Sergio Rogledi

Onset of major Pleistocene glaciations in the Alps

During maximum Pleistocene glacial expansions, the Alpine ice cap invaded the Central Europe uplands and Italian Southalpine foothills. Periglacial basins, such as the Po River Basin, are natural collectors of sediments that record the past biological and climatic changes that involve the waxing and waning of major ice caps. In a 200-m-long core from the central Po Plain, stratigraphic evidence for one such major glacial pulse of the nearby Alpine ice cap is recorded by a sequence boundary, termed the R surface, associated with a drastic reorganization of vegetational, fluvial, and Alpine drainage patterns. The R surface, seismically traceable across the Po Plain subsurface, was constrained magnetostratigraphically to the first prominent Pleistocene glacio-eustatic lowstand of marine isotope stage (MIS) 22 at 0.87 Ma. MIS 22 corresponds to the end of the Mid-Pleistocene Revolution, a marked reorganization of Northern Hemisphere glaciation pattern that took place in the late early Pleistocene. We suggest that the R surface formed at Mid-Pleistocene Revolution‐MIS 22 time, during the onset of the first major Pleistocene glaciation in the Alps.

Mass-transport deposits in confined wedge-top basins: surficial processes shaping the messinian orogenic wedge of Northern Apennine of Italy

Among the many cases studied of mass-transport deposits in continental margins, the role of basin topography in controlling the types, distribution, architecture and emplacement of such deposits has not been properly remarked. In the western portion of Northern Apennine foothills, masstransport deposits form two composite Messinian mass-wasting bodies that reveal progressive development strictly controlled by basin topography. Extensively analyzed through stratigraphic and structural studies, they form two major elliptical-shaped bodies in map view; maximum 10 kilometres wide, tens of kilometres in length and with estimated volumes of about 250 km3 each, they are elongated parallel to NW-SE oriented thrust fronts. They are coalescing chaotic masses that consist, at the base, of debris flows formed by monogenic gypsum arenite or breccia and decametric blocks of primary gypsum, whereas at the top they are made up of kilometres-wide outliers of pre-gyspum deposits, which slid away from partially preserved headwall scarps. In the external accumulation zone, the mass wasted deposits show imbricate thrust-stacks composed of scraped-off gypsum debris flow deposits. The types, distribution, architecture and emplacement of the studied mass-transport deposits testify the strict control of the wedge-top basins morphology. The internal and steeper flank of the wedge-top basins was representing the depletion zone of sliding masses; whereas, the outer and less steep flank of the wedge-top basins stopped the moving masses and formed the accumulation zones. The relief of the wedge-top basins was progressively modifying during the intra-Messinian tectonic pulse that, affecting the entire Northern Apennine orogenic wedge, triggered the studied mass-transport deposits

Evidence for late Alpine tectonics in the Lake Garda area (northern Italy) and seismogenic implications

We investigated the recent evolution of the Po Plain–Alps system by integrating subsurface geophysical data from the Po Plain with new stratigraphic and structural observations from the Southern Alps margin. Inversion of structural data and chronology provided by stratigraphic constraints led to the definition of three tectonic events since the Pliocene, namely, the intra-Zanclean, the Gelasian, and the middle Pleistocene, driven by an axis of maximum compression formerly oriented NE (intra-Zanclean) and then to the NNW (Gelasian and middle Pleistocene). The associated deformation has been accommodated by two sets of faults consisting of NNE-trending thrust faults, mostly represented in the western sector of Lake Garda, and NW-trending strike-slip faults, observed in the southern and eastern sectors. The interplay between these two sets of faults is interpreted to produce short ( w w > 6.5) along the NW-trending strike-slip faults. In this framework, the newly defined Nogara fault and the Sant’Ambrogio fault, all pertaining to the NW-trending system, are regarded as potential candidates for the seismogenic source of the January A.D. 1117 event, the most destructive earthquake in the Po Plain.

Reassessing the biostratigraphy and the paleobathymetry of the Gonfolite Lombarda Group in the Como area (northern Italy)

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 elastics, 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 NNl. The deposition of the Prestino Mudstones also occurred during zone NNl. 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 die Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones.