Nd isotope composition and rare earth element distribution in early Paleozoic biogenic apatite from Baltoscandia: A signature of Iapetus ocean water

Nd isotopic composition of Late Devonian seawater in western Thailand: Geotectonic implications for the origin of the Sibumasu terrane

“…The Paleozoic oceans exhibited a similar Nd isotopic composition to that of the modern ones (e.g., Keto and Jacobsen, 1988;Holmden et al, 1996;Felitsyn et al, 1998;Dopieralska et al, 2006). Hence, reservoirs with a strong non-radiogenic composition of seawater could occur only in very proximal paleoceanographic settings and within epicontinental seas.…”

“…In addition, Nd isotopes have the singular benefit of providing information about age domains of eroded source rocks (dePaolo, 1988). While numerous studies documenting the Nd isotopic composition of seawater and its circulation patterns were published for the Cenozoic and Mesozoic (e.g., Stille et al, 1996;Thomas et al, 2003;Scher and Martin, 2004;Puceat et al, 2005;Gourlan et al, 2008;Dera et al, 2009), reconstructions from the Paleozoic are still rare (Holmden et al, 1996(Holmden et al, , 1998Felitsyn et al, 1998;Fanton et al, 2002;Dopieralska, 2009). The largest dataset of Nd Paleozoic seawater signatures is available from the Upper Devonian, but it is limited to the Variscan realm in Europe and North Africa (Dopieralska, 2003;Dopieralska et al, 2006).…”

Seawater rare-earth element patterns preserved in apatite of Pennsylvanian conodonts?

“…However, fundamental to this process is the assumption that no fractionation of the REEs from seawater concentrations occurs during uptake by the solid phases, release into pore waters, and subsequent uptake by the apatite. If REE uptake by biogenic apatite occurs during diagenesis, any original vital effects are likely masked or lost (Felitsyn et al, 1998). Shields and Stille (2001) expressed similar concerns regarding REE concentrations and ratios preserved in authigenic phosphorites.…”

“…In addition to seawater-like REE shale-normalized patterns, fossil biogenic and authigenic apatite display two other common patterns: MREE-enriched (commonly referred to as ''bell-shaped") and flat; the MREE-enriched pattern is most common (McArthur and Walsh, 1984;Wright et al, 1987;Grandjean and Albarède, 1989;Grandjean-Lécuyer et al, 1993;Kidder and Eddy-Dilek, 1994;Laenen et al, 1997;Felitsyn et al, 1998;Picard et al, 2002;Trotter and Eggins, 2006). While early studies argued that biogenic apatite contains greatly enriched but unfractionated geochemical signatures of seawater (e.g., Wright et al, 1987), MREE enrichment has not been observed in modern oceanic waters (Klinkhammer et al, 1983, and references therein;Byrne and Sholkovitz, 1996, and references therein).…”

“…Use of the REE paleoceanographic proxy is grounded on observations from modern phosphatic ichthyoliths for which seawater-like shale-normalized REE patterns are observed, including examples of preserved negative Ce-anomalies (Elderfield and Pagett, 1986;Wright et al, 1987;Toyoda and Tokonami, 1990). The preservation of seawater-like patterns with large, but variable, enrichments in absolute REE concentrations in fossil apatite has led some workers to conclude that postmortem REE enrichment occurs soon after the organism dies, during exposure at the sediment-water interface (e.g., Wright et al, 1987;Felitsyn et al, 1998). However, Toyoda and Tokonami (1990) demonstrated that diffusion of REEs into biogenic apatite is too slow to produce the observed elevated REE concentrations in fossil apatite prior to burial, so that REEs are likely scavenged from pore waters.…”