Provenienza dei sedimenti arenitici nel bacino di Tracia (eo-oligocene, Turchia nord-occidentale e Grecia nord-orientale)

The Thrace Basin is the largest and thickest Tertiary sedimentary basin of the eastern Balkans region and constitutes an important hydrocarbon province. It is located between the Rhodope-Strandja Massif to the north and west, the Marmara Sea and Biga Peninsula to the south, and the Black Sea to the est. It consists of a complex system of depocenters and uplifts with very articulate paleotopography indicated by abrupt lateral facies variations. Its southeastern margin is widely deformed by the Ganos Fault, a segment of the North Anatolian strike-slip fault system . Most of the Thrace Basin fill ranges from the Eocene to the Late Oligocene. Maximum total thickness, including the Neogene-Quaternary succession, reaches 9.000 meters in a few narrow depocenters. This sedimentary succession consists mainly of basin plain turbiditic deposits with a significant volcaniclastic component which evolves upwards to shelf deposits and continental facies, with deltaic bodies prograding towards the basin center in the Oligocene. This work deals with the provenance of Eocene-Oligocene clastic sediments of the southern and western part of Thrace Basin in Turkey and Greece. Sandstone compositional data (78 gross composition analyses and 40 heavy minerals analyses) were used to understand the change in detrital modes which reflects the provenance and geodinamic evolution of the basin. Samples were collected at six localities, which are from west to est: Gökçeada, Gallipoli and South-Ganos (south of Ganos Fault), Alexandroupolis, Korudağ and North-Ganos (north of Ganos Fault). Petrologic (framework composition and heavy-mineral analyses) and stratigraphic-sedimentologic data, (analysis of sedimentologic facies associations along representative stratigraphic sections, paleocurrents) allowed discrimination of six petrofacies; for each petrofacies the sediment dispersal system was delineated. The Thrace Basin fill is made mainly of lithic arkoses and arkosic litharenites with variable amount of low-grade metamorphic lithics (also ophiolitic), neovolcanic lithics, and carbonate grains (mainly extrabasinal). Picotite is the most widespread heavy mineral in all petrofacies. Petrological data on analyzed successions show a complex sediment dispersal pattern and evolution of the basin, indicating one principal detrital input from a source area located to the south, along both the İzmir-Ankara and Intra-Pontide suture lines, and a possible secondary source area, represented by the Rhodope Massif to the west. A significant portion of the Thrace Basin sediments in the study area were derived from ophiolitic source rocks and from their oceanic cover, whereas epimetamorphic detrital components came from a low-grade crystalline basement. An important penecontemporaneous volcanic component is widespread in late Eocene-Oligocene times, indicating widespread post-collisional (collapse?) volcanism following the closure of the Vardar ocean. Large-scale sediment mass wasting from south to north along the southern margin of the Thrace Basin is indicated (i) in late Eocene time by large olistoliths of ophiolites and penecontemporaneous carbonates, and (ii) in the mid-Oligocene by large volcaniclastic olistoliths. The late Oligocene paleogeographic scenario was characterized by large deltaic bodies prograding northward (Osmancik Formation). This clearly indicates that the southern margin of the basin acted as a major sediment source area throughout its Eocene-Oligocene history. Another major sediment source area is represented by the Rhodope Massif, in particolar the Circum-Rhodopic belt, especially for plutonic and metamorphic rocks. Considering preexisting data on the petrologic composition of Thrace Basin, silicilastic sediments in Greece and Bulgaria (Caracciolo, 2009), a Rhodopian provenance could be considered mostly for areas of the Thrace Basin outside our study area, particularly in the northern-central portions of the basin. In summary, the most important source area for the sediment of Thrace Basin in the study area was represented by the exhumed subduction-accretion complex along the southern margin of the basin (Biga Peninsula and western-central Marmara Sea region). Most measured paleocurrent indicators show an eastward paleoflow but this is most likely the result of gravity flow deflection. This is possible considered a strong control due to the east-west-trending synsedimentary transcurrent faults which cuts the Thrace Basin, generating a series of depocenters and uplifts which deeply influenced sediment dispersal and the areal distribution of paleoenvironments. The Thrace Basin was long interpreted as a forearc basin between a magmatic arc to the north and a subduction-accretion complex to the south, developed in a context of northward subduction. This interpretation was challenged by more recent data emphasizing the lack of a coeval magmatic arc in the north and the interpretation of the chaotic deposit which outcrop south of Ganos Fault as olistoliths and large submarine slumps, derived from the erosion and sedimentary reworking of an older mélange unit located to the south (not as tectonic mélange formed in an accretionary prism). The present study corroborates instead the hypothesis of a post-collisional origin of the Thrace Basin, due to a phase of orogenic collapse, which generated a series of mid-Eocene depocenters all along the İzmir-Ankara suture (following closure of the Vardar-İzmir-Ankara ocean and the ensuing collision); then the slab roll-back of the remnant Pindos ocean played an important role in enhancing subsidence and creating additional accommodation space for sediment deposition.

Sedimentary environments and climate change: a case study (late Miocene, central Crete)

In this study, conditions of deposition and stratigraphical architecture of Neogene (Tortonian, 11-6,7Ma) sediments of southern central Crete were analysed. In order to improve resolution of paleoclimatic data, new methods were applied to quantify environmental parameters and to increase the chronostratigraphic resolution in shallow water sediments. A relationship between paleoenvironmental change observed on Crete and global processes was established and a depositional model was developed. Based on a detailed analysis of the distribution of non geniculate coralline red algae, index values for water temperature and water depth were established and tested with the distribution patterns of benthic foraminifera and symbiont-bearing corals. Calcite shelled bivalves were sampled from the Algarve coast (southern Portugal) and central Crete and then 87Sr/86Sr was measured. A high resolution chronostratigraphy was developed based on the correlation between fluctuations in Sr ratios in the measured sections and in a late Miocene global seawater Sr isotope reference curve. Applying this method, a time frame was established to compare paleoenvironmental data from southern central Crete with global information on climate change reflected in oxygen isotope data. The comparison between paleotemperature data based on red algae and global oxygen isotope data showed that the employed index values reflect global change in temperature. Data indicate a warm interval during earliest Tortonian, a second short warm interval between 10 and 9,5Ma, a longer climatic optimum between 9 and 8Ma and an interval of increasing temperatures in the latest Tortonian. The distribution of coral reefs and carpets shows that during the warm intervals, the depositional environment became tropical while temperate climates prevailed during the cold interval. Since relative tectonic movements after initial half-graben formation in the early Tortonian were low in southern central Crete, sedimentary successions strongly respond to global sea-level fluctuation. A characteristic sedimentary succession formed during a 3rd order sea-level cycle: It comprises mixed siliciclastic-limestone deposited during sea-level fall and lowstand, homogenous red algal deposits formed during sea-level rise and coral carpets formed during late rise and highstand. Individual beds in the succession reflect glacioeustatic fluctuations that are most prominent in the mixed siliciclastic-limestone interval. These results confirm the fact that sedimentary successions deposited at the critical threshold between temperate and tropical environments develop characteristic changes in depositional systems and biotic associations that can be used to assemble paleoclimatic datasets.

Geochronology, geochemistry and isotopic compositions of the volcanic rocks from oceanic (Hawaii) and continental (Eifel) intra-plate environments

The Eifel volcanism is part of the Central European Volcanic Province (CEVP) and is located in the Rhenish Massif, close to the Rhine and Leine Grabens. The Quaternary Eifel volcanism appears to be related to a mantle plume activity. However, the causes of the Tertiary Hocheifel volcanism remain debated. We present geochronological, geochemical and isotope data to assess the geotectonic settings of the Tertiary Eifel volcanism. Based on 40Ar/39Ar dating, we were able to identify two periods in the Hocheifel activity: from 43.6 to 39.0 Ma and from 37.5 to 35.0 Ma. We also show that the pre-rifting volcanism in the northernmost Upper Rhine Graben (59 to 47 Ma) closely precede the Hocheifel volcanic activity. In addition, the volcanism propagates from south to north within the older phase of the Hocheifel activity. At the time of Hocheifel volcanism, the tectonic activity in the Hocheifel was controlled by stress field conditions identical to those of the Upper Rhine Graben. Therefore, magma generation in the Hocheifel appears to be caused by decompression due to Middle to Late Eocene extension. Our geochemical data indicate that the Hocheifel magmas were produced by partial melting of a garnet peridotite at 75-90 km depth. We also show that crustal contamination is minor although the magmas erupted through a relatively thick continental lithosphere. Sr, Nd and Pb isotopic compositions suggest that the source of the Hocheifel magmas is a mixing between depleted FOZO or HIMU-like material and enriched EM2-like material. The Tertiary Hocheifel and the Quaternary Eifel lavas appear to have a common enriched end-member. However, the other sources are likely to be distinct. In addition, the Hocheifel lavas share a depleted component with the other Tertiary CEVP lavas. Although the Tertiary Hocheifel and the Quaternary Eifel lavas appear to originate from different sources, the potential involvement of a FOZO-like component would indicate the contribution of deep mantle material. Thus, on the basis of the geochemical and isotope data, we cannot rule out the involvement of plume-type material in the Hocheifel magmas. The Ko’olau Scientific Drilling Project (KSDP) has been initiated in order to evaluate the long-term evolution of Ko’olau volcano and obtain information about the Hawaiian mantle plume. High precision Pb triple spike data, as well as Sr and Nd isotope data on KSDP lavas and Honolulu Volcanics (HVS) reveal compositional source variations during Ko’olau growth. Pb isotopic compositions indicate that, at least, three Pb end-members are present in Ko’olau lavas. Changes in the contributions of each component are recorded in the Pb, Sr and Nd isotopes stratigraphy. The radiogenic component is present, at variable proportion, in all three stages of Ko’olau growth. It shows affinities with the least radiogenic “Kea-lo8” lavas present in Mauna Kea. The first unradiogenic component was present in the main-shield stage of Ko’olau growth but its contribution decreased with time. It has EM1 type characteristics and corresponds to the “Ko’olau” component of Hawaiian mantle plume. The second unradiogenic end-member, so far only sampled by Honololu lavas, has isotopic characteristics similar to those of a depleted mantle. However, they are different from those of the recent Pacific lithosphere (EPR MORB) indicating that the HVS are not derived from MORB-related source. We suggest, instead, that the HVS result from melting of a plume material. Thus the evolution of a single Hawaiian volcano records the geochemical and isotopic changes within the Hawaiian plume.

The pre-alpine evolution of the basement of the Pelagonian Zone and the Vardar Zone, Greece

The Pelagonian Zone and the Vardar Zone in Greece represent the western part of the Hellenide hinterland (Internal Hellenides). While the Pelagonian Zone comprises predominantly crystalline basement and sedimentary cover rocks, the Vardar Zone has long been regarded as an ophiolite-decorated suture zone separating the Pelagonian Zone from the Serbo-Macedonian Massif to the east. Felsic basement rocks from both areas, with the main focus put on the Pelagonian Zone, were dated in order to identify the major crust-forming episodes and to improve the understanding of the evolutionary history of the region. The interpretation of the single-zircon geochronology results was aided by geochemical investigations. The majority of the basement rocks from the Pelagonian Zone yielded Permo-Carboniferous intrusion ages around 300 Ma, underlining the importance of this crust-forming event for the Internal Hellenides of Greece. Geochemically these basement rocks are classified as subduction-related granitoids, which formed in an active continental margin setting. An important result was the identification of a Precambrian crustal unit within the crystalline basement of the Pelagonian Zone. Orthogneisses from the NW Pelagonian Zone yielded Neoproterozoic ages of c. 700 Ma and are so far the oldest known rocks in Greece. These basement rocks, which are also similar to active margin granitoids, were interpreted as remnants of a terrane, the Florina Terrane, which can be correlated to a Pan-African or Cadomian arc. Since the gneisses contain inherited zircons of Middle to Late Proterozoic ages, the original location of the Florina Terrane was probably at the northwestern margin of Gondwana. In the Vardar Zone an important phase of Upper Jurassic felsic magmatism is documented by igneous formation ages ranging from 155 to 164 Ma. The chemical and isotopic composition of these rocks is also in accord with their formation in a volcanic-arc setting at an active continental margin. Older continental material incorporated in the Vardar Zone is documented by 319-Ma-old gneisses and by inherited zircons of mainly Middle Palaeozoic ages. The prevalence of subduction-related igneous rocks indicates that arc formation and accretion orogeny were the most important processes during the evolution of this part of the Internal Hellenides. The geochronological results demonstrate that most of the Pelagonian Zone and the Vardar Zone crystalline basement formed during distinct pre-Alpine episodes at c. 700, 300 and 160 Ma with a predominance of the Permo-Carboniferous magmatic phase.

Weathering of Fe-bearing minerals under extraterrestrial conditions, investigated by Mössbauer spectroscopy

The weathering of Fe-bearing minerals under extraterrestrial conditions was investigated by Mössbauer (MB) spectroscopy to gain insights into the role of water on the planet Mars. The NASA Mars Exploration Rovers Spirit and Opportunity each carry a miniaturized Mössbauer spectrometer MIMOS II for the in situ investigation of Martian soils and rocks as part of their payload. The MER flight instruments had to be modified in order to work over the Martian diurnal temperature range (180 K – 290 K) and within the unique electronic environment of the rovers. The modification required special calibration procedures. The integration time necessary to obtain a good quality Mössbauer spectrum with the MIMOS II flight instruments was reduced by 30 % through the design of a new collimator. The in situ investigation of rocks along the rover Spirit's traverse in Gusev crater revealed weakly altered olivine basalt on the plains and pervasively altered basalt in the Columbia Hills. Correlation plots of primary Fe-bearing minerals identified by MB spectroscopy such as olivine versus secondary Fe-bearing phases such as nanophase Fe oxides showed that olivine is the mineral which is primarily involved in weathering reactions. This argues for a reduced availability of water. Identification of the Fe-oxyhydroxide goethite in the Columbia Hills is unequivocal evidence for aqueous weathering processes in the Columbia Hills. Experiments in which mineral powders were exposed to components of the Martian atmosphere showed that interaction with the atmosphere alone, in the absence of liquid water, is sufficient to oxidize Martian surface materials. The fine-grained dust suspended in the Martian atmosphere may have been altered solely by gas-solid reactions. Fresh and altered specimens of Martian meteorites were investigated with MIMOS II. The study of Martian meteorites in the lab helped to identify in Bounce Rock the first rock on Mars which is similar in composition to basaltic shergottites, a subgroup of the Martian meteorites. The field of astrobiology includes the study of the origin, evolution and distribution of life in the universe. Water is a prerequisite for life. The MER Mössbauer spectrometers identified aqueous minerals such as jarosite and goethite. The identification of jarosite was crucial to evaluate the habitability of Opportunity's landing site at Meridiani Planum during the formation of the sedimentary outcrop rocks, because jarosite puts strong constrains on pH levels. The identification of olivine in rocks and soils on the Gusev crater plains provide evidence for the sparsity of water under current conditions on Mars. Ratios of Fe2+/Fe3+ were obtained with Mössbauer spectroscopy from basaltic glass samples which were exposed at a deep sea hydrothermal vent. The ratios were used as a measure of potential energy for use by a microbial community. Samples from Mars analogue field sites on Earth exhibiting morphological biosignatures were also investigated.

Structural and strain analysis in the Late Paleozoic coastal accretionary wedge of central Chile

Abstract In this study structural and finite strain data are used to explore the tectonic evolution and the exhumation history of the Chilean accretionary wedge. The Chilean accretionary wedge is part of a Late Paleozoic subduction complex that developed during subduction of the Pacific plate underneath South America. The wedge is commonly subdivided into a structurally lower Western Series and an upper Eastern Series. This study shows the progressive development of structures and finite strain from the least deformed rocks in the eastern part of the Eastern Series of the accretionary wedge to higher grade schist of the Western Series at the Pacific coast. Furthermore, this study reports finite-strain data to quantify the contribution of vertical ductile shortening to exhumation. Vertical ductile shortening is, together with erosion and normal faulting, a process that can aid the exhumation of high-pressure rocks. In the east, structures are characterized by upright chevron folds of sedimentary layering which are associated with a penetrative axial-plane foliation, S1. As the F1 folds became slightly overturned to the west, S1 was folded about recumbent open F2 folds and an S2 axial-plane foliation developed. Near the contact between the Western and Eastern Series S2 represents a prominent subhorizontal transposition foliation. Towards the structural deepest units in the west the transposition foliation became progressively flat lying. Finite-strain data as obtained by Rf/Phi and PDS analysis in metagreywacke and X-ray texture goniometry in phyllosilicate-rich rocks show a smooth and gradual increase in strain magnitude from east to west. There are no evidences for normal faulting or significant structural breaks across the contact of Eastern and Western Series. The progressive structural and strain evolution between both series can be interpreted to reflect a continuous change in the mode of accretion in the subduction wedge. Before ~320-290 Ma the rocks of the Eastern Series were frontally accreted to the Andean margin. Frontal accretion caused horizontal shortening and upright folds and axial-plane foliations developed. At ~320-290 Ma the mode of accretion changed and the rocks of the Western Series were underplated below the Andean margin. This basal accretion caused a major change in the flow field within the wedge and gave rise to vertical shortening and the development of the penetrative subhorizontal transposition foliation. To estimate the amount that vertical ductile shortening contributed to the exhumation of both units finite strain is measured. The tensor average of absolute finite strain yield Sx=1.24, Sy=0.82 and Sz=0.57 implying an average vertical shortening of ca. 43%, which was compensated by volume loss. The finite strain data of the PDS measurements allow to calculate an average volume loss of 41%. A mass balance approximates that most of the solved material stays in the wedge and is precipitated in quartz veins. The average of relative finite strain is Sx=1.65, Sy=0.89 and Sz=0.59 indicating greater vertical shortening in the structurally deeper units. A simple model which integrates velocity gradients along a vertical flow path with a steady-state wedge is used to estimate the contribution of deformation to ductile thinning of the overburden during exhumation. The results show that vertical ductile shortening contributed 15-20% to exhumation. As no large-scale normal faults have been mapped the remaining 80-85% of exhumation must be due to erosion.

UHP metamorphic rocks of the Eastern Rhodope Massif, NE Greece: new constraints from petrology, geochemistry and zircon ages

In this PhD thesis, a multidisciplinary study has been carried out on metagranitoids and paragneisses from the Eastern Rhodope Massif, northern Greece, to decipher the pre-Alpine magmatic and geodynamic evolution of the Rhodope Massif and to correlate the eastern part with the western/central parts of the orogen. The Rhodope Massif, which occupies the major part of NE Greece and S Bulgaria, represents the easternmost part of the Internal Hellenides. It is regarded as a nappe stack of high-grade units, which is classically subdivided into an upper unit and a lower unit, separated by a SSE-NNW trending thrust plane, the Nestos thrust. Recent research in the central Greek Rhodope Massif revealed that the two units correspond to two distinct terranes of different age, the Permo-Carboniferous Thracia Terrane, which was overthrusted by the Late Jurassic/Early Cretaceous Rhodope Terrane. These terranes are separated by the Nestos suture, a composite zone comprising metapelites, metabasites, metagranitoids and marbles, which record high-pressure and even ultrahigh-pressure metamorphism in places. Similar characteristic rock associations were investigated during this study along several well-constrained cross sections in vincity to the Ada, Sidiro and Kimi villages in the Greek Eastern Rhodope Massif. Field evidence revealed that the contact zone of the two terranes in the Eastern Rhodope Massif is characterized by a mélange of metapelites, migmatitic amphibolites/eclogites, strongly sheared orthogneisses and marbles. The systematical occurrence of this characteristic rock association between the terranes implies that the Nestos suture is a continuous belt throughout the Greek Rhodope Massif. In this study, a new UHP locality could be established and for the first time in the Greek Rhodope, metamorphic microdiamonds were identified in situ in their host zircons using Laser-Raman spectroscopy. The presence of the diamonds as well as element distribution patterns of the zircons, obtained by TOF-SIMS, indicate metamorphic conditions of T > 1000 °C and P > 4 GPa. The high-pressure and ultrahigh-pressure rocks of the mélange zone are considered to have formed during the subduction of the Nestos Ocean in Jurassic times at ~150 Ma. Melting of metapelitic rocks at UHP conditions facilitated the exhumation to lower crustal levels. To identify major crust forming events, basement granitoids were dated by LA-SF-ICPMS and SHRIMP-II U-Pb analyses of zircons. The geochronological results revealed that the Eastern Rhodope Massif consists of two crustal units, a structurally lower Permo-Carboniferous unit corresponding to the Thracia Terrane and a structurally upper Late Jurassic/Early Cretaceous unit corresponding to the Rhodope Terrane, like it was documented for the Central Rhodope Massif. Inherited zircons in the orthogneisses from the Thracia Terrane of the Eastern Rhodope Massif indicate the presence of a pre-existing Neoproterozoic and Ordovician-Silurian basement in this region. Triassic magmatism is witnessed by the zircons of few orthogneisses from the easternmost Rhodope Massif and is interpreted to be related to rifting processes. Whole-rock major and trace element analyses indicate that the metagranitoids from both terranes originated in a subduction-related magmatic-arc environment. The Sr-Nd isotope data for both terranes of the Eastern and Central Rhodope Massif suggest a mixed crust-mantle source with variable contributions of older crustal material as already indicated by the presence of inherited zircons. Geochemical and isotopic similarity of the basement of the Thracia Terrane and the Pelagonian Zone implies that the Thracia Terrane is a fragment of a formerly unique Permo-Carboniferous basement, separated by rifting and opening of the Meliata-Maliac ocean system in Triassic times. A branch of the Meliata-Maliac ocean system, the Nestos Ocean, subducted northwards in Late Jurassic times leading to the formation of the Late Jurassic/Early Cretaceous Rhodope magmatic arc on remnants of the Thracia Terrane as suggested by inherited Permo-Carboniferous zircons. The ~150 Ma zircon ages of the orthogneisses from the Rhodope Terrane indicate that subduction-related magmatism and HP/UHP metamorphism occurred during the same subduction phase. Subduction ceased due to the closure of the Nestos Ocean in the Late Jurassic/Early Cretaceous. The post-Jurassic evolution of the Rhodope Massif is characterized by the exhumation of the Rhodope core complex in the course of extensional tectonics associated with late granite intrusions in Eocene to Miocene times.

Characterization of fold-related fractures in the carbonate rocks of the Cingoli anticline, northern Apennines, Italy

Thrust fault-related folds in carbonate rocks are characterized by deformation accommodated by different structures, such as joints, faults, pressure solution seams, and deformation bands. Defining the development of fracture systems related to the folding process is significant both for theoretical and practical purposes. Fracture systems are useful constrains in order to understand the kinematical evolution of the fold. Furthermore, understanding the relationships between folding and fracturing provides a noteworthy contribution for reconstructing the geodynamic and the structural evolution of the studied area. Moreover, as fold-related fractures influence fluid flow through rocks, fracture systems are relevant for energy production (geothermal studies, methane and CO2 , storage and hydrocarbon exploration), environmental and social issues (pollutant distribution, aquifer characterization). The PhD project shows results of a study carried out in a multilayer carbonate anticline characterized by different mechanical properties. The aim of this study is to understand the factors which influence the fracture formation and to define their temporal sequence during the folding process. The studied are is located in the Cingoli anticline (Northern Apennines), which is characterized by a pelagic multilayer characterized by sequences with different mechanical stratigraphies. A multi-scale analysis has been made in several outcrops located in different structural positions. This project shows that the conceptual sketches proposed in literature and the strain distribution models outline well the geometrical orientation of most of the set of fractures observed in the Cingoli anticline. On the other hand, the present work suggests the relevance of the mechanical stratigraphy in particular controlling the type of fractures formed (e.g. pressure solution seams, joints or shear fractures) and their subsequent evolution. Through a multi-scale analysis, and on the basis of the temporal relationship between fracture sets and their orientation respect layering, I also suggest a conceptual model for fracture systems formation.

Dynamic development of hydrofractures

Natürliche hydraulische Bruchbildung ist in allen Bereichen der Erdkruste ein wichtiger und stark verbreiteter Prozess. Sie beeinflusst die effektive Permeabilität und Fluidtransport auf mehreren Größenordnungen, indem sie hydraulische Konnektivität bewirkt. Der Prozess der Bruchbildung ist sowohl sehr dynamisch als auch hoch komplex. Die Dynamik stammt von der starken Wechselwirkung tektonischer und hydraulischer Prozesse, während sich die Komplexität aus der potentiellen Abhängigkeit der poroelastischen Eigenschaften von Fluiddruck und Bruchbildung ergibt. Die Bildung hydraulischer Brüche besteht aus drei Phasen: 1) Nukleation, 2) zeitabhängiges quasi-statisches Wachstum so lange der Fluiddruck die Zugfestigkeit des Gesteins übersteigt, und 3) in heterogenen Gesteinen der Einfluss von Lagen unterschiedlicher mechanischer oder sedimentärer Eigenschaften auf die Bruchausbreitung. Auch die mechanische Heterogenität, die durch präexistierende Brüche und Gesteinsdeformation erzeugt wird, hat großen Einfluß auf den Wachstumsverlauf. Die Richtung der Bruchausbreitung wird entweder durch die Verbindung von Diskontinuitäten mit geringer Zugfestigkeit im Bereich vor der Bruchfront bestimmt, oder die Bruchausbreitung kann enden, wenn der Bruch auf Diskontinuitäten mit hoher Festigkeit trifft. Durch diese Wechselwirkungen entsteht ein Kluftnetzwerk mit komplexer Geometrie, das die lokale Deformationsgeschichte und die Dynamik der unterliegenden physikalischen Prozesse reflektiert. rnrnNatürliche hydraulische Bruchbildung hat wesentliche Implikationen für akademische und kommerzielle Fragestellungen in verschiedenen Feldern der Geowissenschaften. Seit den 50er Jahren wird hydraulisches Fracturing eingesetzt, um die Permeabilität von Gas und Öllagerstätten zu erhöhen. Geländebeobachtungen, Isotopenstudien, Laborexperimente und numerische Analysen bestätigen die entscheidende Rolle des Fluiddruckgefälles in Verbindung mit poroelastischen Effekten für den lokalen Spannungszustand und für die Bedingungen, unter denen sich hydraulische Brüche bilden und ausbreiten. Die meisten numerischen hydromechanischen Modelle nehmen für die Kopplung zwischen Fluid und propagierenden Brüchen vordefinierte Bruchgeometrien mit konstantem Fluiddruck an, um das Problem rechnerisch eingrenzen zu können. Da natürliche Gesteine kaum so einfach strukturiert sind, sind diese Modelle generell nicht sonderlich effektiv in der Analyse dieses komplexen Prozesses. Insbesondere unterschätzen sie die Rückkopplung von poroelastischen Effekten und gekoppelte Fluid-Festgestein Prozesse, d.h. die Entwicklung des Porendrucks in Abhängigkeit vom Gesteinsversagen und umgekehrt.rnrnIn dieser Arbeit wird ein zweidimensionales gekoppeltes poro-elasto-plastisches Computer-Model für die qualitative und zum Teil auch quantitativ Analyse der Rolle lokalisierter oder homogen verteilter Fluiddrücke auf die dynamische Ausbreitung von hydraulischen Brüchen und die zeitgleiche Evolution der effektiven Permeabilität entwickelt. Das Programm ist rechnerisch effizient, indem es die Fluiddynamik mittels einer Druckdiffusions-Gleichung nach Darcy ohne redundante Komponenten beschreibt. Es berücksichtigt auch die Biot-Kompressibilität poröser Gesteine, die implementiert wurde um die Kontrollparameter in der Mechanik hydraulischer Bruchbildung in verschiedenen geologischen Szenarien mit homogenen und heterogenen Sedimentären Abfolgen zu bestimmen. Als Resultat ergibt sich, dass der Fluiddruck-Gradient in geschlossenen Systemen lokal zu Störungen des homogenen Spannungsfeldes führen. Abhängig von den Randbedingungen können sich diese Störungen eine Neuausrichtung der Bruchausbreitung zur Folge haben kann. Durch den Effekt auf den lokalen Spannungszustand können hohe Druckgradienten auch schichtparallele Bruchbildung oder Schlupf in nicht-entwässerten heterogenen Medien erzeugen. Ein Beispiel von besonderer Bedeutung ist die Evolution von Akkretionskeilen, wo die große Dynamik der tektonischen Aktivität zusammen mit extremen Porendrücken lokal starke Störungen des Spannungsfeldes erzeugt, die eine hoch-komplexe strukturelle Entwicklung inklusive vertikaler und horizontaler hydraulischer Bruch-Netzwerke bewirkt. Die Transport-Eigenschaften der Gesteine werden stark durch die Dynamik in der Entwicklung lokaler Permeabilitäten durch Dehnungsbrüche und Störungen bestimmt. Möglicherweise besteht ein enger Zusammenhang zwischen der Bildung von Grabenstrukturen und großmaßstäblicher Fluid-Migration. rnrnDie Konsistenz zwischen den Resultaten der Simulationen und vorhergehender experimenteller Untersuchungen deutet darauf hin, dass das beschriebene numerische Verfahren zur qualitativen Analyse hydraulischer Brüche gut geeignet ist. Das Schema hat auch Nachteile wenn es um die quantitative Analyse des Fluidflusses durch induzierte Bruchflächen in deformierten Gesteinen geht. Es empfiehlt sich zudem, das vorgestellte numerische Schema um die Kopplung mit thermo-chemischen Prozessen zu erweitern, um dynamische Probleme im Zusammenhang mit dem Wachstum von Kluftfüllungen in hydraulischen Brüchen zu untersuchen.

Palaeotsunami imprints in the near-coast sedimentary records of the Gulfs of Lakonia and Argolis (Peloponnese, Greece)

From historical accounts it is well-known that the coasts of the Gulfs of Lakonia and Argolis (southern and eastern Peloponnese, Greece) have been repeatedly affected by tsunamis during historical times. It is assumed that these palaeotsunamis left sedimentological and geomorphological traces in the geological record which are still detectable these days. As both gulfs are located within one of the seismically most active regions in whole western Eurasia in particular the nearby Hellenic Trench is regarded as the main trigger for tsunami generation. Against this background, selected near-coast sedimentary archives were studied by means of sedimentological, geomorphological, geophysical, geochemical and microfaunal investigations in order to detect signatures of Holocene palaeotsunamigenic activity. The investigations revealed allochthonous sediment layers featuring distinctive sedimentary characteristics of marine high-energy event deposits in most of the investigated study areas. In order to differentiate between the geomorphodynamic driving mechanisms for the deposition of the associated marine high-energy event layers, a multi-method approach was used. The detected high-energy marine deposits are suggested to be of tsunamigenic origin. Radiocarbon dating results allowed establishing local event geo-chronostratigraphies and correlations on a local and regional scale as well as correlations with already described palaeotsunami findings on a supra-regional scale. The geochronological dataset attests repeated tsunamigenic activity at least since the 5th millennium BC up to the 17th century AD. For the studied areas in southeastern Lakonia up to four palaeotsunami event generations were identified, for central Lakonia three and for the investigated areas around the Argolis Gulf also up to four. Comparing the findings with literature data, chronological correlations were found with palaeotsunami deposits detected in near-coast geological archives of Akarnania, of the southwestern, the western and northwestern Peloponnese, with event deposits found on Crete and on the Ionian Islands of Cefalonia and Lefkada as well as with findings from southeastern Sicily (Italy) and Cesarea (Israel). By the identification of multiple palaeotsunami event layers, disturbing autochthonous near-coast sedimentary records of the Gulfs of Lakonia and Argolis during the last seven millennia, a significant tsunami frequency is attested for these regions.