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TitleRare earth elements in conodont apatite: seawater or pore-water signatures?
AuthorTrotter, J A; Barnes, C R; McCracken, A D
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 462, 2016 p. 92-100,
Alt SeriesEarth Sciences Sector, Contribution Series 20160001
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceManitoba; Ontario; Newfoundland and Labrador; Quebec; Nunavut
NTS2D; 2E; 2L; 2M; 11O; 11P; 12A; 12B; 12E; 12F; 12G; 12H; 12I; 12P; 16D; 16E; 16K; 16L; 16M; 16N; 22H; 25G; 25H; 25I; 25J; 25K; 25L; 25M; 25N; 25O; 25P; 26; 27; 36A; 36B; 36C; 36D; 36E; 36F; 36G; 36H; 36I; 36J; 36P; 37; 38A; 38B; 38F; 38G; 41G; 41H; 41J; 47C; 47D; 47E; 47F; 47G; 47H; 48; 52E; 52L; 52M; 57E; 57H; 58E; 58F; 58G; 58H; 59A; 59B; 62F; 62G; 62H; 62I; 62J; 62K; 62N; 62O; 62P; 63A; 63B; 63C; 63F; 63G; 63H; 63I; 63J; 63K; 68E; 68H
AreaWilliston Basin; Manitoulin Island; Anticosti Island; Canadian Arctic Archipelago; Cornwallis Island; Baffin Island; Devon Island
Lat/Long WENS-102.0000 -95.0000 55.0000 49.0000
Lat/Long WENS -83.2500 -81.5000 46.2500 45.5000
Lat/Long WENS -59.5000 -54.0000 52.0000 47.5000
Lat/Long WENS -64.7500 -61.5000 50.0000 49.0000
Lat/Long WENS -97.0000 -60.0000 76.7500 61.7500
Subjectspaleontology; geochemistry; Nature and Environment; micropaleontology; microfossils; conodonts; pore water samples; models; apatite; paleoenvironment; biogeochemistry; biogenesis; sea water geochemistry; marine sediments; mass spectrometer analysis; absorption; diagenesis; alteration; Laurentia; Animals; Phanerozoic; Paleozoic; Silurian; Ordovician
Illustrationsplots; tables
ProgramScience laboratory network
AbstractRare earth element (REE) compositions of Lower Palaeozoic conodont microfossils from different sites in Laurentia are presented and compared to modern pore-water REE compositions reported in the literature. These data are modelled to account for matrix-induced fractionation of REEs during uptake by apatite. The apatite-water partition co-efficients (Kd) for adsorption of REEs are applied to a range of modern pore-water compositions (i.e. Pore-waterN × Kd), the resultant data being similar to Palaeozoic conodont apatite compositions. Similar resemblances to modern pore-water REE compositions are shown by palaeofluids derived from conodonts using the inverse relationship in REE adsorption kinetics (i.e. Bioapatite/Kd), with rare low concentration samples yielding HREE-enriched patterns. These results clearly show the importance of matrix effects and hence the post-mortem physico-chemical processes by which elemental uptake occurs in fossil biogenic minerals, which are crucial to consider when interpreting geochemical signatures. Furthermore, the similarities between apatite REE compositions of conodonts and those derived from modern pore-waters challenge prior hypotheses of seawater REE evolution inferred directly from conodont apatite, and question the reliability of conodont apatite as archives of seawater REE chemistry. These outcomes likely have broader implications for fossil bioapatites in general given the physico-chemical processes occurring within marine sediments and the inherent behaviour of apatite-REE systematics.
Summary(Plain Language Summary, not published)
The rare earth element (REE) compositions in the mineral found in some fossils has been used to interpret shifts in ocean environments over geological time, thus contributing to interpretations of hydrocarbon basin evolution. In this study of conodonts, which are jaw parts of extinct fish-like animals, the conclusion is that fossil apatites are not reliable archives of REE seawater chemistry and instead reflect chemical changes within the seabed sediments. Conodonts are primarily used for determining the geological age and thermal history of rocks. Both of these are critical in studies of sedimentary basins and for improving the success of hydrocarbon exploration. In addition, the conodont apatite mineral is increasingly used in geochemical studies of ancient environments - added value to the original collection use.

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