf. grandis SPATH, 1930, coll. Busnardo Faculté des Sci-ptian,D. deshayesi Zone,D. grandis Subzone, 14 cm. e.— Cheloniceras crassum SPATH, 1930,eshayesi Zone, D. grandis Subzone, 6.1 cm. f.— Deshayesites grandis SPATH, 1930, coll. Pictetone, D. grandis Subzone, 6.58 cm. g.— Deshayesites grandis SPATH, 1930, coll. Pictet MHNG], early Aptian, D. deshayesi Zone, D. grandis Subzone, reworked in the late D. furcata Zone,e phosphatic conglomerate, base of the Frayol Formation, Pélican [+63.8m], early Aptian,ceras minimum CASEY, 1961, coll. Pictet MHNG GEPI 82466, from the phosphatic conglom-s Subzone, reworked in the lateD. furcata Zone, 3.01 cm. j.—Dufrenoyia furcata (SOWERBY,ation, Pélican [+63.8m], early Aptian,D. furcata Zone,D. fucata Subzone, reworked in the

82468, from the phosphatic conglomerate, base of the Frayol Formation, Pélican [+63.8m],te D. furcata Zone, 3.76 cm. l.— Dufrenoyia dufrenoyi (d'Orbigny, 1840), coll. Pictet MHNG], early Aptian, D. furcata Zone, D. dufrenoyi Subzone, reworked in the late D. furcata Zone,, from the phosphatic conglomerate, base of the Frayol Formation, Pélican [+63.8m], early

Fig. 10. Correlation of detrital index (DI) values, calcite and phyllosilicate contents along a transect from the internal to external Languedoc platform. Seven major DI peaks are reported for the A2, A2', and the base of the A3 sequences. Sequencestratigraphic interpretations are indicated on the left side of each lithological log.



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Fig. 11. Correlation of δ13C and δ18O records along a transect from the internal to external Languedoc platformwith the δ13C record. Segments C2 to C7 according to Menegatti et al. (1998) are reported on the δ13C curves and calibrated to ammonitezones and sub-zones from Fig. 4.



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Fig. 12. Transect from the internal to external Languedoc platform with the total phosphorus content record. Seven phosphorus peaks or intervals (P1 to P7) are highlighted and used for: i) correlations; ii) for sedimentological analyses, indicatingcondensation and reworking mainly associated with the formation of the discontinuities; iii) and for sequential stratigraphic interpretations, indicating the different TS directly above the sequence boundaries.



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Fig. 13. Model of formation of microkarsts on top of the upper Urgonian Member showing three phases of infill.


proximal–distal transect across the platform. The geochemical recordsare calibrated by ammonite biostratigraphy (Moullade et al., 1998;Moreno-Bedmar et al., 2009, 2012a) and add themselves informationon the age of the sections, in particular for the D. deshayesi Zone. Theammonite biostratigraphy used here allows for a new age model forthe negative δ13C excursion, whichmarks the onset of the Selli episode.

4.4.1. Carbon and oxygen-isotope stratigraphyThe measured δ13C values vary between 0.0 and 3.6‰ (Fig. 11). The

top interval of the Urgonian Formation exhibits values around 2‰. Inthe dilated and more complete sections of the Chabert Formation at

Bourg-St-Andéol and Chabert, the lower part of the Violette Membershows a progressive decrease from ~2‰ to ~0‰ δ13C. The upper part ofthe Violette Member documents a trend towards more positive δ13Cvalues increasing from ~0‰ to ~1.4‰. The positive gradient steepens inthe lower part of the RocherenardMember, coincidingwith a sudden de-crease in carbonate contents. The δ13C record reaches values around~2.5‰ at the top of the Rocherenard Member. The thicker marly intervalseparating the second from the third crinoidal bar shows a rather stableδ13C trend between 2.4 and 2.8‰, which is followed by an increase upto 3.3‰. The δ13C record reaches a maximum in the third crinoidal barof around ~3.2‰, before decreasing to 1.3‰ in the Picourel Member.


The δ18O values are very variable from one section to another andrange between−3.6 and−1.7‰ formost of the sections, and are as neg-ative as −6.4‰ in the Picourel Member. For the uppermost part of theUrgonian Formation and for the lower part of the Violette Member, theδ18O record shows relatively constant values between −3.0 and−2.3‰. In the higher part of the VioletteMember, the δ18O values rapidlybecome more positive (−1.7‰) and decrease progressively upwards toreach values around −4‰. The Rocherenard Member shows stableδ18O values around−3.2‰. At the base of the thicker marly interval sep-arating the second from the third crinoidal bar, the δ18O values start to in-crease again until the middle of the marl. In the upper part of the thickermarly interval and through the third crinoidal bar, the δ18O record be-comes very variable with values between−4 and−2‰. In the PicourelMember, the values increase from−3.2 to−1.6‰.

At the base of the Bourg section (Malaubert outcrop sampled in theRhône river), both carbon and oxygen-isotope records showmore pos-itive values than those of the other sections (+2.5‰ for δ13C and +1%for δ18O).

4.4.2. Phosphorus contentsTotal phosphorus contents display background levels between 100

and 200 ppm (Fig. 12). Erosional surfaces and hardgrounds are markedby very distinct peaks (P1 to P7) in phosphorus contents between 1200and 15000 ppm. These maxima are used as a correlation tool and in theinterpretation of the sequence stratigraphy. These peaks are more pro-nounced in distal sections (e.g., Chabert, Pélican until 15000 ppm) com-pared to proximal sections (e.g., Michelet, max. 1295 ppm).

A first major peak (P1) is situated above the limit betweenthe Urgonian and Chabert Formations, inside the basal transgressivemarl–limestone alternation or basal bed from the lowermost VioletteMember, with values between 370 (Michelet) and 1700 ppm (Pélican).A second important level (P6) is located near the top of the Chabert For-mation between the Rocherenard and the Picourel Members. A furtherone (P7) is located at the top of the Picourel Member. The phosphaticconglomerate at the base of the Frayol Formation corresponds to theamalgamation of P6 and P7. Some smaller peakswithin the Chabert For-mation reach values of 250 to 320 ppm and are used for correlation(Fig. 12). Four intervals of correlation are used inside the Chabert For-mation: (P2) a horizon within the Violette Member dated the base ofthe R. hambrovi Subzone shows a maximal value around 300 ppm;(P3) a second, double peak between 100 and 200 ppm at the base ofthe RocherenardMember; (P4) a third consists of a progressive increasefrom 100 to 200–250 ppm in themarly interval intercalated in themid-dle of the RocherenardMember; and (P5) an increase of variable inten-sity ranging from50–100 ppm to 100–200ppmwithin the upper part ofthe Rocherenard Member.

5. Discussion

5.1. Fauna and depositional environment

The microfacies and facies show a fluctuating evolution throughoutthe sections studied here, with a general trend from an inner-platformto a pelagic setting in two steps. The lithologies and fauna trace threemain depositional environments and fauna associations, which areseparated by three discontinuities (D1 to D3) and related drowningevents.

The first lithology is represented by the Urgonian Formation, whichincludes the products of a photozoan, oligotrophic carbonate factorydominated by a rudist–coral–miliolid–dasycladacea assemblage.

Following the termination of the Urgonian platform and the subse-quent formation of a firm- or hardground (D1), the platform adaptedto a heterozoan environment following a first important transgression,

Fig. 14. Sequence of time frames showing the different depositional phases of the sedimentaVanneau (2005). The main sequence stratigraphic surfaces and system tracts are indicated.

documented by the Chabert Formation. In this environment, a mesotro-phic carbonate-producing community prevailed, composed of crinoids,bryozoans, endobiont bivalves, sea urchins, and ammonites. Foraminif-eral assemblages in thin sections showa distinct decrease in thenumberof species, with low specific diversity and heterogeneity, and anabundance of opportunistic species adapted to higher trophic levels(Bergamin et al., 1999; Frezza et al., 2005), like biseriate foraminiferaand Lenticulina. Nautilids, which are also considered as rather opportu-nistic cephalopods (Jereb and Roper, 2005), are equally abundant inthe sediments of the Chabert Formation with the genus Eucymatocerasand Heminautilus. These genera present specialized forms of theexternal platform (Tintant et al., 2001). Ammonites show an importantdiversification of heteromorphic genera, linked to the increasing preysand the expansion of their biotope (Westermann, 1996), correspondingto external platform facies F1 to F4. A rich diversity of large heteromor-phic ammonites developed especially within the distal hemipelagicsetting.

The Rocherenard and Picourel Members terminate each by an ero-sive discontinuity (D2 and D3), on top of which follows the third mainlithology type, sandy and black clayey marl of the Frayol Formation.The remains of coleoid cephalopods are absent in the Chabert Forma-tion, while they become very abundant in the clay and marlstone fromthis deeper-water formation.

5.2. Sequence-stratigraphic interpretation, emersion and drowningunconformities

A sequence-stratigraphic interpretation, based on: i) field observa-tions; ii) the stratigraphic evolution of microfacies providing transgres-sive and regressive trends within the sections (see description of thesections); iii) detrital index (DI) peaks from mineralogical analyses;iv) and phosphorus peaks, allows for the recognition of the third-order shallowing-upward sequences A1 (the upper Urgonian Memberand the Lafarge Formation) and A2, a third condensed sequence A2′(Pictet et al., 2012) for the uppermost lower Aptian, and a shallowing-upward sequence A3 for the early late Aptian. These sequences andtheir systems tracts are precisely dated and correlated by Aptian ammo-nite biostratigraphy (Fig. 4) according to Ropolo et al. (2006, 2008b) andReboulet et al. (2011, 2014). The threemain unconformities (D1, D2 andD3) are recorded, separately or amalgamated, in all studied sections(Fig. 4) and separate the sequences distinguished here.

5.2.1. The termination of the A1 sequence (D. forbesi Zone), upper UrgonianMember

This sequence is dominated by a photozoan rudist–coral carbonatetypical of the Urgonian Formation (Fig. 13, phase 1) or by thehemipelagic carbonate belonging to the Lafarge Formation. Thehighstand systems tract (HST) of the A1 sequence reaches a thicknessof more than 30 m. It terminates by shallowing-upward prograding fa-cies (Fig. 14a) until the emersion of at least the internal platform(Fig. 14b). The distal platform shows a thickening-upward successioncomposed of an alternation of massive, biomicritic limestone andmarly interbeds, which becomes progressively richer in carbonate up-wards, forming a massive limestone unit of a few metres thickness to-wards the top. This systems tract mainly belongs to the D. forbesi Zone(Kilian and Reboul, 1915).

5.2.2. SB A2, Middle early Aptian (upper D. forbesi Zone) drowning event(D1)

An important unconformity D1 is located between the Urgonian andthe Chabert Formations and terminates a thickening-upward succession.This discontinuity is known since Lory (1860) and is placed by Arnaud-Vanneau et al. (1978) in their sequential stratigraphy scheme as Sb A2.

ry units on the Languedoc platform. Microfacies types are defined according to Arnaud-

Fig. 15. a. Photograph from the Michelet section showing the erosive discontinuity D3 between the glauconitic limestone from the Picourel Member (Pic. Mb) and the glauconitic sandymarl from the Frayol Formation.b. Scheme showing the lateral contact between thediscontinuities (corresponding to sequence boundaries). Erosion associatedwith discontinuityD3 (lateD. dufrenoyi Subzone) incised the sedimentary column up to the top interval of the Urgonian Formation, below the discontinuities D2 (upper D. grandis Subzone) and D1 (intra D. forbesiZone).


Sensu Vail et al. (1987), this discontinuity D1 corresponds to a type-1sequence boundary separating the A1 and A2 sequences across theLanguedoc platform and elsewhere along the northern Tethyanmargin.This interpretation is supported by internal platform sections in whichthis surface – well visible in the Michelet (Fig. 5a) and Mezelet (Fig. 6)outcrops of the Ibie Valley – is located on top of pure carbonate sedi-ments and represents a well-developed epikarstic surface (Fig. 5b).The epikarstic pockets are filled in by reddish microbreccia (Fig. 5c),vadose silts and micrites containing ostracods, rhizoliths (Fig. 5d–e),gypsum (Fig. 5f), and numerous spores and pollen (Fig. 5g). The surfaceoriginated in a supratidal environment (Yilmaz and Altimer, 2001,2006; Burla et al., 2008, 2009; Rameil et al., 2010; Najarro et al.,2011a), probably under arid conditions because of the presence ofgypsum, a not very developed karst, and the presence of only sparsesoil and rootmarks (Fig. 13, phase 2). This discontinuity is also recordedas a subaerial surface in the Subalpine Chains (Fouke et al., 1995; Mossand Tucker, 1995, 1996), in the Jura mountains (Charollais et al., 1994;Godet et al., 2010), and in the Helvetic Alps (Föllmi, 2012; Godet, 2013).On the external platform, this discontinuity is registered by afirmground (Fig. 7c) showing numerous Thalassinoides burrows, indi-cating a slow-down or halt in sediment accumulation. In addition to

the evidence for karst development on top of the internal platform,the surface shows numerous borings of bivalves, and is covered byferruginous and phosphatic crusts, which include an open-marinefauna composed of Exogyra aquila and Plicatula placunea. This indicatesa pronounced deepening phase, with the installation of fully marineconditions on top of the epikarst (Fig. 13, phase 3). The deepeningphase is associated with phosphogenesis and marks the drowningof platform carbonates (Schlager, 1981; Föllmi et al., 1994, 2006), alsorecorded in the Swiss Alps by the Rohrbachstein Interval (Linder et al.,2006; Föllmi and Gainon, 2008).

5.2.3. A2 sequence (upper D. forbesi Zone to the lower D. grandis Subzone),Violette and Rocherenard Members (lower andmiddle Chabert Formation)

Following this first drowning episode, production along a carbonateramp took up in a heterozoan mode, as is documented by the mixedsiliciclastic, marl, and crinoidal and bryozoan-rich carbonate of theViolette and Rocherenard Members, which corresponds to sequenceA2. The transgressive systems tract (TST) at the base of sequence A2 is0.1 to 2 m thick. The transgressive surface sensu Vail et al. (1987)(TS2) starts with a reworked marine bioclastic grainstone withmiliolids, or with open-marine glauconitic sandy infills, with

Fig. 16. a.Michelet: δ18O/δ13C cross-plotwith a R square of 0.16 showing low variance except for the last point.b.Bourg-St-Andéol: R square of 0.25with low variance. c.Chabert: very lowvariance with a R square of 0.06 showing the absence of major late diagenetic effects.


bioperforations, and/or a ferruginous crust on top of the hardground(Fig. 13, phase 3; Fig. 14b). The abundance of phosphate and glauconitemarks a first interval of condensation or increased reworking of grains,which is also documented by the presence of the notable phosphoruspeak P1 with values until 1726 ppm (Chabert). The TST itself is com-posed by a bed or a thinning-upward alternation of hemipelagic marland sandy limestone (Fig. 7d), and by marl (Fig. 7e). This intervalshows a deepening-upward trend ranging from microfacies F4 to F0or FT when this subunit is reduced to a single bed. The maximumflooding surface (MFS2) is marked by a blue to grey, clayey interval ofhemipelagic mudstone (microfacies F0; Fig. 14c). Glauconite and phos-phate are rare in this more dilated interval, while the detrital peak DI1allows the precise location of the MFS. This interval enriched in detritalminerals is visible in theMichelet (+1.5m) and Chabert (+9.8m) sec-tions. The associated microfauna shows the appearance of calcispheresand planktonic foraminifera (Hedbergella), while ammonites becomescarcer. The early HST (Fig. 14c) is 0.3 to 26 m thick. The microfaciesshows a shallowing-upward trend. The late HST (Fig. 14d to f) is be-tween 1.35m and 34 m thick, andmarked by an increase in Lenticulina,bryozoans, echinoids and crinoids (microfacies F3 to F4). This intervalincludes three shallowing-upward limestone bars (Fig. 7f and g) orbeds, which are interpreted as parasequences (hst′, hst″, hst‴). Thelower two parasequences (hst′ and hst″) are separated by a thin marlyinterval, which is regarded as a parasequence mfs (PMFS″). A thickermarly interval (Fig. 14e) is intercalated between the middle and upperlimestone bars. This interval corresponds to a further parasequencemfs (PMFS‴) with a return to a deeper hemipelagic to pelagic setting(F1 to F3). The third and uppermost limestone interval (hst‴) consistsof an alternation dominated by an echinodermal packstone (microfaciestype F3 to F4; Fig. 14f). This interval contains higher amounts of glauco-nite and phosphate grains, which indicate condensation and/orreworking by bottom water agitation. Endobiotic fauna is more com-mon, also indicating a slower sedimentation rate.

5.2.4. SB A2′, terminal early Aptian (middle D. grandis Subzone) drowningevent (D2)

A second important discontinuity is located between theRocherenard and the Picourel Members (Fig. 14g), which indicates thetermination of the phase of heterozoan platform sedimentation.

The surface represents a firmground marked by a drowning discon-tinuity showing erosion by intensive bioturbation and/or by bottomcurrents. The presence of a phosphate-rich interval (Picourel Member)on top of this second unconformity indicates a further platform drown-ing episode associated with condensation, phosphogenesis and aslowed-down or halted carbonate production. The discontinuity regis-ters a detrital peak (DI6), which is detected in the Michelet, and Bourgsections, while it is amalgamated with the following maximum DI7 inthe Chabert section. This renewed interruption in carbonate productionconstitutes a secondmajor crisis in the platform ecosystem (Masse and

Fenerci-Masse, 2009, 2011). In a sequence-stratigraphic sense, this dis-continuity D2 is considered as a drowning discontinuity separating thesequences A2 and A2′ (SbA2′). This discontinuity is dated as themiddleD. grandis Subzone and correlates in time with a drowning phase re-corded in the Helvetic Alps by the Plaine Morte Bed (Linder et al.,2006; Föllmi and Gainon, 2008).

5.2.5. A2′ sequence (upper D. grandis Subzone to upper D. dufrenoyiSubzone), Picourel Member

Seqeuence A2′ is represented by the Picourel Member, which in thePicourel section consists of a condensed glauconite-rich and phosphaticmarl–limestone alternation. This unit is framed by two discontinuities(D2 and D3), which are interpreted as sequence boundaries. For thisreason, these sediments are viewed as a new sequence A2′ (Pictetet al., 2012; Fig. 14g) not present in the sequence-stratigraphic schemeof Haq and Shutter (2008) and Haq (2014). This sequence is likely in-complete, as it was eroded during the formation of the overlying discon-tinuity D3 concluding this sequence. In the sections other than thePicourel and Michelet sections, the entire sequence is missing, replacedby a phosphatic conglomerate at the base of the A3 sequence. This newsequence is also distinguishable in Switzerland (Linder et al., 2006), inSpain (Millán et al., 2011), and in Iran (Vincent et al., 2010). Sedimento-logical features like abundant authigenic minerals and a rich endobioticfauna record a reduction in sedimentation rate, allowing the colonisa-tion by numerous bivalves and irregular echinoids, but also the forma-tion and reworking of phosphate and glauconite grains (lobed grains),and phosphatisation of the fossils. Due to the pronounced condensation,TS2′ is detected just above the discontinuity D2 by the important phos-phate peak P6, close to theMFSwhich is also just above the discontinu-ity surface, indicated by the DI6 peak.

5.2.6. SB A3, terminal early Aptian (upper D. dufrenoyi Subzone) drowningevent (D3)

A third major discontinuity (D3) caps the Picourel or RocherenardMembers when the former is missing (Fig. 14h). The discontinuity isrepresented once again by a type-1 sequence boundary sensu Vailet al. (1987), which separates sequences A2′ and A3. In some parts ofthe platform (Michelet and Pélican sections), this discontinuity D3 in-tersects with the underlying D2 discontinuity, leading to the formationof a conglomerate level including fossils reworked from the underlyingsediments. The discontinuity D3 is erosive (Michelet section; Fig. 15a)and may reach as deep down as the Urgonian Formation and cut intoits upper surface in internal areas (Michelet section; Fig. 15b), concen-trating large fossils at the base of the erosive structures, and leading tothe presence of an important angular unconformity, similar to an in-cised valley (Michelet section). A similar type of erosion and the super-position of the upper Aptian sediments directly on the UrgonianFormationwas also observed by Arnaud-Vanneau et al. (1978) in the in-ternal platforms bordering the Vocontian Basin (Bauges, Aravis,

Fig. 17. Correlation of the carbon-isotope curveswith indication of the segments distinguished byMenegatti et al. (1998) and ammonite biostratigraphy between the lithological logs (1mscale bar) from La Bédoule (Bouches-du-Rhône, SE France; Conte, 1975; Renard et al., 2005) and the Chabert sections (Ardèche, SE France). Boundaries between the different segments arecorrelated by dashed lines. The ammonite biozonation is correlated according to Moreno-Bedmar et al. (2009, 2010, 2012a) and to the one proposed by Conte (1975) and applied byBusnardo (1984) and Ropolo et al. (2000, 2006). The main sequence stratigraphic surfaces are reported on the right side of the Chabert section.


northern Vercors, Chartreuse, Vaucluse and southern Var region), whilethey were deposited on top of the A2 sequence (upper Orbitolina beds)inmore distal areas of the platforms near the Vocontian Basin (southernVercors, Diois Dévoluy and Monts du Vaucluse). The geometries of in-cised valleys associated to this discontinuity and the replacement on in-ternal ramps of the Chabert Formation by younger sediments areinterpreted as the result of an important sea-level fall accompanied byan emersion phase on a large part of the ramp near the early/late Aptianboundary (Bover-Arnal et al., 2014). Both themicrite aswell as bivalves,ammonites, and benthic foraminifera in the uppermost bed in proximalsections (Michelet) below the discontinuity are strongly recrystallised

in microsparite or in drusic sparite. The bulk rock shows a negative car-bon and oxygen-isotope shift, which may indicate meteoric fluid circu-lation linked to an emersion phase.

5.2.7. A3 sequence (upper D. dufrenoyi Subzone and E. martini Zone),Frayol Formation

This sequence represents a third major palaeoecological changein the carbonate factorywith the complete disappearance of the carbon-ate beds. Sediment deposition is dominated by black marl (Frayol For-mation). These sediments include a deep open-marine faunasuggesting an important transgression starting near the early/late


Aptian boundary (uppermost D. furcata Zone). This transgression phaseis recorded in other localities of the Tethys like in the Helvetic Alps(Linder et al., 2006; Föllmi et al., 2007; Föllmi and Gainon, 2008),where it induced the formation of the phosphatic Luitere Bed, an equiv-alent of the basal phosphatic conglomerate observed at the base of theFrayol Formation. It was also recorded in other basins like in Spain(Moreno-Bedmar et al., 2012b), Mexico (Moreno-Bedmar et al.,2012b; Bover-Arnal et al., 2014), the United States (e.g., Hill, 1893;Stoyanow, 1949), Colombia (e.g., Riedel, 1938; Etayo-Serna, 1979) andVenezuela (e.g., Renz, 1982; Arnaud et al., 2000). The latest early Aptiantransgression and deepening phase did not allow the carbonate plat-form to return and reinstall for a longer time period (up to the laterAptian Acanthohoplites nolani Zone) on the northern Tethyan margin.The TST starts with the transgressive surface (TS3), which is within aglauconite and quartz-rich level (DI7), and covered by a phosphaticconglomerate, including numerous reworked fossils. The phosphatepeak P7, linked to this phosphatized lag deposit, is also a good indicatorof the TS3. The TS is dated from the upper D. dufrenoyi Subzone. Themaximum flooding surface (MFS3) is placed in the black hemipelagicclay (microfacies F0), just belowmarl–limestone alternations not repre-sented on the lithological logs.

5.3. Carbon-isotope versus biostratigraphy

The δ18O/δ13C cross-plots of the three sections (Fig. 16) show lowvariance with a R square between 0.06 for the hemipelagic sedimentsand 0.16 for the more internal section indicating an overall weak dia-genetic effect (e.g. Joachimski, 1994; Railsback et al., 2003; Vincentet al., 2004; Immenhauser et al., 2008). Sediments near the top ofthe Chabert Formation of the more internal section show an earlydiagenetic influence, which may have been more significant in the in-terval, in which negative trends in carbon and oxygen isotope recordsco-occur. The more positive values from the base of the Bourg-St-Andéol section (Malaubert outcrop) are probably due to the factthat the section was sampled along the Rhône River, affecting the iso-topic signature.

The Ardèche sections and particularly the Chabert section are wellpreserved andwell dated by ammonite biostratigraphy. The δ13C recordof the Chabert section is well correlated with that of the La Bédoulestratotype section and especially the negative excursion is wellexpressed and more dilated than the corresponding excursion in theItalian sections (Fig. 17; Menegatti et al., 1998; Renard et al., 2005;Stein et al., 2012). The ammonite biozonal calibration between the sec-tions described here and the La Bédoule section shows some discrepan-cies and some common features.

This is related to the differences in the ammonite biozonation usedhere, which is the one developed by Moreno-Bedmar et al. (2009,2010, 2012a) (see also Najarro et al. (2011b); Gaona-Narvaez et al.(2013)), and the one proposed for the La Bédoule section by Conte(1975) and applied by Busnardo (1984) and Ropolo et al. (2000,2006). A first difference with La Bédoule is our attribution of an impor-tant lower portion of the C3 segment to the D. forbesi Zone rather thanthe D. deshayesi Zone, based on the presence of Procheloniceras at thebase of the Chabert Formation in two sections (Michelet and Bourg-St.-Andéol). Sensu Ropolo et al. (2008a, 2008b), the last representativesof this genus are characteristic for the D. weissi Zone, equivalent of theD. forbesi Zone (Moreno-Bedmar et al., 2010). A common feature ofthe study here and the studies both by Ropolo et al. (2000, 2006) in LaBédoule, as well as by Moreno-Bedmar et al. (2009) in the eastern Ibe-rian Chain is the presence of the isotope segments C4 to C6 within theR. hambrovi Subzone. But in the sections studied here, the R. hambroviSubzone extends downwards near the base of the Chabert Formationand slightly overlapswith the upward extension of younger representa-tives of the genus Procheloniceras. This discrepancy is partly related tothe difficulty to find the index species Roboloceras hambrovi, whichwas well adapted to shallow-water environments, than in the deeper

environments like those represented by the Violette Member (Ropoloet al., 2008a). The newly observed downward extension of R. hambrovidoes not solve the problematic of the position of the Subzone into theD. forbesi or into the D. deshayesi Zone (Conte, 1975; Moullade et al.,1998; Renard et al., 2005; Ropolo et al., 2008a) but allows at least to po-sition with certainty the whole controversial interval into theR. hambrovi Subzone. The problematic reliability of R. hambrovi as achronostratigraphical index species was also noted by Ropolo et al.(2008a) and Skelton et al.(2013). The use of the carbon-isotopechemiostratigraphymay help to solve this problem, since the index spe-cies R. hambrovi is always restricted to the C3 to C6 segments (e.g.Moullade et al., 2000; Renard et al., 2005; Moreno-Bedmar et al.,2008; Bover-Arnal et al., 2011; and this study). Finally, bothbiozonations assign the C7 segment to theD. deshayesi Zone, andmainlyto theD. grandis Subzone. The top of the La Bédoule section is correlatedwith the Picourel Member from the Picourel section (Fig. 17), where animportant decreasing δ13C trend is observed during the D. furcata Zone,attributed to the C8 segment.

5.4. Phosphorus accumulation and the detrital index

The phosphorus records show four significant peaks (P1, P2, P6and P7; Fig. 12), which are positioned just above firmgrounds orhardgrounds, at the same level as the lag deposits, condensed levels,andDI peaks. They appear to indicate transgressive surfaces (TS) and con-densation events. P1 occurs at the base of the Chabert Formation,which islinked to TS2. P2 is detected just above a firmground covered by serpulidsand overlain by a level rich in shark teeth and endobiontic fauna, indica-tive of a smaller condensation event or a break in sedimentation. P6 cor-responds to a larger increase in phosphorus contents at the base of thePicourel Member, which probably corresponds to TS2′. The most impor-tant phosphorus peak P7 coincides with the nodular phosphatic bed atthe base of the Frayol Formation, the TS3 from the A3 sequence.

The detrital index includes seven well-expressed maxima (DI1 toDI7; Fig. 10), which are an expression of sea-level change and changesin carbonate production related to the Selli episode. In this context, IDpeaks correspond to MFS when they appear isolated, or to winnowingphases and transgressive surfaces, if they co-occur with peaks in phos-phorus contents. DI1 is associatedwith the deepest environments with-in the Violette Member and is interpreted as an enrichment related to areduced accumulation rate due to maximum flooding (MFS2). Thesmaller maximum DI2 coincides with P2, which corresponds to asmall firmground likely related to condensation and winnowing. Maxi-mum DI3 corresponds to a marly level, intercalated in crinoidal lime-stone, which is interpreted as a minor mfs (PMFS″). It corresponds tothe onset of a more rapid increase in the δ13C record (C4 segment).DI4 is regarded as a minor mfs (PMFS‴) inside the marly interval sepa-rating the twomain carbonate bars. Peak DI5 in the Rocherenard Mem-ber is not marked by a clear sedimentological change. The presence of aminor mfs, or a parasequence boundary, or a change in the weatheringregime may explain this maximum. P6 and DI6 coincide just above afirmground at the base of the Picourel Member, and are interpreted tocorrespond to a TS (TS2′). P7, situated at the base of the Frayol Forma-tion, is interpreted as a TS (TS3). DI7 is not interpreted here as we didnot sample and analyse the higher part of the Frayol Formation.

5.5. Relations between platform drowning and the Selli episode

The three successive platform drowning phases documented fromthe Ardèche area are well dated by ammonite biostratigraphy and areconstrained by the evolution of the carbon-isotope record. The firstand third drowning unconformities share the fact that they were pre-ceded by emersion phases,which are documented by karstic or erosion-al surfaces, but also by negative anomalies in the carbon and oxygenisotope records. As such the onset of the drowning episodes postdates


the formation of the sequence boundaries, related to the emersionsurfaces.

The first drowning phase is part of an important environmentalshift from oligotrophic platform growth to a heterozoan carbonate-producing ecosystem, and went along with an important transgressionassociated with significant phosphorus and detrital input. This impor-tant phase of environmental change predates the onset of the Selli epi-sode as is indicated by the stratigraphic position of the pronouncednegative excursion in the δ13C record, indicative of the onset of theSelli episode (Weissert, 1981; Menegatti et al., 1998; Föllmi, 2012),which is observed within the sediments of the Chabert Formation,above the discontinuity D1.

The second phase of platform drowning is a part of a larger shift to-wards more detrital input and phosphogenesis, which weakenedheterozoan carbonate production, announcing the third drowningphase. This second phase may correspond to the Aparein event, report-ed from the D. furcata Zone in southern Italy (Cobianchi et al., 1997;Luciani et al., 2006), northern Spain (“Aparein” level; García-Mondéjaret al., 2009; Millán et al., 2009), and Mexico (La Peña Formation; Scott,1990). This drowning is marked by a long-term decrease in the δ13Crecord, which encompasses at least the upper part of theD. grandis Sub-zone and the whole D. furcata Zone. The Aparein event is considered asthe expression of a second anoxic phase within the Selli episode, as de-fined in Föllmi (2012).

A third phase of platform drowning induced a stop in heterozoancarbonate production and a shift to the deposition of black hemipelagicmarl, which is marked by substantial sea-level rise. This third phase,dated here from the uppermost D. furcata Zone, may correspond tothe “Niveau Noir” NN1 event (Bréhéret and Delamette, 1988), the ex-pression of a third anoxic phase. The NN1 is usually dated from thebase of the E. martini Zone but this study and others (Atrops andDutour, 2002; Dauphin, 2002; Moreno-Bedmar et al., 2013) clearlyshow the overlap of the index species around the early–late Aptianboundary with the appearance of Epicheloniceras already in theD. furcata Zone and the continuation of D. furcata in the lowerE. martini Zone (Atrops and Dutour, 2002, 2005). As such, the two lastphases are associated with the Selli episode, and are related to the dif-ferent steps of this major episode of environmental change.

At least two of the three drowning events are preceded by sea-levelfall, which occurred before the transgression associated with thedrowning event. Each transgression seems to be accompanied by a neg-ative carbon-isotopic excursion, like the negative excursion C3 abovethe drowned Urgonian Formation, linked with the onset of the Sellievent, and thenegative excursion C8 during theD. furcata Zone, possiblylinked to the Aparein event (García-Mondéjar et al., 2009; Millán et al.,2009). Of interest is also the observation that the phosphorus contentsshow important excursions towards higher values at the base of eachdrowning event.

The difference in age between the drowning of the Urgonian plat-form and the onset of the Selli episode was already pointed out by ear-lier authors (Föllmi et al., 2006, 2007; Föllmi and Gainon, 2008) andquantified by Huck et al. (2011) at around 260 kyr. Stein et al. (2011)discussed short-lasting anoxic events during the early Aptian as pre-ludes to the Selli episode, and all by all, the important changes duringthe early Aptian predating the Selli episode identified in the Ardèchearea appear to confirm the importance of major environmental changeaccompanied by sea-level change already during the earlier part of theearly Aptian. Changes in sea level and nutrient input were also impor-tant during the Selli episode, and continued to be important also duringthe late Aptian.

6. Conclusions

The lower Aptian succession from the Ardèche area is well exposedand of great interest for the study of the late early Aptian platformdrowning episodes near and during the oceanic anoxic Selli episode.

Sections comprising the Selli episode, are relatively thick, and rich inammonites.

The demise of the oligotrophic Urgonian platform is associated withan emersion phase followed by a drowning event during the D. forbesiZone. This event is followed by the installation of a transgressivehemipelagic marl–limestone alternation, also dated from the D. forbesiZone. This basal part is overlain by pelagic and hemipelagic marl,which are largely dated from the lower R. hambrovi Subzone, andmarked by a large δ13C negative excursion (C3) related to the onset ofthe Selli anoxic episode. The installation of heterozoan carbonate pro-duction is also dated as the R. hambrovi Subzone, and continued in theD. deshayesi Zone.

On top of the Rocherenard Member, a second drowning event wasidentified, which dates as the middle D. grandis Subzone, and which isassociated with important phosphogenesis.

A further ramp emersion and a final drowning episode, dated fromthe uppermost D. dufrenoyi Subzone, is registered on top of the phos-phatic beds of the PicourelMember, corresponding to the clasts formingthe phosphatic conglomerate from the base of the Frayol Formation,which were likely formed during this last important emersion phase.Whereas the latter two drowning events coincidewith the Selli episodeas defined by Föllmi (2012), the first one implied in the disappearanceof the Urgonian platform, clearly predates the Selli episode, as is seenfrom the carbon-isotope record. The major palaeoenvironmental, tro-phic and sea-level changes associated with all three drowning eventsdemonstrate that these changes are an important ingredient of theearly Aptian, thereby partly predating the Selli episode.

Acknowledgements

We are grateful to François Gischig and Pierre Desjaques (Universityof Geneva), who carefully prepared the thin sections.We thank BernardClavel and Robert Busnardo for their initial assistance. We thank YvesDutour (Aix-en-Provence Museum) for checking some ammonite iden-tifications.We gratefully acknowledge the Swiss National Science Foun-dation and the University of Lausanne for their financial support, andthe reviewers Hubert Arnaud and Josep Moreno-Bedmar for their de-tailed and very constructive remarks.

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Three successive phases of platform demise during the early Aptian and their association with the...

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