The Fisher Valley basin (FVB), located adjacent to the Onion Creek salt diapir, Paradox basin, Utah, USA, constitutes one of the thickest collections of Quaternary sediments within the Colorado Plateau. These sediments are important for constraining regional paleoclimate environments as well as recent tectonic movement of the Onion Creek salt diapir. Here, we combine magnetic susceptibility data with previously published age constraints (Bishop Tuff and Lava Creek B ash) into a cyclostratigraphic analysis of these sediments. We present a refined and astronomically tuned age model that demonstrates that deposition of the upper basin fill was between ca. 765 ka and 212 ± 8 ka. Correlating this chronologic model to environmental magnetic proxies, we show that from ca. 765 ka to ca. 535 ka, magnetic mineral assemblages deposited during glacials were characterized by generally finer grain sizes (elevated χARM/χlow) than during interglacials. These data are consistent with glacial periods being characterized by either wetter conditions amenable to pedogenesis, or drier conditions associated with increased concentrations of windblown dust. Interglacials are characterized by generally coarser magnetic grain sizes (lower χARM/χlow), consistent with periods of episodic alluvial and colluvial deposition in the FVB.
At ca. 535 ka, χARM/χlow reach their lowest value (coarsest magnetic grain size) and then begin a progressive transition to higher values, consistent with a generally fining upward stratigraphic sequence throughout the rest of the section. This transition at ca. 535 ka coincides with a peak in sediment accumulation rate of ∼19 cm/k.y. and is most plausibly linked to halokinetic activity of the nearby Onion Creek salt diapir. Thus, although sediments in the FVB appear to be sensitive to global climate patterns between 765 ka and ca. 535 ka, local tectonic processes appear to episodically obscure this sensitivity.
