IMPLICATIONS OF BIFUNGITES FROM THE UPPER DEVONIAN OF WEST VIRGINIA, USA

Recent highway construction in east-central West Virginia, USA, has exposed kilometre-long outcrops of Upper Devonian strata. Within these siliciclastic sediments are the records of numerous small-scale transgressive-regressive episodes associated with the deposition of the Acadian Clastic Wedge. In particular, strata of the Blizzard Member of the Foreknobs Formation (formerly Chemung) have been under investigation for the past two years. Excavation has brought to light well-preserved, marine body fossils; bedding-surface exposures of sedimentary structures; and numerous trace fossils.

The trace fossils in the Blizzard are restricted to two zones separated by 60.3 metres of strata. The upper trace fossil zone is 19.8 metres thick with a prolific assemblage of trace fossils dominated by Bifungites, Arenicolites, and a variety of horizontal traces. The lower zone is only a few metres in thickness, is marked by "diffuse" upper and lower boundaries, and contains the same trace fossil assemblage but fewer trace fossils are present and Arenicolites is more abundant than Bifungites. These assemblages appear to belong to a "mixed" Skolithos and Cruziana ichnofacies, both characteristic of relatively high-energy, shallow-marine environments but of different water depths. The associated sediments are fine- to very fine-grained siliciclastics with ripple-scale crossbedding. The upper trace fossil zone is nearly devoid of body fossils; a few, centimetre-thick shell lags are found in the lower zone.

Examination of numerous Bifungites expressed either as epichnial molds, hypichnial casts, or clay-filled endichnia causes us to speculate that some Bifungites ichnospecies may be preservational artifacts related to the grain size and consistency of the enclosing sediment. The formation of the arrow-shaped protrusions of Bifungites is not associated with feeding. It may represent an attempt by the tracemaker to suspend its body above water-logged sediment at the bottom of the u-tube by increasing its surface area. Another possible explanation for this behaviour is that the arrow-shaped portions of the trace may have allowed the tracemaker to "hold on" to the enclosing sediment with one end of its body when faced with a predator attempting to extract it from the burrow.