Growth-interruption surfaces within chaetetid skeletons: Records of physical disturbance and depositional dynamics

Records of growth interruptions within spongiomorph and colonial skeletons provide a unique window into the disturbance dynamics of ancient shallow marine benthic environments at ecological time scales. The utility of growth-interruption surfaces for inferring the frequency of physical disturbance and the relative rate of sediment accumulation is illustrated by chaetetid skeletons from several Middle Pennsylvanian (Desmoinesian) sequences of southeastern Kansas. Five different growth-interruption surfaces are recognized within these calcareous demos-ponges: (1) breaks in growth with apparent continuity of tubules across the surface, (2) surfaces of rejuvenation or recolonization with reorientation of tubules, (3) sediment-filled tubules or trapped sediment partings, (4) encrusted surfaces, and (5) biocorroded or bored surfaces. A single skeleton may contain several types of surfaces, and individual surfaces may change in character across the skeleton. The type and spacing of growth-interruption surfaces vary with chaetetid growth form. Together with growth form, these surfaces provide a basis for paleoen-vironmental interpretation.