Factors affecting ⁸⁷Sr/⁸⁶Sr preservation in conodont apatite : An example from the Ordovician of Baltoscandia

Summary, in English

Despite frequent use of conodonts as an archive for seawater ⁸⁷Sr/⁸⁶Sr, available diagenetic screening tools are inconsistent predictors of primary seawater ⁸⁷Sr/⁸⁶Sr preservation. Here, we attempt to isolate variables affecting the preservation of seawater ⁸⁷Sr/⁸⁶Sr in conodonts. We present new Middle–Late Ordovician (∼470–450 Ma) conodont ⁸⁷Sr/⁸⁶Sr from mid-paleolatitude (30–45°S) carbonate successions from central Sweden (Fjäcka, Kårgärde) and Estonia (Uuga Cliff, Viki borehole) which have low Conodont Alteration Index (CAI) values of 1–1.5. Coeval ⁸⁷Sr/⁸⁶Sr measurements from Kårgärde and Estonian sections are offset from global seawater by ∼ +2 × 10⁻⁴ but preserve the overall structure of the seawater curve, suggesting minor diagenetic Sr exchange. ⁸⁷Sr/⁸⁶Sr measurements from the more argillaceous Fjäcka section show extensive alteration with highly radiogenic values as much as ∼6 × 10⁻⁴ greater than global seawater and a stratigraphic trend that diverges from the seawater curve. This may be explained by highly radiogenic Sr contribution from the Kinnekulle K-bentonite and Fjäcka shale units that occur at Fjäcka section. We compiled 1164 conodont ⁸⁷Sr/⁸⁶Sr measurements spanning ∼485–250 Ma and categorized measurements by host rock, sample preparation, paleolatitude, and CAI. Boxplots and Mann-Whitney U testing of residual values relative to the seawater curve (⁸⁷Sr/⁸⁶Sr_conodont – ⁸⁷Sr/⁸⁶Sr_seawater) reveal that paleolatitude and associated differences in sedimentation rate affect preservation of seawater ⁸⁷Sr/⁸⁶Sr values in conodonts. The relative abundance of clay minerals did not significantly correlate with residual values for conodonts from mid- or low-latitude deposits. We recommend that future investigations of seawater ⁸⁷Sr/⁸⁶Sr records using conodont apatite target low-latitude settings with high sedimentation rate and CAI ≤ 2.

• Author: Christopher T. Conwell; Matthew R. Saltzman; Anders Lindskog; Mats E. Eriksson; Elizabeth M. Griffith; Stephen A. Leslie; Cole T. Edwards; Olle Hints; Achim D. Herrmann
• Department/s: Department of Earth and Environmental Sciences (MGeo); Department of Geology
• Publishing year: 2026-03-01
• Language: English
• Publication/Series: Palaeogeography, Palaeoclimatology, Palaeoecology
• Volume: 685
• Links: http://dx.doi.org/10.1016/j.palaeo.2025.113524
• Document type: Journal article
• Publisher: Elsevier
• Topic: Geology
• Keywords: Carbonates; Chemostratigraphy; Conodont; Diagenesis; Geochemistry; Sr isotope
• Status: Published
• ISBN/ISSN/Other: ISSN: 0031-0182