Implications of New Detrital-zircon and U-Pb Age Data for the Stratigraphy, Depositional History, Provenance and Paleogeography of Upper Jurassic and Lower Cretaceous Strata within the Carson Range of Western Nevada, USA

New U-Pb data indicates lowest Cretaceous metamorphosed sedimentary and
volcanic rock are preserved within the Genoa Peak and Spooner Lake pendants of
the Carson Range, western Nevada. These rocks, referred to as the South Camp Peak
sequence, consist of well sorted, clast supported, chert-pebble conglomerate, gradational
into dark grey, massive to parallel-bedded, quartzite, quartz arenite, siltstone,
minor black slate, and calcareous siltstone and silty carbonate. These clastic rocks are
overlain by fiamme-bearing, subaerial ash-flow tuff interbedded with lesser coarsegrained,
lithic-rich clastic rocks. A third unit, the tuff breccia of Genoa Peak, lies
southwest of the South Camp Peak sequence, but the contact between it and the ashflow
tuffs to the northeast is not exposed.
The presence of parallel and flaser bedding suggests that the clastic rocks of the
South Camp Peak sequence were deposited under shallow-water or strandline conditions.
A channel-mouth bar setting is suggested by the presence tightly packed, tabular
beds of well-sorted, chert-pebble conglomerates. This depositional environment
transitioned to low energy shallow marine conditions and eventually subaerial settings
during the deposition of the fiamme-bearing, ash-flow tuffs and coarse-grained,
feldspatholithic clastic rock.
Strata of the South Camp Peak sequence overlies ca. 163 Ma volcanic rock correlative
with the upper part of the Peavine sequence along an unconformable contact.
Detrital zircon (DZ) obtained from the quartzite and chert-pebble conglomerate at
the base of the South Camp Peak sequence included five grains of Tithonian age (ca.
150–147 Ma). Three younger grains yielded earliest Cretaceous ages spanning ca.
141–139 Ma. These younger grains indicate deposition of the sequence may be Berriasian.
This depositional age is similar to that of other lowest Cretaceous siliciclastic
strata exposed near Taylorsville, California and within several roof pendants of the
Sierra Nevada southwest of the Carson Range. Deposition in all these areas appears
to have coincided in time with deposition of the oldest siliciclastic strata within the
Great Valley of California.
Age populations of DZ from the basal part of the South Camp Peak sequence
indicate that both local and distal sources contributed sediment to the depositional
site. The DZ suggest uplift and erosion of the local igneous rocks began by ca. 147
Ma. The Tithonian–Oxfordian age DZ likely represents Peavine sequence rock. Older
Jurassic and Triassic DZ were likely derived from igneous rocks within the Northern
Sierra and/or Pine Nut terranes or the Triassic continental arc in the eastern Sierra
Nevada. A sediment contribution from sources such as the Mesozoic erg deposits of
the Colorado Plateau is indicated by abundant Proterozoic DZ, most of which display a Grenvillian age signature. The mix of distally and locally derived DZ suggests the
South Camp Peak sequence depositional site was located near the terminus of a complex
drainage system very early in the Cretaceous.
Key Words: Carson Range, South Camp Peak sequence, Lower Cretaceous, Detrital Zircon,
Northern Sierra terrane