The stratigraphic significance of self‐organization: Exploring how autogenic processes can generate cyclical carbonate platform strata

Autogenic spatial self-organization can produce coherent patterns of ordered cyclical strata through interaction of system components, independent of initial conditions and without external forcing. Previous numerical modelling work that partially explored self-organized cyclicity in carbonate strata is expanded, refined and tested using a different numerical model formulation of an existing carbonate forward model 'CarboCAT'. Results show that cross-platform sediment transport creates a series of self-organized prograding islands and shorelines that generate upward-shallowing autocycles, defined by strong statistical evidence for ordered facies successions. A subtidal factory in front of each shoreline supplies sediment that drives shoreline progradation and these subtidal supply-zone widths are also self-organized to an optimal characteristic width due to island progradation, such that an accommodation creation/sediment supply ratio of around one maintains self-organized shoreline progradation. The resulting island progradation rate determines autocycle thickness, which is very different from the accommodation control assumed in most sequence stratigraphic and cyclostratigraphic interpretations. This self-organization process is comparable to the reaction-diffusion model first suggested by Alan Turing. The simplest possible combination of processes that leads to self-organization are water-depth-dependent production, straight long-distance cross-platform transport and uniform subsidence. Additional more complex processes can produce self-organization, but also more diverse island morphologies, less ordered autocyclic strata and more variable lateral facies continuity. Exploration of the model parameter space shows that self-organization occurs for only a limited range of accommodation creation/sediment supply ratios. The modelling is calibrated and checked for realism against shoreline progradation rates measured on the Peros Banhos carbonate platform, British Indian Ocean Territory, and a Holocene Abu Dhabi shoreline, suggesting that this is a realistic and perhaps ubiquitous process in geological history. Given the fundamental nature of processes modelled here, and the match with observed processes in modern depositional systems, it seems possible that similar autogenic, self-organizing processes have operated on many carbonate platforms and are an important component in the stratigraphic record.