Περίληψη:
The microstructure and geochemical composition of foraminiferal tests
are valuable archives for the reconstruction of paleoclimatic and
paleoecological changes. In this context, the late Miocene
Globigerinoides obliquus shells from Faneromeni section (Crete Island)
were investigated through Scanning Electron Microscopy (SEM) imaging,
Energy Dispersive System (EDS) analysis and X-Ray Diffraction (XRD)
spectroscopy in order to evaluate their potential as paleoenvironmental
archives in the eastern Mediterranean. Investigation of diagenetic
features, in late Miocene sediments from the Faneromeni section, shows
that carbonate precipitation and cementation occur in various
lithologies, particularly in carbonate rich portions, such as bioclastic
or clayey limestones. We identified 3 different diagenetic stages
(early, intermediate, advanced), as a function of taphonomy in the study
area. The comparison of microstructural and geochemical characteristics
reveals a sequence of preservation states with “glassy” to
“frosty” to “chalky” shells, indicative of the progressive
diagenetic alteration of late Miocene planktic foraminiferal calcite.
The early diagenetic stage occurs during the Tortonian, and consists of
intermediates between “glassy” and “frosty” individuals. Around
the Tortonian/Messinian (T/M) boundary at the second diagenetic stage,
planktonic foraminifera have a clear “frosty” appearance, showing a
gradual high-Mg calcite (to dolomite) crystal overgrowth development and
dissolution of biogenic calcite. During the late Messinian and
progressively through the Messinian Salinity Crisis (MSC), planktonic
foraminifera present a “chalky” taphonomy. The additional
precipitation of authigenic high-Mg inorganic calcite and dolomite
crystals in the exterior of the tests characterizes the advanced
diagenetic stage. The measured amount of diagenetic Mg-rich (10-14%
molar Mg on average) calcite and/or dolomite coatings is compatible with
results obtained on modern eastern Mediterranean core-top sediments. The
assessment of such a diagenetic alteration contributes to a more precise
reconstruction of sea surface temperatures (SSTs) during the Neogene,
such that only when the changing proportions of the texture are
accounted for, would geochemical measurements and subsequent
paleoenvironmental interpretations be more meaningful. However, further
investigations should extend this approach to test the robustness of our
findings across a range of taphonomies, ages and burial settings.
Συγγραφείς:
Antonarakou, Assimina
Kontakiotis, George
Vasilatos, Charalampos
and Besiou, Eva
Zarkogiannis, Stergios
Drinia, Hara
Graham
Mortyn, P.
Tsaparas, Nikolaos
Makri, Panayota
Karakitsios,
Vasileios
