Triassic stratigraphy in the Lucero uplift, Cibola, Valencia and Socorro Counties, New Mexico
Spencer G. Lucas and Andrew B. Heckert
Triassic strata exposed in the Lucero uplift of Cibola, Valencia and Socorro Counties are nonmarine red beds of the Moenkopi Formation and Chinle Group. Moenkopi Formation strata disconformably overlie Middle Permian (Guadalupian) limestones and dolomites of the San Andres Formation and are mostly grayish red, trough-crossbedded and ripple-laminated micaceous litharenites intercalated with beds of intraformational conglomerate and grayish red, micaceous siltstone and mudstone. Charophytes, ostracods and capitosauroid amphibians indicate the Moenkopi Formation in the Lucero uplift is of Middle Triassic (early Anisian) age. Overlying Chinle Group strata consist of (ascending) the Shinarump, Bluewater Creek, Petrified Forest, Owl Rock and Rock Point Formations. In the Lucero uplift, strata of the San Pedro Arroyo Formation laterally replace Bluewater Creek Formation strata south of the Rio Salado. Shinarump Formation strata are extrabasinal conglomerates (mostly Paleozoic limestone clasts) and sandstones as much as 17 m thick that disconformably overlie Moenkopi strata. Locally, pedogenically modified sandstones, conglomerates and siltstones - the "mottled strata" - laterally replace Shinarump conglomerates and sandstones. Bluewater Creek Formation strata are at least 70 m thick and are mostly reddish brown siltstones, mudstones and ripple-laminated sandstones The distinctive McGaffey Member - 5-6 m of mostly ripple-laminated sandstone - is present in the upper half of the Bluewater Creek Formation in the northern part of the Lucero uplift. Below the McGaffey Member, the Bluewater Creek Formation contains an Adamanian (late Carnian) tetrapod fauna that includes cf. Buettneria, indeterminate phytosaurs and Stagonolepis. The base of the Petrified Forest Formation in the Lucero uplift is the Sonsela Member; evidently the Blue Mesa Member has been removed by erosion at the pre-Sonsela unconformity. Sonsela strata are as much as 15 m thick and are mostly trough-crossbedded micaceous litharenite and intrabasinal calcrete-pebble conglomerate. Overlying Painted Desert Member strata are mostly reddish-brown bentonitic mudstone at least 100 m thick. Owl Rock and Rock Point strata are only exposed in the Petaca Pinta area (SW 1/4 T6N, R6W and SE 1/4 T6N, R7W). The Owl Rock is mostly grayish- red and very pale green, calcareous mudstone and grayish-red purple bioturbated sandy siltstone and is up to 37 m thick. Rock Point strata are up to 70 m thick and consist of laterally extensive beds of massive, moderate- reddish brown sandy siltstone and laminar to trough-crossbedded moderate reddish brown quartzose sandstone. Middle Jurassic (Entrada) to Upper Cretaceous (Dakota) strata disconformably overlie Upper Triassic Chinle Group rocks in the Lucero uplift.
- Lucas, Spencer G.; Heckert, Andrew B., 1994, Triassic stratigraphy in the Lucero uplift, Cibola, Valencia and Socorro Counties, New Mexico, in: Mogollon Slope, west-central New Mexico, Chamberlin, Richard M.; Kues, Barry S.; Cather, Steven M.; Barker, James B.; McIntosh, William C., New Mexico Geological Society, Guidebook, 45th Field Conference, pp. 241-254.