Séminaire : KOELLING Martin

Dr Martin KOELLING

Géochimiste, MARUM - Université de Bremen

donnera une conférence intitulée :

"The effect of sea level change on the internal age structure of reefs. Forward modeling and visualization of reef growth using a sea level driven spreadsheet model (SEALEX)"

A reef growth model has been developed using an Excel spreadsheet. The 1D forward model is driven by a user definable sea-level curve. Other adjustable model parameters include maximum coral growth rate, coral growth rate depth dependence and light attenuation, subaerial erosion and subsidence. A time lag for the establishment of significant reef accretion may also be set. During the model run, both, the external shape and the internal chronologic structure of the growing reef as well as the paleo-water-depths are continuously displayed and recorded.
We tested the model on fossil reef systems growing in a range of different tectonic settings such as both on slowly subsiding islands like Tahiti (subsidence rates of 0.25 m ka− 1) and rapidly subsiding islands like Hawaii (subsidence rate of 2.5 mka− 1) as well as rapidly uplifting coastal settings like Huon Peninsula (uplift rates of 0.5 to 4 m ka− 1) and more slowly uplifting settings like Haiti (uplift rates of 0.55 mka− 1). The model runs show the sensitivity of the resulting overall morphology and internal age structure to different model parameters. Additionally the water depth at the time of deposition is recorded. This allows the constructions of virtual borehole logs with the coral age profiles and the paleo water depth at the time of growth both displayed and recorded.