Dresden Lakes Pecopteris Frond Fossil
Time: Pennsylvanian (~300 m.y.a.)
mm = 1 inch): Plant fossil is 230 mm long by 140 mm across
Dresden Lakes, Francis Creek Shale, Grundy County, Illinois
The Mazon Creek deposits of the region near Braidwood, Illinois rival
the other famous Lagerstatten of the Burgess Shale, Solnhofen, and
Liaoning for the variety of detailed life preserved. Many exquisitely-preserved
specimens are found in the ironstone nodules that make up the deposits.
The majority of collecting areas are the spoil heaps of abandoned
coal mines. This particular nodule, however, comes from Dresden Lakes
in Grundy County Illinois. Like the better-known Pit 11 site near
Braidwood, Illinois, this location became the site for cooling ponds
for a nuclear power plant. The site is well known for the dark coloration
that while esthetically pleasing is somewhat harder to photograph.
I recently had an opportunity to acquire a collection that was made
in the 1950’s. The Pteridophyte (tree fern) Psaronius became
a dominant form supplanting the lycopds. The leaf fronds and pinnules
of Psaronius were given the form genus designation of Pecopteris,
a highly variable form whose classification is still under review.
This is a fine large example which fills is enclosing nodule. Nodules
of this size are quite rare.