ABSTRACT

The Monte Antola Formation consists of a thick section of calcareous turbidites deposited at oceanic depths (below the calcium carbonate compensation level). Diagenetic features of the unit emphasize major differences between shallow and deep-marine diagenesis. The relatively stable original mineralogy and the absence of au early fresh water flush in the Monte Antola sediments allowed considerable compaction to occur before cementation, yielding a characteristic close-packed texture with relatively small volumes of cement. "Early" diagenesis consisted of remobilization of unstable opaline silica of sponge spicules and radiolarian tests. "Late" diagenesis included the precipitation of separate iron-free and ankeritic dolomite generations and extensive calcite cementation. Formation of ecrystallization textures (microspar and pseudospar zones and veins) was controlled by original sediment grain-size and occurred after cementation, but before stylolitization. Weathering has resulted in oxidation of pyrite and associated dedolomitization (calcite after dolomite). Dedolomitization of ferroan dolomites results in the formation of ferroan calcites (maintaining original dolomite zonation) which retain ferrous iron in the lattice, not as ferric oxide/hydroxide coatings.