Renata G Lucchi

Mid-late Pleistocene glacimarine sedimentary processes of a high-latitude, deep-sea sediment drift (Antarctic Peninsula Pacific margin)

The effects of glaciation on sediment drifts is recognised from marked sedimentary facies variation in deep sea cores taken from the continental rise of the Antarctic Peninsula Pacific margin. Nineteen sediment cores were visually described, logged for magnetic susceptibility, and X-radiographed. About 1000 analyses were performed for grain size, clay minerals and biostratigraphy (foraminifera, nannofossils and diatoms). Four sediment types associated with distinct sedimentary processes are recognised based on textural/compositional analysis. (1) Hemipelagic mud forms the bulk of the interglacial sediment, and accumulated from the pelagic settling of bioclasts and ice-rafted/wind-transported detritus. (2) Terrigenous mud forms the bulk of the glacial sediment, and accumulated from a combination of sedimentary processes including turbidity currents, turbid plumes, and bottom current reworking of nepheloid layers. (3) Silty deposits occurring as laminated layers and lenses, represent the lateral spillout of low-density turbidity currents. (4) Lastly, glacial/interglacial gravelly mud layers derive from settling of ice-rafted detritus. Five depositional settings are interpreted within sediment Drift 7, each characterised by the dominance/interaction of one or several depositional processes. The repetitive succession of typical sedimentary facies is inferred to reflect a sequence of four climatic stages (glaciation, glacial, deglaciation, and interglacial), each one characterised by a distinctive clay mineral assemblage and bioclastic content. Variations in clay mineral assemblage within interglacial stage 5 (core SED-06) suggest minor colder climatic fluctuations, possibly correlatable with substages 5a to 5e.

Glacial contourites on the Antarctic Peninsula margin: insight for palaeoenvironmental and palaeoclimatic conditions

Abstract Deep-sea finely laminated and barren glacial sediments occur in the sediment drift field offshore the Pacific margin of the Antarctic Peninsula where a weak contour current flows at present to the SW. Atypical sedimentary facies were related to the coexistence and interaction of different sedimentary processes. Three ‘end-members’ of radiograph facies were defined to represent the sedimentary sequences controlled by a dominant process, as follows. (1) Direct influence of turbidity currents on sedimentation is observed in the area surrounding the Alexander Channel system with silty layers interbedded with laminated mud free of ice-rafted debris (IRD). (2) Distal meltwater turbid flows dominate the more proximal area of the top plateau with structureless and coarser-grained sediments containing IRD. (3) Along the crest of the drift, persistent weak bottom currents control the deposition of fine-grained sediments conveyed into the system through other processes. These laminated sediments contain IRD and are, atypically, not bioturbated, because of unusual, climatically related, environmental conditions of suppressed primary productivity and oxygen-reduced deep waters. These glacial contourites were observed on most of the Antarctic margin with the exception of the areas in which polynyas were maintained during the glacial stages. Glacial contourites can be used as a proxy to define temporal and spatial extension of the Antarctic sea-ice.

Biostratigraphic characterization and Quaternary microfossil palaeoecology in sediment drifts west of the Antarctic Peninsula – implications for cyclic glacial–interglacial deposition

Abstract The SEDANO Project recovered 19 gravity cores on sediment drifts from the Pacific continental margin of the Antarctic Peninsula [Camerlenghi et al. (1997a) High-resolution terrigenous sedimentary record of the sediment drifts on the Antarctic Peninsula Pacific margin. In: Ricci, C.A. (Ed.), The Antarctic region. Museo Nazionale dell’Antartide, Siena, pp. 705–710]. Fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils, diatoms, planktonic and benthic foraminifera, framed in a depositional process reconstruction. Barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles, respectively. Analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles. The unit boundaries were drawn more accurately by means of the microfossil distribution. On the basis of micropalaeontological and sedimentological evidence, Interglacial Unit C is correlated to Oxygen Isotope Stage 5, thus dating the unit boundaries at 127 and 70 ka. Peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment. A calcareous nannofossil cold-taxa association is present in most cores examined, and its consistent distribution within Interglacial Unit C indicates key environmental relationships. The occurrence of calcareous nannofossils has been related to temperature tolerance, sea-ice cover reduction, nutrient availability, and factors limiting primary productivity. Our results confirm that coccolithophorids occurred at southern high latitudes, in the western marginal basins of the Antarctic Peninsula, during short periods of the Late Quaternary. A foraminiferal assemblage, made up of sinistral Neogloboquadrina pachyderma and few benthics, occurs only in interglacial units. Correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes.

Recent Submarine Landslides on the Continental Slope of Storfjorden and Kveithola Trough-Mouth Fans (North West Barents Sea)

Up to 12 submarine landslides retain a morphological evidence as concave amphitheater-like depressions of various sizes on the middle and upper slope of the Storfjorden and Kveithola Trough-Mouth Fans (TMFs), NW Barents Sea. The largest of them show lateral scarps 35–40 m high that reach the continental shelf edge and cover an area of at least 1,120 km2. Submarine landslides are translational, with headwall and laterals scarps clearly cut into Last Glacial Maximum debris flows deposits. The largest landslides seem to be rooted at the base of a terrigenous/hemipelagic sedimentary unit inferred to be of Middle Weichselian age (Marine Isotopic Stage 3). Stratigraphic, lithological and geotechnical observations suggest that the rapid deposition of a thick sequence of fine-grained, high water content interlaminate plumites is the most important controlling factors in the generation of submarine landslides on the southern Storfjorden and Kveithola TMFs.

One Million Years of Climatic Generated Landslide Events on the Northwestern Barents Sea Continental Margin

Relatively recent, shallow landslides are imaged both on swath bathymetry, sub-bottom and multichannel seismic reflection (MCS) data from the upper-middle continental slope on the Storfjorden and Kveithola Trough Mouth Fans, NW Barents Sea margin. Giant paleo-landslide deposits, detected only by MCS profiles, are characterized by chaotic acoustic units up to about 250 m thick on the lower continental slope. The thickest, oldest landslide, dated between 1 and 0.8 Ma, took place just after the large-scale intensification of glaciation in the Barents Sea. The apparent spatial coincidence of landslides and channels with the boundary between the two fan systems, that are generated due to huge quantities of sediments transported to the continental slope by paleo-ice streams, suggests a common controlling climatic process for their development. Most probably the slides are related to the abundance of basal meltwater beneath the ice sheet, which in addition to determining ice stream motion and lubrication also influences the behavior of mass wasting processes.

A Holocene paleosecular variation record from the northwestern Barents Sea continental margin

A high-resolution paleomagnetic and rock magnetic study has been carried out on sediment cores collected in glaciomarine silty-clay sequences from the continental shelf and slope of the southern Storfjorden trough-mouth fan, on the northwestern Barents Sea continental margin. The Storfjorden sedimentary system was investigated during the SVAIS and EGLACOM cruises, when 10 gravity cores, with a variable length from 1.03 m to 6.41 m, were retrieved. Accelerator mass spectrometry (AMS) 14C analyses on 24 samples indicate that the cores span a time interval that includes the Holocene, the last deglaciation phase and in some cores the last glacial maximum. The sediments carry a well-defined characteristic remanent magnetization and have a valuable potential to reconstruct the paleosecular variation (PSV) of the geomagnetic field, including relative paleointensity (RPI) variations. The paleomagnetic data allow reconstruction of past dynamics and amplitude of the geomagnetic field variations at high northern latitudes (75°–76° N). At the same time, the rock magnetic and paleomagnetic data allow a high-resolution correlation of the sedimentary sequences and a refinement of their preliminary age models. The Holocene PSV and RPI records appear particularly sound, since they are consistent between cores and they can be correlated to the closest regional stacking curves (UK PSV, FENNOSTACK and FENNORPIS) and global geomagnetic model for the last 7 ka (CALS7k.2). The computed amplitude of secular variation is lower than that outlined by some geomagnetic field models, suggesting that it has been almost independent from latitude during the Holocene.

Drilling Glacial Deposits in Offshore Polar Regions

High latitudes are of fundamental importance in the Earths climate system—they house ice sheets that govern global sea level heights, influence how much solar energy is reflected back to space, and create deep and bottom waters that drive the oceans ability to circulate energy and nutrients across the globe.

Slope Instability of Glaciated Continental Margins: Constraints from Permeability-Compressibility Tests and Hydrogeological Modeling Off Storfjorden, NW Barents Sea

Climate variations control sediment supply to the continental slope as well as glacial advances and retreats, which (a) cause significant stress changes in the sedimentary column and redistribution of interstitial fluids, (b) induce a particular margin stratigraphic pattern and permeability architecture and (c) are at the origin of isostatic adjustments that may reactivate faults. We test this hypothesis using a combination of geophysical and geotechnical data from the Storfjorden Trough Mouth Fan, off southern Svalbard. The results of compressibility and permeability testing are used together with margin stratigraphic models obtained from seismic reflection data, as input for numerical finite elements models to understand focusing of interstitial fluids in glaciated continental margins and influence on timing and location of submarine slope failure. Available results indicate values of overpressure of 0.23–0.5 (slope-shelf) that persist to present-day. This overpressure started to develop in response to onset of Pleistocene glaciations and reduced by half the factor of safety of the continental slope.

Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream

The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.

Polar marine diatoms: key markersfor Cenozoic environmental shifts. Sedimentary and paleo-environmental reportsfrom Antarctic continental margin (Ross Sea, Wilkes Land and Prydz Bay)

Lucchi, Renata G. ... et. al.-- 87° Congresso della Societa Geologica Italiana e 90° Congresso della Societa Italiana di Mineralogia e Petrologia, The Future of the Italian Geosciences - The Italian Geosciences of the Future, 10-12 September 2014, Milan, Italy.-- 1 pageThe Montellina Spring (370 m a.s.l.) represents an example of groundwater resource in mountain region. It is a significant source of drinking water located in the right side of the Dora Baltea Valley (Northwestern Italy), SW of Quincinetto town. This spring shows a morphological location along a ridge, 400 m from the Renanchio Torrent in the lower sector of the slope. The spring was investigated using various methodologies as geological survey, supported by photo interpretation, structural reconstruction, NaCl and fluorescent tracer tests, discharge measurements. This multidisciplinary approach, necessary due to the complex geological setting, is required for the importance of the Montellina Spring. It is interesting in the hydrogeological context of Western Alps for its high discharge, relatively constant over time (average 150 l/s), and for its location outside a fluvial incision and suspended about 40 m above the Dora Baltea valley floor (Lasagna et al. 2013). According to the geological setting, the hydrogeological reconstruction of the area suggests that the large amount of groundwater in the basin is essentially favoured by a highly fractured bedrock, covered by wide and thick bodies of glacial and gravitational sediments. The emergence of the water along the slope, in the Montellina Spring, is essentially due to a change of permeability between the deep bedrock and the shallow bedrock and/or surficial sediments. The deep bedrock, showing closed fractures and/or fractures filled by glacial deposits, is slightly permeable. The shallow bedrock, strongly loosened as result of gravitational phenomena, and the local gravitational sediments are, on the contrary, highly permeable. The concentration of water at the spring is due to several reasons. a) The spring is immediately downward a detachment niche, dipping towards the spring, that essentially drains the water connected to the change of permeability in the bedrock. b) It is along an important fracture, that carries a part of the losses of the Renanchio Torrent. c) Finally, it is favored by the visible and buried morphology. Although it is located along a ridge, the spring occurs in a small depression between a moraine and a landslide body. It also can be favored by the likely concave trend of buried base of the landslide. At last, tracer tests of the Renanchio Torrent water with fluorescent tracer are performed, with a continuous monitoring in the Montellina Spring. The surveys permit to verify and quantify the spring and torrent hydrogeological relationship, suggesting that only a small fraction of stream losses feeds the spring.