T17 Where Does the Wind Blow? Aeolian Systems in Time and Space I

Sunday, 4 November 2018
8:00 AM - 12:00 PM
Room 138-139

PALEOCLIMATIC VARIATION REVEALED BY ROCK MAGNETIC DATA FROM PLIO-PLEISTOCENE SEDIMENTS OF THE FISHER VALLEY BASIN, UTAH: A HIGH-FIDELITY RECORD OF PALEOCLIMATE CONDITIONS FOR THE COLORADO PLATEAU?

Paper number: T17-14
Program: Technical Sessions
Time: 11:25 AM – 11:40 AM

Authors

Abstract

The climatic conditions of the Colorado Plateau during the latest Cenozoic are poorly understood due to the paucity of preserved sedimentary sequences from this time period. A notable exception in terms of preservation is the ~150 m thick Pliocene-Pleistocene sequence exposed in the Fisher Valley Basin (FVB), near Moab, Utah. These deposits, which were sourced from nearby exposures of Paleozoic and Mesozoic red beds, were deposited in accommodation space associated with the Plio-Pleistocene rise of the Onion Creek salt diaper and display repeating cycles of fine to coarse gavel, eolian sand, and paleosols within the section. Magnetic susceptibility (χ) data from the entire section (sampling at 25 cm intervals) (mean: 1.88E-04, median: 1.55E-04, and mode: 1.42E-04 SI Vol) demonstrate a noticeable cyclicity that we tentatively interpret to represent Milankovitch cycles. The Bishop ash deposit (ca. 0.73 Ma) is exposed in the section and essentially defines the boundary above which χ values display a noticeable increase in intensity as well as amplitude of fluctuation. This change in overall rock magnetic characteristics is interpreted to be associated with the Mid-Pleistocene transition (MPT) interval, where Earth’s climate cycles shifted from a 41-ka to a dominant 100-ka periodicity. Rock magnetic analyses (magnetic hysteresis and magnetic susceptibility as a function of temperature) show that the mineralogy is primarily made up of high coercivity magnetic phases such as hematite or goethite. Magnetic susceptibility as a function of temperature (χ vs T) experiments reveal Neel temperatures close to about 680°C, confirming that the magnetic signal is primarily carried by hematite with a small concentration of magnetite. This agrees with previous studies done by Colman (1988) who identified that the primary magnetic carrier was detrital hematite sourced from the nearby Pre-Cenozoic red beds.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321592

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