Rare earth elements in the clay fraction of coaliferous sediments of the Arkagalinskoe (Magadan district) and Dolinskoe (Sakhalin Island) coalfields

The study of REE distribution in the clay fraction of sedimentary rocks from two coalfields made it possible to distinguish several types of REE distribution, which correlate with their mineral composition. It is shown that the REE fractionation was related to the mineral reconstruction of the primary clay fraction and some detrital minerals in the course of postsedimentary transformations of rocks during diagenesis, early catagenesis, and beginning of late catagenesis. These transformations were governed by several factors, such as the composition of sediments; hydrochemical features of accumulation environment; the chemical composition, dynamics, and feeding sources of pore solutions; the porosity and permeability of sediments and rocks; and the content of organic matter and its reaction ability.     

Cretaceous Rocks of the Penzhina Bay: Mineralogy,Petrography, and Geodynamic Sedimentation Conditions

Cretaceous sedimentary and volcanosedimentary rocks from northwestern Kamchatka are considered. The stadial analysis has revealed variable impacts of three major provenances upon the Cretaceous Penzhina sedimentary basin. The provenances were composed of volcanic and volcanosedimentary rocks (Uda–Murgal island arc and Okhotsk–Chukotka volcanic belt) and granitic–metamorphic rocks (the mature Asian continental margin). Sediments were largely accumulated owing to the erosion of island-arc volcanics during reactivation of the Uda–Murgal island arc (Hauterivian–Barremian) or the Okhotsk–Chukotka volcanic belt (middle Albian–Cenomanian). Eroded granitic–metamorphic rocks of the mature Asian continental margin (Berriasian–Valanginian) or Asian metamorphic–volcanic rocks (Santonian–Campanian) were supplied to the basin during tectonically quiet periods (Berriasian–Valanginian and late Cenomanian–Campanian). Compositional changes in provenances were related to active tectonic processes at the continental margin, including evolution and closure of the Uda–Murgal island-arc system and origin of the Okhotsk–Chukotka volcanic belt. The postsedimentary modification of Cretaceous rocks deposited in forearc trough beyond the tectonically active accretionary prism is characterized by a low degree of clastic component alteration.     

Formation of laumontite in sedimentary rocks: A case study of sedimentary sequences in Russia

Analysis of the authigenic laumontite distribution in sedimentary complexes of the Russian Federation is presented. The mineral occurs in sections characterized by various types of lithology, genesis, tectonic setting, and burial depth. Distribution area of this mineral spacially coincide with domains of the alkaline (mainly sodic) groundwater. It is inferred that the formation of authigenic laumontite in sedimentary sequences represents the hydrogenous catagenetic mineralization related to the circulation of heterogeneous alkaline groundwaters in them. This phenomenon resembles hydrothermal processes in areas of intense volcanism and likely represents a process typical of sedimentary sequences.     

Rare Earth Elements in Coal-Bearing Deposits: Distribution Features and Geochemical Significance

The examination of Lower Cretaceous coals and clayey fractions of terrigenous host rocks of the Zyryanka Basin has revealed a generally negative type of the relative REE distribution (with a predominance of LREE over HREE) and a similar behavior of Th and U. Analogous characteristics are typical for metamorphic and igneous rocks of intermediate composition dominating in the provenance. In terms of the concentration and distribution of REE, Th, and U coal-bearing terrigenous rocks of the Zyryanka Basin are close to Phanerozoic clays and silty sandstones of the Russian Platform, while coals of the Zyryanka Basin are similar to metal-free coals of various basins (Kizel, Pennsylvanian, and others). Average REE and Th contents in the studied coals are five times lower than those in host terrigenous rocks. The coals differ from these rocks by relatively elevated HREE concentrations largely due to adsorption mechanism of the HREE accumulation. Data obtained on the REE, Th, and U distribution in coals and clayey fractions of host rocks are of fundamental significance for the comparitive analysis of the behavior of these elements in metal-bearing coals of various basins.