Preservation of sea water Sr and Nd isotopes in fossil fish teeth; bad news and good news

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doi: 10.1016/S0012-821X(04)00030-5
Author(s): Martin, E. E.; Scher, H. D.
Author Affiliation(s): Primary:
University of Florida, Department of Geological Sciences, Gainesville, FL, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 220(1-2), p.25-39. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 84 refs.; illus., incl. 2 tables
Summary: We analyzed 87Sr/86Sr ratios in foraminifera, pore fluids, and fish teeth for samples ranging in age from Eocene to Pleistocene from four Ocean Drilling Program sites distributed around the globe: Site 1090 in the Cape Basin of the Southern Ocean, Site 757 on the Ninetyeast Ridge in the Indian Ocean, Site 807 on the Ontong-Java Plateau in the western equatorial Pacific, and Site 689 on the Maud Rise in the Southern Ocean. Sr isotopic ratios for dated foraminifera consistently plot on the global seawater Sr isotope curve. For Sites 1090, 757, and 807 Sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values, as are values for fossil fish teeth. In contrast, pore fluid 87Sr/86Sr values at Site 689 are more radiogenic than contemporaneous seawater, and the corresponding fish teeth also record more radiogenic values. Thus, Sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values; furthermore, there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve, and the associated offset between the fish teeth and the seawater curve. These data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange Sr with its surroundings during burial and diagenesis. Therefore, Sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores, but cannot be used to fine-tune age models. In contrast to the Sr isotopic system, our Nd concentration data, combined with published isotopic and rare earth element data, suggest that fish teeth acquire Nd during early diagenesis while they are still in direct contact with seawater. The concentrations of Nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids. As a result, Nd isotopes are not altered during burial and later diagenesis. Therefore, fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater Nd isotopic compositions from the time of deposition. Abstract Copyright (2004) Elsevier, B.V.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Alkaline earth metals; Atlantic Ocean; Biostratigraphy; Cenozoic; Chemical composition; Chemostratigraphy; Chordata; Diagenesis; Eocene; Foraminifera; Geochemistry; Indian Ocean; Invertebrata; Isotope ratios; Isotopes; Leg 113; Leg 121; Leg 130; Leg 177; Metals; Microfossils; Mid-ocean ridges; Models; Nannofossils; Nd-144/Nd-143; Neodymium; Ninetyeast Ridge; ODP Site 1090; ODP Site 689; ODP Site 757; ODP Site 807; Ocean Drilling Program; Ocean floors; Ontong Java Plateau; Pacific Ocean; Paleogene; Pisces; Plantae; Pleistocene; Preservation; Protista; Quaternary; Radioactive isotopes; Rare earths; Sea water; Sedimentation; Sedimentation rates; Sr-87/Sr-86; Stable isotopes; Strontium; Teeth; Tertiary; Trace elements; Vertebrata; West Pacific
Coordinates: N033622 N033626 E1563730 E1563728
S170128 S170123 E0881054 E0881048
S425449 S425449 E0085359 E0085359
S643101 S643100 E0030600 E0030559
Record ID: 2005071198
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands