Post–2.6 Ma tectonic and topographic evolution of the northeastern Sierra Nevada: The record in the Reno and Verdi basins

Abstract

A coarse conglomerate, known as "the Gravel of Reno," fi lls a deep channel incised into a 2.6 Ma sedimentary section a few km west of Reno, Nevada. The canyon and its conglomerate fi ll record an abrupt shift in both provenance and paleocurrent direction compared with the underlying lake-marginal Neogene strata. Notably, the intermediate volcanic provenance of the Neogene section is supplemented in the overlying conglomerate by large plutonic clasts derived from the Sierran batholith. The syntectonic Gravel of Reno signals the initiation of Pleistocene faulting along the eastern edge of the Sierra Nevada near latitude 40° N.Structures within the Neogene and Quaternary rocks reveal the progressive deformation of the Sierra Nevada's eastern margin. There is no discordance between the basal Gravel of Reno conglomerate and the underlying Neogene sedimentary section, and both are presently tilted 23° east. Therefore, signifi cant tilting did not occur until after channel incision and deposition of the basal conglomerate. The dip within the Gravel of Reno decreases with stratigraphic height, documenting ongoing tilting during deposition. Several pervasive fault sets cut the Neogene rocks; one set of normal faults probably predates much of the tilting, but strike-slip faults appear to have been active synchronously with it. Fault sets include early west-and northwest-dipping normal faults, and two mutually cross-cutting sets of strike-slip faults: northwest-striking dextral faults and northeast-striking sinistral faults. The most continuous mappable fault surfaces, with probably much of the most recent movement, are north-striking faults with normal or oblique-slip motion. Overall, these faults accommodate east-west extension. In summary, the structural style at the northern termination of the Carson Range is characterized by distributed slip along many minor faults, and faulting was synchronous with tilting of the sedimentary section.Gravity studies constrain the location and geometry of the main structures as they pro ject eastward under the Reno basin. A negative anomaly extends eastward from the east-tilted Gravel of Reno. This gravity low (and the Gravel of Reno it represents) terminates eastward against a steep, northstriking gravity gradient under central Reno; we interpret this to mark a west-dipping normal fault, the "Virginia Street fault," which was active throughout deposition of the coarse clastic section. A more localized and pronounced gravity low in west Reno corresponds to the eastward projection of the eastdipping Neogene diatomite that is exposed at the ground surface. The abrupt termination of this negative gravity anomaly requires that the diatomite terminates eastward at depth, therefore documenting the eastern margin of the Neogene lacustrine environment. Other gravity anomalies document both the relief on the sub-Neogene unconformity and a complex pattern of faults that offset Neogene and younger rocks in the Reno basin, consistent with the multiple fault sets seen in outcrop west of Reno.

Constraints on the history and topography of the Northeastern Sierra Nevada from a Neogene sedimentary basin in the Reno-Verdi area, Western Nevada

“…Pliocene to Holocene sedimentary rocks and structures document the formation of this topography. See the companion paper (Cashman et al, 2012) for a discussion of this more recent geologic history.…”

Fluid Pressure‐Triggered Foreshock Sequence of the 2008 Mogul Earthquake Sequence: Insights From Stress Inversion and Numerical Modeling

“…Directly above the Mogul sequence area, discontinuous surface faults are cutting Tertiary sediments, volcanic units, and older granites at a variety of orientations (Bell & Garside, ; Ruhl, Abercrombie, et al, ). In addition, local quaternary faults are mapped at various orientations, which suggests a long history of overprinting and deformation in a highly fractured shallow subsurface (Bell & Garside, ; Cashman et al, ).…”

Birth of a plate boundary at ca. 12 Ma in the Ancestral Cascades arc, Walker Lane belt of California and Nevada

“…Extensive Cenozoic volcanic and sedimentary rocks, excellent exposure, and abundant previous geological mapping in the Walker Lane make it an excellent region in which to study rifting processes (e.g., Fig. 2; Henry and Perkins, 2001;Trexler et al, 2012;Putirka and Busby, 2007;Busby et al, 2008aBusby et al, , 2008bFaulds and Henry, 2008;Busby and Putirka, 2009;Cashman et al, 2009Cashman et al, , 2012Jayko, 2009aJayko, , 2009bNorton, 2011;Cousens et al, 2012;Jayko and Bursik, 2012;Putirka and Platt, 2012;Riley et al, 2012;Trexler et al, 2012;Wakabayshi, 2013).…”