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TitleEarly and Middle Jurassic palynoevents of the Lusitanian Basin (Portugal) in the proto-Atlantic context
AuthorCorreia, VORCID logo; Riding, J B; Duarte, L V; Henriques, M H; Fernandes, P; Pereira, Z; Fensome, R A; Williams, G L; MacRae, R A
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 45, 2022 p. 74
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20210673
PublisherGeological Association of Canada
MeetingGAC-MAC Halifax 2022 - Geological Association of Canada - Mineralogical Association of Canada Joint Annual Meeting 2022; Halifax, NS; CA; May 15-18, 2022
Mediadigital; on-line
File formatpdf
SubjectsScience and Technology; sedimentology; Nature and Environment; biostratigraphy; palynostratigraphy; Lusitanian Basin; Jurassic
ProgramOffshore Geoscience
Released2022 05 15
AbstractThe Lusitanian Basin is located in central western Portugal and is mainly composed of Jurassic sediments. The macro and microfossil biostratigraphy of this depocentre is well studied, but palynological works are scarce. We address this with a high-resolution palynostratigraphic study of a Lower and Middle Jurassic succession of the Lusitanian Basin, based mainly on dinoflagellate cysts. We analyzed 301 productive samples of palynomorphs from eight outcrops. The resulting biostratigraphic scheme identified 28 significant palynomorph bioevents in the late Pliensbachian-earliest Bathonian interval, which includes: the Toarcian Oceanic Anoxic Event (T-OAE, or Jenkyns Event); the Global Boundary Stratotype Section and Point (GSSP) for the Toarcian Stage at Peniche; the GSSP for the Bajocian Stage at Cabo Mondego; and the Auxiliary Boundary Stratotype Section and Point (ASSP) for the Bathonian Stage at Cabo Mondego. This high-resolution dinoflagellate cyst record documents the first known appearance of this group of palynomorphs in the Lusitanian Basin at the base of the late Pliensbachian, with first occurrences (FOs) of four species. It also reflects the dramatic changes occurring during the T-OAE among marine organisms, including the extinction of taxa. In the Lusitanian Basin, the beginning of the T-OAE occurred at the base of the Hildaites levisoni ammonite biozone and is marked by the extinction of Luehndea spinosa, the temporary disappearance of Nannoceratopsis spp., and a general reduction in dinoflagellate cyst abundance; an increase in prasinophyte abundance also occurs. These bioevents correlate with the negative carbon (delta-13Ccarb) and oxygen (delta-18O) isotope excursion records previously established for the Lusitanian Basin. The increase in dinoflagellate cyst FOs during the early Bajocian to earliest Bathonian documents the Middle Jurassic radiation of this planktonic group. Despite their relatively long stratigraphic ranges, the spore Kraeuselisporites reissingeri and the pollen Classopollis spp., Araucariacites australis and Callialasporites spp. are good local additional stratigraphic indicators. As expected, the dinoflagellate cyst assemblages suggest that the Lusitanian Basin is an intermediate area between the Boreal and Tethyan realms, with taxa characteristic of both. It thus represents a transition between northern and southern Europe during the early phases of opening the North Atlantic Ocean. Comparison of the Lusitanian Basin Early to Middle Jurassic assemblages with those from the Orpheus Graben and southern Grand Banks, offshore eastern Canada will be of great interest as the two areas were at equivalent paleolatitude and only a few hundred kilometres apart across the nascent Atlantic Ocean and precursor rift at the time.
Summary(Plain Language Summary, not published)
The Lusitanian Basin in Portugal contains of Jurassic sediments, and part of the succession is used as an international standard for control of the international geological timescale. The study involves an analysis of palynological assemblages from the Lower and Middle Jurassic parts of the Lusitanian Basin succession, based mainly on dinoflagellate cysts. These fossils are important tools in dating Jurassic sediments, and the work identified 28 events (first and last appearances of species), which provide a framework in time for the deposits. The interval studied includes the Toarcian Oceanic Anoxic Event, a major oceanographic episode for which the palynology provides important details and thus help us understand how major changes occur in the world's oceans. Comparison of the Lusitanian Basin assemblages with those from offshore eastern Canada is also of great interest as the two areas were only a few hundred kilometres apart across the Atlantic precursor rift and nascent ocean.

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