Anna Świerczewska

Deformation bands and the history of folding in the Magura nappe, Western Outer Carpathians (Poland)

Abstract Deformation bands ( db ) which are indicative for soft-sediment deformation during the folding of flysch sediments are widespread within the Eocene strata of the Magura nappe. Four types of db have been distinguished: (1) db with no cataclasis of detrital sand grains; (2) db with traces of feldspar cataclasis; (3) db with strong cataclasis of detritic feldspar grains; and (4) db with feldspar and quartz cataclasis. In all types of db , calcite cementation occurred after the formation of the deformation bands. No calcite cataclasis was observed in the deformation bands. The bands developed progressively, from (1) to (4), during and after regional folding. Folding occurred when the host strata were poorly indurated and/or under low confining pressure. The earliest db (bands with no cataclasis) formed contemporaneously with water-escape sheets. We conclude that regional folding started not later than during the deposition of the host strata. Calcite mineralization was introduced into the host strata and into the db along cross-fold joints after the completion of regional folding. Within the studied portion of the Magura nappe, regional folding started not later than during Eocene time. Folding was completed when the host strata were not yet fully indurated, most probably still during the Eocene.