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| Titel |
Sr Isotopes at the Onset of the Ice Ages at the Northern Apennines |
| VerfasserIn |
Rita Fuchs, Boaz Lazar, Lucia Angiolini, Gaia Crippa, Mordechai Stein |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145522
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| Publikation (Nr.) |
 EGU/EGU2017-9470.pdf |
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| Zusammenfassung |
| Sr isotopes can be used to constrain the marine Sr budget. The temporal variations in the
87Sr/86Sr ratios (radiogenic Sr) have been reconstructed over the past few decades based on
marine macro and micro fossils data (e.g. brachiopods and foraminifera). It is used to
constrain the sources and amounts of strontium that dictate the temporal variations in oceanic
Sr throughout the Phanerozoic. On the other hand, the study of processes controlling the
composition stable Sr isotopes (δ88∕86Sr) is very new and only limited research was
conducted on this topic during the past few years. Up to date, no δ88∕86Sr data
are available for considerable parts of Earth’s history and the contribution of the
potential Sr sources to the oceans is poorly constrained. Here, we set to examine the
behavior of radiogenic and stable Sr isotopes in the marine environment of the
northern Apennines (Italy) during the time interval of the late Pliocene to early-Middle
Pleistocene – upon the onset of ice ages in the northern latitudes. We collected fossil
mollusks from outcrops of the Arda and Stirone Rivers that are rich in bivalves,
brachiopods, foraminifera (that were used for establishing the chronostratigraphy of the
sections) and other genera. Ecological and sedimentological analysis of the section
suggest a normal marine environment of depth range of several tens of meters that
existed on the southern flanks of the large Po embayment. In order to evaluate the
potential of the fossil assemblages in the Arda and Stirone sections to serve as
reliable recorders of the marine δ88∕86Sr of seawater during the desired period, we
examined mineralogical and chemical properties of the fossils (e.g. distribution of trace
elements like Sr and Mg in the skeletons, microstructures like secondary fillings of
punctate shells in brachiopod) and measured the 87Sr/86Sr ratios. Among the species
analyzed, Aequipecten opercularis (bivalve) and Glycymeris inflata (bivalve) have
aragonite skeletons that show normal late Pliocene - early Pleistocene marine values of
87Sr/86Sr ratios (∼ 0.709). On the other hand, the calcite skeleton organisms from
the same bed, Ostrea edulis (bivalve) and Terebratula scillae (brachiopod), show
continental effect on the 87Sr/86Sr isotopes (values ranging from 0.7084 to 0.7089). It
should be noted that these two groups of organisms have also different life styles
and metabolic rates. Measuring the δ88∕86Sr values on the fossils with “normal”
marine radiogenic Sr composition and those with continental radiogenic Sr signal
may provide additional constraints on the sources and processes that affected the
geochemistry of these species and yield a reliable marine δ88∕86Sr value for that period. |
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