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Cordilleran Section (104th Annual) and Rocky Mountain Section (60th Annual) Joint Meeting (19–21 March 2008)

Paper No. 9
Presentation Time: 11:10 AM

STRUCTURAL AND BIOCHRONOLOGIC ANALYSIS OF THE NORTHERN DRY HILLS, HUMBOLDT COUNTY, NEVADA: EVIDENCE FOR RECLASSIFICATION OF THE ETCHART FORMATION


SIEBENALER, Samuel A.1, TAYLOR, W.J.1, CASHMAN, P.H.2, TREXLER Jr, J.H.2 and DAVYDOV, V.I.3, (1)Geoscience, UNLV, 4505 Maryland Pkwy, Las Vegas, NV 89154-4010, (2)Department of Geological Sciences and Engineering, MS 172, University of Nevada, Reno, NV 89557, (3)Department of Geology and Geophysics, Boise State University, 1910 University Drive, Boise, ID 83725, Siebena3@unlv.nevada.edu

The eastern Dry Hills, north of the Osgood Mountains in northern Nevada, was originally mapped as the Pennsylvanian to Permian Etchart Formation, part of the Antler Overlap Sequence. Our studies document that this unit contains a record of at least two late Paleozoic deformations separated by angular unconformities, and thus, redefinition of this unit is merited.

The lowest unit is sandy to sandy limestone that contains turbidites and at least three distinct conglomerates. Its base is associated with micrite limestone and an inter-layered conglomerate with ~100% carbonate clasts. This unit is presently undated. The top of this unit is an angular unconformity.

The middle unit is largely thick-bedded grainstones. Fusulinids from this unit yielded a Missourian to Virgilian (Kasimovian to Gzhelian) age. Measured fold axes and structural analysis of them show a set of NE-trending folds with that do not occur in the overlying unit. The top of this unit is bounded by an angular unconformity.

The upper unit is mostly fossil-rich grainstone with turbidite deposits. This unit contains at least one clast-supported conglomerate with varying amounts of both chert and carbonate clasts. Fusulinids from this unit are Wolfcampian in age, Asselian -Sakmarian to Artinskian. Measured fold axes and structural analysis of them show a set of NNW-trending folds. These folds also overprint the middle unit.

These unconformities and facies differences require that the Etchart Limestone be redefined. The middle and highest units are age equivalent to the Antler Peak Limestone (Lower Strathern Formation) and Upper Strathern Formation, respectively. Consequently, we advocate these names for the units.

The folds and angular unconformities indicate two tectonic events that correlate to unconformities previously documented elsewhere. One event occurred after Missourian to Virgilian (Kasimovian to Gzhelian) and formed the NE-trending folds in the Antler Peak equivalent unit. The unconformity bounding the top of this unit is equivalent to the P1 unconformity of Trexler et al (2003). The second event formed the NNW-trending folds and took place after deposition of the upper Strathearn equivalent, which is Wolfcampian in age (P2). These results provide further evidence of tectonism in Pennsylvanian and Permian time.

Session No. 4

T3. Pennsylvanian to Early Triassic Deformation and Sedimentation in the Western United States
Wednesday, 19 March 2008: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 40, No. 1, p.39
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