Open Access
Table1
Facies classification of the Butte Iouton limestones: biological contents, sedimentary and diagenetic features, and their paleoenvironmental interpretations.
| Facies | Dominant biota | Sedimentary structures | Stratal pattern | Diagenetic features | Paleoenvironmental interpretation | |
|---|---|---|---|---|---|---|
| F1A | Oolitic-peloidal grainstone | Gastropods: Melanopsis, Tarebia, Neritina | Seldom visible cross-stratifications. Good sorting (unimodal) to bimodal distribution | Massive, can form up to 2–3 metres thick units with peloidal rich grainstones (F1B) | – Micritization of shells and ooids cortices – Intragranular microporosity development – Microrhombic micrite overgrowths – Minor compaction features at grain contact |
Moderate to high energy, shallow, oligo-mesohaline, perennial lake environments, at the vicinity of oolitic shoals |
| F1B | Peloidal grainstone | Gastropods: Melanopsis, Tarebia, Neritina | Seldom visible cross-stratifications. Bimodal distribution of the grains | Massive, can form up to 2–3 metres thick units with oolitic-rich grainstones (F1A) | – Micritization of shells and ooids cortices – Intragranular microporosity development – Minor compaction features at grain contact |
Moderate energy, shallow, oligo-mesohaline, perennial lake environments, in backshoal setting |
| F1C | Oncoidal-ooidal-peloidal grainstone | Scarce gastropods | Gravel lenses of coarse-sized grains | Centimetre-thick strata | – Micritization of shells and ooids cortices – Intragranular microporosity development – Minor compaction features at grain contact |
Moderate to high energy, shallow, oligo-mesohaline, perennial lake environments |
| F2A | Mollusk-rich peloidal packstone-grainstone | Bivalves (Polymesoda), gastropods (Hydrobids, Tarebia), ostracods, scarce charophytes | Structureless | Few centimetres to decimetre tabular beds | – Microsparry and sparry calcite cements – Dissolution of molluscan shells |
Shallow, oligo-mesohaline lake with low to moderate water energy |
| F2B | Characean-rich peloidal wackestone-packstone | Characean gyrogonites and stems, ostracods, mollusks (Polymesoda, Tarebia, hydrobids) | Structureless | Centimeter-thick tabular to nearly horizontal beds forming up to 4 m thick set of platelets limestones | – Dissolution of aragonitic shells – Microsparry to sparry calcite cements in molds |
Shallow, perennial oligo-mesohaline lake with Characean meadows |
| F2C | Peloidal wackestone to packstone with calcitic rafts | Bivalves (Polymesoda), gastropods (Tarebia) | Structureless | Decimetre tabular beds | – Dissolution of aragonitic shells | Shallow, perennial oligo-mesohaline lake, within or at vicinity of unpreserved macrophyte meadows |
| F2D | Molluscan-ostracodal wackestone | Ostracods, gastropods (Lymnaea, Viviparus, Planorbis, Tarebia) | Inhomogeneous micrite, burrowing and bioturbation | Decimetre tabular beds to metre beds | – Dissolution of aragonitic shells | Low energy, shallow freshwater to oligohaline pools and sheltered areas of the lake margin |
| F3 | Planar-laminated bindstone | Characean gyrogonites and stems, ostracods, gastropods (mainly Melanopsis) | Alternation of subhorizontal to wavy and crinkled millimeter-thick micritic and microsparitic laminae | Up to 2 m-thick intervals of massive to platy limestones | – Dissolution of aragonitic shells – Microsparry to sparry calcite cements in molds |
Low energy, very shallow freshwater to oligohaline lake margin |
| F4 | Carbonate breccia with pseudomorphs after gypsum | No preserved biota | Structureless | Decimetre thick tightly cemented and irregularly bedded limestone. Gradual transition with underlying oolitic grainstone | – Circumgranular cracks – Dissolution vug and conduits formations – Root traces – Intrasediment growth of microlenticular gypsum – Calcite pseudomorphs after gypsum – Sparry calcite cements |
Paleosoil in evaporitic setting |
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