PALEOMAGNETISM OF UPPER PRECAMBRIAN SEDIMENTARY-ROCKS FROM THE DESERT RANGE, NEVADA

About 300 oriented samples were obtained from upper Precambrian and possibly lowest Cambrian strata in a homoclinical sequence conformable with Lower Palaeozoic strata in the Desert Range, Nevada. These samples are from miogeoclinal sedimentary rocks of the uppermost Johnnie Formation (upper Precambrian) and overlying Stirling Quartzite (uppermost Precambrian and Lower (?) Cambrian). For about 100 of the samples, thermal demagnetization revealed a characteristic magnetization with a low inclination. The characteristic magnetization of the uppermost Johnnie has two polarities, which allows its direction to be established despite incomplete removal of a secondary component of recent origin. Petrographic and stratigraphic evidence suggest that this characteristic magnetization was acquired penecontemporaneously with deposition. The age of the magnetization probably lies in the range 675-575 m.y. B.P., based on estimates of sedimentation rates in the Desert Range and on proposed lithologic correlations and isotopic age control elsewhere in the Cordilleran Geosyncline. -Authors