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

Neil Patrick Griffis,Eduardo Da Rosa,Fernando Vesely,Roland Mundil,Bastien Linol,Qing-Zhu Yin,Isabel Patricia Montañez,John Isbell,Brenhin Keller,Nick Fedorchuk,Jon Richey,Thammy Mottin,Roberto Iannuzzi

doi:10.1130/g46740.1

Abstract

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.

Highlights

The Late Paleozoic Ice Age (LPIA), spanning 340–280 Ma, has produced the only known archive of a permanent icehouse-to-greenhouse turnover on a planet populated by complex terrestrial ecosystems and metazoan life (Gastaldo et al, 1996)
The spatial and temporal distribution of continental ice throughout southern Gondwana during the LPIA and its ultimate demise have been attributed in large part to the long-term (107 to 108 yr) drift of southern Gondwana away from the South Pole during the Carboniferous–Permian
We present a temporally refined record of glaciation in southwestern to south-central Gondwana across the latest Carboniferous and early Permian, built using highprecision, single-crystal zircon U-Pb chemical abrasion thermal ionizing mass spectrometry (CA-TIMS) dating of volcaniclastic deposits located within the earliest postglacial sediments of the Paraná Basin, Brazil, and two glacialdeglacial cycles in the Karoo Basin, South Africa (Visser, 1997)

Summary

Introduction

The Late Paleozoic Ice Age (LPIA), spanning 340–280 Ma, has produced the only known archive of a permanent icehouse-to-greenhouse turnover on a planet populated by complex terrestrial ecosystems and metazoan life (Gastaldo et al, 1996). We present a temporally refined record of glaciation in southwestern to south-central Gondwana across the latest Carboniferous and early Permian, built using highprecision, single-crystal zircon U-Pb chemical abrasion thermal ionizing mass spectrometry (CA-TIMS) dating of volcaniclastic deposits located within the earliest postglacial sediments of the Paraná Basin, Brazil, and two glacialdeglacial cycles (deglaciation sequences DS III and DS IV) in the Karoo Basin, South Africa (Visser, 1997).

Results

Conclusion