Petrographic signature of gravel fraction from late Quaternary glacigenic sediments in the Ross Sea (Antarctica): Implications for source terranes and Neogene glacial reconstructions

The Ross Embayment is a key region to study the dynamics of the ice sheets during colder and warmer than present climatic conditions, because both the East and West Antarctic Ice sheets shed into the Ross Sea. Numerical modeling and reconstructions of the paleo ice flows during the Last Glacial Maximum show variable contribution of East and West Antarctic Ice sheets based on a variety of proxies.. In this study, we present the first petrographic and minero-chemical investigation of gravel-sized fraction of Last Glacial Maximum subglacial-glacimarine sediments collected with piston cores in a W-E transect across the Ross Sea. The clasts petrographic features are compared with outcropping geology to individuate the sediment source regions. The gravel content of the glacigenic diamictite was classified on the basis of petrographic and minero-chemical features, and three main petrofacies were identified. They reflect changes in the basement geology of the source regions, allowing the reconstruction of paleo ice flow pattern and their comparison with scenarios built up with other datasets. Moreover, the comparison with the Oligocene to Pleistocene glacigenic sediments provided information about the changes of the gravel signature across the Ross Sea and the erosion history of the source regions during Cenozoic

Geological map of Tuscany (Italy)

The main map covers the territory of the Tuscany Region, in Central Italy and shows the main stratigraphic and tectonic features of the internal part of the Northern Apennines. This is characterized by nappe superposition well exposed in the Apennine chain (in the eastern part of the map), as well the effects of post-nappe extensional tectonics, originating in Miocene-Pliocene and younger basins bordered by metamorphic core complexes, covering most of the central and southern part of the Region. The map is at 1:300,000 scale and is based on 1:10,000 field mapping

Geology of the ‘Coltre della Val Marecchia’ (Romagna-Marche Northern Apennines, Italy)

A detailed geological map at 1:50,000 scale of the Marecchia Valley and adjoining areas (Northern Apennines, NA, Italy) is presented here. The Marecchia Valley represents a geological ‘unicum’ for the NA and it has been the focus of scientific debate for a long time, due to the occurrence in the area of the ‘Coltre della Val Marecchia (CVM)’, a complex stack of allochthonous and semi-allochthonous units emplaced in a foredeep basin during the Late Miocene to Early Pliocene. In order to clarify the geological evolution for this area, the lithostratigraphic relationships and the tectonic framework have been studied, allowing better understanding of the complex relationships between tectonics and sedimentation. The main result has been a new evolutionary framework for this sector of the orogen during the Late Miocene-Early Pliocene. Several new findings about the geological-structural setting and stratigraphy, result from the geological map presented here. These are overall supported by stratigraphic and tectonic evidence, which suggest time and modes of the CVM allochthonous emplacement within the Messinian-early Pliocene foredeep successions. Relationships between the allochthonous and autochthonous formations allowed recognition of two different bodies in the CVM, gravitationally emplaced following different trajectories and timing

Miocene climate cooling and aridification of Antarctica may have enhanced syn-extensional magmatism in the western Ross Sea

Continental rift systems are commonly characterized by volcanism with parental basaltic magmas sourced from the mantle. Erosion of the rift shoulders and sedimentation in the adjacent basins can affect the stress and thermal fields at depth, thereby affecting partial mantle melting. However, the sensitivity of magmatic activity to such surface forcing is elusive. Geological observations from the western Ross Sea, Antarctica, suggest rift onset in the Cretaceous with a transition from wide-rifting to narrow-rifting at the boundary between the Antarctic craton and the Transantarctic Mountains. Miocene climate cooling during rifting in the western Ross Sea, in addition, leads to an abrupt decrease in sedimentation rate, synchronous to the emplacement of the McMurdo Volcanic Group. This represents the largest alkali province worldwide, extending both inland and offshore of Transantarctic Mountains and western Ross Sea, respectively. Here, we use coupled thermo-mechanical and landscape evolution numerical modeling to quantify melt production in slowly stretching rift basins due to changes in erosion/deposition rates. The model combines visco-elasto-plastic deformation of the lithosphere and underlying mantle during extension, partial rock melting, and linear hillslope diffusion of the surface topography. The parametric study covers a range of slow extension rates, crustal thicknesses, mantle potential temperatures and diffusion coefficients. Numerical simulations successfully reproduce the ~150–200-km-wide extension of western Ross Sea and Miocene-to-present asthenospheric melt production (McMurdo Volcanic Group). Results further show that slow rifts magmatism is highly sensitive to sediment deposition within the basin, which inhibits mantle decompression melting and delays the crustal breakup. Regional climate-driven sedimentation rate changes are thus likely to have affected the syn-rift magmatic history of the western Ross Sea, Antarctica, supporting the relevance of interactions between surface and deep-seated processes across extensional settings

Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene

Sand-rich turbidite system of the Late Oligocene Northern Apennines foredeep: physical stratigraphy and architecture of the "Macigno costiero" (coastal Tuscany, Italy

The 'Macigno costiero' turbidite system characterized the oldest foredeep clastic wedge of the Northern Apennines during the Late Oligocene collisional phase. The cropping-out thickness is about 500m. The features of the 'Macigno costiero' indicate a sand-rich, low-efficiency turbidite system. The system developed within a partially confined basin, which was part of a complex foredeep system. The stacking pattern of the turbidite system was determined through the analysis of facies and physical stratigraphy. It consists of a succession organized in sedimentary units, which are characterized by particular associations of facies linked to distinct depositional environments. Several architectural elements are seen: (1) unchannelized and channelized lobes; (2) distributary channels with channel-fill, overbank and channel-margin deposits; (3) main channel with channel-fill, channel-margin and interchannel deposits. Five turbidite stages were identified. From the bottom up they consist of four lobe stages and one proximal channel stage. The lobe stages are characterized by thickening-coarsening upward trends, from distal lobes to proximal lobes up to the channel-lobe transition zone. The uppermost, fifth stage is linked to a main channel complex with stacked channel-fill, channel-margin and interchannel deposits. This final stage also marks the maximum progradation of the system up to its closure due to the synsedimentary overthrusting of the orogenic wedge

Compositional evolution of the Macigno Fm. of southern Tuscany along a transect from the Tuscan coast to the Chianti Hills

The Macigno deep-sea turbidite unit was part of the diachronically migrating foredeep system that characterized the collisional phases of the Apennine orogen at the Oligocene-Miocene transition. Detrital modes of the Macigno sandstones along a transect transversal to the chain in southern Tuscany show homogeneity in the framework composition but differences in the composition of finegrained lithics. Three petrofacies characterize this portion of the foredeep system: the «petrofacies A», present in the innermost successions (Baratti area), shows considerable amounts of carbonate (CE) and volcanic (Lv) lithics; the «petrofacies B», occurring in the central section of the studied transect (Sassetta area) shows low CE and high Lv content; the «petrofacies C», seen in the external and eastern sections (Poggio Ritrovoli and Chianti area), has low CE and Lv contents. The modal analysis indicates that the occurrence of volcanic and carbonate grains tends to decrease from the internal to the external portions of the Macigno. The source of the «petrofacies A» sandstones was an area characterized by crystalline and volcanic terranes, associated with carbonate covers; they could be represented by the Corsica-Sardinia Massif. In contrast, the source of the «second » and «third» petrofacies sandstones is thought to be mainly in basement domains such as the Western-Central Alps crystalline terranes

The early depositional phases of the northern Apennine foredeep-thrust belt system: implications from the "Macigno costiero" (Late Oligocene, Italy)

The late Chattian "Macigno costiero" represents the innermost and the oldest portion of the well developed siliciclastic wedge of the migrating Oligo- Miocene foredeep-thrust-belt system of the Northern Apennine. Its stratigraphic features help to understand the early phases of the sin-collisional sedimentation and the evolution of such a thrust belt. In the turbiditic siliciclastic sequence, carbonates were found at different stratigraphic levels (chaotic-debris flow key-level, calcareous turbidites and Subligurian olistostromes and olistoliths). Stratigraphical studies of the sequence based on facies analysis, petrographical observations and biostratigraphical analysis of calcareous nannofossils allow to suggest some hypotheses of the palaeogeographic setting and the evolution of the foredeep-thrust belt system. The vertical distribution of the sediments and their sedimentological characters show a low efficiency sand-rich turbidite system (sensu Mutti and Normark, 1987), characterised by a prograding fan terminated by the emplacement of slices of the orogenic wedge. Olistostromes and olistoliths found in the turbidite succession were the precursor of the allochthonous nappe. The proposed hypothesis shows that turbidite sediments were probably fed transversally to the basin, from a shallow marine shelf adjacent to a crystalline basement. The "Macigno costiero" was deposited in an internal position of the foredeep system

The early depositional phases of the northern Apennine foredeep-thrust belt system: implications from the "Macigno costiero" (Late Oligocene, Italy)

The late Chattian "Macigno costiero" represents the innermost and the oldest portion of the well developed siliciclastic wedge of the migrating Oligo- Miocene foredeep-thrust-belt system of the Northern Apennine. Its stratigraphic features help to understand the early phases of the sin-collisional sedimentation and the evolution of such a thrust belt. In the turbiditic siliciclastic sequence, carbonates were found at different stratigraphic levels (chaotic-debris flow key-level, calcareous turbidites and Subligurian olistostromes and olistoliths). Stratigraphical studies of the sequence based on facies analysis, petrographical observations and biostratigraphical analysis of calcareous nannofossils allow to suggest some hypotheses of the palaeogeographic setting and the evolution of the foredeep-thrust belt system. The vertical distribution of the sediments and their sedimentological characters show a low efficiency sand-rich turbidite system (sensu Mutti and Normark, 1987), characterised by a prograding fan terminated by the emplacement of slices of the orogenic wedge. Olistostromes and olistoliths found in the turbidite succession were the precursor of the allochthonous nappe. The proposed hypothesis shows that turbidite sediments were probably fed transversally to the basin, from a shallow marine shelf adjacent to a crystalline basement. The "Macigno costiero" was deposited in an internal position of the foredeep system

Sedimentation in the Northern Apennines-Corsica tectonic knot (Northern Tyrrhenian Sea, Central Mediterranean): offshore drilling data from the Elba-Pianosa Ridge

The Northern Tyrrhenian Sea is located on the collisional zone between the Alpine Corsica and the Northern Apennines and is a key area for gaining a better understanding of the complex relationships between these two systems. The knowledge of the wide offshore part of this zone, located between Corsica (France) and mainland Italy, is based primarily on the analysis of several seismic profiles tied to the outcropping geology and unpublished preliminary reports of few offshore wells. The here presented study of two offshore wells provides a revision of the sedimentology, biostratigraphy and petrography of the thick, mainly siliciclastic, Tertiary successions (about 3,600 m) composing the Elba–Pianosa Ridge (EPR), a structural/ morphological high separating the Tuscan Shelf to the east from the Corsica Basin to the west. A comparison with similar deposits cropping out in the surrounding onshore areas (Northern Apennines, Corsica, Tuscan Archipelago, Piedmont Tertiary Basin) provides additional constraints for refinement of the complex geodynamic and regional setting in which the EPR evolved