Fezouata Formation

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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.

Biota[change | change source]

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]

Geology[change | change source]

Depositional setting[change | change source]

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]

Preservation[change | change source]

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]

Location[change | change source]

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]

History[change | change source]

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]

References[change | change source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Van Roy P. et al. 2010. Ordovician faunas of Burgess Shale type. Nature 465: 215–218. [1]
  2. (BBC News) Victoria Gill, "Fossil find resolves ancient extinction mystery": accessed 13 May 2010
  3. Cheloniellids are an extinct group of arthropods.
  4. Van Roy, P (2008). "Exceptionally preserved faunas from the Lower Ordovician of the Anti-Atlas, Morocco" in First international Conference and Exhibition, Marrakech, Morroco. . 
  5. Jones, Nicola 2010. Wierd wonders lived past the Cambrian. Nature News 465 [2]