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.

A ~220,000-year record recovered in a 120-m-long sediment core from Bear Lake, Utah and Idaho, provides an opportunity to reconstruct climate change in the Great Basin and compare it with global climate records. Paleomagnetic data exhibit a geomagnetic feature that possibly occurred during the Laschamp excursion (ca. 40 ka). Although the feature does not exhibit excursional behavior (≥40° departure from the expected value), it might provide an additional age constraint for the sequence. Temporal changes in salinity, which are likely related to changes in freshwater input (mainly through the Bear River) or evaporation, are indicated by variations in mineral magnetic properties. These changes are represented by intervals with preserved detrital Fe-oxide minerals and with varying degrees of diagenetic alteration, including sulfidization. On the basis of these changes, the Bear Lake sequence is divided into seven mineral magnetic zones. The differing magnetic mineralogies among these zones reflect changes in deposition, preservation, and formation of magnetic phases related to factors such as lake level, river input, and water chemistry. The occurrence of greigite and pyrite in the lake sediments corresponds to periods of higher salinity. Pyrite is most abundant in intervals of highest salinity, suggesting that the extent of sulfidization is limited by the availability of SO 4 2‒ . During MIS 2 (zone II), Bear Lake transgressed to capture the Bear River, resulting in deposition of glacially derived hematite-rich detritus from the Uinta Mountains. Millennial-scale variations in the hematite content of Bear Lake sediments during the last glacial maximum (zone II) resemble Dansgaard-Oeschger (D-O) oscillations and Heinrich events (within dating uncertainties), suggesting that the influence of millennial-scale climate oscillations can extend beyond the North Atlantic and influence climate of the Great Basin. The magnetic mineralogy of zones IV–VII (MIS 5, 6, and 7) indicates varying degrees of post-depositional alteration between cold and warm substages, with greigite forming in fresher conditions and pyrite in the more saline conditions.

Abstract We have studied the rock magnetic and palaeomagnetic properties of a 41 m long core (Hole M0058A) recovering calcareous sediments located seaward of Noggin Reef, offshore Queensland, Australia to decipher the magnetostratigrapy of the site. We deployed 1 cm 3 samples at every 10 cm down-core and subsampled the core by means of U-channels in order to obtain a continuous record. Stepwise alternating field demagnetization from natural remanent magnetization to 80 mT showed that the characteristic remanent magnetization was isolated at low demagnetization fields between 0 and 15 mT. We conducted magnetic granulometry analyses and Curie point determinations. The low-field v. temperature analyses indicate the presence of Ti-poor magnetite with Curie points from 560 to 563 °C. Hysteresis loop experiments were performed. The results show M rs / M s and H cr / H c ratios corresponding to single domain to multi-domain and super-paramagnetic to single domain ranges. Both discrete and continuous inclination results indicate a remarkable correlation of three excursional inclinations occurring during intervals of low intensity of magnetization closely corresponding to the Laschamp ( c. 41 ka), Skálamælifell ( c. 94 ka) and Blake ( c. 115–120 ka) ‘aborted reversals,’ and indicate that the base of the core is much older than the Blake excursion.