Blind testing of rock varnish microstratigraphy as a chronometric indicator: results on late Quaternary lava flows in the Mojave Desert, California

A new strategy for analyzing the chronometry of constructed rock features in deserts

“…Although ongoing research is now attempting to identify discrete Holocene laminae (cf. Cremaschi, 1996) in our study area, at the present time, the calibration in the study area only discriminates Holocene from terminal Pleistocene (Liu et al, 2000) and older (Liu, 2003) ages.…”

“…The study of varnish microlaminations (VML; Dorn, 1990;Cremaschi, 1996), refined by extensive independent calibrations of layering patterns (Liu and Dorn, 1996 Liu, 2003), permits assignment of correlative surface ages into broad time classes that correspond with regional climatic events. A blind test administered by the editor of Geomorphology (Marston, 2003) ended with the following conclusion on the VML approach:…”

“…We followed the methods used to develop Liu's calibration (Liu and Dorn, 1996;Liu et al, 2000;Liu, 2003), in terms of broad sampling parameters for a boulder and in terms of the types of millimeter-sized microbasins that are the focus of making ultra-thin sections. In brief, varnish analysis requires stable boulders from loci that address the question of interest; in this case, the loci must be related to alteration of boulder position.…”

Environmental history recorded in aeolian deposits under stone pavements, Mojave Desert, USA

“…This stable phase may have provided a sufficient time window for the formation of a new generation of stone pavement during a short period of increased aridity and thus decreased grass cover density (cf. aridity pulse around 14 ka in Liu (2003) or between Younger Dryas and Holocene wet phase WH12 in Liu and Broecker (2007)). …”

“…However, they usually cover only narrow time windows, suffer from truncation and reworking during new activity periods and can sometimes be ambiguous to interpret in terms of type and timing of constructing processes (Bateman et al, 2012). Specific components of the environmental history have been retrieved from special archives, such as rock varnish micro-laminations (eg., Liu, 2003;Liu and Broecker, 2007), packrat-midden remains (Koehler et al, 2005), calcium carbonate formations * corresponding author Email address: mdietze@gfz-potsdam.de (Michael Dietze) (Winograd et al, 2006) and soil-sediment successions (von Suchodoletz et al, 2009). However, most of these archive types also can be discontinuous, cover only small time windows or are prone to reworking and erosion.…”