Article: Patterns of stromatoporoid growth in level-bottom environments

Stromatoporoids in argillaceous level-bottom limestones of the Upper Visby Beds in the Silurian of Gotland, Sweden, show a variety of features of growth form, within a spectrum of coenosteal shapes from laminar through low to high domical. Many coenostea show interdigitations of sediment in their margins, attributable to intermittent sedimentation, while others show abrupt changes in growth direction, which are the results of movement, often leading to overturning. Stromatoporoids frequently survived these agents and continued to grow, often resulting in different morphotypes from those which would have been produced in the absence of sedimentation and movement; serious problems of shape identification and shape classification exist as a consequence. Variations in the effects of sedimentation and movement are recognizable in the specimens studied and the Stromatoporoids therefore record a variety of events occurring at the sea bed during their lives. The four most abundant stromatoporoid species in the Upper Visby Beds show variations in morphology. Densastroma pexisum Yavorsky is commonest and in general has a taller shape than Clathrodictyon simplex Nestor, Pseudolabechia hesslandi Mori, and Stromatopora impexa Nestor. The reasons for such variations are unclear but may be related to a number of factors such as sedimentation, current activity, substrate consistency, or availability of food and oxygen.