Silurian chitinozoans of Amêndoa - Mação syncline (Central Portugal)

Abstract

The sequence of Silurian age of central Portugal outcropping in Amêndoa-Mação Syncline (figure 1) comprises four formations: Vale da Ursa, Aboboreira, Castelo and Chão Lopes (Cooper, 1980, Romão et al., 1998 and Romão, 2000).

Vale da Ursa Formation is characterized by dark, pyritic and micaceous quartzites and an age Rhuddanian to Aeronian is accept for the top of formation, based in graptolites (Piçarra, 2007).

The Aboboreira Formation is a micaceous black shale sequence with sandstone intercalations changing towards to the top to dark silstones, an age Aeronian (middle Llandovery) to basal Gorstian (lower Ludlow) is accept based in graptolites (Piçarra, 2007).

The Castelo Formation is characterized by shales and siltstones intercalated with grey quartzites. The samples from this formation yield a moderately well-preserved chitinozoan association with Cingulochitina convexa (Laufeld, 1974) and Angochitina echinata Eisenack, 1931, suggesting the elongata and philipi Biozones of Ludlow age (upper Gorstian to early Ludfordian) (Vaz, 2010).

The Chão Lopes Formation is characterized by black shales with nodules intercalated with centimetric levels of shales and micaceous siltstones. This formation yield a moderately well-preserved chitinozoan association with Urnochitina urna Eisenack 1934, which is the chitinozoan index of the Pridoli. (Vaz, 2010).

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015