Sedimentologic Roles Reefs

Cambrian calcified microbes assumed unrivaled importance as reef builders (see Pratt et al., this volume). Most well-studied Early Cambrian reefs are biohermal lenses surrounded by mudrocks and consist of varying mixtures of calcified microbes, among which Epiphyton, Renalcis, and Angusticellularia are prominent, together with archaeo-cyaths. Overall, there is little doubt that calcified microbes were more abundant than archaeocyaths in Early Cambrian reefs (Copper 1974). Middle-Late Cambrian reefs are less well known but include extensive biostromes in high-energy ooid grainstone shoal environments. During this interval archaeocyaths are virtually absent, and with few exceptions (Hamdi et al. 1995), these reefs are almost wholly microbial in character and contain conspicuous Gordonophyton, Razumovskia, Tarthinia, and Tubomor-phophyton, although these have often been misidentified (Ahr 1971; McIlreath 1977; James 1981; Markello and Read 1981; Astashkin et al. 1984; Coniglio and James 1985; Waters 1989). These Middle-Late Cambrian examples in particular show that these calcified microbes were capable of constructing strong, early lithified reefs in grainy mobile shoal environments, independently of metazoans.

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