Slab of transition zone from Lake Neosho Shale to Worland Limestone

Limestone lens from the upper part of the bioclastic shale where it is
gradational to Worland Limestone. Two grayish brown phosphate
nodules lie at the base, and a third spherical nodule at the lower left
corner was just missed by the saw. At the far right, a disarticulated
shell is filled with micrite and a tiny spherule of phosphate. Other
grayish brown objects are tiny phosphate nodules or fragments of
nodules. Composition and origin of the irregular dark mass at upper
left center and the oblique reddish streak beneath it are unknown.
Micritic limestone (mottled gray) precipitation seems to have been
concentrated above the two large nodules at the base, but whether
the presence of carbonate is causally related to the phosphate is
unclear. Grayish green calcareous shale rich in skeletal debris (this is
the "bioclastic shale") arches over the limestone. Varying concentration
of carbonate in the shale is reflected by color and texture--segments
richer in carbonate are lighter colored and grainier; darker green is
more clay rich. Mottling suggests the carbonate sediment was
bioturbated, but the shale seems to have been avoided by burrowers.
At the lower left is a partially crushed articulated brachiopod shell that
became filled only with clay. Skeletal debris was apparently too coarse
to infiltrate between the closed valves of the brachiopod.

View close-up

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