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 δ34SCAS 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, δ34SCAS 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
δ34Spyr values range between -35‰ and
+7‰, with an average of ~ -17‰ within the Halliku
Formation. The overlying Kuldiga and Saldus formations record
δ34Spyr 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)
δ13Ccarb replotted from Young et. al.,
2010. B) δ34SCAS this study. C)
δ34Spyr this study. D)
Δ34S, this study. E) I/(Ca+Mg) ratios, this study.