 |
| Titel |
Bivalve shells as high resolution biomineral archives of early Pleistocene
seasonality |
| VerfasserIn |
Gaia Crippa, Lucia Angiolini, Melanie Leng |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126007
|
| Publikation (Nr.) |
 EGU/EGU2016-5674.pdf |
|
|
|
|
|
| Zusammenfassung |
| Bivalves are among the best tools for palaeoclimatic and palaeoenvironmental reconstructions
because they are known to precipitate their shells in isotopic equilibrium with the seawater in
which they live. Also, the analysis of their shell microstructure shows that these organisms
modify their shell fabric in response to environmental variations forming growth
lines. However, diagenetic processes may alter fossil bivalve shell microstructure
and shell isotopic composition; for this reason it is important to perform screening
tests to check if the shell is pristine and thus confidently identify biogenic calcium
carbonate as a reliable proxy of primary seawater chemistry. Here, we performed a
detailed study of the microstructure of ten aragonite bivalves shells belonging to
Glycymeris insubrica, Glycymeris inflata and Arctica islandica, collected from the lower
Pleistocene Arda River marine succession (northern Italy), to check their preservation for
subsequent sclerochemical stable isotope analyses (δ18O, δ13C). To assess shell
preservation 4 different screening techniques were used: Scanning Electron Microscopy
(SEM), Catholuminescence (CL), X-Ray Powder Diffraction (XRD) and Feigl’s
solution.
Shells of species of Glycymeris, under SEM, show an outer crossed lamellar
layer, an inner irregular and cone complex crossed lamellar layer and an irregular
simple prismatic pallial myostracum; all the layers are penetrated by cylindrical
tubules. Arctica islandica has an outer homogenous/crossed lamellar/crossed acicular
layer, an inner fine complex crossed lamellar layer and an irregular simple prismatic
pallial myostracum. The comparative analysis with recent fabrics shows a consistent
pattern for species of both Glycymeris and Arctica genera, the recent and fossils shell
microstructures being almost identical. Analyses at CL, XRD and Feigl’s solution
support that these fossil species have a non luminescent shells composed of pure
aragonite.
The excellent preservation and the distinct growth lines of the Arda taxa makes them a
powerful archive to study, through sclerochemistry, the change in seasonality during the early
Pleistocene, a time interval characterized by several climatic oscillations linked to
glacial/interglacial cycles, in the Mediterranean area. |
|
|
|
|
|
|