Earth's descent into the Cryogenian

The Cryogenian period (ca. 720-635 Ma) is marked by two global glaciations, where ice reached equatorial latitudes and persisted for millions of years. These "snowball Earth" glaciations represent Earth's most extreme climate state and likely shaped the landscape and facilitated the biotic revolution that followed. Despite decades of research, the climatic triggers driving Earth's descent into the Cryogenian remain enigmatic.
This PhD thesis investigates Earth's decent into the Cryogenian through the lens of the Dalradian Supergroup of Scotland and Ireland, placing findings within a global framework. New geochronological, geochemical, and sedimentological data are presented, including maximum depositional ages that refine the Dalradian chronostratigraphy and confirm the Port Askaig Formation's placement within the 'Sturtian' Cryochron. These insights are integrated into a global late Tonian age model that resolves ambiguities in the carbon isotope record and highlights the Garvellach carbon isotope anomaly as a key stratigraphic marker for defining the basal Cryogenian. Additionally, the refined model identifies a pronounced shift in the global silicate weathering flux prior to glaciation, as evidenced by Sr-isotope data. This shift can be tied to the emplacement of the Franklin Large Igneous Province and, for the first time, linked mechanistically to glacial onset via geochemical evidence.