Environmental interpretation of atrypid shell beds from the Middle to Upper Devonian boundary of the Holy Cross Mts and Cracow Upland

Abstract

As indicated by a comparative analysis of atrypid shell beds yielded by stromatoporoid-coral limestones at the Middle to Upper Devonian boundary at Chęciny (Holy Cross Mts) and Dębnik (Cracow Upland), the atrypid Desquamatia was widely tolerant of environmental conditions. It formed a pioneer association able to colonize intershoal, poorly aerated habitats (Dębnik), as well as those periodically influenced by restricted logoons in conditions of fluctuating (?·lowering) salinity (Chęciny). The shell size and morphology of Desquamatia is variable depending upon environmental variation related especially to the environmental stress and toxicity being higher at Dębnik than at Chęciny. Atrypid shell beds produced by monotypic population of Desquamatia are characteristic of Givetian to Frasnian transitional beds in Poland, West Europe, and the United States. In the systematic part of the paper the atrypid Desquamatia (Seratrypa) gIobosa (Gürich) and the associated cyrtospiriferid Uchtospirifer nalivkini Lyashenko are described.