Contribuição dos quistos de dinoflagelados para reconstituições paleoambientais e correlação biostratigráfica no Cenomaniano da Nazaré (Portugal)

Lígia Nunes de Sousa Pereira de Castro, Pedro Oliveira, Zélia Pereira, Pedro Callapez

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Abstract

The middle Albian-lower Turonian Western Continental Margin of the Iberia stands out in the post-rift record of the Western Iberian Continental Margin by its marine character and abundance in fossils. In this study the stratigraphy and palynology of the basal sequences recorded in Nazaré, one of its main outcrops, are focused with emphasis on the transition between the lower and middle Cenomanian. For this purpose, four marly levels interbedded with limestones with oyster biostroms, have been sampled, with the result of nine samples with diverse palynological contents. From the subsequent laboratorial analysis, we highlight: (1) low diversity of dinocysts (indicative of proximal coastal conditions); (2) dominance of peridinioid dinocysts (indicative of low or variable salinity in proximal conditions and/or nutrient abundance in areas of resurgence or terrestrial influx); (3) large predominance of euryhaline dinocysts (with preference for brackish conditions in transitional environments); (4) sporadic presence of taxa from open marine to oceanic environments; (5) common occurrence of abundant foraminifera test linings (usually associated with shallow environments); (6) dominance of gymnosperm pollen (possible coastal vegetation); (7) low occurrence of bissacate pollen, suggesting proximal depositional conditions, near to the production source; (8) presence of prasinophytic algae (low salinity), including Botryoccocus sp. (local fluvial influences). The paleoenvironmental inferences based on the dinocysts assemblages suggest a transition from proximal (coastal plain) to restricted marine (lagoon) conditions, being in line with previous interpretations of the macrofauna and the articulation of lithofacies. The assemblages reflect the predominance of typical tethyan taxa (Subtilishphaera sp., Florentinia spp., Spiniferites spp., Xenascus ceratioides), associated to warm waters (Oligosphaeridium pulcherrimum, Palaeohystrichophora infusorioides), but also containing proto-Atlantic species such as Trithyrodinium suspectum. In biostratigraphic terms, it is known in the bibliography that, for the Portuguese and European Cenomanian, several dinoflagellate assemblages have been described with different interpretations and correlations. Near Lisbon, was indicated Palaeohystrichophora infusorioides, Xenascus ceratioides and Xiphophoridium alatum for the upper and middle Cenomanian, as well as for Spiniferites ramosus, Florentinia sp., Canningia spp., Epelidosphaeridia spinosa, Oligosphaeridium sp. and Oligosphaeridium pulcherrimum for the upper and middle Cenomanian. It was suggested an Interval Zone with Paleohystrichophora infusorioides for the boreal Cenomanian. In the NW Europe, it was also presented a biozonation with first occurrence of Trithyrodinium suspectum and last occurrence of Gonyaulacysta spp.; it was also identified the predominance of Paleohystrichophora infusorioides and Spiniferites ramosus. In the Cenomanian of Spain, the assemblage Paleohystrichophora. infusorioides, Spiniferites ramosus, Cannigia reticulata, Xenascus ceratoides, Trithyrodinium suspectum and Florentinia mantelli was proposed. Considering this data, the suggested stratigraphic interval for the base of the carbonate platform of Nazaré should be assigned to the middle to upper Cenomanian, a position higher than the relative age based in other biostratigraphic indicators (lower terminal Cenomanian to basal Middle Cenomanian). The common occurrence of Trithyrodinium suspectum in several of the sampled levels may suggest the need for a review of the first occurrence of this taxon for the Upper Cretaceous of the Iberian Peninsula.
Original languagePortuguese
Pages (from-to)205-207
JournalVulcânica - Revista Portuguesa de Vulcanologia
Volume2
Publication statusPublished - 13 Jul 2018
EventX Congresso Nacional de Geologia”, Ponta Delgada (Açores). - S. Miguel (Açores), S. Miguel (Açores), Portugal
Duration: 8 Jul 201813 Jul 2018

Keywords

  • Quistos de dinoflagelados
  • Biostratigrafia
  • Paleoambiente
  • Cenomaniano
  • Nazaré (Portugal)

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