TIMING AND POTENTIAL CAUSES FOR THE DEMISE OF EARTH’S PENULTIMATE ICEHOUSE
Résumé
Icehouse climate systems comprise an abbreviated portion of Earth history, though they have profound impacts on biogeochemical cycling, sea water chemistry, the evolution of continental crust, and biota. On the 105-108-year timescale, increased greenhouse gas concentration, principally pCO2, is well-documented as a driver of icehouse-greenhouse turnovers. In the Phanerozoic, the turnover from icehouse to greenhouse climate systems has been correlated with increased rates of continental arc volcanism and a decrease in silicate weathering across low latitude tropical belts. These processes control atmospheric pCO2 on 107-to-108-year timescales, whereas contributions (and sinks) of pCO2 on shorter timescales (≤106 years) are largely unresolved in deep-time records as a result of limited temporal constraints. To that extent, we present a high-resolution U-Pb zircon CA-TIMS calibrated ice and volcanic record for the late Paleozoic icehouse (LPIA) to greenhouse turnover. U-Pb zircon data from interglacial and postglacial deposits from South America and southern Africa indicate a stepwise deglaciation, occurring first in the mid-latitudes of southern Brazil during the latest Carboniferous, in high-latitude Namibia in the earliest Permian and culminating in the polar regions of Gondwana (South Africa) in latest Early Permian. Our study finds that base-level records across this region are tightly coupled. Highstand sedimentation in all basins is correlative with ice-minima events, whereas lowstand sedimentation is associated with a return of glaciation in the higher-latitude regions. Fundamental shifts in the nature and scale of glaciation are congruent with new high-resolution U-Pb zircon CA-TIMS age control from at least two large volcanic provinces in the latest Carboniferous and early Permian. Our data suggest a causal relationship between the Gondwana deglaciations and large igneous volcanic events. The presented data are the first record of climatic forcing for the LPIA, calibrated at a resolution ≤106-years.