Computerized Modeling of Rock-Varnish Dating
425
tendency to be ordered at the high levels. A change from positive correlations
to negative ones is observed with geological age, for example for Fe-Mn and
Fe-Ti pairs.
3. Values of the generalised geochemical indicator GI rv, which change non-continuously from one level to another.
These geochemical differences permit the use of various geochemical coefficients for rock-varnish dating. Considering the multifactor character of geochemical processes and the complex composition of the formations analyzed,
this task could be solved only in consideration of all primary signs and their ratios, and using the geochemical indicator mentioned above, which gives the
maximal approximation of calculated ages to data obtained by other methods.
Fig. 4 shows that the divergence value in age dates is no more than 5-10% .
As a result of this investigation, the data base for the system was created, allowing absolute and relative dating of the geomorphic surfaces of Makhtesh Ramon and adjacent regions of the plateau Negev, by using the chemistry of rockvarnish coating. This approach put forward the complex problem of dating different geomorphic surfaces and revealing climatic changes in different environments.
Acknowledgements
Supported by the Russian Fundamental Research Foundation (RFFI), Grant No
96-05-66197, and in part by the University after Ben-Gurion in Beer-Sheva (Israel). We especially wish to thank our colleagues Dr.G.Nechelustov, for performing
electron microprobe analyses of rock varnish and development the special technique for unpolished samples, and Dr.O.Kulikov, for the thermoluminescencal
data which we used for the absolute dating scale of different geomorphic levels.
References
Allen, c.c., 1978, Desert varnish of the Sonoran desert: Optical and electron probe microanalysis: Journal of Geology, v.86, p.p. 743-752.
Ben-David R. and Mazor E., 1988, Stages of the evolution of the Makhtesh Ramon and its
drainage system: Israel. Journal Earth Sciences, v. 37, No 2-3, p.p.125-135.
Chukhrov F.Y., Gorshkov A.I., Rudnitskaya E.S., Beresovskaya V.V. and Sivtsov A.V., 1980,
Manganese Minerals in clays: A Review. Clays and Clay Minerals, v. 28, No 5, p.p. 346-354.
Dorn R.I. and Oberlander T.M., 1981, Rock varnish origin, characteristics, and usage: Zetschrift fur Geomorphologie, v. 25, p.p. 420- 436.
Dorn R.I., DeNiro M.J. and Ajie H.O., 1987, Isotopic evidence for climatic influence on alluvial-fan development in Death Valley, California: Geology, v. 15, No 2, p.p. 108-11 o.
Dorn R.I., Tanner D.L., Turrin B.D. and Dohrenwend J.,c., 1987, Cation-ratio dating of Quaternary materials in the east central Mojave Desert, California: Physical Geography, v. 8,
p.p.72-8l.
Dorn R.I. and Phillips EM., 1991, Surface exposure dating: Review and critical evaluation:
Physical Geography, 12,4, pp. 303-333.
425
tendency to be ordered at the high levels. A change from positive correlations
to negative ones is observed with geological age, for example for Fe-Mn and
Fe-Ti pairs.
3. Values of the generalised geochemical indicator GI rv, which change non-continuously from one level to another.
These geochemical differences permit the use of various geochemical coefficients for rock-varnish dating. Considering the multifactor character of geochemical processes and the complex composition of the formations analyzed,
this task could be solved only in consideration of all primary signs and their ratios, and using the geochemical indicator mentioned above, which gives the
maximal approximation of calculated ages to data obtained by other methods.
Fig. 4 shows that the divergence value in age dates is no more than 5-10% .
As a result of this investigation, the data base for the system was created, allowing absolute and relative dating of the geomorphic surfaces of Makhtesh Ramon and adjacent regions of the plateau Negev, by using the chemistry of rockvarnish coating. This approach put forward the complex problem of dating different geomorphic surfaces and revealing climatic changes in different environments.
Acknowledgements
Supported by the Russian Fundamental Research Foundation (RFFI), Grant No
96-05-66197, and in part by the University after Ben-Gurion in Beer-Sheva (Israel). We especially wish to thank our colleagues Dr.G.Nechelustov, for performing
electron microprobe analyses of rock varnish and development the special technique for unpolished samples, and Dr.O.Kulikov, for the thermoluminescencal
data which we used for the absolute dating scale of different geomorphic levels.
References
Allen, c.c., 1978, Desert varnish of the Sonoran desert: Optical and electron probe microanalysis: Journal of Geology, v.86, p.p. 743-752.
Ben-David R. and Mazor E., 1988, Stages of the evolution of the Makhtesh Ramon and its
drainage system: Israel. Journal Earth Sciences, v. 37, No 2-3, p.p.125-135.
Chukhrov F.Y., Gorshkov A.I., Rudnitskaya E.S., Beresovskaya V.V. and Sivtsov A.V., 1980,
Manganese Minerals in clays: A Review. Clays and Clay Minerals, v. 28, No 5, p.p. 346-354.
Dorn R.I. and Oberlander T.M., 1981, Rock varnish origin, characteristics, and usage: Zetschrift fur Geomorphologie, v. 25, p.p. 420- 436.
Dorn R.I., DeNiro M.J. and Ajie H.O., 1987, Isotopic evidence for climatic influence on alluvial-fan development in Death Valley, California: Geology, v. 15, No 2, p.p. 108-11 o.
Dorn R.I., Tanner D.L., Turrin B.D. and Dohrenwend J.,c., 1987, Cation-ratio dating of Quaternary materials in the east central Mojave Desert, California: Physical Geography, v. 8,
p.p.72-8l.
Dorn R.I. and Phillips EM., 1991, Surface exposure dating: Review and critical evaluation:
Physical Geography, 12,4, pp. 303-333.