New Mexico Geological Society Annual Spring Meeting — Abstracts

Our study, supported by the NMWRRI, revealed the presence in ~15% of our subsurface and surface samples of superlattice clay(s), corrensite (of Lipman [1954] which is a chlorite/swelling chlorite) and/or chlorite/smectite, in the Leonardian Yeso Formation in and west of the Roswell Basin. The origin of either of these clay minerals, identified in the <2 size fract10n by X-ray diffraction analysis, is best understood by Bodine's and Standaert's (1977) hyperhalmyrolisis; this process is the alteration of a pre-existing clay after its deposition but before its burial and isolation from the hypersaline brine of the depositional basin. The existence of such a brine is required for the Yeso's thinly interbedded limestone, dolomite, gypsum, anhydrite, local rock salt, shale and sandstone lithologies.

The Yeso Formation of the north and northwest shelf of the Delaware Basin is the lithostratigraphic correlative, by being below the Glorieta Formation, and chronostratigraphic correlative, by being Leonardian, to the similar lithologies of the Clear Fork Group on the north and northwest shelf of the Midland Basin. Palmer (1987) and Fisher (1988) report chlorite/swelling chlorite, chlorite/smectite and several other superlattice clays in the Clear Fork Group and regard them as characteristic of evaporite environments and rare in continental weathering environments. Our study expands by at least 46% the area underlain by superlattice clay-bearing Leonardian strata of probable coastal sabkha depositional environment.