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Petrology and Origin of Petroliferous Breccias in Ochoan Evaporites, Western Delaware Basin

Joseph E. Crawford

Heterolithic breccias associated with solution-collapse features in Permian Ochoan evaporites of the western Delaware basin contain petroleum and hydrogen sulfide gas. A kinematic and geochemical model is proposed for their origin, based on petrologic study.

As noted from detailed core analyses and selective surface mapping of the region, the breccias are a product of postdepositional dissolution of evaporites along prominent fracture trends. The breccias exhibit vertical tabular to pipelike subsurface morphologies. In the area of study, brecciation is developed to a depth of about 600 m and indistinctly propagates into fracture systems within the underlying clastics of the Guadalupian Delaware Mountain Group.

Phase equilibria relations between gypsum and anhydrite within petroliferous zones indicate formation-water chemistry is compatible with oil-field waters of the Bell Canyon lithostratigraphic unit.

Breccia clasts of Permian Ochoan to Lower Cretaceous(?) lithostratigraphic affinity are preserved in the heterolithic breccias, constraining the time of development of breccias and indicating a relative time of petroleum entrapment. This latest period of solution-collapse and brecciation was initiated during the middle Pleistocene and is likely to have continued as a regionally active process up to the present.

The occurrence of petroleum in the identified breccia is subeconomic as far as we know but may help us understand the time distribution of hydrocarbons within the Delaware Mountain Group.

AAPG Search and Discovery Article #91034©1988 AAPG Southwest Section, El Paso, Texas, 21-23 February 1988.