A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

Abstract

Petrological and δ 13 C analyses were under taken on contiguous specimens of coal and intercalated minor organicrich clastic sedi ments collected from coal seams spanning the CretaceousPaleogene boundary in the Alberta and Saskatchewan portions of the Western Interior Basin. The generally high smectite content of the coal suggests that the original mires were largely small, discon nected, and rheotrophic, readily receiving abundant waterborne detrital clastic mate rial of largely volcanic origin. Nevertheless, using the distinctive claystone that marks the CretaceousPaleogene boundary as a regional datum , it is possible to correlate cycles in the vitrinite and inertinite compo sition of the coals over >500 km. Estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composi tion represent regional, cyclic fluctuations in wildfire and oxi da tion of the peatlands and overlying canopy at a frequency of hundreds to thousands of years. The likely causes of these fluctuations were cyclic, regionalscale changes in temperature. The Cretaceous Paleogene boundary event occurred early during a phase of gradually increasing tem perature and/or decreasing rainfall, but peak wildfire and desiccation of peat occurred up to 14,000 yr later than the Cretaceous Paleogene boundary, and the mires did not experience significant water stress in the im mediate aftermath of the extinction event. A persistent, 1.5‰-3.0‰ negative δ 13 C excur sion occurs across the CretaceousPaleogene boundary, but it cannot be readily separated from four, further negative excursions later in the earliest Danian. The negative carbon isotope excursion linked to the Cretaceous Paleogene boundary began a few hundred years before the event itself, and recovery occurred within 21 k.y., and possibly in as little as just a few thousand years, consistent with recently calibrated shallowmarine δ 13 C records. Hence, the atmospheric and surface ocean carbon pools were coupled at this time. The absence of evidence for catastrophic change in the climatic regime at the time of the CretaceousPaleogene extinction in these mires supports the notion that the negative shift in atmospheric δ 13 C was brought about by changes in the δ 13 C composition of the sur face ocean. This is consistent with the greater magnitude of extinction experienced by ma rine fauna relative to the terrestrial realm.

Stratigraphic and geochemical expression of Barremian–Aptian global climate change in Arctic Svalbard

“…Carbon isotopic ratios (d 13 C) from terrestrial (plant) organic material have been previously used to study global carbon-isotope excursions (CIEs) in the Cretaceous (e.g., Ando et al, 2002;Heimhofer et al, 2003;Robinson and Hesselbo, 2004;Gröcke et al, 2005;Herrle et al, 2015;Jerrett et al, 2015). These studies (which use either discrete plant fragments or disseminated T org from well-dated sections) all record >3‰ excursions also found in the carbonate record showing that the preservational style of woody material does not influence the recorded d 13 C wood when identifying large reproducible patterns in atmospheric carbon isotopic compositions, including Hesselbo et al (2000), Hesselbo et al (2003), Robinson and Hesselbo (2004), Gröcke et al (2005), and Jerrett et al (2015).…”

“…These well-documented perturbations may be used to correlate marine and terrestrial sections from around the globe (e.g., Jenkyns, 1995;Mene gatti et al, 1998;Ando et al, 2002;Herrle et al, 2015). A number of studies have specifically used discrete, identifiable fragments of fossil plant material for their carbon-isotope stratigraphy (e.g., Gröcke et al, 1999;Heimhofer et al, 2003;Robinson and Hesselbo, 2004;Weissert and Erba, 2004;Gröcke et al, 2005;Jerrett et al, 2015) with the caveat that "only large [>2‰] reproducible patterns can be indicative of long-term shifts in atmospheric carbon-isotopic compositions" (Robinson and Hesselbo, 2004, p. 134).…”

Conceptual models for short‐eccentricity‐scale climate control on peat formation in a lower Palaeocene fluvial system, north‐eastern Montana (USA)

“…() in which multiple sources of evidence failed to support that scenario. Subsequent to the KPB, peat‐forming environments in the Western Interior Williston Basin seem to gradually change from low‐lying mires (Fastovsky, ; Jerrett et al ., ) to raised mires (Flores & Keighin, ; Flores et al ., ).…”

“…Fastovsky & Bercovici (2016) cited various literature supporting the scenario of wildfire-induced deforestation but did not consider work by Belcher et al (2009) in which multiple sources of evidence failed to support that scenario. Subsequent to the KPB, peat-forming environments in the Western Interior Williston Basin seem to gradually change from low-lying mires (Fastovsky, 1987;Jerrett et al, 2015) to raised mires .…”

“…In the Tullock Member, peat compaction leading to splaying and avulsion could have been regionally triggered if peat consolidation during dry periods (which might have included wildfires) resulted from a response to orbitally forced climate changes. A regional-scale (possibly climatic) control on wildfires has been suggested, based on inertinite distribution patterns in coal seams across the KPB in the Ravenscrag Formation in Alberta and Saskatchewan (Jerrett et al, 2015). The inertinite macerals in coal samples of the Tullock Member ( Fig.…”