New Mexico Geological Society Annual Spring Meeting — Abstracts

The Chama Basin of north-central New Mexico and the Zuni Mountains of central New Mexico contain several excellent outcrop exposures of the Upper Triassic Chinle Group. The Shinarump, Salitral and Poleo formations, which comprise the lower half of the Chinle Group, encompass the Carnian to early Norian stages of the Late Triassic, based on vertebrate biostratigraphy. Each of these units was sampled at three localities in the Chama Basin and one locality in the Zuni Mountains. Sites spanning the gradational Shinarump/Salitral Formation contact yielded an in situ grand mean of D = 352.9?, I = 49.3?, α₉₅ = 20.1?, k = 38.7. Sites in the El Cerrito Bed of the medial Salitral Formation yielded an in situ grand mean of D = 177.4?, I = 10.7?, α₉₅ = 15.6?, k = 63.5. The Youngsville Member of the Salitral Formation and the Poleo Formation are exclusively of reverse polarity, with an in situ grand mean of D = 188.3?, I = 16.8?, α₉₅ = 19.4?, k = 23.4 and D = 182.7?, I = -0.3?, α₉₅ = 5.3?, k = 36.5 respectively. Rock magnetic experiments indicate that the magnetic remanence in these strata is carried by the high coercivity mineral hematite. In general, the lower Chinle Group tends to be dominantly reversed polarity. The Shinarump Formation is noted for intense color mottling and the local occurrence of copper and uranium mineralization. Locally, the lower member of the Salitral Formation (Piedra Lumbre Member) is also very mottled, with colors ranging from whites and yellows through reds, purples and blues that reflect intense pedogenic alteration of the sediments. Several specimens from different sites in the Shinarump and both members of the Salitral Formation yield incoherent magnetizations, suggesting that pedogenic alteration may have erased any original Late Triassic magnetization. However, the majority of sites sampled yield data of good to excellent quality, and tentative correlations can now be made between the lower Chinle Group and stratigraphic sections of similar age in the Tethys region of southern Europe and in eastern North America.