Carbonate strata of the Cambrian to Devonian Bouvette Formation underlies the Castle Mountain area in central Yukon. Locally, within the Bouvette Formation, calcareous, fossiliferous clastic rocks are interstratified with volcaniclastic and volcanic rocks. The volcanic rocks are inferred to be post-early Silurian based on preliminary fossil ages of graptolites found in underlying limestone. I propose extensional tectonism temporarily disrupted carbonate platform development in the early Silurian in this area. Crustal extension resulted in normal faulting and local subsidence. Thermal uplift, related to underplating of igneous bodies, resulted in subaerial exposure and subsequent erosion of chert, carbonate and volcanic rocks. Basins and slopes (areas between thermally uplifted blocks and subsiding areas) collected material eroding from exposed strata and volcanic rocks deposited during eruptions.