Necrogeomorphology and the life expectancy of desert bedrock landforms

Abstract

This paper presents the first estimates for the life expectancy of the very surface of bedrock desert landforms, such as bornhardts, cliff faces, fault scarp, inselbergs, ridge crests, and slickrock. The correlative dating method of varnish microlaminations yields minimum ages for the timing of the last spalling event caused by the physical weathering process of dirt cracking. Minimum percentage of a bedrock surface spalled per thousand years is a metric that can be estimated using multiple varnish lamination ages. Understanding rates of surface spalling provides a quantitative measure of Gilbert’s (1877: 105) weathering-limited ‘rate of disintegration’, because this metric directly links to the rock disintegration process of dirt cracking. Rates of percent surface spalled then translate into estimates of how long it takes for the very surface of a desert bedrock landform to die. For a variety of example landforms in the southwestern USA, the maximum time required to completely resurface a desert bedrock landform by spalling from dirt cracking ranges from 89 to 600 ka.

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California

“…In our studies on Arabian varnishes, we had observed a positive iron intercept in regression analyses of D Fe vs. D Mn , which we suggested to be due to the presence of an Fe oxyhydroxide layer either at the base or the top of the varnish. Such an Fe oxyhydroxide layer has been suggested to act as a catalyst for the formation of the Mn oxyhydroxides [ 17 , 20 ]. In contrast, regression analyses on the data in this study showed no consistent pattern ( Table 3 ).…”

“…In part, this may be due to Liu and Broecker’s sampling strategy, as they were measuring the varnish thickness in the deepest part of microbasins, millimeter-sized depressions in the rock surface where varnish has accumulated relatively undisturbed. It may also reflect the possibility that once a certain varnish thickness has been reached, loss by processes like cracking and spalling prevents further thickness growth [ 20 – 22 ]. This is supported by the fact that the oldest varnishes in Liu and Broecker’s [ 19 ] data set (>50 ka) show the lowest apparent growth rates (0.6–2.0 μm ka -1 ), whereas the Holocene varnishes all appear to have much higher rates (12–40 μm ka -1 ).…”

Archaeometric studies on the petroglyphs and rock varnish at Kilwa and Sakaka, northern Saudi Arabia

“…This agrees with our previous observation of a positive Fe intercept in regression analyses of D Fe versus D Mn , which suggests the presence of an Fe oxyhydroxide layer at the base of the varnish. This layer might act as a catalyst for the formation of the Mn oxyhydroxides (Dorn, 2018; Macholdt et al, 2019). As in our previous work, we find no significant correlation between N Mn and N Fe , and no evidence of a relationship between N Fe and the age of the rock art based on thematic considerations (Andreae et al, 2020; Macholdt et al, 2018, 2019).…”

Introduction to the special issue on necrogeography and physical geography

“…The special issue on necrogeography and physical geography advocates for the development of necrogeography as part of physical landform and landscape processes, so as ‘necrogeomorphology’ illustrated by the following contributions: Nash (2018) addresses traditional necrogeography based on burial practices in cemeteries, impacting gravestones and memorials. The author presents a review paper of necrogeography from the framework of deathscapes based on the commemoration of death and its portrayal of cultural change; and, physically, where places of burial appear in the urban periphery as sites of potential contagion and contribute to air pollution as mercury vapours are released from crematoria. Dorn (2018) addresses it in this volume by looking at the life expectancy of entire surfaces of (22) desert bedrock landforms (bornhardts, cliff faces, fault scarps, inselbergs, pediments, ridge crests, bedrock under tors) in the Sonoran, Great Basin and Mojave Deserts as part of ‘landscape death’ in the tradition of closed-system conceptual models of landform evolution developed by Davis (1899, 1902, 1905) and Penck (1924). Migoń et al’s (2018) landform decay of focus in this special issue is that of sandstone-capped mesas through continuous development until death.…”

“…Dorn (2018) addresses it in this volume by looking at the life expectancy of entire surfaces of (22) desert bedrock landforms (bornhardts, cliff faces, fault scarps, inselbergs, pediments, ridge crests, bedrock under tors) in the Sonoran, Great Basin and Mojave Deserts as part of ‘landscape death’ in the tradition of closed-system conceptual models of landform evolution developed by Davis (1899, 1902, 1905) and Penck (1924).…”