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Andrei M. Sarna-Wojcicki

Publications and source records attributed to Andrei M. Sarna-Wojcicki.

31 records · Page 2Linked to original sources
USGS2000

Revised age of the Rockland tephra, northern California: Implications for climate and stratigraphic reconstructions in the western United States: Comment

Lanphere et al. (1999) presented new data for the age of the Rockland pumice tuff breccia of Wilson (1961) using the incremental-heating 40 Ar/ 39 Ar technique. Their age, ∼610 ka, is ∼200 ka older than zircon fission-track ages obtained on this tuff by Meyer et al. (1980 ; 1991) . Application of new 40 Ar/ 39 Ar technologies to tephrochronometry is an important advance that allows more precise dating of widespread tephra layers. Although the new age may be correct, I urge caution in accepting it in place of grain-discrete fission-track dates and other data that suggest a younger age for this unit.

California↗
USGS1999

Late Cenozoic stratigraphy and tephrochronology of the western Black Mountains piedmont, Death Valley, California: Implications for the tectonic development of Death Valley

Geologic mapping combined with the tephrochronology of spatially isolated sedimentary sections along the western Black Mountains piedmont adjacent the Death Valley fault zone (DVFZ) improves the late Cenozoic stratigraphy from relative age to correlated age. Pliocene tephra layers identified in Funeral Formation conglomerates at Artist Drive and Copper Canyon include a “Nomlaki-like” tephra bed (ca. 3.4 Ma), the tuffs of Mesquite Spring (3.1–3.3 Ma), and a tuff of the lower Glass Mountain family (1.86–1.92 Ma). We informally name the early(?) to middle Pleistocene Mormon Point formation1, which contains tephra layers correlated with the upper Glass Mountain/Bishop family of tephra layers (0.76–1.2 Ma), the Lava Creek B ash bed (ca. 0.66 Ma), and the Dibekulewe ash bed (ca. 0.51 Ma). Identification of these tephra layers indicates that the maximum age of the overlying and inset lacustrine gravel and alluvial fan deposits is 0.51 Ma. The correlated age stratigraphy indicates that the dextral-oblique DVFZ has stepped basinward at Mormon Point and Copper Canyon since the late Pliocene. In contrast, during that same time the DVFZ at Artist Drive has not stepped basinward, but developed into a graben. The age of faulting on the low-angle (~19°–40°) Mormon Point turtleback fault is bracketed between 0.76 and 0.18 Ma, and the overlying Mormon Point formation shows no evidence of tilting, indicating slip on the turtleback fault was at a low-angle. Early Quaternary slip on the low-angle turtleback fault conflicts with the present versions of the pure shear, rolling-hinge, and detachment/rift models for Death Valley extension. Early Quaternary slip is most compatible with turtleback faults as folded or warped detachment fault. We propose that the warping is thermally driven and related to the Black Mountains igneous complex.

California, Nevada↗
USGS1997

Age and correlation of tephra layers, position of the Matuyama-Brunhes chron boundary, and effects of Bishop Ash eruption on Owens Lake, as determined from drill hole OL-92, Southeast California

Tephra layers in the ~323-m-deep Owens lake drill hole OL-92 correlate to tephra layers that have been identified and dated elsewhere in the western United States. Tephra layers identified are the Bishop ash bed (758 ka) at 309.2–298.6 m; the Dibekulewe (ash) bed (ca. 470 ka to ca. 610 ka) at ~224 m; and one of several ash beds in Walker Lake (ca. 60 ka to ca. 80 ka) at ~50.7 m. Other tephra layers, the ages of which are poorly constrained, have also been identified. Age constraints from a sedimentation-rate curve based on dry bulk density and independently derived magnetostratigraphy provide new age constraints to the undated or poorly dated tephra layers: ca. 740 ka for the ash of Thermal Canyon, and ca. 510 ka for the Dibekulewe (ash) bed. Bishop tephra fell into a deep Owens Lake, but the lake shallowed as ash was rapidly reworked by wind and water within the Owens Lake basin. The shallowing of the lake was the result in part to filling with the large volume of ash that was deposited in the basin and then reworked into the lake, but the filling was also an effect of the onset of a moderately warm interstadial period of hemispheric or global extent corresponding to oxygen-isotope stage 19. The lake deepened again as the last several meters of the 10-m-thick, composite ash bed were deposited in the lake. Despite its great thickness, reworking of the light ash must have been rapid. The position of the Matuyama-Brunhes paleomagnetic boundary is estimated to be between 311.4 m and 314.8 m, and most likely between 311.4 m and 312.9 m, in the core, based on (1) the pattern of magnetic inclinations in the Owens Lake core as compared with those at other sites in the region; (2) estimates of the time elapsed between the magnetic reversal and the deposition of the Bishop ash bed; and (3) the probable range of sediment-deposition rates in Owens Lake during this time.

California↗
USGS1995

Ribbon Cliff landslide Washington, and the earthquake of 14 December 1872

Estimates of the epicentral location and maximum intensity of the earthquake of 14 December 1872, the largest and oldest historic earthquake documented in the Pacific Northwest, are controversial largely because the estimates are based on ground effects. The Ribbon Cliff landslide is one of the more critical ground effects used to argue that the epicenter was in the vicinity of Lake Chelan in central Washington. Sketchy historical accounts link the Ribbon Cliff landslide to the 1872 earthquake, but a subsequent study disputed the historical accounts and, on the basis of dendrochronology, concluded that the landslide occurred more than 100 yr prior to the earthquake. However, Quaternary stratigraphic relations and the results of multiple dating techniques reported here indicate that the main Ribbon Cliff landslide probably occurred within a 14-yr period that includes the time of the 1872 earthquake. Although our study supports the historical accounts that link the landslide to the December 1872 earthquake, it does not prove that seismic shaking triggered the landslide.

Washington↗
USGS1990

Environmental changes in the Tule Lake basin, Siskiyou and Modoc Counties, California, from 3 to 2 million years before present

Pollen and diatom analyses of a core from the town of Tulelake, Siskiyou County, California, for the period between 3 and 2 Ma reveal a paleoclimatic and paleolimnologic sequence recording a long, warm time interval that lasted from about 2.9 to 2.6 Ma and had a short, cooler interval within it. During this warm interval, the regional vegetation surrounding ancient Tule Lake was a mixed coniferous forest, and Tule Lake was a warm monomictic lake. Approximate modern analogs for this Pliocene fossil record at Tulelake are found at least 2 degrees farther south. The Tulelake warm interval appears to have correlatives in the North Atlantic oxygen isotope record and in the pollen record of the Reuverian in the Netherlands. An interval beginning at about 2.4 Ma was characterized at Tule Lake by slow sedimentation, by changes in the relative amounts of algae in the lake, and by an increase in the maximum percentages of Artemisia pollen.

California↗
USGS1979

Chemical correlation of some late Cenozoic tuffs of Northern and Central California by neutron activation analysis of glass and comparison with X-ray fluorescence analysis

Glasses separated from several dacitic and rhyolitic late Cenozoic tuffs of northern and central California were analyzed by neutron activation for more than 43 elemental abundances. Eighteen elements--scandiurn, manganese, iron, zinc, rubidium, cesium, barium, lanthanum, cerium, samarium, europium, terbiurn, dysprosiurn, ytterbiurn, hafniurn, tantalurn, thorium and uranium--were selected as most suitable for purposes of chemical correlation on the basis of their natural variability in silicic tuffs and the precision obtainable in analysis. Stratigraphic relations between tuffs and replicate chemical analyses on individual tuffs make it possib1e to calibrate a quantitative parameter, the similarity coefficient, which indicates the degree of correlation for the tuffs studied. The highest similarity coefficient (0.99) was obtained for analyses of two tuffs (potassium-argon dated at about' 6.0 m.y.) exposed in the Merced(?) and Petaluma Formations of Sonoma County, which represent different paleoenvironments, shallow-water marine and fresh water or brackish marine, respectively. Corre1ation of these formations on the basis of criteria other than tephrochronoloqy would be difficult. Results of neutron activation analysis in general confirm earlier correlations made on the basis of analysis by X-ray fluorescence but also make it possible to resolve small compositional differences between chemically simi1ar tuffs in stratigraphic proximity. The Lawlor Tuff (potassium-argon dated at about 4.0 m.y.) is identified at two new localities: in a core sample obtained from a bore hole east of Suisun Bay, and from the Kettleman Hills of western San Joaquin Valley. This identification permits correlation of the uppermost part of the marine Etchegoin Formation in the San Joaquin Valley with the continental Livermore Gravels of Clark, the Tassajara Formation, and the upper part of the Sonoma Volcanics in the cel1tral Coast Ranges of California. A younger tuff near the top of the marine San Joaquin Formation in the Kettleman Hills has been identified at both new 1oca1ities .

Professional Paper↗
USGS1974

Faults and their potential hazards in Santa Cruz County, California

This report and map area designed to provide Santa Cruz County with basic data on the location, pattern, recency of movement, potential for future surface rupture, and anticipated earthquake magnitudes and recurrence intervals for several of the faults located there for consideration in the county's land-use planning program and the preparation of its seismic safety element. This report does not consider other seismic hazards such as ground shaking, seismically induced ground failure, or tsunamis (seismically generated sea waves) that can accompany offshore earthquakes of large magnitude.

California↗