Fezouata Formation

The Upper and Lower Fezouata formations of Morocco are Burgess Shale type deposits dating to the Lower Ordovician.^[1] In the fossilized fauna were numerous organisms previously thought to have died out after the mid-Cambrian.^[2] The discovery proves conclusively that the Burgess Shale biota did not go extinct in the Cambrian.

Over 1500 non-mineralized Burgess Shale types, representing 50 taxa, have been recovered from the formations. There are also a less abundant shelly fauna.^[1] The make-up of the community varies significantly through the stratigraphic sequence, with both abundances and faunal composition changing as time progresses.^[1] Small (1–3 mm wide) burrows are present in the sediment, but major burrowing is absent; this may suggest a paucity of oxygen in the water or sediment.^[1]

Particularly notable is the presence of bryozoa and graptolites,^[1] forms that are absent in the Cambrian period. Various echinoderms indicate a normal range of salinity, and the overall shelly assemblage is not significantly different from the normal shelly fauna expected in open Ordovician waters.^[1]

The non-mineralized (soft-bodied) fossils contains a range of forms familiar from the Burgess Shale. Other Ordovician oddballs are also present, including cheloniellids and horseshoe crabs in abundance.^[1][3]

The fossiliferous strata were deposited in quiet, deep waters, below the influence of wave action in all but the fiercest of storms. Such storms, or similar high-energy events, would have mobilized sediment that could be quickly deposited, trapping animals and leading to their preservation.^[1] Consequently, the assemblage is dominated by benthic organisms.^[1]

Fossils of the Fezouata formation, which are usually squashed flat (although some do retain some degree of their original three-dimensionality) are often coated with a dusting of pyrite, and tin; this aspect of the fossil preservation is very similar to that at Chengjiang.^[1] Non-mineralized appendages are often preserved.^[1]

The fossils a span an area of 500 km², in southeast Morocco's Draa Valley, north of Zagora. Fossils are found are found through a 1.1 km-thick column of rock that spans the two lowest epochs of the Ordovician.^[1]

The lagerstätten were first identified in the late 1990s^[4] when a local fossil collector, Ben Moula, showed some of the finds to a PhD student who was then working in the area.^[5]