Ar Dating of the Kern River Ash Bed and Related Tephra Layers: Implications for the Stratigraphy of Petroleum-Bearing Formations in the San Joaquin Valley, California

ARTICLE IN PRESS

Quaternary International 178 (2008) 246–260

Geochemical correlation and 40Ar/39Ar dating of the Kern River ash bed and related tephra layers: Implications for the stratigraphy of petroleum-bearing formations in the San Joaquin Valley, California

Dirk Barona,Ã, Robert M. Negrinia, Elizabeth M. Goloba, Don Millerb, Andrei Sarna-Wojcickic, Robert J. Fleckc, Bradley Hackerd, Alex Erendie

aDepartment of Physics and Geology, California State University, Bakersfield, 9001 Stockdale Highway, Bakersfield, CA 93311, USA bBankers Petroleum, 601 East Daily Drive, Camarillo, CA 93010, USA cU.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA dDepartment of Earth Science, University of California, Santa Barbara, CA 93106, USA eChevron Corporation, Bakersfield, CA 93311, USA

Available online 27 March 2007

Abstract

The Kern River ash (KRA) bed is a prominent tephra layer separating the K and G sands in the upper part of the Kern River Formation, a major petroleum-bearing formation in the southern San Joaquin Valley (SSJV) of California. The minimum age of the Kern River Formation was based on the tentative major-element correlation with the Bishop Tuff, a 0.75970.002 Ma volcanic tephra layer erupted from the Long Valley Caldera. We report a 6.1270.05 Ma 40Ar/39Ar date for the KRA, updated major-element correlations, trace-element correlations of the KRA and geochemically similar tephra, and a 6.070.2 Ma 40Ar/39Ar age for a tephra layer from the Volcano Hills/Silver Peak eruptive center in Nevada. Both major and trace-element correlations show that despite the similarity to the Bishop Tuff, the KRA correlates most closely with tephra from the Volcano Hills/Silver Peak eruptive center. This geochemical correlation is supported by the radiometric dates which are consistent with a correlation of the KRA to the Volcano Hills/Silver Peak center but not to the Bishop Tuff. The 6.1270.05 Ma age for the KRA and the 6.070.2 Ma age for the tephra layer from the Volcano Hills/Silver Peak eruptive center suggest that the upper age of the Kern River Formation is over 5 Ma older than previously thought. Re-interpreted stratigraphy of the SSJV based on the new, signiﬁcantly older age for the Kern River Formation opens up new opportunities for petroleum exploration in the SSJV and places better constraints on the tectonostratigraphic development of the SSJV. r 2007 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction For example, in 2006 the field produced over 31 million barrels of oil. The Kern River Formation crops out as uplifted and The maximum age of the Kern River Formation tilted Neogene sediments that are dissected by the Kern (8 Ma) is based on the presence of early Hemphillian River between the southern Sierra Nevada mountains of mammalian fossils near the base of the formation (Savage California and the southern San Joaquin Valley (SSJV) et al., 1954; Lindsay et al., 1987; Tedford et al., 1987). The (Fig. 1). The Kern River Formation is the reservoir rock minimum age of the Kern River Formation is based on a for the Kern River oil field, one of the largest oil fields in tentative geochemical correlation of the Kern River ash California. The Kern River oil field has produced almost 2 (KRA) bed, which is found between the K and G sands billion barrels of oil since its discovery in 1899 and (Fig. 2), with the Bishop Tuff (Fig. 1) (Sarna-Wojcicki, continues to produce over 30 million barrels per year. written communication to M. McGuire, 1988; McGuire et al., 1989). The Bishop Tuff is a volcanic tephra ÃCorresponding author. Tel.: +1 661 654 3044. layer erupted from the Long Valley Caldera (Fig. 1) E-mail address: [email protected] (D. Baron). at 0.75970.002 Ma (Izett and Obradovich, 1994;

119ºW 118º

Long Valley 6 38ºN Caldera 7 Volcano To S 5 Hills

N White M Silver I Peak Range

ountains E 1 Bi E 95

V Inyo Mountains 37º 6 37º

A 395 3 Deat 4 R NV Southern h San J CA D oaquin Valley 99 Valley

A 36º A 36º

Bakersfield Arch 5 Crestline (approx.) N 025 mi 2 Ba km 0 40

35º Mo 35º Kern River 58 Formation

119º 118º 117º

Fig. 1. Location of tephra samples, Long Valley Caldera, Volcano Hills/Silver Peak Range, and the Kern River Formation. The black lines on the map indicate roads and the major cities are also noted (Ba ¼ Bakersﬁeld, Mo ¼ Mojave, Bi ¼ Bishop, To ¼ Tonopah). This map shows the numbered location of samples used in this study. (1) Bishop Tuff sample BT-11-D1; (2) Kern River ash samples Luck 218 696.50/6980 (shown at the end of the arrow next to 2); (3) Lava Creek B tephra samples JRK-DV5/JRK-DV57, (4) Lava Creek B sample TECO-30A; (5) Fish Lake Valley tephra sample FLV-SP-3; and (6) Friant tephra sample Friant-5A. The sampling location for the fourth Lava Creek B tephra, ORNA-1, in northeastern Nevada is shown on the outline of the state of California in the upper right corner and numbered 7. The cross-section that appears in Fig. 2 is shown as the dotted, WSW–ENE trending line across the Kern River Formation.

Sarna-Wojcicki et al., 2005). The initial correlation of the Formation. Improved age control of the Kern River KRA to the Bishop Tuff was based on only nine major Formation and its stratigraphic relation to other adjacent elements determined by electron microprobe analysis formations may generate new petroleum exploration (EMA). In the initial unpublished report (Sarna-Wojcicki, opportunities and a better understanding of the tectonos- written communication to M. McGuire, 1988), Sarna- tratigraphic development of the SSJV. Wojcicki cautioned that additional chemical analyses We report: (1) 40Ar/39Ar age (sanidine) of the KRA; would be needed for a definitive correlation. The similarity (2) new major-element microprobe analyses and 40Ar/39Ar of the Bishop Tuff to the 0.8–1.2 Ma Upper Glass age for a tephra layer from Fish Lake Valley, Nevada, Mountain ash beds prevents a definitive correlation based erupted from the Volcano Hills/Silver Peak range in on major-element compositions alone (Sarna-Wojcicki Nevada (Fig. 1); and (3) new trace-element analyses by et al., 1984). solution inductively coupled plasma mass spectrometry The objective of this study is to provide additional major (ICP/MS) of KRA, Bishop Tuff, and the Volcano Hills/ and trace-element geochemical data and radiometric ages Silver Peak tephra layer. We also measured the trace- of the KRA and related tephra for a more definitive element composition of four samples of the 0.639 Ma Lava correlation of the KRA, thereby providing a better Creek B ash bed (Lanphere et al., 2002) from the constraint for the minimum age of the Kern River Yellowstone Caldera complex in Wyoming in order to ARTICLE IN PRESS 248 D. Baron et al. / Quaternary International 178 (2008) 246–260

Fig. 2. Cross-section showing the major sand units of the Kern River Formation and deeper, older formations in the southern San Joaquin Valley. Cross- section along the dotted line shown in Fig. 1 and along dip. The Kern River ash is found between the K and G sands of the Kern River Formation. The lower age of the Kern River Formation of 8.2 Ma is indicated at the bottom of the R sands. After Miller et al. (1998). measure the variability of trace-element composition of been recognized and informally named (R2, R1, R, K2, samples from one eruption to help evaluate the significance K1, K, G, C1, C) within the producing interval of the Kern of trace-element correlations between samples from differ- River Formation (Nicholson, 1980)(Fig. 2). ent sources. Finally, we measured the trace-element In the SSJV, the Kern River Formation dips gently to composition of a tephra layer from Friant, California the west (o101) toward the depocenter. SeveralNNW or (Fig. 1), that is thought to have erupted from the Long WNW trending normal faults cut through these sedi- Valley Caldera. ments (Nicholson, 1980; Bartow, 1991). The Kern River Formation lies on the Bakersfield Arch (Fig. 1), a broad, 2. Background SSW-plunging anticlinal high, in part responsible for the uplift that led to outcrops which exposed the sediments 2.1. Kern river formation along the margin of the valley. The uplift associated with the Bakersfield Arch most likely commenced during the The Kern River Formation (Fig. 1) is discussed in early Eocene (Reid and Cox, 1989). Although probably not several reviews and studies including those by Hackel active in the Oligocene through middle Miocene, correla- (1965), Nicholson (1980), Bartow et al. (1983), Miller tions across the Bakersfield Arch indicate renewed activity (1986), Olson et al. (1986), Graham et al. (1988), Kuespert beginning in the early Miocene. This antiformal feature is (1990), Kuespert and Sanford (1990), and Bartow (1991). probably active today as evidenced by the topographic Most early studies interpreted the Kern River Formation separation of the Lake Tulare and Kern-Buena Vista Lake as a braided-stream deposit associated with a broad depocenters to the north and south of the Bakersfield Arch. alluvial fan or series of fans fed by Sierra Nevada streams. The maximum age for the Kern River Formation is well More recently, Graham et al. (1988) reinterpreted the established by the presence of Hemphillian (late Miocene- middle and upper part of the formation as a glacio-fluvial early Pliocene) fauna near the base of the formation environment based on the presence of sand grains modified (Savage et al., 1954; Lindsay et al., 1987; Tedford et al., by glacial transport and faceted cobbles. As a result, the 1987). Correlative fauna in the Mehrten formation from Kern River Formation consists predominantly of coarse- the northern San Joaquin Valley are found within a few grained sediments with occasional layers of fine sands, silts, meters of a tuff dated at 8.2 Ma (Bartow et al., 1983). and even clays. Nine major oil-producing sand layers have The minimum age of the Kern River Formation is ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 249 tentatively based on the geochemical correlation of the evident from sedimentary structures and the gradational KRA found in the upper Kern River Formation (Fig. 2) contact with overlying mud units. Both the top and base with the Bishop Tuff (Sarna-Wojcicki, written communica- are concordant with flat-laminated sedimentary structures tion to M. McGuire, 1988; McGuire et al., 1989). This of a low-energy depositional setting. In the larger setting, correlation suggests that the Kern River Formation con- these beds grade upwards into interchannel muds asso- tinued to be deposited for some time after 0.759 Ma ago. ciated with the fluvially dominated deposits of the Kern River Formation. The KRA has been inferred from well 2.2. Description of the KRA log signatures of several nearby wells at the same stratigraphic position between the ‘‘G’’ and ‘‘K’’ reservoir The KRA (Fig. 3) was cored in the Texaco Luck #198 sands, indicating it is not an isolated or reworked well (note that Texaco is now Chevron), located in Section interclast. The KRA characteristically exhibits a low- 30, T28S, R28E (Mt. Diablo Baseline and Meridian), density and high-porosity spike in density-neutron logs during routine reservoir evaluation. The basal portion (Fig. 4). An isopach map constructed from log data from (225.9–226.0 m (741.2–741.4 ft)) of the tephra layer is 227 wells indicates that the ash resides in discontinuous devoid of sedimentary structures and interpreted as an air lenses possibly due to channeling by WNW-oriented fall ash concordantly overlying a mud unit. The upper streams subsequent to the deposition of a sheet-like ash portion of the tephra layer, from 226.0–224.8 m body into relatively quiet water (Fig. 5). The discontinuous (741.4–737.5 ft), appears reworked. The reworking is nature of the ash is consistent with the lack of outcrops of the KRA where the zone between the K and C sands is exposed (Miller et al., 1998).

2.3. Description of tephra samples analyzed by ICP/MS

2.3.1. KRA—samples Luck 218 695.50, Luck 218 6980 Collected from the Kern River oil ﬁeld, Bakersﬁeld, CA (Fig. 1). The Luck 218 well is located in Township 28S, Range 28E, and Section 30 (Mt. Diablo Baseline and Meridian) (118199.7620N, 35146.5590W). These samples were recovered from sidewall cores taken in Texaco (now Chevron) Well Luck 218 at 212.3 m (696.5 ft) and 212.8 m (698.0 ft) (Miller et al., 1998) The samples are from a distal ash bed found between the K and G sands of the Kern River Formation (Fig. 2).

2.3.2. Bishop Tuff—sample BT-11-D1 Collected just outside of Bishop, California (118123.7190N, 37122.0010W). The age of the Bishop Tuff has been previously reported by Sarna-Wojcicki et al. (2005) as 0.75970.002 Ma. The source of the Bishop Tuff is the Long Valley Caldera (Fig. 1) located north of Bishop, California.

2.3.3. Friant tephra—sample Friant-5A This sample was recovered from the Friant pumice quarry near Friant, California, just north of Fresno, California (119142.5890W, 36159.3270N) (Fig. 1)(Reheis et al., 2002). Another sample from this location was dated at 0.750170.0123 Ma (Sarna-Wojcicki et al., 2000). The source of tephra from the Friant pumice quarry has been difﬁcult to determine and controversial. Previous work (Izett et al., 1988) differentiated the Friant tephra layer from the Bishop Tuff. Subsequent enlargement of the quarry at Friant exposed the air fall Bishop Tuff and identiﬁed the previously Fig. 3. Photograph of the Kern River ash bed in the core from Texaco named ‘‘Friant ash’’ as a mixture of reworked Bishop Tuff Well Luck 198 in the immediate vicinity of Well Luck 218 from which the Kern River ash sidewall samples analyzed in this study were taken. Labels and younger pyroclastic deposits from the headwaters of indicate depth below the ground surface in feet. The Kern River ash bed the San Joaquin River (Sarna-Wojcicki, unpublished data). occurs between depths 737.5 and 741.2 ft. After Miller et al. (1998). The Friant-5A sample has been correlated chemically to the ARTICLE IN PRESS 250 D. Baron et al. / Quaternary International 178 (2008) 246–260

Fig. 4. Segment of density-neutron log from Texaco Luck 198 well showing the interval containing the Kern River ash bed. The ash layer is characterized by high-amplitude spikes indicating low density (r ¼ 1.65 g/cm3) and high porosity (F ¼ 60–65%). For purposes of constructing the isopatch map shown in Fig. 4, the thickness of the tephra layer is deﬁned by a cutoff value of (rp1.65 g/cm3). After Miller et al. (1998).

30 29

500 m

Fig. 5. Isopatch map of the Kern River ash bed in the Kern River Formation in the vicinity of Sections 29 and 30 of T28S, R28E. The map was constructed from density-neutron logs of oil wells. The outer line indicates the extent of the tephra layer. In the area between the zero thickness outer line and the shaded area, the tephra layer has a thickness between 0 and 1.3 m (4 ft). In the shaded area, the tephra layer has a thickness greater than 1.3 m (4 ft). After Miller et al. (1998).

Bishop Tuff, using microprobe and INAA analyses (Sarna- 2.3.5. Lava Creek B tephra—samples JRK-DV5 Wojcicki et al., 2000). and JRK-DV57 The JRK-DV samples were collected in the Mormon 2.3.4. Fish Lake Valley tephra—sample FLV-SP-3 Point area of Death Valley, California between 1161450W, This sample is from the Fish Lake Valley area in the 361040N and 1161460W, 361030N(Knott et al., 1999) western part of central Nevada shown in Fig. 1, located at (Fig. 1). These samples were light gray, ﬁne grained, and 1181050W, and 371450N(Reheis et al., 2002). The sample composed mostly of platy shards. Trace-element analyses was taken from pumice clasts in the ash-ﬂow unit. The using ICP/MS were previously reported (Knott, 1998). The source of this tephra is the Volcano Hills/Silver Peak source of the 0.639 Ma Lava Creek B tehpra is the Range in western Nevada shown in Fig. 1. Yellowstone caldera complex of Wyoming and Idaho. ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 251

2.3.6. Lava Creek B tephra—sample ORNA-1 3.3. 40Ar/39Ar dating of the Fish Lake Valley tephra from This sample was collected in the Humboldt River the Silver Hills/Volcano Hills eruption Canyon near Oreanna, NV, in the Lake Tecopa area (T 29N R 33E S6, Mt. Diablo Baseline and Meridian, Fig. 1) Mineral separates were prepared from tephra samples by (Davis, 1978; Golob, 2005). These samples were light crushing and sieving to sizes appropriate to disaggregate gray, fine grained, and composed mostly of platy shards grains. Different size fractions were washed and sonicated (Davis, 1978). in deionized water to remove any loose material. Volcanic glass, heavy minerals, and lithic grains were removed using magnetic and heavy liquid methods. Feldspar grains were leached with 1 N HCl, followed by 8% HF to remove 2.3.7. Lava Creek B tephra—sample TECO-30A 40 39 This sample was collected from the Lake Tecopa area in adhering glass, and separated for laser-fusion Ar/ Ar. eastern California at 11611602900W, 3515801200N(Fig. 1). Sanidine and plagioclase were separated as much as Previous work on this sample has been reported by Sarna- possible with heavy liquids, but the paucity of crystals Wojcicki et al. (1984, 1987). and the fine grain sizes of most samples resulted in incomplete separations. K/Ca ratios of the analyses show that many of the concentrates were feldspar mixtures. Samples were irradiated for 16 h in the US Geological 3. Methods Survey TRIGA Reactor Facility in Denver, CO. The neutron flux monitor used in all irradiations was Taylor 3.1. Major-element analysis by EMA Creek Rhyolite sanidine, 85G003, with an age of 27.92 Ma, as reported by Duffield and Dalrymple (1990). This age is EMA was performed at the USGS Tephrochronology standardized to an average age of 513.9 Ma for inter- Laboratory in Menlo Park, CA. Sample preparation and laboratory standard hornblende, MMhb1 (Samson and analytical methodology were according to Sarna-Wojcicki Alexander, 1987), and the Menlo Park intra-laboratory et al. (2005). standard biotite, SB-3. Decay and abundance constants for all ages reported are those recommended by Steiger and Jager (1977). 3.2. 40Ar/39Ar dating of the KRA Samples were analyzed using 40Ar/39Ar laser-fusion techniques described by Dalrymple (1989). Neutron- Sanidine grains of volcanic origin were sampled, produced 39Ar together with the radiogenic 40Ar, atmo- separated, and dated via the 40Ar/39Ar method, using laser spheric 40Ar, and any extraneous 40Ar was evolved by step-heating methods in 13 heating increments. The fusing extremely small amounts of material with a core sample was disaggregated with a mortar and pestle, continuous laser (York et al., 1981). Ar analyses were placed in a high-powered sonic cleaner for 4–10 h, performed on the same mass spectrometer and using the sieved (480 mm), and density separated using heavy liquids same argon extraction system described by Dalrymple (bromoform, density 2.85 g/cm3). An initial density (1989). Analytical errors in 40Ar/39Ar ages are reported at separation (density 42.53 g/cm3) eliminated most of the the 1s level. glass portion of the sample (490%). The nonmagnetic portion that remained after numerous magnetic Frantz 3.4. Trace-element analysis by solution ICP/MS separations was still quite dirty. A density separation of 2.59 g/cm3was attempted to separate the quartz and Samples were provided to the USGS Tephrochronology plagioclase fractions. Immersion oils aided the identifica- Laboratory in Menlo Park, CA as sidewall core plugs or tion of sanidine grains, which comprised about 25% of the collected from outcrops. The samples were treated using sample at this stage of the separation. Sanidine grains, of 10% diluted HCl and HF to remove coatings on the glass predominantly very-fine grain size (62–125 mm), were hand shards and altered rinds. Volcanic glass was separated from picked (positive picking) using a brush and a binocular other tephra components using a high-low-Franz-mag- microscope based on crystal habit. Samples were etched in netic-separation method. Following this separation, the a sonic bath for 15 min, then etched for 2 min in 8% HF. samples were nearly pure (99% or greater) isotropic A 13-step age spectrum of the sample was then obtained at volcanic glass shards. The purified glass separates were the Geochronology Laboratory at Stanford University by then provided to CSU Bakersfield for ICP/MS analysis. step heating the entire sample with a defocused laser Glass separates were weighed on a Denver Instrument beam. The neutron flux monitor used in all irradiations Company TC-204 scale to the nearest 0.1 mg inside was Taylor Creek Rhyolite sanidine, 85G003, with an microwave digestion vessels to obtain approximately age of 27.92 Ma. The analytical error in the 40Ar/39Ar age 0.03 g of sample. Then, 1 mL of high-purity concentrated is reported at the 1s level. Additional information trace-metal grade hydrofluoric acid (Omnitrace by EM about the dating technique can be found in Hacker Science) and 3 mL concentrated trace-metal grade nitric et al. (1996). acid (Omnitrace Ultra by EM Science) acid were added to ARTICLE IN PRESS 252 D. Baron et al. / Quaternary International 178 (2008) 246–260 the glass separate samples in the microwave digestion data set (as a Euclidian distance), (2) grouping the objects vessels. One vessel was prepared as a blank with just the into a binary, hierarchical dendrograms, and (3) determin- acids and no tephra sample included. Vessels containing ing where to cut the dendrogram into clusters. The samples were placed in a sample holder and the samples calculated distances are plotted as dendrograms, with the were digested in an Anton Paar Multiwave Microwave groups displaying shorter distances having greater correla- Digester using US Environmental Protection Agency tions. At the top of these charts, a cophenetic correlation method 3052 (US Environmental Protection Agency Office coefficient using a cophenet function in MatLab is of Solid Waste, 1996). After digestion, the contents of the calculated and labeled as C ¼ 0.815330. This function microwave digestion vessels were poured into pre-cleaned compares the distances between objects in the distance 50 mL polypropylene centrifuge tubes (Corning). The vector and the linking of objects in the cluster tree to microwave vessels were then rinsed out with nanopure determine a correlation. The closer the C value is to 1, the water (18.3 MO cm). The rinse was added to the rest of the better the correlation and, therefore, the more significant digested samples in the centrifuge tubes and the tubes were the dendrogram solution. Dendrogram analysis is useful in then brought up to 50 mL with nanopure water. Dilution determining groupings of data, in this case by similarity of of 1:10 were prepared in pre-cleaned 15 mL polypropylene the volcanic glass compositions in the samples. centrifuge tubes (Falcon 2097 BlueMax Jr.) using 2% The third way to evaluate trace-element correlations HNO3 prepared from trace-metal grade concentrated between tephra samples was binary scatter plots using HNO3 (Omnitrace Ultra by EM Science) and nanopure several combinations of element pairs from the analysis water. and visually examining the plots for groupings of samples. Samples were analyzed for 42 trace elements on a Perkin Elmer ELAN 6100 ICP Mass Spectrometer. The instru- 4. Results ment was calibrated using commercial multi-element standards traceable to NIST (Spec CertiPrep) that were 4.1. Major-element analysis by EMA prepared in a matrix similar to the samples. Mid-range standards were run between each sample to monitor for EMA major-element compositions of the KRA and instrument drift. Concentrations of the analyzed element in geochemically similar tephra layers from the Long Valley the original samples (in ppm) were calculated from the and Silver Peak/Volcano Hills volcanic fields are listed in digested sample mass, the dilution factor, and the Table 1. The tephra layers are listed in order of their concentrations (in mg/L) measured in the diluted digestion similarity coefficient (Sarna-Wojcicki et al., 1984)withthe solutions. Concentrations in the blank run through the KRA. Although the Long Valley samples are geochemi- microwave digestion and dilution procedures were gener- cally very similar to the KRA (similarity coefficients ally very low compared to the actual samples but were 0.92–0.90), the five closest matches (similarity coefficients subtracted from the sample concentrations to account for 0.95–0.93) are samples from the Silver Peak/Volcano Hills very small amounts of contamination from the digestion eruption. Note that Silver Peak/Volcano Hills samples vessels and reagents used. were analyzed after 1998 when the original tentative Three different techniques were used to evaluate the correlation of the KRA to the Bishop Tuff was made by large data set (9 samples 42 elements each) from samples McGuire et al. (1989). that were all of a very similar composition. These techniques were similarity coefficients, clustering (dendro- 4.2. 40Ar/39Ar dating gram) analysis, and binary scatter plots of selected elements. The spectrum of the KRA sample is shown in Fig. 6. All Similarity coefficients are commonly used when compar- of the step ages are equivalent within the uncertainty of the ing chemical data from different tephra samples (e.g. analysis and yield a weighted mean age of 6.1070.05 Ma. Sarna-Wojcicki et al., 1984). For many of the elements A summary of the 40Ar/39Ar dating of nine samples from analyzed, the concentrations measured in the solutions the Silver Peak/Volcano Hills eruption is listed in Table 2. were quite low and close to the limits of detection. To avoid Ages for the individual samples range from skewing the correlations by elements with concentrations 5.80170.026–6.03870.016 Ma, with a weighted mean age close to their detection limits, we calculated normalized of 6.070.2 Ma. concentrations. The maximum value for each element was identified. Next, all of the values measured for that element 4.3. Trace-element analysis by ICP/MS were divided by the maximum to get a normalized value (between 0.0 and 1.0) for each sample that was then used The concentrations of 42 trace elements reassured by for calculating similarity coefficients. ICP/MS are listed in Table 3. The similarity coefficients Hierarchical clustering analysis of the samples was calculated from the measured trace-element concentrations completed in MatLab (Golob, 2005). Hierarchical cluster- are listed in Table 4. When all 42 elements, even those with ing is performed using the following three steps: (1) finding very low concentrations close to their detection limits or similarity or dissimilarity between pairs of objects in the poor correlation to other samples, were included in the ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 253

Table 1 Summary of major-element microprobe analyses and correlations of the Kern River ash, tephras from the Long Valley Caldera eruption, and tephras from the Volcano Hills/Silver Peak eruptive center

Source Sample Date SiO2 Al2O3 Fe2O3 MgO MnO CaO TiO2 Na2OK2O Total Sim. coeff.

KR Luck 218 24/2/88 77.75 12.57 0.72 0.05 0.06 0.44 0.12 3.92 4.39 100.02 N/A VH FLV-VH-5A 2/4/91 77.14 12.75 0.72 0.04 0.07 0.44 0.11 3.89 4.85 100.01 0.9562 VH FLV-VH-5B 2/4/91 77.29 12.69 0.70 0.05 0.07 0.43 0.10 3.85 4.82 100.00 0.9397 SP FLV-SP-2 22/4/91 76.79 13.07 0.71 0.05 0.07 0.44 0.10 3.73 5.02 99.98 0.9315 SP FLV-SP-3 31/1/91 77.18 12.76 0.73 0.07 0.07 0.44 0.09 3.71 4.95 100.00 0.9256 VH FLV-VH-1 02/4/91 76.98 12.78 0.71 0.06 0.05 0.49 0.12 3.36 5.45 100.00 0.9192 LV PICO-39A 01/7/85 77.77 12.51 0.72 0.03 0.06 0.45 0.07 3.89 4.47 100.01 0.9185 LV FLV-94-WP 21/7/89 78.08 12.37 0.72 0.03 0.06 0.45 0.05 3.82 4.43 100.01 0.9175 LV 66W5,T5-7 — 77.59 12.74 0.74 0.03 0.05 0.45 0.07 3.88 4.44 99.99 0.9163 LV FLV-69-PA 21/7/89 78.04 12.31 0.74 0.02 0.06 0.44 0.05 3.77 4.55 99.98 0.9115 LV BT-7 01/7/85 77.57 12.48 0.73 0.02 0.05 0.43 0.07 3.88 4.78 100.01 0.9059 LV BT-7(2) 01/7/85 77.63 12.48 0.74 0.03 0.05 0.42 0.07 3.87 4.71 100.00 0.9068 LV FLV-SP-1 22/4/91 76.87 12.99 0.71 0.04 0.08 0.41 0.10 3.67 5.13 100.00 0.9062 LV YJC-1-87 9/11/87 77.28 12.91 0.73 0.04 0.05 0.44 0.07 3.74 4.75 100.01 0.9061 LV 63CJ — 77.37 12.69 0.73 0.04 0.05 0.45 0.08 3.60 4.99 100.00 0.9060 LV FLV-SP-9 11/96 76.79 13.18 0.67 0.08 0.06 0.57 0.10 3.52 5.04 100.01 0.9058 LV FLV-136-WP 16/4/90 77.86 12.35 0.74 0.03 0.04 0.44 0.08 3.90 4.57 100.01 0.9054 LV PICO-5 01/7/85 77.46 12.51 0.70 0.03 0.07 0.45 0.07 3.76 4.96 100.01 0.9033 LV D77-2D — 77.39 12.66 0.73 0.03 0.05 0.45 0.07 3.72 4.89 99.99 0.9020 LV FLV-161-CS 08/3/91 77.48 12.80 0.71 0.03 0.06 0.45 0.06 3.45 4.96 100.00 0.9010

Tephras are listed in order of their similarity coefﬁcient with the Kern River ash. KR—KERN River ash, uppermost tephra layer found in Texaco Luck 198 core, in Kern River Formation, near Oildale, California. VH—tephra layers from Volcano Hills, north of Fish Lake Valley, western Nevada. SP—tephra layers from Silver Peak Range, western Nevada. LV—tephra layers from Long Valley Caldera/Mono Craters area. Includes Bishop Tuff, Bailey Ash Bed, and Glass Mt. tephra.

10.0

9.0

8.0

7.0 1300ºC 800ºC 950ºC 900ºC 1000ºC 1050ºC 1100ºC 1150ºC 1200ºC 6.0 1250ºC 5.0 TFA = 6.15 ± 0.06 Ma Age (Ma) 4.0 WMPA = 6.13 ± 0.06 Ma

3.0

2.0

1.0

0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Cumulative 39Ar

Fig. 6. 40Ar/39Ar step-heating age spectrum of sanidine separated from the Kern River ash in the Kern River Formation from Texaco Luck #198 well. TFA is total fusion age. WMPA is the weighted mean plateau age. Explanations of the dating technique can be found in Hacker et al. (1996). calculation, similarity coefficients range from 0.47 to 0.90. a smaller number of elements are included or elements that The similarity coefficients calculated using all 42 measured are poorly correlated are excluded from the statistical elements are listed in the upper right part of Table 4. The analysis. Including all 42 elements in the data analysis, even similarity coefficients based on all 42 measured elements samples that are known to be from the same eruption have are lower than those reported in other studies in which only similarity coefficients p0.90 and as low as 0.82 ARTICLE IN PRESS 254 D. Baron et al. / Quaternary International 178 (2008) 246–260

Table 2 Summary of 40Ar/39Ar ages of samples from the Fish Lake Valley tephra layer originating from the Silver Peak/Volcano Hills eruptive center

Run # 40Ar* (mol) K/Ca 40Ar* (%) 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar Age (Ma)

FLV-SP-1 (feldspar) 95Z0377B 6.504637E14 0.528589 45.30895 2.393210 0.926412 0.004635 6.01658770.053278 0377C 1.282777E13 18.716720 91.07287 1.192296 0.026179 0.000326 6.02180470.036266 0377D 8.955019E14 64.971870 93.79618 1.154570 0.007542 0.000203 6.00533270.036670 0377E 8.968036E14 51.298740 95.52244 1.136601 0.009552 0.000134 6.02038770.036593

Wtd. meana 6.01670.020 MSWDb 0.0416

FLV-SP-2 (feldspar) 95Z0379A 1.271735E13 11.174360 97.91142 1.121433 0.043849 0.000050 6.07367870.036321 0379B 1.353686E13 52.894800 97.07277 1.129513 0.009264 0.000073 6.06518270.036115 0379D 9.791298E14 4.028790 94.75075 1.149701 0.121615 0.000196 6.02650070.036966 0379E 1.442689E13 15.736310 95.30007 1.140575 0.031138 0.000149 6.01278670.035856 0379F 7.644462E14 6.544862 94.20603 1.152609 0.074864 0.000205 6.00674870.038010

Wtd. mean 6.03870.016 MSWD 0.6995

FLV-SP-3 (sanidine) 95Z0378A 4.818766E14 23.157930 90.53875 1.188674 0.021159 0.000345 5.96024070.040240 0378B 7.656705E14 38.243100 97.09329 1.118157 0.012813 0.000072 6.01241270.036966 0378C 5.295012E14 45.442560 93.29560 1.167320 0.010783 0.000227 6.03112070.039616 0378D 4.394757E14 23.955090 94.59723 1.142791 0.020455 0.000173 5.98692370.040997 0378E 3.102650E14 11.515970 89.54744 1.213736 0.042548 0.000400 6.01919570.046978 0378F 1.960826E14 16.907950 93.27762 1.175686 0.028980 0.000234 6.07315770.060391

Wtd. mean 6.00870.017 MSWD 0.6497

FLV-SP-4 (plagioclase) Sample contaminated. No consistent age

FLP-VH-2A (feldspar) 95Z0328A 9.502372E14 28.500930 97.15992 1.135570 0.017192 0.000073 5.99996670.042403 0328B 3.505418E14 2.117631 92.22448 1.199295 0.231254 0.000336 6.01554370.064808 0328C 8.035755E14 4.435558 95.31301 1.162007 0.110463 0.000173 6.02329470.046798 0328D 9.297103E14 6.163489 95.34561 1.161309 0.079496 0.000163 6.02180470.045499 0328E 4.511954E14 2.271120 94.07845 1.177136 0.215721 0.000252 6.02314570.056730 0328F 1.153767E13 6.198765 97.06635 1.134498 0.079044 0.000093 5.98878670.043821

Wtd. mean 6.01070.020 MSWD 0.0998

FLP-VH-2B (plagioclase) 95Z0401B 2.235235E14 1.598245 93.76148 1.166639 0.306522 0.000287 5.93162070.058680 0401C 4.510796E14 5.207570 96.53443 1.150042 0.094088 0.000119 6.01904670.046372 0401E 8.682740E15 2.855936 93.33331 1.189275 0.171552 0.000273 6.01837570.116891

Wtd. meana 5.98870.035 MSWDb 0.7194

FLV-VH-2C (feldspar) 95Z0402A 7.690362E14 11.379810 92.84109 1.200543 0.043057 0.000261 6.02448770.043422 0402C 2.595645E14 1.363012 95.46758 1.167358 0.359410 0.000234 6.02486070.055281 0402D 6.280161E14 35.607470 97.62488 1.144026 0.013761 0.000055 6.03656170.043979 0402E 1.085112E13 28.977220 95.87193 1.153992 0.016910 0.000125 5.97984270.042057 0402F 9.303207E14 25.522370 87.69598 1.272592 0.019199 0.000494 6.03208970.043399

Wtd. mean 6.01870.020 MSWD 0.2860

FLV-VH-2D (sanidine) 95Z0403C 7.658120E14 43.352340 67.85653 1.642607 0.011303 0.001749 5.99236370.046828 0403D 7.246506E14 43.278640 96.25919 1.167446 0.011322 0.000110 6.04140670.043394 0403E 7.656208E14 42.266230 97.63171 1.146151 0.011593 0.000054 6.01584170.042948 0403F 1.413477E13 43.670830 89.61595 1.244235 0.011220 0.000399 5.99467470.042258

Wtd. mean 6.01270.022 MSWD 0.2702 ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 255

Table 2 (continued )

Run # 40Ar* (mol) K/Ca 40Ar* (%) 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar Age (Ma)

FLV-VH-2E (sanidine) 95Z0407A 3.023324E13 34.868070 93.77476 1.187599 0.014053 0.000213 5.83636970.041187 0407B 6.823624E14 31.268080 93.71505 1.163129 0.015671 0.000210 5.71272070.054700 0407C 5.335132E14 0.635053 93.45483 1.168462 0.771185 0.000423 5.72583870.062667 0407D 1.657683E13 64.577790 97.44383 1.143986 0.007588 0.000060 5.84210870.043025 0407E 3.988721E13 35.334350 96.69168 1.154357 0.013867 0.000092 5.84956170.040628 0407F 7.304430E14 1.544504 94.32619 1.159050 0.317186 0.000266 5.73098070.053152

Wtd. meanc 5.80170.026 MSWD 1.7714

aWeighted mean. bMean square of weighted deviates. cForced.

Table 3 Concentrations of 42 trace elements measured by ICP/MS after microwave digestion

Element Kern River ash Bishop Tuff Friant tephra Fish Lake Valley tephra Lava Creek B tephra

Luck 218 695.50 Luck 218 6980 BT-11-D1 Friant-5A FLV-SP-3 JRK-DV5 JRK-DV57 ORNA 1 TECO 30A

Asa 3.49 4.78 4.87 3.78 5.50 2.84 1.68 1.46 1.84 Ba 14.80 24.03 4.79 105.10 7.37 170.01 115.12 155.72 105.42 Be 5.67 5.85 4.84 4.27 6.88 5.89 6.27 6.11 6.14 Bi 0.53 0.99 0.50 0.54 1.37 0.77 0.45 0.39 0.54 Cd 0.12 0.21 0.12 0.12 0.14 0.25 0.18 0.20 0.22 Ce 58.06 60.51 40.82 72.06 54.38 171.23 169.37 177.79 150.75 Co 0.26 0.35 0.13 0.30 0.21 0.55 0.27 0.25 0.30 Cs 4.23 5.13 5.08 4.33 6.06 3.64 3.41 3.30 3.63 Cu 25.95 22.55 2.94 40.00 16.06 31.81 16.71 6.07 5.44 Dy 2.73 2.86 4.09 3.21 2.42 13.38 14.29 14.43 13.12 Er 1.94 2.02 2.52 1.98 1.89 7.88 8.39 8.33 7.87 Eu 0.19 0.20 0.03 0.14 0.19 0.55 0.49 0.59 0.42 Ga 14.71 17.57 13.87 17.86 16.72 27.59 23.29 24.80 24.40 Gd 3.22 3.45 4.36 4.27 2.86 15.30 15.79 16.00 14.19 Hf 7.03 6.98 4.92 5.23 15.41 11.84 11.51 12.08 10.70 Ho 0.61 0.64 0.85 0.65 0.61 2.71 2.91 2.89 2.72 In 0.09 0.25 0.06 0.07 0.27 0.21 0.13 0.11 0.17 La 31.79 33.40 17.23 36.84 30.83 86.89 86.09 85.75 75.82 Li 2.71 3.36 37.24 36.66 15.25 24.39 14.87 50.24 34.20 Lu 0.38 0.38 0.41 0.31 0.47 1.06 1.13 1.13 1.06 Mn 463.24 552.51 260.78 252.86 544.91 306.11 262.97 280.73 276.00 Nd 17.95 18.46 17.29 23.77 15.39 70.38 67.93 72.01 60.54 Ni 9.90 9.04 7.83 10.95 7.59 18.27 15.46 16.10 15.10 Pb 41.10 36.67 29.52 36.68 37.52 32.91 31.31 32.35 35.53 Pd 3.38 3.38 2.24 3.19 3.13 7.35 6.73 7.22 6.33 Pr 5.71 5.99 4.77 7.35 5.14 18.88 18.70 19.44 16.78 Rb 158.39 187.83 156.94 147.57 203.57 195.29 178.06 176.62 187.55 Sb 0.77 0.76 1.21 1.20 1.09 0.32 0.34 0.28 0.33 Sc 68.48 80.76 55.95 47.46 86.17 60.57 57.78 58.24 61.20 Sm 3.00 3.10 3.96 3.97 2.45 13.24 13.46 14.02 12.26 Sn 5.00 4.86 5.18 4.90 7.82 9.63 9.98 8.95 9.95 Sr 9.09 16.06 4.19 19.32 5.93 10.16 6.51 7.37 5.69 Tb 0.46 0.47 0.66 0.55 0.44 2.28 2.37 2.36 2.16 Th 23.83 24.92 24.44 20.59 46.99 30.61 33.89 26.17 30.15 Tl 0.91 1.22 0.88 0.82 0.90 3.72 0.88 0.89 0.97 Tm 0.33 0.34 0.39 0.31 0.39 1.15 1.23 1.22 1.15 U 5.18 5.95 7.08 5.77 7.13 6.28 6.15 6.13 6.42 V 1.23 1.80 0.04 0.63 0.95 0.73 0.08 0.04 0.14 Y 17.52 18.00 22.82 17.54 16.66 68.61 74.01 71.96 68.43 Yb 2.29 2.36 2.68 2.06 2.50 7.25 7.76 7.67 7.20 Zn 47.31 60.06 31.75 43.69 44.09 136.96 86.40 87.19 91.03 Zr 1064.6 1230.9 790.7 989.6 1228.6 1580.3 1375.2 1465.3 1354.4

aAll concentrations are in ppm. ARTICLE IN PRESS 256 D. Baron et al. / Quaternary International 178 (2008) 246–260

Table 4 Similarity coefﬁcients calculated from normalized trace-element concentrations

Sample Kern River ash Bishop Tuff Fish Lake Valley Lava Creek B

Luck 218 695.50 Luck 218 6980 BT-11-D1 Friant-5A FLV-SP3 JRK-DV5 JRK-DV57 ORNA 1 TECO30A

Luck 218 695.50 — 0.86 0.70 0.78 0.80 0.49 0.51 0.49 0.51 Luck 218 6980 0.94 — 0.65 0.75 0.79 0.51 0.50 0.47 0.51 BT-11-D1 0.73 0.72 — 0.73 0.67 0.42 0.48 0.50 0.50 Friant-5A 0.83 0.83 0.74 — 0.69 0.51 0.52 0.51 0.54 FLV-SP-3 0.89 0.91 0.71 0.76 — 0.48 0.51 0.47 0.50 JRK-DV5 0.41 0.42 0.42 0.43 0.42 — 0.82 0.90 0.88 JRK-DV57 0.41 0.42 0.42 0.44 0.40 0.94 — 0.82 0.90 ORNA-1 0.40 0.41 0.41 0.43 0.39 0.95 0.97 — 0.87 TECO-30A 0.44 0.45 0.43 0.46 0.43 0.93 0.92 0.90 —

The coefﬁcients in the upper right part were calculated using all 42 elements measured by ICP/MS. Coefﬁcients listed in the lower left italicized part were calculated using 20 selected elements including all lanthanide elements. See text for complete list of selected elements.

(Lava Creek B samples ORNA-1 and JRK-DV57). similarity coefficients based on the subset of 20 elements The two samples of the KRA have a similarity coefficient are below 0.46. of 0.87. A dendrogram based on the hierarchical clustering The KRA samples correlate best with the Fish Lake analysis of the nine tephra samples based on concentra- Valley tephra layer from the Silver Peak/Volcano Hills tions of 42 elements is shown in Fig. 7. The dendrogram eruption (similarity coefficients 0.79 and 0.80) and to clearly groups the samples into three sets: (1) the four Lava somewhat lesser extent with the Friant tephra (0.75 and Creek B samples, (2) the Bishop Tuff sample and the Friant 0.78). The similarity coefficients of 0.65 and 0.70 between tephra, and (3) the KRA and the Fish Lake Valley tephra. the Bishop Tuff sample and the two KRA samples are The cophenetic correlation coefficient of 0.81 indicates a significantly lower. The similarity coefficients between the good solution. Bishop Tuff, and the Friant and Fish Lake Valley tephra Binary scatter plots of eight element combinations are layers are in a similar range (0.73–0.67). All the other shown in Fig. 8. In these binary plots, all the Lava Creek B similarity coefficients are below 0.55. samples consistently plot together. Similarly, the two KRA Similarity coefficients reported in the literature are always plot together. The KRA also always groups with commonly calculated excluding elements with concentra- the Fish Lake Valley tephra layer. The Friant tephra tions close to detection limits, and elements which are groups either with the Bishop Tuff sample or with the known to be problematic or of limited diagnostic value KRA samples. (e.g. Sarna-Wojcicki et al., 1984). This practice results in generally higher similarity coefficients. We therefore also 5. Discussion calculated similarity coefficients based on the 14 lanthanide elements (which can be measured very reliably by ICP/MS) 5.1. Correlation of the KRA and six other elements (Mn, Pb, Pd, Rb, Sc, Zr) which are relatively abundant or known to be useful for disti- Similarity coefficents based on major-element composi- nguishing tephras (Sarna-Wojcicki et al., 1984). Using this tion show that the KRA is geochemically similar to tephra subset of 20 elements results in higher similarity coefficients erupted from the Long Valley Caldera eruption. However, for related tephra and generally lower coefficients for the highest correlation is with the Fish Lake Valley tephra unrelated tephras (shaded, lower left part of Table 4). layers from the Silver Peak/Volcano Hills volcanic center in However, the overall groupings remain the same as when Nevada. In addition, the 40Ar/39Ar date of 6.1270.05 Ma using all 42 elements. The best correlation remains that for the KRA is consistent with the 6.070.2 Ma age of the between the four Lava Creek B samples (0.97–0.90). tephra layer from Fish Lake Valley known to have erupted The similarity coefficient between the two KRA samples from the Silver Peak/Volcano Hills complex. It is not is 0.94. The similarity coefficients between the KRA consistent with a correlation to the 0.75970.002 Ma samples and the Fish Lake Valley tephra (0.89 and 0.91) Bishop Tuff. The 6.070.2 Ma age of the Fish Lake Valley are only slightly lower than those between samples known tephra layer coincides with the caldera collapse and to be from the same eruption. Similarity coefficients rhyolite air fall tuff of Silver Peak/Volcano Hills volcanic between the KRA and the Bishop Tuff are significantly center (Robinson, 1972). lower at 0.72 and 0.73. Similarity coefficients between Similarity coefficents, hierarchical clustering, and binary Bishop Tuff, Friant tephra, and Fish Lake Valley tephra plots based on the ICP/MS analysis of 42 trace elements all remain in a similar range (0.76–0.71) and all other consistently show that the nine samples fall into three ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 257

450 C =0.813350

400

350

300

250

200

150 LUCK 218, 698.0 LUCK 218, 696.5 FLVSP3 FRIANT5A

100 TECO30A JRKDV57 JRKDV5 BT11D1 ORNA1

Group 3 Group 2 Group 1 Kern River Ash/ BishopTuff/ Lava Creek B Fish Lake Valley Friant Ash

Fig. 7. Dendrogram based on the hierarchical clustering analysis of the nine tephra samples based on concentrations of 42 elements. The dendrogram clearly groups the samples into three sets, first the four Lava Creek B samples, second the Bishop Tuff sample and the Friant tephra, and third the two Kern River ash samples and the Fish Lake Valley tephra from the Volcano Hills/Silver Peak eruptive center. The cophenetic correlation coefficient of 0.81 indicates a good solution. groups. Not surprisingly, the best-correlated group consists the definitive correlation of tephra layers, especially if there of the four samples from the 0.639 Ma Lava Creek B are several very similar candidate sources. In such cases, eruption. The second-best correlated group consists of the careful trace-element correlations, age dating, and exam- two KRA samples and the tephra from Fish Lake Valley ination of the stratigraphic context of the layers will all from the 6.070.2 Ma Silver Peak/Volcano Hills eruption. improve the correlation. In addition, similarity coefficients The Bishop Tuff sample from the 0.75970.002 Ma Long are not absolute, they depend on how many and which Valley Caldera eruption and the Friant tephra sample form elements are included in the statistical analysis. the third group. This last grouping is less consistent than the others. The Friant tephra sample is also quite similar to the 5.2. Implications for the stratigraphy and petroleum group-two samples as indicated by relatively high similarity exploration in the SSJV coefficients and some of the binary element scatter plots. Based on the radiometric dating, new major-element The new correlation of the KRA and the consequently correlations, and trace-element correlations reported here, much older upper age of the Kern River Formation open the KRA is the distal tephra layer erupted from the up interpretations for a significantly different origin and Volcano Hills/Silver Peak Range area of western Nevada, stratigraphic position of the Kern River Formation in the rather than the Bishop Tuff, as initially proposed by San Joaquin Valley. Although the uppermost part of the McGuire et al. (1989). The 6.1270.05 Ma age for the KRA Kern River Formation is yet undated, at least the lower and the 6.070.2 Ma age for the Volcano Hills/Silver Peak and middle part of the formation is Miocene to early eruptive center suggest that the upper age of the Kern Pliocene in age. Thus the purported glacio-fluvial origin for River Formation is over 5 Ma older than previously the Kern River Formation (Graham et al., 1988) is not thought. likely to be associated with Pleistocene glaciations in the This study demonstrates that correlations based on a Sierra Nevada. Pliocene (5.35–4.2 Ma) glacial deposits small number of major elements may not be sufficient for (ice-rafted debris and diamictites) have been found in the ARTICLE IN PRESS 258 D. Baron et al. / Quaternary International 178 (2008) 246–260

100 100 90 90 80 80 70 70 60 60 50 50 40 40 Sc (ppm) La (ppm) 30 30 20 20 10 10 0 0 020 40 60 80 100 120 140 160 180 0 5 10 15 20 25 30 Ba (ppm) Ga (ppm) 16 80 14 Lava Creek B 70 12 60 10 50 8 40 Fish Lake Valley/

6 Nd (ppm) Sm (ppm) Bishop Tuff Kern River Ash 30 4 20 2 10

0 0 0 100200 300 400 500 600 020 40 60 80 100120 140 160 180 200

Mn (ppm) Ce (ppm) 18 18 16 16 14 14 12 12 10 10 8 8 Gd (ppm) Gd (ppm) 6 6 4 4 2 2 0 0 0 100200 300 400 500 600 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Mn (ppm) Ho (ppm) 1800 1800 1600 1600 1400 1400 1200 1200 1000 1000 800 800 Zr (ppm) Zr (ppm) 600 600 400 400 200 200 0 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 02040 60 80 100 120 140 160 Lu (ppm) Zn (ppm)

Fig. 8. Binary scatter plots of eight element combinations from ICP/MS analysis. Kern River ash samples (K) Luck 218 695.50and (J) Luck 218 6980;(&) Bishop Tuff from the Long Valley Caldera (BT-11-D1); (E) Fish Lake Valley ash from the Volcano Hills/Silver Peak eruptive center FLV-SP-3; (D) Friant tephra (Friant-5A); and Lava Creek B samples from the Yellowstone Caldera complex ( ) JRK-DV5; (B) JRK-DV57, (+) ORNA-1, () TECO- 30A. The Lava Creek B samples consistently plot together. Similarly, the two Kern River ash samples always group Fish Lake Valley from the Volcano Hills/Silver Peak eruptive center. The Friant tephra groups primarily with the Bishop Tuff sample but also with the Kern River ash samples or all by itself. The circles mark the three groups; Kern River ash and Fish Lake Valley (solid), Bishop Tuff (dashed), and Lava Creek B (dotted). ARTICLE IN PRESS D. Baron et al. / Quaternary International 178 (2008) 246–260 259

Gulf of Alaska (Lagoe and Zellers, 1996) and similar provided by the CSU Bakersfield University Research deposits dated at 3.0–3.5 Ma have been found in the same Council. Anne Draucker and Cari Meyer (CSUB) helped region. The above ages for glaciation in the northeastern with the ICP/MS analyses. Hana Baker, and Victor Pusca Pacific region are consistent with the onset of glaciers (Chevron) helped with the statistical analyses. Elmira Wan throughout the northern hemisphere (Zachos et al., 2001). (USGS) prepared the ash samples for ICP/MS analysis. However, as a whole, the Pliocene was much warmer This paper was improved significantly by insightful and than the Pleistocene and glacial ice much less abundant in thorough reviews from Jeff Knott and another anonymous the Pliocene (Zachos et al., 2001). A glacial origin for the reviewer. middle of the Kern River Formation would thus require higher Pliocene elevations of the Sierra Nevada than we see References today. Unfortunately, paleorelief estimates for the Pliocene Sierra Nevada suggest comparable but somewhat lower Axelrod, D.I., 1997. Paleoelevation estimated from Tertiary floras. elevations than that of today (Unruh, 1991; Axelrod, 1997; International Geology Review 39, 1124–1133. Wakabayashi and Sawyer, 2001). Alternatively, the sedi- Bartow, J.A., 1991. The Cenozoic evolution of the San Joaquin Valley, California. US Geological Survey Professional Paper 1501, 40. ments analyzed by Graham et al. (1988) may, in fact, be Bartow, J.A., Pittman, G.M., Gardner, M., 1983. The Kern River Pleistocene in age and separated stratigraphically from the Formation, southeastern San Joaquin Valley, California. US Geolo- KRA by an unconformity within the middle Kern River gical Survey Bulletin 1529-D, 17. Formation that represents several millions of years. Bartow, J.A., McDougall, K., 1984. Tertiary stratigraphy of the south- A late Miocene age of the Kern River Formation is not eastern San Joaquin Valley, California, U. S. Geological Survey Bulletin 1529-J, 41. inconsistent with Bartow and McDougall (1984),whoplace Bowersox, J.R., 2003. Pliocene age of the Etchegoin Group, San Joaquin the deposition of the Kern River Formation over a time Basin, California. American Association of Petroleum Geologists interval between 8 and 1 Ma. However, the definitiveness of Search and Discovery Article #90014. the new KRA age raises questions regarding the relationship Dalrymple, G.B., 1989. The GLM continuous laser system for 40Ar/39Ar oftheKernRiverFormationtotheEtchegoinFormation. dating; description and characteristics. In: Shanks III W.C., Criss, R.E., (Eds.), New frontiers in stable Isotope Research: Laser Probes, Ion Previous regional correlations (Dunwoody, 1986) and field Probes, and Small-Sample Analysis. US Geological Survey Bulletin, Vol. studies (Park, 1965) note the marine Etchegoin Formation as 1890, pp. 89–96. Pliocene across the Fruitvale and Kern Front oil fields, an Davis, J., 1978. Quaternary tephrochronology of the Lake Lahontan area, age supported by the biostratigraphy reviewed in Bowersox Nevada and California. Nevada Survey, Archeological Research Paper (2003). With this interpretation and new ash age, the Kern no. 7, 137pp. Duffield, W.A., Dalrymple, G.B., 1990. The Taylor Creek Rhyolite of River Formation ash bed (and associated producing zones) New Mexico; a rapidly emplaced field of lava domes and flows. would have to be older than the Etchegoin and equivalent in Bulletin of Volcanology 52, 475–487. age to the sediments underlying the Etchegoin west of the Dunwoody, J.A., (Chair), 1986. Correlation section no. 8 (revised) across Kern Front oil field that are currently assigned to the Chanac southern San Joaquin Valley from San Andreas Fault to Sierra Formation. Nevada foothills. Pacific Section American Association of Petroleum Geologists. The new age also dramatically alters the stratigraphic Golob, E.M., 2005. Tephrochronology of four Neogene volcanic ash units relationship of the Kern River Formation with respect to from California and Nevada, U.S.A., using laser ablation ICP/MS: other formations in the San Joaquin Valley, particularly implications for petroleum-bearing formations in the San Joaquin those that are also oil-bearing (e.g. Monterey Formation, Valley, California. M.Sc. Thesis, California State University, Bakers- Belridge Diatomite, and the Reef Ridge Formation). This field, 79pp. Graham, S.A., Carroll, A.R., Miller, G.E., 1988. Kern River Formation as altered stratigraphic relationship could produce additional a recorder of uplift and glaciation of the southern Sierra Nevada. In: opportunities for the petroleum industry. As the strati- Graham, S.A., Olson, H.C., (Eds.), Studies of the Geology of the San graphy of the San Joaquin Valley is reinterpreted and Joaquin Basin; Vol. 60, Pacific Section Society for Sedimentary studied in cross-sectional format, sands that had previously Geology, pp. 311–319. correlated to non-productive formations may now corre- Hackel, O., 1965. Geology of southeastern San Joaquin Valley, California. Pacific Section American Association of Petroleum Geologists–Society late to the Kern River Formation, providing additional for Economic Geologists–Society for Sedimentary Geology Guide- opportunities for exploration in the San Joaquin Valley. book, 40pp. The KRA is a thick enough unit that it was likely also Hacker, B.R., Mosenfelder, J.L., Gnos, E., 1996. Rapid emplacement of deposited well beyond the locality of this study. Thus, the Oman ophiolite: Thermal and geochronological constraints. potential exists for finding this ash in cores in stratigraphic Tectonics 15, 1230–1247. Izett, G.A., Obradovich, J.D., Mehnert, H.H., 1988. The Bishop ash bed context farther west in the San Joaquin Valley, thereby (middle Pleistocene) and some older (Pliocence and Pleistocene) resolving the stratigraphic problems discussed in the chemically similar ash beds in California, Nevada, and Utah. US previous paragraphs. Geological Survey Bulletin 1675, 37. Izett, G.A., Obradovich, J.D., 1994. 40Ar/39Ar age constraints for the Acknowledgments Jaramillo Normal Subchron and the Matuyama-Brunhes geomagnetic boundary. Journal of Geophysical Research 99, 2925–2934. Knott, J.R., 1998. Late Cenozoic tephrochronology, stratigraphy, Larry Knauer (Chevron) arranged for funding for this geomorphology, and neotectonics of the western Black Mountains work from Texaco (now Chevron). Additional funding was Piedmont, Death Valley, California: Implications for the spatial and ARTICLE IN PRESS 260 D. Baron et al. / Quaternary International 178 (2008) 246–260

temporal evolution of the Death Valley fault zone. PhD Dissertation, Reid, S.A., Cox, B.F., 1989. Early Eocene uplift of the southernmost San University of California, Riverside, 407pp. Joaquin Basin, California. American Association of Petroleum Knott, J.R., Sarna-Wojcicki, A.M., Meyer, C.E., Tinsley III, J.C., Geologists Bulletin 73, 549. Wells, S.G., Wan, E., 1999. Late Cenozoic stratigraphy and Robinson, P.T., 1972. Petrology of the potassic Silver Peak volcanic center, tephrochronology of the western Black Mountain Piedmont, Death western Nevada. Geological Society of America Bulletin 83, 1693–1708. Valley, California: implications for the tectonic development of Death Samson, S.D., Alexander, E.C., 1987. Calibration of the interlaboratory Valley. In: Wright, L.A., Troxel, B.W. (Eds.), Cenozoic basins of the 40Ar/39Ar dating standard, MMhb-1. Chemical Geology (Isotope Death Valley Region, Geological Society of America Special Paper Geoscience Section) 66, 27–34. 333. Boulder, CO, pp. 345–366. Sarna-Wojcicki, A.M., Bowman, H.R., Meyer, C.E., Russell, P.C., Kuespert, J.G., 1990. Kern River Formation along Alfred Harrell Woodward, M.J., McCoy, G., Rowe Jr., J.J., Baedecker, P.A., Highway, eastern Kern County. In: Kuespert, J.G., Reid, S.A. Asaro, F., Michael, H., 1984. Chemical analyses, correlations, and ages (Eds.), Structure, Stratigraphy and Hydrocarbon Occurrences of the of upper Pliocene and Pleistocene ash layers of east-central and southern San Joaquin Basin, California, Vol. 64. Pacific Section Society for California. US Geological Survey Professional Paper 1293, 40. Sedimentary Geology, pp. 293–300. Sarna-Wojcicki, A.M., Morrison, S.D., Meyer, C.E., Hillhouse, J.W., Kuespert, J.G., Sanford, S.J., 1990. Kern River Field history and geology. 1987. Correlation of upper Cenozoic tephra layers between sediments In: Kuespert, J.G., Reid, S.A. (Eds.), Structure, Stratigraphy and of the western United States and eastern Pacific Ocean and comparison Hydrocarbon Occurrences of the San Joaquin Basin, California, Vol. with biostratigraphic and magnetostratigraphic data. Geological 64. Pacific Section Society for Sedimentary Geology, pp. 55–58. Society of America Bulletin 98, 207–223. Lagoe, M.B., Zellers, S.D., 1996. Depositional and microfaunal response Sarna-Wojcicki, A.M., Pringle Jr., M.S., Wijbrans, J., 2000. New to Pliocene climate change and tectonics in the eastern Gulf of Alaska. 40Ar/39Ar age of the Bishop Tuff from multiple sites and sediment Marine Micropaleontology 27, 1–4. rate calibration for the Matuyama–Brunhes boundary. Journal of Lanphere, M.A., Champion, D.E., Christiansen, R.L., Izett, G.A., Geophysical Research 105 (B9), 431–443. Obradovich, J.D., 2002. Revised ages for tuffs of Yellowstone plateau Sarna-Wojcicki, A.M., Reheis, M.C., Pringle, M.S., Fleck, R.J., Burbank, D., volcanic field: assignment of the Huckleberry Ridge Tuff to a new Meyer,C.E.,Slate,J.L.,Wan,E.,Budahn,J.R.,Troxel,B.,Walker,J.P., geomagnetic polarity event. Geological Society of America Bulletin 2005. Tephra layers of Blind Spring Valley and related upper Pliocene and 114, 559–568. Pleistocene tephra layers, California, Nevada, and Utah: isotopic ages, Lindsay, E.H., Johnson, N.M., Opdyke, N.D., Butler, R.F., 1987. correlation, and magnetostratigraphy. US Geological Survey Professional Mammalian chronology and the magnetic polarity time scale. In: Paper 1701, 69. Woodburne, M.O., (Ed.), Cenozoic Mammals of North America: Savage, D.E., Downs, T. and Poe, O.J., 1954. Cenozoic landlife of southern Geochronology and biostratigraphy. pp. 269–284. California. In: Jahns, R.H. (Ed.), Geology of Southern California, McGuire, M.D., Cullip, R.J., Huggins, C.A., 1989. Pleistocene volcanic California Division of Mines and Geology Bulletin, vol. 170, pp. 43–58. ash layers in Kern River oil field. American Association of Petroleum Steiger, R.H., Jager, E., 1977. Subcommission on geochronology; Geologists Bulletin 73, 545. convention on the use of decay constants in geo- and cosmochronol- Miller, G.E., 1986. Sedimentology, depositional environment, and ogy. Earth and Planetary Science Letters 36, 359–362. reservoir characteristics of the Kern River Formation, southeastern Tedford, R.H., Galusha, T., Skinner, M.F., Taylor, B.E., Fields, R.W., San Joaquin Basin. M.Sc. Thesis, Stanford University, 80pp. Macdonald, J.R., Rensberger, J.M., Webb, S.D., and Whisler, D.P., Miller, D., Negrini, R., McGuire, M., Huggins, C., Minner, M., Hacker, B., 1987. Faunal succession and biochronology of the Arikareean through Sarna-Wojcicki, A., Meyer, C., Fleck, R., Reid, S., 1998. New upper age Hemphillian interval (late Oligocene through earliest Pliocene epochs) constraint on the Kern River Formation. In: Reid, S.A., (Ed.), Outcrops in North America. In: Woodburne, M.O. (Ed.), Cenozoic Mammals of of the Eastern San Joaquin Basin, Guidebook for the San Joaquin North America: Geochronology and Biostratigraphy. pp. 153–210. Geological Society Fall 1998 Field Trip. pp. 23-32. Unruh, J.R., 1991. The uplift of the Sierra Nevada and implications for Nicholson, G., 1980. Geology of the Kern River oil field. In: Kern River Late Cenozoic epeirogeny in the western Cordillera. Geological Oil Field Fieldtrip Guidebook. Pacific Section American Association Society America Bulletin 103, 1395–1404. of Petroleum Geologists–Society for Economic Geologists–Society for US Environmental Protection Agency, Office of Solid Waste, 1996. SW- Sedimentary Geology Guidebook, pp. 7–17. 846 test methods for evaluating solid waste, physical/chemical Olson, H.C., Miller, G.E., and Bartow, J.A., 1986. Stratigraphy, methods, method 3052—Microwave-assisted acid digestion of siliceous paleoenvironment and depositional setting of Tertiary sediments, and organically based matrices. US Environmental Protection Agency southeastern San Joaquin Basin. In: Southeast San Joaquin Valley website, SW-846 on-line 3000 series methods, /www.epa.gov/ Field Trip, Kern County, California Part II: Structure and Strati- epaoswer/hazwaste/test/3_series.htmS (accessed November 30, 2006). graphy, Pacific Section American Association of Petroleum Geologists Wakabayashi, J., Sawyer, T.L., 2001. Stream incision, tectonics, uplift, and San Joaquin Geological Society Guidebook. pp. 18–46. and evolution of topography of the Sierra Nevada, California. Journal Park, W.H., 1965. Kern Front oil field. California Division of Oil and Gas of Geology 109, 539–562. Summary of Operations 51 (1), 13–22. York, D., Hall, C.M., Yanase, Y., Hanes, J.A., Kenyon, W.J., 1981. Reheis, M., Sarna-Wojcicki, A.M., Reynolds, R., Repenning, C., Mifflin, M., 40Ar/39Ar dating of terrestrial minerals with a continuous laser. 2002. Pliocene to middle Pleistocene lakes in the western Great Basin: Geophysical Research Letters 8, 1136–1138. Ages and connections. In: Hershler, R., Currey, D., Madsen, D. (Eds.), Zachos, J., Pagani, M., Sloan, L., Thomas, E., Billups, K., 2001. Trends, Great Basin aquatic systems history. Smithsonian Institution, Washing- rhythms, and aberrations in global climate 65 Ma to present. Science ton, DC, pp. 53–108. 292, 686–693.