Sylvain Richoz

My research is focused on:

1) the interactions between climate-induced change in seawater chemistry and palaeoecological networks and the resultant consequences for carbonate deposition systems

2) the development or refinement of proxies to reconstruct past environments.

I am focusing on the Triassic, which is a wonderful time to explore such interactions. This period begins with the most profound mass-extinction on Earth and ends with another of the ‘big five’. In between these two mass-extinctions, there are times of slow recovery, crises, origination and the flourishing of marine biota. Major constituents of today’s marine ecosystems such as scleractinian corals, photosymbiosis in corals and calcareous nannoplankton appear during the Triassic. The impacts of these important newcomers on the marine ecosystem and on the carbonate depositional system have only been poorly understood to date.

Methodologically, my first priority is detailed studies of structures and depositional architectures of sedimentary successions, and the establishment of robust regional and stratigraphical frameworks.  To reach these goals, extensive field data are essential. Since 2000, I have developed field expertise on the tethyan Triassic in Central Europe (Austria, Slovenia, Croatia, Hungary, Slovakia), in Turkey, Oman, Iran and the Indian Himalaya.

Once the regional and stratigraphical framework is well established, geochemical analyses and palaeobiological studies can be carried out. I think that an important effort has still to be produced to understand the behaviour of new palaeoenvironmental proxies (e.g. non-conventional isotopes, trace elements, biomarkers) during the early diagenesis of the sediments and their applicability in different palaeoecological settings. The Triassic with its extreme environments is of particular interest for this purpose, but this should be tested all other the Phanerozoic.

Two projects are going on:

1) Triassic microbialite reefs and post-extinction oolites

Microbialites were widespread during Precambrian time and became again abundant during the Early Triassic. A continuing problem is the precise determination of the conditions of growth, the processes leading to a non-obligatory calcification and the phylogenetic affiliations of the microorganisms involved in microbialite formation. In the same way, end-Silurian, end-Permian and end-Triassic extinction events are characterized by the deposition of ubiquitous oolites. The sedimentological, palaeoecological, isotopic and biogeochemical comparisons of the different types of microbial structures and of the oolites in different palaeoenvironmental settings will allow us to better understand the conditions of growth of the post-extinction microbialites and oolites and to assess water chemistry changes on shallow shelves in the aftermath of these major mass extinctions.

2) Emergence of pelagic calcification and its influence on seawater chemistry

Around the Norian-Rhaetian boundary (Late Triassic) the first coccolithophorids appeared alongside an explosion of calcareous nannolith productivity, and a noticeable bloom in reef abundance and diversity. This is in surprising contrast to a major extinction in conodonts, ammonoids and the bivalve Monotis observed at around the same time.  I aim to establish the detailed timing of these events. One particular point of interest is the emergence of the calcifying plankton in the marine ecosystem shifting the major carbonate production from the shallow seas to the open marine realm. This is a paradigm change. To better understand the influence of the emergence of planktonic calcification on sea-water chemistry, I want to combines palaeontological studies of the calcareous nannoplankton, geochemistry on traditional (C_carb, C_org) and non-traditional isotope system (Ca, Mg, Sr) and climate models.

Publication list from Google Scholar