Dating Rock Varnishes by the Cation Ratio Method With Pixe, Icp, and the Electron Microprobe

Abstract

The measurement of rock varnish cation-ratios [(K+Ca)/Ti] and barium is evaluated by analyzing the same varnish scrapings with PIXE, inductively coupled plasma, neutron activation and wavelength dispersive electron microprobe. Results among these different methods are generally similar for ratios, but absolute concentrations differ in part due to uncertainties associated with weighing small samples. Barium concentrations are typically less than 1 % by weight; higher concentrations can be found in varnishes with depressions eroded into the varnish by fungi and lichens, and later infilled with aeolian detritus often including barium sulfate. Since these infilled hollows are known to produce anomalous varnish cation ratios, high barium values can, therefore, be used as an indicator that a sample is inappropriate for cation-ratio dating. The glacial chronology at Pine Creek, California, is revised in light of new data and a better understanding of variables influencing varnish chemistry.

Rock varnish in New York: An accelerated snapshot of accretionary processes

“…New York varnishes display the same sub-micron cross-sectional texture of layering imposed by clay minerals, contain clay minerals as seen in HRTEM imagery, and host a variety of microbial forms that are enhanced in Mn in in situ EDS observations. There are dozens of elements enhanced in arid varnish over background values (Bard et al, 1978;Dorn et al, 1990;Lakin et al, 1963;Nowinski et al, 2010), including the zinc and barium observed here. However, rhenium enhancement has not been observed previously in arid varnishes.…”

“…While Mn and Ba often display a spatial autocorrelation at the micron scale, this is not always the case. In other varnishes collected from arid regions, barium does not appear to be correlated with Mn (Dorn, 2007;Dorn et al, 1990;Krinsley et al, 1990).…”

Geomorphological analysis of neotectonic deformation, northern Owens Valley, California

“…The network was active when the Q 3 surface was active, but not afterwards. The glacial deposits of the northern Owens Valley generally consist of three major post-Bishop Tuff moraine systems, recording extensive glaciation within the last 200 ka (Gillespie, 1988;Dorn et. al., 1990;Phillips et al, 1990).…”

Soil Development on Late Pleistocene Moraines at Pine Creek, East-Central Sierra Nevada, California

“…Only accurate field mapping and (Sharp and Birman, 1963) or Casa Diablo (Curry, 1971). d Minimum radiocarbon age on till from rock varnish (Dorn et al, 1987). e Minimum ages provided by accumulation of 26-Al and 10-Be in till boulders (Nishiizumi et al, 1993).…”

“…g Rock varnish cation-ratio analysis providing minimum ages (Dorn et al, 1990). Tioga age from site #24 of Dorn et al (1990) (Table 1).…”