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Zastosowania skamieniałości śladowych w analizie facjalnej i wysokorozdzielczej stratygrafii sekwencji - przykład z kambru polskiej części kratonu wschodnioeuropejskiego

Pacześna J.

Przegląd Geologiczny

2001

Vol. 49 nr 12

1137-11

Trace fossils are a good tool for identification and interpretation of sedimentary environments. The basic procedure of ichnofacies analysis is to define the interactions between the ecological structure of trace fossil assemblage and the abiotic factors of environment. The ichnologic criteria are very good and easily recognizable indicators of the environmental architecture of parasequences and their bounding surfaces. Furthermore, the trace fossil assemblages can be used as indicators ofpaleobathymetric trends in geological sequences, thus indicating contrasting stacking patterns of packages of parasequences. The Middle Cambrian parasequence package of the Podlasie Depression (central part of the Polish segment of the East European Craton) shows a distinctly upward shallowing trend interfingering between upper offshore, lower and upper shoreface environmental zones. These parasequences are arranged into a regressive, progradational parasequence set of highstand system tract. Another trend appears in the retrogradational parasequence set of transgressive system tract in the Lower Cambrian deepening upward succession of the Podlasie Depression. In the upper parts of the sequence, parasequences with more deep-water assemblages of trace fossils, indicating the upper offshore environments, prevail. Based on the ichnologic criteria, stratigraphically significant discontinuities can be delineated. The more readable in an ichnologic record are the flooding surface bounding parasequences, parasequence sets and transgressive or regressive surfaces of coastal erosion. Discontinuity surfaces are marked by substrate-controlled Glossifungites assemblage of trace fossil excavated in semiconsolidated, flrmground substrates previously highly biolurbated by a softground ichnofossil assemblage.