Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana

Abstract

The demise of the Late Paleozoic Ice Age has been hypothesized as diachronous, occurring first in western South America and progressing eastward across Africa and culminating in Australia over an ∼60 m.y. period, suggesting tectonic forcing mechanisms that operate on time scales of 106 yr or longer. We test this diachronous deglaciation hypothesis for southwestern and south-central Gondwana with new single crystal U-Pb zircon chemical abrasion thermal ionizing mass spectrometry (CA-TIMS) ages from volcaniclastic deposits in the Paraná (Brazil) and Karoo (South Africa) Basins that span the terminal deglaciation through the early postglacial period. Intrabasinal stratigraphic correlations permitted by the new high-resolution radioisotope ages indicate that deglaciation across the S to SE Paraná Basin was synchronous, with glaciation constrained to the Carboniferous. Cross-basin correlation reveals two additional glacial-deglacial cycles in the Karoo Basin after the terminal deglaciation in the Paraná Basin. South African glaciations were penecontemporaneous (within U-Pb age uncertainties) with third-order sequence boundaries (i.e., inferred base-level falls) in the Paraná Basin. Synchroneity between early Permian glacial-deglacial events in southwestern to south-central Gondwana and pCO2 fluctuations suggest a primary CO2 control on ice thresholds. The occurrence of renewed glaciation in the Karoo Basin, after terminal deglaciation in the Paraná Basin, reflects the secondary influences of regional paleogeography, topography, and moisture sources.

Influence of temporally varying weatherability on CO<sub>2</sub>–climate coupling and ecosystem change in the late Paleozoic

“…Higher pCO 2 in the latter half of the Pennsylvanian is compatible with the hypothesized waning of large Early to Middle Pennsylvanian glaciers in the Late Pennsylvanian (c.f. Fielding et al, (2008), including widespread terminal deglaciation in a major glacial depocenter in south-central Gondwana (Parana Basin, Brazil) toward the close of the Carboniferous (Griffis et al, 2018;Griffis et al, 2019). Declining pCO 2 toward a nadir in the earliest Permian is also consistent with a renewed increase in the geographic distribution of glacial deposits in Gondwana beginning in the Late Pennsylvanian and peaking (apex) in the earliest Permian ( Fig.…”

“…3b ). The first (298 to Ma) coincides, within age uncertainty, with a major deglaciation event in the Karoo (southern Africa) and Kalahari (Namibia) basins of south-central Gondwana (296.41 Ma +0.27/-0.35 Ma;Griffis et al, (2019)). The second short-term rise in pCO 2 (294.5 to 292.5 Ma) overlaps with the onset of widespread ice loss in several southern Gondwanan ice centers ( Fig.…”

“…acute glaciation in the Kasimovian and with repeated deglaciations in south-central Gondwana in the early Permian (Griffis et al, 2018;Griffis et al, 2019), as well as with restructuring of marine and terrestrial ecosystems ( Figs. 3b-d).…”

Influence of temporally varying weatherability on CO<sub>2</sub>-climate coupling and ecosystem change in the late Paleozoic

“…2b; S1b). The short-term interval of elevated pCO 2 (304 to 302.5 Ma) is coincident with a ∼ 1.5 ‰ decline in seawater δ 13 C (Grossman et al, 2008;Chen et al, 2020), which is compatible with a decline in the CO 2 sink provided by terrestrial organic C (peats) burial (gray bar in Fig. 2b) and/or a peak in pyroclastic volcanism between ∼ 310 and 301 Ma (Soreghan et al, 2019).…”

Pangea B and the Late Paleozoic Ice Age

“…Magnetostratigraphy is thus of limited use for global correlation of glacial and associated deposits of the LPIA. Fortunately, wider applications of U-Pb zircon geochronology are providing valuable means of correlations and age constraints in the Permo-Carboniferous (Griffis et al, 2019;Machlus et al, 2020;Metcalfe et al, 2015).…”