Abstract

Quarrying of the Rockhouse Limestone Member of the Ross Formation (Lower Devonian, west-central Tennessee) and the underlying Decatur limestone has exposed a bedding surface containing the crests of 48 elongate, subparallel mudmounds that are 1 to 14 m in length, average 2 m in width and are 1 to 2 m in height. Drill core data indicates that four vertical phases occurred in the development of the mudmounds. Phase I involved the introduction of an allochthonous fossiliferous terrigenous mud probably resulting from a storm event. Colonization and stabilization of patches of mud, less mobile than the surrounding sediment due to early lithification and algal binding, occurred in Phase II. This early lithification, relative to the surrounding high energy regime was responsible for promoting the development of the mudmounds. Phase III consisted of a stationary cavernous network of mud in which encrusting Buskopora served a dual role as a coelobite and as the chief sediment binder and “framework” builder. This represents the first reported occurrence of a coelobite as the dominant in a succession sequence. Phase IV represented the interruption of the dominance stage due to changing environmental conditions in the form of increased terrigenous input, with faunal diversity increasing and sediment influxes onto the mound altering the community structure. Development of all of the mounds was terminated by another influx of mud that blanketed the area.