Dolomitization in three cores of Lower Leonardian, periplatform carbonates in the subsurface Midland basin post-dated mineralogic stabilization and calcite cementation, which occurred in the deep-sea, shallow-burial (<2000 ft subbottom: 610 m) environment. Mean δ18O compositions of dolomites from two of the cores located in the northern Midland basin are slightly depleted relative to presumed Lower Permian seawater (°18O=-2.65 o/oo and -1.85 o/oo, respectively), but overlap those of associated precursor limestones and prior-precipitated calcite cements (δ18O=-2.6 to -3.1 o/oo). Carbon isotopic compositions of these dolomites define a limited range of positive δ13C values (1.5 to 2.3 o/oo). Isotopic and trace-element data suggest initial dolomite formation in the shallow-burial, subbottom environment, in the absence of sulfate reduction or methanogenesis, in rock-dominated diagenetic systems. Mean oxygen and carbon isotopic compositions of dolomites in the third core, located in the east-central Midland basin, are more depleted (δ18O=-4.1 o/oo; δ13C=3.3 o/oo). Isotope and trace-element data also suggest initial formation of these dolomites in the shallow-burial, subbottom environment, but from marine fluids depleted in δ18O as a result of the prior precipitation of calcite cements. Dolomitization in all three cores began in the Permian, at subbottom depths perhaps as shallow as 2000 ft (610 m). Sr isotopic data, in conjunction with the burial depth-temperature history of these wells, suggest that dolomite formation and recrystallization were complete by the end of the Permian, when the rocks were buried to about 6000 ft (1830 m). Subsequent diagenesis, which included significant porosity creation via dissolution, occurred in the deeper mesogenetic environment during the Mesozoic. © 1994 Springer.