MAGNETOSTRATIGRAPHY

Lucas et al. (2009) stated that Fassett (2009) resurrected the short normal polarity intervals of the lower Ojo Alamo Sandstone first espoused by Lindsay et al. (1981), reaffirmed by Lindsay et al. (1982), and later rejected by Butler and Lindsay (1985). (This "resurrection" is discussed in great detail in Fassett, 2009.) This is literally true for three of the four localities of Lindsay et al. (1981), however Lucas et al. (2009) fail to mention that this same normal interval was not rejected at one of the Lindsay et al. (1981) localities, and more importantly, that a short normal Fassett (2009)polarity interval was independently found in the lower part of the Ojo Alamo in the western part of the Ojo Alamo Sandstone type area by Fassett and Steiner (1997) and at Mesa Portales (documented in Fassett, 2009). (The Mesa Portales paleomagnetic section, published for the first time in Fassett (2009), represents important new data – thus the title of Fassett (2009) – confirming the Paleocene age of the Ojo Alamo Sandstone.) The Mesa Portales data set is especially important because at that locality, Paleocene pollen assemblages are present at multiple levels within the lower Ojo Alamo normal zone and in the underlying reversed polarity zone in the lower Ojo Alamo. Lucas et al. (2009) agreed that palynology is an unequivocal age determinant for K-T boundary strata in the Western Interior (as they so indicate for the San Juan River locality). They must then also agree that the presence of Paleocene palynomorphs in the normal and reversed polarity intervals in the lower Ojo Alamo at Mesa Portales uniquely identify these intervals as magnetochrons C29n and C29r, respectively. It thus follows that these same polarity intervals identified at the other localities along the Ojo Alamo Sandstone outcrop northwest of Mesa Portales are also C29n and C29r and are thus Paleocene in age.

In this part of their paper, Lucas et al. (2009) stated that a four- to six-m.y. hiatus is present at the base of the Ojo Alamo and that a two to 4 m.y. hiatus is present somewhere above all of the dinosaur fossils in the lower Ojo Alamo that they consider to be in place. However, as stated above, both palynologic and paleomagnetic data indicate that the Ojo Alamo Sandstone is Paleocene throughout the San Juan Basin, thus the presence of a multi-million year unconformity within the Ojo Alamo Sandstone is not supported by the data in hand.