Computerized Modeling of Rock-Varnish Dating
N. Gorelikova, N. Patyk -Kara, 1. Chizova, J.Plakht, A. Sivtsov
1
Introduction
One type of epigenetic alteration of recent sedimentary formations is desert
weathering. Rock varnish is a widespread feature of a stony desert landscape
throughout the world. It is a product of complicated physical and chemical
processes under arid and semiarid environments. Despite the interest in rock
varnish of both archeologists and geologists, the mechanism of varnish formation is controversial. Most workers believe that the formation of rock varnish is
responsible for changing pH and Eh conditions on its surface layer, which results in solution and subsequent deposition of matter (Tricart et al. 1960).
These researchers consider this process as insolative weathering of deserts
which consists of circulation in mineralised solutions to a rock surface, evaporation and mineral deposition. Some investigators advance arguments which
indicate a biogenic nature of manganese layers (Krumbein et al.I981). In addition, it is also believed opinion that patina has a primary eolian origin (Allen
1978; Dorn et al. 1981).
Recently, considerable attention has been focused on new methods for quantitative age determinations of patinated surfaces. At present, there are a dozen
new methods for quantitative age dating of rock-varnish. Rock-varnish coatings
from arid environments have currently gained importance in the dating of geomorphic events and revealing climatic changes (Dorn et al. 1991).
From a modern viewpoint, rock varnish is formed under conditions of high
Eh and pH, which are common to deserts at low altitudes with annual precipitation of no more than 150 mm. Microorganisms, lichens and bacteria, which consume energy in the course of manganese oxidation, play an important part in
manganese absorption by clay particles. It was found that coating composition,
primarily of manganese and ferrum content, calibrated against other methods,
makes the age dating of native phenomena (terraces, fans, pediments, etc.) and
artefacts in the range from hundreds to 1 million years possible (Hunt 1961;
Hooke et al. 1969; Krumbein et al. 1981).
N. Gorelikova, N. Patyk -Kara, 1. Chizova, J.Plakht, A. Sivtsov
1
Introduction
One type of epigenetic alteration of recent sedimentary formations is desert
weathering. Rock varnish is a widespread feature of a stony desert landscape
throughout the world. It is a product of complicated physical and chemical
processes under arid and semiarid environments. Despite the interest in rock
varnish of both archeologists and geologists, the mechanism of varnish formation is controversial. Most workers believe that the formation of rock varnish is
responsible for changing pH and Eh conditions on its surface layer, which results in solution and subsequent deposition of matter (Tricart et al. 1960).
These researchers consider this process as insolative weathering of deserts
which consists of circulation in mineralised solutions to a rock surface, evaporation and mineral deposition. Some investigators advance arguments which
indicate a biogenic nature of manganese layers (Krumbein et al.I981). In addition, it is also believed opinion that patina has a primary eolian origin (Allen
1978; Dorn et al. 1981).
Recently, considerable attention has been focused on new methods for quantitative age determinations of patinated surfaces. At present, there are a dozen
new methods for quantitative age dating of rock-varnish. Rock-varnish coatings
from arid environments have currently gained importance in the dating of geomorphic events and revealing climatic changes (Dorn et al. 1991).
From a modern viewpoint, rock varnish is formed under conditions of high
Eh and pH, which are common to deserts at low altitudes with annual precipitation of no more than 150 mm. Microorganisms, lichens and bacteria, which consume energy in the course of manganese oxidation, play an important part in
manganese absorption by clay particles. It was found that coating composition,
primarily of manganese and ferrum content, calibrated against other methods,
makes the age dating of native phenomena (terraces, fans, pediments, etc.) and
artefacts in the range from hundreds to 1 million years possible (Hunt 1961;
Hooke et al. 1969; Krumbein et al. 1981).