Conference Agenda

Coccolithophore photosynthesis and biocalcification influence the organic and inorganic carbon cycle and atmospheric CO₂ absorption into the oceans. We investigated the Upper Albian-Lower Cenomanian interval of the Piobbico Core-Monte Petrano composite section (Umbria-Marche Basin, Italy) to understand if changes in nannofossil assemblages and calcite paleofluxes can be linked to variations in the ocean alkalinity. Total nannofossil calcite paleofluxes were gathered for the Marne a Fucoidi (marlstones and marly limestones) and Scaglia Bianca (limestones) from the absolute abundances of the most common taxa and volume/mass of individual taxon, obtained by counting all nannofossil specimens in 1 mm² of ultrathin sections and by normalizing to 1 year. Precise sedimentation rate estimates are available based on high-resolution integrated biostratigraphy, chemostratigraphy and cyclostratigraphy.

Out of 36, only 10 genera constitute 95% of nannofossil assemblages. The amount of calcite produced by individual nannofossil taxa is highly variable and strictly dependent on the ultrastructure and dimensions. Lithostratigraphically, the beginning of the limy sedimentation of the Scaglia Bianca does not align with changes in nannofossil paleofluxes since the increase occurs in the transitional interval with lowered terrigenous input (in late Albian times). Paleoenvironmental changes in temperature, fertility, chemistry influenced calcareous nannoflora with species-specific responses. Overall, high terrigenous input (Marne a Fucoidi) limited coccolithophore calcification, while fluctuations in nannofossil calcite paleofluxes (Scaglia Bianca) might derive from changes in marine carbonate chemistry (ocean alkalinity) possibly affecting calcification patterns at species-specific level.

The “Hill 991” section, located within Monte Cucco Regional Park (Umbria Region, Italy), presents a continuous and well-preserved 48-meter-thick stratigraphic succession spanning the upper Aptian to lower Albian (~117–105 Ma) interval of the Umbria–Marche Basin (western Tethyan Ocean). This succession, part of the “Marne a Fucoidi” Formation, includes multiple black-shale horizons interpreted as the sedimentary expression of Oceanic Anoxic Event 1b (OAE1b). The section was systematically logged, sampled at high resolution, and correlated with established reference sections (e.g., Poggio le Guaine). CaCO₃ content, magnetic susceptibility, and biostratigraphic data were integrated to identify major biotic turnovers and refine correlations within the Aptian–Albian interval. The results confirm the stratigraphic continuity of the section and allow recognition of all OAE1b sub-events. We also provide evidence of significant microfossil (i.e., foraminifera, radiolaria) changes along the record that are ascribed to variations in paleo-productivity, -dissolution and -oxygenation. These findings underscore the potential of the “Hill 991” section as a complementary Umbria-Marche’s reference site to “Poggio le Guaine” core for reconstructing palaeobiological, paleoclimatic, and paleoenvironmental dynamics during this critical interval of Earth history.

Foraminifera and ostracod biostratigraphic data have been integrated to improve the age-constraints of the middle Cretaceous carbonate successions at 2 sections (El Hammimat and Kef Gouriret) from the Oum El Bouaghi area, north-eastern Algeria. 33 ostracod and 17 planktic foraminifera species have been identified and applied to establish the biostratigraphic framework of the studied sections. Three ostracod assemblages corresponding to two partial range zones have been recognized, the Rehacythereis bartensteini biozone, middle Aptian in age, which is subdivided into two subzones, the Protocythere bedoulensis (upper Gargasian) and the Cytherella circumrigosa (lowermost Clansayesian), as well as the Rehacythereis zoumoffeni biozone, late Aptian – early Albian in age. Two foraminifera assemblages attributing to two partial range zones have been identified, the Globigerinelloides algerianus and the Hedbergella infracretacea of the upper Gargasian and lowermost Clansayesian respectively.

These ostracod and foramininfera biozones are well correlated with there equivalents previously described from Tethyan margins (Oertli, 1958; Bischoff, 1963; Babinot et al., 2007; Coccioni and Petrizzo et al., 2012; Premoli Silva, 2015; Trabelsi et al., 2021), providing therefore new constraints on the chronostratigraphy of the middle Cretaceous carbonate successions of north-eastern Algeria, established here for first time at the studied sections. Regional correlation reflect tectono-sedimentary control on the spatio-temporal distribution of lithofacies within the studied area.