Calibration of chron C29r: New high-precision geochronologic and paleomagnetic constraints from the Hell Creek region, Montana

Abstract

The mass extinction at the Cretaceous-Paleogene boundary marks one of the most important biotic turnover events in Earth history. Yet, despite decades of study, the causes of the Cretaceous-Paleogene boundary crises remain under debate. An important tool that has the capacity to greatly improve our understanding of the events around the Cretaceous-Paleogene boundary is the geomagnetic polarity time scale (GPTS). The GPTS is used for age control in numerous Cretaceous-Paleogene boundary studies, including the timing of Deccan Traps volcanism, a majority of studies in marine sections, and studies on climate and ecological change across the Cretaceous-Paleogene boundary. The current calibration of the GPTS for circum-Cretaceous-Paleogene boundary polarity chrons (C30n-C28n) from the Geologic Time Scale draws heavily on astronomical tuning and uses a 40 Ar/ 39 Ar age for the Cretaceous-Paleogene boundary as a tie point that has since been shown to be 200 ka too old. Furthermore, complex sedimentation has been recorded in marine sections immediately following the Cretaceous-Paleogene boundary, which can possibly obscure orbital signals and complicate cyclostratigraphic interpretation. An independent test of the cyclostratigraphy for this time period is imperative for confidence in the astronomical time scale. Further, polarity reversal ages given in the GPTS do not include uncertainty estimates, making them unsuitable for quanti-

Nature and timing of biotic recovery in Antarctic benthic marine ecosystems following the Cretaceous–Palaeogene mass extinction

“…), and was more recently precisely dated to 328 000 ± 15 000 yr after the mass extinction by Sprain et al . (). A further increase in standing species richness occurs at the base of the SF (Fig.…”

Constructing a Timescale of Biotic Recovery across the Cretaceous–Paleogene Boundary, Corral Bluffs, Denver Basin, Colorado

“…C30n-C28r) from the Castle Pines core, Kiowa core (Hicks et al, 2003) and Corral Bluffs to studies in the San Juan Basin (Butler and Lindsay, 1985;Peppe et al, 2013), Hell Creek region of Montana (LeCain et al, 2014;Sprain et al, 2018), and the Williston Basin in North Dakota (Peppe et al, 2009). Solid red line represents the K-Pg boundary as defined in the respective studies.…”

“…Given the reported provinciality of mammalian faunas during the Puercan (Lofgren et al, 2004), it is critical to the understanding of regional recovery dynamics to have independent age controls at key fossil localities in order to correlate coeval faunas across the Western Interior. It is now possible to tie our new magnetostratigraphy at Corral Bluffs to other key K-Pg boundary sites in the Western Interior (Butler and Lindsay, 1985;Swisher et al, 1993;Peppe et al, 2009;LeCain et al, 2014;Sprain et al, 2018;Buckley, 2018; Figure 7). The Pu1 localities within the Denver Basin occur within C29r, including the Alexander locality which is thought to represent an intermediate between Pu1 and Pu2 faunas (Hicks et al, 2003;Eberle, 2003;Middleton et al 2004).…”

“…Counties, Montana has yielded Pu1 and Pu3 mammal fossils and is among the best paleontologically sampled K-Pg boundary intervals with extensive chronostratigraphic controls (Swisher et al, 1993;Clemens, 2013;LeCain et al, 2014;Wilson, 2014;Sprain et al, 2018). Swisher et al (1993) and LeCain et al (2014) identified paleomagnetic reversals interpreted to represent C30r-C28n within the Hell Creek and Fort Union formations in Garfield and McCone…”

“…Counties. Sprain et al (2018) further refined the magnetostratigraphy of the Hell Creek region across 14 sections that are interpreted to span C30n through C29n. Pu1 assemblages within the Hell Creek region of Montana are located within C29r.…”