Carbon and oxygen isotope records from Paleosols spanning the Paleocene-Eocene boundary, Bighorn Basin, Wyoming

Abstract

The isotopic composition of paleosol carbonate and organic matter were investigated in the Bighorn Basin, Wyoming to explore changes in the carbon cycle and climate across the Paleocene-Eocene boundary. In three different measured sections, soil carbonate δ δ 13 C values change in phase with marine surface water carbonates on both long (∼7 m.y.) and short (∼ ∼100 k.y.) time scales. The carbon cycle perturbations at the Paleocene-Eocene Boundary Thermal Maximum (PETM) and the Eocene Warm Interval (EWI) are recorded in multiple sections, providing unambiguous links between marine and continental deposits. The PETM and EWI δ δ 13 C excursions in the Bighorn Basin are larger than those in the surface ocean, but the reasons for this amplification are unclear. Organic matter samples from the Bighorn Basin yield noisy δ δ 13 C records that do not mirror global changes, perhaps due to diagenetic alteration or postformational contamination. The δ δ 18 O values of soil carbonate are subject to multiple climatic influences that are often antagonistic. Although the δ δ 18 O shifts at the PETM and EWI are small, the shift at the PETM is statistically significant in two of the measured sections. Assuming a plausible range of values for the meteoric water δ δ 18 O/mean annual temperature relationship, the perturbation in soil carbonate δ δ 18 O at the PETM is consistent with an increase in meteoric water δ δ 18 O of ∼ ∼2‰ and changes in local temperature of 3-7 °C.

A Palaeogene perspective on climate sensitivity and methane hydrate instability

“…At this stage, a conservative interpretation of the proxy data would indicate a pattern of global surface warming in the range of 5-6 • C rather than the 5-9 • C quoted by Zeebe et al (2009). This is also consistent with available estimates of warming from the terrestrial record: 3-7 • C from carbonate soil nodule d 18 O (Bowen et al 2001;Koch et al 2003); 4-6 • C from d 18 O of biogenic phosphate (Fricke et al 1998;Fricke & Wing 2004); and approximately 5 • C from leaf margin analysis (Wing et al 2005).…”

Climate directly influences Eocene mammal faunal dynamics in North America

“…The PETM has been well studied and documented (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). In continental records from the western U.S., a temperature spike (to Ϸ20-25°C) has been shown to occur simultaneously with the earliest Eocene mammalian faunas (Wa-0), coincidental with a sharp interval of mammalian immigration (4,15).…”

Temperature and atmospheric CO 2 concentration estimates through the PETM using triple oxygen isotope analysis of mammalian bioapatite

“…The mean oxygen isotope composition of tooth enamel phosphate (δ 18 O PO4 ) in the Ectocion specimens investigated increases by 2.2‰ from the late Clarkforkian (Cf-3) to the CIE in the early Wasatchian (Wa-0), considering the mean values for each mammalian biozone. From Wa-0 to Wa-2, a decrease in mean δ 18 O PO4 of 1.6‰ is observed (different meter levels within Wa-2 do not show any difference in δ 18 O PO4 , so they were combined ( Fig.…”

“…These studies rely solely on δ 18 (49), and thus triple oxygen isotope analyses of bioapatite from fossil mammals can be used as a paleo-CO 2 proxy (see ref. 50 for more details).…”

“…Studies relying on the relationship of paleotemperature to δ 18 O in mammalian bioapatite already exist for the Paleocene-Eocene transition in the Clarks Fork and Bighorn Basin (Wyoming) based on various mammalian taxa, targeting either the carbonate oxygen component (δ 18 O CO3 ) of mammalian tooth enamel, the phosphate oxygen component (δ 18 O PO4 ), or both in a combined approach (8,17,20,21,(51)(52)(53).…”