School of Earth Sciences - Research Publications
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ItemNew Chronological Constraints from Hypogean Deposits for Late Pliocene to Recent Morphotectonic History of the Alpi Apuane (NW Tuscany, Italy)(MDPI, 2021-02)A sedimentary sequence of fluvial deposits preserved in the Corchia Cave (Alpi Apuane) provides new chronological constraints for the evolution of the cave system and the timing and rate of uplift of this sector of the Alpi Apuane since the late Pliocene. Supported by magnetostratigraphic analysis performed on fine-grained fluvial deposits, and by radiometric dating of speleothems, we suggest that the deposition of fluvial sediments occurred between ~1.6–1.2 Ma. This implies that the host volume of rock was already located close to the local base level, adding key information about the recent tectonic evolution of the Alpi Apuane. A few before ~1 Ma, an erosive phase occurred due to the base-level lowering, followed by continuous speleothem deposition since at least 0.97 Ma. From that time, Monte Corchia uplifted at a maximum rate of ~0.5 mm/year, which is consistent with isostatic uplift mainly driven by erosional unloading. The petrographical study of the fluvial deposits highlights the presence of material derived from the erosion of rocks that today are absent in the cave’s catchment area, suggesting a different surface morphology during the Early Pleistocene. This study highlights the potential of cave sediments as archives for reconstructing the uplift history of mountain ranges.
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ItemNo Preview AvailableStructure of V-ATPase from the mammalian brain.(american association for the advancement of science, 2020-03-13)In neurons, the loading of neurotransmitters into synaptic vesicles uses energy from proton-pumping vesicular- or vacuolar-type adenosine triphosphatases (V-ATPases). These membrane protein complexes possess numerous subunit isoforms, which complicates their analysis. We isolated homogeneous rat brain V-ATPase through its interaction with SidK, a Legionella pneumophila effector protein. Cryo-electron microscopy allowed the construction of an atomic model, defining the enzyme's ATP:proton ratio as 3:10 and revealing a homolog of yeast subunit f in the membrane region, which we tentatively identify as RNAseK. The c ring encloses the transmembrane anchors for cleaved ATP6AP1/Ac45 and ATP6AP2/PRR, the latter of which is the (pro)renin receptor that, in other contexts, is involved in both Wnt signaling and the renin-angiotensin system that regulates blood pressure. This structure shows how ATP6AP1/Ac45 and ATP6AP2/PRR enable assembly of the enzyme's catalytic and membrane regions.
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ItemNo Preview AvailablePersistent influence of obliquity on ice age terminations since the Middle Pleistocene transition(AMER ASSOC ADVANCEMENT SCIENCE, 2020-03-13)Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration.
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ItemMagnesium in subaqueous speleothems as a potential palaeotemperature proxy(NATURE RESEARCH, 2020-10-06)Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles.