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Jeffrey P. Fitts

Publications and source records attributed to Jeffrey P. Fitts.

3 recordsLinked to original sources
USGS2017

Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na2O, TiO2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO3 and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the ??18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation. ?? 1997 University of Washington.

Quaternary Research↗
USGS1997

Responses of sediment geochemistry to climate change in Owens Lake sediment: An 800-k.y. record of saline/fresh cycles in core OL-92

Geochemical parameters of sediments from drill hole OL-92 indicate that Owens Lake was saline, alkaline, and highly productive during interglacial periods, and was hydrologically open and relatively unproductive during glacial periods. Abundance of CaCO 3 , organic carbon, and cation-exchange capacity of the clay fraction show cyclic variation down the core. Six minima in these components during the past 500 k.y. are interpreted as caused by intensive overflow that occurred during Sierran glacial advances. Maxima in these components indicate closed-lake conditions, reflecting warmer and more arid interglacial climates. The pattern of CaCO 3 abundance suggests that closed lake conditions predominated over the past 500 k.y. The absence of gaylussite and gypsum in the sediments, however, indicates lake salinity never exceeded about 15 wt %, a limit which requires flushing of accumulated salts every 10 k.y. Oscillations of CaCO 3 generally indicate a 100-k.y. dominant cycle, a characteristic of the marine δ 18 O record. Four of the last five marine isotope terminations are clearly shown in the Owens Lake record. The last interglacial at Owens Lake appears to have occurred between 120 ka and 50 ka. The roughly 10-k.y. offset between this interval and marine oxygen-isotope stage 5 reflects either error in the age-depth model, or alternatively, a time lag between changes in Northern Hemisphere ice volumes and the manifestation of local climate change in lake geochemistry and sedimentology.

California↗