ABSTRACT The Searles Lake Formation in Searles Valley, southeastern California, represents deposition of the paleo–Owens River into a Pleistocene and Holocene pluvial terminal lake. A prior 32–10 ka estimated age for the upper part of the Searles Lake Formation relied on uncalibrated, conventional radiocarbon dates. We present accelerator mass spectrometer radiocarbon dates that indicate the base of the Searles Lake Formation at the Poison Canyon type section is 46 ka. That age is consistent with paleomagnetic data at Poison Canyon and the Tire Farm locality, which record high-latitude Southern Hemisphere virtual geomagnetic poles that we assign to the 41 ka Laschamp excursion. The presence of Searles Lake at 46–43 ka also is consistent with a Pacific storm track that extended south of 37.5°N at that time. At the head of Salt Wells Valley–Poison Canyon, sediments that we interpret as a Searles Lake highstand were radiocarbon dated at 14.1 ka.

Abstract Cored slope sediment from the Salerno Gulf in the eastern Tyrrhenian Sea ca. 20 km from the Italian coast preserves small-scale changes of Earth’s magnetic field behavior (paleomagnetic secular variation; PSV) between 25,000 years B.P. to the present. The age of the cored sediment is calculated from tephrochronology, 14 C dates, and correlation to European PSV curves ( Turner and Thompson, 1981 , 1982 ; Thouveny et al., 1990 ) and relative intensity in sediment cored from the Mediterranean Sea ( Tric et al., 1992 ). The analyzed sediments span for the first time the full Holocene and late Pleistocene PSV record in the eastern Tyrrhenian Sea, and results compare well with PSV records for Lac du Bouchet, France ( Thouveny et al., 1990 ). Sedimentation rates, established by PSV dating, are in good overall agreement with sedimentation rates calculated in a second core recovered about 300 m away that was dated by 14 C and used for paleoclimate research ( Buccheri et al., 2002 ). However, there are variations in the precision of the dating that depend on the chronologic method used. Moreover, it was found that in the late Pleistocene and to the Pleistocene–Holocene boundary, the sedimentation rate on the continental slope was controlled by global rapid sea-level pulses and cold climatic phases that induced reduction and/or rapid increments in the sediment deposition rate. However, in the middle Holocene during phases of continuous relative sea-level increase, the sedimentation rate on the slope was less sensitive to climatic control than on the continental shelf, whereas from the late Holocene to the present it seems that on both the continental shelf and slope local factors such as volcanic supply and human deforestation could have caused an increase in the sedimentation rate.

During glacial (pluvial) climatic periods, Death Valley is hypothesized to have episodically been the terminus for the Amargosa, Owens, and Mojave Rivers. Geological and biological studies have tended to support this hypothesis and a hydrological link that included the Colorado River, allowing dispersal of pupfish throughout southeastern California and western Nevada. Recent mitochondrial deoxyribonucleic acid (mtDNA) studies show a common pupfish (Cyprinodontidae) ancestry in this region with divergence beginning 3–2 Ma. We present tephrochronologic and paleomagnetic data in the context of testing the paleohydrologic connections with respect to the common collection point of the Amargosa, Owens, and Mojave Rivers in Death Valley during successive time periods: (1) the late Pliocene to early Pleistocene (3–2 Ma), (2) early to middle Pleistocene (1.2–0.5 Ma), and (3) middle to late Pleistocene (<0.7–0.03 Ma; paleolakes Manly and Mojave). Using the 3.35 Ma Zabriskie Wash tuff and 3.28 Ma Nomlaki Tuff Member of the Tuscan and Tehama Formations, which are prominent marker beds in the region, we conclude that at 3–2 Ma, a narrow lake occupied the ancient Furnace Creek Basin and that Death Valley was not hydrologically connected with the Amargosa or Mojave Rivers. A paucity of data for Panamint Valley does not allow us to evaluate an Owens River connection to Death Valley ca. 3–2 Ma. Studies by others have shown that Death Valley was not hydrologically linked to the Amargosa, Owens, or Mojave Rivers from 1.2 to 0.5 Ma. We found no evidence that Lake Manly flooded back up the Mojave River to pluvial Lake Mojave between 0.18 and 0.12 Ma, although surface water flowed from the Amargosa and Owens Rivers to Death Valley at this time. There is also no evidence for a connection of the Owens, Amargosa, or Mojave Rivers to the Colorado River in the last 3–2 m.y. Therefore, the hypothesis that pupfish dispersed or were isolated in basins throughout southeastern California and western Nevada by such a connection is not supported. Beyond the biologically predicted time frame, however, sparse and disputed data suggest that a fluvial system connected Panamint (Owens River), Death, and Amargosa Valleys, which could account for the dispersal and isolation before 3 Ma.

Abstract A wide variety of dating methods are used in Quaternary research, and each method has many applications and limitations. Because of this variety, we cannot discuss the applications and limitations of all methods here. The more versatile and widely used methods, including 14 C, K/Ar, fission-track, U-series, paleomagnetism, thermoluminescence, and amino acid dating are treated more comprehensively in this chapter than other methods that are shown on the summary chart. The summary chart is provided here to give an overview of dating work and research for the Quaternary. This summary consists mainly of a table (Plate 2) that is modified and updated from Colman and Pierce (1977, Plate 1, ref. 66). The table is intended as an overview and concise guide to Quaternary dating methods. It contains many subjective judgments and should not be considered definitive; the entries for applicability, age range, and optimum resolution are particularly interpretive. Details concerning assumptions, analytical techniques, uncertainties, and interpretations should be obtained from specialized references using the key references in Plate 2 as a guide. The dating methods described range from well-known and established techniques to experimental procedures whose results are subject to considerable interpretation. Key references included on Plate 2 are intended as an entry into the vast literature on dating methods; space prohibits a more complete listing. We have emphasized recent review papers and notable examples of applications as sources of additional references and information. Dating methods discussed in other sections of this chapter are indicated by asterisks in.