BIVALVE CRINKLE BED
The term crinkle bed has been used to refer to
some bivalve shell pavements. The bedding plane shown below is a good
example. This is a weathered, friable mudshale derived from the
Mississippian-aged Hinton Formation of West Virginia, USA. The surface is
packed with decalcified clam shell fossils that appear to be consistent with Modiolus
(Mollusca, Bivalvia, Pteriomorphia, Mytiloida, Mytilidae) and Septimyalina
(Mollusca, Bivalvia, Pteriomorphia, Pterioida, Pteriina, Myalinidae).
Low-diversity, high-abundance fossil surfaces such as this are often inferred
to be from marginal marine facies.
Stratigraphy: Hinton Formation, middle Chesterian Series (= lower Namurian Series),
Upper Mississippian.
Locality:
Oakvale School outcrop - roadcut through Divide Ridge, on western side of Rt.
112, across from Oakvale School, immediately south of Rt. 460, far-southeastern
Mercer County, far-southern West Virginia, USA.
Bivalve crinkle bed (above & below; ~12 cm across) - a decalcified
bivalve shell pavement.
Above:
high-angle illumination
Below:
low-angle illumination
Bivalve crinkle bed (low-angle illumination; ~6 cm across) - a
decalcified bivalve shell pavement.
Bivalve crinkle bed (low-angle illumination; ~7 cm across) - a decalcified bivalve shell pavement.
Hinton Formation - Oakvale School outcrop in southern West Virginia,
looking west (Ohio State University geologists for scale). The bivalve
crinkle bed shown above is from this roadcut. The rocks here are
overturned beds of the Hinton Formation (Upper Mississippian). Stratigraphic
up is to the right (north). Rocks are dipping ~50° to the south.
The beds are mostly reddish and greenish-gray mudshales with some resistant
siltstone & sandstone interbeds. Some of the sandstones have shale
rip-up clasts. Well-defined burrows can be found in some of the hard
mudshales and sandstones. Observed body fossil occurrences here include
bivalve pavements (see above) and poorly defined, carbonized plant fossil
fragments in the shales. Some loose shale & sandstone samples have
fault slickenlines.
Some info. from:
Hoare (1993) - Journal of Paleontology 67(3).
Vance et al. (2006) - Geological Society of America
Abstracts with Programs 38(7): 67.