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.
Abstract. Earth's penultimate icehouse period, the late Paleozoic ice age (LPIA), was a time of dynamic glaciation and repeated ecosystem perturbation, which was under conditions of substantial variability in atmospheric pCO2
and O2. Improved constraints on the evolution of atmospheric
pCO2 and O2∕CO2 ratios during the LPIA and its
subsequent demise to permanent greenhouse conditions are crucial for
better understanding the nature of linkages between atmospheric
composition, climate, and ecosystem perturbation during this time. We
present a new and age-recalibrated pCO2 reconstruction for
a 40 Myr interval (∼313 to 273 Ma) of the late Paleozoic
that (1) confirms a previously hypothesized strong
CO2–glaciation linkage, (2) documents synchroneity between
major pCO2 and O2∕CO2 changes and compositional
turnovers in terrestrial and marine ecosystems, (3) lends support for
a modeled progressive decrease in the CO2 threshold for
initiation of continental ice sheets during the LPIA, and (4)
indicates a likely role of CO2 and O2∕CO2
thresholds in floral ecologic turnovers. Modeling of the relative role
of CO2 sinks and sources active during the LPIA and its
demise on steady-state pCO2 using an intermediate-complexity climate–carbon cycle model (GEOCLIM) and comparison to the new
multi-proxy CO2 record provides new insight into the
relative influences of the uplift of the Central Pangean Mountains,
intensifying aridification, and increasing mafic rock to granite rock
ratio of outcropping rocks on the global efficiency of CO2
consumption and secular change in steady-state pCO2
through the late Paleozoic.
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