BayCEER Workshop 2008

Paleoecological modeling of nutrient dependency and predator-prey relations in a carbonate-sedimentary environment

Carbonate-sedimentary environments are characterized by different groups of organisms cohabiting in competition for space, nutrients and other life-determining factors. The model used in this approach - SIMSAFADIM - calculates the sedimentation in a three-dimensional basin involving clastic, carbonate and mud sedimentation. Carbonate production is simulated using ordinary differential ’predator-prey’ equations that express the relation between three species associations competing for resources. Due to the importance of nutrient supply for the associations and their unlike preferences of food availability, nutrients have been included in the model as an additional parameter. The species associations are classified in three categories - oligotrophic, mesotrophic, heterotrophic - according to their favored nutrient concentrations (low, intermediate or high). Observed blooms of the heterotrophic species following transgressive phases can be explained by increased nutrient input due to intense rainfall events and nutrient solution from the former non-marine soil. Thus, a pulsing function for nutrients correlated to sea-level changes has been added to the model. Based on geologic field data from stratigraphic sections of the lower Cretaceous in the Western Maestrat Basin (E- Iberian Chain; E- Spain), the SIMSAFADIM model is being calibrated and tested for further application. The parameters defined from the field observations are used as input parameters for the model. Once, accordance is reached between the one-dimensional field data and the model output, the resulting parameter configuration can be used as input for the three-dimensional model routine to calculate the stratigraphic architecture of the sedimentary basin. The model is a potential tool for predicting basin geometries from locally isolated core samples; in many cases, these are the only available source for geologic parameters whereas the exact sedimentary setting is unknown. Restrictions to the model are difficulties in determining exact data for the input parameters from geologic observations and in simulating erosion or abrupt mass extinction events.