Laminoid, weakly fused sponge spicule networks are intercalated between convex stromatolitic laminae in an upper Cambrian (Furongian) reef. Sponges are small, millimeter to centimeter-sized lithistids that encrusted automicritic laminae and in turn were encrusted by microbial biofilms, eventually leading to columnar, crudely laminated ‘stromatolites'. Weakly fused desmas, now replaced with fine, blocky calcite, possess an arcuate geometry along the medial to distal ray axes. Minimal decay and separation of sponge tissue from these spicules produced arcuate, filament-like cavities that obscure the former presence of spicule networks when viewed in cross-section. Further deterioration produced peloidal networks and voids. These observations have important implications when reconstructing middle to late Cambrian reef-building communities. Until recently, these periods were assumed to be virtually devoid of calcified metazoan reefal components. An increasing number of recent studies, however, are demonstrating that metazoan reef-builders were more prevalent. This paper adds a unique element to the nature of framebuilding by demonstrating that lithistid sponge-microbial reef-building communities constructed laminated ‘stromatolites,' and thus may have had a flourishing ecology within late Cambrian microbial buildups.

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