Muttoni, G.

40Ar/39Ar geochronology constraints to aggradational phases and grain size variations show that the two large gravel beds occurring in the sedimentary filling of the Liri fluvial-lacustrine basin (central Italy) recorded the occurrence of deglaciation events synchronous within uncertainties with global meltwater pulses at ca. 450 and 350 ka. In particular, we find a precise match between the ages of gravel deposition and the occurrence of moderate sea-level rise events which anticipate those more marked during the glacial termination V and IV in the Red Sea relative sea level curve, as already verified by data from the Tiber River catchment basin. Such correspondence suggests that gravel deposition is facilitated by melting of Apennine mountain range glaciers, which provide the water transport energy and a surplus of clastic input to the rivers draining the mountain regions and flowing into the Tyrrhenian Sea. Therefore, the thick gravel beds intercalated in the sedimentary filling of the catchment basins of the major rivers in central Italy may be regarded as an equivalent proxy of large deglaciation events, similar to the ice-rafted debris in northern Atlantic. Consistent with this hypothesis, we also show the close correspondence between the occurrence of particularly mild (warmer) minima of the mean summer insolation at 65° N and these early aggradational phases, as well as with other anomalous early sea-level rises occurring c. 750 ka and 540 ka at the onset of glacial termination VIII and VI, and 40 ka at the onset of the so-called Heinrich events.

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.

A critical assessment of the available magnetostratigraphic and/or radiometric age constraints on key sites bearing hominin remains and/or lithic industries from southern Europe (Italy, France, Spain) leads us to propose that the main window of early hominin presence in southern Europe is broadly comprised between the Jaramillo subchron and the Brunhes–Matuyama boundary (i.e., subchron C1r.1r, 0.99–0.78 Ma). Within the dating uncertainties, this ~200 ky time window broadly coincides with the late Early Pleistocene global climate transition that contains marine isotope stage (MIS) 22 (~0.87Ma), the first prominent cold stage of the Pleistocene. We suggest that aridification in North Africa and Eastern Europe, particularly harsh during MIS22 times, triggered migration pulses of large herbivores, particularly elephants, from these regions into southern European refugia, and that hominins migrated with them. Finally, we speculate on common pathways of late Early Pleistocene dispersal of elephants and hominins from their home in savannah Africa to southern Europe, elephant and hominin buen retiro. In particular, we stress the importance of the Po Valley of northern Italy that became largely and permanently exposed only since MIS22, thus allowing possibly for the first time in the Pleistocene viable new migration routes for large mammals and hominins across northern Italy to southern France and Spain in the west.

The Pleistocene history of climate control on sedimentation in the Southern Alps-Po Plain system, northern Italy, was reconstructed using an integrated magnetostratigraphic, palynological, and petrographical approach on a 47-m-deep core. The core mainly consists of lacustrine sediments pertaining to the Bagaggera sequence, deposited at the foothills of the Southern Alps during the late Matuyama subchron (0.99-0.78 Ma). At that time, climate worsened globally and locally it caused the progradation of an alluvial fan unit onto the nearby Po Plain, triggering lake formation by damming of a tributary valley. These new data are used in conjunction with data from the literature to highlight and track the effects of climate forcing on sedimentation during the late Matuyama subchron in different orographic and geodynamic settings of the Southern Alps-Po Plain system as part of the greater Alpine area. We found that the episodes of alluvial fan and braidplam progradation observed in the southern foreland of the Alps during the late Matuyama global cooling seem broadly synchronous with the deposition of most of the so-called Gunz and Alterer Deckenschotter deposits in the northern forelands of the Alps as well as with the first major waxing of the Alpine valley glaciers, possibly around the Marine Isotope Stage 22 (~0.87 Ma).

The Piànico-Sèllere is a lacustrine succession from northern Italy that records a sequence of climatic transitions across two Pleistocene glacial stages. The intervening interglacial stage is represented by well-preserved varves with calcitic (summer) and clastic (winter) laminae. There is a tight coupling between climate-driven lithologic changes and magnetic susceptibility variations, and stable paleomagnetic components were retrieved from all investigated lithologies including the largely diamagnetic calcite varves. These components were used to delineate a sequence of magnetic polarity reversals that was interpreted as a record of excursions of the Earth’s magnetic field. Comparison of the magnetostratigraphic results with previously published data allows discussion of two possible models which have generated controversy regarding the age of the Piànico Formation. The data indicates that the Piànico Formation magnetostratigraphy correlates to geomagnetic field excursions across the Brunhes/Matuyama transition, and consequently the Piànico interglacial correlates to marine isotope stage 19. This correlation option is substantially consistent with K-Ar radiometric age estimates recently obtained from a tepha layer interbedded in the Piànico Formation. The alternative option, considering the Piànico interglacial correlative to marine isotope stage 11 within the Brunhes Chron as supported by tephrochronological dating reported in the literature, is not supported by the magnetostratigraphic results.

Il record stratigrafico continentale è per sua natura discontinuo e difficilmente databile. A questo bisogna aggiungere anche il fatto che la maggior parte dei depositi continentali affioranti sono accessibili grazie alla dissezione del territorio, avvenuta generalmente per cause tettoniche (uplift). Ne consegue che i depositi continentali accessibili allo studio, oltre a essere discontinui per loro natura, lo sono a maggior ragione per essere il prodotto di una competizione tra tassi di sedimentazione e tassi di sollevamento, che porta a successioni stratigrafiche tendenzialmente condensate e/o discontinue. Serie più complete ed espanse si possono al contrario recuperare laddove la subsidenza è attiva, garantendo una registrazione più o meno continua degli eventi stratigrafici. Le aree subsidenti, essendo aree depresse, sono caratterizzate da affioramenti molto scarsi e limitati alla parte più superficiale e recente della successione sedimentaria ivi contenuta. Tuttavia, è possibile recuperare una maggiore stratigrafia mediante sondaggi. Recentemente, molti sforzi sono stati fatti per ottenere sequenze sedimentarie relativamente lunghe grazie all’utilizzo di sondaggi ubicati sia in bacini di avampaese (Pianura Padana), sia in bacini intermontani (Ceprano, Bagaggera, Leffe, Pianico). I sondaggi sono stati oggetto di analisi interdisciplinari che hanno permesso di datare e riconoscere eventi nella serie stratigrafica carotata. Il contributo maggiore per le datazioni è sempre venuto dall’applicazione della magnetostratigrafia, calibrata con il vincolo biostratigrafico fornito dalla palinologia o la micropaleontologia. In Pianura Padana è stato possibile datare un evento regionale quale l’intensificazione dell’attività glaciale del Pleistocene, riconosciuto in 11 sondaggi profondi e tracciato sismicamente dal Piemonte al Mare Adriatico, vincolandolo con la magnetostratigrafia al Subchron tardo Matuyama (0.78–0.99 Ma). Lo stesso evento è stato riconosciuto e datato nei bacini intermontani di Leffe e Bagaggera. Nel bacino di Ceprano invece la magnetostratigrafia applicata a un sondaggio ha permesso di datare il cranio dell’ominide più antico d’Italia, riferendolo, mediante un modello di età, alla parte media del Chron Brunhes. Gli esempi illustrati sono riportati con lo scopo di sottolineare il fondamentale contributo che può derivare dall’applicazione di sondaggi e metodi di analisi interdisciplinari nella datazione di depositi continentali e nel riconoscimento di eventi stratigrafici, altrimenti poco apprezzabili nei singoli e discontinui affioramenti.

Facies analysis applied to several up to 220-m-deep cores, taken by Regione Lombardia in the central-northern Po Plain, allowed to recognize an overall regressive sequence consisting of cyclotemic shallow marine and fluvial-deltaic deposits overlain by distal to proximal braidplain sediments. Magnetostratigraphy, coupled with calcareous nannoplankton biostratigraphy, was used to date marine and fluvial-deltaic sediments to the early Pleistocene and continental sediments to the middle–late Pleistocene. Sediment accumulation rates were of ~0.3-0.4 mm/yr in the early Pleistocene, whereas an overall reduction in sediment accumulation rates to ~0.06-0.08 mm/yr, associated to relevant unconformities, characterized the middle-late Pleistocene. Stratigraphic evidences from petrographic, sedimentologic and palynologic analyses highlight in the Regione Lombardia cores a drastic reorganization of vegetational, fluvial, and Alpine drainage patterns, associated to a sequence boundary termed the “R surface”. 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 at the end of the Mid-Pleistocene Revolution, when climate worsened globally and locally caused the onset of the first major Pleistocene glaciation in the Alps. Most marine deposits in the cores lie above sea level highstands of corresponding age, suggesting that they have been uplifted. In order to estimate the observed rock uplift, sediments were back-stripped to elevations at times of deposition (expressed in meters above current sea level) by applying a simple Airy compensation model. The correlation of the isostatically corrected sedimentary facies to a glacio-eustatic reference curve obtained from classic oxygen isotope studies highlights a positive elevation mismatch (rock uplift) in the range of 70-120 m, which occurred after the onset of the major Pleistocene glacial-interglacial cycles at rates of at least 0.15-0.09 mm/yr. Although the driving forces of the observed rock uplift cannot be unambiguously identified, but its timing of onset after the beginning of the major Pleistocene glacial-interglacial cycles and the low seismicity observed in the most of the Regione Lombardia area seem to point to an isostatic readjustment of the chain probably due to the long-term erosional removal of sediments during major Pleistocene glacial advances.

Paleomagnetic analyses were conducted on two cores drilled at Ceprano in central Italy where an incomplete hominin cranium was discovered in1994, as well as on two additional cores from the nearby site of Fontana Ranuccio that yielded hominin remains associated with an Acheulean industry. No evidence for the 0.78 Ma Brunhes–Matuyama boundary was found at Ceprano down to 45 m below the level that yielded the hominin cranium. The Ceprano lithostratigraphy and the paleomagnetic age constraints are broadly consistent with the stratigraphy of the Liri lacustrine sequence of the Latina Valley, constrained by published K–Ar ages between ~0.6 and ~0.35Ma, and according to an age model with magnetic susceptibility supported by pollen facies data, suggest that the level that yielded the hominin cranium has an age of ~0.45 (+0.05, −0.10) Ma. Evidence for the Brunhes–Matuyama boundary was found at Fontana Ranuccio about 40 m below the hominin level, consistent with a K–Ar age of ~0.46 Ma reported for this level. Hence the Ceprano and Fontana Ranuccio hominin occurrences may be of very similar mid-Brunhes age.

The Anagni intra-appennine basin is specially rich in palaeontological and archaeological sites, spanning between middle Villafranchian and upper Pleistocene. The Italian Insitute of Human Palaeontology has carried out researches in this region in the last thirty years. At Costa San Giacomo middle Villafranchian yellow sands contain Mastodon arvernensis and Elephas meridionalis. At Colle Marino, a travertine layer and lime-clay contains mode 1 lithic industry, below any volcanic layers whose lower limit is 700 Ky old. Excavations have been restarted at Fontana Ranuccio, a 458 Ky Acheulean site with rich mammalian fauna (Elephas antiquus, Ursus deningeri, Bos primigenius, Dama clactoniana, Equus mosbachensis), a remarkable bone industry and 4 human teeth. Drillings, for about 40 m, have identified Matuyama-Brunhes limit 23 m under the main volcanic pyroclastite, in a thick limnic clay layer.

Four cores have been taken from the surroundings of the city of Milan, in the framework of the Milan CARG project. The northernmost drillings (Milano Triulza RL10, Milano Parco Nord RL11) were drilled to 100-m depth; the southernmost drillings (Peschiera Borromeo RL8, Gaggiano RL9) reached a depth of 180 m and 150 m, respectively. A total of 530 m of sediments was recovered. The overall core lithostratigraphy is composed by three superimposed lithologic sequences, consisting, from the bottom, of alternated silt and medium- to fine-grained sand, arranged in fining-upward cycles, interpreted as meandering alluvial plain; the central sequence develops with coarse-grained sand, pebbly sand and subordinated gravel, interpreted as distal braidplain. Medium- to coarse-grained, poorly sorted, massive sand and pebbly sand, and clast-supported gravels with sandy matrix, interpreted as proximal braidplain, characterize the upper sequence. As a whole, the central and the upper sequence can be regarded as a prograding braidplain, composed by severall small-scale fining-upward cycles. Paleomagnetic properties were studied on a total of 79 samples collected from cohesive fine-grained sediments with a common average sampling frequency in the order of one sample every 3/4 core-meters. The intensity of the NRM (measured at the Alpine Laboratory of Paleomagnetism) was in the order of 10 -3 - 10-4 A/m and orthogonal projections of demagnetization data typically indicated the existence of a lower unblocking temperature component, superimposed to a higher unblocking temperature component. The higher temperature component was removed to the origin of the demagnetization axes mainly in the magnetite and hematite temperature ranges between ~350 and ~680 °C and it is interpreted as the characteristic component. This characteristic component bears either positive (down-pointing) or negative (up-pointing) inclinations with overall mean values of 60° ± 15 and -54° ± 16, respectively, and is regarded as acquired at or shortly after sediment deposition (DRM or pDRM). At least a magnetic polarity reversal has been recognized in each core, in the depth range of 60-80 m, and it has been interpreted, by means of the available pollen biostratigraphy and the regional framework reported in Carcano & Piccin (2002), Muttoni et al. (2003), Scardia et al. (2006), as the Brunhes/Matuyama boundary; in cores RL 8 and RL9 also the Jaramillo Subchron was recognized. The major lithologic change observed in each core, produced by a depositional switch from distal meandering alluvial plain to a prograding braidplain, occurs during a reverse polarity period, interpreted as Subchron Late Matuyama, and it is well constrained between the Subchron Jaramillo and the Brunhes/Matuyama boundary in cores RL8 and RL9; the same age constrain can be inferred in cores RL10 and RL11. This episode, already observed by Carcano & Piccin (2002), has been correlated by Muttoni et al. (2003) to an important Pleistocene climatic event, related to the onset of the major glaciations at the southern foothills of the Alps occurred at ~0.87 ka, during the Subchron Late Matuyama.