STRUCTURAL ORGANIZATION AND GROWTH OF SILURIAN CHAIN CORALS

Colonies of Halysites coral make up one of the most important components of reef-margin framestone found within carbonate build-ups of the Huntington Member of the Silurian Wabash Formation of northeast Indiana. Partial to complete silicification allows for their separation from the dolo-mudstone matrix such that two- and three-dimensional geometry is easily observed. Small to medium sized colonies (2-30 cm diameter) display the distinctive cateniform geometry characteristic of Halysites. Pseudo-hexagonal lacunae are defined by corallites joined at triple junctions. Such junctions are typically separated by one to four corallites defining sublinear to irregular serial chains. Two-dimensional geometries of coral colonies are compared with results of hexagonal-based cellular models of colony growth. Lateral budding of coral colonies is simulated by an algorithm wherein the probability of branching increases with increasing lateral extension according to the relationship P=1-[1/(x-1)ⁿ], where x is the number of consecutive serial corallites and n is a power law scaling constant.