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Table 3
Sedimentary facies of the lower Oligocene Cyrènes Limestones and Marronnier Clay and their interpretation. (*) indicates facies also present in Eocene − lowermost Oligocene (?) deposits (Table 1). Reference for the interpretations: 1: Freytet and Plaziat (1982); 2: Renaut and Gierlowski-Kordesch (2010); 3: Leeder (2016); 4: Bhattacharya (2010); 5: Miall (2010).
| Facies | Grain size | Bed thickness | Description | Pedogenic features | Interpretation |
|---|---|---|---|---|---|
| Cl | mudstone | 1 to 20 cm | Sets of <1 mm-thick planar laminations. Surfaces are planar, rarely undulated, with algal filament casts. | Rare (mud cracks filled-up with gypsum). | Microbialite1 |
| Fl (*) | mudstone to siltstone | 1 to 5 cm | See table 1 for a full description. | none | Lacustrine laminites2 |
| Fp | mudstone to siltstone | 1 to 10 cm | Mudstones to siltstones/wackestones rich in plant debris, with varying carbonate content. Structure is commonly laminated (with 1-5 mm-tick laminations; see Supplementary Fig. S1d), more rarely massive. Sets of changing grain-size and organic content alternate at pluricentimeter to centimeter frequency. Differs from facies Clm (table 1) on two points: (1) Complete bivalve (cyrenae) molds in high concentration can be found within sets or at set boundaries; (2) Lenticular gypsum is rare, but is sometimes present in continuous layers. | none | Mixed marls and bioclastic deposits on a high-energy ramp (lower shoreface)2 |
| Cb | mudstone to wackestone | 5 to 20 cm | Matrix-supported limestone with a micritic, clayey to sandy matrix. Structure is commonly massive, more rarely with mm-thick laminations. Carbonate intraclasts, broken clasts of gastropods (including Limnae) and bivalves are common. Vertical and horizontal burrows can occur, as well as lenticular gypsum (though less repetitively than in facies Cr). | Rare (mud cracks filled-up with gypsum). | Mixed marls and bioclastic deposits on a high-energy ramp (upper shoreface)2 |
| Sp (*) | Very fine to medium sand | 5 to 20 cm thick | See table 1 for a full description. | none | Delta mouth bar sands3 |
| Cr | mudstone | 1 to 10 cm | Sets of fine-grained, micritic limestones with rarer silty layers. Structure is either laminated (with 1-5 mm-thick laminations) or massive. They sometimes include charophytes, but they are otherwise abiotic. The facies is characterized by regular alternations (at the scale of several centimeters) of continuous layers of lenticular gypsum crystals (1 to 20 mm in size; see Supplementary Fig. S1e). Gypsum crystals are matrix-supported or can be so numerous that they form a crystal-supported bed within the limestones. | rare (mud cracks filled-up with gypsum). | Flood deposits −evaporative cycles on a high-energy ramp (upper shoreface)3 |
| Gyp (*) | clay to medium sand | 5 cm to 80 m | See table 1 for a full description. | none | Cumulate evaporites in perennial saline lake2 |
| Gyh | Siltstone to medium sand | 2-5 cm | Small sets (2-5 cm) of gypsum sands with cross-laminations and wavy surfaces. Cosets can form thick benches of indurated gypsum. Discontinuous sets of carbonated siltstones are sometimes present, with wavy surfaces, forming a heterolithic flaser bedding. Flame structures and soft-deformation features (undulated bedding) are common. | none | Reworked evaporites on a high energy lacustrine ramp (upper shoreface)2 |
| Cm | Mudstone | 20 cm to 50 cm | Pink to white, massive limestones with a silty to sandy micritic matrix. They are sometimes gypsiferous (with grain-supported to matrix supported gypsum sands) with Occasional cavities and vugs (see Supplementary Fig. S1f). They often display tiny (<1 cm long) rootlets that are either oxidized or filled with green clay. The base and thickness of sets are irregular; they laterally grade into facies Cr or Cb. | Common: small rootlets. | Palustrine marsh deposits1,2 |
| Fmcp | Mudstone | 5 cm to 1 m | Sets of green, blue to greyish (more rarely light brown) massive mudstones with variable carbonate content. Carbonate intraclasts and broken pieces of tuffa are sometimes present, as well as horizontal burrows filled-up with silt or gypsum sands. | Occasionally present: mottles, slickensides, vertical fractures (sometimes with gypsum), pedogenic nodules, rhizoliths and root traces | Marls on a low-energy ramp (upper shoreface)2 |
| Ci | fine sand | 20-70 cm thick | Well-sorted sandy limestones organized in discontinuous, subhorizontal laminations. Structure also includes rare troughs of cross laminations (1 cm thick) and troughs of bigger (1-5 mm) bioclasts. | None | Wave swash deposits in a bioclastic beach / backshore environment4 |
| Ct | very fine to coarse sand | 15 to 50 cm thick | Sandy limestone rich in poorly-sorted bioclasts, broken oncoids and intraclasts, in small channelized bodies (meter-wide). Sets have a sharp base and are fining upward. Structure is either massive or displays small troughs (1-5 cm) of cross laminations. | None | Bioclastic sand bar5 |
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