Reduction of equatorial land area and silicate weathering consumption of CO2 with transformation from Pangea B to Pangea A in the Permian and the ultimate demise of the Late Paleozoic Ice Age
Abstract
The Late Paleozoic Ice Age (LPIA) was comprised of pulses of glaciation in mid- to high paleolatitude regions of Gondwana (southern Africa and South America, India, Antarctica, Australia) from the mid-Carboniferous (~330 Ma), peaking in the Early Permian (~300 to ~290 Ma), 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 ice sheets in eastern Australia in the Late Permian (~260 to 255 Ma) (1). The LPIA onset is plausibly attributed to drawdown of atmospheric CO2 from intense silicate weathering of the equatorial Variscan-Alleghenian mountain belt whose denudation eventually allowed pCO2 levels to return to higher levels sufficient to bring the LPIA to an end (2). Virtually all climate models for the Late Paleozoic have used a static Pangea assembly. Here we consider the effects of the well-documented tectonic transformation of Pangea from a 'B' configuration, with the northwestern margin of South America adjacent to eastern North America in the Early Permian, to the classic Pangea A configuration, with the northwestern margin of Africa now against eastern North America in the Late Permian. The transformation occurred along a dextral shear zone that ran obliquely across the equatorial humid belt between the southern (Gondwana) and northern (Laurasia) supercontinental subassemblies between ~275 Ma and 260 Ma (3). The resulting ~40% reduction of land area between 5°S to 5°N would have proportionately reduced the silicate weathering uptake of CO2 in this most potent venue, the warm equatorial humid belt. This leads us to suggest that if higher pCO2 from erosional collapse of the equatorial mountain belt led to the waning of the LPIA, the yet higher pCO2 from reduction in equatorial land area probably led to its coup de grace by the end of the Permian. More speculatively, the higher pCO2 may have forestalled a return to ice age conditions in the Late Permian from an increase in silicate weathering uptake of CO2 expected from the emplacement of basalts of the Emeishan large igneous province in the equatorial humid belt at 260 Ma (4).
(1) Montañez and Poulsen (2013) Annual Reviews Earth Planet. Sci. 41, 24.1-24.28. (2) Goddéris et al. (2017) Nature Geoscience 10, 382-386. (3) Muttoni et al. (2009) GeoArabia 14, 17-48. (4) Xu et al. (2018) JGR 124, 2597-2617.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGP51A..02K
- Keywords:
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- 1525 Paleomagnetism applied to tectonics: regional;
- global;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 8157 Plate motions: past;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS