First Regional Lowstand - Highstand Maps of a Guadalupian High-Frequency
Sequence
(Lower Seven Rivers HFS G -17) Northern Delaware Basin Area, New Mexico and West Texas
TYRRELL, WILLIS W., Consulting Geologist, 5718 Bentway Dr., Charlotte, NC, [email protected] and JOHN A. DIEMER, Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223
The lower Seven Rivers Formation on the Northwest Shelf ranges to over 350 feet (100m)
thick. We include it and its basinal equivalents in the Lower Seven Rivers HFS (high
frequency sequence
). On the Northwest Shelf it includes carbonate -dominated outer shelf,
shelf crest, and middle shelf facies tracts and the most widespread evaporite -dominated
inner shelf facies. It can be mapped in the subsurface using distinctive wireline
log
character. On the shelf the Lower Seven Rivers HFS extends upward from the top part 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 carbonate or evaporite highstand deposits. In the Guadalupe Mountains this HFS
(G-17 of Kerans and Tinker, 1999) is exposed along the West Face and its shelfal strata
have been
well
studied by others from North McKittrick Canyon to Rocky Arroyo. Along the
shelf margin the Lower Seven Rivers HFS includes the lower Capitan reef. In the adjacent
Delaware Basin, this HFS includes locally productive lowstand sandstone at the top of the
Cherry Canyon Formation and the overlying highstand Hegler Limestone Member of the Bell
Canyon Formation.