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How were Silurian sea-level changes connected to glacial episodes in Gondwana?
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Silurian Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the middle part of the Silurian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
Silurian sea-level changes were intrinsically linked to the dynamics of the Gondwanan ice sheet. The transition from the Ordovician Period to the Silurian was marked by a dramatic rise in global sea level as the extensive glaciers of the Late Ordovician ice age melted, reflooding vast continental platforms.12
Throughout the Silurian, smaller global sea-level fluctuationsâranging from 30 to 50 metresâcontinued to occur. These fluctuations are believed to have been coordinated by minor changes in the size of the surviving Gondwanan ice cap. Evidence for this connection includes:3
- Glacial Episodes: Global drawdowns in sea level during the Silurian are directly linked to at least three successive glacial episodes identified in the Brazilian sector of Gondwana.3
- Stratigraphic Evidence: Tillites found in South America that date to the Llandovery Epoch support the model that fluctuating ice volumes on Gondwana drove these sea-level cycles.3
- Highstands: The initial major rise in sea level at the start of the Silurian corresponds to the melting of the massive Late Ordovician glaciers, which facilitated the recovery of faunal groups following the Ordovician-Silurian extinction.23