Anomalous cold in the Pangaean tropics

The late Paleozoic archives the greatest glaciation of the Phanerozoic.Whereas high-latitude Gondwanan strata preserve widespread evidencefor continental ice, the Permo-Carboniferous tropics have longbeen considered analogous to today's: warm and shielded fromthe high-latitude cold. Here, we report on glacial and periglacialindicators that record episodes of freezing continental temperaturesin western equatorial Pangaea. An exhumed glacial valley andassociated deposits record direct evidence for glaciation thatextended to low paleoelevations in the ancestral Rocky Mountains.Furthermore, the Permo-Carboniferous archives the only knownoccurrence of widespread tropical loess in Earth's history;the volume, chemistry, and provenance of this loess(ite) ismost consistent with glacial derivation. Together with emergingindicators for cold elsewhere in low-latitude Pangaea, theseresults suggest that tropical climate was not buffered fromthe high latitudes and may record glacial-interglacial climateshifts of very large magnitude. Coupled climate-ice sheetmodel simulations demonstrate that low atmospheric CO₂ and solarluminosity alone cannot account for such cold, and that otherfactors must be considered in attempting to explain this "best-known"analogue to our present Earth.