UPPER QUATERNARY EVOLUTION OF THE NORTHERN ARGOLIS GULF, NAFPLIO AREA

The recent palaeogeographic history of the Gulf of Argolis was studied by means of marine geophysical surveys and sediment sampling for subsequent laboratory analyses. Data interpretation suggests a relatively smooth seafloor gradient, characterized by an amphitheatrical pattern of the sea bottom. Prominent beetling features comprise the Bourtzi islet near Nafplio coast, small ridges in the southern margin of the studied area, and several conical ridges in the central part of the gulf. Four unconformities were identified, defining four different sedimentary units. Granulometry measurements allowed the mapping of present-day seafloor sediment distribution, where fine sediments prevail; the only exception was observed at the eastern coastal areas, where sand con-tent reaches 70%. Contouring of granulometry statistical parameters highlights a NW towards SE transfer of fine-grain sediments. Finally, taking into account the results of the present study and all available information for the broader area, a model for the Upper Quaternary palaeogeographic evolution of the Argolis Gulf was constructed

NEOGENE TECTONIC ROTATIONS IN THE VICINITY OF THE NORTH AEGEAN TROUGH: NEW PALAEOMAGNETIC EVIDENCE FROM ATHOS AND SAMOTHRAKI (GREECE)

Μελετώνται δύο μετα-ορογενείς πλουτωνίτες, ο γρανίτης του Αθω (Ερηγορίου) και της Σαμοθράκης, και τα ηφαιστειακά πετρώματα της Σαμοθράκης, που βρίσκονται στην ευρύτερη περιοχή της Τάφρου του Βορείου Αιγαίου. Πραγματοποιήθηκε λεπτομερής παλαιό μαγνητική μελέτη, με σκοπό τον καθορισμό της ηλικίας και του μηχανισμού των τεκτονικών περιστροφών. Επιπλέον μετρήθηκε η ασθενούς πεδίου ανισοτροπία της μαγνητικής επιδεκτικότητας (AMS) και έγιναν πειράματα ισόθερμης παραμένουσας μαγνήτισης και θερμομαγνητικές αναλύσεις. Τέλος, καθορίστηκε ραδιομετρικά η ηλικία του γρανίτη του Αθω (43.3 ±1.0 Μα K/Ar σε βιοτίτη). Οι μετρηθείσες μαγνητικές αποκλίσεις αναδεικνύουν δεξιόστροφη περιστροφή για τον Άθω (16.6e) και τη Σαμοθράκη (36.3°). Η ηλικία της περιστροφής εκτιμάται μικρότερη των 18 Μα για τη Σαμοθράκη, ενώ η πολύ μικρότερη περιστροφή του τεκτονικού τεμάχους του Άθω χαρακτηρίζεται νεώτερη από Ηωκαινική. Συγκρίνοντας τα νέα παλαιό μαγνητικά αποτελέσματα με τα ήδη δημοσιευμένα για τον ευρύτερο βορειοελλαδικό χώρο, προτείνουμε ότι οι τεκτονικές περιστροφές στην περιοχή της Τάφρου του Βορείου Αιγαίου, που καθορίστηκαν με παλαιό μαγνητικές μετρήσεις, χρονολογούνται μετά το Κάτω Μειόκαινο και ελέγχονται από κύρια ρήγματα οριζόντιας μετατόπισης και πληθώρα μικρότερων δευτερευόντων ρηγμάτων.The present study focuses on two post-orogenic plutons, the Athos (Grigoriou) and Samothraki granites, as well as the Samothraki volcanics, located in the vicinity of the North Aegean Trough. A detailed palaeomagnetic study was carried out, with the aim of constraining the age and mechanism of tectonic rotations. In addition, anisotropy of low field magnetic susceptibility (AMS) was studied and isothermal remanent magnetization (IRM) and thermomagnetic analyses were performed. Finally, a radiometric age for the Athos granite was obtained (43.3 ± 1.0 Ma K/Ar biotite). The measured declinations indicate clockwise rotations of the Athos (16.6°) and Samothraki (36.3°) blocks. The age of rotation is constrained to be <18 Ma at Samothraki, whereas the much smaller rotation of the Athos block can only be dated as younger than Eocene. Comparing the new palaeomagnetic data to the published dataset for Northern Greece, we suggest that the palaeomagnetically determined rotations in the vicinity of the North Aegean Trough are dominantly of post-Early Miocene age, and are controlled by major strike-slip faults and distributed "small" or minor faults

Full-vector archaeomagnetic dating of a medieval limekiln at Pinilla Del Valle site (Madrid, Spain)

Archaeomagnetic dating based on the full geomagnetic field vector was carried out on a limekiln excavated at Pinilla del Valle archaeological site (Madrid, Spain). The limekiln tradition in this area is largely documented by historical sources for recent centuries but the date of the studied kiln's last use was unknown. The combination of mean archaeomagnetic directional and absolute archaeointensity results shows that the kiln was last used between ad 1296 and 1413, in good agreement with two independent radiocarbon dates. This study provides the first archaeomagnetic evidence that the local limekiln tradition dates back to at least late medieval times. Furthermore, the inclusion of these data in the Iberian secular variation curve and geomagnetic field models will help to improve the archaeomagnetic dating technique.Spanish Ministry of Economy and Competitiveness, MINECO and the European Regional Development Fund (projects CGL2012-38481 and CGL2012-32149). AGacknowledges partial financial support given by PAPIIT IN-105214

Application of computer-aided tomography techniques to visualize kelp holdfast structure reveals the importance of habitat complexity for supporting marine biodiversity

Ecosystem engineers that increase habitat complexity are keystone species in marine systems, increasing shelter and niche availability, and therefore biodiversity. For example, kelp holdfasts form intricate structures and host the largest number of organisms in kelp ecosystems. However, methods that quantify 3D habitat complexity have only seldom been used in marine habitats, and never in kelp holdfast communities. This study investigated the role of kelp holdfasts (Laminaria hyperborea) in supporting benthic faunal biodiversity. Computer-aided tomography (CT-) scanning was used to quantify the three-dimensional geometrical complexity of holdfasts, including volume, surface area and surface fractal dimension (FD). Additionally, the number of haptera, number of haptera per unit of volume, and age of kelps were estimated. These measurements were compared to faunal biodiversity and community structure, using partial least-squares regression and multivariate ordination. Holdfast volume explained most of the variance observed in biodiversity indices, however all other complexity measures also strongly contributed to the variance observed. Multivariate ordinations further revealed that surface area and haptera per unit of volume accounted for the patterns observed in faunal community structure. Using 3D image analysis, this study makes a strong contribution to elucidate quantitative mechanisms underlying the observed relationship between biodiversity and habitat complexity. Furthermore, the potential of CT-scanning as an ecological tool is demonstrated, and a methodology for its use in future similar studies is established. Such spatially resolved imager analysis could help identify structurally complex areas as biodiversity hotspots, and may support the prioritization of areas for conservation