Seasonality and interannual climate variability during the Late Miocene: Testing and tuning climate models using oxygen isotope stratigraphy, growth increment analysis and new ground data


Prof. Dr. Thomas Brachert

Dipl. Geol. R. Mertz-Kraus


Nationale Zusammenarbeit:
Dr. Steve Galer
MPI für Chemie, Mainz

PD. Dr. M.M. Joachimski
Universität Erlangen

Dr. J. Fiebig
Universität Frankfurt a.M.


Internationale Zusammenarbeit:
Dr. Markus Reuter
Universität Graz, Österreich

Dr. Charolampos Fassoulas
Universität Heraklion, Griechenland

Dr. Georgios Illiopoulos
Universität Heraklion, Griechenland

Dr. W. Sharp
Berkeley Geochronology Centre, USA


Projektförderung:
Deutsche Forschungsgemeinschaft


Hintergrund:

Miocene shallow water carbonates are generally considered inadequate for palaeoclimatic analyses, because their stratigraphic record is punctuated by abundant gaps. However, sclerochronological records of corals document atmospheric variability ? an aspect hitherto unknown to Miocene palaeoclimatology. Skeletons in a pristine state of preservation required for sclerochronology have been detected in debrites intercalated with rhythmically stratified deep-water clay and marl (Tortonian/Messinian age, Krousonas area, Central Crete; Br 1153/7). A multi-scale oxygen isotope analysis of based on these periplatform sediments therefore has the potential to track climate variability on annual, decadal and millennial time-scales in response to insolation forcing and aridisation of the Mediterranean area over the course of the Late Miocene. Additional outcrops will be explored in Central Crete (Phaistos area) A climate model run based on a single sclerochronological record (for 10 Ma, Central Crete) obtained during a previous project (Br 1153/7) reflects real biofacies distributions surprisingly well: warmer than present temperatures in the Mediterranean, and colder temperatures in the E Atlantic. Predicted Late Miocene temperatures and variability in the E Atlantic will be tested using the classical biofacies approach along the ?Macronesian transsect? (Azores, Madeira, Canary and Cape Verde islands). Careful palaeontological analysis will provide information regarding long-term climate changes and the location of potential refugia for tropical biota during times of ecological perturbations in the Mediterranean area.

 
Skelettarchitektur
Abbildung 1: Skelettarchitektur der Korallengattung Tarbellastraea. Auflicht (a, c), Röngenfoto mit jährlichen Dichtebändern (b)  und REM (Rasterelektronenmikroskop; d). Die REM-aufnahme dokumentiert erhebliche Korrosion des Skeletts durch Lösung, jedoch keine sekundären Zementationserscheinungen. Aus Mertz et al. (2008) PPP.
 
Salinität und Saisonalität
Abbildung 2: Die Entwicklung von Salinität und Saisonalität während des oberen Miozän, Kreta. Aus Mertz et al., 2009, Chemical Geology.



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