| Silveirinha Formation | |
| Period: | Ypresian |
| Age: | Ypresian (MP7 or Neustrian) ~ |
| Type: | Geological formation |
| Prilithology: | Sandstone, siltstone |
| Otherlithology: | Conglomerate |
| Subunits: | Rio Mondego Member |
| Underlies: | Bom Sucesso Formation |
| Overlies: | Taveiro Formation |
| Coordinates: | 40°N -8.8°W |
| Paleocoordinates: | 35.6°N -10°W |
| Region: | Região Centro |
| Extent: | Mondego Basin |
| Namedfor: | Silveirinha clay pit |
| Namedby: | Autunes et al. |
| Year Ts: | 1981 |
| Location Ts: | Silveirinha clay pit |
| Coordinates Ts: | 40.0081°N -8.8213°W |
| Region Ts: | Coimbra District |
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]
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.
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]
See also: Paleocene-Eocene Thermal Maximum. The climate in the Early Eocene was substantially warmer than today.
The Silveirinha clay pit after which the formation is named was first discovered in 1977 by Rui Pena dos Reis of Coimbra University. The unit is one of few earliest Eocene fossiliferous formations that provided a rich amphibian and reptile fauna.[4] 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.[5]
The formation has provided the following fossils:[1]