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- New data on the palynology of the Triassic–Jurassic boundary of the Silves Group, Lusitanian Basin, PortugalPublication . Vilas Boas, Margarida; Pereira, Zélia; Cirilli, Simonetta; Duarte, Luís Vítor; Fernandes, PauloNew evidence is presented on the Triassic–Jurassic boundary in the northern Lusitanian Basin, Portugal, based onmiospore assemblages from a composite Upper Triassic to Lower Jurassic succession of the Silves Group. The lat-ter comprises, from base to top, the Conraria, Penela, Castelo Viegas and the Pereiros formations. Three informalpalynologicalzones havebeendocumented andcomparedwith coevalpalynozonesfromWestandSouth Europeprovidingnew biostratigraphic data to detail the age of the lower and upper formationsofthe SilvesGroup and toreview previous age attribution.A Norian, possibly earliest Rhaetian age, is documented for the Conraria Formation on the basis of a palynologicalassemblage referable to theClassopollis meyerianus–Granuloperculatipollis rudis(CG) zone. The Penela andCastelo Viegas formations did not allow a palynostratigraphic revision, due to the not promising lithology for pal-ynological studies. The Pereiros Formation is dated on the basis of microflora assemblages referable, from bottomto top, theIschyosporites variegatus–Kraeuselisporites reissingeri(IK) zone of late Rhaetian–earliest Hettangian ageandPinuspollenites minimus(Pm) zone of Hettangian age. The discontinuity between the underlying CasteloViegas Formation and the overlying Pereiros Formation did not allow to define the lower boundary of the IKpalynozone. The Triassic–Jurassic boundary lies in the lower part of Pereiros Formation within the IK zone. Themicroflora assemblages from the Lusitanian Basin show close affinity to those of eastern N America and westernTethys areas.
- Palynology and palynofacies studies in the lowermost Jurassic of the Lusitanian Basin (Pereiros Formation of the Silves Group), Portugal: evidence of the first transgressive episodePublication . Vilas Boas, Margarida; Pereira, Zélia; Cirilli, Simonetta; Duarte, Luís Vítor; Sêco, Sérgio Luís Rodrigues; Fernandes, PauloThe Silves Group of the Lusitanian Basin in Portugal represents the initial infill of the continental rifting basins that formed during the breakup of northern Pangaea regions. Evaporites, especially halite, mark the transition from continental to marine settings and the beginning of the deposition in passive margin basins. This work presents the results of the palynostratigraphic and palynofacies analysis of two partial sections from the Pereiros Formation at the top of the Silves Group. The two sections are composed of sandstones, mudstones and dolostones interpreted as deposited in fluvial and lacustrine settings without apparent marine influence. The palynological content is diverse and wellpreserved, dating both sections to the early Hettangian (Lower Jurassic), indicated by the presence of spores Ischyosporites variegatus, Kraeuselisporites reissingeri, Porcellispora longdonensis and the pollen grains Perinopollenites elatoides and Pinuspollenites minimus. The palynological content of one of the sections (Lamas I) is noticeable by microforaminifera linings, suggesting evidence for a hitherto marine incursion at this age in the Silves Group stratigraphy. The beds that yielded the microforaminifera linings are interpreted as having been deposited in an estuarine-type setting, created by the first and short-lived marine transgressive event in the Lusitanian Basin during the early Hettangian.