THE QUEENSTON SEDIMENTARY COMPLEX: A LINK WITH LATE ORDOVICIAN GLACIATION?

Intense tropical weathering of silicic rocks in one or more terranes that collided with the southern margin of Laurentia during Late Ordovician Taconic tectonism is suggested to be linked with onset of Late Ordovician glaciation. The Late Ordovician Queenston clastic wedge complex in the Appalachians includes relatively coarse-grained sediments derived from Taconic orogenic highlands. Queenston complex detritus includes sand and gravel derived from metamorphic rocks as well as sands and muds that came from granitic and sedimentary source rocks. The Queenston sedimentary complex accumulated before and during the interval of Late Ordovician glaciation, as determined from graphic correlations based on conodonts. The influences of exotic terrane accretion and consequent weathering of freshly-exposed silicic rocks on suppression of atmospheric carbon dioxide concentration and the consequences for global climate change should be considered. An approximately 4.5 percent lower solar constant in the Late Ordovician, coupled with a slight decline in atmospheric carbon dioxide concentration, related to silicate weathering, may have been sufficient to trigger icehouse conditions culminating in Late Ordovician Gondwanan continental glaciation. That short-lived glaciation would have terminated when tropical weathering led to formation of a soil mantle over silicic source rocks. Such a cover would have shielded them from further weathering and rapid erosion, thus restoring carbon dioxide uptake into the atmosphere and return to greenhouse climatic conditions. The Queenston clastic wedge complex is judged to be a signature of this feedback loop scenario.