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In the northern Sierra Nevada, California, the pre–Upper Devonian Shoo Fly Complex has been subdivided into the following, from structurally lowest to structurally highest: (1) Lang sequence, (2) Duncan Peak chert, (3) Culbertson Lake allochthon, and (4) Sierra City melange. Detailed studies have been completed recently on the rocks in the Culbertson Lake allochthon in the Bowman Lake/Culbertson Lake area. The results of geochemical, sedimentologic, stratigraphic, and structural studies of rocks in the Culbertson Lake allochthon suggest that: (1) the allochthon is composed of a lower fault-bounded succession of basaltic rock and a complexly imbricated upper sandstone–dominated sequence; (2) the structurally lowest unit in the allochthon contains alkalic basalts that formed in a seamount or ocean island setting; (3) sedimentologic and stratigraphic patterns in the structurally higher units may be the result of sedimentation and deformation in a trench setting; (4) the allochthon is composed of a complex of northeast-dipping, thrust-fault–bounded slices, and is an imbricate structure; and (5) the imbricate structure, in terms of present-day geographic coordinates, formed as a result of generally westward-directed translations (i.e., northwest, west, or southwest) prior to the Late Devonian and probably after the Cambrian.

Data presented here generally support models that portray the Shoo Fly Complex as having formed in a subduction complex setting that developed near enough to a continental landmass to receive sand-sized detritus derived from it. However, current data do not uniquely constrain the location of the continental landmass that provided sand-sized detritus to the Shoo Fly Complex, nor do they rule out the possibility that the sand-rich portions of the Shoo Fly Complex were deposited as part of a continental margin submarine fan system that was subsequently accreted and imbricated within a subduction complex. The continental landmass supplying continental detritus to the Shoo Fly Complex may have been located in western North America, or it may have been located somewhere in Panthalassa.

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