FIGURE 1 OF LUCAS ET AL. (2009)
There are several serious errors and omissions in figure 1 of
Lucas et al. (2009). The asterisks to the right of the stratigraphic column are said to indicate levels of "Ar/Ar dated ash beds." The Cretaceous 40Ar/39Ar ages
at the levels shown were first reported in
Fassett and Steiner (1997) and the 40Ar/39Ar age for the Paleocene Nacimiento Formation ash bed was reported in
Fassett (2009). Why
Lucas et al. (2009) did not show these ages on their figure 1 and cite their origin is puzzling. The age of the Nacimiento Formation ash bed
was reported to be 64.4 Ma in
Fassett (2009), yet Lucas and others show it to be 64.0 Ma; the placement of this ash-bed level should be the equivalent of 0.4 m.y. below the 64.0 Ma level on this figure. Two dated ash beds are shown just below the 74.0 Ma age on figure 1. The ages of these beds are 74.55 Ma and 74.56 Ma (Fassett and Steiner, 1997) and thus should be placed much lower in the section than where they are shown. The age scale on the left side of the stratigraphic column is inconsistent with 0.5 m.y. intervals being the same width as a 1.0 m.y.
interval. The lithology of the Ojo Alamo Sandstone is incorrectly shown on
figure 1 because the interval between the upper and lower conglomeratic
sandstone beds in the Ojo Alamo Sandstone type area always contains multiple
sandstone beds and never consists entirely of mudstone as figure 1 shows.
More importantly, the base of magnetochron C29n of "This paper" on figure 1 of
Lucas et al. (2009) is shown to be 64.0 Ma. Gradstein et al. (2004), however, stated that the top of chron C29n is 64.432 Ma and its base 65.118 Ma. Clearly the position of C29n on figure 1 is badly misplaced. In the column labeled "Fassett (2009)", the Ojo Alamo polarity chrons should be labeled as follows: the upper normal chron is C29n.1n, the underlying reversed-polarity chron is C29n.1r, and the lower normal chron is C29n.2n per
Fassett (2009). In addition, the lower paleomagntic normal chron is incorrectly placed and sized on figure 1. The base of this chron in
Fassett (2009) is located very close to the base of the Ojo Alamo in the type area and is stated to average 11 m thick, thus if the thickness of chron C29n.2n were correctly scaled on figure 1 of Lucas et al., it would be much thicker than it is shown. It is assumed that these errors resulted from undue haste in preparing this paper rather than any other intent. It is especially surprising that the many errors on figure 1 of
Lucas et al. (2009) could have survived the scrutiny of all eight authors of this report.