Foraminiferal research to understand past coastal marine environment (SAEON Seminar, 12 Nov 2021) скачать в хорошем качестве

Foraminiferal research to understand past coastal marine environment (SAEON Seminar, 12 Nov 2021)

Presenter: Athi Mfikili (Elwandle Coastal Node) Title: Foraminiferal research – tapping into unfamiliar territory to understand past coastal marine environment Abstract: Foraminifera are single-celled micro-organisms with a shell test that is either secreted (i.e., carbonate, organic or siliceous) and/or agglutinated with foreign particles. Unlike their counterparts, diatoms, foraminifera are exclusively found in marine environments, often found floating in the water column (planktonic) or living on the sea floor or estuarine environments such as salt marshes (benthic). Foraminifera have an evolutionary history that extends back to the Cambrian (i.e., more than 500 Ma) and have evolved since then with approximately 60,000 fossil and modern species validly recognised. To date, there are over 16,000 living foraminiferal species belonging to 1691 genera, making this group one the most abundant microfossils in the marine realm. Although foraminifera have a cosmopolitan distribution throughout the entire marine realm, the individual taxa are restricted to specific environmental niches, e.g. benthic species occur in the shallow continental margin and intertidal areas, such as salt marshes, whereas planktonic species are exclusively found in open waters of the ocean. Given their abundance in the marine environment and high preservation potential after death, foraminiferal assemblages have been confidently utilized in paleo-sea-level and environmental reconstruction studies. My research presents anomalous sedimentary deposits preserved in the stratigraphic record of the Swartkops Estuary and low-lyingDwarskersbos coastal plain. We use foraminiferal assemblages as proxies to identify and interpret past extreme marine inundation events in these contrasting environments along the South African coast. Generally, the foraminiferal assemblages of these two localities are dominated by Ammonia spp., but the SwartkopsEstuary was characterised by a diverse assemblage of inner shelf species as well as occasional planktonic. On the other hand, Elphidium crispum was consistently present at Dwarskersbos, suggesting the inner shelf as the likely source. Taphonomically, the Swartkops Estuary foraminiferal assemblage was characterised by well-balanced, fragmented, and corroded tests ranging between 14-30% and 10-31%, respectively, compared to the fragmented tests of the Dwarskersbos. These results suggest that these sedimentary deposits were sourced from open marine environments by extreme marine wave events. Although these findings are not conclusive about the occurrence of extreme marine events, they demonstrate the potential of foraminiferal datasets to provide useful interpretation of extreme marine wave deposits such as tsunami and storm surge. This information contributes to the understanding of these events along the South African coast and assist coastal managers to conduct hazard and risk assessments more effectively for future events. We also hope that this work on foraminiferal analysis is a first step towards incorporating these microfossils into our LTER monitoring.