SEALEX — Internal reef chronology and virtual drill logs from a spreadsheet-based reef growth model

Abstract

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. Because the model is implemented as a macro in a popular spreadsheet program, it may be easily adapted or extended to model the growth of different reef and carbonate platform settings. Single model runs take a few minutes on a standard (2 GHz CoreDuo) desktop computer under Windows XP. The model may be used to investigate the effects of different boundary conditions such as maximum reef growth, erosion rates, subsidence or uplift on both, the general morphology of the reefs, and the internal chronologic structure. These results can then be compared to observed data allowing different hypothesis concerning reefs development to be tested. The model may also be used to assist in finding sampling locations in reef bodies that are likely to contain critical information for sea level studies. SEALEX is available online at http://www.rcom.marum.de/English/SEALEX_reef_growth_model.html.