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Seven Rivers and Yates Formations


Type log through the Seven Rivers Formation. Cochran 14; Champlin Oil and Refining Company George E. Bensen No. 1, contains numerous salt beds in the Guadalupian section.

Yates Formation

The Yates Formation is a 100- to 175-ft-thick siliciclastic unit. The moderately high gamma-ray character, regional extent, and consistent thickness make this unit an optimum stratigraphic marker. Several anhydrite beds of subregional extent within the Yates provide additional log character. Very near the Capitan Reef margin, the Yates log character is obscured because it is laterally equivalent to back reef carbonate or to Capitan Reef facies. Interpretation of the depositional environment of the Yates is problematic from log character because sandstones and siltstones are accumulated in both marine and eolian flat environments. In the Palo Duro Basin north of the study area, cores through the Yates contain massive to disrupted (haloturbated) silt and very fine sandstone with illuviated clays, suggesting incipient soil formation interpreted as eolian flat facies accumulated as water level rose during a period of generally low sea level.

Seven Rivers Formation

The Seven Rivers Formation is composed of cyclically interbedded mudstones, salt, anhydrite, and dolomite. Several thick anhydrite beds at the top of the Seven Rivers Formation were the most extensive units in the section and were useful stratigraphic markers toward the basin margins. Regionally the amount of dolomite in the Seven Rivers Formation increases toward the Delaware Basin margin. In the New Mexico parts of the Delaware Basin Margin, the Seven Rivers is composed of shallow-water back-reef carbonate and is transitional into reef facies (Garber and others, 1989; Sarg, 1981). Log suites located for this study, however, were inadequate to correlate the lithologies. Halite is recognized on logs and in core descriptions over much of the study area, but clean salt beds are of limited thickness (<100 ft) and areal extent. The thickest Guadalupian net salt (100 to a maximum of 500 ft in several beds) identified is in the northernmost tier of counties in the study area (Cochran, Hockley, Lubbock, and Crosby) and in the Ector County in the depocenter of the Midland Basin. Because of the limited potential as a salt cavern resource and difficulty mapping significant units, detailed stratigraphic analysis of salt in the Seven Rivers Formation was not undertaken.

Stratigraphic Units and Type Logs
Salado and Tansill Formations