Pangea B and the Late Paleozoic Ice Age

Abstract

The Late Paleozoic Ice Age (LPIA) was the penultimate major glaciation of the Phanerozoic. Published compilations indicate it occurred in two main phases, one centered in the Late Carboniferous (~315 Ma) and the other in the Early Permian (~295 Ma), before waning over the rest of the Early Permian and into the Middle Permian (~290 Ma to 275 Ma), and culminating with the final demise of Alpine-style ice sheets in eastern Australia in the Late Permian (~260 to 255 Ma). Recent global climate modeling has drawn attention to silicate weathering CO 2 consumption of an initially high Greater Variscan edifice residing within a static Pangea A configuration as the leading cause of reduction of atmospheric CO 2 concentrations below glaciation thresholds. Here we show that the best available and least-biased paleomagnetic reference poles place the collision between Laurasia and Gondwana that produced the Greater Variscan orogen in a more dynamic position within a Pangea B configuration that had about 30% more continental area in the prime equatorial humid belt for weathering and which drifted northward into the tropical arid belt as it transformed to Pangea A by the Late Permian. The presence of widespread equatorial coal basins with Euramerica flora in the footprint of the Greater Variscan orogen during the Late Carboniferous is more compatible with a heterogeneous horst-and-graben morphology, characterized by uplifted crystalline massifs acting as loci of intense silicate weathering CO 2 consumption and supplying sediment for proximal basins as venues of organic carbon burial, than a contiguous high mountain plateau, as assumed in recent climate modeling of the LPIA and its demise. The culminating phase of the LPIA occurred at about 275 Ma with the transformation from Pangea B to Pangea A and the attendant reduction of continental area in the equatorial humid belt, as well as with continued northward drift that placed what remained of the Greater Variscan orogen into the Zechstein arid belt in the Late Permian, by which time the geologic landscape was largely blanketed with siliciclastics. The resulting warming from reduced silicate weathering and thus increasing pCO 2 was interrupted at 260 Ma with a cooling trend that coincided with emplacement of the Emeishan large igneous province on the equatorial South China Craton as well as the drift of the Cimmerian continental blocks through the equatorial humid belt due to opening of the Neo-Tethys. A return to ice age conditions from the increase in silicate weathering uptake of CO 2 was avoided by drift of the Emeishan large igneous province out of the equatorial belt, that in conjunction with massive outgassing from emplacement of the Siberian Traps in high latitudes at the end of the Permian (252 Ma), helped steer the climate system to sustained non-glacial conditions.

Late Carboniferous paleoelevation of the Variscan Belt of Western Europe

“…When compared to modern observations, globally cooled conditions may have increased the lapse rate over high altitudes (∼ 5000 m; e.g. Poage and Chamberlain, 2001;Heavens et al, 2015;Kent and Muttoni, 2020). Global temperatures during the Late Carboniferous may have been up to 10 • C cooler than modern temperatures (Feulner, 2017).…”

“…1; e.g. Domeier and Torsvik, 2014;Kent and Muttoni, 2020). Here, we use the empirical isotope-elevation relationship (Poage and Chamberlain, 2001) for global low-to-mid latitude mountain belts in order to estimate a Variscan paleoelevation.…”

“…During the Late Carboniferous, the Pangea assemblage moved northward from 10 • S to ∼ 5 • N between ∼ 315 and ∼ 290 Ma (e.g. Edel et al, 2018;Kent and Muttoni, 2020) and was characterized by a unique and long E-W trending mountain chain, including the French Massif Central (Fig. 1, e.g.…”

“…However, Late Carboniferous-Early Permian coal deposits do not support a very high elevation plateau (e.g. Kent and Muttoni, 2020;Strullu-Derrien et al, 2021). Although the Westphalian and Stephanian deposits support the presence of a topographic high, the activity of detachment zones during the Late Carboniferous indicates that the orogen was collapsing (e.g.…”

Quantifying the Extent of the Paleo‐Asian Ocean During the Late Carboniferous to Early Permian

“…To interpret the tectonic evolution of the PAO, we first integrate our new paleomagnetic observations with previous results. Inclination shallowing is extensively observed in paleomagnetic results from clastic rocks, especially redbeds (Kent & Muttoni, 2020;Tauxe & Kent, 2004). We update the paleomagnetic data set of Zhang, Huang, Zhao, Meert, et al (2018) for the CAOB, North China and Siberia using a more moderate flattening factor of f = 0.7 for clastic data (see Text S4 for details; Bilardello and Kodama, 2010;Zhou et al, 2018;.…”