A detailed carbon isotope record has also been published from the Kardla core, Estonia, where the HICE was also identified (Kaljo et al., 2001; Young et al., 2010). The I/(Ca+Mg) values within the upper Halliku Formation show a consistent absence of iodine (0 μmol/mol) but begin to increase within the Kuldiga Formation (Conochitina scabrabiozone) to a maximum value of 1.6 μmol/mol. The values fall to near zero (< 0.1 μmol/mol) at the top of the formation (Fig. 3). Iodine contents increase again within the Saldus Fm to a maximum of 1.5 μmol/mol and then decline to near-zero values within the basal Õhne Formation. Finally, I/(Ca+Mg) ratios increase steadily throughout the Õhne Formation (Spinachitina fragilis biozone) to a maximum of 2 μmol/mol. The δ³⁴S_CAS data from the Kardla core show a negative perturbation in the lowermost Halliku Formation, within the Katian lower Conochitina rugata chitinozoan biozone, from maximum values of +30‰ to minimum values of +20‰. Subsequently, δ³⁴S_CAS values remain relatively invariant, ranging between +20‰ to +25‰ into the Hirnantian (late C. rugata through S. scabra biozones), where average values trend to +30‰ in the upper Kuldiga through Õhne formations (S. fragilis biozone). The corresponding δ³⁴S_pyr values range between -35‰ and +7‰, with an average of ~ -17‰ within the Halliku Formation. The overlying Kuldiga and Saldus formations record δ³⁴S_pyr values that steadily increase to a maximum value of +37‰, and these values return to a new baseline of ~ -30‰ in the overlying Õhne Formation.

Figure 3. Geochemical and lithologic profile of the Kardla Drill Core, Estonia. Chitinozoan biozones and lithologies are modified from Kaljo et. al., 2001 and Young et. al., 2010. A) δ¹³C_carb replotted from Young et. al., 2010. B) δ³⁴S_CAS this study. C) δ³⁴S_pyr this study. D) Δ³⁴S, this study. E) I/(Ca+Mg) ratios, this study.