Ultra-depleted hydrogen isotopes in hydrated glass record Late Cretaceous glaciation in Antarctica

Abstract

The Early Jurassic Butcher Ridge Igneous Complex (BRIC) in the Transantarctic Mountains contains abundant and variably hydrated silicic glass which has the potential to preserve a rich paleoclimate record. Here we present Fourier Transform Infrared Spectroscopic data that indicates BRIC glasses contain up to ~8 wt.% molecular water (H2Om), and low (<0.8 wt.%) hydroxyl (OH) component, interpreted as evidence for secondary hydration by meteoric water. BRIC glasses contain the most depleted hydrogen isotopes yet measured in terrestrial rocks, down to δD = −325 ‰. In situ 40Ar/39Ar geochronology of hydrated glasses with ultra-depleted δD values yield ages from 105 Ma to 72 Ma with a peak at c. 91.4 Ma. Combined, these data suggest hydration of BRIC glasses by polar glacial ice and melt water during the Late Cretaceous, contradicting paleoclimate reconstructions of this period that suggest Antarctica was ice-free and part of a global hot greenhouse.

Permafrost in the Cretaceous supergreenhouse

“…We conclude that thaw of permafrost 76 after the Hautiverian cold snap promoted global warming of Cretaceous climates and fertilized the oceans. Antarctic evidence for glaciation of the South Pole during the Late Cretaceous 18 raises the likelihood that permafrost occurred at that time in Antarctica. Further investigation on recent permafrost analogues and of Cretaceous oceanic deposits may shed light on the exact contribution of permafrost thaw 79 to the radiative forcing of global Cretaceous events.…”

Permafrost in the Cretaceous supergreenhouse

“…We conclude that thaw of permafrost 76 after the Hautiverian cold snap promoted global warming of Cretaceous climates and fertilized the oceans. Antarctic evidence for glaciation of the South Pole during the Late Cretaceous 18 raises the likelihood that permafrost occurred at that time in Antarctica. Further investigation on recent permafrost analogues and of Cretaceous oceanic deposits may shed light on the exact contribution of permafrost thaw 79 to the radiative forcing of global Cretaceous events.…”

“…Additional evidence includes Cretaceous landforms in Yukon and Alaska 16 , patterned ground in China 17 , and ice-rafted dropstones in desert oases indicating colddesert conditions in interdunes similar to those in the Badain Jaran Desert 11 . Recently, the discovery of ultra-depleted hydrogen isotopes from Antarctica has suggested glaciation of the South Pole during the Late Cretaceous 18 , and there is isotopic evidence for continental ice sheets in China during the Early Cretaceous 19 . Collectively, these studies hint at the likely occurrence of Cretaceous periglacial and permafrost environments in polar and high-altitude regions.…”