Multi‐proxy constraints on the significance of covariant δ¹³C values in carbonate and organic carbon during the early Mississippian

Abstract

This study investigates the covariation between carbonate and organic δ13C values in a proximal to distal transect of four outcrops in the Madison Limestone in the Western United States Rockies, combined with δ34S values of carbonate associated sulphate, the concentration of acid‐insoluble material and measurements of total organic carbon. These new geochemical datasets not only allow for an evaluation of carbon isotope covariance during one of the largest perturbations to the global carbon cycle over the past 550 Myr, but also constrain the cause of the excursion in carbonate δ13C values. The results support the hypothesis that a period of anoxia did not play a role in generating the positive carbonate δ13C values, but rather favour interpretations by previous workers that the proliferation of land plants destabilized the Carboniferous carbon cycle, setting the stage for a significant change in the carbonate δ13C values of contemporaneous marine carbonates. These results also demonstrate that one of the largest perturbations to the global carbon cycle did not produce synchronous variations in carbonate and organic δ13C values, emphasizing the importance of local depositional controls on carbon isotope covariance in the geological record in both modern and ancient environments.

Unravelling evidence for global climate change in Mississippian carbonate strata from the Derbyshire and North Wales Platforms, UK

“…The Mississippian marks a critical point in Earth"s history, as the proliferation of land plants led to a decrease in pCO 2 and global tectonic reorganisation led to continental amalgamation, modification of ocean circulation patterns, global cooling and transition from a greenhouse to an icehouse climate (Mii et al, 1999;Smith and Read, 2000;Barham et al, 2012;Qiao and Shen, 2015;Oehlert et al, 2019). Ice advance and retreat was initiated in the Mississippian, with two principal perturbations, one in the Tournasian (approximately 355 -350 Ma) and one in the late Viséan to early Serphukovian (Mii et al, 1999;Buggisch et al, 2008;Armendariz et al, 2008;Montanez and Poulsen, 2013;Godderis et al, 2017;Oehlert et al, 2019;Rosa et al, 2019). The frequency and amplitude of sea level fluctuation apparently increased after each of these events, with the transition to full icehouse conditions in the Pennsylvanian (Mii et al, 1999;Montanez and Poulsen, 2013).…”

Stratigraphy and facies of mid-Palaeozoic successions in southern Mongolia

“…Lower in the section (Siphonodella isosticha-Upper Siphonodella crenulata biozone to Lower Gnathodus typicus biozone), one of the largest δ13Ccarb excursions in the Phanerozoic in the early Mississippian were reported from various regions (e.g., Bruckschen et al 1999;Saltzmann et al 2004;Oehlert et al 2019). As this critical period is also exposed in the studied section (see conodont record above), geochemical studies are necessary to prove evidence of this important δ13Ccarb excursion in the early Mississippian of the Bayankhoshuu Ruins section.…”

“…Interestingly, the paleokarst observed in this study coincided with a regressive cycle reported from the Madison Limestone in North America. The Madison Limestone represents a secondorder super sequence that internally consisted of six third-order sequences (Westphal et al 2004;Katz et al 2007;Oehlert et al 2019). The beginning of the second-order regressive cycle is roughly correlated with the base of the Scaliognathus anchoralis-Doliognathus latus biozone, but there is no evidence of exposure horizon or karstic surfaces which is similar to coeval sections in Belgium (Hance et al 2002).…”