Evolution of the Eocene shallow carbonate platform in Tunisia: Carbon isotopes stratigraphy and petroleum implications

doi:10.21203/rs.3.rs-1955221/v1

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Evolution of the Eocene shallow carbonate platform in Tunisia: Carbon isotopes stratigraphy and petroleum implications

https://doi.org/10.21203/rs.3.rs-1955221/v1

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This study aims to comprehend how the SW Neo-Tethys carbonate platform responded to Eocene global warming events and the possible relations with developing the middle Eocene carbonate oil reservoir (Reneiche member). The Eocene deposits of the Southern Neo-Tethys margin (Tunisia) are NW-SE-oriented facies belts with evident variations in thickness and facies. Along a homoclinal ramp, the Cherahil Formation's shallow carbonate platform facies progressively shift into the Souar Formation's globigerinids-clays. Major controls have been exerted on the central Tunisia platform by synsedimentary tectonics, sea-level oscillations, and warming events. Ten facies were identified and are attributed to at least three sedimentary models. The middle-upper Eocene sedimentary environments are wave dominant, influenced by storms and tide in a shallow water depth, passing during the Oligocene into a sandy fluvial and estuarine environment. Sequence stratigraphic analysis points towards shallowing upward trend interrupted during the lower Bartonian by a significant transgression. This sea-level rise coincides with a shift towards a short maximum nummulite carbonate production absent since the nummulitic limestones of the El Garia Formation (Ypresian). Proximal facies of dominant lumachellic marls shift to a thickening-upward sequence of transgressive facies culminating in a maximum nummulitic carbonate production during the middle Eocene transgression and coincides broadly at the global scale with the occurrence of the Middle Eocene Climatic Optimum (MECO). Previous biostratigraphic studies confirm the position of the Reneiche/Siouf member and here by the bulk carbon isotope record (δ¹³C) characterized by a negative carbon isotope excursion in the middle of the Siouf member followed by a positive excursion at the top of this member, which is comparable to the δ¹³C record through the MECO in the reference sections. In response to the MECO, the early Bartonian is recognized as crucial for the large benthic foraminifera in various shallow-marine settings along the Tethys margins.

Larger benthic foraminifera

Carbonate oil reservoir

Central Tunisia

Warming events

Early Bartonian

Early Eocene Climatic Optimum

Early Paleogene warming events favoured the development of nummulitic carbonate reservoirs.
Eocene deposits were controlled by tectonics, eustatic sea level, and global warming.
Mesotrophic conditions during the early Bartonian in shallow carbonate platform.
Middle Eocene carbon isotope stratigraphy in shallow carbonate platform

The primary factors maintaining life in ancient shallow carbonate platforms include sunshine, nutrition, substrate type, temperature, depth, transparency, energy, and chemical composition of the water (e.g., Strasser, 1988; Flugel and Flügel, 2004). The climate influences these variables, the hinterland (siliciclastics and nutrients), oceanic currents (heat and nutrients), relative sea level (water depth and tidal regime), and the morphology of the shoreline and platform (changing currents and sediment dispersion). Ancient shallow-marine carbonate platforms frequently show stacking of various facies in their sedimentary records, which implies repeated changes in depositional conditions over time (e.g., Strasser, 1988; Flugel and Flügel, 2004). Both internal and external variables, such as lateral movement of sediment bodies and/or changes in the ecology of the carbonate-producing organisms, can cause these changes (e.g., Strasser, 1988, 2018). External factors that can cause these changes include climate change and/or sea level

The Paleogene Neo-Tethyan carbonate platforms' evolution was mainly controlled by tectonic activity, eustatic sea-level fluctuations, and profound long-term climatic evolution. These carbonate platform systems are excellent depositional archives and are sensitive to climate change, such as the transition from the greenhouse world to the icehouse world (e.g., Nocchi et al., 1988; Jorry, 2004; Scheibner and Speijer, 2008; Höntzsch, 2011; Salama et al., 2014; Tomassetti et al., 2016; Martín-Martín et al., 2021). The middle-upper Eocene Cherahil Formation records cyclic sedimentation of marl/limestone alternations (e.g., Bonnefous and Bismuth, 1982a; Racey et al., 2001; Amami Hamdi and Ben Ismail Lattrache, 2013; Amami-Hamdi et al., 2016). It has great importance in the petroleum system of central Tunisia and Gulf of Gabes because its sediments provide both reservoir and cap rocks (e.g., Burollet, 1956; Bonnefous and Bismuth, 1982; Ben Ferjani et al., 1990; Bismuth, 1996; Mejri et al., 2006).

The intricate evolution of shallow-marine ecosystems during the Paleogene has been demonstrated in numerous case studies on Tethyan carbonate platforms (e.g., Martín-Martín et al., 2021b; Tosquella et al., 2022). Coherent platform models, which consider tectonic, climatic, and local regulating mechanisms, are still uncommon in the SW Neo-Tethys. How the Paleogene hyperthermal events would affect the carbonate platform has not yet been determined. In order to reconstruct the effects of long-term climate change and intricate local environmental perturbations on shallow-marine carbonate platforms, We studied one complete section covering the Cherahil Formation in a shallow carbonate platform system. High-resolution microfacies, stable carbon isotopes, and comparisons of the recorded successions with other Tethyan carbonate platforms will allow us to understand the regulatory processes and the timeframe of Palaeogene platform evolution. The main goals of this work are to characterize the depositional environment, evaluate sedimentation controls, and clarify the relationship between the occurrence of nummulitic limestone and the Paleogene global warming events.

The middle-upper Cherahil Formation is widely developed in the central Tunisian basin. It consists of shallow-marine marl and lumachellic limestone with some highly dolomitized levels, passing during the early Bartonian into highly fossiliferous nummulite bioclastic limestone (e.g., Burollet, 1956; Bismuth and Bonnefous, 1980; Bonnefous and Bismuth, 1982). Sedimentological studies on the middle Eocene outcrops in central Tunisia are limited and sparse (Chermiti et al. 2018; Njahi Derbali and Touir 2019). Rocks are principally carbonates and represent lagoonal facies in the lower part, evolving into more open-marine facies as pointed out by the abundance of benthic organisms (e.g., Ben jemia-fakhfakh, 1991; Ben-Ismail-Lattrache, 2000; Ben-Ismail-Lattrache et al., 2014; Amami-Hamdi et al., 2016). The Bougobrine section (238-m) was logged and sampled for facies analysis in the northern Touila range (Fig. 2), approximately 3 kilometres to the SW of Sidi Saad Lake (Kairouan, central Tunisia).

Figure 1 about here

3.1. Sedimentology

The Bougobrine section was carefully sampled/logged, and each sample (36 samples) was taken after digging a few centimetres (10 to 30 cm). The stratigraphic analysis includes tracking of depositional units, facies types assessment, and fossils content. The definition of facies is based on a detailed field analysis of the depositional features: fossil content, texture, sedimentary structures, the abundance of carbonate grains (mainly skeletal grains), the character of bounding surfaces, and thickness. Also, each macro-facies were supplemented by observations of at least one thin section. Friable materials were washed after treatment with H₂O₂ and sieved into three grain-size fractions (500, 250, and 63 µm). The picked microfossils were identified and counted in abundance using an Optika stereomicroscope. The limestone bed textures were studied on thin sections under a petrographic microscope, and the allochems abundance was calculated compared to the whole rock. The texture was described according to Dunham´s (1962) classification.

3.2. Bulk Carbon Isotopes

Samples prepared for geochemical analysis were grounded using a ceramic ball mill at the University of Copenhagen. Bulk carbonate carbon analyses have been performed on 66 samples across the Siouf member (0.7 m to 1m resolution). Measurements were carried out following the method of Spótl and Vennemann (2003) for mass spectrometry using a Micromass Iso Prime Isotope Ratio Mass Spectrometer at the Stable Isotope Laboratory in the Department of Geoscience and natural resources management at the University of Copenhagen. Only the carbon isotopes are considered here. Isotope ratios are reported in the conventional delta value relative to the V-PDB standard, with a σ2 of 0.04‰ for δ¹³C.

4.1. Lithostratigraphic units

The Bougobrine section (238 m) can be discriminated into three major intervals (Fig. 2): (i) the Lutetian Cherahil (A) member is composed of alternating lumachellic marls, dolomitic limestone, and marly limestone;(ii) the lower Bartonian corresponds to bioclastic limestone comprising numerous gastropods, nummulites, and small echinoderms of the Siouf member; (iii) the Bartonian to Priabonian Cherahil (B) member is distinguished by marly limestones containing oysters evolving into silty shales during the Priabonian.

Figure 2 about here portrait

Seven units were identified (Fig. 2). Unit 1 is 35 m thick and comprises alternations of lumachellic marls and marly limestones. Unit 2 is an interval marked by marls across about 30 m, intercalated with lumachellic marls, and is topped by a bioclastic limestone bed. Unit 3 is 45 m thick and comprises lumachellic marls beds with scarce oysters. Unit 4 (25 m) corresponds to lumachellic marl at the base and a succession of bioclastic limestones at the top. Unit 5 shows the first appearance of LBF associations (nummulites, discocyclina, and alveolina). This unit corresponds to the Siouf member and is defined as interbedded lumachellic marl and chalky limestones that evolve into nummulite-rich limestones with echinoderms and crinoids. Unit 6 is represented by thicker marly limestone beds with scare oysters and thinner bioclastic limestone levels. A 2-m bed of lumachellic marls caps this 60-m unit. Unit 7 (25 m) is characterized at the base by lumachellic marls followed by thick grey silty shales with scare gypsum.

4.3. Ostracods biostratigraphy and regional correlations

A correlation with the previously published works (Amami-Hamdi et al., 2014; Aïda Amami Hamdi and Ben Ismail Lattrache, 2013) and internal reports (Tunisian National Oil Company, ETAP) allows attributing ostracod zones to the Bougobrine section (supplementary materials). The Bougobrine section covers the Loculicytheretta semipunctata ostracod zone f1976) to the Loculicytherettaaff. Gortanii Zone (Priabonian, Bismuth et al., 1978; Oertli, 1976) in the lumachellic facies of the Cherahil Fm. (Figs. 2, 3, and 4).

Figure 3 about here

The Loculicytheretta semipunctata ostracod zone corresponds to the first 50 m of the Bougobrine section. In Tunisia, this zone is of the early Lutetian age (Amami Hamdi & Ben Ismail Lattrache, 2013; Bismuth et al., 1978; Oertli, 1976). The 50–90 m interval is attributed to the Loculicytheretta semirugosa zone (middle Lutetian, Aïda Amami Hamdi & Ben Ismail Lattrache, 2013; Bismuth et al., 1978; Oertli, 1976). The extinction of Loculicytheretta minuta within the Siouf member defined the 90–120 m interval as the Loculicytheretta minuta Zone. Bismuth et al. (1978) and Oertli (1976) dated this zone as upper Lutetian. The Loculicytheretta cavernosa zone covers the Siouf member to the 208-m level and has been attributed to the Bartonian (Oertli 1976; Amami Hamdi and Ben Ismail Lattrache 2013b). The last ostracod zone in the Bougobrine section is the Loculicytheretta aff. Gortanii Zone was attributed by Bismuth et al. (1978) and Oertli (1976) to the Priabonian. The Siouf member is assigned to the lower Loculicytheretta cavernosa Zone (lower Bartonian, Amami Hamdi & Ben Ismail Lattrache, 2013).

Figure 4 about here

4.2. Facies analysis

The establishment of the depositional model is based on the description of macro-and microfacies, sedimentary structures, and geometry of the sedimentary bodies. Ten facies types have been distinguished in the Bougobrine section (Table 1).

4.2.1. Facies F1: Lumachellic limestone

This facies alternates with Facies 2 and dominates the Cherahil (A) deposits. The predominance of well-preserved oyster shells distinguishes these facies in their position during life, together with a dearth of well-preserved gastropod shells. We use the term lumachellic limestone to define oyster’s shell levels found in life position in a matrix of fine carbonate mud (often marly). The observed mono-specific marine fossils are favoured in a restricted environment with low detrital inputs. Microscopic analysis showed mudstone textures composed of scare ostracods (10%, Bairdia sp. and Protobuntonia sp.) and rare benthic foraminifera (BF, 3%, Lenticulina) and planktonic foraminifera (PF, 1%) associated with gastropods (15%), oysters (35%), and bioclasts (10%). Some levels show some lenticular gypsum and enhanced dolomitization. The muddy matrix and the preservation of the oysters in mass and in life position suggest no transport and deposition in protected environments of low-energy conditions such as a restricted bay (lagoon, Jorry (2004)).

Table 1. about here

4.2.2. Facies F2: Marly limestone

Metric levels of marly limestone with in life position oysters and gastropods. The oysters are much less abundant than in facies 1. The facies is represented by metric levels rich in gastropods and bivalves. Microscopic analysis shows mud- to packstone texture rich in gastropods (10%), oyster (25%), and bioclasts (10%) with abundant ostracods (20%, Cytherella sp. and Loxochoncha sp), scare BF (10%), and PF (5%) reflecting an increase in the water depth. The occurrence of oysters with a marly matrix and low detrital input indicates a restricted environment. The high amount of mud, the lower abundance of oysters and the higher abundance of PF compared to Facies 1 suggest a more distal environment than Facies 1 within the restricted bay.

4.2.3. Facies F3: Lamellibranch and gastropods rich dolo-limestone

Facies 3 is a vuggy dolomitic limestone composed of small-sized lamellibranchs and gastropods. The vuggy porosity is due to the dissolution of fossil skeletons (Fig. 5i). The wackestone texture, with BF (7%), no PF, ostracods (3%), lamellibranchs (25%), gastropods (30%), and the observed oblique stratifications indicate a high-energy domain of the intertidal zone with a tendency towards the supratidal zone as testified by the high dolomitization at some levels.

4.2.4. Facies F4: Dolomitic limestone

This facies is composed of hard-cemented dolomitic layers. These dolomitic beds also contain scattered quartz grains within the matrix. Dolomitic levels indicate burial diagenesis in the supratidal and evaporitic depositional settings. The rock of this facies is brownish, thick-bedded, and highly laden with rare fragmented shells of oysters. These particles are embedded in a micritic matrix. The shell fragments are recrystallized with dolomite rhombs and coarse-grained quartz.

4.2.5. Facies F5: Chaotic lumachells accumulation

Chaotic accumulations of oyster’s shell (Fig. 5l) are observed during the lower Lutetian and consist of an interval made up of chaotically arranged lumachells. This chaotic oyster shells accumulation was instantaneously detached, transported, and deposited by a strong wave that filled the intertidal to the supratidal environment after crossing the entire embayment. Different orientations of oyster and gastropod shells, the dominance of broken fragments, and the scarcity of entire fossils in life positions suggest that a wave would have been responsible for the deposition of this facies, as most characters are incompatible with the depositional regime as observed in Facies 1. Facies 5 indicates a high-energy environment and the deposition in a more proximal environment than Facies 1.

4.2.6. Facies F6: Bioclastic limestone rich in nummulithoclasts

These nummulites and nummulithoclasts bearing wack- to packstone layers (Fig. 5m) are made up entirely of nummulites and bioclasts, mostly nummulithoclasts elements, of a highly fragmented and abraded nature. The matrix is also composed of small (1 mm) nummulithoclasts. The hummocky cross-stratification could generate the low-angle parallel lamination (Fig. 5j and 5k) with the chaotic arrangement of these facies (HCS, Bey et al., 2015). Microscopic analysis showed a rich BF (25%) associated with ostracods (10%), bivalves (15%), nummulithoclasts (30%), and common PF (Subbotina corpulenta, Acarinina topilensis, 15%). The top of this facies within the Siouf member shows green algae (dasycladales) and rare debris of echinoderms. The matrix shows a similar composition as Facies 9 but with less BF. The lack of mud within the matrix and the abundance of nummulites point to a relatively more open marine environment. The rich benthic fauna and the occurrence of Lenticulina (10%) advocate a shallow subtidal environment.

Figure 5 about here portrait

4.2.7. Facies F7: Chalky limestone

This facies is associated with the lower Siouf member, composed primarily of chalky bioclastic limestone with little nummulithoclast content (Fig. 5h). Few hard dolomitic limestones interbed are observed with disseminated calcite crystals. This microfacies is composed of allochems represented by ostracods (5%), BF (10%, miliolids (6%) and Orbitolites sp. (5%)), bivalves (25%), gastropods (4%), and algae (2%) cemented by calcite. These allochems are well preserved, and their chambers are filled with calcite. The microcrystalline calcitic cement, the dolomitization, and the allochems components advocates for a shallow inner lagoon environment with enhanced evaporation (supratidal).

4.2.8. Facies F8: Argillaceous-silty marl

F8 is observed during the upper Lutetian and near the Lutetian/Bartonian boundary (within the Siouf member). The rock is azoic and silty, with cm-scaled conglomerates and fine grains of quartz. The abundance of detrital elements suggests a tendency toward emersion. It consists of a thin layer of greenish silty marl (30 to 50 cm, Fig. 5n) between the lower Siouf bioclastic limestones.

4.2.9. Facies F9: Bioclastic limestone rich in nummulites and echinoderms

Facies 9 illustrates the maximum nummulite carbonate production during the middle Eocene. This interpretation is supported by the accumulation of nummulites, association with other macrofossils such as crinoids, echinoderms, gastropods, and random orientation of nummulite tests within the sediment (Figs. 5d to 5g). The packstone to grainstone texture (Figs. 6c and 6d) with the high abundance of echinoderms and crinoids indicates high energy within open and warm marine environments (da Silva & Boulvain, 2006; Martini et al., 2007; Schneider et al., 2004). A microscopic examination of these beds revealed the highest PF content measured in the Bougobrine section (18%) represented essentially by Turborotalia sp., Dentoglobigerina galavisi, Acarinina topilensis, and Morozovella lehneri (CUSHMAN AND JARVIS), which indicate the upper Lutetian to lower Bartonian (E13 biozone). The packstone–grainstone texture contains echinoderms, bivalves (15%), abundant BF (25%, Miliolidae) with nummulithoclasts (30%), and radiolarians (5%). F9 represents subtidal deposits of a well-oxygenated environment with moderate energy. The differences between F9 and F6 are related to the higher energy level of the F9 with a more open marine condition, as illustrated by the lesser amount of micrite, the dominance of large nummulites, and the abundance of PF.

Figure 6 about here portrait

4.2.10. Facies F10: Green silty shale with scare gypsum

This homogenous greenish gypsum shale facies is characterized by the nearly complete absence of skeletal grains with silt. Some levels contain oysters. The mudstone texture with the silt fraction indicates a low-energy lagoonal back-ramp setting, which intertidal mudflats may represent. Facies 10 is up to 20 m thick and is rich in PF (10 to 8%), ostracods (20%, Buntonia ramosa), broken bivalves (10%), bryozoa (5%), and BF (10%, Miliolidae) associated with silt and quartz. The upper part of F10 shows much less abundant microfauna.

Figure 7 about here portrait

4.4. Sequence stratigraphy in a shallow carbonate platform

4.4.1. Sequence T-R 1

T-R 1 sequence is 36.5 m thick and corresponds to the lithostratigraphic unit 1. Its lower boundary corresponds to the unconformity surface between the limestones deposits of the Ypresian and the overlying lumachellic limestone of the Cherahil Formation. Abundant ostracods and oysters characterize the transgressive system tract (TST, 24 m thick). The upper boundary of this sequence witnessed the first appearance of highly dolomitized levels. The maximum flooding surface (MFS) is underlined at the 24 m level, where an increase in PF is observed. The highstand system tract (HST, 12.5 m thick) is represented by the alternations between azoic dolo-limestones and marls containing bivalves (40%), gastropods (30%) with rare ostracods, and BF (8%). The absence of PF and the low abundance of BF in these marly levels suggest a shallower water depth than the first 24 m.

Figure 8 about here

4.4.2. Sequence T-R 2

This sequence is 28.5 m thick. The TST (15 m thick) alternates between lumachellic limestone and marly beds. The MFS is placed at a 42 m level where the examination of a thin section shows wackestone to packstone textures containing PF (10%) and BF (25%) and ostracods (20%), associated with fragments of echinoderms. The HST is a 13.5 m-thick sequence corresponding to a thinning-up alternation between lumachellic beds with rare gastropods and frequent dolomitization. The abundance of oysters and gastropods during the HST indicates that shallowing-up reduced the accommodation space and established a more restricted environment. The dolomitic limestone bed at 80 m level corresponds to the upper boundary of the T-R 2 sequence. The top of this bed is a ravined surface indicating a subaerial exposure surface followed by the TST of sequence T-R 3.

4.4.3. Sequence T-R 3

This sequence is 26.5 m thick and covers unit 3 of the Cherahil A. Its lower boundary lines up with Facies 4's dolomitic limestone. The bioclastic limestone strata vary in thickness throughout the TST (3 m to 2 m). In the limestone levels, there is a packstone texture with a significant BF (15%), PF (5%) and ostracod content (10%). The MFS of sequence T-R 3 is placed within the marl bed at 71 m level. This level shows fragments of echinoderms and bryozoans with PF (15%) and BF (20%). The HST is represented by high dolomitization of the limestone beds and ends with a thin lumachellic marls level testifying to the significant reduction of the accommodation space (shallowing of the water depth) followed by a thick and azoic dolomitic limestone bed. The surface of this level represents the upper boundary of sequence T-R 3.

4.4.4. Sequence T-R 4

T-R 4 (34.5 m) is composed of upper unit 3 in addition to all of unit 4. It corresponds to the uppermost of Cherahil A member. The TST starts after the dolomitic limestone bed at 90 m level and continues with interbedding lumachellic limestones with well-preserved oysters and bioclastic limestone (mud- to wackestone) with low BF abundance (less than 15%). The MFS is placed at a 105 m level where a rich PF (15%) and BF (20%) are observed. The thinning-up alternation of the HST corresponds to dolomitic limestone and marls. The upper boundary of this sequence corresponds to Facies 8 with cm-scaled conglomerates and fine grains of quartz with a scarce fauna. This surface corresponds to a subaerial exposure surface that precedes the deposition of the Siouf member.

4.4.5. Sequence T-R 5

The lower boundary falls in the argillaceous-silty marl of Facies 8 followed by the TST corresponding to the Siouf member (25 m). The TST shows an alternation of LBF-rich bioclastic limestones with abundant echinoderms and nummulites. Across the Siouf member, the coarsening-upward trend indicates a gradual increase in deposition energy, culminating at the top of this member by the packstone to grainstone texture with abundant LBF. The MFS is placed at the top of the Siouf member (142 m) with large nummulites, echinoderms, crinoids (F9), and abundant BF with common PF. The abundant and diverse faunal assemblage within Facies 9 indicates the most distal environment. The TST occurs during the lower Bartonian and is characterized by a maximum abundance of large nummulites (Nummulites gizehensis) and red algae. The HST is represented by thinning-upward bioclastic limestones separated by thick marls levels with rare benthic microfauna (10%). The upper boundary of sequence T-R 5 corresponds to the dolomitic limestone of F4.

4.4.6. Sequence T-R 6

This sequence falls within the middle part of unit 6 (Fig. 7) and is delimited by two dolomitic limestone beds at 164 m and 178 m, respectively. The TST covers the interval between 165 m to 171 m and shows a microfauna represented by BF (20%) associated with PF (8%) and ostracods (5%). The MFS is placed at the 172 m level, where the highest PF abundance is observed (5%). The HST consists of thinning-upwards beds of marls with oysters, gastropods, and rare microfauna and ends with silty marls.

4.4.7. Sequence T-R 7

It is a 10.5 m thick sequence starting with dolomitic limestone at 179 m level. Ostrea-enriched marls that resemble sequence T-R 6 make up most of the deposits. The lumachellic limestones (187 m level) form the upper boundary of T-R 7. The MFS is located within the marls of sequence T-R 7 (184 m) with the richest microfossils association. A 3 m-thick sequence of marls with rich oyster shells (up to 30%) and rare PF forms the HST.

4.4.8. Sequence T-R 8

This depositional sequence is 17.5 m thick and corresponds to the upper part of Unit 6. This sequence's lower and upper boundaries fall within the brownish lumachellic limestone of F1. T-R 8's middle part relates to ostrea-enriched marls with uncommon gastropods, frequent ostracods, and BF. PF is particularly rare in this sequence. The TST (12 m thick) starts with lumachellic limestone and evolves into marls rich in ostracods (25%) and BF (20%) with rare PF (10%). The HST is recognized by a drop in ostracod and BF abundance together with the presence of silt.

4.4.9. Sequence T-R 9

The sequence is 28 m thick and corresponds to unit 7 (Fig. 7). The presence of PF and BF at the base of this sequence (20–25%) suggests a transgressive trend that peaks (MFS) at the 219 m level. An abrupt transition outlines the MFS into less frequent PF. The occurrence of silt identifies the HST (20 m thick) within the greenish marls with few fragmented bivalves. This horizon shows scarce fauna (bioturbation, micritization). The top of this sequence corresponds to the Eocene-Oligocene boundary outlined by a thick sandstone level.

4.5. Bulk δ¹³C Isotope Data

The recognition of the MECO's isotopic signal in the Siouf member was the primary goal of the carbon isotope stratigraphy, which was based on 66 samples. Study samples include the Siouf member's 34 samples, 28 samples below, and four samples above (Fig. 9). Levels with high dolomitization and erosion are prevented to assure the best results. The bulk carbonate δ¹³C values show several significant patterns (Fig. 9): a progressive increase from − 1.6‰ to 1.12‰ between 63 m to 74.2 m, followed by decreasing trend reaching a negative excursion of -0.62‰ at 86.2 m level. Another steep decreasing trend began after this point, reaching a maximum of 2.07‰ at 98 m. Values remain stable from around 2‰ up to 102 m.

δ¹³C curve in the Siouf member starts with a small positive excursion of 1.6‰ at 121 m. A fast decrease follows this excursion in the δ¹³C values reaching a pronounced negative excursion (-0.74‰) at 123.8 m. Although the δ¹³C record gradually increases during the upper Siouf member, the δ13C records are more complex and strongly correlate to the observed lithological changes. The highest positive δ¹³C excursion of 4.32‰ is detected at the top of the Siouf member (149 m). The onset of this last positive excursion coincides with the maximum carbonate production and an abrupt increase in sea level. After the Siouf member, a decreasing trend occurred and ended up within the marls of unit 6 (at 169.7-m) with a minimum of ∼-0.37‰.

Figure 9 about here portrait

5.1. Eustatic and climatic controls on sedimentation

A low gradient homoclinic ramp model (Figs. 10 and 12) is proposed, similar to the model proposed by Jorry (2004) and Jorry et al. (2006) for the Ypresian-Lutetian deposits. An inner ramp, a middle ramp, and an outer ramp make up a carbonate ramp. Open marine facies distinguish the outer ramp with PF and radiolarians (Souar Formation, Messaoud et al., 2021). The restricted inner ramp (lagoon) is dominated by restricted to semi-restricted shallow marine facies.

The vertical stacking of facies points towards shallowing upward sequences interrupted during the upper Lutetian-lower Bartonian (Reneiche/Siouf member) by a major transgression which induced the renewal of nummulitic carbonate production factories that had been interrupted since the latest Ypresian. The Bougobrine section starts with restricted bay (lagoonal) facies as attested by the dominance of lumachels. Marly limestone, bioclastic mudstone/wackestone, and high-energy facies made of bioclastic wackestone are less abundant. The Lutetian's shallowing-upward cycles exhibit meters-scale, 2 to 4-m cyclicity in response to cyclic subsidence, eustatic sea-level oscillations, and sediment supply. These cycles begin with subsidence when the transgressive facies are deposited. The sea-level fall usually favours shallower deposits on top (e.g., Bonnefous and Bismuth, 1982; Bismuth, 1996; Ben-Ismail-Lattrache, 2000; Tlig et al., 2010; Taktak et al., 2012). The important alternation of marls and limestone (about 60 alternations) and the lateral thickness and facies variations support our interpretation of cyclic sea-level fluctuations. Repeated tectonic subsidence and uplift of epicontinental platform basins in a passive margin of the SW Neo-Tethys could not explain the frequency and magnitude (2–4 m thickness and 100–200 kyr duration) of the observed cycles.

Figure 10 about here portrait

Low detrital inputs, even though the sedimentation occurs mainly in shallow water during the Lutetian, imply relatively low tectonic activities (e.g., Bouaziz et al., 2002; Khomsi et al., 2006; Mejri et al., 2006) coupled with arid to semi-arid paleoclimatic conditions (Chermiti et al. 2018; Njahi Derbali and Touir 2019). Shallow water with low detrital inputs and warm paleoclimate favoured the development of a thick series of lumachels during the Lutetian. The upper Lutetian is marked by an acute eustatic fall associated with the Lu4 (Haq et al. 1987) sequence boundary, followed by a fast-sea-level rise during the lower Bartonian. This recovery is manifested in the field by the widely extended transgressive deposit, the Siouf member, on different older series from the Kasserine Island to the Halk El Menzel platform. This transgression is also marked on the border of Kasserine island and the Gafsa basin by the deposition of the Djebs evaporites (Burollet, 1956; Comte and Dufaure, 1973; Jamoussi et al., 2001; Kadri et al., 2015). The lower Bartonian shallow subtidal environment show packstone/grainstone texture with abundant LBF (nummulites) and small-echinoderms. These nummulites were the main carbonate-producing benthos during the Eocene (e.g., Abu El Ghar, 2012; Bassi et al., 2013; Jorry, 2004; Less & Özcan, 2012; Papazzoni & Sirotti, 1995; Tomassetti et al., 2016).

After the thick T-R 5 sequence (lower Bartonian), sequences began to thin out, which suggests that the available accommodation space has been significantly reduced. The facies analysis of the Priabonian series reflects enhanced weathering inputs via the deposition of thick detrital silty shales (F10). The Late Eocene is attributed to a widespread sea-level lowstand in central Tunisia (Ben Ismail-Lattrache & Bobier, 1984; Burollet, 1956). These conditions prevented the development of the Lutetian oyster communities. During this period, the basin became shallower, and the short-term transgressions of the Bartonian were replaced by short-term regressions, which affected the nature of the sedimentation.

5.2. Early Bartonian abrupt facies change

The dominance of oysters, the mono-specific marine fossils, and the occasional dolomitization (Facies 1, 2, 3, and 4) during the Lutetian predominated only in lagoonal environments with low water circulation and relatively high salinity (e.g., Bismuth, 1996; Carlucci et al., 2014; Chermiti et al., 2018; Coster et al., 2012; Kocsis et al., 2014; Matmati et al., 1992; Sallam et al., 2018). The observed dolomitization within facies F1 and F4 could be attributed to the regression of the sea level in the phreatic and meteoric zones accompanied by high moldic porosities (Spalluto, 2012; Tawfik et al., 2017).

Figure 11 about here portrait

The nine third-order depositional sequences are arranged in a long-term shallowing upward trend (Figs. 7 and 8) interrupted by the transgression that favoured the Siouf member's deposition. The transition to the Siouf member is accompanied by a change from mud- wackestone to pack-grainstone. Grainstone texture, well-developed nummulites, abundant BF/echinoderms, and common PF, in the limestone layers of the Siouf member point to the deepest deposits recorded in the Cherahil Formation inside the shallow subtidal zone.

F6 and F9 (Siouf member) are thick-bedded, grainy limestones with rich fauna content (nummulites, BF, bivalves, echinoderms, and small-gastropods). The abundance and high diversity of skeletal fauna distinguish these facies from the restricted inner platform facies (e.g., Aghaei et al., 2013; Jank et al., 2006). The pack- grainstone texture indicates a depositional environment with high hydrodynamic energy (e.g., Dunham, 1962; Flugel, 2004). The association of echinoderms (Echinolampas, (Jorry 2004)), LBF (Discolina spp., Nummulites spp.) indicate a more open water circulation (Aghaei et al., 2013; Jorry, 2004; Lanterno & Edouard, 2019; Tomassetti, Benedetti, & Brandano, 2016). The nummulite occurrence is favoured between the fair-weather and storm-wave base in warm (Figs. 11 and 12), mesotrophic, and well-oxygenated waters following previous interpretations on the lower Eocene nummulitic beds of El Garia Formation in Tunisia (Jorry, 2004; Jorry et al., 2006). The texture and fossils content of F9 indicate maximum nummulite carbonate production during a high sea level. This facies shows very similar content to the El Garia Formation (Ypresian) described by Jorry (2004) and Jorry et al. (2006) as nummulithoclasts facies rich in ostracods and BF with common echinoderms (Echinolampas) and nummulites suggesting. The carbonate production induced by the MECO abruptly ceased favouring the return of shallowing deposits in harmony with the fast cooling upward following the MECO event (Post-MECO, Bohaty et al., 2009; Sluijs et al., 2013; Spofforth et al., 2010).

5.3. Carbon isotope stratigraphy

The evolution of the global carbon cycle, expressed in the ratio of stable carbon isotopes (ō13C), is controlled by significant carbon fluxes driven by volcanism, tectonics, the expansion of ice sheets, and changing Earth parameters. However, global signals are superimposed by regional carbon fluxes, which are related to changes in sea level, productivity, and carbon burial, especially on marginal shelves (e.g., Galeotti et al., 2010; Giorgioni et al., 2019; Crouch et al., 2020; Dickson et al., 2021).

Our δ¹³C curves show three distinctive features:

The δ¹³C pre-MECO max at 122 m occurs at the base of the Siouf member. This shift to more positive δ¹³C ratios requires the input of isotopically heavier carbon (¹³C), and the long-term enrichment in heavier carbon isotopes is strongly related to eustatic sea-level rise (e.g., Mitchell et al., 1996; Stap et al., 2010; Eldrett et al., 2020). High and positive δ¹³C values correspond to phases of sediment accumulation during transgressions. Thus, the lower Bartonian transgression could induce δ13C pre-MECO Max (Haq et al., 1987; Hardenbol et al., 1998; Miller et al., 2005).
The δ¹³C MECO min at 134 m level within the Siouf member. This negative shift correlates well (Fig. 9) with the negative shift in δ¹³C found during the MECO in Turkey (Giorgioni et al. 2019), NW Atlantic (ODP 1051, Bohaty et al., 2009), Southern Ocean (ODP 748B, Bohaty et al., 2009), and the Alano section (Italy, Luciani et al., 2010).
The δ¹³C post-MECO max at 149 m occurs at the end of the Siouf member. This strong positive shift may be influenced by the return of aragonite-producing organisms from the platform (gastropods, bivalves). In carbonate platforms, aragonite-producing species flourish, particularly during peak sea levels.

These three isotopic events have been previously identified on the δ¹³C_org in the Souar section (Tunisian dorsal, Messaoud et al., 2021). The decreasing trend in the bulk δ¹³C record just after the Siouf limestone suggests increasing carbon burial at the shelf, related to the sea-level drop during the Late Eocene (Burollet 1956; Ben Ismail-Lattrache and Bobier 1984). All the δ¹³C records (Fig. 9) display variations within the MECO interval (Giorgioni et al. 2019).

Unstable oceanographic/carbon cycle conditions and coincidence between a 400 kyr and a 2.4 Myr orbital eccentricity minimum have, however, been proposed as global forcing factors to explain the δ¹³C signal across the MECO (Edgar et al., 2010; Giorgioni et al., 2019; Van der Ploeg et al., 2018; Sluijs et al., 2013; Westerhold and Rohl, 2013).

In the Neo-Tethys, the carbon cycle during the middle Eocene was affected by the episodic continental runoff, which may have lowered the seawater's heavy carbon isotopes (Giorgioni et al., 2019; Jovane et al., 2007; Rego et al., 2018). Significant paleo-circulation changes due to the restriction of the westward subtropical Eocene Neo-Tethys (STENT) current (Jovane et al. 2009) and increased primary productivity associated with the biological pump (e.g., Boscolo Galazzo et al., 2013; Luciani et al., 2010; Savian et al., 2014; Toffanin et al., 2011) affected the local expression of the δ¹³C signal.

5.4. SW Neo-Tethys carbonate platform evolution

The establishment of the nummulitic limestone during the early Bartonian reflects the presence of ancient warm water (e.g., Flugel, 1992; Brasier, 1995; Hottinger, 1997; Jorry, 2004; Jorry et al., 2006; Less and Özcan, 2012; Bassi et al., 2013; Tomassetti et al., 2016; Rego et al., 2020). Here, we attribute the Middle Eocene “maximum” marine carbonate production event materialized in central Tunisia by the Siouf member as a response to the warming peak of the MECO (Figs. 12 and13). The coincidence of this sedimentological shift with geochemical and biological (apparitions, disappearances, the proliferation of specific taxa) events may be due to environmental changes. Therefore, a high-resolution time calibration independent of environmental perturbations must be carried out. These results are very similar to those recorded during the Early Eocene Climatic Optimum (EECO), which coincides with the deposition of the Ypresian nummulitic limestones of the El Garia Formation in the same marginal setting of the Neo-Tethys (Racey et al. 2001; Tlig et al. 2010; Taktak et al. 2011), suggesting that similar mechanisms occurred during the Eocene warming events that favoured the development of nummulitic carbonate series.

The magnitude of the EECO and the MECO is reflected in the thickness and nummulites proliferation difference between the El Garia Formation (150-m in some areas, Jorry, 2004) and the Reneiche member (maximum of 25-m). Although our results show significant similarities with Northern Neo-Tethys margins regarding the age of the MECO, the installation of nummulitic limestone banks remains characteristic of the MECO in the South-Western Neo-Tethys.

Figure 12 about here

In the South-Western Neo-Tethys, the MECO induced the proliferation of tropical carbonate platforms dominated by larger foraminiferal shells of nummulites (e.g., Jorry 2004; Höntzsch, 2011) during the early Bartonian. These nummulitic limestone series were developed under a warm climate (Brasier 1995; Jorry 2004) with high sedimentation rates (up to > 100 m/m.y.), and abundant large BF association dominated by nummulites (e.g., Bassi et al. 2013; El Baz 2019; Jorry 2004). Eocene nummulitic limestones series constitute an important hydrocarbon reservoir in the northern and northeast African provinces (e.g., Bey et al., 2015; Jorry, 2004; Racey et al., 2001; Swei and Tucker, 2015; Taktak et al., 2010; Taktak et al., 2012).

Scheibner and Speijer (2009), Höntzsch (2011), and Höntzsch et al. (2013) show that global warming during the Early Palaeogene caused a massive decline in coral reefs and a coeval shift to large benthic foraminifera (LBF). The authors directly link the larger foraminifera turnover's evolutionary impact at the Palaeocene-Eocene boundary to the PETM. A transient period with an increasing abundance of LBF K-strategist taxa is also present during the MECO (Höntzsch, 2011; Nebelsick et al., 2005). During the Late Eocene, the general cooling trend (Late Eocene cooling event; McGowran et al. (2009)) caused the extinction of LBF (e.g., discocyclinids; early Palaeogene Nummulites; Prothero et al., 2003).

Figure 13 about here

The high primary marine productivity induced by the MECO ceased abruptly, favouring the return of shallowing deposits (Fig. 10), consistent with the fast cooling following the upward post-MECO (Bohaty et al., 2009). The late Bartonian - Priabonian interval remains poorly identified in Tunisia since it corresponds to a widespread sea-level lowstand. In central Tunisia and the Tunisian dorsal, the Priabonian corresponds to silty greenish silt within the upper Globigerinatheka semiinvoluta Zone (P11), indicating that the Priabonian contemporaneous the installation of a shallow environment with enhanced erosion (Bismuth, 1996; Burollet 1956; Ben Ismail-Lattrache and Bobier 1984).

5.5. Paleogeographic extension of the Reneiche/Siouf member

In the shallow carbonate platform of central Tunisia, Amami-Hamdi et al. (2016) and Ben Ismail-Lattrache (2000) studied the Siouf limestone member in central Tunisia (Jebel Jebil) and report only a 5 m thick limestone series rich in LBF: Nummulites gizehensis, Discocyclina roberti, Discocyclina sella, Operculina spp. and Alveolina spp (Fig. 14). In another section in central Tunisia (Jebel Serj), the same member is only 40 cm thick (Amami Hamdi & Ben Ismail Lattrache, 2013) admitting Nummulites and Alveolina elongata Orbigny in addition to bryozoans, echinoderms, lamellibranchs (Ostrea lamellosa), and algae (Fig. 14). In the Bargou area (northern central Tunisia) the Reneiche/Siouf member is identified by a micritic argillaceous limestone bed (30-cm thick) rich in iron oxide, phosphate, and glauconite (Fig. 14). The fauna association is represented by BF (Peneroplis, Buliminides genera, Bolivina spp., S. kamali, and Nummulites gizehensis) and PF characteristic of the Orbulinoides beckmanni zone (E13, lower Bartonian). In southern central Tunisia (Ben Ismail-Lattrache, 2000), this member becomes very dolomitic, bioclastic, and contains iron oxide concretions indicating an upper intertidal depositional environment (Matmati et al., 1992).

The preferential nummulitic carbonate production in central Tunisia during the early Bartonian is mainly related to the structuration of continental shelves and the isolated platforms during the middle Eocene (Bonnefous & Bismuth, 1982; Comte & Dufaure, 1973; Jorry, 2004). Enhanced syn-sedimentary tectonic control explains the high variations in thickness and nummulites content of this limestone member (e.g., Bonnefous & Bismuth, 1982; Ismail-Lattrache, 2000; Khomsi et al., 2006).

We interpret the Reneiche/Siouf member as a discontinuous bioclastic system developed during the lower Bartonian maximum sea-level flooding (Fig. 13). This member extends in the subsurface over the southern Pelagian margin, where it is proven a producing reservoir, and reappears in the Cap-Bon and locally in northern Tunisian Atlas (Comte and Dufaure, 1973; Mejri et al., 2006; Taktak et al., 2012). The trend is superimposed along the edge of the early Eocene transitional area and can be traced as a narrow belt that took place over a gentle homoclinal ramp (e.g., Elfessi, 2017; Fakhfakh Ben Jemai, 2001; Ben Ferjani et al., 1990; Jorry, 2004; Mejri et al., 2006; Taktak et al., 2012).

Platform to basin correlation highlights the absence of Reneiche/Siouf member in the Tunisian dorsal related to the development of an upwelling zone that drastically reduced in situ calcareous nannoplankton and carbonate productivity and triggered instead of the deposition of radiolarian-rich clays (Messaoud et al. 2021).

Figure 14 about here portrait

In NE Tunisia, The Eocene Souar sedimentary succession (Fig. 14) of the Tunisian dorsal (Ben Ferjani et al., 1990; Ben Ismail-Lattrache & Bobier, 1984; Burollet, 1956) consists of a thick (up to 1100 m) sequence of offshore globigerinid-rich clays extending from the Nannotetrina alata group (CNE9, Lutetian) to the Isthmolithus recurvus zone (CNE18, Priabonian). The lower Bartonian sea-level rise (40.4 Ma, Ben Ismail-Lattrache, 2000) is associated with a glauconitic event during the lower Bartonian. It is interesting to note that previous works (e.g., Banerjee et al., 2016; Bansal et al., 2020; Boukhalfa et al., 2015; Sluijs et al., 2014) suggested a link between glauconitic concentrations and warming events during the Paleogene.

In the Cap Bon peninsula (NE Tunisia), where Burollet (1956) first defined the Reneiche limestone member, Ben Ismail-Lattrache et al. (2014) attributed the 20-m-thick of mud- to wackestone series containing nummulithoclasts, LBF (orthophragmines, discocyclinids, alveolinids, and nummulitids) and PF (globigerinids) to the Reneiche member. The authors used the 1 group's first appearance at this member's base as an indicator of the Lutetian/Bartonian boundary (SBZ 16/17) followed by the extinction of Orbitoclypeus douville (lower Bartonian, Less & Özcan, 2012) in the middle of the Reneiche limestones. In NE Tunisia, the Reneiche member is attributed to the transgression near the Globorotalia lehneri (E11) - Orbulinoides beckmanni (E12) zones transition at 40.4 Ma (Fig. 14, Ben Ismail-Lattrache, 2000; Ben Ismail-Lattrache & Bobier, 1984).

The analysis of Tethyan carbonate platform successions from central Tunisia reveals the following results regarding the paleoenvironmental evolution of shallow- marine carbonate factories during the Eocene. Large-scale correlations and carbon isotope stratigraphy lead to these outcomes:

The supratidal facies show pseudomorphs of evaporitic minerals with strong diagenetic dolomitization, dissolved carbonates, and scarce fauna. The restricted bay is dominated by lagoon mud- to packstone facies, lumachels, and ostracods. Nummulitic facies mainly dominate the shallow subtidal. The elementary sequence begins with supratidal to shallow intertidal deposits, followed by more distal facies (deep intertidal to subtidal). These alternations are pronounced during the Lutetian and Bartonian and much less expressed during the Priabonian when the sea level variations are less evident due to the significant regression.
The Cherahil Formation facies occurs as a shallowing-up sequence trend interrupted in the middle part by a deep-water interval (Siouf member). The occurrence of nummulites after the Lutetian-Bartonian boundary correlates to the continuing warming trend, culminating during the MECO (lower Bartonian). The disappearance of nummulites and increased detrital input are indicators of the post-MECO cooling during the upper Bartonian and Priabonian.
The Reneiche/Siouf member (25 meters) deposited in a shallow-marine environment records a short-lived shelf interval and is considered a local response to the MECO. A significant impact of this event in the Tunisian dorsal is missing.
In the SW Neo-Tethys, the MECO event broadly coincides with the lower Bartonian transgression, and both induced high nummulitic carbonate production. Correlation from southern central Tunisia to the Cap Bon peninsula reveals that the facies shift induced by these two events allows a long-range platform-to-basin correlation. Syn-depositional tectonics influenced the thickness of this member, which varies between 20 cm to 25 m.
The biotic and paleoenvironmental changes are significant during the early Bartonian. The fossiliferous assemblage is a subtropical association dominated by non-framework organisms, large benthic foraminifera, coralline algae, and sometimes green algae. Larger benthic foraminifer assemblages suggest a shallow ramp under essentially mesotrophic conditions.

Acknowledgments

We are grateful to the department of geoscience and natural resources management, Copenhagen University, for financing the isotope analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Credit authorship contribution statement

Jihede Haj Messaoud: Conceptualization, Methodology, Software, Data analysis, Data Curation, Visualization, Investigation, Writing – original draft, Writing – review and editing.

Nicolas Thibault: Conceptualization, Supervision.

Mohammed H. Aljahdali: Validation, review & editing.

Chokri Yaich: Conceptualization, Methodology.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article supplementary materials.

Abu El Ghar MS (2012) Sequence stratigraphy and cyclicity in the Middle Eocene of the Fayoum ranges, Western Desert, Egypt: Implications for regional sea level changes. Mar Pet Geol 29:276–292. https://doi.org/10.1016/j.marpetgeo.2011.01.008
Aghaei A, Mahboubi A, Moussavi-Harami R, et al (2013) Facies analysis and sequence stratigraphy of an Upper Jurassic carbonate ramp in the Eastern Alborz range and Binalud Mountains, NE Iran. Facies 59:863–889. https://doi.org/10.1007/s10347-012-0339-8
Amami-Hamdi A, Ben Ismail-Lattrache K, Dhahri F, Saïd-Benzarti R (2014) Middle to Upper Eocene ostracofauna of central Tunisia and Pelagian Shelf: Examples of Jebel Bargou and the Gabes Gulf. Arab J Geosci 7:1587–1603. https://doi.org/10.1007/s12517-012-0816-y
Amami-Hamdi A, Dhahri F, Jomaa-Salmouna D, et al (2016) Quantitative analysis and paleoecology of Middle to Upper Eocene Ostracods from Jebel Jebil, central Tunisia. Rev Micropaleontol 59:409–424. https://doi.org/10.1016/j.revmic.2016.10.001
Amami Hamdi A, Ben Ismail Lattrache K (2013a) Middle to Upper Eocene ostracods and associated foraminifera of the Jebel Serj section (central Tunisia). Biostratigraphical, paleoecological and paleobiogeographical significance. Rev Micropaléontologie 56:159–174. https://doi.org/10.1016/j.revmic.2013.10.002
Amami Hamdi A, Ben Ismail Lattrache K (2013b) Middle to Upper Eocene ostracods and associated foraminifera of the Jebel Serj section (central Tunisia). Biostratigraphical, paleoecological and paleobiogeographical significanc. Rev Micropaléontologie 56:159–174. https://doi.org/10.1016/j.revmic.2013.10.002
Banerjee S, Bansal U, Vilas Thorat A (2016) A review on palaeogeographic implications and temporal variation in glaucony composition. J Palaeogeogr 5:43–71. https://doi.org/10.1016/j.jop.2015.12.001
Bansal U, Banerjee S, Pande K, Ruidas DK (2020) Unusual seawater composition of the Late Cretaceous Tethys imprinted in glauconite of Narmada basin, central India. Geol Mag 157:233–247. https://doi.org/10.1017/S0016756819000621
Bassi D, Nebelsick JH, Puga-Bernabéu Á, Luciani V (2013) Middle Eocene Nummulites and their offshore re-deposition: A case study from the Middle Eocene of the Venetian area, northeastern Italy. Sediment Geol 297:1–15. https://doi.org/10.1016/j.sedgeo.2013.08.012
Ben-Ismail-Lattrache K (2000) Precision on Lutetian-Bartonian passage of Middle Eocene deposits in central and north-eastern Tunisia. Rev Micropaléontologie 43:3–16
Ben-Ismail-Lattrache K, Bobier C (1984) Sur l’evolution des paleo-environnements marins Paleogenes des bordures occidentales du Detroit Siculo-Tunisien et leurs rapports avec les fluctuations du paleo-ocean mondial. Mar Geol 55:195–217. https://doi.org/10.1016/0025-3227(84)90069-0
Ben-Ismail-Lattrache K, Özcan E, Boukhalfa K, et al (2014) Early Bartonian orthophragminids (Foraminiferida) from Reineche Limestone, north African platform, Tunisia: Taxonomy and paleobiogeographic implications. Geodin Acta 26:94–121. https://doi.org/10.1080/09853111.2013.858950
Ben Ferjani A, Burrollet PF, Mejri F (1990) Petroleum geology of Tunisia. Mém ETAP, Tunis, n°1 194
Ben Ismail-Lattrache K (2000) Précision sur le passage Lutétien-Bartonien dans les depôts éocenes moyens en Tunisie centrale et nord-orientale. Rev Micropaléontologie 43:3–16. https://doi.org/10.1016/S0035-1598(00)90060-6
Ben jemia-Fakhfakh H (1991) Les calcaires de l’Eocène inférieur en Tunisie centro- septentrionale: sédimentologie, paléogéographie. Université Franche Comté, Besançon,
Bey S, Ben Alaya S, Ben Jemia HF (2015) Integrated CMR, FMI and facies analyses to assess porosity types and distribution of the Middle Eocene limestones - Case study of gas reservoir, Pelagean sea, Tunisia. Soc Pet Eng - SPE North Africa Tech Conf Exhib 2015, NATC 2015 808–825. https://doi.org/10.2118/175795-ms
Bismuth, H. (1996) L’Eocène moyen et supérieur de Tunisie: Faciès et biostratigraphie. Sém ATEIG, sur les évènements l’Eocène en Tunisie 6
Bismuth H, Bonnefous J (1980) Biostratigraphie des dépôts carbonatés de l’Eocène moyen et supérieur dans l’offshore tunisien nord-oriental. 26 ème congrès Géol Inter Paris
Bismuth H, Keij AJ, Oertli HJ, Szcechura J (1978) The genus Loculicytheretta (Ostracoda). Bull Cent Rech Explor Elf-Aquitaine 227–263
Bohaty SM, Zachos JC, Florindo F, Delaney ML (2009) Coupled greenhouse warming and deep-sea acidification in the Middle Eocene. Paleoceanography 24:1–16. https://doi.org/10.1029/2008PA001676
Bonnefous J, Bismuth H (1982a) Les faciès carbonatées de la plateforme de l’Eocène moyen et supérieur dans l’offshore Tunisien Nord-oriental et en mer pélagienne: implications paléogéographiques et analyses micropaléontologique. Bull Centr Rech Explor Pro ELF Aquitaine, 6:337–403
Bonnefous J, Bismuth H (1982b) Les facies carbonates de plate forme de l’éocène moyen et supérieur dans l’offshore tunisien nord- oriental et en mer pélagienne: implications paléogéographiques et analyse micropaleontologique. Bull Centres Rech Explor Prod Elf- Aquitaine 6:337–403
Boscolo Galazzo F, Giusberti L, Luciani V, Thomas E (2013) Paleoenvironmental changes during the Middle Eocene Climatic Optimum (MECO) and its aftermath: The benthic foraminiferal record from the Alano section (NE Italy). Palaeogeogr Palaeoclimatol Palaeoecol 378:22–35. https://doi.org/10.1016/j.palaeo.2013.03.018
Bouaziz S, Barrier, Soussi M, et al (2002) Tectonic evolution of the northern African margin in Tunisia from paleostress data and sedimentary record. Tectonophysics 357:227–253. https://doi.org/10.1016/S0040-1951(02)00370-0
Boukhalfa K, Amorosi A, Soussi M, Ismail-Lattrâche K Ben (2015) Glauconitic-rich strata from Oligo-Miocene shallow-marine siliciclastic deposits of the northern margin of Africa (Tunisia): geochemical approach for basin analysis. Arab J Geosci 8:1731–1742. https://doi.org/10.1007/s12517-014-1288-z
Brasier MD (1995) Fossil indicators of nutrient levels: Evolution and extinction in relation to oligotrophy. In: Bosence DW, Allison PA (eds) Marine Palaeoenvironmental Analysis from Fossils. Geological Society Special Publication, pp 133–150
Burollet PF (1956) Contribution à l’étude stratigraphique de la Tunisie centrale. Ann. Mines et geol., Tunis 18
Carlucci JR, Westrop SR, Brett CE, Burkhalter R (2014) Facies architecture and sequence stratigraphy of the Ordovician Bromide Formation (Oklahoma): a new perspective on a mixed carbonate-siliciclastic ramp. Facies 60:987–1012. https://doi.org/10.1007/s10347-014-0412-6
Chermiti A, Moumni Y, Khiari N, Ben Youssef M (2018) Facies analysis, sequence stratigraphy and paleoenvironment reconstruction of the Paleogene deposits in central Tunisia (Faidh section). J African Earth Sci 144:183–195. https://doi.org/10.1016/j.jafrearsci.2018.04.013
Comte D, Dufaure P (1973) Quelques précisions sur la stratigraphie et la paléogéographie tertiaires en Tunisie Centrale et centro-orientale du Cap Bon à Mezzouna. Ann des Mines la Géologie 26:241–256
Coster P, Benammi M, Mahboubi M, et al (2012) Chronology of the Eocene continental deposits of Africa: Magnetostratigraphy and biostratigraphy of the El Kohol and Glib Zegdou Formations, Algeria. Bull Geol Soc Am 124:1590–1606. https://doi.org/10.1130/B30565.1
Crouch EM, Shepherd CL, Morgans HEG, et al (2020) Climatic and environmental changes across the early Eocene climatic optimum at mid-Waipara River , Canterbury Basin , New Zealand. Earth-Science Rev 200:. https://doi.org/10.1016/j.earscirev.2019.102961
da Silva AC, Boulvain F (2006) Upper Devonian carbonate platform correlations and sea level variations recorded in magnetic susceptibility. Palaeogeogr Palaeoclimatol Palaeoecol 240:373–388. https://doi.org/10.1016/j.palaeo.2006.02.012
Dickson AJ, Bagard ML, Katchinoff JAR, et al (2021) Cenozoic sea-level and cryospheric evolution from deep-sea geochemical and continental margin records. Mar Pet Geol 9:1–11. https://doi.org/10.1016/j.palaeo.2021.110563
Dunham RJ (1962) Classification of carbonate rocks according to depositional texture. AAPG Mem 108–121
Edgar KM, Wilson PA, Sexton PF, et al (2010) New biostratigraphic, magnetostratigraphic and isotopic insights into the Middle Eocene Climatic Optimum in low latitudes. Palaeogeogr Palaeoclimatol Palaeoecol 297:670–682. https://doi.org/10.1016/j.palaeo.2010.09.016
El Baz SM (2019) Middle Eocene larger benthic foraminifera from Egypt and their similarity to the southern tethyan provinces. J African Earth Sci 152:95–100. https://doi.org/10.1016/j.jafrearsci.2019.02.001
El Ghali A, Ben Ayed N, Bobier C, et al (2003) Les manifestations tectoniques synsédimentaires associées à la compression éocène en Tunisie : Implications paléogéographiques et structurales sur la marge Nord-Africaine. Comptes Rendus - Geosci 335:763–771. https://doi.org/10.1016/S1631-0713(03)00117-2
Eldrett JS, Vieira M, Gallagher L, et al (2020) Late Cretaceous to Palaeogene carbon isotope, calcareous nannofossil and foraminifera stratigraphy of the Chalk Group, Central North Sea. Mar Pet Geol 104789. https://doi.org/10.1016/j.marpetgeo.2020.104789
Elfessi M (2017) New insights into the stratigraphic, paleogeographic and tectonic evolution and petroleum potential of Kerkennah Islands, Eastern Tunisia. J African Earth Sci 125:88–102. https://doi.org/10.1016/j.jafrearsci.2016.10.015
Fakhfakh Ben Jemai H. (2001) Lithostratigraphy, paleontology and reservoir characterisation of the Eocene deposits in Tunisia. ETAP , Hydrocarb. Proj. Prog. Report.
Flugel E (1992) Phanerozoic reef evolution: basic questions and data base. Facies 167–278
Flugel E, Flügel E (2004) Microfacies of Carbonate Rocks, Analysis, Interpretation and Application. Springer-Verlag, Berlin 976
Galeotti S, Krishnan S, Pagani M, et al (2010) Orbital chronology of Early Eocene hyperthermals from the Contessa Road section, central Italy. Earth Planet Sci Lett 290:192–200. https://doi.org/10.1016/j.epsl.2009.12.021
Giorgioni M, Jovane L, Rego ES, et al (2019) Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum. Nature 9:1–10. https://doi.org/10.1038/s41598-019-45763-2
Haq BU, Hardenbol J, Vail PR (1987) Chronology of fluctuation sea levels since the Triassic. Science (80- ) 1156–1167
Hardenbol J, Thierry J, Farley MB, et al (1998) Mesozoic and Cenozoic sequence chronostratigraphic framework of European Basins. In: De Graciansky PC, Hardenbol J, Jacquin T, Vail P. (eds) Mesozoic and Cenozoic Sequence Stratigraphy of European Basins, 60th edn. SEPM Special Publication, pp 3–14
Höntzsch S (2011) Palaeogene carbonate platforms under climatic and tectonic stress – case studies from Egypt and Spain. University of Bremen
Höntzsch S, Scheibner C, Brock JP, Kuss J (2013) Circum-Tethyan carbonate platform evolution during the Palaeogene: The Prebetic platform as a test for climatically controlled facies shifts. Turkish J Earth Sci 22:891–918. https://doi.org/10.3906/yer-1207-8
Hottinger L (1997) Shallow benthic foraminiferal assemblages as signals for depth of their deposition and their limitations. Bull Soc Géol Fr 168:491–505
Jamoussi F, Abbès C, Fakhfakh E, et al (2001) Découverte de l’Éocène continental autour de l’archipel de Kasserine, aux Jebels Rhéouis, Boudinar et Chamsi en Tunisie centro-méridionale : Nouvelles implications paléogéographiques. Earth Planet Sci 333:329–335. https://doi.org/10.1016/S1251-8050(01)01657-3
Jank M, Wetzel A, Meyer C (2006) Late Jurassic sea-level fluctuations in NW Switzerland (Late Oxfordian to Late Kimmeridgian): closing the gap between the Boreal and Tethyan realm in Western Europe. Facies 52:487–519
Jorry S (2004) The Eocene Nummulite Carbonates (Central Tunisia and NE Libya): Sedimentology, Depositional Environments, and Application to Oil Reservoirs. Université de Genève
Jorry S, Hasler CA, Davaud E (2006) Hydrodynamic behaviour of Nummulites: Implications for depositional models. Facies 52:221–235. https://doi.org/10.1007/s10347-005-0035-z
Jovane L, Coccioni R, Marsili A, Acton G (2009) The late Eocene greenhouse-icehouse transition: Observations from the Massignano global stratotype section and point (GSSP), in Koeberl, C., and Montanari, A., eds., The Late Eocene Earth—Hothouse, Icehouse, and Impacts. Geol Soc Am 149–168. https://doi.org/10.1130/2009.2452(10)
Jovane L, Florindo F, Coccioni R, et al (2007) The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy. Bull Geol Soc Am 119:413–427. https://doi.org/10.1130/B25917.1
Kadri A, Essid EM, Merzeraud G (2015) “Kasserine Island” boundaries variations during the Upper Cretaceous-Eocene (central Tunisia). J African Earth Sci 111:244–257. https://doi.org/10.1016/j.jafrearsci.2015.07.027
Khomsi S, Bédir M, Soussi M, et al (2006) Highlight of Middle-Late eocene compressional events in the subsurface of eastern Tunisia (Sahel): Generality of the Atlasic phase in North Africa. Comptes Rendus - Geosci 338:41–49. https://doi.org/10.1016/j.crte.2005.11.001
Kocsis L, Ounis A, Baumgartner C, et al (2014) Paleocene-Eocene palaeoenvironmental conditions of the main phosphorite deposits (Chouabine Formation) in the Gafsa Basin, Tunisia. J African Earth Sci 100:586–597. https://doi.org/10.1016/j.jafrearsci.2014.07.024
Lanterno D, Edouard L (2019) Les « bancs à nummulites » de l’Éocène mésogéen et leurs implications. Arch des Sci. https://doi.org/10.5169/seals-739896
Less G, Özcan E (2012) Bartonian-Priabonian larger benthic foraminiferal events in the western tethys. Austrian J Earth Sci 105:129–140
Luciani V, Giusberti L, Agnini C, et al (2010) Ecological and evolutionary response of Tethyan planktonic foraminifera to the Middle Eocene Climatic optimum (MECO) from the Alano section (NE Italy). Palaeogeogr Palaeoclimatol Palaeoecol 292:82–95. https://doi.org/10.1016/j.palaeo.2010.03.029
Mansoura M, Ben Salem H, Ben Haj Ali M (2005) Carte geologique de la Tunisie a 1/ 2000000
Martín-Martín M, Guerrera F, Tosquella J, Tramontana M (2021a) Middle Eocene carbonate platforms of the westernmost Tethys. Sediment Geol 415:105861. https://doi.org/10.1016/j.sedgeo.2021.105861
Martín-Martín M, Guerrera F, Tosquella J, Tramontana M (2021b) Middle Eocene carbonate platforms of the westernmost Tethys. Sediment Geol 415:105861. https://doi.org/10.1016/j.sedgeo.2021.105861
Martini R, Cirilli S, Saurer C, et al (2007) Depositional environment and biofacies characterisation of the Triassic (Carnian to Rhaetian) carbonate succession of Punta Bassano (Marettimo Island, Sicily). Facies 53:389–400. https://doi.org/10.1007/s10347-007-0115-3
Masrouhi A, Ghanmi M, Youssef M Ben, et al (2007) Definition of a thrust nappe with two Palaeogene units in the Lansarine plateau (northern Tunisia): A new structural element of the Tunisian Atlas and revaluation of the Tertiary compression phases. Comptes Rendus - Geosci 339:441–448. https://doi.org/10.1016/j.crte.2007.03.007
Matmati MF, M’Rabet A, Ben Ismail K (1992) Etude sédimentologique et paleogeographique des facies carbonates et evaporitiques de l’Eocene inferieur dans la region de Faid- Nara et Lassonda (Tunisie centrale). Note Serv geol Tunisie, 58:29–42
Mc Gowran B, Berggren WA, Hilgen F, et al (2009) Neogene and Quaternary coexisting in the geological time scale: the inclusive compromise. Earth Sci Rev 249–262
Mejri F, Burollet FP, Ben Ferjani A, et al (2006) Petroleum geology of Tunisia: A renewed synthesis
Messaoud H., Thibault N, Bomou B, et al (2021) Integrated stratigraphy of the middle-upper Eocene Souar Formation (Tunisian dorsal): Implications for the Middle Eocene Climatic Optimum (MECO) in the SW Neo-Tethys. Palaeogeogr Palaeoclimatol Palaeoecol 581:. https://doi.org/10.1016/j.palaeo.2021.110639
Messaoud JH, Thibault N, Yaich C, et al (2020) The Eocene–Oligocene transition in the South‐Western Neo‐Tethys (Tunisia): astronomical calibration and paleoenvironmental changes. Paleoceanogr Paleoclimatology 35:. https://doi.org/10.1029/2020PA003887
Miller KG, Kominz MA, Browning J V., et al (2005) The Phanerozoic record of global sea-level change. Science (80- ) 310:1293–1298. https://doi.org/10.1126/science.1116412
Mitchell SF, Paul CRC, Gale AS (1996) Carbon isotopes and sequence stratigraphy. Geol Soc London, Spec Publ 104:11 LP – 24. https://doi.org/10.1144/GSL.SP.1996.104.01.02
Njahi Derbali Z, Touir J (2019) Sedimentology and sequence stratigraphy of the middle and upper Eocene succession from Jebel Kabbara (central Tunisia). J African Earth Sci 160:103599. https://doi.org/10.1016/j.jafrearsci.2019.103599
Nocchi M, Parisi G, Monaco P, et al (1988) Eocene and early oligocene micropaleontology and paleoenvironments in SE Umbria, Italy. Palaeogeogr Palaeoclimatol Palaeoecol 67:181–244. https://doi.org/10.1016/0031-0182(88)90154-X
Oertli H (1976) The evolution of Loculicytheretta in the Eocene. Abh Verh Natur- wiss Ver Hamburg, NF, 18/19 153--160
Papazzoni CA, Sirotti A (1995) Nummulite biostratigraphy at the Middle/Upper Eocene boundary in the northern Mediterranean area. Riv Ital di Paleontol e Stratigr 101:63–80. https://doi.org/10.13130/2039-4942/8566
Prothero DR, Ivany LC, Nesbitt EA (2003) From greenhouse to icehouse: the marine Eocene–Oligocene transition. Columbia Univ Press New York 541
Racey A (2001) A review of eocene nummulite accumulations: Structure, formation and reservoir potential. J Pet Geol 24:79–100. https://doi.org/10.1111/j.1747-5457.2001.tb00662.x
Racey A, Bailey HW, Beckett D, et al (2001) The petroleum geology of the early eocene el garia formation, Hasdrubal field offshore Tunisia. J Pet Geol 24:29–53. https://doi.org/10.1111/j.1747-5457.2001.tb00660.x
Rego ES, Jovane L, Hein JR, et al (2020) Mineralogical evidence for warm and dry climatic conditions in the Neo-Tethys (eastern Turkey) during the middle Eocene. Sedimentology 501:45–57. https://doi.org/10.1016/j.palaeo.2018.04.007
Rego ES, Jovane L, Hein JR, et al (2018) Mineralogical evidence for warm and dry climatic conditions in the Neo- Tethys ( eastern Turkey ) during the middle Eocene. Palaeogeogr Palaeoclimatol Palaeoecol 501:45–57. https://doi.org/10.1016/j.palaeo.2018.04.007
Salama W, El Aref M, Gaupp R (2014) Facies analysis and palaeoclimatic significance of ironstones formed during the Eocene greenhouse. Sedimentology 61:1594–1624. https://doi.org/10.1111/sed.12106
Sallam ES, Erdem NÖ, Sinanoğlu D, Ruban DA (2018) Mid-Eocene (Bartonian) larger benthic foraminifera from southeastern Turkey and northeastern Egypt: New evidence for the palaeobiogeography of the Tethyan carbonate platforms. J African Earth Sci 141:70–85. https://doi.org/10.1016/j.jafrearsci.2018.01.009
Savian JF, Jovane L, Frontalini F, et al (2014) Enhanced primary productivity and magnetotactic bacterial production in response to Middle Eocene warming in the Neo-Tethys Ocean. Palaeogeogr Palaeoclimatol Palaeoecol 414:32–45. https://doi.org/10.1016/j.palaeo.2014.08.009
Scheibner C, Speijer R. (2008) Late Paleocene – early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change. Earth Sci Rev 90:71–102. https://doi.org/10.1016/j.earscirev.2008.07.002
Scheibner C, Speijer RP (2009) Recalibration of the shallow-benthic zonation across the Paleocene-Eocene boundary: The Egyptian record. Geol Acta 195-214.
Schneider J, de Wall H, Kontny A, Bechstädt T (2004) Magnetic susceptibility variations in carbonates of the La Vid Group (Cantabrian Zone, NW-Spain) related to burial diagenesis. Sediment Geol 166:73–88. https://doi.org/10.1016/j.sedgeo.2003.11.016
Sluijs A, Van Roij L, Harrington GJ, et al (2014) Warming, euxinia and sea level rise during the paleocene-eocene thermal maximum on the gulf coastal plain: Implications for ocean oxygenation and nutrient cycling. Clim Past 10:1421–1439. https://doi.org/10.5194/cp-10-1421-2014
Sluijs A, Zeebe RE, Bijl PK, Bohaty SM (2013) A Middle Eocene carbon cycle conundrum. Nat Geosci 6:429–434. https://doi.org/10.1038/ngeo1807
Spalluto L (2012) Facies evolution and sequence chronostratigraphy of a “mid”-Cretaceous shallow-water carbonate succession of the Apulia Carbonate Platform from the northern Murge area (Apulia, southern Italy). Facies 58:17–36. https://doi.org/10.1007/s10347-011-0266-0
Spofforth DJA, Agnini C, Pälike H, et al (2010) Organic carbon burial following the Middle Eocene climatic optimum in the central western Tethys. Paleoceanography 25:1–11. https://doi.org/10.1029/2009PA001738
Spótl C, Vennemann TW (2003) Continuous-flow isotope ratio mass spectrometric analysis of carbonate minerals. Rapid Commun Mass Spectrom 17:1004–1006. https://doi.org/10.1002/rcm.1010
Stap L, Lourens LJ, Thomas E, et al (2010) High-resolution deep-sea carbon and oxygen isotope records of Eocene Thermal Maximum 2 and H2. Geology 38:607–610. https://doi.org/10.1130/G30777.1
Strasser A (1988) Shallowing-upward sequences in Purbeckian peritidal carbonates (lowermost Cretaceous, Swiss and French Jura Mountains. Sedimentology 35:369–383
Strasser A (2018) Cyclostratigraphy of Shallow-Marine Carbonates – Limitations and Opportunities. In: Stratigraphy & Timescales. Elsevier Ltd, pp 151–187
Swei GH, Tucker ME (2015) Hydrocarbon potential of Middle Eocene carbonates, Sirt Basin, Libya. J African Earth Sci 111:363–374. https://doi.org/10.1016/j.jafrearsci.2015.07.009
Taktak F, Bouaziz S, Tlig S (2012) Depositional and tectonic constraints for hydrocarbon targets of the Lutetian-Langhian sequences from the Gulf of Gabes - Tunisia. J Pet Sci Eng 82–83:50–65. https://doi.org/10.1016/j.petrol.2011.11.004
Taktak F, Kharbachi S, Bouaziz S, Tlig S (2010) Basin dynamics and petroleum potential of the Eocene series in the gulf of Gabes, Tunisia. J Pet Sci Eng 75:114–128. https://doi.org/10.1016/j.petrol.2010.10.010
Taktak F, Rigane A, Boufares T, et al (2011) Modelling approaches for the estimation of irreducible water saturation and heterogeneities of the commercial Ashtart reservoir from the Gulf of Gabès, Tunisia. J Pet Sci Eng 78:376–383. https://doi.org/10.1016/j.petrol.2011.06.023
Tawfik M, El-Sorogy AS, Moussa M (2017) Relationships between sequence stratigraphy and diagenesis of corals and foraminifers in the Middle Eocene, northern Egypt. Turkish J Earth Sci 26:147–169. https://doi.org/10.3906/yer-1602-2
Tlig S, Sahli S, Er-Raioui L, et al (2010) Depositional environment controls on petroleum potential of the Eocene in the North of Tunisia. J Pet Sci Eng 71:91–105. https://doi.org/10.1016/j.petrol.2010.01.009
Toffanin F, Agnini C, Fornaciari E, et al (2011) Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: Clues from the central-western Tethys (Alano section, NE Italy). Mar Micropaleontol 81:22–31. https://doi.org/10.1016/j.marmicro.2011.07.002
Tomassetti L, Benedetti A, Brandano M (2016) Middle Eocene seagrass facies from Apennine carbonate platforms (Italy). Sediment Geol 335:136–149. https://doi.org/10.1016/j.sedgeo.2016.02.002
Tosquella J, Martín-Martín M, Guerrera F, et al (2022) The Eocene carbonate platform of the central-western Malaguides (Internal Betic Zone, S Spain) and its meaning for the Cenozoic paleogeography of the westermost Tethys. Palaeogeogr Palaeoclimatol Palaeoecol 589:110840. https://doi.org/10.1016/j.palaeo.2022.110840
Van der Ploeg R, Selby D, Cramwinckel, M J, et al (2018) Middle Eocene greenhouse warming facilitated by diminished weathering feedback. Nat Commun 9:1–10. https://doi.org/10.1038/s41467-018-05104-9
Westerhold T, Rohl U (2013) Orbital pacing of Eocene climate during the Middle Eocene Climate Optimum and the chron C19r event: Missing link found in the tropical western Atlantic. Geochemistry, Geophys Geosystems 14:4811–4825. https://doi.org/10.1002/ggge.20293

Table 1. Dominant components of the distinguished facies along with the facies interpretation. The dominance of lumachellic limestone distinguishes the proximal inner ramp, and the distal inner ramp (subtidal) is distinguished by the dominance of LBF and the frequent PF.

Facies number	Facies name	Microfacies Texture	Main components	Interpretation
1	Lumachellic limestone	Packstone	Oysters, Gastropods	Intertidal
2	Marly limestone	Mudstone	Oysters, Gastropods	Deep intertidal
3	Lamellibranch and gastropods rich dolo-limestone	wackestone	Lamellibranches, Gastropods	Supratidal to intetidal
4	Dolomitic limestone	Mudstone	Azoïc, Quartz grains, Calcite crystals	Supratidal
5	Chaotic lumachells accumulation	Mud- to wackestone	Shell debris, oysters	Intertidal
6	Bioclastic limestone rich in nummulithoclasts	Wackestone - Packstone	Nummulithoclasts, Echinoderm’s debris	Shallow Subtidal
7	Chalky limestone	Mudstone	Bivalves, Algae, Calcite	Supratidal
8	Argillaceous-silty marl	Mudstone	Conglomerates, Quartz grains, karsts	Continental
9	Bioclastic limestone rich in nummulites and echinoderms	Packstone-grainstone	Benthic foraminifera (nummulites), Echinoderms, Planktonic foraminifera	Shallow Subtidal
10	Green silty shales with scare gypsum	Mudstone	Gypsum, and nearly complete absence of skeletal grains, except for rare fragments of bivalve shells	Sabkha

No competing interests reported.

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Evolution of the Eocene shallow carbonate platform in Tunisia: Carbon isotopes stratigraphy and petroleum implications

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Abstract

Figures

Highlights

Introduction

Geological Setting

Materials And Methods

3.1. Sedimentology

3.2. Bulk Carbon Isotopes

Results

4.1. Lithostratigraphic units

4.3. Ostracods biostratigraphy and regional correlations

4.2. Facies analysis

4.2.1. Facies F1: Lumachellic limestone

4.2.2. Facies F2: Marly limestone

4.2.3. Facies F3: Lamellibranch and gastropods rich dolo-limestone

4.2.4. Facies F4: Dolomitic limestone

4.2.5. Facies F5: Chaotic lumachells accumulation

4.2.6. Facies F6: Bioclastic limestone rich in nummulithoclasts

4.2.7. Facies F7: Chalky limestone

4.2.8. Facies F8: Argillaceous-silty marl

4.2.9. Facies F9: Bioclastic limestone rich in nummulites and echinoderms

4.2.10. Facies F10: Green silty shale with scare gypsum

4.4. Sequence stratigraphy in a shallow carbonate platform

4.4.1. Sequence T-R 1

4.4.2. Sequence T-R 2

4.4.3. Sequence T-R 3

4.4.4. Sequence T-R 4

4.4.5. Sequence T-R 5

4.4.6. Sequence T-R 6

4.4.7. Sequence T-R 7

4.4.8. Sequence T-R 8

4.4.9. Sequence T-R 9

4.5. Bulk δ13C Isotope Data

Discussion

5.1. Eustatic and climatic controls on sedimentation

5.2. Early Bartonian abrupt facies change

5.3. Carbon isotope stratigraphy

5.4. SW Neo-Tethys carbonate platform evolution

5.5. Paleogeographic extension of the Reneiche/Siouf member

Conclusions

Declarations

References

Table 1

Additional Declarations

Supplementary Files

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4.5. Bulk δ¹³C Isotope Data