Agent-based Modelling of Microbialite Formation through Sedimentation and Precipitation Dynamics

Fossil microbialites resulting from the interplay of sedimentation and microbially induced precipitation are among the oldest evidence of life on Earth and help geobiologists interpret many sedimentary environments. However, the factors governing their internal structure and external morphology are still poorly understood. Additionally, abiotic processes can mimic the morphology of some microbialites, complicating their use as "biosignatures''. The presence and style of internal structures such as clots and laminations may help solve both problems, but existing models of microbialite growth address only external morphology and do not show explicitly how internal structures emerge. In this work, we present an agent-based model of microbialite formation using a fast, open-source, high-level microbialite modelling framework, written in Julia. We separate and label sedimentation and microbially induced precipitation, and allow external periodic forcing to control either or both. We qualitatively reproduce a wide range of internal and external morphologies found in real microbialites. Importantly, we find that microbialites with the same external morphology can differ greatly in their internal structure, a result that was impossible to observe with previous approaches. Further exploration and extension of our model may offer new approaches to resolving the ambiguity of potential microbialites in the rock record. Finally, we present the first interactive microbialite simulation, that enables live parameter updating through an accessible interface that can be used as a tool for both research and teaching.