Continental ichnofossil diversity from
the Silurian Bloomsburg Formation, Schuylkill Gap, Pennsylvania
Ireland, Scott M.,
Simpson, Edward L.,
Fillmore, David, Szajna, Michael J., and Lucas, Spencer G., 2014,
Continental ichnofossil diversity from the Silurian Bloomsburg
Formation, Schuylkill Gap, Pennsylvania: Geological Society of
America Abstracts with Programs, Northeastern Section - 49th
Annual Meeting Lancaster, PA, (23–25 March), v. 46, no. 2.
The Ordovician invertebrate invasion into continental settings is
problematic, with few noncontroversial examples reported. Silurian
examples of continental ichnofossils are rare. In eastern
Pennsylvania, the Silurian Bloomsburg Formation consists of fluvial
deposits with a low-diversity ichnofauna. The rarity of reported
Silurian continental ichnoassemblages makes this documentation
significant by expanding our understanding of continental
ichnodiversity as recorded in the Bloomsburg Formation.
The Bloomsburg Formation exposed at Schuylkill Gap consists of
erosionally based channel sandstones, composing fining-up sequences
from medium-grained sandstones to overbank mudstones. Channel fills
are dominated by medium-scale trough cross beds, ripple
stratification and thinner graded beds. Laminated graded beds of
fine-grained siltstones pass vertically into thick overbank mudstone
deposits. Reduction halos around rhizome traces, mud cracks,
microbial mats and some well-developed Bk horizons characterize the
overbank deposits. The Bloomsburg fluvial systems are low gradient
and relatively low sinuosity systems. The strata contain a
low-diversity ichnofauna that includes: 1) sinuous burrows,
nonmeniscate (?Planolites) and meniscate (Taenidium),
2) bilobate, oval resting traces (Rusophycus), 3) slightly
sinuous trails with a medial ridge and perpendicular scratches (Cruziana),
4) walking traces that consist of two rows of parallel circular
depressions (Diplichnites), and 5) complex bilaterally
arcuate walking traces (Palmichnium). This ichnoassemblage is
consistent with that previously reported from the Bloomsburg
Formation with the addition of Palmichnium and less abundant, ?Planolites
and Taenidium. In Bloomsburg Formation at the Schuylkill Gap,
epifaunal arthropod traces are the dominant ichnofossils,
characteristic of the well-known Diplichnites ichnoguild reported
from overbank environments from the Silurian to Devonian.
Continental ichnofossil diversity from
the Silurian Bloomsburg Formation, Schuylkill Gap, Pennsylvania