Terrestrial Evidence for Two Greenhouse Events in the Latest Cretaceous

Abstract

We present a terrestrial record of stable carbon and oxygen isotopes from paleosol carbonate for climate interpretations between ca. 71.0 and 63.6 Ma. Isotopic ratios point to covarying and elevated atmospheric CO 2 pressures and temperatures between ca. 70.0 and 69.0 Ma and ca. 65.5 and 65.0 Ma. These two greenhouse episodes were characterized by atmospheric CO 2 levels between 1000 and 1400 ppmV (V = volume) and by mean annual temperatures in west Texas between 21 and 23 °C (~35°N paleo-latitude). Atmospheric CO 2 and temperature relations indicate that a doubling of pCO 2 was accompanied by an ~0.6 °C increase in temperature. A temperature gradient of ~0.4 °C per degree of latitude is proposed for North America across the Cretaceous-Tertiary boundary when comparing temperature proxies from west Texas with paleobotanical work in North Dakota. Our data demonstrate strong coupling between terrestrial climates and ocean temperatures that were possibly forced by Deccan trap volcanic degassing, leading to dramatic global climate changes.

Use of multiple oxygen isotope proxies for elucidating Arctic Cretaceous palaeo-hydrology

“…Precipitation estimates for the PCF ranged between 500 to 1500mm/yr (Spicer & Parrish 1990). Globally, there is evidence for two warming events in the Maastrichtian (Li & Keller 1998;Barrera & Savin 1999;Nordt et al 2003;Wilf et al 2003) that may overlap with the timing of the PCF deposition. The older of these two warming events occurred between 69.5 and 68.5 Ma and is associated with increases in atmospheric pCO 2 concentrations of 1000-1200 ppmv (Nordt et al 2003).…”

“…Globally, there is evidence for two warming events in the Maastrichtian (Li & Keller 1998;Barrera & Savin 1999;Nordt et al 2003;Wilf et al 2003) that may overlap with the timing of the PCF deposition. The older of these two warming events occurred between 69.5 and 68.5 Ma and is associated with increases in atmospheric pCO 2 concentrations of 1000-1200 ppmv (Nordt et al 2003). This increase in pCO 2 may have caused global mean annual temperatures to be c. 22 8C and is correlated with an increase in ocean temperatures of c. 3 8C and associated with the initiation of increased volcanic activity in the Indian Deccan traps (Hofman et al 2000).…”

North Atlantic warming during global cooling at the end of the Cretaceous

“…of the Maastrichtian is well documented (e.g., Li and Keller, 1998;Wilfet al, 2003), and an earlier warming pulse ca. 69 Ma has been proposed (Nordt et al, 2003). Evidence for the ca.…”

“…Biostratigraphy, magnetostratigraphy, and chemostratigraphy (age model; see footnote one) demonstrate that there are samples from 1050C and 1052E that fall both on the warming trend proposed herein and between the warming pulse in the last ~0.5 m.y. of the Maastrichtian (e.g., Li and Keller, 1998;Wilf et al, 2003) and the proposed 69 Ma warming pulse (Nordt et al, 2003). Previous studies have suggested that the North Atlantic became an intermediate or deep-water source during the Maastrichtian (e.g., Frank and Arthur, 1999;D'Hondt and Arthur, 2002), and if subsurface waters exported from the North Atlantic were replaced by surface waters flowing north from the South Atlantic, the resulting heat piracy would explain divergent 8 ls O trends between the two Atlantic basins (e.g., Crowley and North, 1991;Seidov and Maslin, 2001;Fig.…”

A Late Cretaceous Coniferous Woodland From the San Juan Basin, New Mexico

“…The described floral assemblages are not sufficiently di− verse to allow an analysis of the vegetation in relationship to climate and palaeogeography, especially that the Maastrich− tian climate was evolving particularly rapidly, including both the coolest interval of the Late Cretaceous (Wolfe and Upchurch 1987: 44) and two warmer intervals (Nordt et al 2003). Moreover, a major reorganisation of oceanic circula− tion patterns took place at the early/late Maastrichtian bound− ary, resulting in global cooling and continentalisation of the climate, as well as in extinctions in marine the domain (Frank and Arthur 1999 and references therein).…”