Table 1 Types of stones comprising the mega-stones of Menga dolmen.
Type | Classification of limestones basad on the scheme of Folk50 | Grain size (mm) | Mineralogical composition | Skeletal grains | Non-skeletal grains | Matrix | Texture classifications (Dunham51) | Microstructure and sedimentary structure | Sediment supply | Paleoenvironment |
|---|---|---|---|---|---|---|---|---|---|---|
1 | Bioclastic calcirudite | > 2 | 70–80% calcite, 25–18% quartz, limestone, iron oxides, feldspar and glauconite 5–2% | Main components: Bryozoans, bivalves (Clamys, pectinid) Other components: echinoids, coralline corals, benthic foraminifers (amphisteginas, globigerinas), brachiopods, balanids | Intraclasts (limestone) pellets | Low sparite and absence of micrite | Rudstone | Syndepositional intergranular voids, parallel-laminated | Factory zone | Submarine canyon |
2 | Bioclastic calcarenite | < 2 | 70–80% calcite, 25–18% quartz, limestone, iron oxides, feldspar and glauconite 5–2% | Main components: Coralline algae Other components: nodular and branching bryozoans, bivalves, solitary corals, echinoderm spines | Pellets | Contains carbonate mud | Packstone-rudstone, crusts are bindstones | Syndepositional intergranular voids, parallel-laminated | Factory zone | Submarine canyon |
3 | Bioclastic calcirudite/micro-breccia | > 2 | 70–80% calcite, 25–18% quartz, limestone, iron oxides, feldspar and glauconite 5–2% | Bivalves (pectinid), bryozoans, coralline algae | Pellets | Contains carbonate mud | Rudstone | Syndepositional intergranular voids, parallel-laminated | Factory zone | Submarine canyon |
4 | Calcareous breccia | > 2 | 70% calcite, 15% quartz, 8% feldspar, iron oxides (oncolites), sandstone and flint 2%. To a lesser extent: filositicates, slates, coal | Bivalves (pectinid), bryozoans, coralline algae | Dolomite, oolitic limestones, marly limestones | Contains carbonate mud | Rudstone | Synsedimentary cement, low-angle, parallel-laminated, overlapping edges | River | Submarine canyon |
5 | Bioclastical calcarenite | < 2 | 70–80% calcite, 25–18% quartz, iron oxides, feldspar and glauconite 5–2% | Bivalves (Clamys, pectinid), brachiopods, echinoderm spines bryozoans, echinoides | Pellets | Low sparite and absence of micrite | Rudstone | Syndepositional intergranular voids, low-angles, parallel-laminated, burrows | Foreshore (Beach) |
