Pliocene Marine Deposits Research Articles

Age and Depositional Environment of Whale-Bearing Sedimentary Succession from the Lower Pliocene of Tuscany (Italy): Insights from Palaeomagnetism, Calcareous Microfossils and Facies Analyses

A c. 31 m thick section straddling the fossil find of an Early Pliocene baleen whale (“Brunella”, hereafter), made in 2007 in the sedimentary fill of the Middle Ombrone Basin of Tuscany, is investigated for depositional age and environment combining palaeomagnetic, micropalaeontological (Foraminifera and calcareous nannofossils) and sedimentary facies analyses. Resting unconformably onto Late Miocene continental deposits, the Early Pliocene marine deposits include, from bottom to top, a coarse-grained wave-winnowing lag, the few metres-thick fossiliferous sandstone bedset from which Brunella was unearthed, and several metres of clays. The stratigraphic organisation of these deposits indicate deposition in a deepening upward inner shelf environment. Successful isolation of characteristic remanent magnetisation and calcareous nannofossil content indicate the investigated marine section was deposited during the interval of polarity Chron C3n.2n corresponding to the basal part of the Mediterranean nannofossil zone MNN13 (between Helicosphaera sellii Base common and the Amaurolithus primus Top) and allow estimating the depositional age of Brunella to c. 4.6 Ma. Sedimentary facies, benthic Foraminifera association and anisotropy of magnetic susceptibility characterising the deposits that embedded Brunella suggest deposition above the fair-weather base level.

Late evolution of the inner Northern Apennines from the structure of the Monti del Chianti-Monte Cetona ridge (Tuscany, Italy)

The Neogene and Quaternary tectonic evolution of the inner Northern Apennines (i.e southern Tuscany and northern Tyrrhenian Sea), as well as its crustal features (i.e. low crustal thickness, Neogene-Quaternary magmatism, widespread geothermal anomalies, lateral segmentation of the stacked tectonic units, extensive deep sedimentary basins), are framed in different geodynamic scenarios: compressional, extensional or both, pulsing. Consequently, the basin and range structure that characterises the northern Tyrrhenian Sea and southern Tuscany is considered as a consequence of (i) out-of-sequence thrusts and related thrust-top-basins, (ii) polyphased normal faulting that formed horst and graben structures or (iii) a combination of both. This paper provides a new dataset from a sector of the eastern inner Northern Apennines (i.e. Monti del Chianti - Monte Cetona ridge) contributing to this scientific debate. New fieldwork and structural analysis carried out in selected areas along the ridge allowed to define the chronology of the main tectonic events on the basis of their influence on the marine and continental sedimentation. The dataset supports for early Miocene - (?) Serravallian in-sequence and out-of-sequence thrusting. Thrusting produced complex staking patterns of Tuscan and Ligurian Units. Extensional detachments developed since later middle Miocene and controlled the Neogene sedimentation in bowl-shaped structural depressions, later dissected by normal faults enhancing the accommodation space for Pliocene marine deposits in broad NNW-trending basins (Siena-Radicofani and Valdichiana Basins). In this perspective, no data supports for active, continuous or pulsing, compressional tectonics after late Serravalian. As a result, in the whole inland inner Northern Apennines the extensional tectonics was continuously active at least since middle Miocene and controlled the basins development, magmatism and structure of the crust and lithosphere.

Witnesses of the early Pliocene sea-level rise in the Manilva Basin (Málaga, S Spain)

The Sierra de la Utrera, a relief in the Manilva Basin (Málaga, SW Spain), shows bored surfaces at different heights above present-day sea level, from 96 m to 287 m. Borings occur in the eastern, central, and western parts of the Canuto de la Utrera, a prominent gorge in the central southern part of the relief excavated in Mesozoic limestones, as well as on the western end of the Canuto Chico, a smaller canyon in the northern part. Pliocene marine deposits fossilized the bored surfaces. Bored boulders of the substrate are embedded in the Pliocene sediments. The traces Gastrochaenolites ispp., Entobia ispp., Caulostrepsis ispp., Circolites kotoucensis, and Ericichnus asgaardi have been identified. Among these, Caulostrepsis is found only in the reworked blocks. This ichnoassemblage, attributed to the archetypical Entobia Ichnofacies of rocky shores, represents boring activity in high-energy, very-shallow-water settings, close to the sea level, and with a virtually null sedimentation rate. The vertical distribution of bored surfaces attests to a progressive sea-level rise. The onlap of the Pliocene deposits on the substrate is consistent with the deepening trend. Planktonic foraminiferal assemblages collected from the sediment adjacent to the Sierra de la Utrera demonstrate that boring activity spanned, at most, 1 Ma during the early Pliocene, Zanclean (biozones MPl 1 and MPl 2), ranging from 5.33 to 4.36 Ma.

Geomorphology, denudation rates, and stream channel profiles reveal patterns of mountain building adjacent to the San Andreas fault in northern California, USA

Relative horizontal motion along strike-slip faults can build mountains when motion is oblique to the trend of the strike-slip boundary. The resulting contraction and uplift pose off-fault seismic hazards, which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges. Sparse geomorphic markers, topographic analyses, and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern San Andreas fault. Between Jenner and Mendocino, California, emergent marine terraces found southwest of the San Andreas fault record late Pleistocene uplift rates between 0.20 and 0.45 mm yr−1 along much of the coast. However, on the northeast side of the San Andreas fault, a zone of rapid uplift (0.6−1.0 mm yr−1) exists adjacent to the San Andreas fault, but rates decay northeastward as the coast becomes more distant from the San Andreas fault. A newly dated 4.5 Ma shallow-marine deposit located at ∼500 m above sea level (masl) adjacent to the San Andreas fault is warped down to just 150 masl 15 km northeast of the San Andreas fault, and it is exposed at just 60−110 masl to the west of the fault. Landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of, and adjacent to, the San Andreas fault are 0.16−0.29 mm yr−1, but they are only 0.03−0.07 mm yr−1 west of the fault. Basin-average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock. Calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties. The lower-elevation areas of this landscape that show high channel steepness (and hence calibrated erosion rate) are distinct from higher-elevation areas with systematically lower channel steepness and denudation rates. These two areas do not appear to be coincident with lithologic contacts. Assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream-propagating kinematic wave that separates high and low channel steepness values, the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase. This analysis suggests that rock uplift rates along the coast changed from 0.3 to 0.75 mm yr−1 between 450 and 350 ka. This zone of recent, relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the Gualala block into the thinner, weaker oceanic crust left at the western margin of the North American plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary. The warped Pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses, and further indicate that the zone of rapid uplift may herald elevated off-fault seismic hazard if this uplift is created by periodic stick-slip motion on contractional structures.

The Canary record of the evolution of the North Atlantic Pliocene: New 40Ar/39Ar ages and some notable palaeontological evidence

Abstract Two new 40Ar/39Ar ages (*) and previously published K/Ar ages of basaltic pillow lava flows are coeval with closely-related fossiliferous marine layers, allowing us to establish the beginning (5.8; 5.0; 4.8 Ma at Ajui, Fuerteventura Island and 4.8 ± 0.03 Ma (2σ)* at Tamaraceite) and a middle stage (4.20 ± 0.18 Ma (2σ)* at La Esfinge in Gran Canaria Island) of Early Pliocene marine deposits in the Canary Islands. Here the presence of tropicopolitan fossils (Megaselachus megalodon, Janthina typica) suggests the influence of a possible Central American Circumtropical Current during the Pliocene and in the North Atlantic basin. The presence of both Janthina typica and the Argonauta argo also indicate the occurrence of tropical storms in the area of the Canary Islands around that time. In addition, the pillow lava flow at La Esfinge overlies a submarine pyroclastic layer containing Ostrea offreti that was preserved in its life position, a fossil from the terminal Miocene and commonly found on the south eastern Iberian Peninsula. At La Cruz on Fuerteventura Island, a dune formed above marine deposits lies beneath a palaeosol and a basaltic lava flow that was K/Ar dated at 2.9 Ma. Near El Marmol in Gran Canaria the corresponding palaeosol lies between lava flows K/Ar dated at 3 Ma. Based on these observations, we argue in this paper that the first appearance of the Canary Current, the eastern boundary current of the North Atlantic sub-tropical gyre, occurred between 4.2 Ma and 2.9 Ma ago. This was followed by a major sea level drop (of about 40 m) and the formation of a first fossil-bearing palaeosol which indicate that major climate change that took place around 2.95–2.82 Ma.

Depositional environment and age of some key Late Pliocene to Early Quaternary deposits on the underfilled Cedrino paleovalley (Orosei): Insight into the Neogene geodynamic evolution of Sardinia

In order to better constrain the relationship between tectonics and sedimentation of the Eastern Sardinian Margin, from the Messinian to the present day (METYSS project), a lithostratigraphic study was carried out on the Late Neogene deposits along the Cedrino Valley (eastern Sardinia). The late Neogene evolution is documented from sedimentological and tectonic analysis, biostratigraphic dating, and by mapping and logging stratigraphic sections. Previous authors have differentiated an early Pliocene marine formation from an older continental formation, possibly Miocene, the entire system being covered by late Pliocene to Quaternary lava flows. Preliminary biostratigraphic data suggest the absence of the lowermost Pliocene, based on the absence of Globorotalia margaritae and the presence of Globorotalia puncticulata, implying a sediment age between 3.81 and 2.41 Ma. At the foot of the Fiuli cliff, some mud clasts include a coccolith microflora, Tortonian in age, suggesting reworking. The Pliocene marine deposits consist of a single filling sequence instead of a succession of superimposed sequences as we would expect during this period of time; the occurrences of terms rarely respect the usual transgressive-regressive succession. Contrasting bathymetric environments (fore-shore, pro-delta, shelf or upper slope) can be abruptly superimposed on top of the other, along few meter thick intervals. A rapidly flooded term is observed in several sites and indicates a spatial variability over only a few kilometers distance. Some deep water deposits are in the middle of the infilling Pliocene sequence, whereas shallower water deposits can be repeated along a vertical section, or even interrupted by emersion. These marked differences can express syn-, or possibly post-sedimentation tectonic uplifts. The 10–25° bed dips originated through local tectonic uplift. At Fiuli, the geometry of the bedding planes is indicative of tilting toward the west, in a direction opposite to the one observed at Onifai. These Pliocene series form a wide syncline with an approximately NNE–SSW axis. This morpho-structural behavior appears to be largely atypical of this East-Sardinian coastal area.

Late Quaternary tectonics in the inner Northern Apennines (Siena Basin, southern Tuscany, Italy) and their seismotectonic implication

Defining the most recent Quaternary tectonics represents a challenging task for neotectonic, palaeoseismological and seismotectonic studies. This paper focuses on an integrated approach to reconstructing the latest Quaternary deformation affecting the northern part of the Siena Basin (inner Northern Apennines, i.e., southern Tuscany, Italy) near the town of Siena, and to discuss the seismological implications. Field work and structural and stratigraphic analyses, coupled with the interpretation of reflection seismic lines, have been combined to define the geometry, kinematics and age of mesoscopic to map-scale faults which have affected the mainly Quaternary continental and Pliocene marine deposits. The resulting dataset describes a tectonic setting characterized by coeval SW- and NW-trending transtensional and normal faults, respectively, dissecting alluvial sediments younger than 23.9±0.23ka. Seismic interpretation sheds light on the geometrical setting of the faults at deeper levels, down to 1–2km, and provides support for the presence of a wide brittle shear zone defined by conjugated fault segments, locally giving rise to an asymmetrical negative flower-like structure. Faults and their damage zones have controlled (and still control) the discharge of gas vents (mainly CO2 and H2S) and hydrothermal circulation (which deposits travertine) since at least 23.216±0.124ka. The resulting complete data set provides support for our description of the Neogene–Quaternary tectonics which were active until the late Quaternary, providing additional information about the seismotectonic framework of an area characterized by low seismicity and generally low-magnitude earthquakes (M<4), but having experienced significant seismic events over the last few centuries.

New and revised occurrences of Dihoplus megarhinus (Mammalia, Rhinocerotidae) in the Pliocene of Italy

Several rhinoceros remains, collected in the Pliocene deposits of Northern Italy and usually ascribed to Dicerorhinus or Rhinoceros megarhinus, are revised; furthermore, unpublished Pliocene remains are also described. The material is compared with the respective anatomical elements of Dihoplus megarhinus, Stephanorhinus jeanvireti and Stephanorhinus etruscus. Based on morphological and morphometrical comparisons, the presence of Dihoplus megarhinus is confirmed in at least ten sites. In other Late Pliocene fossiliferous localities, the presence of S. jeanvireti and/or S. etruscus is recorded. D. megarhinus occurred in Italy at the beginning of the Early Pliocene. It was well represented in Val di Pugna (Tuscany) and in several Pliocene marine deposits near Bologna by fragmentary mandibles, some postcranial remains and few teeth. The species disappeared before the beginning of the Villafranchian (Late Pliocene) when S. jeanvireti and S. etruscus co-occurred both in the site of Villafranca d’Asti and Montopoli. S. jeanvireti disappeared in Italy at the Pliocene-Early Pleistocene transition whereas S. etruscus was widespread in Central and Southern Italy.

Geological map of Pliocene-Pleistocene deposits of the Ambra and Ombrone valleys (Northern Siena Basin, Tuscany, Italy)

The study area is located across the Chianti Ridge (Tuscany, Italy), between the Upper Valdarno Basin and the Siena Basin. This area covers about 25 km2, forming a narrow belt oriented N–S and drained by the Ambra and Ombrone creeks, which flow northward and southward, respectively. Field mapping was carried out at 1:10,000 scale through an allostratigraphic-sedimentological approach. The study area deposits represent the infill of a SW-draining paleovalley, cut both in pre-Neogene bedrock and marine Pliocene deposits of the Siena Basin. The valley-fill succession consists of two main allounits (V1 and V2), which are conformably stacked in the northern sector of the study area, and unconformably offset in the southern sector. V1 comprises gravelly to sandy fluvial deposits, whereas V2 deposits show noticeable downvalley variability. V2 consists of poorly drained floodplain deposits in the northern sector of the paleovalley, whereas gravel and sand-bed river deposits fill its southern part. Alluvial-fan and palustrine deposits are also associated with V2 fluvial facies. A normal fault trending NW–SE is the main structural feature of the area. This fault cuts the V2 unit lowering the upstream reach and is thought to have promoted the marked facies changes observed in the fluvial deposits of unit V2.

Aproximación a la correlación marino-continental del Plioceno inferior en el Sur de España. El yacimiento de micromamíferos de Alhaurín el Grande-1 (Cuenca de Málaga, Cordillera Bética, España)

Un nuevo yacimiento de micromamíferos en Alhaurín el Grande (Málaga, Sur de España) situado sobre depósitos marinos del Plioceno inferior permite una aproximación a la correlación marino-continental para esa época. El relleno sedimentario marino del Plioceno inferior en el conjunto de la cuenca de Málaga comprende tres secuencias transgresivas-regresivas (unidades Pl-1, Pl-2 y Pl-3) limitadas por discordancias. A techo de la secuencia intermedia Pl-2, sedimentos turbosos han liberado restos de Rodentia, Lagomorpha, Insectivora y Crocodylia. La presencia de Cricetus barrieri Mein &amp; Michaux, 1970 en asociación con dos múridos, uno con morfología primitiva (Apodemus gudrunae Van de Weerd, 1976) y otros más evolucionados próximo a Occitanomys brailloni Michaux, 1969 y Stephanomys donnezani cordii Ruiz Bustos, 1986, permiten inferir una edad Rusciniense inferior (biozona MN14). En función de los foraminíferos planctónicos, los datos bioestratigráficos indican que los sedimentos marinos justo por debajo del nivel de micromamíferos pertenecen a la biozona MPL-2 del Zancliense inferior. Los datos paleomagnéticos disponibles muestran que el nivel de micromamíferos se localiza entre el subcron geomagnético normal C3n3n (4.89-4.80 Ma) y el subcron C3n2n (4.63-4.49 Ma), limitando la edad del yacimiento a la parte superior del Zancliense inferior.

Facies associations map of the Pliocene marine deposits of the central-southern Siena Basin (Tuscany, Italy)

The Siena Basin is a post-collisional basin of the inner Northern Apennines (Tuscany, Italy) characterized by a thick siliciclastic Neogene infill, mainly composed of marine sediments with subordinate alluvial deposits close to basin margins. The central-southern sector of the basin shows a more complex stratigraphy with the occurrence of sandy deposits also in distal areas, far from the basin margin. The aim of this paper is to provide a new 1:10,000-scale geological map of this key sector (about 45 km2) of the Siena Basin, helpful for a better reconstruction of its sedimentary evolution. The new fieldwork was based on the identification and mapping of different facies associations (expression of different sedimentary environments), whose shifts in time and space provide elements to understand the basin-fill history. The recognition of two main intra-Pliocene erosional surfaces allowed the subdivision of the succession into three alloformations. Therefore, a more complex depositional history, with respect to the previous knowledge for this key-sector of the Siena Basin, has been reconstructed, thus highlighting the importance of this kind of approach with respect to the classical lithostratigraphic criteria.

Active tectonics in the Malaga Basin: evidences from morphotectonic markers (Western Betic Cordillera, Spain)

The Malaga Basin is located in the westernmost part of the Betic Cordillera. This alpine cordillera in the south of Spain is the most active region of the Iberian Peninsula. Some of the most destructive earthquakes occurred historically in Spain took place within the Malaga Basin. In this work we focus on geomorphic and morphotectonic observations in the aim of finding active tectonic structures that could be seismogenic sources. First, we study the spatial arrangement and age of the Quaternary alluvial fan system as well as the drainage pattern of the basin, followed by the analysis of the distribution of regional markers like marine erosive surfaces and the extend of Pliocene marine deposits in the Malaga Basin. The tectonic structures inferred as active by the morphotectonic analysis are grouped into four main families: N60º-85ºE folds associated with blind thrust faults, N20º-30ºE and N40º-50ºE high angle dip-slip faults, and N165º-170ºE tear faults. Finally, their seismic potential in terms of maximum moment magnitude (Mw) is assessed by means of empirical relationships, varying between 6.0 and 7.0 depending on the hypothesis considered.

Geologia dell’area di Rapolano Terme in Provincia di Siena (Appennino Settentrionale)

Geologia dell’area di Rapolano Terme in Provincia di Siena (Appennino Settentrionale)

Biostratigraphie d’après les foraminifères et paléoenvironnements des séries post-Éocène du sondage ASHTART 28, golfe de Gabès (Tunisie)

The Cenozoic sequence of Ashtart 28 well drilled in the Gulf of Gabes (Tunisia) is the subject of a biostratigraphical study. The samples recovered in cuttings from 390 m and downwards allowed to recognize, above the Late Eocene sediments, a sedimentary series, lithologically diversified, nearly 1600 m thick. Marine Pliocene deposits, generally attesting a low bathymetry, lie unconformably above the Messinian (Oued Bel Khedim formation), which shows the usual features of the Mediterranean confinement. The underlying Messinian pre-evaporitic platform series (Melqart formation), that is over 250 m thick, is typical of a perireefal environment. The sediments assigned to the Tortonian (Somâa Sands formation) are continental and occur unconformably above the approximately 500-metres-thick Middle Miocene strata (Saouaf, Mahmoud, Aïn Grab and Salammbô pars formations). The marine Lower Miocene and Oligocene sediments (Salammbô pars and Ketatna formations), that are more than 300 m thick, lie in continuity under the Middle Miocene. The infralittoral Chattian sequence has especially supplied a diversified assemblage of larger foraminifera recovered in other west-mediterranean basins. Datings were obtained based on planktonic and larger benthic foraminifera (Miogypsinidae, Nummulitidae, Lepidocyclinidae) and by correlations obtained by means of well loggings and lithostratigraphy. Benthic foraminifera, mainly listed for the Miocene and Oligocene, are studied from a systematic, stratigraphic and paleogeographic point of view. The paleoenvironments of deposits are defined for each considered stratigraphic interval. Comparisons are sketched with other drillings of the Gulf of Gabes. Thanks to the numerous data obtained by this detailed study, the Ashtart drilling can serve as a reference for the Tertiary sequence of this part of the Mediterranean domain.

Pliocene dinoflagellate cyst stratigraphy, palaeoecology and sequence stratigraphy of the Tunnel-Canal Dock, Belgium

AbstractDinoflagellate cysts and sequence stratigraphy are used to date accurately the Tunnel-Canal Dock section, which contains the most complete record of marine Pliocene deposits in the Antwerp harbour area. The Zanclean Kattendijk Formation was deposited between 5.0 and 4.4 Ma during warm-temperate conditions on a shelf influenced by open-marine waters. The overlying Lillo Formation is divided into four members. The lowest is the Luchtbal Sands Member, estimated to have been deposited between 3.71 and 3.21 Ma, under cooler conditions but with an open-water influence. The Oorderen Sands, Kruisschans Sands and Merksem Sands members of the Lillo Formation are considered a single depositional sequence, and biostratigraphically dated between 3.71 andc. 2.6 Ma, with the Oorderen Sands Member no younger than 2.72–2.74 Ma. Warm-temperate conditions had returned, but a cooling event is noted within the Oorderen Sands Member. Shoaling of the depositional environment is also evidenced, with the transgressive Oorderen Sands Member passing upwards into (near-)coastal high-stand deposits of the Kruisschans Sands and Merksem Sands members, as accommodation space decreased. Applying sequence stratigraphy to our section implies that the Kattendijk/Lillo Formation boundary corresponds to the sequence boundary (SB) Za2 (4.04 Ma), the Luchtbal/Oorderen sands boundary to SB Pia1 (3.21 Ma), and the top of the Merksem Sands to SB Pia2 (2.76 Ma). Finally, the Belgian deposits are compared with marine Pliocene deposits of eastern England.

On the occurrence of Early Pliocene marine deposits in the Ierapetra Basin, Eastern Crete, Greece

On the occurrence of Early Pliocene marine deposits in the Ierapetra Basin, Eastern Crete, Greece

Pliocene marine deposits at Punta Maldonado, Guerrero state, Mexico

Diverse and abundant Foraminifera and Ostracoda assemblages were recovered from a measured stratigraphic section at Punta Maldonado, Guerrero state, Mexico. The planktonic species indicate an early Pliocene age, between 5.3 and 3.6 Ma; an early late Pliocene (around 2.4 Ma) planktonic assemblage also was recorded from isolated deposits. These ages contradict the Cretaceous–Paleogene age previously assigned to the sedimentary succession at Punta Maldonado. All indicators—benthic assemblages, ichnofacies, lithology, grain size, primary structures, mineralogy, body rock geometry, and facies—suggest deposition in the foreshore and offshore transition zones of a storm-dominated shallow siliciclastic shelf. The Ostracoda and Foraminifera indicate deposition around the outer neritic/upper bathyal boundary, which suggests an uplift of 320–400 m in the area during the Pliocene. This study represents the first report of Pliocene marine rocks in the southwestern coast of Mexico; the data presented contribute to regional geotectonic models.

Faults linkage, damage rocks and hydrothermal fluid circulation: Tectonic interpretation of the Rapolano Terme travertines (southern Tuscany, Italy) in the context of Northern Apennines Neogene-Quaternary extension

The tectonic history of Neogene-Quaternary extensional structures has been documented in the inner part of the Northern Apennines (Rapolano Terme area) from Quaternary travertines and faults relationships. In particular, structural studies, field mapping and tectono-stratigraphical considerations on the pre-Neogene, Pliocene and Quaternary units indicate two fault populations of different ages. The travertines, broadly exposed in the Rapolano Terme area, were related to hydrothermal fluid circulation and upwelling along the damage zones of Pleistocene normal faults. These structures were superimposed upon normal (mainly NNW–SSE and SW–NE oriented) and transtensional (mainly SW–NE oriented) faults, Early–Middle Pliocene in age, related to development of the Siena Basin. The age of such Pliocene normal and transtensional faults has been inferred on the basis of the relationships between tectonic elements and Pliocene deposits. In fact, Middle Pliocene marine sandy and gravelly sediments suture the faults. The Pleistocene normal faults (mainly SW–NE oriented) reactivated the oldest SW–NE transtensional faults, cut the NNW–SSE normal faults, and displaced Middle Pliocene marine deposits. Pleistocene-Holocene travertines and present-day thermal springs mainly occur at the intersection points between the Pleistocene SW–NE faults and the Pliocene NNW–SSE normal faults, or along the SW–NE Pleistocene normal faults.

Pliocene climatic cycles and altitudinal forest development from 2.7 Ma in the Northern Apennines (Italy): Evidence from the pollen record of the Stirone section (∼ 5.1 to ∼ 2.2 Ma)

Marine Pliocene deposits from Northern Apennines (Italy) have been submitted to palynological studies in order to obtain a floristic, vegetational, and climatic record. The history of the Pliocene land environment and climate has been reconstructed on the basis of the chronostratigraphic framework available for the Stirone section. The Zanclean is characterized by long and relatively stable subtropical to warm-temperate climatic conditions. During the Piacenzian and Gelasian, a cooling is testified by both the reduction as well as the disappearance of some mega-mesothermic elements and the increase of microthermic ones. Laminated sediments, calibrated at ca 2.8 Ma, indicate a wet period characterized by repeated warmer/cooler fluctuations. Cyclic alternations between mega-mesothermic and meso-microthermic elements, starting after ca 2.7 Ma, are characterized by the opposition of coniferous (Picea mainly) and deciduous forests elements. The major increase of Picea has been stratigraphically correlated with the maximum expansion of the Arctic ice.

The Plio–Pleistocene evolution of extensional tectonics in northern Tuscany, as constrained by new gravimetric data from the Montecarlo Basin (lower Arno Valley, Italy)

A detailed gravimetric study has been integrated with the most recent stratigraphic data in the area comprised between the Arno river and the foothills of the Northern Apennines, in northern Tuscany (central Italy). A Plio–Pleistocene basin lies in this area; its sedimentary succession can be subdivided from the bottom, in five allostratigraphic units: (1) Lower–Middle Pliocene shallow marine deposits; (2) Late Pliocene (?)–Early Pleistocene fluvio-lacustrine deposits; (3) late–Early Pleistocene–Middle Pleistocene alluvial to fluvial red conglomerates (Montecarlo Formation); (4) Middle Pleistocene alluvial to fluvial red conglomerates (Cerbaie and Casa Poggio ai Lecci Formations); (5) alluvial to fluvial deposits of Late Pleistocene age. The Bouguer anomaly map displays a strong minimum in the northeastern sector of the basin, and a gentle gradient from west to east. The map of the horizontal gradients permits to recognise three major fault zones, two of which along the southwestern and northeastern margins of the basin, and one along the southeastern edge of the Pisani Mountains. A 2.5D gravimetric modelling along a SW–NE section across the basin displays a thick wedge of sediments of density 2.25g/cm3 (about 1700m in the depocenter) overlying a layer of density 2.55g/cm3, 1000m thick, which rests on a basement of 2.72g/cm3. The most of the sediment wedge is here referred to Upper Pliocene (?)–Lower Pleistocene, because borehole data show Pliocene marine deposits thinning northward close to the southern margin of the area. The layer below is referred to Ligurids and upper Tuscan Nappe units; the densest layer is interpreted as composed of Triassic evaporites, quartzites and Palaeozoic basement. According to Carmignani low-angle extensional tectonics began between Serravallian and early Messinian, thinning the Apennine nappe stack. At the end of Middle Pliocene, syn-rift deposition ceased in the Viareggio Basin (west of the investigated area) as demonstrated by Argnani and co-workers, and high-angle extensional tectonics migrated eastward up to the Monte Albano Ridge. A syn-rift continental sedimentary wedge developed in Late Pliocene–Early Pleistocene, until its hanging wall block was dismembered, during late Early Pleistocene, by NE-dipping faults, causing the uplift of its western portion (the Pisani Mountains). This breakup caused exhumation and erosion of Triassic units whose clastics where shed into the surrounding palaeo-Arno Valley in alluvial–fluvial deposits unconformably overlying the Lower Pleistocene syn-rift deposits. In the late Pleistocene SW–NE-trending fault systems created the steep southeastern edge of the Pisani Mountains and the resulting throw is recorded in Middle Pleistocene deposits across the present Arno Valley. This tectonic phase probably continues at present, offshore Livorno, as evidenced by the epicentres of earthquakes.