SELF-ORGANIZED PATTERN FORMATION IN SEDIMENTARY GEOCHEMICAL SYSTEMS

Geochemical self-organization is a process whereby a geochemical system acquires oscillatory behaviors or spatially repetitive patterns through its own internal autogenic dynamics. The concept of self-organization provides a new perspective for understanding the formation of repetitive patterns in sedimentary rocks, without invoking any unjustified external periodic allogenic force or template. Geochemical self-organization requires a system to be far from equilibrium and to have a positive feedback among the physical and chemical processes involved. Identification of a plausible mechanism for a specific self-organizational phenomenon usually boils down to finding a positive feedback consistent with laboratory and field observations. In this paper, we review the concepts and principles of geochemical self-organization, highlight some of the driving mechanisms and examples that typify sedimentary geochemical systems, and consider some of the basic techniques for model analysis. Two specific examples, formation of banded iron formations and development of periodic patterns in the distribution of porosity in dolomites, are presented in some detail to illustrate the insights generated from numerical modeling and linear stability analysis. Last, we offer some speculations on other chemical sedimentary and diagenetic features that might have self-organizational origins. Testing those hypotheses will require new types of sampling strategies and analyses not normally employed by sedimentologists and sedimentary petrologists.