Stratigraphy of upper Paleozoic volcanic rocks and regional unconformities in part of the northern Sierra terrane, California
Upper Paleozoic volcanic rocks in the southern part of the Taylorsville strike belt are unconformably truncated at the North Fork of the American River by a lens of Upper Triassic conodont-bearing limestone and Lower and Middle Jurassic graywacke-slate flysch deposits of the Sailor Canyon Formation. The volcanic sequence consists of submarine felsic pyroclastic debris flows and tuffaceous slate of the Late Devonian Sierra Buttes Formation, andesitic turbidites of the Taylor Formation, a lower tuff-siltstone member and an upper chert member of the Peale Formation, and fine-grained tuff of the Reeve Formation. Newly discovered radiolarians date the chert member of the Peale as latest Late Mississippian and(or) Early Pennsylvanian. Shelly fossil fragments found 50 m above the chert member date the lower part of the Reeve in this area as late Early Permian. These rocks formed in the distal part of the submarine volcanic apron, presumably in an island-arc setting, and were deposited unconformably on quartz-rich clastic rocks and tectonically interlayered chert of the pre–Late Devonian Shoo Fly Complex. The Peale marks a period of quiescence in the late Paleozoic volcanism that culminated in deep-water chert deposition during latest Mississippian to the Middle Pennsylvanian. The Peale-Reeve contact is a regional hiatus, probably nondepositional in the south and becoming erosional to the north, that spans most or all of the Late Pennsylvanian and Early Permian. Post-late Early Permian to pre-Late Triassic deformation produced northeast-trending folds and a southeast-trending fault in the late Paleozoic volcanic rocks that are truncated nearly orthogonally by the Late Triassic unconformity and northwest-trending folds in the Jurassic Sailor Canyon Formation.