LOWER AND MIDDLE ORDOVICIAN STRATIGRAPHY IN THE HOT CREEK AND MONITOR RANGES, CENTRAL NEVADA
The vicinities of Hot Creek Canyon in the Hot Creek Range and Clear Creek Canyon in the Monitor Range, heretofore essentially un-described localities in central Nevada, have Lower and Middle Ordovician successions that can be correlated with the type sections in Antelope Valley. The two areas were in the western part of the miogeosyncline during Ordovician time. In the Early Ordovician a predominantly carbonate sequence was laid down in moderately shallow water, judging from the frequent local abundance of fossils and primary structures. Of principal interest in the Lower Ordovician are: the lithology and mixed trilobite assemblage of the oldest Ordovician rocks at Clear Creek, suggesting accumulation of sediment on a depositional slope; and a regular alternation of different limestone lithologies in a sequence at Hot Creek, suggesting cyclic sedimentation. A marked increase in deposition of clastic material occurred during the Middle Ordovician, commencing with fine clastic rocks of the Copenhagen Formation and culminating in sandstones of the Eureka Quartzite. Hot Creek and Clear Creek canyons received a thinner section than did the Antelope Valley region in Middle Ordovician time (Copenhagen), if not also earlier. The easternmost indication at this latitude of thrusting associated with the eugeosyncline-miogeosyncline border is a thrust sliver of chert of eugeosynclinal facies preserved at Clear Creek Canyon.