Middle–Late Devonian island-arc volcanosedimentary complexes in northwestern Rudny Altai

Abstract

A volcanosedimentary complex of Middle–Late Devonian deposits in northwestern Rudny Altai is described. Analysis of sedimentologic processes, the kind of manifestation and specific composition of volcanism, and petrographic and chemical compositions of sedimentary rocks permitted reconstruction of paleogeographic and geodynamic settings, which confirmed the hypothesis of the island-arc nature of the Rudny Altai zone in the Middle–Late Devonian. Also, an alternative variant of its rift nature is considered. The rift buildings are referred to as local isolated complexes confined to positive paleovolcanic structures rising above the bottom in the fore-arc basin. The denudated part of the rift system is formed mainly by slope facies. Clastics of rift buildings, together with fragments of silicite and felsic-volcanics layers, compose widespread olistostrome breccias. We have established the humid type of lithogenesis, which, together with minor sea level fluctuations, favors karst processes and the formation of red-colored and bauxite-like rocks. The coeval volcanics composing lava flows and tuff layers are mainly rhyolites and are often of ultrafelsic composition.

C isotopic variations in the lower–middle Frasnian (lower Upper Devonian) of the Rudny Altai

“…When compared to the chart of Upper Devonian events (House, 2002; Gradstein et al 2012) the attained carbon isotope curve demonstrates a marked degree of synchronism between the negative δ 13 C excursion and the Upper Devonian (Frasnian) Middlesex global event. The decrease in the amount of reef debris and the occurrence of calcarenite turbidites in the studied section suggest that the negative δ 13 C excursion is coeval with landward reef progradation and marine transgression (Saraev et al 2012), further corroborating the suggested correlation with the Middlesex Event. The latter was accompanied by a sea-level rise and the advent of anoxia in the water column and could be responsible for a decline in biological productivity or supply of isotopically light carbon to the world's sedimentary basins as a consequence of erosion of accumulated organic matter.…”

“…3) characterized by a significant negative δ 13 C excursion. This stratigraphic level is marked by palaeokarst features indicative of a short subaerial exposure of the biostrome (Saraev et al 2012). Apart from this level, synchronous decreases in δ 18 O and δ 13 C and coeval increases in Fe/Sr and/or Mn/Sr in a few samples were attributed to diagenetic alteration (Fig.…”

“…2). A detailed description of the section BYa-9011, together with the occurrence of microfauna, has been provided in a number of publications (Bakharev et al 2004; Izokh, Yolkin & Bakharev, 2004; Saraev et al 2012). Below is a brief description of the section:

Figure 2. Location of the Frasnian section on the right bank of Gryaznukha Brook, downstream of Razdol’noe Village.

…”

Geological History of the Great Altai: Implications for Mineral Exploration

“…(1) Middle Late Paleozoic Rudny-Altai zone that formed on the Siberian active margin as a result of the subduction of Ob-Zaisan oceanic plate [9][10][11];…”

“…and complex compositions of rich ores, with high concentrations of Cu + Pb + Zn and impurities. 6), and Artemiev (7) deposits in Irtysh (Ir) district; Zolotukhino (8) and Orlovka (9) deposits in Zolotushino (Zo) district; Zmeinogorsk (10) and Korbalikha (11) deposits in Zmeinogorsk (Zm) district; Talaya (12) and Rubtsovsk (13) deposits in Rubtsovsk (Ru) district. 6), and Artemiev (7) deposits in Irtysh (Ir) district; Zolotukhino (8) and Orlovka (9) deposits in Zolotushino (Zo) district; Zmeinogorsk (10) and Korbalikha (11) deposits in Zmeinogorsk (Zm) district; Talaya (12) and Rubtsovsk (13) deposits in Rubtsovsk (Ru) district.…”