Constructing a time scale of biotic recovery across the Cretaceous–Paleogene boundary, Corral Bluffs, Denver Basin, Colorado, U.S.A.

Abstract

The Cretaceous–Paleogene (K–Pg) boundary interval represents one of the most significant mass extinctions and ensuing biotic recoveries in Earth history. Earliest Paleocene fossil mammal faunas corresponding to the Puercan North American Land Mammal Age (NALMA) are thought to be highly endemic and potentially diachronous, necessitating precise chronostratigraphic controls at key fossil localities to constrain recovery dynamics in continental biotas following the K–Pg mass extinction. The Laramide synorgenic sedimentary deposits within the Denver Basin in east-central Colorado preserve one of the most continuous and fossiliferous records of the K–Pg boundary interval in North America. Poor exposure in much of the Denver Basin, however, makes it difficult to correlate between outcrops. To constrain fossil localities in coeval strata across the basin, previous studies have relied upon chronostratigraphic methods such as magnetostratigraphy. Here, we present a new high-resolution magnetostratigraphy of 10 lithostratigraphic sections spanning the K–Pg boundary interval at Corral Bluffs located east of Colorado Springs in the southern part of the Denver Basin. Fossil localities from Corral Bluffs have yielded limited dinosaur remains, mammal fossils assigned to the Puercan NALMA, and numerous fossil leaf localities. Palynological analyses identifying the K–Pg boundary in three sections and two independent, but nearly identical, 206Pb/238U age estimates for the same volcanic ash, provide key temporal calibration points. Our paleomagnetic analyses have identified clear polarity reversal boundaries from chron C30n to chron C28r across the sections. It is now possible to place the fossil localities at Corral Bluffs within the broader basin-wide chronostratigraphic framework and evaluate them in the context of K–Pg boundary extinction and recovery.

The Boltysh impact structure: An early Danian impact event during recovery from the K-Pg mass extinction

“…The revised age for the Boltysh impact event coincides with a tentative warming period of ~3°C over a duration of 10 ka at ~65.35 Ma as recorded in the Corral Bluffs (61). However, the chronostratigraphic framework applied to these sections is that of Fuentes et al (62) who determined average sedimentation rates between each pair of dated tie-points using interpolated ages for three paleomagnetic chron boundaries [C30n/C29r, 66.398 (61). However, because it is recorded by the Boltysh crater lake sediments and the deep ocean cores globally, there is no reason why the Lower C29n hyperthermal should not be recorded at Corral Bluffs.…”

New earliest Paleocene (Puercan) periptychid ‘condylarths’ from the Great Divide Basin, Wyoming, USA

“…However, the absence of Ectoconus (the first appearance of which defines the onset of Pu2), and the presence of the Pu1 index taxon Oxyprimus suggest the Littleton fauna is best placed in Pu1. Like other Pu1 faunas, the strata containing the Littleton fauna are within the Palaeogene portion of magnetochron C29r (Hicks et al 2003;Fuentes et al 2019).…”

New Skull Material of Taeniolabis taoensis (Multituberculata, Taeniolabididae) from the Early Paleocene (Danian) of the Denver Basin, Colorado

“…c, Magnetostratigraphic, lithostratigraphic, chronostratigraphic, and biostratigraphic logs showing stratigraphic placement of localities at which specimens of T. taoensis (denoted by red stars) occur. Stratigraphy is tied to the Geomagnetic Polarity Time Scale (Gradstein et al 2012;Ogg 2012) using rema-nent magnetization of the rocks in the Corral Bluffs study area, two CA-ID-TIMS U-Pb-dated volcanic ashes (denoted by yellow stars; these ash beds are at the same stratigraphic level and are interpreted as being the same laterally continuous bed that crops out approximately 750 m apart), and the palynologically defined K/Pg boundary (italicized dates) (Fuentes et al 2019;Lyson et al 2019a). The composite lithostratigraphic log is dominated by intercalated mudstone and sandstone, reflecting a variety of fluvial facies (Lyson et al 2019a).…”

“…Importantly, Lyson et al (2019a) documented the presence of Taeniolabis taoensis, whose appearance defines the onset of the Pu3 interval zone (Lofgren et al 2004) in the Denver Basin for the first time. This, coupled with the chronostratigraphic framework of Fuentes et al (2019), provided a temporal foundation to determine the timing of the Pu2/Pu3 transition in the Denver Basin.…”

“…Precise stratigraphic placement for each specimen was obtained using the methods outlined in Lyson et al (2019a; see also Table 1). This, coupled with the chronostratigraphic framework developed for the Corral Bluffs study area by Fuentes et al (2019), allowed us to obtain precise ages for each T. taoensis specimen (Table 1). The chronostratigraphic framework is derived from the identification of three magnetochron boundaries (C30n/C29r, C29r/C29n, and C29n/C28r), the palynologically defined K/Pg boundary, and two chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) 206 Pb/ 238 U dates on zircons separated from thin (ca.…”