Palaeoceanographic linkage of geochemical and graptolite events across the Silurian–Devonian boundary in Bardzkie Mountains (Southwest Poland)

Abstract

The Silurian–Devonian (S–D) transition in the Bardzkie Mountains is developed as deep-water, graptolitic black shales. The highest Silurian transgrediens Zone and the first Devonian uniformis Zone are separated by a thin (30 cm) interval of a linograptid `interregnum'. Thirteen samples from the S–D transition have been analysed for major and minor elements. Si/Al, Si/Al/TOC, Ga/Al 2 O 3 , V/V+Ni ratios and TOC, Mn, Zr, Ti, Re, Mo, Cd, Cu and REE have been found to correlate with the habitat replacement of the graptolite assemblages. The linograptid burst, accompanied by changing sediment geochemistry across the S–D boundary, are attributed to short-term shallowing of the upwelling system which introduced specific nutrient-rich waters into the mixed layer.