Evolution of fossil blue hole limestones and the critical zone in a greenhouse world

2020-2022: UNESCO/IUGS International Geoscience Program IGCP 661 funded by the Austrian Academy of Sciences

Principal Investigators:

Michael Wagreich (University of Vienna)
Benjamin Sames (University of Vienna)
Khaled Trabelsi (University of Sfax and University of Tunis El Manar, Tunisia)

Andrea Mindszenty (ELTE University Budapest, Hungary)
Miklos Kazmer (ELTE University Budapest, Hungary)


IGCP 661 investigates the critical zone of karst systems, the Austrian sub-project looks on the evolution of fossil blue hole limestones from Cretaceous and Eocene greenhouse climate phases.


IGCP project themed on "Global comparative research on structure, substance cycle and environment sustainability of the critical zone in karst systems".
The new IGCP project will mainly pay attention to some scientific issues such as the structure, evolution, cycle of carbon-water-calcium and function of the critical zone and its sustainable utilization of the resources and environments.

The karst IGCP project focusses, among others, on the following aspects: (1) influence of Himalaya uplift, highland in Middle East Area and the orogeny of Alps to the formation and evolution of karst; (2) influence of geological structure and differentiation of climate and vegetation on types, hydrogeological structure and characteristic of the critical zone; (3) the hydro-ecological and carbon sink function, influence factors, recording index, and maintaining mechanism of the critical zone.

Blue holes, marginal-marine karst sinkholes developed as underwater caves on indurated carbonate strata such as limestone or dolomites and open to the surface, contain biota and deposits of freshwater to marine waters within the critical zone. Blue holes form related to significant sea-level drop, exposure and karstification, followed by sudden sea-level rise. The evolution of fossilized blue hole successions, if dated accordingly, gives valuable information on critical zone archives, palaeoclimate evolution, (karst) groundwater levels and circulation, and sea-level fluctuations.

The proposed project investigates two fossilized sinkhole archives from greenhouse times to evaluate palaeoclimate trends, palaeo-groundwater- and sea-level evolution to compare this to the current path into a greenhouse world related to recent global warming and rising sea-levels. The case studies are from the late phase of the long-term Cretaceous extreme greenhouse (the Turonian Cretaceous Thermal Maximum hothouse phase, Northern Calcareous Alps, Unterlaussa, Upper Austria) and the Eocene (Eocene Climatic Optimum, EECO greenhouse phase, above Eocene bauxites at Ghánt, Hungary). This Austrian subproject of IGCP 661 deals with the following themes:

(1) The influence of orogeny of the Eastern Alps to the formation and evolution of karst and its fossil Critical Zone;

(2) the influence of geological structure and greenhouse climate on types, structure and characteristic of the critical zone and its groundwater-sea level interactions.

(3) Influence of geological structure and differentiation of climate on types, hydrogeological structure and characteristic of the critical zone

Methods applied include field sedimentology, microfacies analysis, biostratigraphy, cyclostratigraphy, geochemistry and isotope geochemistry. The expected outcome will be 1) a more precise stratigraphy of the blue hole limestone successions, (2) a precise cyclostratigraphy and thus estimates of the time duration of sinkhole fills during sea-level rise in greenhouse times, (3) a facies model and the evolution of biota and biodiversity of blue hole fills related to rising sea-level, (4) information on groundwater and regional climate evolution during overall hothouse/greenhouse times in relation to the Anthropocene trajectories.

Bauxite mine at Großraming/Unterlaussa, Austria

Cretaceous karst sinkhole filled by bauxite, abandoned bauxite mine at Großraming/Unterlaussa, Austria (© M. Wagreich)