Biostratigraphy and paleoclimatology of the Eocene-Oligocene boundary section at Toadstool Park, northwestern Nebraska, USA

Eocene–Oligocene latitudinal climate gradients in North America inferred from stable isotope ratios in perissodactyl tooth enamel

“…Paleosol, paleontological, and sedimentological studies suggest significant aridification across the EOT (Evanoff et al, 1992;Retallack, 2007;Terry, 2001). In contrast, more recent isotopic studies indicate a large (~7°C) decrease in mean annual temperature (MAT) but no major change in aridity (Zanazzi et al, 2007;Zanazzi et al, 2009)…”

Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition

“…Hren et al, 2013;Dupont-Nivet et al, 2007) and to a lesser extent 40 Ar/ 39 Ar dating of volcanic tuffs (e.g. Boardman and Secord, 2013;Zanazzi et al, 2007;Zanazzi et al, 2009) and floating astronomical time scales (Xiao et al, 2010). Combined, these studies indicate that although terrestrial environmental change broadly coincided with the EOT-1 and Oi-1 interval at some localities (Hren et al, 2013;Xiao et al, 2010), at others it apparently predates changes associated with the marine EOT by 100-600 kyr (Boardmann and Secord, 2013;Zanazzi et al, 2007;Zanazzi et al, 2009;Zhang and Guo, 2014).…”

“…1.0 ‰ δ 18 O positive shift (Oi-1 event) at 33.6 Myr, close to the base of magnetochron C13n, related to further cooling and Antarctic ice-sheet expansion (Coxall et al, 2005;Katz et al, 2008;Wade et al, 2012). Coeval terrestrial records from the Americas, Europe, and Asia exhibit a wide range of responses to marine cooling and Antarctic ice-sheet growth, from relative climatic stability (Grimes et al, 2005;Kohn et al, 2004;Retallack et al, 2004) to a >4 °C drop in mean annual temperature (MAT) (Hren et al, 2013;Wolfe, 1994;Zanazzi et al, 2007;Zanazzi et al, 2009), and a shift towards more arid conditions (Boardman and Secord, 2013;Dupont-Nivet et al, 2007;Xiao et al, 2010;Zhang and Guo, 2014). Where significant environmental changes are present in the terrestrial record, their timing relative to the marine EOT is established based on magnetostratigraphy, (e.g.…”

“…The ChadronianOrellan boundary is considered broadly equivalent to the EOT (Prothero and Swisher, 1992;Swisher and Prothero, 1990). Stable isotope analyses of fossil mammal teeth and bones from Toadstool Geologic Park (hereafter TGP), a key WRG locality in NW Nebraska (Figure 1.A), shows a 1.0-1.5 ‰ increase in mean δ 18 O across the Chadronian-Orellan transition, interpreted as 7.1 ± 3.1˚C drop in MAT (Zanazzi et al, 2007;Zanazzi et al, 2009). A ca.…”

“…Additionally, calibration of the TGP stable isotope record (Boardman and Secord, 2013;Zanazzi et al, 2007;Zanazzi et al, 2009) Ar dates from the WRG, and the ATPS06 are accurate, the implication is that cooling and/or aridification in central North America was offset from the early Oligocene Antarctic glaciation.…”