Numerical forward modelling of peritidal carbonate parasequence development: implications for outcrop interpretation

The mechanisms responsible for formation of peritidal parasequences have be en a focus of debate between proponents of contrasting autocyclic and alloc yclic models. To contribute to this debate a three-dimensional numerical fo rward model of carbonate production, transport and deposition has been deve loped. Shallowing-upward parasequences are produced in the model via carbon ate island formation and progradation, with an element of self-organization , and no external forcing. These autocyclic parasequences have characterist ics comparable with peritidal parasequences observed in outcrop. Modelled p arasequence thickness and duration depend primarily on subsidence rate and sediment transport rate, illustrating the significance of sediment flux in formation of peritidal parasequences. Adding an element of stochastic varia tion of sediment transport rate and transport path leads to formation of no nuniform-thickness parasequences that generate Fischer plots showing appare nt hierarchies similar to those often interpreted as evidence of eustatic f orcing. The model results do not rule out allocylic mechanisms, but suggest that shoreline and island progradation are also plausible mechanisms to cr eate variable-thickness, shallowing-upward peritidal parasequences and shou ld be considered in interpretations of such strata.