TECTONIC IMPLICATIONS OF REVISED UPPER PALEOZOIC STRATIGRAPHY AT EDNA MOUNTAIN, NORTH-CENTRAL NEVADA

Detailed mapping and biostratigraphic studies of the upper Paleozoic section at Edna Mountain, Nevada, redefine two tectonically significant conglomerates and suggest revised importance for a third. The lowest upper Paleozoic conglomerate at Edna Mountain, formerly correlated with Battle Formation, underlies the Morrowan-Atokan Highway Limestone, and therefore pre-dates the Atokan Battle Formation. We propose the name Iron Point Conglomerate for the older unit at Edna Mountain. A stratigraphically higher conglomerate informally known as the Highway Conglomerate was previously interpreted to be interbedded with the Highway Limestone. Our work shows that it unconformably overlies the Highway Limestone along a subaerial erosion surface, and is therefore a separate, younger, formation.

The Iron Point Conglomerate contains well rounded, predominantly quartzite, clasts; it records shallow marine to fluvial deltaic conditions in early Pennsylvanian, and possibly late Mississippian, time. It grades upward into the Highway Limestone; west-verging folds formed in both during mid-Pennsylvanian time. The folds are trimmed, then overlain by the Missourian Antler Peak Formation along the regional C6 unconformity. Regionally, the Iron Point Conglomerate overlies the regional C2 or C3 unconformity; without direct age control on the conglomerate, it isn't possible to distinguish which.

The type section of the Battle Formation overlies the Roberts Mountains allochthon; there is Atokan limestone in the section. The Battle Formation is dominated by rounded chert and quartzite clasts, but high in the section also contains Atokan limestone clasts. This appears to record erosion of the Highway Limestone or its age equivalent. The Battle Formation overlies the regional C4 unconformity and correlates with the Tomera Formation at Carlin Canyon.

The Highway Conglomerate overlies a karst developed on the Highway Limestone; the clasts in this distinctive unit are predominantly angular chips of the Cambrian-Ordovician Preble Formation. The Preble occupies the footwall of the mid-Pennsylvanian Iron Point normal fault, and was probably tectonically denuded by slip on this fault. The Highway Conglomerate is overlain by the Missourian Antler Peak Limestone on the regional C6 unconformity.