Abstract

Students and new workers being introduced to the Lower and Middle Permian subsurface stratigraphy of the Delaware Basin area are often confused by the large number of published names, varying age assignments, and interpretation of outcrop defined sequence stratigraphy in the subsurface. Regional subsurface cross sections are among the best illustrations for understanding Permian stratigraphy as well as bringing attention to stratigraphic problems. Although still very useful, classic subsurface cross sections and correlation charts published before 1975 need some updating. The suggested revisions reflect ongoing evolution of thought concerning interpretation of shelf-to-basin correlations, age relationships, and the usefulness of operational wireline log interpretation of sequence stratigraphy.

Although we are reluctant to nit-pick correlations on classic regional cross sections which reflect the understanding of most experts at the time, later generally accepted interpretations should be pointed out to new workers and students. This paper discusses some updated interpretations in the northern Delaware Basin area of Eddy and Lea counties, New Mexico, where wireline logs of most wells can be viewed on the website of the Oil Conservation Division of the New Mexico Energy, Minerals and Natural Resources Department.

Wireline log interpreted correlations and other data reviewed in this paper include:

• Basin starvation during deposition of the Abo Formation and lower Yeso Formation (Drinkard Member).

• The Tubb Sandstone - 3rd Bone Spring Sand correlation which we favor (a revision of the WTGS 1964 cross section, and Silver and Todd, 1969).

• Shelf equivalents of the Cutoff Sand and the 1st and 2nd Bone Spring Sands.

• Age and basinal equivalents of the San Andres Formation (a revision of most pre-1990 cross sections).

• Top of the Cherry Canyon Formation and Manzanita Member stratigraphy.

• Basin wide stratigraphy of the Reef Trail Member of the Bell Canyon Formation.

• Some Cisuralian (Lower Permian) correlations remain controversial Including:

• Basinal equivalent of the Glorieta Member (= 1st Bone Spring Sand?).

• Top of the Leonardian Stage in the basin (= base of the Cutoff Sand?).

• Top of the Wolfcampian Stage and the mid-Wolfcampian unconformity.

• Base Permian - Top Pennsylvanian System in the central Delaware Basin.

Four new or revised shelf-to-basin strati-graphic cross sections summarize some of the updates mentioned above. Each is at the same scale and tied to a common well in the northern Delaware Basin in order to geographically compare relationships between the Northwestern Shelf, Central Basin Platform, and outcrops in the Guadalupe Mountains.