Computerized Modeling of Rock-Varnish Dating
417
Some of these levels were dated by thermoluminescence analysis by O.Kulikov
(Vlasov et a1.l988). These age data were used for the absolute age scale (Table 1).
The arid and hyperarid climatic environment of Makhtesh Ramon provided
intensive formation of coating rock varnish covering more than 70% pebbles on
surfaces of terraces, fans and pediments. This is a black thin patina (1-311) on
an external surface of pebbles.
For the purpose of using rock varnish as an age marker, the chemistry of the
patina was sampled from different geomorphic levels - 5-, 10-, 15-,25-, 30-m
terraces of wadi Ramon, 10-, and 25 m pediments, as well as from the depression
bottom at 400 m elevation (see Table 1).
4
Chemical Composition
Rock-varnish chemistry was studied under electron microprobe analysis (Camebax). The special technique developed by G.Nechelustov for unpolished surfaces was
used because of the extreme thinness of the patina. The intensity of X-ray radiation
for compact samples with rough surface differs from that for polished sections. A
rough surface in samples strongly distorts the absorption correction value and is reflected on the coefficient of inverse scattering. Therefore, no standard corrections
procedure applies to such samples. In order to correct geometric effects, use was
made of a ratio intensity line to an intensity phone as an analytical parameter.
The chemical analysis of Fe-Mn matter was conducted under an electron microprobe procedure using energy-dispersive analysis. Analytical material was presented by 67 analyses, characterizing 15 samples from distinct geomorphic levels (Table
2). The distribution of chemical elements forming the basis of coating - K, Na, Mg,
Ca, AI, Si, Ti, Cr, Mn, Fe - was determined. Most differences in the content of elements are common to such elements as Fe, Mn, Ti, Si, AI, Mg. However, there is no
clear relationship between initial signs and their age. In our opinion, it is the result
of some immaturity of these formations compared to those from other regions. This
conclusion is supported by correlative analysis data. Nevertheless, the elemental differences in coating varnish, formed under various conditions, permitted mathematical analysis of the data obtained and showed the relation between the chemistry of
the rock varnish and its age.
Table 2 Electron microprobe analyses of rock varnish samples from Makhtesh Ramon
(Camebax)
Element concentration, weight %
Sample no. Absolute
Na
height a
Mg
Al
Si
K
Ca
Ti
Cr
Mn
Fe
I(RVE-I)
400 a
0.85 2.40 11.66 22.08
1.65 1.3
0.58 O.oz 7.06 8.29
" "
400 a
0.88 2.34 12.07 19.47
1.44 1.73 0.53 o.oz 8.61 9.99
II
"
400 a
0.24 2.7
13.54 20.57
1.86 1.3
0.5
0.02 6.63
8.58
" "
400 a
0.88 2.18 10.21
19.44
2.5
1.58 0.73 0.03 10.37 10.11
417
Some of these levels were dated by thermoluminescence analysis by O.Kulikov
(Vlasov et a1.l988). These age data were used for the absolute age scale (Table 1).
The arid and hyperarid climatic environment of Makhtesh Ramon provided
intensive formation of coating rock varnish covering more than 70% pebbles on
surfaces of terraces, fans and pediments. This is a black thin patina (1-311) on
an external surface of pebbles.
For the purpose of using rock varnish as an age marker, the chemistry of the
patina was sampled from different geomorphic levels - 5-, 10-, 15-,25-, 30-m
terraces of wadi Ramon, 10-, and 25 m pediments, as well as from the depression
bottom at 400 m elevation (see Table 1).
4
Chemical Composition
Rock-varnish chemistry was studied under electron microprobe analysis (Camebax). The special technique developed by G.Nechelustov for unpolished surfaces was
used because of the extreme thinness of the patina. The intensity of X-ray radiation
for compact samples with rough surface differs from that for polished sections. A
rough surface in samples strongly distorts the absorption correction value and is reflected on the coefficient of inverse scattering. Therefore, no standard corrections
procedure applies to such samples. In order to correct geometric effects, use was
made of a ratio intensity line to an intensity phone as an analytical parameter.
The chemical analysis of Fe-Mn matter was conducted under an electron microprobe procedure using energy-dispersive analysis. Analytical material was presented by 67 analyses, characterizing 15 samples from distinct geomorphic levels (Table
2). The distribution of chemical elements forming the basis of coating - K, Na, Mg,
Ca, AI, Si, Ti, Cr, Mn, Fe - was determined. Most differences in the content of elements are common to such elements as Fe, Mn, Ti, Si, AI, Mg. However, there is no
clear relationship between initial signs and their age. In our opinion, it is the result
of some immaturity of these formations compared to those from other regions. This
conclusion is supported by correlative analysis data. Nevertheless, the elemental differences in coating varnish, formed under various conditions, permitted mathematical analysis of the data obtained and showed the relation between the chemistry of
the rock varnish and its age.
Table 2 Electron microprobe analyses of rock varnish samples from Makhtesh Ramon
(Camebax)
Element concentration, weight %
Sample no. Absolute
Na
height a
Mg
Al
Si
K
Ca
Ti
Cr
Mn
Fe
I(RVE-I)
400 a
0.85 2.40 11.66 22.08
1.65 1.3
0.58 O.oz 7.06 8.29
" "
400 a
0.88 2.34 12.07 19.47
1.44 1.73 0.53 o.oz 8.61 9.99
II
"
400 a
0.24 2.7
13.54 20.57
1.86 1.3
0.5
0.02 6.63
8.58
" "
400 a
0.88 2.18 10.21
19.44
2.5
1.58 0.73 0.03 10.37 10.11