RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES6004, doi:10.2205/2008ES000306, 2008
[2] According to numerous data, the particles of metallic (native) iron and nickel are common on the Earth surface, but their temporal distribution is very poorly studied. Unfortunately, thermomagnetic analysis (TMA) of sediments had not been used for this purpose. Recently, TMA up to 800oC was employed during petromagnetic (rock-magnetic) studies of sediments at the K/T boundary [Grachev et al., 2005; Molostovsky et al., 2006; Pechersky et al., 2006a, 2006b]; (D. M. Pechersky et al., in press, 2008a,b). As a result, it has been found that metallic iron in low concentration, usually below 0.001%, is widespread in sediments [Pechersky, 2008a, 2008b]. No enrichment by metallic iron was found close to the K/T boundary. A possible influence of oxidation of iron particles and their re-deposition has led to an idea that it is worth studying how iron particles are distributed in younger sediments, of Miocene and Pliocene ages; however, we abstained from investigating present-day sediments, which may be contaminated by anthropogenic input. The Khalats (Turkmenia) and Kvirinaki (Georgia) sections were selected for such studies as both have already been sampled. These sections satisfy main provisions for such studies, which run as follows: they are about 1500 km apart, local factors, including possible oxidation of iron particles and their re-deposition, can be ruled out; the sediments accumulated in very different physical-geographic environment; the sediments contain abundant fossils for reliable biostratigraphic dating; magnetostratigraphical information is available for both sections (Tables 1 and 2). The Khalats section comprises continental sediments, mostly cobble conglomerates with lenses of sand, sandstone and sandy siltstone. Fine-grained varieties were sampled for paleo- and petromagnetic studies. According to biostratigraphic data, this section represents a nearly continuous succession of Middle Miocene and early Late Miocene age, from the upper part of the Sakaraul-Kotsakhurian stage to the late Sarmatian stage (Table 1). Correlation of paleomagnetic data with the magnetochronostratigraphic scale of Berggren et al. [1995] showed that the Khalats section includes magnetic chrons from C5Cn to C4Ar, which corresponds to the age interval from 16.5 to 9.5 Ma (Table 1). In contrast to the Khalats sections, the Kvirinaki section is composed of marine terrigenous sediments with noticeable carbonate content. According to biostratigraphic data, this section encompasses a large part of the Middle and Late Miocene, from the Tarkhanian stage to the Middle Sarmatian stage, with a large hiatus between the Chokrakian and Karaganian stages (Table 2). Correlation of paleomagnetic data with the magnetochronostratigraphic scale of Berggren et al. [1995] showed that the Kvirinaki section includes magnetic chrons from C5Br to C5n, which corresponds to the age interval from 15.9 to 10.2 Ma with the gap from 14.6 to 13.0 My (Table 2). Thus the sections cover similar intervals, which is very important for establishing the synchronism, or the lack thereof, of iron-enriched levels.
[3] This paper presents the results of magnetolithologic and magnetomineralogical study of the Khalats and Kvirinaki sections, the distribution of metallic iron particles being out primary goal.
Citation: 2008), Native iron in Miocene sediments, Russ. J. Earth Sci., 10, ES6004, doi:10.2205/2008ES000306.
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