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Post-Permian Salt Dissolution
under Burial Conditions—Continued
 

Examination of the residues left after regional low-angle salt dissolution in the Palo Duro Basin shows that salt has dissolved and residue formed by incremental dissolution of the uppermost salt over a wide area accompanied by passive subsidence of overlying strata. Horizontal fractures in overlying strata are evidence of a vertical extension, syntaxial gypsum fillings (Gustavson and others, 1994) show that the fracture opening occurred incrementally as underlying salt was dissolved, and that creation of voids leading to catastrophic collapse did not occur in this setting. Insoluble residues are identified as evidence that impure salt beds have been dissolved.

 
core thin

Photograph (a) and photomicrograph (b) of the same sample (DOE Stone and Webster Sawyer core, 833.7 ft below datum).

Wavy-laminated mudstone and anhydrite insoluble residue formed after dissolution of halite shows diagnostic features of regional low-angle salt dissolution: (1) mixtures of insoluble components from halite with unusual wavy lamination as a result of accretion of newly released insoluble components against existing insoluble residue, (2) beds in positions laterally equivalent to preserved salt, and (3) syntaxial horizontal gypsum-filled fractures in overlying units.

 

In the Palo Duro Basin, inclusion of late diagenetic minerals formed in halite in the insoluble residue, in particular limpid dolomite, indicate that halite dissolution occurred in the burial environment after dolomite precipitation (Gao and others, 1990). Integration of evaporite diagenesis with dissolution-zone processes is an important tool for separating burial dissolution from syndepositional and base-of-cycle dissolution.

In the Midland Basin, regional low-angle salt dissolution and passive letdown of overlying strata is a probable mechanism for salt thinning over areas on the east edge of the basin and over the south part of the Central Basin Platform.

 

 

Insoluble residue formed by dissolution of mudstone-halite mixtures. Gruy Federal Rex White core, 613 ft below datum.

Focused Dissolution and Collapse