Tremolada, F.

Calcareous nannofossil and foraminiferal analyses have been carried out on outcrops from the type-area of the Gonfolite Lombarda Group (Como, northern Italy). In these marine fine- to coarse-grained clastics, rapidly accumulating at the southern front of the uprising Alpine range during the Oligo-Miocene, a scarce, but reliable, sequence of calcareous nannofossil events has been observed, allowing to refine the previous age assignments. Planktonic foraminifera were found to be extremely rare and provided limited biostratigraphic information. The Villa Olmo Conglomerate and the Chiasso Formation contain the Last Occurrence (LO) of Sphenolithus distentus and the First Occurrence (FO) of Triquetrorhabdulus carinatus, which are characteristic of the nannofossil zones NP24 and NP25 (Chattian), respectively. The lower part of the Como Conglomerate was deposited during the zone NP25, whilst the upper part of the Como Conglomerate straddles the Chattian/Aquitanian boundary in zone NN1. The deposition of the Prestino Mudstones also occurred during zone NN1. However, the upper part of this formation has been dated as Burdigalian during nannofossil zone NN2. The deposition of the upper part of the Val Grande Sandstone has been assigned to the NN3 zone owing to the presence of the taxon Sphenolithus belemnos, which is restricted to NN3. The upper part of the investigated section is characterized by the deposition of the Lucino Conglomerate and its fine-grained members (Lucinasco and Lurate Caccivio Mudstones). The Lucinasco Mudstones have been dated as late Burdigalian corresponding to zone NN4, whilst the overlying Lurate Caccivio Mudstones were deposited during the Langhian part of the zone NN5, based on the presence of S. heteromorphus and the absence of H. ampliaperta. On the whole, the base and the top of the outcropping Gonfolite Lombarda Group result from our study to be younger than hitherto proposed, allowing to resolve certain previous conflicts with the few radiometric dates available for clasts from the Gonfolite Lombarda Group. The depth of deposition was upper bathyal during the Chattian and the Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones.

Calcareous nannofossil biostratigraphic investigations have been carried out on samples collected from the Tabiago section, Brianza, northern Italy. This section records early Maastrichtian (CC23b nannofossil zone) to early Eocene (NP10 nannofossil zone) calcareous nannofossil assemblages. The Cretaceous-Tertiary transition is characterized by major changes in sedimentation rates and two likely stratigraphic gaps. The Cretaceous Brenno Formation was deposited with a high sedimentation rate (~20 m/m.y.), whilst the Tabiago Formation of Paleogene age records a drastic decrease (~10 m/m.y.). The absence of the CC26 zonal marker Micula prinsii may indicate a stratigraphic hiatus or an extremely condensed level in the latest Maastrichtian. However, only two samples have been collected and analyzed in this interval due to low exposure of the outcrop, and the absence of M. prinsii could be the result of diagenetic overprint or insufficient sampling. A stratigraphic hiatus or a very condensed interval corresponds to the upper part of NP1 nannofossil zone and Pα foraminiferal Zone and P1a Subzone in the early Paleocene. The poor exposure of the outcrop prevents to precisely locate the zonal boundaries between NP4 and NP5 and between NP9 and NP10 and impedes the documentation of possible further stratigraphic gaps or condensed intervals.

Calcareous nannofossil and foraminiferal analyses have been carried out on outcrops from the type-area of the Gonfolite Lombarda Group (Como, northern Italy). In these marine fine- to coarse-grained clastics, rapidly accumulating at the southern front of the uprising Alpine range during the Oligo-Miocene, a scarce, but reliable, sequence of calcareous nannofossil events has been observed, allowing to refine the previous age assignments. Planktonic foraminifera were found to be extremely rare and provided limited biostratigraphic information. The Villa Olmo Conglomerate and the Chiasso Formation contain the Last Occurrence (LO) of Sphenolithus distentus and the First Occurrence (FO) of Triquetrorhabdulus carinatus, which are characteristic of the nannofossil zones NP24 and NP25 (Chattian), respectively. The lower part of the Como Conglomerate was deposited during the zone NP25, whilst the upper part of the Como Conglomerate straddles the Chattian/Aquitanian boundary in zone NN1. The deposition of the Prestino Mudstones also occurred during zone NN1. However, the upper part of this formation has been dated as Burdigalian during nannofossil zone NN2. The deposition of the upper part of the Val Grande Sandstone has been assigned to the NN3 zone owing to the presence of the taxon Sphenolithus belemnos, which is restricted to NN3. The upper part of the investigated section is characterized by the deposition of the Lucino Conglomerate and its fine-grained members (Lucinasco and Lurate Caccivio Mudstones). The Lucinasco Mudstones have been dated as late Burdigalian corresponding to zone NN4, whilst the overlying Lurate Caccivio Mudstones were deposited during the Langhian part of the zone NN5, based on the presence of S. heteromorphus and the absence of H. ampliaperta. On the whole, the base and the top of the outcropping Gonfolite Lombarda Group result from our study to be younger than hitherto proposed, allowing to resolve certain previous conflicts with the few radiometric dates available for clasts from the Gonfolite Lombarda Group. The depth of deposition was upper bathyal during the Chattian and the Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones.

Detailed investigations carried out in support of the new Italian geological map at the scale 1:50 000 (CARG Project) resulted in the definition of new formal lithostratigraphic units (Brenno Fm, Tabiago Fm, Cibrone Fm) within the previously undifferentiated Scaglia and in the first integrated studies on calcareous plankton, including calcareous nannofossils. The Tabiago Formation consists of marls and pelagic limestones with some intercalations of turbidites containing large shallow-water displaced foraminifera in the upper part. Its age ranges from the Early Paleocene (foraminiferal Zone P1b, nannofossil Zone NP2) to the Middle Eocene (foraminiferal Zone P12, nannofossil Zone NP15). The lowermost biozones of the Paleocene (P0, Pα=P. eugubina, and P1a) are missing. The Cibrone Formation is represented by scattered outcrops and consists of marls and silty marls with minor arenites. Its age is Middle Eocene (Zone P12, Zone NP15-NP16). The Paleocene portion of the well-exposed Tabiago section is characterized by alternating couplets of soft marls and hard limestones. A multidisciplinary investigation was undertaken in order to understand the environmental significance of these repetitive cycles. Abundance and composition of the planktonic foraminiferal populations, degree of bioturbation, and calcium carbonate content were measured. In the marly semicouplet the fauna is relatively poor; it is enriched in specimens of the genus Subbotina, an indicator of nutrient-rich, colder waters. In the calcareous semicouplet the fauna is enriched in taxa of the genus Morozovella, an indicator of warm, nutrient-poor tropical waters. A possible interpretation of the sedimentary rhythms is that the marly interbeds were deposited in periods of high seasonality, when enhanced circulation brings nutrient enrichment at the surface and good ventilation at the bottom. On the contrary, the calcareous interbeds were deposited at times of low seasonality with sluggish circulation and nutrient-poor surface waters. In order to evaluate the possible extra-terrestrial forcing of the observed cyclicity, a spectral analysis was carried out on hundreds of quantitative data concerning foraminiferal composition and carbonate content. The Milankovitch frequency for precession (21 ky), obliquity (41 ky) and short excentricity (100 ky) cycles were recorded with the strongest signal related to obliquity.

The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (‘‘molassa’’). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.

A candidate for the oldest human occupation site in Italy is Monte Poggiolo where the lithic tool-bearing levels are currently dated to ~ 1 Ma based on electron spin resonance (ESR). The low analytical precision of ± 30% at 2σ makes it unclear whether the date actually conflicts with a recent reassessment of age constraints on key hominin sites from Italy, France, and Spain pointing to a uniformly young timing for the earliest habitation of southern Europe during the late Early Pleistocene climate transition within reverse magnetic polarity subchron C1r.1r (0.988–0.781 Ma). Our new magnetostratigraphic and biostratigraphic results show a sequence of stable normal and reverse polarities in a regional lithostratigraphic context that indicate the Monte Poggiolo tool-bearing site post-dates the Jaramillo normal polarity subchron, most probably occurring at ~ 0.85 Ma immediately after the pronounced cooling that culminated with marine isotope stage 22 when the associated regression may have opened new migration routes through the Po Valley for large mammals and hominins.