An approach to the description and interpretation of ichnofabrics in paleosols

GENISE, JORGE F, E.S. BELLOSI &MIRTA GONZÁLEZ

Teh application of ichnology to Stratigraphic Analysis

The Geological Society Spetial publication 228

Lugar: Londres; Año: 2004; p. 355 - 382

Abstract: Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.