New Mexico Geological Society Annual Spring Meeting — Abstracts

Jurassic strata are intermittently exposed along the western, northern and northeastern limbs of the Tijeras syncline (Cedar Crest-Sandia Park areas, Bernalillo County). The singlemost complete and well exposed section crops out in the NW1/4 SW1/4 sec. 31, TIIN, R5E and well represents the outcrop belt. Here, the Jurassic strata are 169 m thick and are (ascending): (1) Dewey Bridge Member of Entrada Sandstone, 11.5 m of mostly reddish brown, ripple laminated, fine sandstone that disconformably overlies red-bed mUdstones of the Upper Triassic Petrified Forest Formation of the Chinle Group; (2) Slick Rock Member of Entrada Sandstone, yellow, coarse, trough-crossbedded sandstone about 10.5 m thick; (3) Luciano Mesa Member of Todilto Formation, 2.2 m of thinly laminated, kerogenic limestone; (4) Tongue Arroyo Member of Todilto Formation, 20.5 m of massive, white gypsum; (5) Summerville Formation, 31 m of red, ripple-laminated sandstone, massive gypsiferous sandstone and cyclically bedded, variegated siltstone, shale and nodular limestone; (6) Salt Wash Member of Morrison Formation, 21 m of fine to coarse, troughI crossbedded feldspathic sandstone with lenses of clay-pebble conglomerate and red-bed mudstone; (7) Brushy Basin Member of Morrison Formation, 32 m of mostly covered, smectitic green claystone with some thin lenses of nodular limestone and fine-grained sandstone; (8) Jackpile Member of Morrison Formation, 32 m of trough-crossbedded kaolinitic sandstone overlain by the Oak Canyon Member of the Cretaceous Dakota Formation. The Jurassic section in the Tijeras syncline thus is very similar to that exposed nearby in the Hagan basin and at Galisteo Dam, though thinner. The unit mapped in the Tijeras syncline by Ferguson et al. (1996, NMBM&MR Open File Digital Map OF-DM-1) as the Bluff Sandstone is actually the Salt Wash Member of the Morrison Formation.