Carbonate secreting organisms in clastic shelf systems and their potential as environmental archive : an interdisciplinary perspective on past and present marine ecosystems

Abstract

High nutrient, low-latitude carbonate systems are known to produce sediments that, in terms of skeletal composition, are reminiscent of their extra-tropical counterparts. Such carbonate systems and associated carbonate grain assemblages in tropical to warm temperate settings are unique in the present-day world and clearly deserve more scientific attention. Moreover, it is crucial to gain a better understanding of those ecosystems, including their drivers and players, because such marine settings potentially represent models for ancient depositional systems as well as for predicted future environmental scenarios. One of the modern occurrences of eutrophic tropical carbonates is the northern Mauritanian Shelf. The marine environment is characterized by an eastern boundary upwelling system that pushes cool and nutrient-rich intermediate waters onto a wide epicontinental platform (Golfe d´Arguin) where the waters warm up to tropical temperatures. The resulting facies is mixed carbonate-siliciclastic with a dominant, cool water-related heterozoan association while similarly tropical mollusk assemblages develop in the shallowest parts of the shelf forming the Banc d'Arguin. Another important example is the Uruguayan Shelf. The oceanography off southeastern South America is dominated by a marine confluence that plays a key role in the regional and South Atlantic-wide circulation. The study shows how fossil bivalve mollusks can contribute to a better understanding of present and past environmental settings, characterized by cool and warm water intrusions, and how geochemical analyses help to identify the palaeodynamics of the Uruguayan Shelf. The presented doctoral thesis presents a multidisciplinary approach that helps to better understand tropical and sub-tropical marine ecosystems in the context of climate change and highlights the importance of marine carbonate secretors as environmental archive.