Palaeozoic stromatoporoid diagenesis: a synthesis

Abstract Palaeozoic stromatoporoids, throughout their 100-million + year history (Middle Ordovician to Late Devonian and rare Carboniferous), are better preserved than originally aragonite molluscs, but less well-preserved low magnesium-calcite brachiopods, bryozoans, trilobites corals. However, the original mineralogy of stromatoporoids remains unresolved, details diagenesis patchy. This study approximately 2000 literature recognises three diagenetic stages, applicable geological history. Timing processes may vary in between stages; some components not always present. Stage 1, on or just below sediment surface, comprises following: micrite filling upper gallery space after death, then any remaining by non-ferroan ferroan calcite decreasing oxygen pore-waters; partial lithification associated from which be exhumed redeposited, evidence general early middle shallow-marine carbonates; microdolomite formation, with Mg interpreted have been derived high-Mg (HMC) (likely overlaps 2). 2, short distance comprising fabric-retentive recrystallisation (FRR) stromatoporoid skeletons forming irregular (FRIC), mostly orientated normal growth layers, best seen cross-polarised light. FRIC stops at margins contact bioclasts. geometry varies, indicating taxonomic control. Evidence that formed includes syntaxial continuation into sub-stromatoporoid cavities (Type 1 cement), although others were pre-occupied cement fills 2 cement) before FRR, preventing cavities. Likely contemporaneous argillaceous micrites drew carbonate adjacent during reorganisation limestone–marl rhythms also diagenetic. 3, largely shallow burial, dissolution silicification, these occurred earlier histories (more data required); burial pressure stylolites.