Edgewise phosphate nodule on ragged erosion surface in Lake Neosho Shale
Close-up of the contact between the phosphatic shale
and bioclastic
shale subunits of the Lake Neosho Shale. The contact is exceptionally
irregular and ragged where the phosphatic shale seems to have
splintered. Bioclastic grains and clay infiltrated the crevices and filled
them. An oblate phosphate nodule reworked from the underlying
phosphatic shale came to rest in edgewise position at a sheltered spot
formed by topographic microrelief on the sea floor. The "X" marks
a
spherical hollow in the crevice filling where a phosphate nodule had
been deep in the crevice (it fell out upon exposure). Other indeterminate
clasts lie between the locations of the two nodules. Apparently all of the
larger sediment particles came to rest here due to the sheltering effect
of the crevice and the associated microrelief. The numerous light-colored
specks in the bioclastic shale are minute fossil fragments.
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