The oldest fossil record in the Iberian Peninsula; lower Ediacaran acritarchs of the Tentudía Formation, Ossa-Morena Zone (OMZ), Southwest Iberian Massif.

Abstract

A diverse assemblage of acritarchs, that represents the oldest fossil record of the Iberian Massif, is described from Ediacaran metasedimentary rocks of the Tentudía Formation included in the Ossa Morena Zone stratigraphy (Southwestern Iberia). The microfossils found include Assesserium pyramidalis, Cavaspina sp. A, Ceratosphaeridium sp. A, Dictyotidium sp. A, Multifronsphaeridium sp. A, Schizofusa zangwenlongii, Tanarium megaconicum Tanarium sp. A, and Tanarium ? sp. B, This assemblage is diagnostic of the mainly lower Ediacaran Doushantuo-Pertatataka acritarchs (c. 633—565 Ma.). The lithological diversity of the Tentudía Formation suggests that these Ediacaran sedimentary rocks were deposited in a diversity of environments (platform, slope and submarine fans, including mass transport deposits in a back-arc basin that extended into the southern part of the Central Iberian Zone. The mass transport deposits are represented in the Ossa-Morena Zone by the Salvaleón Olistostrome composed by turbidites including chert clast probably derived from the shelf. The migration of the mass transport deposits into the Central Iberian Zone (Orellana Formation) indicates the migration of the back-arc basin depocenter. Later inversion of the back-arc basin is marked by the deformation of the lower Ediacaran sedimentary rocks Serie Negra Group in the Ossa-Morena Zone and Domo Extremeño Group in the Central Iberian Zone. In the upper Ediacaran-Terreneuvian a carbonate platform (Ibor Group) was established in the southern part of the Central Iberian Zone unconformably overlying the previously deformed Domo Extremeño Group. The most proximal areas in the Ossa-Morena Zone are represented by the Malcocinado Formation which overlies the Serie Negra Group and the distal areas of the southern part of the Central Iberian Zone are represented by distal shelf and slope deposits of the Cijara Formation, which are overlain by mass transport deposits that include carbonate olistolites from the Ibor Group (such as the Fuentes and Membrillar olistostromes).