Downloaded from specialpapers.gsapubs.org on July 1, 2015 The Geological Society of America Special Paper 439 2008 Late Quaternary MIS 6–8 shoreline features of pluvial Owens Lake, Owens Valley, eastern California A.S. Jayko* U.S. Geological Survey, U.C. White Mountain Research Station, Bishop, California 93514, USA S.N. Bacon* Desert Research Institute, Division of Earth and Ecosystem Sciences, Reno, Nevada 89521, USA ABSTRACT The chronologic history of pluvial Owens Lake along the eastern Sierra Nevada in Owens Valley, California, has previously been reported for the interval of time from ca. 25 calibrated ka to the present. However, the age, distribution, and paleoclimatic context of higher-elevation shoreline features have not been formally documented. We describe the location and characteristics of wave-formed erosional and depositional features, as well as fluvial strath terraces that grade into an older shoreline of pluvial Owens Lake. These pluvial-lacustrine features are described between the Olancha area to the south and Poverty Hills area to the north, and they appear to be vertically deformed ϳ20 Ϯ 4 m across the active oblique-dextral Owens Valley fault zone. They occur at elevations from 1176 to 1182 m along the lower flanks of the Inyo Mountains and Coso Range east of the fault zone to as high as ϳ1204 m west of the fault zone. This relict shoreline, referred to as the 1180 m shoreline, lies ϳ20–40 m higher than the previously documented Last Glacial Maximum shoreline at ϳ1160 m, which occu- pied the valley during marine isotope stage 2 (MIS 2). Crosscutting relations of wave-formed platforms, notches, and sandy beach de- posits, as well as strath terraces on lava flows of the Big Pine volcanic field, bracket the age of the 1180 m shoreline to the time interval between ca. 340 Ϯ 60 ka and ca. 130 Ϯ 50 ka. This interval includes marine oxygen isotope stages 8–6 (MIS 8–6), corresponding to 260–240 ka and 185–130 ka, respectively. An additional age esti- mate for this shoreline is provided by a cosmogenic 36Cl model age of ca. 160 Ϯ 32 ka on reefal tufa at ϳ1170 m elevation from the southeastern margin of the valley. This 36Cl model age corroborates the constraining ages based on dated lava flows and re- fines the lake age to the MIS 6 interval. Documentation of this larger pluvial Owens Lake offers insight to the hydrologic balance along the east side of the southern Sierra Nevada and will assist with future regional paleoclimatic models within the western Basin and Range. Keywords: pluvial Owens Lake, Owens River system, deformed shorelines, marine isotope stage 6, MIS 6, Pleistocene lake, Great Basin, Owens Valley. *E-mail: Jayko: [email protected]; Bacon: [email protected]. Jayko, A.S., and Bacon, S.N., 2008, Late Quaternary MIS 6–8 shoreline features of pluvial Owens Lake, Owens Valley, eastern California, in Reheis, M.C., Hershler, R., and Miller, D.M., eds., Late Cenozoic Drainage History of the Southwestern Great Basin and Lower Colorado River Region: Geologic and Biotic Perspectives: Geological Society of America Special Paper 439, p. 185–206, doi: 10.1130/2008.2439(08). For permission to copy, contact [email protected]. ©2008 The Geo- logical Society of America. All rights reserved. 185 Downloaded from specialpapers.gsapubs.org on July 1, 2015 186 Jayko and Bacon INTRODUCTION The graben floor is underlain by at least four fault-bound struc- tural blocks with late Quaternary and/or Holocene displacement. Owens Valley is part of the Owens River system, which, dur- The valley is asymmetric from west to east due in part to rela- ing wet periods of the Pleistocene, extended from Mono Basin in tive uplift of a horst block that lies west of the Owens Valley fault the north to Death Valley in the southeast (Gale, 1914; Black- zone and east of the Sierra Nevada frontal faults, and in part to the welder, 1933; Smith et al., 1983; Jannik et al., 1991). Throughout deposition of large, late Quaternary alluvial fans along the west- Holocene time, the watershed has been hydrologically connected ern margin of the valley. The location of the Owens River mean- along only a third of its length—from Long Valley to Owens Lake der belt reflects the position of the distal margins of these fans, (Fig. 1). The lower-elevation basins, including Indian Wells, Sear- which have deflected the river eastward toward the base of the les, Panamint, and Death Valleys, have unique lacustrine histories Inyo Mountains (Fig. 1). that are a consequence of the magnitude of glacial-pluvial events, During much of the middle and late Quaternary, a freshwater which in part control the available water in the Owens River sur- lake occupied Owens Valley (Gale, 1914; Smith and Bischoff, face and groundwater systems. So, from an evolutionary perspec- 1997). The current spillway or sill in Owens Valley at ϳ1145 m tive, the duration and times of climate-controlled hydrologic north of Haiwee Reservoir (Gale, 1914) likely last overflowed ca. connectivity of the basins and their respective geochemistries 15.5 cal ka (Bacon et al., 2006) (Fig. 1). However, the sill dropped have affected the distribution of various aquatic species (Hubbs to that elevation during the late LGM following an event that and Miller, 1948; Miller, 1948; Firby et al., 1997; Reheis, 1999; eroded the berm, which confined the early LGM highstand at Reheis et al., 2002a, 2002b). ϳ1160 m.The location of the former 1180 m spillway is unknown. In this study, we report the first age constraints and basin- It may be eroded from the Haiwee area at the southernmost part of wide documentation of shoreline features and fluvial strath ter- Owens Valley, or it may lie further to the south at the southern end races of a pluvial Owens Lake at elevations between ϳ1180 and of Rose Valley, where erosional fluvial terraces formed in late 1200 m, collectively referred to as the 1180 m shoreline. The Quaternary (ca. 440–130 ka) basalt flows were noted by Duffield 1180 m shoreline is distinct from, and considerably older than, and Smith (1978a, 1978b). Although an effort was made to estab- the Last Glacial Maximum (LGM) ca. 25 calibrated (cal) 14Cka lish the location of this feature, it remains problematic. highstand at ϳ1160 m elevation, and it is also separate from the younger, lower-elevation shorelines (Carver, 1970; Beanland Methods and Clark, 1994; Bacon et al., 2006; Orme and Orme, this vol- ume). Beanland and Clark’s (1994) paleoseismic study of the Documentation of the 1180 m shoreline is based primarily on OwensValleyfault zone noted the presence of an ϳ1183 m strand- field observations, crosscutting relations with dated volcanic line along the northwest flank of the Coso Range. Other benches rocks, and a cosmogenic 36Cl erosion age on tufa provided by and notches southeast of Olancha at approximately the same Fred Phillips (New Mexico Tech, 2007, personal commun.). The elevation were also considered to be possible wave-formed plat- spatial distribution of constructional and erosional lacustrine land- forms or river terraces (Beanland and Clark, 1994, their strand- forms and erosional fluvial features associated with the 1180 m line A; sites 1–3 herein; Fig. 1). However, they were uncertain shoreline are described here. A description of each location is whether these sites represented offset from the ϳ1160 m LGM included in Table 1. Elevations estimated by global positioning strandline or if they were older, and so they reported them as system (GPS) were cross-checked with 1:24,000 topographic “Ͼ25 ka (?)” (Beanland and Clark, 1994, p. 6). quadrangle maps and 30 m digital elevation models (DEMs). A tufa sample was analyzed for 36Cl by standard procedures Tectonic Setting (Zreda, 1994), employing addition of a 35Cl spike and dissolu- tion of the carbonate sample in only nitric acid (F.M. Phillips, Owens Valley lies adjacent to the southern part of the Sierra 2007, personal commun.). Field and analytical results are given Nevada in eastern California (Fig. 1), and it is a 15–40-km-wide, in Table 2. The sample age was calculated using the spreadsheet 200-km-long complex graben shaped by active transtensional program CHLOE (Phillips and Plummer, 1996) using the 36Cl tectonism (e.g., Beanland and Clark, 1994; Savage and Lisowski, production parameters of Phillips et al. (2001) and the elevation- 1995; Reheis and Dixon, 1996). The structural setting is impor- latitude scaling of Lal (1991). No correction for secular variation tant because of the high potential for deformation of shorelines of Earth’s magnetic field was applied. The production parameteri- and spillway elevations by active tectonic processes. The valley zation of Phillips et al. (1990) was largely calibrated using samples is bounded by the Sierra Nevada frontal faults on the west and the from the same region, as well as using the same elevation-latitude White and Inyo Mountains fault zones on the east (e.g., Pakiser scaling; thus, the age calculation should be relatively robust. The et al., 1964; Bryant, 1984; Bacon et al., 2005; Slemmons et al., age was calculated assuming that the dissolved material was only 2008). The valley floor is split longitudinally by the active, oblique- CaCO3 (i.e., 56 wt% CaO and 44 wt% CO2), given that dissolu- dextral Owens Valley fault zone, which last ruptured along an tion was only in nitric acid, and thus 36Cl should not have been ϳ120 km segment with a M 7.5–7.7 earthquake in A.D. 1872 liberated from phases other than carbonate minerals (Phillips, (e.g., Beanland and Clark, 1994; Slemmons et al., 2008) (Fig.