Hot shale in an ice world : paleoceanographic evolution of the northern Godwana margin during the Early paleozoic (Tanezzuft Formation, Tunisia)

The Tanezzuft Formation deposited in marine periglacial conditions on the northern Gondwana margin during the end of the "ice-house" climate that characterized the lowermost Silurian. The basal part of this sedimentary sequence is characterized by organic-rich facies with locally very high measured Total Organic Carbon (TOC) content up to values greater than 20%. While deposition of organic-rich sediments during greenhouse time interval is well known, deposition of black shales during ice-house conditions is poorly documented. The extraordinary paleoceanographic conditions that led to the accumulation and preservation of enormous amounts of organic matter in periglacial settings, makes this formation an atypical example of black shales deposition.The study area is situated on the North African Platform in southern Tunisia, on the northern flank of the Ghadames Basin. Petrophysical logs, biostratigraphic, organic- and inorganic-geochemical data from nine wells, are here integrated with the aim of reconstructing the depositional history of the Tanezzuft Formation and the role played by organic matter production, preservation and dilution through time. Data indicate that dilution - that is, depositional style and framework - had an important control on lateral and vertical distribution of the C organic-rich facies. TOC and Hydrogen Index (HI) maxima are found in correspondence of the main transgressive phases, with repetitive stacking patterns strongly associated with source rock properties. Organic matter production, as observed by detailed palynofacies analysis, was mainly marine in nature, with important contribution by Amorphous Organic Matter, Leiosphaeridia/Tasmanaceae and minor amounts of graptolites fragments. Geochemical data indicate that the organic-richest interval ("Hot Shale") of the Tanezzuft Formation deposited under severe anoxic conditions that resulted in enhanced organic matter preservation at the sea-floor. OF-Mod 3D, an organic facies modelling software tool (by SINTEF), is used in order to reconstruct and quantify the peculiar processes that controlled the exceptional accumulation of organic matter at the time of deposition. Modelling results indicate that water stratification was the most plausible process that drove organic-matter sedimentation under mesotrophic conditions. Density stratification was probably controlled by the deglaciation phase after the Hirnantian glaciation and/or by the flooded complex basin physiography that induced an inefficient circulation of the water masses. The complete recovery from these extreme paleoceanographic conditions implied progressive processes that took several hundred thousand years

Multistage dolomitization and distribution of dolomitized bodies in Early Jurassic carbonate platforms (Southern Alps, Italy)

The Early Jurassic dolomitized carbonates are a hydrocarbon exploration target in Northern Italy. Of these carbonates, the Liassic Albenza Formation platform and the overlying Sedrina Formation shelf were studied to define a pervasive dolomitization model and to shed light on dolomite distribution in the subsurface. Field work, as well as analyses of well cores, stable isotopes, trace elements and fluid inclusions, was carried out on the outcropping thrust belt and sub-surface deformed foreland of the Southern Alps. Petrographic analyses showed a first, pervasive, replacement dolomitization phase (D1) followed by volumetrically less important dolomite cement precipitation phases (D2, D3 and D4). The delta(18)O values fall between -8.2 parts per thousand and 0.1 parts per thousand Vienna-Pee Dee Belemnite with the more depleted samples belonging to dolomite cement-rich dolostones; the delta(13)C ranges from 2.6 parts per thousand to 3.7 parts per thousand Vienna-Pee Dee Belemnite. Analysis of trace elements showed different Fe and Mn contents in the sub-surface and outcropping dolostones, and a higher Fe in the younger dolomite cements. An increase in the precipitation temperature (up to 130 degrees C from fluid inclusion data) and a decrease in diagenetic fluid salinity (from sea water to brackish) are observed from the first pervasive replacement dolomite to the dolomite cement phases. Field observations indicate that, in the Albenza Formation, dolomitization was limited to palaeohighs or faulted platform margins in the Early Jurassic carbonates. The pervasive replacement phase is interpreted based on a 'compaction model'; the formation fluids expelled from compacting basinal carbonates could have funnelled along faults into permeable palaeohighs. The high homogenization temperature of the dolomite cements and decreased salinities indicate precipitation at great depth with an influx of meteoric water. These data, along with the thermal history, suggest that the dolomite cements precipitated according to the 'tectonic squeegee' dolomitization model. The dolomite precipitation temperature was set against the thermal history of the carbonate platform to interpret the timing of dolomite precipitation. The dolomite precipitation temperatures (90 to 100 degrees C) were reached in the studied formations first in the thrust fold belt (Early Tertiary, 60 Ma), and then in the foreland succession during the Late Tertiary (10 Ma). This observation suggests that the dolomite precipitation fronts moved southwards over time, recording a 'diagenetic wave' linked to the migration of the orogenic system. Observations suggest that the porosity increased during the first phase of replacement dolomitization while the dolomite cementation phases partially occluded the pores. The distribution of porous dolomitized bodies is therefore linked to the 'compaction dolomitization' model

Trattamento efficace di chilotorace grave e persistente dopo trauma toracico

Post-traumatic chylothorax needs surgical approach when conservative treatment is not successful to reduce chyle leakage. Thoracic duct ligation requires thoracoscopic or thoracotomic access. The authors report on a surgical thoracotomic approach to a severe and unremitting thoracic duct lesion after IX and X ribs and vertebral fractures

Abrupt and persistent shutdown of the thermohaline forcing during MIS5e in the Adriatic Sea: Insights from shallow-water sapropel sediments

During the Quaternary, the Eastern Mediterranean Sea (EMS) experienced cyclical events of stagnation driven by natural climate variability. The resulting deoxygenation left well-preserved evidence in the sedimentary record as organic carbon-rich deposits referred to as sapropels. Although drastic modifications in the degree of dense-water formation over the EMS shelves exerted first-order control on the deoxygenation, most of the focus has been traditionally placed on the deep EMS. To provide a shallow-water perspective, here we investigated the sapropel S5 in the Adriatic shelf (borehole PRAD1-2) deposited during MIS5e (129-116 ka). This archive is strategically located in a region where the Northern Adriatic Dense Water (NAdDW) interacts with the seabed before cascading across the continental slope. We used Zr/Rb and MgO/Al2O3 to assess bottom current energy and north-to-south sediment transport dynamics, both regulated by the changes in NAdDW production intensity. In addition, we used stable isotopes (δ13C and δ18O) of foraminifera, redox sensitive elements (U, Mo and Sb), foraminifera assemblages as well as alkenones to reconstruct the paleo-environmental conditions during the S5 formation.Our study provides an unprecedented reconstruction of the physical forcing controlling the deoxygenation during the S5 formation. Results reveal that the shutdown of the NAdDW occurred in a few centuries (0.67 ± 0.22 kyrs), when freshening of surface waters combined with warming of winter temperatures mutually hampered the dense water formation. A few centuries after the NAdDW shutdown, the Adriatic shelf experienced euxinic waters for about 2 kyrs followed by a progressive reoxygenation that lasted 4 kyrs. We explain this second phase as a general recovery driven by increased surface salinity over the EMS combined with winter cooling. This favoured surface water mixing without, however, producing dense water in the Northern Adriatic and thus collectively the interruption of the dense water production lasted for 6 kyrs since the onset of MIS5e. Overall, our finding highlights that the thermohaline forcing responded to climate change much quicker than inferred by earlier studies that suggested instead a millennial-scale prelude necessary to develop stagnation. In addition, our results provide solid evidence about the large-scale impact of the deoxygenation during S5 that is capable of invading the continental shelf. Comparison with the latest regional models illustrates how none of the future simulations covering different climate change scenarios reproduces an event over the EMS margins comparable with what described in this study