Alamo Sandstone and Animas Formation in the San Juan

Palaeontologia Electronica, 2009

In this issue of Palaeontologia Electronica Lucas, et al. (2009) question the validity of the Fassett (2009) paper that presented evidence for Paleocene dinosaurs in the San Juan Basin of New Mexico and Colorado. Their challenges focus primarily on the lithostratigraphy, palynology, and paleomagnetism of the dinosaur-bearing Ojo Alamo Sandstone, shown by Fassett to be of Paleocene age. The lithostratigraphy of the Ojo Alamo is addressed by Lucas et al. (2009) based on detailed studies of outcrops of this formation in two relatively small areas in the southern San Juan Basin where Ojo Alamo dinosaur fossils have been found. When viewed over its 13,000 km 2 extent, the Ojo Alamo is seen to be a much more complex formation than these authors recognize, thus their perception and description of the lithostratigraphy of this rock unit is limited and provincial. Fassett (2009) presented a detailed discussion of the palynology of the rocks adjacent to the Cretaceous-Tertiary (K-T) interface in the San Juan Basin, including a 67-page appendix and 25 tables listing the 244 palynomorph species identified from these strata. The Ojo Alamo Sandstone produced 103 palynomorphs from five principal localities including one especially prolific sample set from drill core through K-T strata. Without exception, all samples collected from the Ojo Alamo Sandstone for palynologic analysis were found to contain Paleocene palynomorph assemblages. Lucas et al. challenge only one Ojo Alamo palynomorph assemblage from one of the five areas studied, stating that they were unable to find palynomorph-productive samples at that locality. They submit no new palynologic data that refutes the Paleocene palynologic age of the Ojo Alamo Sandstone. In addressing the paleomagnetism of the Ojo Alamo, these authors dismiss the presence of a critical normal-polarity magnetochron discovered in the lower part of the Ojo Alamo-magnetochron C29n.2n of Fassett (2009) with no evidence to justify this dismissal. This magnetochron has been identified at five localities in the basin, thus its existence seems unquestionable. At the Mesa Portales locality, this normal chron was found in Ojo Alamo strata containing Paleocene palynomorph assemblages verifying its identification as chron C29n. Other minor arguments of Lucas et al. (2009) are also addressed in this paper. In sum, Lucas et al. (2009) present no new data to contradict the data presented in Fassett (2009).

2009

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does magnetostratigraphy, because Fassett’s disregard of a major unconformity above the dinosaur-bearing Naashoibito Member renders questionable his use of an uninterrupted magnetostratigraphy to assign a Paleocene age to dinosaur fossils in that unit. Moreover, Fassett’s article failed to adequately dismiss the broadly held conclusions that: (1) the Cretaceous-Tertiary boundary is within the Ojo Alamo Sandstone; (2) the dinosaur-dominated vertebrate fossil assemblage of the lower Ojo Alamo Sandstone (Alamo Wash local fauna of the Naashoibito Member) is of Maastrichtian age; and (3) the isolated, water-worn and/or fragmentary dinosaur bones from the overlying Kimbeto Member are reworked from underlying Cretaceous strata.

Palaeontologia Electronica, 2009

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does magnetostratigraphy, because Fassett’s disregard of a major unconformity above the dinosaur-bearing Naashoibito Member renders questionable his use of an uninterrupted magnetostratigraphy to assign a Paleocene age to dinosaur fossils in that unit. Moreover, Fassett’s article failed to adequately dismiss the broadly held conclusions that: (1) the Cretaceous-Tertiary boundary is within the Ojo Alamo Sandstone; (2) the dinosaur-dominated vertebrate fossil assemblage of the lower Ojo Alamo Sandstone (Alamo Wash local fauna of the Naashoibito Member) is of Maastrichtian age; and (3) the isolated, water-worn and/or fragmentary dinosaur bones from the overlying Kimbeto Member are reworked from underlying Cretaceous strata.

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does magnetostratigraphy, because Fassett's disregard of a major unconformity above the dinosaur-bearing Naashoibito Member renders questionable his use of an uninterrupted magnetostratigraphy to assign a Paleocene age to dinosaur fossils in that unit. Moreover, Fassett's article failed to adequately dismiss the broadly held conclusions that: (1) the Cretaceous-Tertiary boundary is within the Ojo Alamo Sandstone; (2) the dinosaur-dominated vertebrate fossil assemblage of the lower Ojo Alamo Sandstone (Alamo Wash local fauna of the Naashoibito Member) is of Maastrichtian age; and (3) the isolated, water-worn and/or fragmentary dinosaur bones from the overlying Kimbeto Member are reworked from underlying Cretaceous strata.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2016

Abstract Here we provide a detailed description of the upper Campanian sediment succession at Las Aguilas, southern Coahuila, northeastern Mexico, including the first absolute age dating for this interval, paleoenvironmental reconstructions and taphonomic observations on the abundant dinosaur remains at the locality. Stratigraphic investigations of the dinosaur-bearing succession at the Las Aguilas vertebrate fossil area near Porvenir de Jalpa reveal a diverse vertebrate assemblage, including dinosaurs, crocodilians and turtles. New findings in adjacent sites include eusuchian crocodylomorphs, four different kinds of turtles, dromaeosaurids, lambeosaurines, pterosaurs and elasmosaurid plesiosaurs. Strontium isotope measurements on fossil oyster shells provide an absolute age of 73 ± 1 Ma for the lower part of the Las Aguilas section. The locality is thus of late Campanian age. The vertebrate, invertebrate and plant materials as well as the sediment structures observed in a 50 m thick predominantly siliciclastic succession of the Cerro del Pueblo Formation suggest deposition in an extensive delta plain environment. The facies succession indicates a short-termed cyclicity of limnic, brackish and shallow marine environments during the late Campanian–early Maastrichtian Cerro del Pueblo Formation with numerous layers containing dinosaur fossil remains. Resumen Aqui damos una descripcion detallada de la sucesion de sedimentos del Campaniano Superior en Las Aguilas, sur de Coahuila, noreste de Mexico, incluyendo la primera datacion absoluta para este intervalo, reconstrucciones paleoambientales y observaciones taxonomicas sobre la abundancia de restos de dinosaurios en la localidad. Investigaciones estratigraficas de los estratos con dinosaurios en el area fosilifera de Las Aguilas cerca de Porvenir de Jalpa revelan un ensamblaje vertebrado diverso, incluyendo dinosaurios, cocodrilos y tortugas. Nuevos descubrimientos en sitios adyacentes incluyen crocodylomorfos eusuquios, cuatro diferentes tipos de tortugas, dromaeosauridos, lambeosaurinos, pterosaurios, y plesiosaurios elasmosauridos. Mediciones de isotopos de estroncio en conchas de ostiones fosiles proveen una edad absoluta de 73 ± 1 millones de anos para la parte inferior de la seccion de Las Aguilas. La localidad es por lo tanto de edad Campaniana tardia. El material de vertebrados, invertebrados y de plantas asi como las estructuras sedimentarias observadas en una sucesion predominantemente siliciclastica de 50 m de la Formacion Cerro del Pueblo sugieren una depositacion en un ambiente de una extensa planicie deltaica. La sucesion de facies indica una ciclicidad de periodo corto de ambientes limnicos, estuarinos y marinos someros durante el Campaniano tardio-Maastrichtiano temprano de la Formacion Cerro del Pueblo con numerosos estratos conteniendo fosiles de dinosaurios. Palabras Clave: Las Aguilas, sucesion de dinosaurios, Campaniano superior, ambientes deposicionales, Formacion Cerro del Pueblo, Coahuila.

1998

We assign two incomplete dinosaur tracks from the Dakota Sandstone in Socorro County, west-central New Mexico to the ichnogenus Caririchnium sp., widely believed to represent the tracks of an iguanodontid ornithopod dinosaur. This is the first record of Cretaceous dinosaur tracks from west of the Rio Grande rift in New Mexico. Previous work suggests that the Dakota Sandstone in west-central New Mexico is of middle Cenomanian age, which makes these tracks younger than those of the so-called "dinosaur freeway" in the Dakota Group of northeastern New Mexico and eastern Colorado.

Revista mexicana de …, 2004

Late Cretaceous paleobiogeographic studies in northeastern Mexico and the Western Interior of North America. At Saltillo, the CdP is 162 m thick, much thinner than previously reported. To the west, however, the CdP thickens to 449 m at Rincón Colorado (35 km west of Saltillo) and 540 m at Porvenir de Jalpa (70 km west of Saltillo). A substantial stratigraphic interval of interbedded grey-green and red beds is present above the CdP throughout the field area; for consistency, it is assigned to the overlying Cerro Huerta Formation (CH).

1999

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