Biological self-organization; implications for sedimentary rocks with examples form shallow marine settings

Self-organization refers to the emergence of large-scale ordered pattern starting from initially disordered conditions through small-scale interactions between components of a system. Although the influence of biological agents on sediments and landscapes is widely appreciated by sedimentary geologists, the role of life in sedimentary self-organization is less familiar. One of the oldest ecological concepts relevant to self-organization is ecological succession, which is the idea that species colonization of a virgin or a disturbed landscape follows a series of more or less orderly and predictable changes in taxonomic composition and habitat structure. Many early studies of ecological succession in the fossil record confounded allogenic facies succession reflecting environmental shifts with autogenic ecological changes driven by organism interactions. However, evidence for autogenic ecological succession can be found in a variety of depositional contexts and is particularly evident in environments that are influenced by ecosystem engineers (organisms that affect other species by physically modifying or building their habitats), like reefs and shell beds. In addition to influencing change in an ecosystem over time, biologically mediated feedbacks can also produce highly organized spatial patterns. The basic mechanism of spatial self-organization requires at least one negative feedback loop that acts at a distance. Although relatively few examples have been documented in the rock record, self-organized spatial dynamics have the potential to greatly influence the nature of depositional environments by altering the flow of matter and energy. Recognition of biotic feedbacks is necessary for a complete and predictive understanding of the architecture of the stratigraphic record, and it seems likely that with greater awareness of self-organization and autogenesis in the sedimentary record, the number of biologically mediated examples will increase.