Linking early diagenesis and sedimentary facies to sequence stratigraphy on a prograding oolitic wedge: The Bathonian of western France (Aquitaine Basin)

Marine and Petroleum Geology 81 (2017) 169e195

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Research paper

Linking early diagenesis and sedimentary facies to sequence stratigraphy on a prograding oolitic wedge: The Bathonian of western France (Aquitaine Basin) Simon Andrieu a, *, Benjamin Brigaud a, Jocelyn Barbarand a, Eric Lasseur b a b

^t. 504, 91405 Orsay, France GEOPS, Univ. Paris-Sud, CNRS, Universit
e Paris Saclay, Rue du Belv
ed ere, Ba BRGM, 3 avenue Claude Guillemin, BP 36009, 45060 Orl
eans, France

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 September 2016 Received in revised form 22 November 2016 Accepted 10 January 2017 Available online 11 January 2017

To improve the understanding of the distribution of reservoir properties along carbonate platform margins, the connection between facies, sequence stratigraphy, and early diagenesis of discontinuities along the Bathonian prograding oolitic wedge of the northeastern Aquitaine platform was investigated. Eight facies are distributed along a 50 km-outcropping transect in (1) toe-of-slope, (2) infralittoral prograding oolitic wedge, (3) platform margin (shoal), (4) open marine platform interior, (5) foreshore, and (6) terrestrial settings. The transition from shallow platform to toe-of-slope facies is marked in the field by clinoforms hundred of meters long. Carbonate production was confined to the shallow platform but carbonates were exported basinward toward the breakpoint where they cascaded down a 20e25
slope. Ooid to intraclast grainstones to rudstones pass into alternating marl-limestone deposits at an estimated paleodepth of 40e75 m. Three sea-level falls of about 10 m caused the formation of discontinuities corresponding to sequence boundaries. Along these discontinuities, erosional marine hardgrounds formed in a high-hydrodynamic environment at a water depth of less than 10 m, displaying isopachous fibrous cements and meniscus-type cements. The cements pass landward into meniscus and microstalactitic forms along the same discontinuities, which are characteristic of subaerial exposure. During the deposition of transgressive systems tracts, carbonate accumulation remained located mostly on the shallow platform. Energy level increased and carbonates were exported during the deposition of highstand systems tracts forming the infralittoral prograding oolitic wedge. During the deposition of lowstand systems tracts, carbonate production fell to near zero and intraclast strata, derived from the erosion of hardgrounds on the shallow platform, prograded basinward. Early diagenetic cements are related exclusively to discontinuities that are not found within the prograding wedge because of the continuous high sedimentation rate under lower hydrodynamic conditions. This absence of early cementation within the infralittoral prograding oolitic wedge was conducive to porosity conservation, making such features good targets for carbonate reservoir exploration. This study proposes a novel sequence stratigraphy model for oolitic platform wedges, including facies and early diagenesis features. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Infralittoral prograding oolitic wedge Carbonate platform Depositional model Early diagenesis Facies Sequence stratigraphy Jurassic

1. Introduction Numerous studies undertaken since the early 2000s have shown the infralittoral prograding wedge (ILPW) model to be useful for understanding depositional processes on many Mesozoic to Cenozoic carbonate platform edges (e.g. Pomar et al., 2015; Pomar and Haq, 2016). The ILPW model describes a

* Corresponding author. E-mail address: [email protected] (S. Andrieu). http://dx.doi.org/10.1016/j.marpetgeo.2017.01.005 0264-8172/© 2017 Elsevier Ltd. All rights reserved.

progradational platform-margin slope with elongated wedges formed by the export of sediments from the shallow platform to the toe-of-slope area, within which topsets, foresets, and bottomsets can be recognized (Hern
andez-Molina et al., 2000; Pomar et al., 2015). Studies have been conducted to constrain ILPW dynamics within a sequence stratigraphic framework (Pomar and Tropeano, 2001; Mateu-Vicens et al., 2008; Pierre et al., 2010; Amour et al., 2013) but the relationship between sequence stratigraphy and early diagenesis in platform margins has come in for less study and is not fully understood (e.g. Loreau and Durlet, 1999; Morad et al., 2012; Coffey, 2012). Nevertheless, this relationship is of major relevance

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in predicting the spatial and temporal distribution of reservoir properties (Morad et al., 2000; Moore, 2004; Caron et al., 2005). Discontinuities are widely used to constrain sequence stratigraphy models and then for correlation at basin scale and beyond (Durlet and Loreau, 1996; Loreau and Durlet, 1999; Christ et al., 2015). However, the lateral changes in discontinuities and the factors controlling their formation (eustasy, tectonics, sedimentation rate, environmental conditions) are old problems that are still not fully understood despite recent studies (Christ et al., 2012, 2015; Hamon et al., 2016). Marine hardgrounds generally developed above the fair-weather wave-base under high hydrodynamic conditions, but it is difficult to define the precise paleobathymetry of their formation (Christ et al., 2012, 2015). Moreover, examples of hardgrounds forming in upper offshore environments and related to storm-induced waves and currents are also documented (Kennedy and Juignet, 1974; Kennedy and Garrison, 1975; Kim and Lee, 1996; Lasseur et al., 2009; Reolid et al., 2010). Early diagenesis is sensitive to relative sea-level changes and displays high variability along sequence boundaries (subaerial exposure, erosional or non-erosional marine hardground, firmground, etc.) and between different systems tracts (Caron et al., 2012; Morad et al., 2012; Ritter and Goldstein, 2012). This variability as well as the formation and lateral evolution of discontinuities needs to be better constrained via new sequence stratigraphy models combining facies analyses, discontinuity characterization, and early diagenesis. A shallow wave-dominated to tidally-influenced carbonate platform margin surrounded by offshore environments developed in the northeastern Aquitaine Basin during the Bathonian. It featured various environments ranging from terrestrial to toe-ofslope, whose detailed architecture can be studied from numerous high quality outcrops in quarries and boreholes (Foucher, 1986). The biostratigraphic framework is ascertained from brachiopod, ammonite, foraminifer, and ostracod fauna at the sub-stage scale (Foucher, 1986). The objective of this work is (1) to propose a dynamic depositional model within a sequence stratigraphic framework for the northeastern Aquitaine Bathonian platform (50 km-long crosssection), locating and describing the different facies (including their sedimentological and diagenetic features) and surfaces (subaerial exposure, hardgrounds, etc.), and (2) to define the lateral evolution of early diagenetic processes across the platform. The facies are described and classified in such a way as to identify their depositional and eogenetic environments. A paragenetic sequence is proposed, and the diagenetic changes within the various facies are compared.

southeastward to platform interior (foreshore, open marine), platform margin (shoal), platform slope (infralittoral prograding wedge) and then toe-of-slope northwestward (Fig. 2C; Foucher, 1986). In the study area the strike of the shallow platform edge resembles a capital gamma (G) (Fig. 2C; Foucher, 1986). Foucher (1986) studied the ammonite, brachiopod, and foraminifera fauna of the Middle Jurassic outcrops and boreholes of the northeastern Aquitaine platform and defined a reliable lithostratigraphic framework for the Bathonian to the mid Callovian (Fig. 3). The Bajocian deposits in the southeast of the study area are lagoonal dolomite and dolomitic limestones (Dolomies de Montbron Formation) overlain by shallow platform granular ooid facies (Calcaires de Combe Brune, Calcaires de Vilhonneur and Calcaires de Saint-Martial Formations; Fig. 3). These proximal deposits pass laterally northwestward into offshore mudstone to wackestone alternating with marly layers (Calcaires de Nanteuil-en-Vall
ee Formation). The thickness of the Bathonian units, in the proximal as in the distal domains, is about 50 m. The base of the Calcaires de Saint Martial Formation is dated as early Bajocian (Sonninia propiquans to Stephanoceras humphriesianum Zones) by the brachiopod Parvirhynchia parvula and the top of the Calcaires de Nanteuil-en-Vall
ee Formation is dated to the Parkinsonia parkinsoni Zone of the late
ras and Bajocian by the ammonite Parkinsonia sp (Fig. 3; Alme re, 1984; Foucher, 1986; Faure
et al., 2015). The BathoLathuilie nian/Callovian boundary represents an exposure surface located on top of the Calcaires de Saint-Martial, Calcaires de Vilhonneur, and Calcaires de Combe Brune Formations, which are dated by ostracods (Fabanella bathonica) and brachiopods (Burmirhynchia semiglobosa, mid to late Bathonian; Burmirhynchia thierachensis and Burmirhynchia elegantula, late Bathonian; Fig. 3; Foucher, 1986; Garcia et al., 1996). A specimen of Trocholina gigantea has been found at the top of the Calcaires de Combe Brune Formation. These proximal deposits pass northwestward into mudstone to wackestone alternating with marly layers (Calcaires de la Rochefoucault Formation; Fig. 3; Foucher, 1986). The early Callovian is characterized by a sedimentary hiatus above the Calcaires de Combe Brune and the Calcaires de Vilhonneur Formations. The base of the Calcaires crayeux de Montbron Formation, which is made up of lagoonal mudstones to wackestones, is dated as mid Callovian by the brachiopod Aulcacothyris pala (Fig. 3; Foucher, 1986; Garcia et al., 1996). Northwestward, the Callovian deposits are distal clayey limestones dated at their base from the Macrocephalites macrocephalus Zone (early Callovian) by the ammonite Macrocephalitidae (Fig. 3; Foucher, 1986). 3. Material and methods

2. Palaeogeographic and stratigraphic setting 3.1. Sedimentology The Aquitaine Basin is an intracontinental basin in southwestern France where Triassic to Quaternary sedimentary cover overlies the crystalline Variscan basement (Biteau et al., 2006). The study area ^me lies in the northeastern part of this basin, close to Angoule (Fig. 1AeB). From Bajocian to Callovian times, western France formed a shallow epicontinental sea at subtropical latitudes (20e30
N) bordered to the northwest by the Armorican Massif and to the east by the present-day Massif Central, which was probably a paleohigh covered by shallow marine deposits (Fig. 2A; Ziegler, 1988; Thierry and Barrier, 2000). The sediments are predominantly shallow marine carbonates deposited on a vast platform, which was open to the Atlantic, Tethys, and Artic oceans (Fig. 2A; Enay and Mangold, 1980; Thierry and Barrier, 2000). The northern Aquitaine platform is separated into a shallow carbonate platform area southeastward and a deeper platform with offshore carbonate to clayey deposits toward the north and west (Fig. 2B; Foucher, 1986). In the study area, the environments vary from terrestrial

This study is based on the detailed examination of five outcrop sections (Combe Brune, Vilhonneur, Cosses Noires, Chez Trape and Javerlhac) between La Rochefoucault and Nontron supplemented by previous descriptions of three outcrop sections (one around Saint-Sauveur and two around Saint-Martial) and one borehole (Montignac; Foucher, 1986, Fig. 2). The transect extends for 50 km from Montignac in the northwest to Nontron in the southeast. The outcrop sections were logged in detail: lithology, texture, allochem content, and sedimentary structures have all been characterized. Facies were determined on the basis of visual characterization of components (skeletal and non-skeletal grains), textures, sedimentary structures, sorting, and grain size on 37 thin-sections. The porosity types grain contacts, and cements of each facies were analyzed. Porosity was computed for granular grainstone facies with Jmicrovision software by measuring the blue proportion (color of the resin injected into the porosity) on the 37 thin-section scans.

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Fig. 1. A. Location of the study area on a geological map of western France. B. Location of the study outcrops on a simplified geological map of a part of the northeastern Aquitaine Basin.

For each facies, paleodepths were estimated based on the examination of sedimentary structures, textures, and allochems. The classic wave zonation was used, assuming depth values of 10e15 m for the fair-weather wave base in shallow epicontinental seas (Sahagian et al., 1996; Plint, 2010). The standard facies zones of the Wilson model (1975) for rimmed carbonate platforms, modified by (Flügel, 2010, p. 662e663), are used for depositional environment subdivisions and interpretations. 3.2. Sequence stratigraphy Following the definition of Catuneanu et al. (2011), outcrop sections and a borehole were interpreted in terms of sequence stratigraphy to establish a stratigraphic cross-section. Depositional sequences composed of transgressive, highstand and lowstand systems tracts (TSTs, HSTs and LSTs) are bounded either by a subaerial unconformity (SU) when the surface was exposed, or by a

maximum regressive surface (MRS) when the surface was submerged. Maximum regressive surfaces coincide with shifts in stacking patterns between a shallowing-upward trend during the deposition of the HST and LST (prograding architecture) and a deepening-upward trend during the deposition of the TST (retrograding architecture). They mark the shallowest depositional environment recorded within a sequence. Maximum flooding surfaces (MFSs) mark a shift between deepening-upward and shallowing-upward trends, and correspond to the deepest facies observed in a sequence. The surfaces that are selected as sequence boundaries vary from one sequence stratigraphy approach to another, and is typically a function of which surfaces are best expressed within the context of each situation (Catuneanu et al., 2011). Because maximum regressive surfaces and subaerial unconformities are well expressed in our study area from the foreshore to the toe-of-slope settings they form sequence boundaries (SBs).

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Fig. 2. A. Paleogeographic location of the study area during the Bathonian (modified from Brigaud et al., 2009a; based on Enay and Mangold, 1980; Ziegler, 1988; Thierry and Barrier, 2000; Hendry, 2002). B. Location of the study area on a paleoenvironmental map of the northern Aquitaine platform (modified from Foucher, 1986; based on Gabilly et al., 1978; Enay and Mangold, 1980; and Mourier, 1983). C. Paleoenvironmental map of the study area (modified from Foucher, 1986; based on Gabilly et al., 1978; and Enay and Mangold, 1980).

3.3. Diagenesis The 37 thin-sections were stained by alizarin-potassium ferricyanide and studied by optical microscopy and

cathodoluminescence microscopy to characterize different generations of cement (early vs burial) and their origin. Cathodoluminescence analyses were carried out on a cold-cathode, operating at 14 kV and at 150e250 mA, coupled to a BX41 Olympus

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Fig. 3. Schematic lithostratigraphic illustration of the study area with the location of ammonite, brachiopod, foraminifer, and ostracod fauna, completed from Foucher (1986). Duration of the stages from Gradstein et al. (2012).

microscope. Cement stratigraphy and diagenetic sequencing were established on the basis of superimposition and cross-cutting relationships from thin-section observations. The proportion of blocky calcite cement was quantified using a point counting JmicroVision Image analysis system (Roduit, 2008) with a minimum of 100 counts per section. Visual estimations of the proportion of the early and burial cement stages were carried out on the 37 thinsections. The diagenetic log method proposed by Durlet et al. (1992) is used to represent paragenetic sequences. 4. Results 4.1. Facies Eight facies were determined (Table 1). They are located on a simplified downdip profile of the northeastern Aquitaine platform during the Bathonian, including terrestrial, platform interior (foreshore, open marine), platform margin (shoal), infralittoral prograding oolitic wedge, and toe-of-slope environments (Fig. 4). A synthetic sedimentological log is proposed to characterize the stratigraphic succession and the vertical evolution of facies and depositional environments (Fig. 5).

4.1.2. Infralittoral prograding oolitic wedge: facies B and C 4.1.2.1. Description. Both facies are located within clinoforms tens to hundreds of meters long and more than 30 m thick, dipping 20
northwestward (Fig. 6AeH). Facies B is a well-sorted ooid grainstone with scarce peloids, oncoids, and bioclasts (bivalves, crinoids, echinoids, foraminifera, solitary corals, brachiopods, gastropods; Fig. 7A and B). Facies C corresponds to poorly sorted rudstone with a high proportion of intraclasts, ooid aggregates, and peloids, and also containing ooids, oncoids, and bioclasts (foraminifers, bivalves, crinoids and echinoids) in minor proportions (Fig. 7C). Intraclastic levels (facies C) within clinoforms are about 2 m-thick. The intraclasts correspond to ooid/oncoid packstones to grainstones with isopachous fibrous cement (IFC, facies E2, Fig. 7C). The present mean macroporosity value is about 7% in facies B and C that display dominating intergranular porosity. In facies B and C, contacts are concave-convex to sutured (Fig. 7D and E. 4.1.2.2. Palaeoenvironmental interpretation. The grainstone to rudstone texture of these facies and the presence of tens to hundreds of meters long clinoforms indicate a high-energy depositional environment along the platform edge slope. 4.1.3. Platform margin e shoal: facies D

4.1.1. Toe-of-slope: facies A 4.1.1.1. Description. Facies A corresponds to mudstone to wackestone alternating with marl layers. The main components are peloids, aggregates containing peloids and bioclasts, crinoids, and sponges. Bivalves, brachiopods, serpulids, ammonites, belemnites, and glauconite grains are also present in minor proportions. This occasionally dolomitized facies displays bioturbations and stylolites (Foucher, 1986). 4.1.1.2. Palaeoenvironmental interpretation. The fine granulometry, the marl layers, the absence of sedimentary structures, the abundant bioturbation, and the presence of ammonites, belemnites, and common echinoderms within this facies indicate a very calm toeof-slope depositional environment below the fair-weather wave base (Figs. 4 and 5).

4.1.3.1. Description. Facies D displays grainstone texture and planar to trough cross-bedding in dunes, with a set thickness that does not exceed 1 m (Fig. 8A). This facies corresponds to well-sorted oolitic grainstones with scarce peloids, oncoids, and bioclasts (bivalves, crinoids, echinoids, foraminifers, solitary and branching corals, brachiopods, gastropods; Fig. 8B). Moldic pores and microporosity in ooids are abundant in facies D, whereas intergranular pores are scarce (Fig. 8B). The present mean macroporosity of this facies is about 2%. Concave-convex and sutured contacts are numerous. 4.1.3.2. Palaeoenvironmental interpretation. In facies D, grainstone texture and planar to trough cross-bedding in dunes indicate a high-energy wave-influenced environment above the fair-weather wave base (Fig. 8A). The depositional environment of this facies corresponds to a shoal setting, located on the platform margin.

174 Table 1 Facies, non-bioclastic and bioclastic components, sedimentary structures, granulometry, sorting and grain size, early diagenesis, compaction structures, and depositional environments of the Bathonian rocks of the northeastern Aquitaine platform. Non-bioclastic components

Bioclastic components

Sedimentary structures

Sorting and grain size

Early diagenesis

Compaction

Energy and depositional environment

Facies A (mudstone to wackestone alternating with marly layers) Facies B (ooid grainstone)

Peloids (F), aggregates containing peloids and bioclasts (C), glauconite grains (R)

Sponges (C), crinoids (C), bivalves (R), brachiopods (R), serpulids (R), ammonites (R), belemnites (R)

Bioturbations, marl/limestone alternations

Well-sorted,

Dolomitization

Stylolites

Toe-of-slope, low energy

Sutured and concaveconvex contacts Sutured and concaveconvex contacts Sutured and concaveconvex contacts Rare fractures, concaveconvex contacts

Platform slope, high energy

Micritic and concentric ooids (A), peloids (R), oncoids (R) Facies C (intraclast Intraclasts (A), ooid rudstone) aggregates (C), peloids (C), ooids (R), oncoids (R) Facies D (ooid Micritic and grainstone) concentric ooids (A), peloids (R), oncoids (R) Facies E (oncoid- Oncoids (A), ooids (C), ooid grainstone intraclasts (C), peloids to packstone) (C), ooid aggregates (C) Facies F (intraclast Intraclasts (A), ooid aggregates (C), peloids rudstone to (C), oncoids (R), ooids packstone) (R) Intraclasts (A), peloids Facies G (A), ooids (C) (intraclast peloidal grainstone) Facies H (charophyte and ostracod marls)

Bivalves (R), crinoids (R), echinoids Large-scale high-angle clinobeds (~20
) (R), foraminifers (R), corals (R), brachiopods (R), gastropods (R)

Well-sorted, 200 mme500 mm

Foraminifers (R), bivalves (R), crinoids (R), echinoids (R)

Poorly sorted, 200 mm to several mm

Large-scale high-angle clinobeds (~20
)

Dolomitization

Bivalves (R), crinoids (R), echinoids Planar and trough cross-bedding in Well-sorted, dunes 200 mme500 mm (R), foraminifers (R), corals (R), brachiopods (R), gastropods (R) Miliolids (R), undifferentiated foraminifers (R), gastropods (R), bivalves (R), crinoids (R), echinoids (R), corals (R), red algae (R)

Planar and trough cross-bedding in Poorly sorted, dunes, microbial peloidal cements. 100 mm to 1 cm Borings and encrusting bivalves below discontinuites

Foraminifers (R), corals (R), bivalves (R), crinoids (R), echinoids (R)

Poorly sorted, 200 mm to several mm

Meniscus-type cements (MTC). Isopachous fibrous cements (IFC), isopachous bladed cements (IBC) and rarely dogtooth cements (DC) below discontinuities Isopachous fibrous cements (IFC), dogtooth cements (DC), meniscus and microstalactitic cements (MC)

Planar bedding, birdseyes, Gastropods (R), miliolids (R), undifferentiated foraminifers (R), desiccation cracks, microbial corals (R), bivalves, (R), crinoids (R), peloidal cements echinoids (R)

Poorly sorted, 200 mm to several mm

Dolomitization, dogtooth cement (DC), meniscus and microstalactitic cements (MC)

Charophyte gyrogonites (R), ostracods (R), foraminifers (R)

Very well-sorted

Microstalactitic cements (MC), rare dogtooth cements (DC)

Desiccation cracks, lignite levels

R ¼ rare: <10%; C ¼ common: 10e20%; F ¼ frequent: 20e40%; A ¼ abundant: >40%.

Platform slope, high energy

Wave-dominated platform margin, shoal, high energy

Wave-dominated platform interior, open marine, high to moderate energy

Platform interior, foreshore, high energy

Sutured and Platform interior, foreshore, high energy concaveconvex contacts, stylolites Terrestrial setting, low energy

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Facies

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4.1.4. Platform interior e open-marine: facies E 4.1.4.1. Description. Facies E displays grainstone texture and planar to trough cross-bedding in dunes, with a set thickness that does not exceed 1 m (Fig. 8C). This facies corresponds to poorly sorted oncoid-ooid grainstones to packstones with intraclasts, peloids, ooid aggregates, and scarce bioclasts (miliolids, undifferentiated foraminifers, gastropods, bivalves, crinoids, echinoids, solitary and branching corals; Fig. 8D). The intraclasts correspond to oncoidooid packstones to grainstones and ooid grainstones. Facies E displays a grain-packstone texture and peloidal microbial fabrics (Fig. 8E). Planar discontinuities, displaying encrusting bivalves and borings with a diameter of about one centimeter, are present in facies E. Early lithification, characterized by marine isopachous fibrous/bladed cements and micritic meniscus cements, occurs below these discontinuities. The denomination E2 is used when facies E is affected by early lithification and borings, and E1 when not (Figs. 4, 5 and 8F). Moldic pores and microporosity in ooids are abundant in facies E, whereas intergranular pores are scarce (Fig. 8G). The present mean macroporosity of this facies is about 2%. Concave-convex and sutured contacts are numerous in facies E when isopachous early cements are absent. 4.1.4.2. Palaeoenvironmental interpretation. In facies E, grainstonepackstone texture, peloidal microbial fabrics and planar to trough cross-bedding in dunes indicate a high to moderate-energy waveinfluenced environment above the fair-weather wave base, more sheltered than the depositional environment of facies D. This facies was deposited in an open marine platform interior setting, partially protected by the ooid shoal. 4.1.5. Platform interior e foreshore: facies F and G 4.1.5.1. Description. Facies F is a poorly-sorted intraclast rudstone to packstone with ooid aggregates, peloids, oncoids, ooids, and bioclasts (foraminifers, solitary corals, bivalves, crinoids and echinoids) in minor proportions, which is only found at the top of the Calcaires de Combe Brune Formation. Facies G is a poorly-sorted intraclast peloidal grainstone with ooids and rare bioclasts (gastropods, miliolids, undifferentiated foraminifers, solitary corals, bivalves, crinoids and echinoids). The intraclasts correspond to peloidal or oncoid-ooid grainstones to packstones. The present near-zero macroporosity is limited to moldic pores and microporosity is present in grains in facies F, while facies G displays intergranular pores. The dogtooth, microsparitic meniscus, and geopetal microsparitic cements, and the early dolomitization/dedolomitization processes in these two facies indicate vadose diagenesis (Purser, 1969, 1978; Longman, 1980; Aissaoui and Purser, 1983; Brigaud et al., 2014). Foucher (1986) described microstalactitic cements in facies G, confirming the occurrence of a vadose environment (Purser, 1969; Longman, 1980; Brigaud et al., 2014). 4.1.5.2. Palaeoenvironmental interpretation. The presence of planar bedding, birdseyes, peloidal microbial fabrics, and desiccation cracks are characteristic of a high-energy foreshore depositional environment (Fig. 8H). 4.1.6. Terrestrial setting: facies H Facies H is made up of dark marls. The very fine granulometry, the occurrence of lignite layers, desiccation cracks, charophyte gyrogonites, and ostracods all suggest a very calm and protected brackish “small ponds” depositional environment (Foucher, 1986). 4.2. Petrographic description of the diagenetic stages Seventeen diagenetic events were identified and ordered in a paragenetic sequence (Fig. 9 and Table 2): (1) early or eogenetic

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stages (turbid syntaxial cements, isopachous fibrous cements, micritic envelopes, dolomitization/dedolomitization 1, meniscustype cements, dissolution of aragonite, meniscus and geopetal microsparitic cements, dogtooth cement, non-luminescent syntaxial cements), (2) burial or mesogenetic stages (dedolomitization 2, compaction, and three blocky calcite cementations). They are replaced on the sedimentary logs in Fig. 10 (diagenetic log graphic visualization; Durlet et al., 1992). 4.2.1. Turbid syntaxial cements (TSC) These cements developed on echinoderm grains and are composed of inclusion-rich calcite crystals. TSCs exhibit a cloudy brown-to-orange luminescence and are non-ferroan (pink-stained by alizarin-potassium ferricyanide; Fig. 11AeB). TSC thickness is mainly between 50 and 200 mm. They are attributed to recrystallized high-magnesium calcite (HMC; Durlet and Loreau, 1996; Loreau and Durlet, 1999) and are present in all the grainstone facies and sections studied (Figs. 9 and 10). 4.2.2. Isopachous fibrous cements (IFC) These cements consist of thin isopachous fibrous fringes (10e50 mm thick) and are composed of inclusion-rich crystals. IFCs exhibit (1) a very thin non-luminescent fringe (<10 mm thick) followed by (2) cloudy brown-to-yellow luminescence fibers (10e50 mm thick, Fig. 11CeF). These cements are non-ferroan and are stained pink by alizarin-potassium ferricyanide. IFCs are located in facies E, a few decimeters to one meter below bored and bivalveencrusted surfaces in the Vilhonneur, Cosses Noires, and Javerlhac quarries (Figs. 9 and 10). They contributed to the early lithification of thin grainstone layers and are crosscut by borings. Such early cements are common in shallow carbonate platforms that developed during the calcite sea periods (Sandberg, 1983) and have been well-illustrated from the Middle Jurassic of the Paris Basin by Purser (1969) and Brigaud et al. (2009b). This cement type is attributed to recrystallized high-magnesium calcite derived from marine phreatic water, as indicated by their patchy luminescence pattern (Durlet and Loreau, 1996; Loreau and Durlet, 1999; Richter et al., 2003; Knoerich and Mutti, 2006). 4.2.3. Micritic envelops (ME) and meniscus-type cement (MTC) Micrite envelopes (about 10 mm thick) developed mostly around bivalve shells, peloids, and ooids (Fig. 11CeD). They formed by (1) the infill of vacated borings of endolithic microorganisms such as cyanobacteria, fungi, and bacteria (e.g. Bathurst, 1966; Friedmann et al., 1971; Kobluk and Risk, 1977a; destructive micritic envelopes) or (2) by calcification of filaments of epilithic organisms protruding into empty pore space (Kobluk and Risk, 1977a, b; Calvet, 1982; Wright, 1986; constructive micritic envelopes). They are known from subtidal (Purser, 1969; Friedmann et al., 1971), intertidal (Strasser et al., 1989; Neumeier, 1998), supratidal, and continental environments (James, 1972; Calvet, 1982; Wright, 1986, 1994). Meniscus-type cements (to distinguish them from vadose meniscus cements; sensu Hillg€ artner et al., 2001) form a micritic meniscus between grains of about 10 mm thick (Fig. 11CeD). They crystallized in subtidal to supratidal environments and are are known as microbial induced fabric whose growth is promoted by €rtner high organic-matter concentrations in the sediment (Hillga et al., 2001). ME and MTC are present in facies E in the Vilhonneur and Cosses Noires quarries, often below discontinuities (Figs. 9 and 10). 4.2.4. Dolomitization/dedolomitization 1 Rhombohedra observed on the margins of grains and in micrite, forming pores or filled by microspar (meniscus cements and geopetal microsparitic cements; see 4.1.6), are present in the Combe

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Fig. 4. Depositional model of the Bathonian facies and their location from the toe-of-slope to the terrestrial settings on the northeastern Aquitaine platform. The range of variation of the fair-weather wave base depth is estimated from Sahagian et al. (1996) and Plint (2010). Facies B: ooid (Oo.) grainstone with rare bivalves (Bi.) and echinoderms (Ech.),

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Brune quarry in facies C and F (Figs. 10, 9 and 12C). The original mineralogy of the crystals cannot be determined exactly, but these features are typical of early dolomitization/dedolomitization processes characterizing exposure surfaces (Purser, 1978). 4.2.5. Dissolution of aragonite shells Dissolution of the aragonitic skeletal debris (mostly gastropods and bivalves) occurred in all the limestones studied. The moldic voids were progressively filled with isopachous bladed cements (IBC) formed shortly after deposition, dogtooth cements (DC), and blocky cement 1 (BC1; Fig. 6G), suggesting very early dissolution. During the Mid Jurassic, in a calcite-sea context (Sandberg, 1983; Dickson, 2004), such early dissolution of aragonite might have occurred either at the sediment/sea-water interface or under very shallow burial conditions (Palmer et al., 1988; Ferry et al., 2007). 4.2.6. Meniscus cements (MC) and geopetal microsparitic cements (GMC) Asymmetrical microsparitic cements forming either meniscus (MC, 10e100 mm) or thick geopetal cements (GMC, 200e500 mm) are present in facies F at the top of the Combe Brune quarry and exhibit large crystals (Figs. 9 and 10; hundreds of micrometers). They exhibit a turbid orange to dark brown luminescence and are non-ferroan (pink-stained by alizarin-potassium ferricyanide; Fig. 12AeC). Meniscus cements are described as being indicative of vadose environments (Purser, 1969; Longman, 1980). The patchy luminescence of these cements may indicate an initial HMC mineralogy, originating from seawater in the vadose zone. GMCs are highly anisopachous and develop at the base of pores (Fig. 12C), in contrast to microstalactitic cements (Purser, 1969). This special shape is indicative of growth under gravitational control. Microsparitic geopetal cements were described in the Jurassic limestones of Burgundy by Aissaoui and Purser (1983), who consider them to have formed in a supratidal to continental setting because of their association with microstalatitic cements, erosional surfaces, and dissolution phenomena indicating the influence of non-marine water. Geopetal microsparitic cements formed during the erosion of substrates affected by early lithification, producing fine microspar detritus that filtered downwards (Aissaoui and Purser, 1983). 4.2.7. Isopachous bladed cement (IBC) These cements exhibit a bladed texture and isopachous fabric with 10e50 mm-long, prismatic and limpid crystals, attesting to a low-magnesium mineralogy (LMC; Durlet and Loreau, 1996). They are non-luminescent and non-ferroan (Fig. 11E and F). Like the isopachous fibrous cements, they are located in facies E, a few decimeters to one meter below major unconformities in the Vilhonneur and Cosses Noires quarries. The origin of these cements remains problematic as they could have originated from marine to meteoric water in the phreatic zone (Durlet and Loreau, 1996). 4.2.8. Dogtooth cements (DC) These cements correspond to 10e200 mm non-luminescent and non-ferroan scalenohedral limpid crystals, which attests to a low-

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magnesium mineralogy (LMC; Durlet and Loreau, 1996). These isolated crystals do not form an isopachous fringe around grains (pink-stained by alizarin-potassium ferricyanide; Fig. 11H). Dogtooth calcite, in the form of scalenohedral or rhombohedral calcite, is recognized in a wide variety of environments from the meteoric to the shallow burial realm, and is also known from marine settings (Flügel, 2010, p. 294). These cements are mainly present at the top of the Combe Brune, Chez Trape, and Javerlhac quarries in facies F and G. They are rarely found in facies E below discontinuities. While TSC, IFC, ME, MTC, MC, IBC, and DC generally make up less than 10% of the total cement volume, they can reach 50% below some discontinuities (Table 2).

4.2.9. Non-luminescent syntaxial cements (NLSC) These are 50e500 mm-long syntaxial cements around echinoderms, and are generally non-luminescent and non-ferroan (pinkstained by alizarin-potassium ferricyanide; Fig. 11AeD and 12D-E). These limpid cements are crystalized in LMC and present in all the studied sections and grainstone facies (B to G; Figs. 9 and 10). They display highly luminescent narrow bands when located below subaerial unconformities, where they are associated with meniscus cements and geopetal microsparitic cements (facies F, Fig. 12D). These highly luminescent bands may also be present in the periphery of NLSC within non-emersive facies. The origin of these non-luminescent cements with highly luminescent narrow bands is subject to much controversy, but they are often considered to have precipitated in meteoric phreatic to shallow-burial contexts (Loreau and Durlet, 1999), which is consistent with their location in the study area. NLSCs represent between 5% and 50% of the cement proportion.

4.2.10. Blocky calcite (BC1, 2, and 3) Three stages of blocky calcite are observed in the inter-granular and intra-granular pores and in overgrowths on early syntaxial calcite cements. Blocky calcite 1, representing about 40%e80% of the total cement volume, is present in every thin-section and displays concentric zoning with dominating bright orange luminescence alternating with dark orange (ferroan) and dark brown (nonferroan) luminescence (Fig. 12DeG). Blocky calcite 2 is non-ferroan calcite cement and displays a dull brown luminescence (Fig. 12DeG). It represents about 5%e50% of the total cement volume. Blocky calcite 3 is a non-ferroan calcite cement that displays a very bright yellow luminescence and is found either (1) as a thin border of a few mm around blocky calcite 2 or (2) as microspar filling rhombohedral pores (100e300 mm; Fig. 12F).

4.2.11. Dedolomitization 2 A second stage of dedolomitization occurred within intraclastic levels of the Combe Brune quarry (facies C and F; Figs. 9 and 10), where rhombohedra present on grain surrounds and in micrite are not filled by early microsparitic cements but by blocky calcite 3 (Fig. 12F; Purser, 1978).

displaying syntaxial cements (Syn. Ce.). Intergranular pores (In. Po.) and concave-convex (C. C.) to sutured (Su.) contacts. Facies C: intraclast (In.) grainstone with rare bivalves (Bi.) and echinoderms (Ech.), displaying concave-convex (C. C.) and sutured (Su.) contacts, and intergranular pores (In. Po.). Rhombohedra, probable initially dolomite (Do.), form pores when they are not filled by microspar. Facies D: ooid (Oo.) grainstone with rare bivalves (Bi.) and echinoderms (Ech.), displaying low intergranular porosity but with moldic pores (Mo. Po.) and microporosity in ooids (Mp Oo.). Concave-convex (C. C.) to sutured (Su.) contacts. Facies E1: oncoid (On.) -ooid (Oo.) grainstone to packstone with intraclasts (In.), bivalves (Bi.), foraminifers (Fo.), peloidal microbial fabrics (Mi. Fa.), and meniscus-type cements (MTC), displaying low intergranular porosity but with moldic pores and microporosity in ooids (Mp Oo.). The contacts between grains are concave-convex (C. C.) and sutured (Su.). Facies E2 (below discontinuities): oncoid (On.)-ooid (Oo.) grainstone to packstone with intraclasts (In.), bivalves (Bi.), gastropods (Ga.), echinoderms (Ech.), miliolids (Mil.), and peloidal microbial fabrics (Mi. Fa.). Moldic macroporisity (Mo Po.), scarce intergranular pores. Grains are surrounded by early fibrous cement (IFC), cross-cut by borings (Bor.). Facies F: intraclast (In.) grainstone to packstone with geopetal microsparitic (GMC) and dogtooth (DC) cements, displaying intergranular porosity (In. Po.). Rhombohedral pores, formed by dolomitization/dedolomitization processes (Do.), are numerous, while sometimes filled by microspar. Facies G: intraclast (In.)-peloid (Pe.) grainstone with ooids (Oo.), bivalves (Bi.), gastropods (Ga.), echinoderms (Ech.), and miliolids (Mil.). The contacts are sutured to concave-convex (C. C.). Birdeyes and rare microstalactitic cements (MC) are present (Foucher, 1986). The present macroporosity, near to zero, is essentially moldic (Mo. Po.). Microporosity appears in ooids.

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Fig. 5. Synthetic sedimentological log with the associated facies, depositional environments, and sequence stratigraphy. This sedimentological log corresponds to the probable stratigraphic succession between the quarries of Vilhonneur and Combe Brune.

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Fig. 6. A. Combe Brune quarry e facies B, C, and F. B to G. Wedge of clinobedded ooid grainstone foresets e facies B and C e Combe Brune quarry. These images are digitally enhanced using Photoshop CS3. H. Boundary between the Bathonian deposits (facies F) and the Callovian deposits composed of one to two meter-thick tabular beds of peloidal mudstone.

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Fig. 7. A. Porous (blue) micritic ooid (Mi. Oo.) grainstone with echinoderms (Ech.), displaying syntaxial cements (Syn. Ce.) and concave-convex contacts (C$C.) e facies B e Combe Brune quarry. B. Scan of a porous (blue) micritic ooid grainstone thin-section e facies B e Combe Brune quarry. C. Porous (blue) intraclast (In.) grainstone with micritic ooids (Mi. Oo.), echinoderms (Ech.), and rhombohedra, probable initially dolomite (Do.). Note the presence of isopachous fibrous cements (IFC) around grains in the intraclasts e facies C e Combe Brune quarry. D. Sutured contact (Su.) in a micritic ooid (Mi. Oo.) grainstone e facies B e Combe Brune quarry. E. Concave-convex contacts (C. C.) between micritic ooids (Mi. Oo.) and a microporous ooid (Mp Oo.) e facies B e Vilhonneur quarry. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

4.3. Facies architecture and depositional sequences Four transgressive-regressive cycles are identified for the Bathonian (MJVIII, MJXI, MJX and MJXI; Andrieu et al., 2016, Fig. 13). They are bounded by five sequences boundaries, named Bj5, Bt1, Bt2, Bt3 and Bt4 (Andrieu et al., 2016). Considering a time range of about 2.2 My for the Bathonian interval (Gradstein et al., 2012), the rough estimate of the average duration of each cycle is 0.6 My, which is near the range of duration for third-order cycles reported by various authors (Haq et al., 1987; Hardenbol et al., 1998;

Schlager, 2004). The early Bajocian (Sonninia propiquans to Stephanoceras humphriesianum Zones) is dated by the brachiopod Parvirhynchia par
ras and Lathuilie re, vula in the Saint-Martial outcrop (Fig. 13; Alme
et al., 2015). In Saint-Martial, the 1984; Foucher, 1986; Faure maximum regressive surface Bj5 marks the transition from intraclast peloidal grainstones with well-developed microbialites, corresponding to foreshore facies (facies G), to oncoid-ooid grainstone to packstone platform interior open marine facies (facies E, Fig. 13; Foucher, 1986). This surface may correspond to the Bajocian/

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Fig. 8. A. Trough cross-bedded ooid grainstone e Vilhonneur quarry e facies D e Calcaires de Vilhonneur Formation, sequence MJIX. B. Micritic ooid (Mi. Oo.) grainstone displaying concave-convex (C$C.) and sutured (Su) contacts, moldic pores (Mo. Po.), and micropososity in ooids (Mp Oo.) e facies D e Cosses Noires quarry. C. Trough cross-bedded ooid/oncoid grainstone e facies E e Cosses Noires quarry. D. Intraclast/oncoid (In/On) grainstone to rudstone e facies E e Cosses Noires quarry. E. Intraclast/oncoid (In/On) grainstone with ooids (Oo.), gastropods (Ga.), and peloidal microbial fabrics (Mi. Fa.) e facies E e Vilhonneur quarry. F. Oncoid/ooid (On./Oo.) grainstone displaying a boring (Bor.) filled by micritic sediments, with truncated grains e facies E e Cosses Noires quarry. G. Dissolved ooids forming moldic pores and microporous ooid e facies E e Cosses Noires quarry. H. Birds-eye in a intraclast (In.) grainstone with ooids (Oo.), peloids (Pe.), and foraminifers (Fo.) e facies G e Chez Trappe quarry.

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Fig. 9. Paragenetic sequence of the Bathonian carbonate of the northeastern Aquitaine platform. The diagenetic stages are composed of: turbid syntaxial cements (TSC), isopachous fibrous cements (IFC), micritic envelops (ME), and meniscus-type cements (MTC, sensu Hillg€artner et al., 2001), dolomitization/dedolomitization (Do), dissolution of aragonite shells, meniscus cements (MC), and geopetal microsparitic cements (GMC), dogtooth cement (DC), non-luminescent syntaxial cements (NLSC), compaction and three blocky calcite cementations (BC1, 2, and 3).

Table 2 Summarized petrographic characteristics of diagenetic carbonate cements in the Bathonian limestones of the northeastern Aquitaine platform. Diagenetic stages Turbid Syntaxial Cement (TSC)

General characteristics

Cathodoluminescence

Alizarin/ ferricyanide

Turbid syntaxial cement around echinoderms Turbid luminescence (cloudy brown- Pink-stained e 50e200 mm to-orange) non-ferroan calcite Isopachous Fibrous Cement Fibrous crystals e 10e50 mm Turbid luminescence (cloudy brown- Pink-stained (IFC) to-yellow) non-ferroan calcite Micritic Envelopes (ME) and Micritic meniscus cements e ~10 mm Orange luminescence Meniscus-Type Cements (MTC) Meniscus Cements (MC) Asymmetrical cements between grains Dark brown to turbid luminescence Pink-stained composed of microspar e 10e100 mm non-ferroan calcite Anisopachous Microsparitic Asymmetrical cements composed of Dark brown to turbid luminescence Pink-stained Cements (AMC) microspar e 200e500 mm non-ferroan calcite Isopachous Bladed Cement Bladed crystals e 10e50 mm Non-luminescent Pink-stained (IBC) non-ferroan calcite Dogtooth Cement (DC) Scalenohedral fringes or isolated crystals e Non-luminescent Pink-stained 10 mm to 200 mm non-ferroan calcite Non-Luminescent Syntaxial Syntaxial cement around echinoderms e 50 Non-luminescent but can occasionally Pink-stained Cement (NLSC) e500 mm non-ferroan present narrow highly luminescent calcite bands Blocky Calcite 1 (BC1) Coarse crystalline e 100 mm to 3 mm Bright orange to brown luminescence Pink- to mauve/bluestained non-ferroan to ferroan calcite Blocky Calcite 2 (BC2) Coarse crystalline e 100 mm to 3 mm Brown luminescence Pink-stained non-ferroan calcite Blocky Calcite 3 (BC3) Appears as a thin border of a few mm or as Very bright yellow luminescence Pink-stained non-ferroan microspar filling rhombohedral pores (100 calcite e300 mm)

Proportion of cements

Facies

<2%

B, C, D, E, F, G

1%e40% below inner platform sequence boundaries <2%

E (early lithification) E

<2%

F, G

~20%

G

<2%

E (early lithification)

<2%

5%e50%

E (early lithification), F, G B, C, D, E, F, G

20%e80%

B, C, D, E, F, G

0%e50%

B, C, D, E, F

0% to 10%

B, C, F

S. Andrieu et al. / Marine and Petroleum Geology 81 (2017) 169e195 Fig. 10. Location of the early and burial diagenetic phases on the five stratigraphic logs studied in this work. Sedimentary sections are ordered on a 20 km-long eastewest cross-section in the Bathonian deposits of the northeastern Aquitaine platform (France), from Combe Brune quarry to Javerlhac quarry. 183

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Fig. 11. A. Cathodoluminescence view of syntaxial cements around an echinoderm (turbid syntaxial cement eTSC e, non-luminescent syntaxial cement e NLSC e and blocky calcite 1 e BC1) in an ooid grainstone e facies B e Combe Brune quarry. B. Alizarinepotassium ferricyanide stain of a syntaxial cement around an echinoderm (turbid syntaxial cement eTSC e, non-luminescent syntaxial cement e NLSC e and blocky calcite 1 e BC1) e facies B e Combe Brune quarry. C. Non-ferroan isopachous fibrous cement (IFC) and ferroan to €rtner et al., 2001), sometimes replaced non-ferroan blocky calcite (BC1) in an oncoid/ooid grainstone e facies E e Vilhonneur quarry. D. Meniscus-type cements (MTC; sensu Hillga by microspar, in an oncoid/ooid grainstone e facies E e Vilhonneur quarry. E. Cathodoluminescence view of an oncoid/ooid grainstone with isopachous fibrous and bladed cements (IFC and IBC) and blocky calcite 1 (BC1) e facies E e Vilhonneur quarry. F. Cathodoluminescence view of an oncoid/ooid grainstone with isopachous fibrous and bladed cemens (IFC and IBC), blocky calcite 1 and 2 (BC1 and BC2) e facies E e Cosses Noires quarry. G. Cathodoluminescence view of a dissolved aragonitic bivalve filled by non-luminescent bladed cement (IBC) and blocky calcite 1 (BC1) e facies E e Cosses Noires quarry. H. Cathodoluminescence view of an oncoid/ooid grainstone with isopachous fibrous and dogtooth cements (IFC and DC) e facies E e Vilhonneur quarry.

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Fig. 12. A. Oncoid-ooid grainstone with intraclasts (In.), ooids (Oo.), and meniscus cements (MC) e facies F e Combe Brune quarry. B. Cathodoluminescence view of a meniscus cement (MC) with a turbid orange to brown luminescence e facies F e Combe Brune quarry. C. Intraclast (In.) grainstone with geopetal microsparitic cement (GMC) developing after the filling of rhombohedra pores illustrating early dolomitization/dedolomitization processes (Do) e facies F e Combe Brune quarry. D. Cathodoluminescence view of syntaxial cements around an echinoderm (turbid syntaxial cement e TSC e non-luminescent syntaxial cement with narrow highly luminescent bands e NLSC e and blocky calcites 1 and 2 e BC1 and BC2) e facies F e Combe Brune quarry. E. Cathodoluminescence view of syntaxial cements around an echinoderm (non-luminescent syntaxial cement e NLSC e and blocky calcites 1 and 2 e BC1 and BC2) and blocky calcite 3 in an ooid grainstone efacies C e Combe Brune quarry. F. Cathodoluminescence view of blocky calcite 3 (BC3) filling rhombohedra, probably initially of dolomite mineralogy in a intraclast grainstone. Syntaxial cements around an echinoderm (non-luminescent syntaxial cement e NLSC e and blocky calcites 1 and 2 e BC1 and BC2) e facies C e Combe Brune quarry. G. Cathodoluminescence view of blocky calcites 1 and 2 in a intraclast/oncoid grainstone to rudstone e facies E e Cosses Noires quarry. H. Alizarinepotassium ferricyanide stain of blocky calcites 1 and 2 in intraclast/oncoid grainstone to rudstone e facies E e Cosses Noires quarry. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

186 S. Andrieu et al. / Marine and Petroleum Geology 81 (2017) 169e195 Fig. 13. Correlation diagram of the Bathonian deposits of the northeastern Aquitaine platform (France) on a 50 km-long MontignaceNontron transect. This illustration is composed of the five outcrop sections studied in this work completed by previous descriptions of four outcrop sections and one borehole (Foucher, 1986). Correlations are based on biostratigraphy (ammonite, brachiopod, foraminifer, and ostracod associations; Foucher, 1986) and four recognized stratigraphic cycles (MJVIII to MJXI) delimited by sequence boundaries (Bt1 to Bt4). In the interest of readability, the horizontal distance from the top to the base of the slope is exaggerated.

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Fig. 14. Depositional model detailed in three steps ((A) Transgressive Systems Tract/Maximum Flooding Surface, (B) Highstand Systems Tract, and (C) Lowstand Systems Tract) for the three sequences of the Bathonian (MJVIII, MJIX, and MJX) on a 50 km-long transect from Saint-Martial to Montignac. The depositional environments, carbonate producers, sedimentary structures, and facies are located for each step.

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Fig. 15. Depositional model of the maximum regressive surface Bt4 on a 50 km-long transect from Saint-Martial to Montignac. The depositional environments, carbonate producers, sedimentary structures, and facies are located.

Bathonian boundary. The maximum flooding surface of sequence MJVIII is highlighted by the presence of toe-of-slope mudstone to wackestone alternating with marly layers (facies A) around Combe Brune and by shoal facies around Saint-Martial, displaying trough cross-bedding in ooid grainstones (facies D, Fig. 13). Above sequences MJIX to MJXI, maximum flooding surfaces are characterized by a wide shoal setting stretching from Combe Brune to SaintMartial (Figs. 13 and 14A). Maximum flooding surfaces are marked in the southeastern shallow platform from Chez Trape to SaintMartial by oncoid grainstones to packstones (facies E) whereas the northwestern shallow platform from Combe Brune to the Cosses Noires displays ooid grainstones (facies D, Figs. 13 and 14A). Around Combe Brune, porous ooid grainstones display large-scale high-angle clinoforms at least 30 m high with a dip of about 20
to the northwest (facies B, Fig. 9AeG, 13 and 14A). These ooid grainstones (facies B) grade laterally into peloidal mudstone to wackestone alternating with marly layers (facies A) deposited in a toe-of-slope environment (Figs. 13 and 14A). Around Montignac, the maximum flooding surfaces are characterized by condensed marl layers or glauconitic limestones (Fig. 13). Within transgressive systems tracts, the environments retrograde sharply southeastward and the oolitic wedge is overlain by limestone/marl alternations (Figs. 13 and 14A). During the deposition of the highstand systems tract of sequences MJVIII to MJXI, the oolitic wedge (facies B) prograded northwestward and overlay the mudstone to wackestone alternating with marly layers (facies A, Figs. 13 and 14B). On the shallow platform, wave-dominated oncoidal grainstones to rudstones (facies E) and foreshore peloidal/intraclast grainstones (facies G) prograded northwestward (Figs. 13 and 14B). During deposition of the lowstand systems tract, corresponding to the uppermost part of the prograding cycle, intraclast rudstones (facies C) overlay the ooid grainstones (facies B) in the Combe Brune quarry, indicative of the erosion of shallow platform deposits and increased hydrodynamism (Figs. 13 and 14C). The sequence boundaries Bt1 and Bt2 are well marked by a subaerial unconformity from Chez Trape to Saint-Martial, with the occurrence of terrestrial marls with lignite layers and Chara gyrogonites (facies H, Fig. 13). They respectively mark a transition from

terrestrial to platform interior open marine (facies E) or foreshore (facies G) environments. Sequence boundary Bt3 is marked by a shift from foreshore facies (facies G) to open marine facies (facies E) from the Chez Trape to Saint Martial quarries (Fig. 13 Foucher, 1986). Around the Vilhonneur and Cosses Noires quarries, the sequence boundaries Bt1 to Bt3 correspond to perforated hardgrounds encrusted by bivalves, stretching on about 10 km and displaying an early isopachous fibrous to bladed marine cement (facies E2). On the platform slope, around Combe Brune, the maximum regressive surfaces are located at the top of the intraclast rudstone levels (facies C). Sequence boundary Bt4 is a major subaerial unconformity from Saint-Martial to Combe Brune marking a hiatus of the early Callovian, as attested by the occurrence of Aulcacothyris pala (middle Callovian) at the base of the Calcaires crayeux de Montbron Formation (Figs. 13 and 15; Foucher, 1986). This subaerial unconformity is marked at Combe Brune by the occurrence of dogtooth, meniscus, and geopetal microsparitic cements, and early dolomitization/dedolomitization processes, which characterize vadose early cementation (facies G, Figs. 13 and 15; Purser, 1969, 1978; Longman, 1980; Brigaud et al., 2014). Throughout the Bathonian, the sedimentation rate was similar in the toe-of-slope environments, the infralittoral prograding oolitic wedge, and the shallow platform, with values about 22e27 m/My (Figs. 13 and 14). 4.4. Depositional model A dynamic depositional model was elaborated based on the facies and depositional architecture of the Bathonian sequences MJVIII to MJX (Fig. 14). Different facies characterizing various environments are identified from the emerged platform to the basin: (1) terrestrial marls with Chara gyrogonites and lignite layers (facies H, Foucher, 1986), (2) foreshore peloid/intraclast grainstones with birdseyes and microstalactitic early cements (facies G, Foucher, 1986), (3) platform interior open marine oncoid-ooid grainstones to packstones with peloidal microbial fabrics, micritic meniscus cements, and planar to trough cross-bedding in dunes (facies E), (4) ooid grainstones with planar to trough cross-bedding

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in dunes forming the shoal (facies D), (5) infralittoral prograding oolitic wedge with clinobedded intraclast to ooid rudstones to grainstones (facies B and C), and (6) toe-of-slope peloidal mudstone to wackestone alternating with marly layers (facies A). The height between the base and the top of the oblique clinoforms observed in the Combe Brune quarry is at least 30 m (Figs. 13, 14 and 16). Borehole data indicate a total thickness of 50 m for the clinobedded intraclast to ooid rudstones to grainstones (Calcaire de Combe Brune Formation; French Geological Survey available online http://infoterre.brgm.fr facies B and D, Figs. 13 and 14). The height of the clinoforms is then at least 30 m and cannot be more than 50 m after compaction, as it corresponds to the total thickness of the limestones where they developed (Fig. 16). Considering that the Bathonian formations of the northeastern Aquitaine platform have been buried under a sediment thickness between 1000 and 1200 m (Bourgueil et al., 1970; Dubreuilh, 1980; Platel, 1996), the decompaction factor for grainstones is about 1.2 (Goldahmmer, 1997). This suggests a paleobathymetry of between 35 m and 60 m from the top to the base of the slope, which corresponds to the decompacted height of the clinoforms (Fig. 16). The initial angle for the clinoforms can be computed using the decompacted thickness and was about 23
, that is three degrees more than the angle measured in the field (20
). The horizontal distance from the top to the base of the slope was between 80 m and 140 m and the length of the clinoforms was 90 me150 m (Fig. 16). The topset of the clinoforms was located above the fair-weather wave base as attested by planar to trough cross-bedding in dunes and grainstone texture (facies D, E, and F). This suggests a depth for the transition between ooid grainstones and mudstone to wackestone alternating with marly layers at the base of the clinoforms equal to the sum of (1) the bathymetry at the top of the clinoforms (10e15 m) plus (2) the height between the top and the base of the clinoforms (35e60 m). Ooids formed above the fair weather wave-base before being exported basinward and formed ooid grainstones as far as the bottom of the infralittoral prograding oolitic wedge. The lateral transition between ooid grainstone and mudstone to wackestone alternating with marly layers is found at a depth of at least 40 m and not more than 75 m (Fig. 16). Facies B and C are interpreted as resulting from sediment accumulation induced by avalanching below the wave-base along a large-scale high-angle slope (23
, Fig. 14, e.g. Swift et al., 1985; Nummedal, 1991; Pomar et al., 2015). Carbonate sediments were transported across the high-energy shallow platform before being exported seaward toward the breakpoint, leading to the progradation of the clinoforms (Fig. 14B and C). The finer particles such as peloids, bioclast fragments, and micrite continued to be transported by bottom currents tens of kilometers beyond the break of the slope (Fig. 14B and C). At Montignac, 20 km from the prograding oolitic to intraclastic wedges, the muddy carbonate sedimentation rate was similar to that on the infralittoral prograding oolitic wedge or the shallow platform, attesting to a significant export of carbonate production toward distal offshore environments (Figs. 13 and 14B and C). However, while the abundance of peloids and bioclast fragments within mudstones to wackestones alternating with marly layers indicates an export of carbonate from shallow platform environments, we cannot exclude the contribution of in situ micrite production or lateral current transport. 5. Discussion 5.1. The northeastern Aquitaine shallow-platform margin: comparison with other prograding wedges The depositional model of the northeastern Aquitaine shallowplatform margin conforms well with the infralittoral prograding

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ndez-Molina et al., 2000; Pomar wedge model (ILPW, sensu Herna and Tropeano, 2001; Fern
andez-Salas et al., 2003; Lobo et al., 2004; Mateu-Vicens et al., 2008; and Pomar et al., 2015) in terms of architecture, dimensions, and dynamics (Table 3).
ndez-Molina et al. (2000) developed the infralittoral Herna prograding wedge (ILPW) model for clastic wave-dominated Spanish coasts during the Late Holocene between the onshore (beach) and the offshore. They suggested that this model could be applied to numerous Late PleistoceneeHolocene sedimentary deposits already described (e.g. Tesson et al., 1993; Trincardi and Field, 1991). The ILPW model described a progradational-margin slope on which topset, foreset, and bottomset are recognized (Hern
andezMolina et al., 2000). Currents induced seaward sediment transport until a break point where they avalanched down the slope below the wave-base, leading to the progradation of the wedges
ndez-Molina et al., formed exclusively by exported grains (Herna 2000). The downlap of the wedges interfingered with basinal muds. Subsequently, Chiocci et al. (2004) emphasized the independence of these progradational sandbodies from sediment composition, as they developed either on clastic or carbonate coasts. Pomar et al. (2015) have made a complete synthesis of the numerous studies conducted on infralittoral prograding wedges (ILPWs), much as Pierre et al. (2010), Heydari and Baria (2005), and Handford and Baria (2007) did for Jurassic series. They suggest that this genetic model is a reliable approach for describing the depositional processes of ancient carbonate margins, especially for Jurassic and Cretaceous times. In Holocene highstand systems tracts, ILPWs are essentially prograding with sedimentation concentrated on the platform
ndez-Molina et al., slope, forming the wedges (Table 3; e.g. Herna
ndez-Salas et al., 2000; Fraser et al., 2005; Lobo et al., 2005; Ferna 2009). This largely prevailing prograding trend is also evidenced by Pomar and Tropeano (2001) at the scale of regressiveetransgressive cycles in the Calcarenite di Gravina formation (Pliocene to Pleistocene), as sedimentation only occurred during highstand sea levels or sea-level falls but not during transgressive intervals. Almost all the sediments produced above the fair-weather wavebase are then exported and deposited on the wedge. In the northeastern Aquitaine platform, the sedimentation rates on the shallow platform, the infralittoral prograding oolitic wedge, and the toe-of-slope are similar at the scale of an entire sequence. This, among other things, is the consequence of a consistent sedimentation rate on the shallow platform during transgressive intervals, instead of ravinement erosion as occurred with the Calcarenite di Gravina formation (Pomar and Tropeano, 2001; Mateu-Vicens et al., 2008, Table 3), and continuity of the sedimentation on the shallow platform during highstand sea levels, even if export then prevails. Finally, at the scale of an entire sequence, the dynamics is more aggrading on the shallow platform and the toe-of-slope than in other ILPW models. Examining the late Pliocene to early Pleistocene prograding wedges of southern Italy, Pomar and Tropeano (2001) and Mateu-Vicens et al. (2008) showed that falls in relative sea-level were marked by exposure of the shoreface deposits leading to the erosion of topsets. Here, maximum regressive surfaces are characterized by marine bored and early cemented marine hardgrounds passing landward into exposure surfaces, and the topsets are preserved (Figs. 13 and 14C). As suggested by Pomar et al. (2015), differences in stacking patterns of ILPWs could be controlled by the rate of sediment supply, tectonics, and eustasy, which modify accommodation space. In our study area, the deposition of about 60 m of decompacted sediments in shallow wavedominated platform environments during the Bathonian (paleodepth <10e15 m; Sahagian et al., 1996; Plint, 2010) suggests substantial tectonic subsidence occurred, which may explain the more aggrading long-term dynamics than in some other prograding

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Fig. 16. Scheme illustrating the dimensions of the infralittoral prograding oolitic wedge after compaction and before compaction, and indicating the inferred depth.

wedges (Pomar and Tropeano, 2001; Mateu-Vicens et al., 2008, Table 3). Four sequences are recorded in the Bathonian deposits of the northeastern Aquitaine platform, as in the eastern (Brigaud et al., 2009a) and western (Andrieu et al., 2016) Paris Basin, and they are interpreted as third-order sequences controlled by global eustasy. As the shallow platform was not fully emerged during maxima of regression, the amplitude of third-order sea-level variations was shallower than the depth of the fair-weather wave base, which can be estimated at 10e15 m in shallow epicontinental seas (Sahagian et al., 1996; Plint, 2010). The small magnitude of eustatic sea-level variations (about 10 m) and high subsidence meant that

entire sequences were preserved, which is not the case of PlioPleistocene records when glacio-eustatic sea-level variations were of much higher magnitudes (Pillans et al., 1998). The sea-level rises and falls of less than 10 m, recorded for the third-order sequences on the northeastern Aquitaine platform, led (1) to episodes of progradation of the oolitic platform wedge during highstand and lowstand systems tract and to small retrogradations over transgressive systems tracts, and (2) to the formation of early cemented subaerial and marine hardgrounds on the shallow platform.

Table 3 Characteristics of the northeastern Aquitaine platform infralittoral prograding oolitic wedge model compared with the characteristics of others infralittoral prograding wedges
ndez-Molina et al., 2000; Pomar et al., 2015). (sensu Herna
ndez-Molina et al., Northeastern Aquitaine platform prograding oolitic Other infralittoral prograding wedges (sensu Herna wedge model 2000; Pomar et al., 2015) Age

Bathonian

Composition

Oolitic-lithoclastic

Lateral extension parallel to the shoreline Yes Down-dip extent (progradation distance) 5e20 km Thickness (depending on accommodation ~50 m space creation and aggradation vs progradation ratio) Internal architecture Oblique Dip of clinobeds 20


Presence of topsets, foresets, and bottom sets Bathymetry variation between topsets and botomsets of the clinobeds Downlap interfingering basinal muds Elongation of the shallow platform margin Dynamics of formation of the prograding wedges Sedimentation

Yes 35e60 m


ndez-Molina et al., 2000) to Aalenian/Bajocian Late Holocene (Herna (Pierre et al., 2010) Oolitic (Pomar et al., 2015), oolitic-peloidal (Pierre et al., 2010), skeletal (Massari and Chiocci, 2006), lithoclastic (Pomar et al., 2015), mixed
ndezcarbonate-siliciclastic (Massari et al., 1999), siliciclastic (Herna Molina et al., 2000) Yes 300 m (Hern
andez-Molina et al., 1995, 1998) to 150 km (Late Jurassic, Saudi Arabia) 15 m (Late Jurassic, Saudi Arabia) - 70 m (Oxfordian; Louisiana; Heydari and Baria, 2005; Handford and Baria, 2007) Sigmoidal to oblique 1.5
(Pleistocene, Italy, Trincardi and Field, 1991; Late PleistoceneHolocene, France, Tesson et al., 1993) to 20
(Albian; Mexico; Osleger et al., 2004) Yes

5e20 m (Kimmeridgian; Spain; Pomar et al., 2015) to 50e70 m (Oxfordian; Louisiana; Heydari and Baria, 2005; Handford and Baria, 2007) Yes Yes Tens of kilometers 10 km (Oxfordian; Louisiana; Heydari and Baria, 2005; Handford and Baria, 2007) to >100 km (Late Jurassic, Saudi Arabia) Similar to infralittoral prograding wedge model Sediments transported along the high-energy platform top before being (sensu Pomar et al., 2015) exported seaward toward the breakpoint where they cascaded down the slope Essentially prograding Aggrading/prograding Sedimentation occurs along the slope but also on Sedimentation is essentially located on the platform slope the platform top and in the offshore environments The export of carbonate/siliciclastic sediments is essentially limited to the Carbonate sediments are exported up to more than prograding wedges Generally homogenous sediment fabric inhibiting appearance of 20 km beyond the prograding wedges significant surfaces Occurrence of coarser lithoclastic levels within oolitic deposits attesting to sea-level fall and increased hydrodynamism

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5.2. Sequence stratigraphy model for a prograding oolitic wedge: linking architecture, discontinuities, and early diagenesis 5.2.1. Sedimentation dynamics and control on discontinuity formation: a balance between carbonate production and export The sedimentary dynamics varies within a similar sequence as a function of the sea-level fluctuations. Transgressive systems tracts are marked by an increase in accommodation space leading to (1) retrogradation of environments and (2) sedimentation essentially located on the shallow platform, as the export of carbonates was low. The ratio between non-exported carbonate production (NEC) and exported carbonate (EC) was then greater than 1, as deposits are much thicker on the shallow platform than on the infralittoral prograding oolitic wedge or in toe-of-slope environments (NEC/ EC > 1, Figs. 14A and 17A, and B). In toe-of-slope environments, transgressive systems tracts and maximum flooding surfaces are merged within condensed clayey or glauconitic levels (Figs. 13 and 14A). During the formation of the highstand systems tract, ooid grainstone to more sheltered oncoid grainstone to packstone were respectively deposited on the platform interior and shoal. However, the decreasing accommodation space on the shallow platform induced progradation of the ooid wedges (facies B and C). This implies substantial export of carbonate production by currents (NEC/EC < 1; Figs. 14B and 17A and B). The lowstand systems tract is composed of an intraclast rudstone level that was deposited on the prograding wedge. Its formation was synchronous with the formation of subaerial unconformities and marine hardgrounds on the shallow platform, which attests to a sedimentary hiatus with a very low accommodation space (Figs. 14C and 17A and B). The same discontinuity evolved laterally from subaerial exposure in terrestrial setting to foreshore (hardground surface with microstalactitic, geopetal microsparitic and meniscus cements; lignite level and desiccation cracks) to erosional marine hardground in the open marine setting (borings, encrusting bivalves, isopachous early cements, early cemented intraclasts; Figs. 14C and 17A and B). Thus, sequence boundaries evolve basinward from subaerial unconformity to marine hardground and top intraclastic lowstand systems tract on the prograding edge slope. The intraclasts contained within the lowstand systems tract are ooid/oncoid grainstones with early isopachous cements, indicating that they originated from the erosion of the shallow platform marine hardground. The lithified surface was eroded under very high hydrodynamic conditions, leading to the fragmentation of lithified carbonate sediments which were transported as far as the slope where they avalanched (facies C, Figs. 13, 14C and 17A and B; Loreau and Durlet, 1999; Christ et al., 2012). The allochems within the lowstand systems tracts are composed of about 80% of intraclasts, the remainder being ooids, echinoderms, and bivalves. Carbonate production on the shallow platform was then near zero and entirely exported during the deposition of the lowstand systems tract (NEC/EC / 0). Intraclastic levels are about 2 m thick and developed on 90 me150 m long clinoforms (mean value ¼ 120 m; Figs. 13 and 16). Considering that intraclasts represent about 60% of the lowstand systems tract rock volume and that hardgrounds stretch for about 10 km over the shallow platform, it can be estimated that intraclasts represent the erosion of the very superficial part of the hardground, of an order of magnitude about 1 cm: (2 m  120 m x 60%)/10 000 m ¼ 1.4 cm). The thickness of the hardground currently observable in outcrops may therefore be very similar to the original thickness of the hardground, which may have been as much as 1 m. However, this estimate omits the intraclasts that were not transported as far as the prograding wedge or finer particles that could have been transported basinward by surface currents. As suggested by Christ et al. (2012), hardgrounds form above the fair-weather wave base

191

during relative sea-level falls. The shallow platform, which is characterized by water depths shallower than the fair-weather wave base (10e15 m in epicontinental seas; Sahagian et al., 1996; Plint, 2010) even at maximum flooding surfaces, is partially exposed at sequence boundaries. This attests to a relative sea-level fall of less than 10 m but certainly more than 5 m. The paleodepth for the formation of these marine hardgrounds was less than 10 m. 5.2.2. Linking the depositional model and sequence stratigraphy with diagenesis: an environmental control on early cementation The eight facies identified display multiple eogenetic cements in variable proportions depending of their depositional environment and/or their stratigraphic location (Fig. 18). Early cements other than syntaxial cements are located exclusively over a thickness of about 1 m below discontinuities corresponding to exposure surfaces (vadose zone: meniscus, microparitic geopetal cements) or marine hardgrounds (marine phreatic zone: isopachous fibrous to bladed cements, micritic envelopes, and pseudo-meniscus cements; Fig. 18). Meniscus-type €rtner et al., 2001) and micritic envelopes are cements (sensu Hillga microbially induced micritic cements that form in environments with abundant organic matter. Here, these cements are especially developed under marine hardgrounds (facies F). The presence of early cements under maximum regressive surfaces has already been suggested by various authors, for example in the Paris Basin (Purser, 1969, 1978; Brigaud et al., 2009a). However, no eogenetic cements other than syntaxial cements are observed within the infralittoral prograding oolitic wedge, even below maximum regressive surfaces (facies B and C; Fig. 18). This reflects a difference in environmental conditions and sedimentation rate between the shallow platform and the infralittoral prograding oolitic wedge. Early cementation is favored by high porosities and permeabilities typical of granular facies and by high hydrodynamism above the fair-weather wave-base resulting in (1) higher rates of water circulation within sediments, providing calcium carbonate ions for early cementation and promoting seafloor lithification (Shinn, 1969; Marshall and Ashton, 1980; Coimbra et al., 2009), and (2) permanent winnowing of the seafloor that induces low or zero sedimentation rates (Immenhauser, 2009). During maxima of regression, all these conditions occurred on the shallow platform, leading to the formation of hardgrounds. Moreover, the near-zero sedimentation rate favored accumulation of organic matter and microbial colonization, leading to the development of microbially-induced cements such as meniscus-type €rtner et al., 2001). cements and micritic envelopes (Hillga In contrast, no continuous winnowing occurred on the prograding wedge because it developed below the fair-weather wave base. Accordingly, it was subject to intensive and continuous sedimentation preventing lithification of the sea-floor. Indeed, hardgrounds and exposure surfaces on the shallow platform correlate with intraclastic deposits down the wedge (lowstand systems tract, Fig. 18). Moreover, lower hydrodynamic conditions on the prograding wedge resulted in a lower rate of water circulation within sediments and so carbonate ions were less abundant for early cementation (Shinn, 1969; Marshall and Ashton, 1980; Coimbra et al., 2009). A high sedimentation rate also reduced organic matter accumulation and was therefore detrimental to microbial colonization preventing the formation of meniscus-type cements and micritic envelops on the prograding wedge €rtner et al., 2001). (Hillga The high sedimentation rate and the lower hydrodynamic conditions on prograding wedges make them one of the very few depositional environments where grainstone facies are not associated with the development of early cementation. This is of major relevance because early marine cements reduce the porosity and

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Fig. 17. A. Evolution of the stacking patterns and related carbonate production and export for a third-order sequence in three steps: transgressive systems tract, highstand systems tract, and lowstand systems tract. B. Sequence stratigraphy model of the northeastern Aquitaine platform wedge.

permeability of the lithified interval, very soon after deposition. Thus, hardgrounds can clearly impact (compartmentalize) reservoir flow behaviour (Christ et al., 2015), especially before the growth of blocky calcite or when blocky calcite is poorly developed. It has

been demonstrated that hardgrounds in chalk deposits form barriers to fluid flow (Scholle and Kennedy, 1974; Richard et al., 2005). In our study, early cements, especially isopachous fibrous cements, can fill as much as 50% of the intergranular space below some

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Fig. 18. Synthesis linking early cements development with sequence stratigraphy and depositional model of the northeastern Aquitaine platform wedge.

hardgrounds (e.g. Bt3). Their absence from the infralittoral prograding oolitic wedge, where blocky calcite is poorly developed, clearly allows the preservation of good porosities during burial. The studied infralittoral prograding oolitic wedge in the Aquitaine platform forms a good analogue, in terms of size and facies distribution, of a carbonate reservoir target.

6. Conclusions A dynamic depositional model is proposed for three third-order sequences of the Bathonian of the northeastern Aquitaine platform. Environments vary from the emerged platform to the basin: (1) terrestrial setting, (2) foreshore, (3) open marine platform interior, (4) shoal, (5) infralittoral prograding oolitic wedge, and (6) toe-ofslope. Carbonate production was essentially non-bioclastic (ooids, oncoids, peloids, and intraclasts) and was limited to the tide-to wave-dominated shallow platform before being transported seaward toward the breakpoint where carbonates cascaded onto the slope, leading to the progradation of the platform margin clinoforms. The finer carbonate particles continued to be transported for tens of kilometers beyond the break of the slope, contributing to high accumulation of micritic carbonate sediments in the toe-ofslope setting. The amplitude of the bathymetry fell from the top to the base of the high angle platform slope (20e25
) was ranging between 35 m and 60 m over a horizontal distance of 80 me140 m.

The depth at the base of the slope, where ooid grainstones pass into mudstone to wackestone alternating with marly layers, is between 40 m and 75 m. The depositional model for the northeastern Aquitaine platform conforms well with the infralittoral prograding
ndez-Molina et al., 2000; Pomar wedge (ILPW) model (sensu Herna et al., 2015). The dynamics of the sedimentation varied within a similar sequence with the eustatic sea-level variations. During the transgressive systems tracts, sedimentation was located essentially on the shallow platform and the export of carbonate production was negligible. Over the highstand systems tract, the export of carbonate production onto the slope and in toe-of-slope environments increased resulting in the progradation of the platform wedge. The lowstand systems tract gave rise to an intraclast rudstone level on the prograding wedge. Its deposition was synchronous with a sedimentation hiatus on the shallow platform, where a same discontinuity passes laterally from a subaerial exposure surface into erosional marine hardground. Carbonate production on the shallow platform was near-zero and high hydrodynamic conditions led to (1) the development of marine hardgrounds and (2) the fragmentation of early-cemented lithified carbonate sediments and their transport as far as the slope where they avalanched forming intraclast rudstones. The constant sedimentation rate and the lower hydrodynamic conditions on the infralittoral prograding oolitic wedge precluded the development of eogenetic cements. This work demonstrates

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that the infralittoral prograding oolitic wedge is a key part of carbonate platforms where early cements are absent, preserving the porosity and permeability during the first step of diagenesis. Finally, this study proposes a sequence stratigraphy model for oolitic carbonate platform wedges combining studies of facies and early diagenesis. This model highlights the changes in carbonate export and production rates within a sea-level cycle, the lateral variability of sequence boundary surfaces over tens of kilometers, and the major impact of paleoenvironmental conditions on early cementation and preservation of reservoir properties. Acknowledgements This work is the outcome of collaborative project No PO4990 between the University Paris-Sud and the BRGM. The project was funded by the BRGM and by a PhD grant from the French Ministry of Research and Higher Education (2013-134). We are grateful to Philippe Blanc (Lithologie Bourgogne) for the high-quality thinsections. The authors thank the anonymous reviewer, Beatriz B
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