A 490 m thick section of shallowing upward peritidal cycles spanning the Triassic-Jurassicboundary is exposed along the northern slope of Mount Sparagio in the San Vito Lo Capo Peninsula(Western Sicily). A detailed microfacies analysis allowed defining the aspects of cyclicsedimentation of this section and especially the stratigraphic occurrence patterns of benthicforaminifera and algae across the T/J boundary.The lower part of cycles commonly shows medium to low energy subtidal facies, typical of theinner lagoon of the carbonate platform. Subtidal facies such as coral bafflestone in some cyclessuggest more open lagoonal conditions (patch reefs), while some higher energy layers such asooidal grainstones or megalodont rudstone/floatstones are interpreted as storm layers. The intertidalfacies consist of planar stromatolites and loferites, while the upper part of cycles is commonlycomposed by flat and black pebbles conglomerates capped by Terra Rossa paleosols.The thickness of cycles is quite irregular and reflects irregular variations of accommodation spaceon the flat topped platform. It ranges from a few tens of cm to 3-4 m (in case of the presence ofthick paleosols), with an average thickness of about 1-1.5 m. Often, the upper part of the cycles and,in particular, the paleosols, is truncated by a ravinement surface generated by the periodic floodingof the platform.The distribution pattern of megalodontids allows to differentiate three different informal units: alower unit containing abundant and large megalodontids (A unit); an intermediate unit characterizedby small and rare megalodontids (B unit) and an upper unit lacking pelecypods (C unit).The foraminiferal assemblages in the units A and B (Triasina hantkeni, Aulotortus permodiscoides,Glomospirella friedli, Aulotortus sp.) match the Triasina hantkeni range zone. Upsection, the abruptdisappearance of all the benthic foraminifera in the subtidal units and the onset of an oligothipicassociation dominated by Thaumatoporella parvovesiculifera, is assumed as the Rhaetian/Hettangian boundary. A gradual recovery of benthic associations is documented upsection by theappeareance of siphovalvulinids such as Siphovalvulina gilbraltarensis.
|Numero di pagine||1|
|Stato di pubblicazione||Published - 2016|