Graptolite turnover and δ13Corg excursion in the upper Wenlock shales (Silurian) of the Holy Cross Mountains (Poland)

Abstract

The mid–late Homerian Age of the Silurian Period was a time of intense changes in biota, oceanic chemistry, and sea level and is known as the lundgreni extinction (for the graptolite extinctions), the Mulde bioevent (for the conodont turnover event) or the Homerian carbon isotope excursion (CIE) probably related to glacially influenced climate perturbation. New information on this interval from the deep water sedimentary and graptolite succession of the Kielce Region (Holy Cross Mountains, Poland) of the northern margin of the Małopolska Block is presented here based on analysis of the Prągowiec Ravine section. The lundgreni–nilssoni graptolite biozones interval have been recognized there. This interval is composed by dark shales with very rare benthic fauna, which indicate the deep open-marine (pelagic) paleoenvironment. Ten samples were taken for the δ13Corg analysis from the lundgreni (2 samples), parvus (2 samples), praedeubeli (2 samples), praedeubeli–deubeli (1 sample), ludensis (2 samples) and nilssoni (1 sample) biozones. According to the δ13Corg results, the first positive δ13Corg excursion of the Mulde Bioevent is well recognized. The δ13Corg values rise from −30.7 – −30.1 ‰ in the lundgreni Biozone to −29.3 – −28.7 ‰ in the parvus Biozone and fall below −30 ‰ in the praedeubeli–deubeli interval. The second positive δ13Corg peak of the Mulde Event was not recognized in the Prągowiec Ravine. Based on the numerical comparisons using Raup-Crick metric of co-occurrences of graptolite species, the upper Homerian was characterized by significant between-biozone turnover of these taxa at the given locality.

Keywords

• Poland
• Holy Cross Mountains
• Silurian
• Mulde Event
• geochemistry
• δ13Corg