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

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 similar 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 delta D = -325 parts per thousand. In situ 40Ar/39Ar geochronology of hydrated glasses with ultra-depleted delta D 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.

Automated summary

The Butcher Ridge Igneous Complex in the Early Jurassic period contains glass with high water content and low hydroxyl component, indicating secondary hydration. The glass also has the most depleted hydrogen isotopes ever measured in terrestrial rocks, suggesting it was hydrated by polar glacial ice and melt water during the Late Cretaceous, contradicting previous reconstructions of an ice-free Antarctica in a global hot greenhouse.