M. T. Krupenin, A. B. Kuznetsov, D. A. Zamyatin, E. A. Pankrushina, S. V. Lepekha
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引用次数: 0
Abstract
Phosphorite breccias compose a 6-m-thick member in the Vendian terrigenous Kernos Formation in the basin of the Mezhevaya Utka and Sylvitsa rivers (Middle Urals). Phosphorite pebbles and gravelites are accumulations of the fragments of redeposited crusts, originally formed during early diagenesis near the surface of sandy–clayey rocks below the water–sediment boundary. Phosphorite is represented by fluorocarbonate apatite with the following parameters: unit cell a ranging from 0.9359 to 0.9363 nm, spectral mode parameters in Raman spectra (ν1 FWHM = 1–2 cm–1 and peak position from 963 to 966 cm–1), and a band at 1095 cm–1 in FTIR spectra. The bands at ~1430 cm–1 and 1453 cm–1 in the FTIR spectra correspond to substitution of the orthophosphorus group by the carbonate ion (B type). According to the thermal analysis data, the CO2 content in apatite is 0.04–0.8%, and the admixture of dispersed organic matter as aliphatic compounds is 0.3–0.8%. Apatite is represented by two generations: primary (basal structureless fine-crystalline cement) and secondary (euhedral crystals up to 10 µm in size). Both generations corrode the detrital quartz grains. Relative to the primary apatite, the secondary variety is enriched in P2O5, CaO, and F, but depleted in SiO2, Fe2O3, Al2O3, MgO, and K2O. The PAAS-normalized REE distribution in the enriched phosphorites has a smoothed profile with a La/Yb ratio of about 2 and positive Ce and Eu anomalies. The average F/P2O5 value (0.09) corresponds to that in typical fluorocarbonate apatites subjected to catagenesis. High 87Sr/86Sr values (0.7130–0.7253) in detrital phosphorites of the Kernos Formation suggest their deposition in a desalinated wave-dominated shallow-marine paleobasin near a significant inflow of continental water (delta) or catagenetic recrystallization.
期刊介绍:
Lithology and Mineral Resources is an international peer reviewed journal that publishes articles on a wide range of problems related to the formation of sedimentary rocks and ores. Special attention is given to comparison of ancient sedimentary rock and ore formation with present-day processes. The major part of the journal is devoted to comparative analysis of sedimentary processes on the continents and in oceans, as well as the genetic aspects of the formation of sedimentary and hydrothermal–sedimentary mineral resources. The journal welcomes manuscripts from all countries in the English or Russian language.