Paleohydrologic response to continental warming during the Paleocene–Eocene Thermal Maximum, Bighorn Basin, Wyoming Mary J. Kraus a, ⁎, Francesca A. McInerney b, f , Scott L. Wing c , Ross Secord d , Allison A. Baczynski b , Jonathan I. Bloch e a Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States b Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, United States c Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20560, United States d Department of Earth and Atmospheric Sciences, University of Nebraska, Lincoln, NE 68588, United States e Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, United States f School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia abstract article info Article history: Received 30 July 2012 Received in revised form 27 November 2012 Accepted 16 December 2012 Available online 22 December 2012 Keywords: PETM Paleoclimate Precipitation Paleosol Global warming Geologically rapid global warming occurred during the Paleocene–Eocene Thermal Maximum (PETM) ~ 56 Ma. Several studies have argued that important changes occurred in the hydrological cycle during the PETM, but results have been inconsistent, ranging from global increases in humidity to drier conditions. Changes in paleosols during the PETM in the southeastern Bighorn Basin document major drying during the body of the event. Paleosol changes also suggest transitional episodes of climate change that both preced- ed and followed the PETM. Qualitative, semi-quantitative, and fully quantitative analyses of a ~ 70 m thick interval of paleosols provide a high-resolution record of changes in soil moisture and precipitation. Those changes are compared to changes in temperature determined from δ 18 O values of tooth enamel from the mammal Coryphodon. A distinct shift to drier soils occurred just prior to the PETM, a conclusion that is con- sistent with previous observations that warming began before the onset of the negative carbon isotope excursion associated with the PETM. Paleosols show a progressive drying trend into the lower part of the PETM and become even drier in the upper part of the body of the PETM. Purple-red paleosols that appear dur- ing the recovery phase of the PETM indicate wetter soils, although they are better drained than paleosols below the onset. The purple-red paleosols continue for ~ 15 m above the recovery and indicate that wetter soil conditions persisted after the recovery. It is not clear whether changes in the paleosols that preceded and followed the PETM reflect global forcing factors like orbital cycles or release of carbon that lacks an isotopic label; however, such mechanisms would provide a unifying explanation for shifts seen in continental and marine environments. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The generally warm climate that characterized the Early Cenozoic was punctuated by a dramatic and short lived (~ 200 kyr) global warming event at the Paleocene/Eocene boundary, ~56 Ma ago (e.g., Kennett and Stott, 1991; Zachos et al., 1993; Westerhold et al., 2009; Cui et al., 2011). During this event, termed the Paleocene Eocene Thermal Maximum or PETM, global temperatures rose between 5 and 9 °C (e.g., Kennett and Stott, 1991; Zachos et al., 2003; McInerney and Wing, 2011). The PETM was coeval with a large (~3–5‰) negative carbon isotope excursion (CIE) that can be detected in both marine and continental strata (e.g., Koch et al., 1992; Zachos et al., 1993, 2005; McInerney and Wing, 2011). Astronomically estimated time spans for the PETM have ranged from 150 kyr (Norris and Rohl, 1999) to 210–220 kyr (Rohl et al., 2000), whereas Murphy et al. (2010) estimated a total duration of ~217 kyr by using extraterrestrial 3 He flux rates to adjust for variability in deep marine sedimentation rates. The first part of the PETM – the onset phase – is defined by a geologically rapid decrease in δ 13 C values (e.g., Bowen et al., 2006). Recent analysis of marine deposits suggests that the onset lasted about 20 kyr (Cui et al., 2011), and continental sections provide a duration of 8–23 kyr (summarized in McInerney and Wing, 2011). The second phase – the body of the PETM – is defined by a period of relatively low but stable δ 13 C values (e.g., Bowen et al., 2006). Maximum warming occurred during the body of the PETM, which lasted ~115 kyr (e.g., Abdul Aziz et al., 2008; Murphy et al., 2010). Termination of the PETM (recovery phase), during which Palaeogeography, Palaeoclimatology, Palaeoecology 370 (2013) 196–208 ⁎ Corresponding author at: Department of Geological Sciences, UCB 399, 2200 Colorado Ave., University of Colorado, Boulder, CO 80309-0399, United States. Tel.: +1 303 492 7251; fax: +1 303 492 2606. E-mail address: mary.kraus@colorado.edu (M.J. Kraus). 0031-0182/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2012.12.008 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo