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The Bone Spring formation (Permian-Leonardian) from 3-km (9,850-ft) deep conventional cores in the northern Delaware basin is a laminated, black, mixed terrigenous-carbonate mudstone with thin intervals of gray, coarse carbonate-debris flows. All carbonates have been pervasively dolomitized, and porosity and permeability were reduced to 3-8% and 1 md, respectively, during several diagenetic events related to burial history.
Three dolomite generations are defined by fluorescence and cathodoluminescence microscopy and electron microprobe, and are further characterized by means of microsampling for carbon and oxygen isotopes. Over a range of 2 ^pmil (PDB), ^dgr13C decreases steadily from the first to last dolomite generation, reflecting constant mixing of rock carbon and organic carbon as hydrocarbons were evolving in the Bone Spring muds. The first dolomite generation was introduced during the time interval between early postdeposition and burial to approximately 1 km (3,280 ft). Dewatering and compaction of the Bone Spring muds accompanied matrix dolomitization, leaching of metastable grains, fracturing, and silicification of carbonate components. The mean ^dgr18O of the high-stronti m, matrix dolomite is -2.1 ± 0.4 ^pmil (PDB). A second dolomite generation may have been late Ochoan; by this time an additional 1.2 km (3,925 ft) of Guadalupian-Ochoan carbonates and evaporites had been deposited. This fluorescent, nearly stoichiometric dolomite cement has a mean ^dgr18O of -3.0 ± 0.3 ^pmil (PDB), and was coeval with hydrocarbon generation in the Bone Spring. It precipitated from fluids that interacted with the overlying evaporites. Hydrocarbon inclusions are contained in this dolomite, which is succeeded by a generation of anhydrite cement. Sulfur isotopes strongly suggest that remobilized Guadalupian anhydrite-sulfur formed this cement.
The last two diagenetic phases, including the third dolomite generation, crystallized at about present burial depth. Coarsely crystalline, luminescent, pore-filling calcian dolomite, containing hydrocarbon inclusions, has a mean ^dgr18O of -5.4 ± 0.6 ^pmil (PDB). Depleted poikilotopic calcite cement (^dgr18O = -10.3 ^pmil, PDB) records the input of Tertiary water.
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