THROUGHOING FLUID-CONDUCTING STRUCTURES: MORPHOGENETIC CLASSIFICATION AND CHARACTERIZATION OF TYPES

Abstract

Throughgoing fluid-conducting structures are the main elements of the plumbing system of the sedimentary cover and play an important role in fluid migration, evolution of sedimentary basins and lithogenesis, formation of fluidogenic deposits (including hydrocarbons and metals), use of geothermal energy sources, risk assessment for geological depositories of radioactive wastes, CO2 and other materials. They are widespread and characterized by a variety of morphology and origins, but are poorly systematized by these attributes, which complicates identification and interpretation of these structures. In this article, based on the analysis and generalization of literature sources and data from own field studies, morphogenetic classification of throughgoing fluid-conducting structures is developed and the characteristics of the defined types are given. At the first level, such structures are divided into four groups according to the nature of the dominant formation processes: tectonic, fluidodynamic, karstic (dissolution) and karstic-gravitational. At the second and third levels, groups and types of the structures are distinguished by structural-morphological and material features, taking into account the peculiarities of mechanisms and conditions of formation. The mechanisms of formation of structures of some types are clarified. It is shown that karstification, particularly hypogenic, is the leading process of formation of the most permeable structures and, accordingly, of the most contrasting hydrogeological anomalies and their geological consequences. Structures of relatively small vertical dimensions and stratigraphic coverage (bed-crossing, suite-crossing) can be elementary and of unambiguous origins, although they frequently show signs of superimposed changes that significantly affect their fluid-exchange function. The proposed classification is applicable mainly to small and elementary structures, while large (cross-formational, cross-sedimentary cover) are usually of complex origin, potentially involving the combined or sequential action of tectonic or hydraulic rupture, fluidization, metasomatism, dissolution / karstification and collapsing. This polygenetic nature is due to the material and mechanical heterogeneity of sections of host strata and changes in the properties of fluids during their upward migration, as well as over time. However, the assignment of structures to certain genetic categories can be carried out by the nature of the dominant formation processes.