The lithostratigraphy of the upper Ordovician of central Portugal

Abstract

A lithostratigraphic scheme for the upper Ordovician of central Portugal is described incorporating previously-erected local lithostratigraphic terms and new units. Thirteen formations (10 new), including 11 members (eight new), with one named bed, are arranged into four groups (three new). A description of each unit is given, together with comments on its age and correlation. Deposition in a storm-dominated, shallow-shelf environment through Llandeilo and Caradoc time is indicated. Differential subsidence occurred to the NE and SW of the Dornes/Maçâo ‘rise’ particularly during the Caradoc. Lower to mid-Ashgill sequences in the north are dominated by volcanic rocks with subordinate carbonate deposition. Farther south a hiatus preceded the regressive deposits associated with the onset of the upper Ordovician glaciation. Hirnantian glaciomarine deposits occur across most of the area, except for the regions of carbonate and volcanic build-ups, and appear to represent the period of waning of the glaciation. The Ordovician/Silurian boundary is difficult to place, but probably lies close to or within a sheet sand-body which underlies a condensed Llandovery sequence. Lithostratigraphic correlation of the study area with W. Brittany, France, is generally good; the relationship of some of the upper Ordovician units in central Portugal aids the interpretation of the relationships of the equivalent deposits in Brittany.

A Kralodvorian (upper Katian, Upper Ordovician) benthic association from the Ferradosa Formation (central Portugal) and its significance for the redefinition and subdivision of the Kralodvorian Stage

“…The present study reports an exceptional fossil association from the silicified limestones of the upper member of the Ferradosa Formation, the Riba de Cima Member (Young 1988), cropping out in the Penacova-Vila Nova de Poiares region (Fig. 1).…”

“…The Ferradosa Formation (> 100 m thick) was defined by Young (1985Young ( , 1988 in the Penacova region (Central Portugal) and has been assigned to the upper BerounianKralodvorian (ca. middle to upper Katian; Ka2-Ka4 stage slices of the global scale).…”

“…In Portugal, diagnostic brachiopods of the Nicolella Community are known from the Porto de Santa Anna and Ferradosa formations (Young 1988) of the Central Iberian Zone of the Buçaco-Penacova region, Central Portugal (Young 1985, Sá et al 2011, Colmenar 2015. These occurrences were first documented by Delgado (1870Delgado ( , 1897Delgado ( , 1908, who discovered fossils in these rocks for the first time and provided the earliest lists of fossils from the levels currently included in both formations.…”

“…These occurrences were first documented by Delgado (1870Delgado ( , 1897Delgado ( , 1908, who discovered fossils in these rocks for the first time and provided the earliest lists of fossils from the levels currently included in both formations. The material studied by Delgado was later revised by Young (1985), who established the current accepted lithostratigraphic scheme for the Upper Ordovician of Central Portugal (Young 1988) adding several new outcrops and reporting new fossil occurrences.…”

Quitinozoários da formação Chão Lopes (Pridoli do Sinclinal Amêndoa: Mação, Portugal)

“…1) compreende 4 formações: Vale da Ursa (YOUNG, 1985(YOUNG, , 1988, Aboboreira, Castelo e Chão Lopes (RO-MÃO et al, 1998;ROMÃO, 2000a). A Formação Vale da Ursa é caracterizada por quartzitos cinzentos com intercalações de xistos negros e é considerada, a parte superior da formação, do Llandovery inferior (Rhuddaniano a Aeroniano) com base em graptólitos (PIÇARRA, 2007) e por correlação lateral com a mesma formação no setor de Dornes (YOUNG, 1988).…”