Geochemical History of the Crystalline Basement and the Sedimentary Cover of the Russian and North American Platforms

Abstract

A vast amount of analytical material (more than 8,000 analyses) on the chemical composition of the main rock types occurring in the crystalline shields and sedimentary covers of the Russian and North American platforms has been compared, taking into account the abundance of these rocks. The comparison covers structures as a whole and separately—their sections representing very large stratigraphical complexes (A. Pt1_2, Pt3. Pz. Mz‐Cz). Based on generalization of these data, the more important development stages in the composition of the shields and platforms were traced for the last 3.5 billion years and the more general tendencies in their geochemical history were outlined. An almost complete uniformity of the “granite” shell's average composition, a striking similarity of the average composition of the sedimentary cover and similar ways of its development have been proved for different continents. At the same time a discrepancy was established in the average compositions of the rocks of the shields and derivative platform sediments, which by their composition are nearer to basic than to acid rocks. This fact obviously indicates a wider spread of the basic rocks during the earlier stages of the development of the Earth's crust. The more general tendencies in the evolution of the rock composition of shield and platform sediments have been retraced. They outlined a causal relationship, with the development of granitization processes of the primary, more basic material, with the passing of denudation products through numerous cycles of weathering and sedimentation and with the biosphere growth and life development which determined the change of the atmospheric and oceanic compositions as well as the oxidation‐reduction conditions on the surface of the Earth and in the formation of sedimentary series.

The low-temperature geochemical cycle of iron: From continental fluxes to marine sediment deposition

“…Thus there are close similarities in the elemental composition of modern and ancient muddy sediments (Garrels and Mackenzie, 1971;Wollast and Mackenzie, 1983), with large differences occurring only for CaO, CO 2 and H 2 O. More specifically the FeT content of shales appears to show little variation through the Phanerozoic (Ronov and Migdisov, 1971), although there is an increase in the ratio of Fe(II) to Fe(III) with time (see above).…”

Millennial-scale variability of marine productivity and terrigenous matter supply in the western Bering Sea over the past 180 kyr

“…A potential source of error in the calculation of Ba bio comes from estimating the aluminosilicate contribution of Ba via Al. Ba/Al ratios range between 5-10 mg g −1 in crustal rocks (Taylor, 1964;Rösler and Lange, 1972) with a crustal average of 7.5 mg g −1 (Dymond et al, 1992). We estimated the regional detrital Ba/Al ratio from surface sediment samples following Klump et al (2000), which resulted in a value of 7 mg g −1 (unpublished data).…”

“…This is an interesting result, since records of %Siliciclastics, %Terrigen, and lithogenous element concentrations are characterized by strong variations on the glacial-interglacial level. Al/Ti ratios varied between 22-34 (mol mol −1 ), with short-lived in- (Ronov and Migdisov, 1971), but also compare with average values for sediment and continental crust (∼ 28;McLennan, 1995;Taylor and McLennan, 1995), river particulate and mud (∼ 30;McLennan, 1995), pelagic clay (∼ 32;McLennan, 1995), as well as the range reported for loess deposits (∼ 26-31; Taylor et al, 1983;Pye, 1987;McLennan, 1995). Values are clearly lower than that of the North American shale composite (∼ 38; Gromet et al, 1984), but higher than Al/Ti ratios of oceanic tholeiitic basalt (∼ 17;Engel et al, 1965) and surface samples from St. George Basin, SE Bering Sea (∼ 24; Gardner et al, 1980).…”

Mineralogical and chemical characteristics of Bajocian-Bathonian shales, G. Al-Maghara, North Sinai, Egypt: Climatic and environmental significance.

“…Six samples, four from the Safa Formation and two from the Bir Maghara Formation, which yielded low CIA values (<61), are excluded as they are enriched in calcite. The high CIA values in the studied shales probably Phan Sh: Phanerozoic Shales (Condie, 1993), UCC: Upper Continental Crust (Taylor and McLennan, 1985), Pierre Shale (Schultz et al, 1980), NASC: North American Shale Composites (Gromet et al, 1984) and RMCS: Russian Mesozoic and Cenozoic Shales (Ronov and Migdisov, 1971 (Condie, 1993) and in the UCC (14 ppm) (Taylor and McLennan, 1985). Similar to Zr, samples 12 and 24 gave extremely high Sc concentrations -268 and 296 ppm respectively.…”

“…Loss on ignition (LOI) was not determined. The data obtained from the studied shales are compared with the average chemical composition of the Phanerozoic Shale (Condie, 1993), Upper Continental Crust (UCC) (Taylor and McLennan, 1985), Normal Pierre Shale (Schultz et al, 1980), North American Shale Composite (NASC) (Gromet et al, 1984), and Russian Mesozoic and Cenozoic Shales (RMCS) (Ronov and Migdisov, 1971). To test the role of chemical weathering in the formation of the studied shales, the Chemical Index of Alteration (CIA) was calculated using the method of Nesbitt and Young (1982).…”