Palynology of the Triassic - Jurassic of the Silves Group in Portugal, its implications on a changing world

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The age of the first pulse of continental rifting associated with the breakup of Pangea in Southwest Iberia: new palynological evidence

Publication . Vilas Boas, Margarida; Paterson, Niall W.; Pereira, Zélia; Fernandes, Paulo; Cirilli, Simonetta

ABSTRACT: In this work, we report the first palynological age for the base strata of the Silves Sandstones of the Silves Group in the Algarve Basin, located in Southern Portugal. The group is the oldest sedimentary unit of the Algarve Basin and was deposited unconformably over late Pennsylvanian turbidites of the Mira Formation, which were folded and faulted during the Variscan Orogeny. The Silves Group comprises a detrital red bed succession, representing the earliest phase of sedimentation associated with the initial rifting of Pangaea. Macrofossils are rare, occurring predominantly in the top layers of this group, and do not accurately constrain the age of the entire group's deposition. From an outcrop exposed in the central Algarve, a grey mudstone bed positioned 2.5 m above the Variscan unconformity plane yielded palynomorphs that date the beginning of sedimentation in this basin to the early Carnian age (Late Triassic). The moderately well preserved and low-diversity palynological association comprises Aulisporites astigmosus, Enzonalasporites densus, Ovalipollis pseudoalatus, Samaropollenites speciosus, Tulesporites briscoensis and Vallasporites ignacii, among others, and is indicative of an early Carnian age.

2022-03Journal article

Open access

New palynostratigraphical data of the Silves Group, Algarve Basin

Publication . Vilas Boas, Margarida; Fernandes, Paulo; Pereira, Zélia; Cirilli, Simonetta

SUMÁRIO: Este trabalho mostra dados palinostratigráficos que permitem aperfeiçoar a idade do Grupo de Silves na Bacia do Algarve. O Grupo de Silves constitui a unidade sedimentar mais antiga desta bacia e foi depositado de forma discordante sobre os turbiditos do Carbonífero superior da Formação Brejeira, dobrados e falhados durante a Orogenia Varisca. Os novos dados obtidos, permitem-nos apontar o início da sedimentação na Bacia do Algarve ao Carniano inferior e datar de idade Carniano todo o pacote sedimentar correspondente aos “Arenitos de Silves”. As camadas da base do “Complexo Margo-Carbonatado de Silves” correspondem ao Carniano superior, e os evaporitos possuem idade compreendida entre o Retiano superior e a base do Hetangiano, representando assim o limite entre o Triássico e o Jurássico, na bacia.

2023-07Conference object

Open access

New data on the palynology of the Triassic Jurassic boundary of the Silves Group, Lusitanian Basin, Portugal

Publication . Vilas Boas, Margarida; Pereira, Zélia; Cirilli, Simonetta; Duarte, L. V.; Fernandes, Paulo

ABSTRACT: New evidence is presented on the Triassic-Jurassic boundary in the northern Lusitanian Basin, Portugal, based on miospore assemblages from a composite Upper Triassic to Lower Jurassic succession of the Silves Group. The latter comprises, from base to top, the Conraria, Penela, Castelo Viegas and the Pereiros formations. Three informal palynological zones have been documented and compared with coeval palynozones from West and South Europe providing new biostratigraphic data to detail the age of the lower and upper formations of the Silves Group and to review previous age attribution. A Norian, possibly earliest Rhaetian age, is documented for the Conraria Formation on the basis of a palynological assemblage referable to the Classopollis meyerianus-Granuloperculatipollis rudis (CG) zone. The Penela and Castelo Viegas formations did not allow a palynostratigraphic revision, due to the not promising lithology for palynological studies. The Pereiros Formation is dated on the basis of microflora assemblages referable, from bottom to top, the Ischyosporites variegatus-Kraeuselisporites reissingeri (IK) zone of late Rhaetian-earliest Hettangian age and Pinuspollenites minimus (Pm) zone of Hettangian age. The discontinuity between the underlying Castelo Viegas Formation and the overlying Pereiros Formation did not allow to define the lower boundary of the IK palynozone. The Triassic-Jurassic boundary lies in the lower part of Pereiros Formation within the IK zone. The microflora assemblages from the Lusitanian Basin show close affinity to those of eastern N America and western Tethys areas. (C) 2021 Elsevier B.V. All rights reserved.

2021Journal article

Open access