New Mexico Geological Society Annual Spring Meeting — Abstracts

The Abo Formation and overlying Yeso Group comprise most of the Lower Permian stratigraphic section in central and southern New Mexico. Traditionally, the Wolfcampian-Leonardian boundary has been equated with the Abo-Yeso contact, and other correlations of these strata have been similarly imprecise due to a lack of biostratigraphically significant fossils. However, new biostratigraphic data from marine strata below (Bursum Formation) and laterally equivalent (Hueco Group) to the Abo Formation, from marine limestones of the Los Vallos Formation of the Yeso Group and from the overlying San Andres Formation, greatly clarify age determinations and regional correlations (e. g., Lucas et al., 2013, 2015; Vachard et al., 2015). Fusulinid and conodont data indicate that the Bursum Formation straddles the Virgilian-Wolfcampian (Carboniferous-Permian) boundary and is mostly of early Wolfcampian (Newwellian/ early Asselian) age. The base of the Abo Formation is a regional unconformity close in age to the base of the middle Wolfcampian (Nealian/Asselian). In southern New Mexico, the red-bed interval of the Robledo Mountains Formation of the Hueco Group, equivalent to part of the upper Abo Formation (Cañon de Espinoso Member) to the north, is of Leonardian (Hessian/Artinskian) age base on microfossils from interbedded and bracketing marine limestones. This means the Wolfcampian-Leonardian boundary is in the upper part of the Abo Formation, though precise placement in nonmarine sections is not possible with available data. Marine limestone beds of the Los Vallos Formation of the Yeso Group in the Fra Cristobal and Caballo Mountains of Sierra County yield microfossils indicative of a late Leonardian (Cathedralian/early Kungurian) age. The San Andres Formation, above the Yeso Group, contains microfossils of late Leonardian (Cathedralian/middle-late Kungurian) age, consistent with ammonoid and conodont data that indicate that the lower part of the San Andres Formation (only this portion is preserved in central and southern NM) is of late Leonardian age. Applying the current ICS numerical calibration of the standard global chronostratigraphic scale thus indicates Bursum deposition took place close to ~299-301 Ma; Abo deposition occurred in the interval ~298-286 Ma; and Yeso deposition took place ~286-276 Ma.

References:

1. References Lucas, S. G., Barrick, J. E., Krainer, K. and Schneider, J. W., 2013, The Carboniferous-Permian boundary at Carrizo Arroyo, central New Mexico, USA: Stratigraphy, v. 10, p. 153-170. Lucas, S.G., Krainer, K. and Vachard, D., 2015, The Lower Permian Hueco Group, Robledo Mountains, New Mexico (U.S.A.): New Mexico Museum of Natural History and Science, Bulletin 65, p. 43-95. Vachard, D., Krainer, K. and Lucas, S., 2015, Late Early Permian (late Leonardian; Kungurian) algae, microproblematica, and smaller foraminifers from the Yeso Group and San Andres Formation (New Mexico; USA): Palaeontologia Electronica, 18.1.21A, p. 1-77.