Oxygen and carbon isotope composition of conodont apatite and carbonates from the Devonian–Carboniferous transition in near-equatorial eastern Laurussia, recorded in the Holy Cross Mountains (Poland)

The Devonian–Carboniferous transition is characterized by global climate cooling triggered by glaciation on the Gondwana palaeocontinent and worldwide extinction in marine and terrestrial realms. This study presents the oxygen isotope composition of conodont apatite and carbon isotope signature in carbonates from the Devonian–Carboniferous transition on the near-equatorial shelf of eastern Laurussia, recorded in the Holy Cross Mountains (Poland). <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O apatite values measured in the uppermost Famennian show an increase of approximately 1‰, consistent with the globally observed rise in this ratio during the middle–late Famennian, which marks the transition from greenhouse to icehouse conditions. We interpret this increase as the combined result of climate cooling and the growth of ice sheets. Notably, the values recorded in the studied area are higher than those reported in other locations of SE Laurussia and western Paleotethys, suggesting an additional local input of 18 O. The highest <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O apatite values in our study coincide with a conspicuous positive excursion of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 13 C carb (∼2.5‰) in the latest Famennian kockeli conodont Zone. We propose that both of these excursions reflect late Famennian climate cooling and anti-estuarine seawater circulation during a highstand period associated with the Late Devonian palaeocurrent system, which probably drove the downwelling of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O-enriched saline waters.