Experiments on Test Destruction in Larger Foraminifera

Larger foraminifera are single celled marine organisms covering their protoplasmic body with chambered, calcareous tests. The construction of giant tests (> 1mm to 13cm) in combination with light dependence of photosynthetic symbiotic microalgae restricts the larger foraminifera to nutrient-depleted, shallow tropical marine environments. Beside stony corals and corallinacean algae, larger foraminifera are today the main calcium carbonate producers in shallow marine environments, especially in the tropical Indo-Pacific. Unlike stony corals, larger foraminifera are able to survive raising sea temperatures caused by the El Niño or atmospheric greenhouse effects that lead to global warming. The greenhouse climate of the Upper Cretaceous induced the development of larger foraminifera, and the warm climate of the Lower Tertiary gave raise to the dominance of larger foraminifera in shallow marine carbonates. During these periods, stony corals were less represented in shallow tropical environments. These carbonates dominated by larger symbiont-bearing foraminifera are the main oil reservoirs today, especially in North Africa and the Middle East. Beside reduced sedimentation rates, transport effects cause accumulation of larger foraminifera leading to carbonates that consist to an extreme percentage of foraminiferal tests, especially in the Lower Tertiary. A weak flow transports the fine sediment between large foraminiferal tests and leads to accumulation, while strong flow affects test transport. Different transport widths, termed sorting, depend on the various test buoyancies based on size, shape and test density, all changing with growth. This project tries to study flow thresholds for entrainment and suspension of all Indo-Pacific larger foraminiferal species. Depending on the substrate surface, entrainment thresholds vary between growth stages of a single species as well as between different species. After being in suspension, movement varies at similar flow intensities according to different size, shape and density. Therefore, plate-like tests with an extreme drag coefficient will be much wider transported than spherical tests. Although foraminiferal tests are almost transported within the sediment during directed flow, they will not be strongly affected by neighboring sediment grains. Permanent oscillatory movement as caused by waves, on the contrary, intensively destroys the test surfaces leading to abrasion or breakage. All these effects should be studied by experiments, which open the door to the interpretation of fossil carbonate depositions.