Fezouata Formation

Over 1500 non-mineralized specimens, representing 50 distinct taxa that have a composition similar to earlier Burgess Shale type biotas, have been recovered from the formations in addition to a less abundant shelly fauna.[6] The make-up of the community varies significantly through the stratigraphic sequence, with both abundances and faunal composition changing as time progresses.[6] 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.[6] Particularly notable is the presence of bryozoa and graptolites,[6] forms that are absent in the Cambrian period. Diverse 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.[6] The non-mineralized cohort contains a range of forms familiar from the Burgess Shale: Demosponges,[8] lobopods, barnacles, annelids, anomalocaridids (e.g. Aegirocassis),[9] possible halkieriids, marrellomorphs, paleoscolecid worms, naraoiids, skaniids as well as the expected problematica. Other Ordovician oddballs are also present, including mitrates,[10] machaeridia,[11] cheloniellids and horseshoe crabs in abundance.[6]

South Polar paleogeography of the Middle Ordovician, 460 Ma

The fossiliferous strata were deposited just above storm wave base (offshore to lower shoreface transition), at between 50 and 150 metres (160 and 490 ft) water depth. Organisms were likely buried in situ.[12] Because of its placement above storm wave base, storms would have mobilized sediment that could be quickly deposited, trapping animals and leading to their preservation.[6][13] Consequently, the assemblage is dominated by benthic organisms.[6]

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.[6] Non-mineralized appendages are often preserved.[6] While the formation as a whole is over 1,000 metres (3,300 ft) thick, only two intervals, 25 metres (82 ft) and 15 metres (49 ft) thick, provide exceptional preservation.[14][15] Both of these intervals are located near the top of the lower formation, corresponding to the Araneograptus murrayi and Hunnegraptus copiosus graptolite zones respectively.[12]

The fossils occur within an area of 500 square kilometres (190 sq mi), in southeast Morocco's Draa Valley, north of Zagora. Stratigraphically productive layers are found through a 1.1 kilometres (0.68 mi)-thick column of rock that spans the Tremadocian and Floian epochs.[6] Two stratigraphic intervals of the formation are fossiliferous: the lower is Late Tremadocian and sits 260 to 330 metres (850 to 1,080 ft) above the base of the formation; the upper, at 570 to 620 metres (1,870 to 2,030 ft), is mid-Floian in age.[1]

The Lagerstätten were first identified in the late 1990s when a local fossil collector, Ben Moula, showed some of the finds to a PhD student who was then working in the area.[16][17]