Identi®cation of primary Ce-anomaly signatures in fossil biogenic apatite: implication for the Cambrian oceanic anoxia and phosphogenesis S. Morad a, * , S. Felitsyn b a Department of Earth Sciences, Uppsala University, 752 36 Uppsala, Sweden b Institute of Precambrian Geology & Geochronology, Russian Academy of Science, 199034 St. Petersburg, Russian Federation Received 18 April 2000; accepted 1 February 2001 Abstract Based on REE analyses of 105 world-wide distributed Cambrian fossil apatite samples and eight late Neoproterozoic phosphate concretions, a close relationship is established between the concentrations of MREE and Ce anomalies. Shale La/ Sm N ratios of 0.35 is suggested as a critical value for the discrimination of the natural Ce anomaly acquired during pre-burial/ earlydiagenesisbybiogenicapatitefromanarti®cialCeanomalyinducedduetothecalculation.Ceanomaliesinapatiteswith ¯at REE distribution and La/Sm N ratio .0.35 may be used as indicative of oceanic anoxia. q 2001 Elsevier Science B.V. All rights reserved. Keywords: REE; Oceanic anoxia; Apatite; Cambrian; Precambrian 1. Introduction Marine biogenic apatite is regarded as one of the main suitable minerals for deciphering the geochem- ical signature e.g. REE content, Nd and Sr isotopes, andpaleo-salinity)ofambientseawater,aswellasfor estimation of the ¯uvial sediment input and rate of sedimentation e.g. Wright et al., 1984; Grandjean et al., 1987; Schmitz et al., 1991; Laenen et al., 1997). Among the most important global phosphogenesis events is the one that took place at the Precam- brian±Cambrian boundary. Such events are believed to have been caused by oceanic turnover that resulted in coverage of continental shelves by nutrient-rich, anoxic waters Cook and Shergold, 1984). An impor- tant but controversial piece of geochemical evidence GermanandElder®eld,1990)todecipheroxicversus anoxicoceanicconditionsisbelievedbysomeauthors to be the Ce anomaly in marine biogenic phosphate Wright et al., 1987; Kidder and Eddy-Dilek, 1994; Macleod and Irving, 1996; Holser, 1997). However, the assumption that REE in marine biogenic apatite re¯ecttheredoxconditionsofambientseawaterfaces two major problems: i) there is a difference in the REE distribution patterns between biogenic apatite and recent seawater McArthur and Walsh, 1984), and ii) enrichment of apatite with REE may occur in the post-mortem stage Holmden et al., 1996) and during diagenesis at very shallow depths below the sea¯oor Sholkovitz et al., 1989). Thus, there is a considerable uncertainty about whether or not REE in marine apatite are reliable indicators of seawater composition. Sedimentary Geology 143 2001) 259±264 0037-0738/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII:S0037-073801)00093-8 www.elsevier.com/locate/sedgeo * Corresponding author. Fax: 146-18-4712591. E-mail address: sadoon.morad@geo.uu.se S. Morad).