Photomicrograph of glendonite concretion
from storm bed in Carolinefjellet Fm., Festningen.
This is a mosaic of thin section
photos of a glendonite concretion from a storm bed at the top
of the Dalkjegla Mbr. within the Carolinefjellet Fm. . Clicking
on it will download a 10MB version. The concretion is a bit more
than 2 cms across, and the photos were taken with crossed nicols.
A core of coarser calcite is surrounded by 'petals' of bladed
carbonate with a complex internal texture. Given that glendonites
are usually calcite pseudomorphs of a unstable hydrous carbonate
mineral the texture may reflect the recrystallization process.
Note between the petals the fine-grained sideritic sediment that
is preserved. We interpret this to represent the sediment the
glendonite grew in before excavation and deposition as part of
the storm bed. It looks like the lower left large petal has been
truncated by some process. Most of the black mineral is pyrite
and there is a pyritization front on the left side (sedimentary
bottom). The large clast in the upper left is a carbonate hardground
with oolites in it, while to the lower left is a chert clast with
a pyrite replament rind. For fun below is the same image but with
an edge detection routine run on it.