Deposition and Diagenesis of the Yates Formation, Guadalupe Mountains and Central Basin Platform



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Texas Tech University


The Middle Permian Yates Formation of the Northwest Shelf and Central Basin Platform contains deposits which accumulated in the following depositional environments: 1) reef, 2) backreef apron, 3) lagoon, 4) intertidal zone, 5) coastal sabkha, 6) continental sabkha, and 7) deflation flat. Outer shelf deposits consist predominantly of carbonates; middle and inner shelf deposits consist dominantly of clastics containing evaporites.

Artesia Group coastal- and continental sabkha deposits contain an assemblage of sulfate crystals and nodules similar in all aspects to that described from the southern margin of the Persian Gulf. Sulfates precipitated interstitially within coastal- and continental sabkha deposits include lensoid and bladed crystals and rosettes of anhydrite after gypsum and nodular anhydrite. Continental sabkha brine pan (salina) deposits contain laminar anhydrite with needle crystals of anhydrite pseudomorphous after gypsum. Early dolomitization of carbonate deposited in coastal sabkhas occurred. Pseudomorphic- and neomorphic replacement of gypsum by anhydrite and replacement of carbonate by sulfate occurred in both coastal- and continental sabkha deposits.

During high stands of sea level, under arid climates, coastal- and continental sabkha and deflation flat deposits prograded seaward, infilling lagoons, and extensive evaporite-bearing deposits were spread over middle and outer shelf areas.

During maximum low stands of sea level, outer-and portions of middle shelf areas received increased rainfall while much of the middle shelf and the entire inner shelf remained arid. Subaerially exposed subtidal-intertidal carbonates of the outer shelf area were subjected to early fresh water diagenesis and became mineralogically stabilized (to calcite), leached and lithified; paleoleaching and replacement of sulfates by length-slow chalcedony also took place in the belt of increased rainfall, pisolitic caliche soils formed in granular backreef carbonates and in sandy parent materials.

During burial, subtidal-intertidal limestones, stabilized and lithified in a fresh water diagenetic environment, became dolomitized and preexisting leached porosity was occluded by sulfate precipitation; in uncemented sands epitaxial overgrowth of quartz on quartz grains and orthoclase on orthoclase grains was followed by precipitation of dolomite and anhydrite cements,

Uplift of Yates sediments in Late Cretaceous-Tertiary time initiated another major episode of fresh water diagenesis which is still in progress and the following reactions are recorded: 1) sulfates have been subjected to leaching, replacement by calcite and length-slow chalcedony and hydration of anhydrite (to gypsum), 2) enlargement of fractures in carbonates by ground water solution, 3) cementation by calcite and length-fast chacedony.



Geology -- Guadalupe Mountains (N.M. and Tex.), Sedimentation and deposition