Abstract


MID-TO-LATE HOLOCENE SEDIMENT DYNAMICS AND DRIVING MECHANISMS IN A MIXED CARBONATE-SILICICLASTIC LAGOON (BORA BORA, FRENCH POLYNESIA, SOUTH PACIFIC)

A multi-proxy approach applied to sediment cores from the mixed carbonate-siliciclastic lagoon of Bora Bora was used to detect palaeoenvironmental changes and to evaluate controlling mechanisms of sediment dynamics during the mid-to-late Holocene. The increase in coarse-grained and clay-sized sediments, productivity, XRF Ca counts and decrease in XRF Cl counts over the past 5 kyrs seem to indicate event deposition and can be correlated with event deposits in nearby Tahaa lagoon explained by higher cyclone activity. Based on this model, intense rainfall during cyclone landfall would enhance erosion and run-off from the volcanic hinterland and lower lagoonal salinity. Reefal sediment would be transported into the lagoon. However, the Ti/Ca proxy for terrigenous input has decreased steadily during that time period. Also, benthic foraminifera assememblages do not indicate reef-to-lagoon transport of sediment. Alternatively, more permanent southeast trade winds during the mid-to-late Holocene could have favored higher hydrodynamic energy conditions, flushed higher amounts of open ocean water and pelagic organisms into the lagoon, enhanced marine productivity and lowered lagoonal salinity. Our alternative model of long-term lagoonal sediment dynamics includes mid-to-late Holocene sea-level change and lagoonward progradation of sand aprons. The observed lagoonal sedimentation patterns during 4.5-0.5 kyrs BP reflect intensified sediment dynamics and gravity-induced slumping at sand apron/lagoon edges due to oversteepening during ongoing progradation. Additional analyses and age dating are in progress and will help to constrain the interpretation summarized here.

Authors

Isaack, A., Goethe University Frankfurt am Main, Germany, isaack@em.uni-frankfurt.de

Gischler, E., Goethe University Frankfurt am Main, Germany, gischler@em.uni-frankfurt.de

Hudson, J. H., ReefTech Inc., USA, hhudson3@bellsouth.net

Anselmetti, F. S., University of Bern, Switzerland, flavio.anselmetti@geo.unibe.ch

Lohner, A., University of Bern, Switzerland, andreas.lohner@gmx.ch

Garbode, E., Goethe University Frankfurt am Main, Germany, eva.garbode@gmx.net

Camoin, G., CEREGE, France, camoin@cerege.fr

Details

Oral presentation

Session #:34
Date: 06/23/2016
Time: 15:30
Location: 311

Presentation is given by student: Yes