Fine-grained carbonate debris flow, Ordovician basin margin, southern Appalachians

Abstract

Abstract This paper documents for the first time, an occurrence of a specific type of sediment gravity flow called fine-grained debris flow (Hampton, 1975). Fine-grained debris flows are those in which maximum grain size does not exceed that of pebbles (64 mm). The pebbly-lime mudstones of the Whitesburg Formation (Middle Ordovician) at Nina in east Tennessee have been interpreted as fine-grained carbonate debris-flow deposits based on evidence for (1) laminar and plug flow transport, (2) deposition by 'freezing', and (3) flow strength provided by muddy matrix. Planar-clast fabric with inverse grading, fragile fossils and shale clasts, projected clasts on bedding surfaces, and lack of scour marks imply laminar-flow transport. Massive internal structures, random orientation of clasts, and poor sorting are suggestive of plug-flow transport. Floating of large clasts in a muddy matrix (unsupported framework) implies flow strength as well as deposition by 'freezing'. Multiple episodes of debris flows occurred locally in a basin-margin sedimentary setting. Speculations are that these episodic debris flows correspond with tectonic pulses associated with basin subsidence.