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The Sunniland Limestone of south Florida produces hydrocarbons from five types of porosity in carbonate reservoirs. (1) Primary interparticle pores are volumetrically most abundant. Secondary pores after dissolution of aragonite are common but less abundant than primary pores and occur both as (2) matrix porosity and (3) vuggy porosity. (4) Fracture porosity is important in one reservoir and occurs at several localities in the lower Sunniland Limestone. (5) Intercrystalline pore space in dolomite occurs in thin intervals in several reservoirs. Any one reservoir contains two or more of the pore types.
Three types of dolomite are present in the Sunniland Limestone. A presumed early tidal-flat (sabkha) dolomite is composed of 1-to-10 µm crystals that are strontium- and calcium-rich and iron-poor compared with other dolomite from the unit. The dolomite is enriched in C13 and O18 relative to PDB-1 standard. It is associated with tidal-flat sedimentary structures and is nonporous. A second dolomite, composed of crystals up to 500 µm along an edge, is porous, iron-rich and strontium-poor relative to earlier dolomite, enriched in C13 but depleted in O18, and is considered to be a later replacement. A rare third type of dolomite is petrographically distinct as pore-filling crystals up to 1 mm in width with markedly undulose extinction ( baroque" dolomite).
Cementation by a thin calcite fringe around grains and a later blocky calcite cement is present locally. The latter cement precipitated in part during or after compactional grain fracture. Sunniland carbonate rocks contain less than 100 ppm manganese, and a manganese/iron value below 0.06. These low values are believed responsible for a lack of cathodoluminescence in Sunniland limestones and dolomites.
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