Gamma-ray spectrometry across the Upper Devonian basin succession at Kowala in the Holy Cross Mountains (Poland)

Abstract

The Upper Devonian sequence at Kowala in the Holy Cross Mountains was logged using gamma-ray spectrometry, for investigating the changes of oxygenation level in the Late Devonian basin. The Th/U ratio indicates that oxygen levels were low throughout the Late Frasnian interval, with low peaks during the Kellwasser Events showing anoxic conditions in the basin. The F-F boundary interval was also oxygen deficient, but there may have been a brief reoxygenation at the boundary itself. By the Famennian crepida Zone, the basin gradually began to reoxygenate, but in the trachytera Zone another anoxic event, the Annulata Event occurred, causing a bloom rather than extinction of specially adapted taxa such as Guerichia. Thus the gamma-ray spectrometry data suggests that basinal anoxia prevailed through much of the Late Frasnian. The F-F extinction might have been the result of prolonged stresses imposed on the ecosystem, particularly during the euxinic Upper Kellwasser Event.