Lots of good new data in this paper that are very useful. Unfortunately it is victimized by having to rely on previously published stratigraphic correlations that are generally erroneous and unsupported by radioisotopic dates, which especially affects some of the key conclusions of the paper. I also still get really confused with the "Chinle Group" terminology especially units like the "Petrified Forest Formation" which is not equivalent to the currently recognized Petrified Forest Member of the Chinle Formation. Trying to go back and forth between the two schemes (Chinle Formation vs. Chinle Group) is very confusing and often leads to mistakes unless one is extremely careful. Still I extend my congratulations to Kate Zeigler in getting this body of work out there. The correlations can be fine-tuned later.
Zeigler, K. E., and J. W. Geissman. 2011. Magnetostratigraphy of the Upper Triassic Chinle Group of New Mexico: Implications for regional and global correlations among Upper Triassic sequences. Geosphere 7:802–829; doi:10.1130/GES00628.1
Abstract - A magnetic polarity zonation for the Upper Triassic Chinle Group in the Chama Basin, north-central New Mexico (United States), supplemented by polarity data from eastern and west-central New Mexico (Mesa Redonda and Zuni Mountains, respectively), provides the most complete and continuous magnetic polarity chronology for the Late Triassic of the American Southwest yet available. Most of the Chinle Group sequence is composed of hematitic mudrocks that typically carry a well-defined, well-grouped magnetization (residing in both pigmentary and detrital hematite), with laboratory unblocking temperatures as high as 680 °C. Demagnetization experiments isolate magnetizations of south- or north-seeking declination and shallow inclination, which are interpreted as early acquired, Late Triassic magnetizations. Our proposed polarity correlations, coupled with biostratigraphic observations and recent U-Pb age determinations on detrital zircon–bearing strata in the Chinle Group in western New Mexico, West Texas, and Arizona, indicate that deposition of Chinle strata likely spanned a much shorter time span than previously considered. If this interpretation is correct, the Chinle Group can be correlated with only part of the Newark Supergroup or the Upper Triassic Tethyan sections. On a local scale, lower Chinle strata in the Chama Basin are significantly older than the Bluewater Creek Formation in western New Mexico, and the base of the Poleo Formation represents a disconformity of >13 m.y. duration. Magnetic polarity chronologies from upper Chinle strata in New Mexico and Utah suggest that strata considered to be part of the Rock Point Formation in north-central New Mexico are not time equivalent to type Rock Point strata in Utah or to the Redonda Formation of eastern New Mexico.
8 hours ago in Variety of Life