Abstract

The use of later Palaeozoic Radiolaria as age indicators in N Nevada has made possible stratigraphic comparisons between a small part of the Golconda Allochthon—the Schoonover Sequence, the structurally underlying Roberts Mountains Allochthon and sequences which formed in a foreland in a foreland basin as the Roberts Mountains Allochthon was emplaced at the North American continent margin (Miller et al. 1984).

Emplacement of the Cambrian to Devonian deeper water Roberts Mountains Allochthon rocks occurred in Kinderhook–Osage time (Johnson & Pendergast 1981) and is usually viewed as a consequence of latest Devonian to early Mississippian Antler orogenesis. The late Devonian to mid-Permian Golconda Allochthon rocks were probably emplaced in the early Mesozoic.

Radiolaria are essential to the elucidation of the older Golconda succession. Hitherto unsuspected similarities between events recorded by these older Golconda rocks and those recorded in the Antler foreland basin seem at variance with the proposal that the Golconda Allochthon is a relatively far-travelled accretionary prism which became part of North America in the early Mesozoic (Speed & Sleep 1982). It might rather seem that the Schoonover basin was the exterior (oceanward) analogue of the Antler foreland basin: it originated during the first, late Devonian, volcaniclastic supply but shared with the foreland basin a Mississippian siliciclastic source in the Roberts Mountains Allochthon and suffered the same intra-Pennsylvanian movements that are recorded in successions. The Schoonover basin existed, therefore, at the continent margin adjacent to the 'Antler volcanic arc' postualated by several authours and to the eroding Roberts Mountains Allochthon.