Shallow-water carbonate response to climatic events: sedimentological, paleoecological and chemostratigraphic approaches to foraminiferal biocalcification during the Paleogene in the Thetyan realm (Dinarids and Oman)
Final Report Abstract
Modern anthropogenic forcing of atmospheric chemistry poses the question of how the Earth System will respond as thousands of gigatons of greenhouse gas are rapidly added to the atmosphere. A similar situation occurred during the early Paleogene, when catastrophic release of carbon to the atmosphere triggered abrupt increase in global temperatures and change in the ecosystems. The best documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar to those expected for the future. This event initiated global warming, changes in nutrient cycle, biotic extinction and migrations. However, in situ record of the PETM within shallow-marine carbonate facies containing abundant autochthonous larger foraminifera and a well preserved PETM signal remains elusive and the responses, if there were any, to these perturbations poorly understood. This proposal has investigated successions from the Adriatic Carbonate Platform (SW Slovenia). This setting was identified as an ideal location to test the hypothesis of a possible causal link between the PETM and evolution of shallow-water organisms. In order to reconstruct paleoenvironmental conditions during deposition, we focused on sedimentological analysis and paleoecological study of benthic assemblages. During the Late Paleocene-earliest Eocene, continuous sedimentation occurred on a shallow-water carbonate ramp system. Larger Foraminifera (LF) represent the common constituent of the benthic assemblages that thrived in this setting throughout the Late Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic analyses documenting the most complete record to date available for the PETM event in a shallow-water marine environment, we correlated chemostratigraphically the evolution of LF with the δ13C curves. This correlation demonstrated that no major turnover in the LF communities occurred synchronous with the PETM, suggesting a too short duration of the PETM perturbations to hint dramatically this group and/or some kind of adaptations in the LF to thrive under unfavorable conditions. The study of Late Thanetian metric-sized microbialite-coral mounds, which developed in the middle part of the ramp, documented the first Cenozoic occurrence of microbially-cemented mounds. The development of these mounds, with temporary dominance of microbial communities over corals, suggest environmentally-triggered “phase shifts” related to frequent fluctuations of nutrient/turbidity levels which preceding the extreme greenhouse conditions of the PETM. The paleoecological study of the coral community in the microbialites-coral mounds, the study of corals from Early Eocene platform from SW France, and a critical, extensive literature research of Late Paleocene – Early Eocene coral occurrences suggested that these corals, even if not forming extensive reefs, were common in biofacies constituents. These corals might have developed ‘alternative’ life strategies to cope with harsh conditions during the greenhouse times of the Early Paleogene, representing a good fossil analogue to modern corals thriving close to their thresholds for survival. These results demonstrate the complexity of the biological responses to extreme environmental conditions, not only in terms of temperature but also nutrient supply, physical disturbance and their temporal variability and oscillating character. The relationship between the evolution of shallow-water biota and global warming events underscores the complexity of the biological responses to environmental perturbations, especially for corals and LF, which are highly sensitive organisms. Their persistence during the warmest time in the Cenozoic hints at possibility to evolve some adaptations, which deserve more studies in order to understand future scenarios. Ongoing work in shallow-water successions from Oman will improve our knowledge about the responses of shallow-water ecosystems in low latitude settings.
Publications
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2006. Evolution of shallow water carbonates communities across the Paleocene-Eocene boundary – A case study from SW Slovenia. SEDIMENT, Göttingen
Zamagni, J., Mutti, M., Košir, A.
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2006. Evolution of shallow-water carbonates communities across the Paleocene-Eocene boundary – constrains from paleoenvironmental and chemostratigraphic analysis (SW Slovenia). “Climate and Biota of the Early Eocene”, Bilbao (Spain)
Zamagni, J., Mutti, M., Košir, A.
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2006. Growth model of Thanetian coralmicrobialites (SW Slovenia): paleoenvironmental interpretation. “Climate and Biota of the Early Eocene”, Bilbao (Spain)
Zamagni, J., Mutti, M., Košir, A.
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2007. Facies analysis and shallow benthic foraminifera paleoecology in a mixed carbonate-silicoclastic system, Early Eocene Minervois Region (SW France). IAS, Patras (Greece)
Zamagni, J., Mutti, M.
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2007. Palaeoecology of larger foraminifera during the late Palaeocene-earliest Eocene transition in the northern Tethys (SW Slovenia): tropical foraminiferal carbonate production under humid mesotrophic conditions? EGU, Wien
Zamagni, J., Košir, A., Mutti, M.
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2007. Thanetian coralmicrobialites from the northern Tethys (SW Slovenia): palaeoenvironmental interpretation. EGU, Wien
Moellerhenn, S., Zamagni, J., Košir, A., Mutti, M.
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2008. Evolution of shallow benthic communities during the Late Paleocene–earliest Eocene transition in the Northern Tethys (SW Slovenia). Facies, v. 54, n. 1, p. 25-43
Zamagni, J., Mutti, M., Košir, A.
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2008. Evolution of shallow water carbonates communities across the Paleocene-Eocene boundary. Carbonate production recording run-off pulses preceding the PETM? IAS, Bochum
Zamagni, J., Košir, A., Mutti, M.
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2008. Paleocene microbialite-coral mounds from the Kras region (SW Slovenia). EGU, Wien
Zamagni, J., Košir, A., Mutti, M.
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2008. Paleocene to earliest Eocene coral assemblages: ecological decline or an alternative state of development? EGU, Wien
Zamagni, J., Košir, A., Mutti, M.
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2009. The first microbialite-coral mounds in the Cenozoic (uppermost Paleocene) from the northern Tethys (Slovenia); environmentally-triggered phase shifts preceding the PETM? Palaeogeography, Palaeoclimatology, Palaeoecology, v. 274, n. 1-2, p. 1-17
Zamagni, J., Košir, A., Mutti, M.
