Silveirinha Formation

The Silveirinha Formation is an Early Eocene (Ypresian, or MP7 or Neustrian in the ELMA classification) geologic formation of the Mondego Basin in the Região Centro of central-western Portugal. The sandstones, siltstones and conglomerates were deposited in an alluvial environment.[1]

Silveirinha Formation
Stratigraphic range: Ypresian
(MP7 or Neustrian)
~55.8–48.6 Ma
TypeGeological formation
Sub-unitsRio Mondego Member
UnderliesBom Sucesso Formation
OverliesTaveiro Formation
Lithology
PrimarySandstone, siltstone
OtherConglomerate
Location
Coordinates40.0°N 8.8°W / 40.0; -8.8
Approximate paleocoordinates35.6°N 10.0°W / 35.6; -10.0
RegionRegião Centro
Country Portugal
ExtentMondego Basin
Type section
Named forSilveirinha clay pit
Named byAutunes et al.
LocationSilveirinha clay pit
Year defined1981
Coordinates40°00′29.0″N 8°49′16.7″W
RegionCoimbra District
Silveirinha Formation (Portugal)

The formation has provided fossils of many mammals, birds, amphibians and reptiles, as well as mollusks and ostracods, and is considered one of the richest Early Eocene faunal assemblages of Europe. The taeniodont, typically known as a North American order; Eurodon silveirinhensis and the ostracod Cypris silveirinhaensis have been named after the formation.

Description

The Silveirinha Formation, named after the Silveirinha clay pit, crops out in the western part of the Mondego Basin in the Região Centro of central-western Portugal.[2] The formation comprises fossiliferous lenticular calcitic conglomerates as well as laminated and cross bedded sands and brownish-red silts.[1]

The conglomerates are interpreted as crevasse-splay deposit in a alluvial plain environment, which eventually flooded and where bogs and possibly oxbows developed, crossed by channels depending on a river system that drained higher areas more north or eastwards.[3]

Climate
See also: Paleocene-Eocene Thermal Maximum

The climate in the Early Eocene was substantially warmer than today.

Paleontological significance

The Silveirinha clay pit after which the formation is named was first discovered in 1977 by Rui Pena dos Reis of Coimbra University.[4] The unit is one of few earliest Eocene fossiliferous formations that provided a rich amphibian and reptile fauna.[5] Most fossils were deposited in the channels after short transportation. Vegetation should have been rich in nearby areas, supporting a rich fauna. Ostracods, gastropods, amphibians and pelomedusid chelonians indicate fresh waters, although rare bivalves show that salt or at least brackish waters were not very far away.[3]

It is hypothesized that the species D. antunesi in the genus Diacodexis was more primitive than the earliest Wasatchian D. ilicis of North America, strongly supporting a Europe to America dispersal of this genus.[6]

Fossil content

The formation has provided the following fossils:[1]

Mammals
Primates
Acreodi
Artiodactyls
Carnivora
Cimolesta
  • Ilerdoryctes cf. sigei[11]
"Condylartha"
Ferae
Glires
Hyaenodonta
  • Didelphodus sp.[7]
Insectivora
Perissodactyls
Taeniodonta
Theriiformes

Birds

Reptiles
Crocodiles
Lizards
Snakes
Turtles

Amphibians

Invertebrates
Mollusks
Ostracods

See also

References
  1. Silveirinha Formation at Fossilworks.org
  2. De la Peña, 1995, p.30
  3. Antunes, 2003, p.20
  4. Estravís, 2000, p.282
  5. Rage & Augé, 2003, p.103
  6. Godinot & De Lapparent, 2003, p.262
  7. Estravís, 2000, p.283
  8. Tabuce et al., 2011, p.146
  9. Estravís & Russell, 1989
  10. Badiola et al., 2009, p.248
  11. Estravís, 2000, p.284
  12. Tabuce et al., 2006, p.41
  13. Antunes et al., 1987
  14. Escarguel, 1999, p.142
  15. Escarguel, 1999, p.251
  16. Estravís, 1994
  17. Estravís, 1990
  18. Estravís & Russell, 1992b
  19. Estravís & Russell, 1992a, p.195
  20. Tabuce et al., 2009
  21. Estravís, 1996
  22. Harrison, 1983
  23. Antunes, 2003, p.7
  24. Antunes, 2003, p.10
  25. Rage & Augé, 2003, p.105
  26. Rage & Augé, 2003, p.107
  27. Rage & Augé, 2003, p.108
  28. Rage & Augé, 2003, p.106
  29. Rage & Augé, 2003, p.109
  30. Lapparent de Broin, 2003, p.118
  31. Rage & Augé, 2003, p.104
  32. Callapez, 2003, p.84
  33. Callapez, 2003, p.85
  34. Colin & Antunes, 2003, p.92

Bibliography
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