Shoo Fly Complex, coherent units
Shoo Fly Complex, coherent units
Ordovician to Middle Devonian
Unit consists of three regionally extensive thrust blocks: the Lang sequence, and the Duncan Peak and Culbertson Lake allochthons. At the base of the unit, the Lang sequence is chiefly interbedded quartz arenite and pelite with scattered lenses and beds of chert and limestone. Locally the sequence is mapped with subunits of breccia; pelite, breccia, and conglomerate; interbedded quartzite and pelite with minor limestone and chert; and thick-bedded quartzite. A lens of limestone in slate and quartzite in the middle of the Lang sequence near Bluenose Mountain west of Mohawk Valley has yielded middle Middle to Late Ordovician conodonts (Harwood, 1992). Relict radiolarians are found locally throughout the unit but are not preserved enough to provide significant age control (Girty and others, 1996), although the presence of radiolarians, which are uncommon in the Cambrian, suggests an age of Ordovician or younger. This unit is intruded by, and therefore predates, the latest Middle to Late Devonian metaplutonic rocks of the Sierra Buttes intrusive complex (unit Gsb).
The Duncan Peak allochthon, which structurally overlies the Lang sequence on an east-dipping thrust fault, is composed chiefly of chert locally interlayered with chert breccia, and black siliceous argillite. This unit lacks good internal age control. Poorly preserved radiolarians are present, suggesting an age of Ordovician or younger, and the unit is intruded by the ~353-380 Ma (earliest Mississippian to early Late Devonian) Bowman Lake batholith (part of unit Gsb), so the Duncan Peak is considered roughly the same age as the similarly situated units structurally above and below.
The uppermost thrust block comprises the Culbertson Lake allochthon, which overlies the Duncan Peak allochthon in the south, but rests directly on the Lang sequence in the north. The Culbertson Lake allochthon is composed of a lower sequence of pillow basalt and basaltic breccia interlayered with chert and overlain by limestone, chert, and argillite. Lower sequence interpreted as intraplate seamount (Girty, 1983). Upper sequence chiefly subarkosic and quartz-rich sandstone interpreted as a submarine fan complex. Unit deformed into west-verging tight to isoclinal folds. This unit also lacks good internal age control, although a chert bed yielded spheroidal radiolarians with simple spines characteristic of early Paleozoic forms (probably Ordovician because radiolarians are rare in the Cambrian; D.L. Jones in Girty and Wardlaw, 1985).
The three structural blocks were tectonically assembled before Late Devonian, prior to intrusion of the Bowman Lake batholith. Unit structurally overlays Shoo Fly Complex - marine sedimentary rocks (unit NSSF).