Alpine Laboratory of Palaeomagnetism ALP

Peveragno, Italy

Alpine Laboratory of Palaeomagnetism ALP

Peveragno, Italy
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Manzi V.,Alpine Laboratory of Palaeomagnetism ALP | Roveri M.,Alpine Laboratory of Palaeomagnetism ALP
Geologica Acta | Year: 2013

The sedimentary record straddling the Paleocene-Eocene boundary in the Ager Basin (southern Central Pyrenees) was investigated by combining facies analysis, sequence stratigraphy and stable isotope data, within an interval characterized by a great variability of depositional environments. The occurrence of the Paleocene-Eocene thermal maximum climatic anomaly is tentatively constrained by analogy with its stratigraphic range in the adjacent Tremp-Graus Basin. The main body of the carbon isotope excursion associated with this thermal maximum may be recorded by lacustrine carbonates characterized by a ~ -3‰ shift in δ13C with respect to analogous deposits of Thanetian age. A similar shift is recorded between in situ and resedimented pedogenic carbonates, a feature that suggests the partial erosion of the Paleocene-Eocene boundary in the Ager Basin.

Dela Pierre F.,University of Turin | Clari P.,University of Turin | Natalicchio M.,University of Turin | Ferrando S.,University of Turin | And 8 more authors.
Marine Geology | Year: 2014

The recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the Messinian (late Miocene) Primary Lower Gypsum unit (5.97-5.60. Ma) of the Piedmont basin (NW Italy) provides information on the palaeoenvironmental evolution at precessional insolation maxima. These cyclic layers consist of irregular alternation of cm-thick grey terrigenous laminae and whitish composite packets; the latter is in turn composed of sub mm-thick wrinkled dolomite-rich laminae that alternate with terrigenous ones. Two types of layers can be distinguished: i) peloidal layers, composed of faecal pellets and irregular diatom-rich aggregates, interpreted as marine snow floccules; and ii) filament bearing layers, composed of interwoven filaments up to 150. μm across, corresponding to remains of Beggiatoa-like giant sulphide-oxidising bacteria. By comparison with present-day settings, the peloidal layers are interpreted as flocculent layers, deposited on anoxic sea bottoms, following episodes of phytoplankton bloom in the upper water column. The filament-bearing layers are considered as chemotrophic microbial mats, growing on dysaerobic sea bottoms. The uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface, induced by bacterial sulphate reduction. The laminated layers are the first reported example of a high frequency climate-driven cyclicity in the non-evaporitic portion of the Primary Lower Gypsum unit. Their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle, culminating with gypsum deposition at the onset of the arid phase. © 2014 Elsevier B.V.

Dela Pierre Francesco F.,University of Turin | Dela Pierre Francesco F.,CNR Institute of Geosciences and Earth Resources | Bernardi E.,University of Turin | Cavagna S.,University of Turin | And 13 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

The Alba succession (Tertiary Piedmont Basin, NW Italy) preserves the northernmost record of the Messinian salinity crisis (MSC) and was deposited on the southern margin of a wide wedge-top basin, related to the involvement of the Piedmont Basin in the Apennine compressional tectonics. Pre-MSC sediments consist of a cyclic succession of marine euxinic shales and calcareous marls, deposited under the influence of precession-modulated climate changes, and document the progressive restriction of the basin prior to the onset of the MSC. They are followed by the Primary Lower Gypsum unit (PLG), deposited during the first MSC stage (from 5.96 to 5.60. Ma). These sediments show a clear precession-related cyclic stacking pattern and record the lateral transition from a shallow water marginal setting in the SW to a deeper one in the NE. In marginal settings, six PLG cycles are recognised, truncated by an erosional unconformity placed at the base of the post-evaporitic sediments. The lowermost five cycles are composed of massive and banded selenite beds separated by thin shale intervals. A sharp change, evidenced by the appearance of the branching selenite facies, is recorded by the 6th gypsum bed that represents a distinctive marker bed, here called Sturani key-bed, that can be mapped throughout the study area. Basinward, the lower PLG cycles are transitional to decimetre-thick carbonate-rich layers interbedded to euxinic shales, that are overlain by the Sturani key-bed. Above the marker bed, other seven PLG cycles are present. The gypsum beds form thinner bodies compared to the Sturani key-bed and are characterised by a greater amount of fine-grained terrigenous fraction, suggesting an increase of continental runoff related, in turn, to humid climate conditions at the end of the first MSC stage. PLG cycles are followed by slumped mudstones and clastic gypsum beds that correspond to the resedimented and chaotic facies (Resedimented Lower Gypsum), deposited in the Mediterranean basins during the second MSC stage (from 5.60 to 5.55. Ma). They are in turn overlain by continental and brackish water facies with Lago Mare fossil assemblages, recording the final stage of the MSC.The Messinian succession of Alba provides the opportunity to reconstruct the lateral facies transition between marginal and distal settings and to shed new light on the deep water MSC sedimentary record. Moreover, the appearance of the branching selenite facies from the 6th PLG cycle upward provides a tool for properly placing the Piedmont record in the MSC chronostratigraphic framework, allowing us to investigate the influence of climate gradients on the sedimentary response to the Mediterranean salinity crisis. © 2011 Elsevier B.V.

Dela Pierre F.,University of Turin | Dela Pierre F.,CNR Institute of Geosciences and Earth Resources | Clari P.,University of Turin | Bernardi E.,University of Turin | And 11 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

The seven Messinian microbial carbonate-rich layers cropping out in the Pollenzo section (Tertiary Piedmont Basin, NW Italy) are interbedded with a precession-related cyclic succession composed of euxinic shale/marl couplets and straddle the onset of the Messinian salinity crisis (MSC). A sharp change of sedimentological, compositional and geochemical characteristics was observed from the onset of the MSC onward, suggesting strong differences in the mechanisms responsible for carbonate precipitation. Pre-MSC beds are mainly composed of dolomite and are interpreted as the product of early diagenesis, formed by bacterial sulphate reduction in the shallow subsurface along the sulphate-methane interface. Dolomite precipitation was temporarily enhanced by an upward flux of methane-rich fluids, possibly sourced by gas hydrate destabilisation. Conversely, from the onset of the MSC onward, carbonate beds are thinly laminated and show abundant filaments interpreted as Beggiatoa-like bacteria, while calcite (and aragonite) are the dominant authigenic phases. These beds are interpreted as microbialites, resulting from the lithification of chemotrophic bacterial mats dominated by sulphide-oxidizing bacteria. The carbonate necessary for their preservation was provided by bacterial sulphate reduction. These microbialites, that appear as the deeper water counterpart of bottom-grown selenite layers deposited in the marginal part of the basin, formed on an anoxic sea bottom under a density stratified water column. The high sulphate concentration in the pore waters, related to the presence of concentrated brines and to the regeneration of sulphate by sulphide-oxidizing bacteria, is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite. Finally, the sharp shift towards negative δ 18O values of carbonates, observed from the onset of the MSC onward, was probably related to fractionation processes operated by sulphate-reducing bacterial communities in the pore waters. This suggests that care must be taken, when dealing with microbial carbonates, in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass. In conclusion, this study suggests that the onset of the MSC had a strong impact on microbial populations governing carbonate precipitation, in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation. © 2012 Elsevier B.V.

Manzi V.,University of Parma | Manzi V.,Alpine Laboratory of Palaeomagnetism ALP | Gennari R.,University of Parma | Gennari R.,Alpine Laboratory of Palaeomagnetism ALP | And 5 more authors.
Journal of Sedimentary Research | Year: 2012

The deposition of varved sedimentary sequences is usually controlled by climate conditions. The study of two late Miocene evaporite successions (one halite and the other gypsum) consisting of annual varves has been carried out to reconstruct the paleoclimatic and paleoenvironmental conditions existing during the acme of the Messinian salinity crisis, ∼ 6 Ma, when thick evaporite deposits accumulated on the floor of the Mediterranean basin. Spectral analyses of these varved evaporitic successions reveal significant periodicity peaks at around 3-5, 9, 11-13, 20-27 and 50-100 yr. A comparison with modern precipitation data in the western Mediterranean shows that during the acme of the Messinian salinity crisis the climate was not in a permanent evaporitic stage, but in a dynamic situation where evaporite deposition was controlled by quasi-periodic climate oscillations with similarity to modern analogs including Quasi-Biennial Oscillation, El Niño Southern Oscillation, and decadal to secular lunar- and solar-induced cycles. Particularly we found a significant quasi-decadal oscillation with a prominent 9-year peak that is commonly also found in modern temperature records and is present in the contemporary Atlantic Multidecadal Oscillation (AMO) index and Pacific Decadal Oscillation (PDO) index. These cyclicities are common to both ancient and modern climate records because they can be associated with solar and solar-lunar tidal cycles. During the Messinian the Mediterranean basin as well as the global ocean were characterized by different configurations than at present, in terms of continent distribution, ocean size, geography, hydrological connections, and ice-sheet volumes. The recognition of modern-style climate oscillations during the Messinian suggests that, although local geographic factors acted as pre-conditioning factors turning the Mediterranean Sea into a giant brine pool, external climate forcings, regulated by solar- lunar cycles and largely independent from local geographic factors, modulated the deposition of the evaporites. Copyright © 2012, SEPM (Society for Sedimentary Geology).

Boschetti T.,University of Parma | Manzi V.,University of Parma | Manzi V.,Alpine Laboratory of Palaeomagnetism ALP | Toscani L.,University of Parma
Aquatic Geochemistry | Year: 2013

In natural resource exploration, Ca-Cl basinal brines are important for understanding the origin and spatial and temporal distribution of hydrocarbons and sedimentary ore deposits. Little attention has been paid to the possible connection between fossil basinal brines and paleo-seawaters and to the implications for reconstructing paleo-seawater compositions. Secular variations of Ca/Mg and Ca/Sr ratios in seawater have been documented mainly using fluid inclusions in halite, calcareous fossils and mineral analyses. However, brines and other sedimentary records connected to paleo-seawater or its evaporated residues may be chemically affected by burial diagenesis or the effects of continental waters of meteoric origin, thus complicating interpretations of the analytical results. To investigate these effects on fluids and minerals related to the Messinian salinity crisis of the Mediterranean basin, we re-evaluate published data from: (1) brackish-to-brine waters from onshore (Northern Apennine foredeep; Levantine basin) and offshore (porewaters from the Deep Sea Drilling Project); (2) Messinian parental seawater deduced from calcareous fossils, fluid inclusions and sulfate minerals; (3) meteoric waters dissolving evaporites. The compositional trends related to seawater evaporation, diagenesis and mixing that affect the Ca/Mg and Ca/Sr molar ratios of the basinal brines are effectively discriminated on a binary plot depicting the proper fields for seawater and meteoric-derived fluids. Brines showing stronger dolomitization start from Ca/Mg and Ca/Sr molar ratios of Messinian seawater deduced from the published analysis of fluid inclusions and open ocean fossils, that are therefore here validated ex post. © 2013 Springer Science+Business Media Dordrecht.

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