STROMATOLITE
Here’s a beautiful, cut slice from a stromatolite
head. Stromatolites are layered structures built up by mats of
cyanobacteria (= blue-green bacteria, often incorrectly called “blue-green
algae”). Stromatolites are fairly common in portions of the shallow-water
marine & nonmarine fossil record, but they also occur in a few modern
localities (e.g., Shark Bay, coastal Western Australia).
This one grew during the Eocene in ancient Lake
Gosiute in southwestern Wyoming, USA. It comes from the Fort Laclede Bed
of the Laney Member, Green River Formation.
Stromatolite (18.6 cm across at its widest) from the Fort Laclede Bed, Laney
Member, Green River Formation (Eocene) of southwestern Wyoming, USA.
Stromatolite (~2.6 cm across; same specimen as above) - close-up of stromatolite
laminations.
Stromatolite (~12 mm across; same specimen as above) - two lacustrine snails got
caught up in pockets of the stromatolite. The snail shell on the left has
oolitic & peloidal sediments filling the lower portions of its whorls &
calcite spar cement filling the upper portions of the whorls - a geopetal
structure.
Stromatolite (~12 mm across; same specimen as above) - sediment filling between two
stromatolite columns. The grains are mostly a mixture of ostracod shells,
oolites, composite oolites, and peloids. Sediment pouch is ~8 mm across.