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


Deutsche Forschungsgemeinschaft


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.

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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