Canada Figure 6 Ordovician brachiopod-rich shell beds have been regarded as the products of autogenic ecologic succession involving gradual accumulation of shells at the sediment surface, culminating in a climax community dominated by epifaunal, attached atrypid or rhynchonellid brachiopods. To evaluate this model, we examined brachiopod-rich shell beds from the Middle Ordovician Verulam Formation of southern Ontario.
Complex shell beds with internal discontinuity surfaces are common.
Many beds are directly overlain by sparsely fossiliferous to barren, laminated shales and mudstones that are interpreted as mud tempestites deposited during mud-blanketing events. These assemblages represent stages in a sequence of storm-generated, allogenic taphonomic feedback.