Dissertation committee:
1. Antonarakou Assimina Professor Faculty of Geology & Geoenvironment NKUA Scientific topics: Micropalaeontology, Marine geology, didactics of Geosciences (Supervisor) aantonar@geo.uoa.gr
2. Mulch Andreas Professor (W3), Goethe-Universität Frankfurt & Senckenberg Biodiversity and Climate Research Centre, Scientific topics: Stable isotope paleoaltimetry, Interactions of mountains, climate and biodiversity, Paleoclimate reconstructions (Member) andreas.mulch@senckenberg.de
3. Krijgsman Wout Professor Utrecht University, Scientific topics: Paleomagnetismstratigraphy, Messinian salinity crisis, Paratethys (Member) w.krijgsman@uu.nl
4. Vasiliev-Popa Iuliana Senior Researcher at Senckenberg Biodiversität und Klima Forschungzentrum, Frankfurt am Main, Germany, Scientific topics: Geology,
Stratigraphy, Organic Geochemistry (Member) Iuliana.VasilievPopa@senckenberg.de
5. Triantaphyllou Maria Professor Faculty of Geology & Geoenvironment NKUA, Scientific topics: Micropalaeontology, palaeoenvironments, Stratigraphy (Member) mtriant@geol.uoa.gr
6. Drinia Hariklia Professor Faculty of Geology & Geoenvironment NKUA, Scientific topics: Palaeoecology – Sequence Stratigraphy - Sedimentology (Member) cntrinia@geol.uoa.gr
7. Tsourou Theodora Assistant Professor Faculty of Geology & Geoenvironment NKUA, Scientific topics: Palaeontology, (Member) ttsourou@geol.uoa.gr
Summary:
The Late Miocene has been considered as a period of crucial paleoclimatic and paleoceanographic changes in the Mediterranean Basin, with significant repercussions to the biotic and abiotic world. Especially, the Tortonian-Messinian Transition (TMT) is recognized as a priority for paleoceanographic and climate reconstruction, due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC). Furthermore, paleoenvironmental reconstructions from periods that were warmer than the present climate, attract great interest as they could predict possible the climate changes in the near future, so the study of TMT provides the development of the modern Mediterranean-type climate. Under this scope, I investigate the severe changes in long-term hydrological cycle and climate in the circum-Mediterranean region, as an analogue for future subtropical hydroclimate. At the end of the Miocene, the Mediterranean region experienced a dramatic hydrological and biotic crisis induced by a strong sequence of geodynamic and climatic drivers.
Herewith, I present a multiproxy analyses study from latest Tortonian to earliest Messinian, from uplifted hemipelagic sediments in eastern Mediterranean (Crete Island, Greece). The chosen study sections, Potamida (western Crete) and Kapariana (central Crete) provide a well astronomically dated archive allowing the examination of the changes in paleoceanographic parameters through the study of variety of life forms. Different types of organisms produce specific organic compounds that serve as molecular biomarkers, a key to better understanding of past climate. A TEX86–derived sea surface temperature (SST) reconstruction performed on samples from Potamida section. The temperature records show a relatively warm phase prevailed until 7.36 Ma, while for the 7.31‒7.28 Ma time interval is observed a high amplitude variation, in SST. The Tortonian/Messinian boundary was characterized by lower SSTs. Within this time-slice and particularly between 7.23 and 7.21 Ma, a ∼10°C cooling trend was recorded in Potamida SST record providing regional evidence of the global Messinian cooling event. Moreover, geochemical analyses were performed from both studied sections in selected foraminiferal tests (Globigerinoides obliquus and Cibicides kullenbergi) as well as in bulk sediments from Kapariana section. Although, only in Potamida section, a combined analysis of biomarkers and oxygen isotopes on planktonic foraminifera are used to estimate the sea surface salinity (SSS) reconstructions of Mediterranean Sea during the TMT. The reconstructed SSS displays low values until 7.36 Ma, and mostly normal sea surface salinities for the following 7.36‒7.32 Ma time interval. After that, during the 7.31‒7.28 Ma time interval are documented oscillations in sea surface salinity. Around the Tortonian/Messinian boundary the upper water column was less saline, followed by constant increased salinity and/or colder bottom waters. The foraminiferal stable oxygen and carbon isotope data from Potamida section are also evident of a decoupling between the surface and the bottom water column and an increasing productivity on latest Tortonian, respectively. The onset of the water column stratification is recorded.at 7.36 Ma and then until 7.32 Ma the time interval is characterized by pulses of increased stratification in the water column. A brief episode of decoupling between bottom and surface waters was observed between 7.32‒7.31 Ma. For the 7.31‒7.28 Ma time interval, a rebound to enhanced stratification, manifested in increased isotopic contrast between planktonic and benthonic foraminifera was further documented, accompanied by stepwise decrease. Besides that, the carbon isotope signals in both sections present a trend to lighter values towards the earliest Messinian. The carbon isotope decreasing, which is in accordance with the global known event Late Miocene Carbon Isotope Shift (LMCIS), reflects changes in the carbon cycle were decisive in the evolution of climate in the progressively isolated eastern Mediterranean Sea. Additionally, a further micropaleontological analysis was performed for the 7.36-7.24 Ma time interval in both study sections as well as from the time equivalent interval from the Faneromeni section (eastern Crete), specifically on Globorotalia menardii, a species that is highly sensitive to water column structure, to study its temporal evolution in terms of size distribution pattern and related correlation with the environmental parameters, mostly with sea surface temperature, salinity, water column stratification and productivity. The interpretation of the results shows that the size fluctuations of G. menardii is better correlated with the oxygen isotopic signal and the SSS reconstructions indicating that the morphological traits are mostly affected by the vertical changes of surface stratification and therefore salinity, showing an inversely proportional relationship, where in high salinity conditions the G. menardii size becomes smaller. This thesis advances our understanding on the paleoceanographic evolution and further extend our knowledge of the paleoclimate variability in the eastern Mediterranean Sea during Late Miocene.
Keywords:
planktonic foraminifera, upper Miocene, Mediterranean Basin, size distribution, temperature, salinity
