THE LOWER SEVEN RIVERS HIGH FREQUENCY SEQUENCE (PERMIAN, GUADALUPIAN, WORDIAN), NORTHERN DELAWARE BASIN AREA, NEW MEXICO AND WEST TEXAS

The lower part of the Seven Rivers Formation on the Northwest Shelf ranges up to 150 m thick. We include it and its basinal equivalents in the Lower Seven Rivers HFS (high frequency sequence) that is recognizable over more than 10,000 square kilometers in southeastern New Mexico and adjacent west Texas. On the Northwest Shelf it includes outer shelf, shelf crest, middle shelf and inner shelf facies tracts and can be mapped in the subsurface using distinctive wireline log character. There the Lower Seven Rivers HFS extends upward from the base of the locally oil-bearing Shattuck Member (Artesia Red Sand) of the uppermost Queen Formation to the base of the equally widespread but rarely productive “Bowers Sand” marker unit. These siliciclastics generally are considered to be shallow marine trangressive deposits comprising reworked relict eolian feldspathic sands and silts related to sea level lowstands. Most of the Lower Seven Rivers HFS on the shelf, however, consists of shelfal carbonates and anhydrite highstand deposits. In the Guadalupe Mountains this HFS is exposed from North McKittrick Canyon to Rocky Arroyo. Along the shelf margin most of the Lower Seven Rivers HFS includes the lowermost Capitan reef. The basal Shattuck Member, however, onlaps or grades into the uppermost Goat Seep reef. In the adjacent Delaware Basin deep water carbonates and associated very fine-grained sandstones probably include the unique Manzanita Limestone Member of the uppermost Cherry Canyon Formation as well as the Hegler Limestone Member of the lowermost Bell Canyon Formation. If so the Lower Seven Rivers is late Wordian, the Wordian-Capitanian stage boundary now being placed within the overlying Pinery Limestone Member of the Bell Canyon Formation.