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Table 2
Depositional facies classification of the Paleogene sedimentary succession of the “Série rouge” and underlying formations in the Vistrenque Basin: biological contents, sedimentary and diagenetic features, and their palaeoenvironmental interpretations.
| Code | Facies | Biological content | Sedimentary structures | Stratal pattern | Diagenetic features | Occurrence | Palaeoenvironmental interpretation |
|---|---|---|---|---|---|---|---|
| F1 | Anhydritic marlstones and anhydrite | –- | Nodular and banded structure | Metre anhydrite banded interval enclosed between anhydrite marlstones | Replacement of gypsum by anhydrite | Uncommon, reported only from one thick interval from “Série grise” Formation | Evaporitic perennial lake |
| F2 | Finely laminated limestones and papyraceous marlstones | Terrestrial plant remains | Millimetre laminations Wavy to plane-parallel | Several decimetres to metre thick intervals | –- | Frequent in the “Série calcaire” & occasional in the “Série grise” | Profundal perennial lake with anoxic condition |
| F3 | Dark grey marlstones with scarce fauna |
Terrestrial plant remains, few ostracod shells | Structureless | Massive and structureless interval. Frequent alternations with the F4 sandstones | Occasional pyrite precipitation | Common in the “Série Grise” and in the Série calcaire Formations | Profundal perennial lake with poorly oxygenated conditions |
| F4 | Glauconite-rich sandstones and fine calcarenites | Azoic. Terrestrial plant remains | Plane parallel laminations and current ripples. Load casts and flame structures | Centimetre to few cm layers in alternation with marlstones/siltstones | –- | Common in the “Série grise” Formation | Gravity-driven currents in the offshore lake |
| F5 | Coarse calcarenites and microconglomerates | Azoic. Terrestrial plant remains | Vertical normal grading, parallel laminations | Centimetre to decimetre beds overlying F3 marlstones and overlain by F4 sandstones | –- | Frequent in the upper part of the “Série grise” Formation | Gravity-driven currents in the offshore lake |
| F6 | Matrix-supported conglomerates | Mostly azoic. Occasional characean grains in the matrix | –- | Decimetre beds intercalated with F3, F4 and F5 facies | –- | Occasional to frequent in the “Série grise” Formation | Gravity-driven currents in the offshore lake |
| F7 | Thinly-bedded quartzose calcarenites | Azoic. Few terrestrial plant remains | –- | Decimetre tabular beds to metre beds. May alternate with F2 marlstones and display subaerial exposure features | Pedogenic modifications at the top of the beds including dessication cracks | Frequent in the upper part of the “Série calcaire” but also at the base of the”Série mixte” Formation | Vicinity of a riverine mouth (lacustrine delta) with local detrital fluxes |
| F8 | Oncolitic limestones | –- | –- | Decimetre to metre beds with subaerially exposed tops | Pedogenic modifications at the top of the beds including dessication cracks | Occasional in the “Série mixte” Formation | Shallow lake littoral and riverine mouth in the lake |
| F9 | Microbial limestones | microbial crusts (?) | –- | Metre thick beds in alternation with palustrine carbonates (F13) | Occasional incipient pedogenic modifications (cracking) | Frequent in the “Série mixte” & “Série calcaire” Formations | Littoral lake in the vicinity of streams and springs |
| F10 | Polymictic Conglomerates and microconglomerates | Azoic | Erosive base (?), grading into F11 and F12 facies. Preferential clast imbrication |
Inframetric to metre beds alternating with sandstones and marlstones (F11/F12) | Occasional pendular cements and micrite coating around clasts | Frequent in the “Série rouge” and less frequent the “Série mixte” Formation | Bed load fill of channels |
| F11 | Fine to medium sandstones (Quartzose sandstones) | Azoic. | Vertical normal grading, Current ripples (?) | Decimetre to metre beds in alternation with F10 and F11 facies | –- | Common in the “Série rouge” and occasional in the “Série mixte” Formations | Slowdown of fluvial stream deposits, overbank deposits |
| F12 | Variegated and mottled calcareous claystones | Azoic | –- | Metre to several metres intervals alternating with F10, F11 and F13 facies | Mainly pedogenesis: root traces, marmorisation vermicular mottling & vivid red coloration, peds | Common in the “Série rouge” and “Série mixte” Formations Occasional in the “Série calcaire” Formation | Floodplain deposits |
| F13 | Brecciated limestones (pedogenically modified carbonates) | Undetermined numerous molluscs, ostracods | –- | Decimetre to few decimetres beds. Often, pedogenesis modify the top of F7/F8/F9 and F12 facies beds | Pedogenesis: perigranular cracks, root traces, pseudo-microkarst, vadose pisoids may also be found. Geopetal silt and blocky calcite in cavities | Frequent in the “Serie mixte” and occasional in the “Série rouge” (lowermost parts) and “Série calcaire” Formation | Very shallow pond/lake or abandoned channel subjected to exposure and vegetation development |
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