New Approach to the Radiocarbon Dating of Rock Varnish, with Examples from Drylands

Dorn, Ronald I.; Clarkson, Persis B.; Nobbs, Margaret; Loendorf, Lawrence L.; Whitley, David S.

doi:10.1111/j.1467-8306.1992.tb01902.x

Cited by 65 publications

(50 citation statements)

References 31 publications

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“…Although we did not have the funds to measure directly the 14C age of the rinds, we add its effect to the measurement error. Theoretically, instead of supporting an earlier interpretation of chronological simplicity (Dorn et al, 1992), our data indicate that geoglyphs were made over an extended period: from before -A.D. 1200 to before -900 B.C. Although our dataset is small, it is consistent with the linguistic hypothesis that the Yuman people migrated from the south and came over the Peninsular Range from coastal California-rather than from the north.…”

Section: Resultssupporting

confidence: 60%

AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

Werlhof¹,

Casey²,

Dorn

et al. 1995

Geoarchaeology

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Giant ground figures are widespread in the lower Colorado River area of southwestern North America, yet their chronology has remained unconstrained by numerical ages. Thirteen AMS 14C measurements reported here indicate that geoglyphs were made from before ˜A. D. 1200 to before ˜900 B. C. We account for potential contamination from prior organics in weathering rinds. All other potential errors point to 14C dates being minimum‐limiting ages for the manufacturing of geoglyphs. Although these ages indicate considerable chronological complexity among geoglyphs, our data are consistent with the linguistic hypothesis that the Yuman people in the desert of southeastern California migrated from Baja California—rather than from the north. These results must, however, be placed under the cloud of uncertainty that hangs over the entire field of AMS dating of rock art: the untested assumption surrounding contemporeneity of organics in a surface context. © 1995 John Wiley & Sons, Inc.

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Section: Resultssupporting

confidence: 60%

AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

Werlhof¹,

Casey²,

Dorn

et al. 1995

Geoarchaeology

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“…Substrate stability has been recognized as important in determining whether or not a rock varnish has time to develop (Dorn and Oberlander, 1982;Drake et al, 1993). Substrate type can also affect how varnish growth occurs (Dorn et al, 1992a). This study adds another factor-the abundance of manganese in solutions flowing over rocks-as a way in which substrate can potentially influence varnish.…”

Section: Discussionmentioning

confidence: 98%

“…For example, rock surfaces on the c. 14000-year-old (I4C dated) shoreline of Searles Lake in eastern California have not been completely coated with varnish, and the ~2000-year-old Nazca geoglyphs in Peru (Dorn et al, 1992a) have developed only millimetre to centimetre sized spots of varnish. Some claim, however, that there are circumstances in which rock varnish can form rapidly (Engel and Sharp, 1958).…”

Section: Introductionmentioning

confidence: 99%

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana, California

Dorn

Meek

1995

Earth Surf Processes Landf

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Manganiferous rock varnish, silica glaze and iron skins have formed on 20-to 40-year-old slag piles near Fontana, southern California. Rapid rock-varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments, combined with the likelihood that Mn-rich solutions flow over slag surfaces. A new model is proposed for the formation of silica glaze, involving soluble AI-Si complexes and the nature of wetting films. Iron skins occur where runoff is concentrated, and where iron bacteria grow.Observations indicate: (i) substrate can be important in supplying Mn, as well as maintaining a stable surface and channelling runoff to microspots where varnish grows; (ii) ignorance of boundary layer pH/Eh conditions makes chemical-physical models of varnish formation speculative; (iii) the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood, but is probably an important limiting factor on varnish growth rates; and (iv) there must be at least two steps in biotic varnishing-accretion of Mn-Fe in casts, followed by cementation of clays by either in situ cast residue or Mn-Fe remobilized from casts. Varnish accretion may be limited by the rate at which both steps occur. Rapid development of readily distinguishable manganiferous rock varnishes at this post-1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock-varnish coatings.

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“…A radiocarbon age of rock varnish dates the time when bits of organic detritus were encapsulated by accreting varnish (Dorn, 1989;Dorn et al, 1992). At best, a rock varnish age measures an event, the beginning of deposition of 'contemporary' I4C in the varnished layer depositing on an exposed surface.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…One seeks to select specimens on which this basal layer can be unambiguously identified and sampled. Details on sample preparation for 14C can be found in Dorn et al (1992).…”

Section: Experimental Methodsmentioning

confidence: 99%

Role of in situ cosmogenic nuclides ¹⁰be and ²⁶al in the study of diverse geomorphic processes

Nishiizumi

Kohl

Arnold

et al. 1993

Earth Surf Processes Landf

201

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The central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings. in the light of these general models, we discuss the information that can be derived about geomorphic processes, utilizing concentrations of in situ produced cosmogenic radionuclides "Be (half-life = 1-5 ma) and 26Al (half-life = 0.7 ma) in a variety of geomorphic contexts: glacial polish and tills; meteorite impact craters; alluvial fans; paleo-beach ridges; marine terraces; sand dunes; and bedrock slopes. We also compare 'oBe-26A1 data with results obtained by other dating methods. We conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time-scales in a wide range of geomorphological problems.

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New Approach to the Radiocarbon Dating of Rock Varnish, with Examples from Drylands

Cited by 65 publications

References 31 publications

AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana, California

Role of in situ cosmogenic nuclides ¹⁰be and ²⁶al in the study of diverse geomorphic processes

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New Approach to the Radiocarbon Dating of Rock Varnish, with Examples from Drylands

Cited by 65 publications

References 31 publications

AMS 14C age constraints on geoglyphs in the lower colorado river region, arizona and california

AMS 14C age constraints on geoglyphs in the lower colorado river region, arizona and california

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana, California

Role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes

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AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

AMS ¹⁴C age constraints on geoglyphs in the lower colorado river region, arizona and california

Role of in situ cosmogenic nuclides ¹⁰be and ²⁶al in the study of diverse geomorphic processes