Relief development of a Mesozoic carbonate platform margin (Southern Alps, northern Italy)

The effect of various erosional processes on the relief development of a carbonate platform margin is documented from outcrops of the Southern Alps, northern Italy, by the occurrence of truncation surfaces and redistribution of remobilized sediments. The periplatform depositional history, with periods of intensive submarine erosion along the north-western Trento plateau margin, is recorded by various carbonate deposits ranging in age from the Early Jurassic to Late Cretaceous with numerous gaps. The first Early Jurassic period of submarine erosion is marked by truncation and extensive tectonic fracturing of lower Liassic oolitic skeletal periplatform deposits. These are overlain by pelmicritic sediments of late Hettangian to Toarcian age. The second period of submarine erosion during the late Early Jurassic resulted in almost complete truncation of the pelmicritic unit. Crinoidal to oolitic periplatform carbonate sands were subsequently deposited along the carbonate margin until the Aalenian/Bajocian. The third truncation surface was produced by partial current erosion of the crinoidal to oolitic periplatform deposits during the late Bajocian to Callovian. The fourth, and most prominent, truncation surface was produced by erosion during the Early Cretaceous cutting down from Aptian/Albian pelagic units to Toarcian periplatform deposits. The resulting submarine relief was completely buried during the late Maastrichtian by onlapping pelagic sediments. The documentation of the depositional history during the Late Mesozoic of the north-western Trento plateau pinpoints the main mechanisms responsible for the relief of the drowned carbonate platform margin. Extensional tectonic activity during differential subsidence and current-induced erosional truncation, followed by gravitational downslope mass transport and rapid pelagic burial mainly determined the morphology of the drowned carbonate platform margin.     

Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of Adria

The Triassic–Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break‐up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre‐Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian–Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian–Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian–Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian–Toarcian boundary. This younger rift bridges the gap between the Hettangian–Sinemurian diffuse rifting and the Callovian–Bathonian break‐up. The late Pliensbachian–Toarcian rift, which eventually lead to continental break‐up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins.     

Differential compaction and early rock fracturing in high‐relief carbonate platforms: numerical modelling of a Triassic case study (Esino Limestone,Central Southern Alps,Italy)

Numerical models were used to investigate the effects of differential compaction on strain development and early fracturing in an early cemented high‐relief Triassic carbonate platform prograding onto basinal sediments, whose thickness increases basinward. Results show that basinal sediment compaction induces stretching of internal platform and slope strata in prograding platforms. When sediments are early cemented, such extensional strain is accommodated by the generation of syndepositional fractures. The amount of stretching is predicted to increase from the oldest to the youngest layers, due to the thickening of the compactable basinal sequences towards the external parts of the platform. Stretching is also controlled by the characteristics of the basin: the thicker and the more compactable the basinal sediments, the larger will be the stretching. Numerical modelling has been applied to the Ladinian–Early Carnian carbonate platform of the Esino Limestone (Central Southern Alps of Italy). This case study is favourable for numerical modelling, as it is well exposed and both its internal geometry (inner platform, reef and prograding clinostratified slope deposits) and the relationship with the adjacent basin can be fully reconstructed, as the Alpine tectonic overprint is weak in the study area. Evidence for early fracturing (fractures filled by fibrous cements coeval with the platform development) is described and the location, orientation and width of the fractures measured. The fractures are mainly steeply dipping and oriented perpendicularly to the direction of progradation of the platform, mimicking local platform‐margin trends. The integration of numerical models with field data gives the opportunity to quantify the extension triggered by differential compaction and predict the possible distribution of early fractures in carbonate platforms of known geometry and thickness, whereas the interpretation of early fractures as the effects of differential compaction can be supported or rejected by the comparison with the results of ad hoc numerical modelling.     

The environmental history of a mountain lake (Lago Paione Superiore, Central Alps, Italy) for the last c. 100 years: a multidisciplinary, palaeolimnological study

A palaeoecological study of an oligotrophic alpine lake, Paione Superiore (Italy), provided a record of historical changes in water quality. Historical trends in lake acidification were reconstructed by means of calibration and regression equations from diatoms, chrysophycean scales and pigment ratios. The historical pH was inferred by using two different diatom calibration data sets, one specific to the alpine region. These pH trends, together with the record of sedimentary carbonaceous particles and chironomid remains, indicate a recent acidification of this low alkalinity lake.Concentration of total organic matter, organic carbon, nitrogen, biogenic silica (BSiO₂), chlorophyll derivatives (CD), fucoxanthin, diatom cell concentration and number of chironomid head capsules increased during the last 2–3 decades. When expressed as accumulation rates, most of these parameters tended to decrease from the past century to c. 1950, then all except P increased to the present day. A marked increase in sedimentary nitrogen may be related to atmospheric pollution and to the general increases in output of N in Europe. High C/N ratios indicate a prevailing allochthonous source of organic matter.Finally, the increase in measured air temperature from the mid-1800's appeared to be related to lake water pH before industrialization: cold periods generally led to lower pH and vice-versa. The more recent phenomenon of anthropogenic acidification has apparently decoupled this climatic-water chemistry relationship.     

Magnetostratigraphy of Early Cretaceous Maiolica sections of the Southern Alps (Cismon and Pra da Stua, Italy)

The bottom part of the Cretaceous Cismon section in the Southern Alps was sampled for high-resolution magnetostratigraphy. Although the almost pure pelagic nannofossil limestones ( c. 90 per cent CaCO₃) of the Maiolica/Biancone Formation are extremely weakly magnetized, stepwise thermal and alternating-field demagnetization removed overprints and isolated a characteristic remanent magnetization which is interpreted as a primary magnetization. The dominant magnetic carrier mineral is magnetite; a small fraction of haematite may be present. A clear reversal pattern can be correlated unambiguously with Mesozoic polarity chrons CM10N to CM8. A less well-constrained magnetostratigraphy from the Pra da Stua section could not be directly correlated with the global polarity scale, but biostratigraphic information allows its assignment to the interval CM10-CM5. A counterclockwise rotation of 56 and a northward translation of 28 latitude for the Cismon locality since the Early Cretaceous are derived from the palaeomagnetic data, consistent with previous results from the Southern Alps. The high-resolution magnetostratigraphy of the Cismon section is used in an effort to refine the Cretaceous timescale by the combination of magnetostratigraphic and cyclostratigraphic results from the same section. The cyclostratigraphic duration estimates of chrons CM10N to CM8 are compared to their equivalents in a number of traditional timescales and found to be shorter by a factor of 1.26-2.58.     

Tracking sand‐fairways through a deformed turbidite system: the Numidian (Miocene) of Central Sicily,Italy

Understanding ancient deep‐water sedimentary systems that accumulated at complex plate boundaries requires confronting the stratigraphic record of deformed sedimentary successions by tracking sand‐fairways and identifying original relationships in later deformed sequences. Here, we investigate the Numidian turbidite system (early to mid‐Miocene) of Central‐East Sicily to explore a deep‐water sedimentary system deposited at an active thrust belt on the Central Mediterranean. Turbidites include multi‐metre thick‐bedded, ultra‐mature quartz sandstones that were sourced from North Africa and are now deformed and dismembered within the Apennine‐Maghrebian orogen. To date, much research has focused on the little‐deformed sections that sample discrete parts of the original turbidite pathways. Yet the bulk of these systems are represented by deformed successions and these have attracted little modern sedimentological and stratigraphic investigation. We present new data based on field mapping, sedimentological/structural fieldwork, and biostratigraphy (planktonic foraminifera and nannofossils) that focus on the Numidian turbidites of Central‐East Sicily. Thickness and facies variations, together with evidence of large‐scale sediment bypass and local substrate reworking, characterize the Numidian turbidites of the study area, consistent with a partially confined turbidite system. Our work demonstrates that the Numidian turbidite system accumulated across active structures and these provided tortuous, evolving corridors through which turbidity currents were routed, transporting coarse sand over many hundreds of km. These results provide insight on structurally confined turbidites in analogous tectonic settings and demonstrate the need to seek sedimentological and stratigraphic data from deformed and dismembered parts of deep‐water systems.     

The long-term succession of high-altitude cladoceran assemblages: a 9000-year record from Sägistalsee (Swiss Alps)

Cladoceran remains were analysed in a 1344 cm long sediment core from Sägistalsee (Swiss Alps, 1935 m asl) which covered the last 9000 years. Planktonic Cladocera were almost exclusively represented by Daphnia species, which occurred throughout the core. The chydorid fauna consisted of four species: Alona quadrangularis, Alona affinis, Acroperus harpae and Chydorus sphaericus of which the former was by far the most frequent species. The chydorid succession was characterised by disappearance and re-appearance of Acroperus harpae and Chydorus sphaericus at about 8400 and 3340 cal. BP, respectively. As a result, there was a long period of about 5000 years in which only two chydorid species were present with strong predominance (88.9%) of Alona quadrangularis. There was also a long-term trend of an increase of Alona affinis at the expense of Alona quadrangularis throughout the core.     

The Pleistocene tectono‐‐sedimentary evolution of the Apenninic foreland basin between Trigno and Fortore rivers (Southern Italy) through a sequence‐stratigraphic perspective

A basin‐scale, integrated approach, including sedimentological, geomorphological and soil data, enables the reliable reconstruction of the infilling history of the southern Apenninic foredeep, with its subsequent inclusion in the wedge‐top of the foreland basin system. An example is shown from the Molise‐Apulian Apennines (Southern Italy), between Trigno and Fortore rivers, where the Pleistocene tectono‐sedimentary evolution of the basin is framed into a sequence‐stratigraphic scheme. Specifically, within the traditional subdivision into Quaternary marine (Qm) and Quaternary continental (Qc) depositional cycles, five third‐order depositional sequences (Qm1, Qm2, Qc1, Qc2 and Qc3) are identified based on recognition of four major stratigraphic discontinuities. The lower sequence boundaries are represented by angular unconformities or abrupt facies shifts and are generally associated with distinctive pedological and geomorphological features. Three paleosols, observed at top of depositional sequences Qm2, Qc1 and Qc2, represent pedostratigraphic markers that can be tracked basinwide. The geomorphological response to major tectono‐sedimentary events is marked by a series of paleosurfaces with erosional, depositional and complex characteristics. Detailed investigation of the relationships between stratigraphic architecture and development of unconformities, paleosols and paleosurfaces suggests that the four sequence boundaries were formed in response to four geomorphological phases/tectonic events which affected the basin during the Quaternary. The first three tectonic events (Lower‐Middle Pleistocene), marking the lower boundaries of sequences Qm2, Qc1 and Qc2, respectively, are interpreted to be related to the tectonic regime that characterized the last phase of thrusting recorded in the Southern Apennines. In contrast, sequence Qc3 does not display evidence of thrust tectonics and accumulated as a result of a phase of regional uplift starting with the Middle Pleistocene.     

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

Peat horizons are characteristic features of delta plains worldwide. In this study, we tested the use of peat‐based correlations to assess the deformation of Holocene strata in the Po coastal plain (Northern Italy). The Holocene stratigraphy, about 30 km inland from the modern coastline consists of a peat‐bearing, estuarine and deltaic succession, up to 23 m thick. Through the analysis of 31 core data and 100 piezocone penetration tests, we identified and mapped three 10–40 cm‐thick peat layers (T1–T3) dated to 6.6–5.8, 5.5–5.0 and 3.3–2.7 cal kyr BP respectively. These peat horizons were found to be suitable stratigraphic markers within the Holocene succession over an area of about 200 km². The mid‐late Holocene palaeogeography, reconstructed through high‐resolution peat correlation, supported by 72 radiocarbon dates, highlights a typical upper delta plain environment, with ribbon‐shaped distributary channels and swamp interdistributary areas. Peat layers are inclined towards E‐NE with gradients that increase downsection from ~0.016% (T3) to 0.021% (T1). The gradient of the oldest peat horizon is one order of magnitude larger than the slope of the modern delta plain (~0.0025%). We infer that peat horizons accumulated during periods of low sediment supply mainly controlled by autogenic processes and were deformed after deposition. Differential compaction of underlying sedimentary strata and recent tectonic activity of the buried Apenninic thrust systems are the most likely drivers of strata deformation. Based on isochore maps, we document that higher sedimentation rates in topographically depressed areas compensated, in part at least, the ongoing deformation, keeping unaltered the topographic gradient and the depositional environment. This study demonstrates that peat‐based correlation and mapping can shed lights on the mechanisms of strata accumulation and deformation in deltaic settings, constituting a robust basis for reconstructing delta evolution.     

Thermal history and exhumation of the Northern Apennines (Italy): evidence from combined apatite fission track and vitrinite reflectance data from foreland basin sediments

ABSTRACT Apatite fission track ages of 20 samples collected from turbidite successions deposited in foreland basins adjacent to the Northern Apennines range between ∼3 and ∼10 Ma. The youngest fission track ages are concentrated in a NW–SE elongated belt, which approximately runs through the centre of the study area, while gradually increasing ages are distributed towards the south-western and north-eastern borders. Integration of apatite fission track data and published vitrinite reflectance values indicate this region of the Apennines experienced continuous but variable exhumation starting from ∼14 Ma. The extent of exhumation and uplift range between 5 and 6 km at the south-western and north-eastern borders of the study area, and ∼7 km in the central part. Exhumation was driven mainly by erosion, with minor faulting in response to structural readjustment related to differential exhumation. Regional exhumation and erosion are interpreted as the result of isostatic rebound following crustal thickening in the lower part of the orogen.     

Characterization of active fault scarps from LiDAR data: a case study from Central Apennines (Italy)

A high-resolution digital elevation model (DEM, 1 ms spacing) derived from an airborne light detection and ranging (LiDAR) campaign was used in an attempt to characterize the structural and erosive elements of the geometry of the Pettino fault, a seismogenic normal fault in Central Apennines (Italy). Four 90- to 280 m-long fault scarp segments were selected and the surface between the base and the top of the scarps was analyzed through the statistical analysis of the following DEM-derived parameters: altitude, height of the fault scarp, and distance along strike, slope, and aspect. The results identify slopes of up to 40° in faults lower reaches interpreted as fresh faces, 34° up the faces. The Pettino fault maximum long-term slip rate (0.6–1.1 mm/yr) was estimated from the scarp heights, which are up to 12–19 m in the selected four segments, and the age (ca. 18 ka) of the last glacial erosional phase in the area. The combined analysis of the DEM-derived parameters allows us to (a) define aspects of three-dimensional scarp geometry, (b) decipher its geomorphological significance, and (c) estimate the long-term slip rate.     

Relations between denudation,glaciation, and sediment deposition: implications from the Plio‐Pleistocene Central Alps

Despite abundant data on the early evolution of the Central Alps, the latest stage exhumation history, potentially related to relief formation, is still poorly constrained. We aim for a better understanding of the relation between glaciation, erosion and sediment deposition. Addressing both topics, we analysed late Pliocene to recent deposits from the Upper Rhine Graben and two modern river sands by apatite fission‐track and (U‐Th‐Sm)/He thermochronology. From the observed age patterns we extracted the sediment provenance and paleo‐erosion history of the Alpine‐derived detritus. Due to their pollen and fossil record, the Rhine Graben deposits also provide information on climatic evolution, so that the erosion history can be related to glacial evolution during the Plio‐Pleistocene. Our data show that Rhine Graben deposits were derived from Variscan basement, Hegau volcanics, Swiss Molasse Basin, and the Central Alps. The relations between glaciation, Alpine erosion, and thermochronological age signals in sedimentary rocks are more complex than assumed. The first Alpine glaciation during the early Pleistocene did not disturb the long‐term exhumational equilibrium of the Alps. Recent findings indicate that main Alpine glaciation occurred at ca. 1 Ma. If true, then main Alpine glaciation was coeval with an apparent decrease of hinterland erosion rates, contrary to the expected trend. We suggest that glaciers effectively sealed the landscape, thus reducing the surface exposed to erosion and shifting the area of main erosion north toward the Molasse basin, causing sediment recycling. At around 0.4 Ma, erosion rates increased again, which seems to be a delayed response to main glaciation. The present‐day erosion regime seems to be dominated by mass‐wasting processes. Generally, glacial erosion rates did not exceed the pre‐glacial long‐term erosion rates of the Central Alps.     

Tectonic geomorphology of the Triglav Lakes Valley (easternmost Southern Alps, NW Slovenia)

We present a study on the impact of litho-structural setting and neotectonic activity on meso- and macro-scale relief production in Alpine areas. The topography of the high alpine Triglav Lakes Valley, NW Slovenia, was studied by means of detailed mapping and stratigraphic study of the valley. The Triglav Lakes Valley is characterised by a generally asymmetric transverse (E–W) profile: a very steep eastern slope, a relatively flat valley and a relatively gentle western slope. On the transverse profile the valley floor is essentially flat, gently dipping towards the east. In the longitudinal cross-section, however, the valley floor is marked by sharply-defined fault blocks extending in a W–E to NW–SE direction. Additionally, the highest block (elevations  2100 m) is in the northern part of the valley, the lowest (elevations  1600 m) in the southern part of the valley. Our research shows that the Triglav Lakes Valley directly represents the topographic expression of Paleogene–Neogene thrusting and faulting, having recorded the following geomorphologic evolutionary stages: 1. an Oligocene to early Miocene W-vergent thrusting phase, with steep W-facing slopes of the eastern part of the valley directly representing the thrusting front; and 2. a Neogene-to-present strike–slip faulting in NNE–SSW direction with two bifurcating right-lateral strike–slip systems. We show that the Triglav Lakes Valley almost perfectly mimics the wedge-shaped damage zone located between these faults.     

Subsidence and thermal history of an inverted Late Jurassic‐Early Cretaceous extensional basin (Cameros,North‐central Spain) affected by very low‐ to low‐grade metamorphism

The Cameros Basin (North Spain) is a Late Jurassic‐Early Cretaceous extensional basin, which was inverted during the Cenozoic. It underwent a remarkable thermal evolution, as indicated by the record of anomalous high temperatures in its deposits. In this study, the subsidence and thermal history of the basin is reconstructed, using subsidence analysis and 2D thermal modelling. Tectonic subsidence curves provide evidence of the occurrence of two rapid subsidence phases during the syn‐extensional stage. In the first phase (Tithonian‐Early Berriasian), the largest accommodation space was formed in the central sector of the basin, whereas in the second (Early Barremian‐Early Albian), it was formed in the northern sector. These rapid subsidence phases could correspond to relevant tectonic events affecting the Iberian Plate at that time. By distinguishing between the initial and thermal subsidence and defining their relative magnitudes, Royden's (1986) method was used to estimate the heat flow at the end of the extensional stage. A maximum heat flow of 60–65 mW/m² is estimated, implying only a minor thermal disturbance associated with extension. In contrast with these data, very high vitrinite reflectance, anomalously distributed in some case with respect to the typical depth‐vitrinite reflectance relation, was measured in the central‐northern sector of the basin. Burial and thermal data are used to construct a 2D thermal basin model, to elucidate the role of the processes involved in sediment heating. Calibration of the thermal model with the vitrinite reflectance (%Ro) and fluid inclusion (FI) data indicates that in the central and northern sectors of the basin, an extra heat source, other than a typical rift, is required to explain the observed thermal anomalies. The distribution of the %Ro and FI values in these sectors suggests that the high temperatures and their distribution are related to the circulation of hot fluids. Hot fluids were attributed to the hydrothermal metamorphic events affecting the area during the early post‐extensional and inversion stages of the basin.     

Foredeep palaeobathymetry and subsidence trends during advancing then retreating subduction: the Northern Apennine case (Oligocene‐Miocene,Italy)

The Northern Apennines provide an example of long‐term deep‐water sedimentation in an underfilled pro‐foreland basin first linked to an advancing orogenic wedge and then to a retreating subduction zone during slab rollback. New palaeobathymetric and geohistory analyses of turbidite systems that accumulated in the foredeep during the Oligocene‐Miocene are used to unravel the basin subsidence history during this geodynamic change, and to investigate how it interplayed with sediment supply and basin tectonics in controlling foredeep filling. The results show an estimated ca. 2 km decrease in palaeowater depth at ca. 17 Ma. Moreover, a change in basin subsidence is documented during Langhian time, with an average decompacted subsidence rate, during individual depocentre life, that increased from <0.3 to 0.4–0.6 mm y^?1, together with the appearance of a syndepositional backstripped subsidence bracketed between 0.1 and 0.2 mm y^?1. This change prevented the basin from complete filling during late Miocene and is interpreted as the foredeep response to initial rollback of the downgoing Adriatic slab. Thus, the Northern Apennine system provides an example of a pro‐foreland basin that experienced both a slow‐ and high‐subsidence regime as a consequence of the advancing then retreating evolution of the collisional system.     

Medium‐term fluvial island evolution in a disturbed gravel‐bed river (Piave River,Northeastern Italian Alps)

River islands are defined as discrete areas of woodland vegetation surrounded by either water‐filled channels or exposed gravel. They exhibit some stability and are not submerged during bank‐full flows. The aim of the study is to analyze the dynamics of established, building, and pioneer islands in a 30‐km‐long reach of the gravel‐bed Piave River, which has suffered from intense and multiple human impacts. Plan‐form changes of river features since 1960 were analyzed using aerial photographs, and a LiDAR was used to derive the maximum, minimum and mean elevation of island surfaces, and maximum and mean height of their vegetation. The results suggest that established islands lie at a higher elevation than building and pioneer islands, and have a thicker layer of fine sediments deposited on their surface after big floods. After the exceptional flood in 1966 (RI > 200 years) there was a moderate increase in island numbers and extension, followed by a further increase from 1991, due to a succession of flood events in 1993 and 2002 with RI > 10 years, as well as a change in the human management relating to the control of gravel‐mining activities. The narrowing trend (1960–1999) of the morphological plan form certainly enhanced the chance of islands becoming established and this explains the reduction of the active channel, the increase in established islands and reduction of pioneer islands.     

Palaeolimnological studies of the eutrophication of volcanic Lake Albano (Central Italy)

We use palaeolimnological techniques to reconstruct the eutrophication history of a volcanic lake (Lake Albano, central Italy) over the past three centuries. The presence of annual varves down to the bottom of the core (c. 1700 A.D.) indicated the lack of bioturbation and likely long-term meromixis. Sedimentation rates were estimated by varve counts (calcite/diatom couplets), indicating a mean rate of 0.15 cm yr^–1. The reconstruction of eutrophication was traced using past populations of algal and photosynthetic bacteria (through their fossil pigment), and geochemistry, as well as fossil remains of chironomids. Phaeophorbidea and the red carotenoid astaxanthin were used to detect past zooplankton development.The first sign of trophic change related to human activities is datedc. 1870 A.D. From that period onward a sharp increase of authigenic CaCO₃, nitrogen, N:P ratio, and dinoxanthin, a characteristic carotenoid of Chrysophyceae and Dinophyceae, is observed.Chironomid analyses showed the near absence of a deep water fauna throughout the core length. The populations of chironomid larvae are restricted to oxygenated littoral zones. In fact, the few fossil remains found are primarily of littoral origin, representing shallow water midges that were transported to profundal waters. The reduction of total chironomid in the uppermost layers of the core is to be related to human land uses.