Encrusting (Ei), Macroboring (Mi), and Dissymmetry (Di) indices are proposed as quantitative descriptors of biogenic nodules. (Ei) measures the amount of encrustation, (Mi) the contribution of boring traces affecting the internal structure of nodules, and (Di) the regularity of the biogenic accretion around the nucleus. The latter has been used to construct a classification scheme of possible shapes for encrustations. Raw data to calculate the indices were obtained from numerical treatments of digitized photographs of nodule cross-sections. The morphometric (Di) and taphonomic (Ei and Mi) indices have been calculated for carbonate nodules from subtidal temperate and tropical settings in New Zealand (Flat Point Beach) and in the Caribbean (St. Bartholomew Island), respectively. Results for nucleated rhodoliths collected from shallow high-energy settings in these two climatic settings show that their morphometric and taphonomic characters are not species-specific (Lithoporella/ Mastophora rhodoliths from St. Barth, and Lithothamnion-Sporolithon rhodoliths from New Zealand), but depend instead on hydrodynamic conditions and on the original shape of nuclei. Acervulinid macroids sampled in deeper waters (28 m) off St. Barth are nucleus-free and have a Macroboring index (Mi) significantly higher than that of rhodoliths from shallower environments, due to discontinuous influence of waves and currents, and low sedimentation rates.

The quantitative descriptors proposed here might: (1) complement the characterization of biogenic nodules in specific depositional environments; (2) aid in hydrodynamic and paleoenvironmental reconstructions of biogenic nodule-bearing deposits; and (3) constitute valuable tools in future comparative studies.

Ecologically complex buildups within the Kimmswick Limestone of the Galena Group (Upper Ordovician, Katian) near St. Louis, Missouri, display unique communities of stromatoporoids, encrusting cyathocystid and edrioblastoid edrioasteroids, camerate and other crinoids, paracrinoids, bryozoans, tabulate, and rugose corals. Substrate stabilization and vertical ecological successions were influenced by labechiid stromatoporoids that transitioned from laminar to domal/pillar morphologies from the base of the reef to its terminus. Cyathocystid edrioasteroids occurred in dense aggregations within cryptic cavities, often inverted in life orientation. Surrounding facies consisted of bryozoan and chert-rich wackestones-packstones, cross-bedded abraded echinoderm grainstones, gastropod-bivalve grainstones, and echinoderm-bryozoan grainstone/rudstones, while reefal facies comprised stromatoporoid-echinoderm boundstones, and stromatoporoid-cyathocystid framestones. Reef geometry and facies distribution reflected both allogenic and autogenic controls fundamental to the initialization and stabilization of the Shady Valley reefs. Four distinct successional series, from initial stabilization of important binders to colonization and diversification of stemmed echinoderm groups and subsequent domination of labechiid stromatoporoid framebuilders, formed the vertical profile of the reefs. Laminar, domal and irregular frame-building stromatoporoids acted as sediment stabilizers and formed ideal substrates for encrusting hardground fauna, supporting the development of cryptic habitats exploited by diverse echinoderms at the acme of reef diversification. Similar Katian hardground ecological successions occur in coeval reefs elsewhere in North America, Europe, Baltica, and South China. However, the scale of the reef architecture, development of complete ecological successions, and the diversity and multiple ecological roles of labechiid stromatoporoids and echinoderms in the Kimmswick Limestone sets it apart.