The Northwest Evaporitic Inner Shelf of the Delaware Basin Area - A Great Place to Evaluate Guadalupian Outcrop - Defined Composite and High Frequency Sequences

ECKARDT, IAN. J., Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223, [email protected], WILLIS W. TYRRELL, 5718 Bentway Dr., Charlotte, NC 28226, JOHN A. DIEMER and DAVID GRIFFING; Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223

The Artesia Group is present throughout the Northwest Shelf of SE New Mexico. It includes the Tansill, Yates, Seven Rivers, Queen, and Grayburg Formations. In a 200 square kilometer subsurface study area in Lea County (T16S, R34 and 35E) it averages 540 m (1775 ‘) thick and is on depositional strike with the subsurface reference section of Tait, et al. (1962). The sequence stratigraphy of the Artesia Group here is correlated and compared to sequence studies by others in the classic Guadalupe Mountains. There, Kerans and Tinker (1999) identify four Composite Sequences (CS 11 - 14) and nineteen High Frequency Sequences (HFS G 10 - 28) in outcropping middle shelf, shelf crest, and outer shelf facies tracts. At the surface the equivalent evaporite-rich, inner shelf facies tract is generally eroded or poorly exposed, however, it is well preserved and penetrated by 1000s of wells in the subsurface of the Northwest Shelf east of the Pecos River.

More than 50 well sections in the study area are used to prepare sequence cross-sections and isopach maps of representative CS and HFS within the Artesia Group inner shelf facies tract. All four of the Artesia Group CS and most of the important HFS identified in the more lithologically variable outcrops of the Guadalupe Mountains can be recognized using widespread siliciclastic markers in the relatively simple evaporite-siliciclastic cycles of the inner shelf facies tract.