Fezouata formation

from Wikipedia, the free encyclopedia

The upper and lower Fezouata formation in the southeast of Morocco are fossil deposits with a fossil from the conservation Unterordovizium that the Burgess Shale are similar. They fill an essential gap in the fossil record between the Cambrian and Soom slate deposits from the late Ordovician. The Fezouata fauna shows that the disappearance of numerous organisms of the Burgess-type fossils after the Middle Cambrian is by no means the result of their extinction, but rather reflects the rarity of this fossil conservation. The fossils were created on an area of ​​500 km² in the south-east of MoroccoDraa Valley , north of Zagora . As stratigraphically productive layers column were found in stone in a 1.1 km thick that the epochs Tremadocian and furongian spans.

Fossil of a marrellomorph from the Fezouata formation

Biota

More than 1500 non- mineralized specimens, which represent 50 different taxa , have a composition similar to that typical of the biota of Burgess slate , were recovered from the formations next to a less species-rich shell limestone fauna. The composition of the community varies greatly due to its stratigraphic sequence, with both the biodiversity and the faunal composition having changed over time. Small (1-3 mm wide) voids are present in the sediment, but larger voids are absent; this can indicate a lack of oxygen in the water or sediment. Particularly noteworthy is the presence of bryozoa ( bryozoans ) and graptolites , forms that were absent in the Cambrian. Various echinoderms indicate normal salinity, and the overall composition of the shell does not differ much from the normal mussel fauna expected in open waters of the Ordovician. The non-mineralized cohort contains a number of typical forms of Burgess slate: horned siliceous sponges , lobopods , annelids ( ringworms ), barnacles , possibly also Halkieriidae , Marrellomorphs , Palaeoscolecidae , Naraoiidae , Skaniidae and the expected problematic. Other Ordovician ecclesiastics are also present, including fellow guesses , machaeridia , and numerous horseshoe crabs .

Emergence

The fossil-bearing layers come from a calm, deep sea area. Under the influence of violent storms, the wave movements reached the sea floor. Such storm events jerked up the sediment and buried marine life on the bottom. Consequently, the composition of benthos is dominated. The rapid covering with sediment was the prerequisite for the Diagenesian processes of this conservation deposit .

Receipt

The smaller fossils of the Fezouata Formation, which make up the largest proportion, are mostly flattened and preserved in pyrite . The pyrite is mostly weathered to form iron oxide . Some larger specimens have been preserved in three dimensions in concretions . This aspect of fossil conservation is similar to the findings from the Chengjiang Faunal Community . Unmineralized body attachments are often preserved. This preservation of soft tissue is what makes the fossil preservation of the Fezouata Formation outstanding, as it allows a much more extensive scientific reconstruction .

discovery

The deposits were first recognized as such in the late 1990s when Ben Moula, a fossil collector from the area, showed some of the finds to a PhD student working on site.

Individual evidence

  1. ↑ a b c d e f g h i j doi : 10.1038 / nature09038
  2. ↑ (BBC News) Victoria Gill, "Fossil find resolves ancient extinction mystery" : accessed 13 May 2010
  3. ↑ doi : 10.1016 / j.geobios.2007.02.006
  4. ↑ A giant Ordovician anomalocaridid, P Van Roy, DEG Briggs 2011
  5. ↑ doi : 10.1016 / j.annpal.2007.06.003
  6. ↑ doi : 10.1038 / nature06474
  7. ↑ A giant Ordovician anomalocaridid doi: 10.1038 / nature09920
  8. ^ Van Roy, P: Exceptionally Preserved Faunas from the Lower Ordovician of the Anti-Atlas, Morocco . In: First international Conference and Exhibition, Marrakech, Morroco ..
  9. ↑ doi : 10.1038 / news.2010.234

Coordinates: 30 ° 10 ′ 44.4 "  N , 5 ° 32 ′ 24"  W.