Geneza nagromadzeń ahermatypowej fauny bentonicznej

Adam Bodzioch



Accumulations of ahermatypic benthic marine fauna are known to vary in origin. The paper presents a scheme of genetic classification of such accumulations, based on differences in degree of redeposition of fauna. The subdivision of accumulations into autochtoneous, parautochtoneous, and allochtoneous (3) is accepted here. The degree of redeposition of fauna may be evaluated taking into account the following criteria: I) number of individuals in life position, 2) disarticulation, 3) crushing, 4) abrasion, 5) orientation, 6) size distribution of individuals, 7) other premises (lithology, sedimentary structures, microfacies, etc.).
Autochtoneous accumulations are defined as originating in place of death of organisms. They may originate in two ways: 1) due to development of fauna under the optimum ecological conditions (high density of seafloor inhabitation, normal rates of sedimentation), and 2) due to reduced rates of sedimentation (when this is the case, density of inhabitation may be low). Table 1 gives the most characteristic features of such accumulations and references to examples in the literature.
Parautochtenous accumulations are defined as originating in environment typical for development of the represented organisms. They originate with contribution of sedimentary agents, mainly responsible for increase in concentration of skeletal elements in sediment. Analysis of organic remains makes possible identification of accumulations formed with contribution of storms, tidal currents, bottom currents, and activity of organisms. Table 2 gives major features of parautoehtoneous accumulations and references to examples in the literature.
Allochtoneous aceumulations are defined as originating far from place of death (and also life) of organisms, due to activity of sedimentological agents capable to transport and concentrate organic remains. On the basis of results of studies on skeletal remains there may be differentiated accumulations formed due to transport by bottom, storm, and tidal currents and turbidites and the mode of origin of a concentration of bioclasts reconstructed. Table 3 gives major features of individual types of allochtoneous accumulations.
Accumulations of skeletal elements in traps (open fissures in sea floor, submarine eaves, channels made by bottom-dwelling organisms) are differentiated as a separate category as transportation mechanism may be different in individual eases.

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