Anthropogenic lead as a tracer of rock varnish growth: Implications for rates of formation

Autor:	Michael N. Spilde, Diana E. Northup, Leslie A. Melim, Penelope J. Boston
Rok vydání:	2013
Předmět:	visual_art TRACER Desert varnish Varnish Smelting Lead (sea ice) visual_art.visual_art_medium Erosion Mineralogy Geology Growth rate Layer thickness
Zdroj:	Geology. 41:263-266
ISSN:	1943-2682 0091-7613
DOI:	10.1130/g33514.1
Popis:	Rock varnish is a thin dark coating best known from deserts, and is believed to grow extremely slowly. Varnish samples from near Socorro, New Mexico (United States), contain as much as 3.7% PbO, derived from nearby smelters operating from A.D. 1870 to 1931. Additional varnish, measuring as much as 4 μm beyond the Pb-rich layer, indicates continued growth from 1931 to 2003. Comparison with other varnish confirms that the Pb is not an artifact. Based on Pb layer thickness, and the period of smelter operation, these very young rock varnishes yield growth rates of 28–639 μm/k.y., substantially higher than previously documented fastest rates of 40 μm/k.y. These rates imply that the average 1–2 μm/k.y. rate for older varnish is not the active growth rate. Rather, it is a long-term value including periods of nondeposition, erosion, and active growth. Therefore, models of rock varnish formation should be reevaluated with consideration of much faster maximum growth rates.
Databáze:	OpenAIRE
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