Stratigraphic significance of Glyptograptus persculptus group graptolites in central Nevada, U.S.A.

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Abstract
Glyptograptids of the G. persculptus group, Glyptograptus laciniosus, and climacograptids of the C. normalis group (herein described as C. miserabilis) occur in the Hanson Creek Interval, or Formation, at Copenhagen Canyon, central Nevada. The graptolites occur in the basal part of an interbedded thin-bedded limestone and chert sequence overlying a quartzsand unit that is recognizable over a wide area in central Nevada and seems to reflect regional shallowing of the seas at the time of its deposition. Dimorphograptus sp. cf. D. confertus is present in the stratigraphically highest beds of the limestone-chert unit. Conodonts suggesting an early Silurian age are present in the graptolite-bearing sequence. Ashgill (late Ordovician) faunas have been found beneath the quartz-sand unit. Analysis of depositional environments of the Ashgill and early Silurian conodont-bearing beds suggests that deposition was continuous from the late Ordovician into the early Silurian in the area. The G. persculptus group glyptograptids display a significant range in variation. Some are relatively narrow and appear to be parallel-sided for much of their length, whereas others are relatively wide and taper noticeably in their proximal regions.