Relationships between Holocene sea-level variations,trophic development,and climatic change in Negra Lagoon,Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Negra Lagoon, a 142 km² coastal lagoon in southern Uruguay. Using a sediment core that extended to the early Holocene, analyses of organic matter, carbonate, diatoms and opal phytoliths allowed us to track changes in trophic state and paleosalinity levels, which were closely related to Holocene sea level variation, temperature and humidity. Diatom Association Zones (DAZ) corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and organic matter. Opal Phytoliths Association Zones (OPAZ) also were identified, temperature and humidity indices were calculated, and climatic trends were inferred. During the middle Holocene (i.e., ~5000–4000 yr BP), cool–dry climatic conditions were established. After ~4000 yr BP, a transition from cool to warm–humid conditions was observed, but fully warm humid conditions established only after ~1700 yr BP. Such climatic amelioration led to increases in trophic state.     

A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia

Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots.     

The Corredoiras orthogneiss (NW Iberian Massif): Geochemistry and geochronology of the Paleozoic magmatic suite developed in a peri-Gondwanan arc

The Corredoiras orthogneiss belongs to the intermediate pressure upper units of the Órdenes Complex (Variscan belt, NW Spain), mainly composed by granodioritic orthogneisses, with small bodies of tonalitic orthogneisses, amphibole-rich orthogneisses and metagabbronorites. In this work we study their chemical and isotopic composition, to gain insight into the linkage between plate tectonics and magmatism and to improve the knowledge of the paleogeographic evolution of the European Variscan Belt.Granodioritic and tonalitic orthogneisses range from intermediate to felsic rocks, with K₂O/Na₂O ratios ≈ 1, typical of calc-alkaline rocks, and high Na₂O content, characteristic of I-type granites. Metagabbronorites are basic rocks, but some of them are contaminated by interaction with the felsic magmas, showing enrichment in SiO₂, Na₂O and K₂O. All Corredoiras metaigneous rocks are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE), resulting in a high LILE/HFSE ratio. These geochemical features are the most characteristic of magmas related to subduction zones; furthermore all orthogneisses display significant negative anomalies in Ta, Nb and Zr, which together with their low contents in Y and Yb match up with granitoids generated in volcanic arcs or subduction zones. SHRIMP U–Pb zircon dating provides a concordia age of 492 ± 3 Ma. Granodioritic orthogneiss has negative εNd_(492 Ma) values (? 2.2 to ? 3.6) and high (⁸⁷Sr/⁸⁶Sr)_i ratios (0.707 to 0.708), on the other hand tonalitic orthogneisses and metagabbronorites have positive εNd_(492 Ma) (1.0 to 2.4) and low (⁸⁷Sr/⁸⁶Sr)_i (0.703 to 0.705), suggesting that granodioritic orthogneisses have a clear crustal influence in their generation, whereas tonalitic orthogneisses and metagabbros can be related to basic magmas extracted from the mantle or from a basic lower continental crust.The Corredoiras chemical characteristics permit us to interpret that this rocks were probably generated in an ensialic island arc and may represent a peri-Gondwanan fragment drifted away to open the Rheic Ocean.     

Differential damage in the semi-confined Munazio Ireneo cubicle in Cagliari (Sardinia): a correlation between damage and microclimate

The Early Christian Munazio Ireneo cubicle in Cagliari (Sardinia) is carved into the rock and is one of the rare monuments of Sardinia belonging to Early Christian Age. It is 166 cm under the planking level and is a semi-confined chamber in which a gate allows exchange with the outside. In 1888, when it was discovered, it was completely painted, but over the years, it suffered a serious damage and all the paintings are nearly disappeared. Now the site shows a high moisture and a differential damage characterised by delamination, powdering, salt crystallisation and biological colonisation. The research offers a multidisciplinary approach to study the salt crystallisation damage, which is a phenomenon still not completely understood today. Studies and analyses highlight that different kinds of damage can be recognised. The cement mortar and the air pollution cause crystallisation of the sulphates. Constant capillary rising and the presence of water infiltration due to the rains, which travelled into the site from the vault, were detected during qualitative inspection. Although the microclimate did not change much in the site and the humidity was almost constant during the monitoring period, the variations in temperature allowed the phase transitions of sodium sulphate, especially in summer. The greatest damage of the porous stone is associated with the phase transitions and crystallisation inside the stone of sodium sulphate, one of the most harmful salts for porous materials because of its high crystallisation pressure.     

SHRIMP U–Pb zircon dating of anatexis in high-grade migmatite complexes of Central Spain: implications in the Hercynian evolution of Central Iberia

U–Pb SHRIMP ages obtained in zircons from the Sotosalbos and Toledo anatectic complexes in Central Spain give new constraints to the evolution of the inner part of the Hercynian Iberian belt. Pre-Hercynian ages in zircons from the Sotosalbos complex (∼464 Ma) are well preserved and reveal that an age diversity of the Lower Paleozoic magmatism in the area exists, as previous data on westernmost orthogneisses yield significant older ages. Zircon ages in the pelite-derived granites from the Toledo complex also show an important Neoproterozoic age component which points to a metasedimentary protolith deposited maximally 560 Ma ago. Younger zircon populations in both complexes at ∼330 Ma in the Sotosalbos region and ∼317 Ma in the Toledo complex indicate an important diachronism between the anatectic processes in both areas but also that these processes are mainly unrelated to the generation of the later Hercynian granite batholith of Central Spain, which could be of deeper crustal derivation. In addition, as migmatization occurred late in the metamorphic cycle, after peak conditions were attained, the age of anatexis is younger than the age of the main Hercynian metamorphic event, which still is not well constrained. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Paleolimnological evidence of Holocene climatic changes in Lake Blanca, southern Uruguay

Paleolimnological data are presented on Holocene climatic changes in Lake Blanca, a small (0.6 km²), coastal fresh waterbody in southern Uruguay. Using a sediment core that extended to 7,300 year BP, analyses of pooid, panicoid and chloridoid phytoliths (Poaceae) allowed us to identify 16 Opal Phytoliths Association Zones (OPAZ). Both temperature and humidity indices were calculated from relative percentages of opal phytoliths and the climatic trends were inferred. During the early Holocene, prior to the first Holocene marine transgression (∼ ∼8,000–7,000 yr BP), cool-arid climatic conditions were inferred. After the first Holocene transgression, predominance of cool-humid conditions was registered until about 4,000 yr BP. A transition from cool-semiarid/arid to alternate warm-temperate and humid-very-humid conditions was detected for ∼∼4,000–1,000 yr BP. Increases in trophic state were observed because of such a climatic amelioration. After ∼ ∼1,000 yr BP, a shift from warm to temperate and cool temperatures was inferred. Such a cooling episode was assigned to a “LIA” which took place by the end of the 18th century and the beginning of the 19th century. A decrease in trophic state was observed during this climatic deterioration. After such a little ice age, present temperate humid conditions were established. The humidity indices calculated from relative percentages of opal phytoliths for the last ∼ ∼70 years were compared to annual rainfall data. Such a comparison showed that opal phytoliths are reliable indicators of humidity.     

The structure and impact of international tourism in the Veneto region,Italy

The Veneto region is one of the major tourist destinations in Italy, attracting some 20 million foreign and 24 million domestic arrivals each year through the variety of natural and cultural resources it has to offer. This paper examines the structure of foreign tourism, highlighting the importance of the Adriatic coast and Venice, and outlines some of the impacts which have resulted from the rapid and unplanned development of mass tourism.     

Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.