The palynostratigraphy of the Upper Maiolica, Selli Level and the Lower Marne a Fucoidi units in the proposed Barremian/Aptian (Lower Cretaceous) GSSP stratotype at Gorgo a Cerbara, Umbria–Marche Basin, Italy
The section of Gorgo a Cerbara in Italy has been proposed as the Global Stratotype Section and Point (GSSP) for the Barremian/Aptian boundary (Lower Cretaceous). This section displays the transition between the white pelagic limestones of the Maiolica Formation (Tithonian–lowermost Aptian) and the polychrome marls of the Marne a Fucoidi Formation (Aptian–Albian). The Oceanic Anoxic Event 1a (OAE 1a) anoxic horizon (Selli Level) is located in the latter formation. Here, we report for the first time a palynostratigraphical assessment of this key section, with a very high resolution in the Selli Level.
Palynomorph groups recorded include acritarchs, microforaminiferal test linings, 58 dinoflagellate cysts, 44 sporomorph taxa, and freshwater fungal and algal bodies. These include such biostratigraphical markers as Rhynchodiniopsis aptiana and Odontochitina operculata among the dinoflagellate cysts and Afropollis cf. jardinus among sporomorphs. Biostratigraphical events recognised allow comparisons with previously studied successions in other similar areas (e.g. Cismon apticore in the Southern Alps, Italy). The distribution of taxa recorded in the Gorgo a Cerbara section is generally consistent with published data, but several differences between the assemblages recorded in the Cismon apticore and in this study were noted.
The best global markers for the Barremian/Aptian boundary are represented by the disappearance of R. aptiana and by the appearance of O. operculata, but in this section these occurred 0.65–1.35 Myr after the magnetostratigraphically defined boundary, within the Selli Level. The angiosperm pollen A. cf. jardinus is recorded only within the Selli Level (from 1.4 to 1.6 Myr after the Barremian/Aptian boundary), consistent with an Early Aptian age. A cluster of 10 extremely short-ranging dinoflagellate cyst excursion taxa appear in this section coincident with the Nannoconid Crisis event and its associated thermal peak, ca. 10–20 kyr before the onset of the OAE 1a. Several short-ranging Pteridophyta spore species are found only within the Selli Level itself.