Publication: Ammonite succession at the Bajocian/Bathonian boundary
in the Cabo Mondego region (Portugal)
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Publication Date
2006
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Taylor & Francis
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Abstract
The Cabo Mondego outcrops exposed along the cliffs, on the western margin of the
Iberian Plate, show an expanded stratigraphic section of Lower Bathonian deposits
containing abundant ammonoids. Upper Bajocian deposits correspond to similar facies,
of muddy limestones alternating with marlstones, although ammonoids are scarce.
A detailed succession of ammonites across the Bajocian/Bathonian boundary has been
recognized at Cabo Mondego, which can form a useful bio- and chronostratigraphic
standard for the Lusitanian Basin. The revision of previous collections from the classical
section and new field samplings of two other separate sections allow the recognition
through up to twenty metres of thickness, the highest zone of Bajocian (Parkinsoni
Zone) and the lowest zone of Bathonian (Zigzag Zone). The Parkinsoni and the Zigzag
zones established for NW European areas and belonging to the Northwest European
Province, can be identified in the Lusitanian Basin, although the ammonite fossil
assemblages are composed of Submediterranean taxa. However, a subdivision of the
Parkinsoni Zone is not possible, due to the scarcity of well preserved ammonoids. The
Zigzag Zone can be recognized and characterized as composed of two subunits (Parvum
and Macrescens subzones) as represented in diverse European basins of the Submediterranean
Province. Ammonite fossil assemblages of the Parvum Subzone may be
grouped into two successive horizons, which are biochronostratigraphically equivalent to
the subdivisions of the Convergens Subzone distinguished in the Digne-Barreˆme area
(SE France). New biochronostratigraphic data on the Bigotitinae, youngest members of
Leptosphinctinae and oldest members of Zigzagiceratinae are relevant in understanding
the evolution and faunal turnover of the West Tethyan Perisphinctidae during earliest
Bathonian. The ammonite succession at the Bajocian/Bathonian boundary in the Cabo
Mondego region (Portugal) represents one of the most complete biostratigraphic records
so far recognized on the Iberian Plate.IAmmonoids, biostratigraphy, chronostratigraphy,
Iberia, Lusitanian Basin, Middle Jurassic, palaeobiogeography.