bluuebunny/crossref_metadata_2025 huggingface dataset:
Geometric and experimental models of extensional fault-bend folds
Authors: Withjack Martha O. , Schlische Roy W.
Published: April 2008

We use geometric and experimental models to study the development of extensional fault-bend folds. The geometric models show that fault shape, fault displacement, and patterns of aggradation/erosion profoundly affect the distribution of growth beds, the magnitude and direction of dip of pregrowth and growth beds, and the location and dip of the outer limit of folding in pregrowth and growth beds. Complex structural and stratigraphic patterns develop if the rate of aggradation/erosion relative to the rate of fault displacement changes through time. The experimental models (with dry sand and wet clay) show that several deformational styles can accommodate extensional fault-bend folding. In sand models, a few, relatively major, secondary antithetic normal faults accommodate most hanging wall deformation. Pregrowth layers, although faulted, remain flat. The effective shear direction parallels the antithetic normal faults, and the shear angle is about 60°–65°. In clay models, numerous, relatively minor, secondary normal faults (antithetic and synthetic) and cataclastic flow accommodate most hanging wall deformation. The deformed pregrowth and growth layers dip gently toward the main fault. The effective shear angle (35°–50°) is considerably less than the dip of the antithetic normal faults. In the sand models and geometric models with a large shear angle (60°), more displacement occurs on the main normal fault and the hanging wall collapses in a relatively narrow zone. In the clay models and geometric models with a small shear angle (35°), less displacement occurs on the main normal fault. Instead, the hanging wall stretches substantially and collapses in a relatively wide zone.
Macroscale dynamics of experimental landscapes
Authors: Bonnet Stephane , Crave Alain
Published: April 2008

We review results from laboratory-scale modelling of erosion and relief dynamics under variable uplift and rainfall rates. Under constant values of these forcing parameters an experimental landscape typically evolves towards a steady-state between uplift and erosion, and we show how the geometry of the steady-state landscape adjusts to the rates of uplift and rainfall. The comparison between these laboratory-scale landscapes and the natural ones is not straightforward because contrary to analogue modelling in tectonics, natural conditions of relief evolution cannot be downscaled to the laboratory without any scale distortions. Laboratory-scale modelling in geomorphology is therefore only experimental, not analogue. Despite these limitations, experimental models may be used to provide physical tests for numerical models and they give insights into first-order behaviours and directions for future research.
Numerical modelling of erosion processes in the Himalayas of Nepal: effects of spatial variations of rock strength and precipitation
Authors: Godard V. , Lavé J. , Cattin R.
Published: April 2008

The interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts. Here we investigate the modalities of deformation in Central Nepal on a
c.
100 ka time scale in response to tectonic and external forcings, through the use of a finite-element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding. We study the complex coupling existing between tectonics and erosion, with special emphasis on the influences of rock strength and rainfall distributions. Our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography. We show that the location of the Main Frontal Thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the Siwaliks Hills. As previously suspected (Burbank
et al.
2003), our simulations demonstrate that the pattern of uplift in Nepal is mainly dependent on both erodability and fault geometry, rather than on rainfall distribution.
Effects of compaction processes on stresses, faults, and fluid flow in sedimentary basins: examples from the Norwegian margin
Authors: Bjørlykke Knut
Published: April 2008

Modelling of sediment compaction requires that the rate limiting processes are understood. The compaction of uncemented sediments at relatively shallow burial depths should be modelled as a function of effective stress following soil mechanical principles and using experimental compaction data for calibration. In siliceous rocks chemical compaction is dominant at depths greater than 2–3 km (80–100°C). Chemical compaction should be modelled as a function of the temperature history and the mineralogical and textural composition of the sediments. The rate of chemical compaction for siliceous sediments is to a large extent a function of the quartz cementation, which is an exponential function of temperature, while the effective stress plays a minor role. In the case of carbonate sediments the kinetics of precipitation of cement is much faster and the effective stress is more important than temperature.

The magnitude and distribution of effective
situ
stresses is a complex function of external tectonic stresses, gravitational forces and fluid pressures. Sediments undergo mechanical compaction when subjected to high effective stress and are much more compressible than basement rocks. Chemical compaction also results in a reduction in rock volume and this has a strong feedback on the
in situ
stresses. If the horizontal stress is greater than the vertical stress, both mechanical compaction and chemical compaction will also occur in the horizontal direction, thus relaxing
in situ
stresses unless there is significant basin shortening. Calculations show that relatively large
in situ
stress anomalies (10 MPa) may be relaxed in 5–10 ka by chemical compaction during basin subsidence. Chemical compaction may also continue during uplift; it is fundamentally different from mechanical compaction and must be modelled separately.
Multiple faults in ductile simple shear: analogue models of flanking structure systems
Authors: Exner Ulrike , Grasemann Bernhard , Mancktelow Neil S.
Published: April 2008

Rotational behaviour and deformation around multiple faults was investigated in analogue experiments using a linear viscous matrix material under simple shear boundary conditions. Previous analogue and numerical studies have shown that, for single faults, characteristic deformation geometries are produced in initially straight marker lines parallel to the shear zone boundary (flanking structures). Observations from several natural shear zones suggest that not only single faults, but often several parallel or conjugate fault planes are subjected to progressive shear resulting in distinctive deflection geometries. If the distance between faults is on the order of their length, or less, then the perturbation flow fields interfere and coalescence, and finite deflection structures develop that are distinctly different from those around single fractures. In particular, coeval contractional and extensional geometries may develop across conjugate faults, although for bulk simple shear the total length of marker lines parallel to the shear zone boundary cannot change. This advises caution in inferring shear-zone parallel contraction or extension from secondary slip surfaces. In contrast to single flanking structures, conjugate flanking structure systems occurring in natural shear zones are reliable shear sense indicators due to their triclinic symmetry.
The deliberate search for stratigraphic and subtle combination traps: where are we now?
Authors: Allan J. R. , Sun S. Q. , Trice R.
Published: April 2008

Stratigraphic and subtle combination traps have a well-documented track record as significant producing hydrocarbon resources. The majority of these success cases come from onshore USA where unprecedented drilling densities combined with a long history of hydrocarbon exploration provide a large portfolio of stratigraphic and subtle combination traps. By comparing USA-based examples with other global cases it is evident that numerous basins still have the potential for exploration success associated with these traps. This paper attempts to raise the awareness of the exploration potential of stratigraphic and subtle combination traps through four approaches. Firstly, a summary of key global statistics related to stratigraphic and subtle combination traps is provided with the intention of demonstrating that they have historically represented a key hydrocarbon resource. Secondly, a classification scheme is introduced and acts as a reference for the observations and case studies presented. The third component of this paper is to present a range of case studies, which serve to demonstrate the exploration history behind successful discoveries associated with stratigraphic and subtle combination traps. The final component is to consider the general exploration history and from this long experience highlight the key techniques necessary for the development of a successful exploration strategy.
Identification of stratigraphic traps with subtle seismic amplitude effects in Miocene channel/levee sand systems, NE Gulf of Mexico
Authors: Godo Theodore J.
Published: April 2008

Stratigraphic traps created and preserved on the unconfined slope of the ancestral Mississippi submarine fan in the northeastern Gulf of Mexico have been found to contain substantial and profitable hydrocarbon reserves. Nearly 2 trillion cubic feet of gas (350 million barrels of oil equivalent) have been produced in the last 13 years in less than 1400 feet (425 m) of water. Drilling results have yielded 31 fields from 45 drilled prospects for a success rate of 69%. The main phase of exploration lasted eight years. The first 3D survey in 1994 sparked a major increase in drilling and success rates until the last field was discovered in 2001. This play has now essentially been exhausted of sizeable opportunities.

The underlying Mesozoic section sources hydrocarbons to the play for middle Miocene slope sands. The unconfined (non mini-basin) slope sands are turbidites and debris flows that were deposited between 5 and 25 miles (8 and 40 km) from their coeval shelf margins. Stratigraphic traps in this environment are created at the margins of the levees as they interfinger with slope shales. Additional geometric modifications of the stratigraphic traps result from post-depositional erosion or ‘cannibalization’. The erosion left ‘monadnocks’, or remnant patches of porous sands, that are encased in low permeability shales. Turbidite channel/levee deposits are the dominant reservoir facies in these ‘patches’; however, they may consist of channel, levee, or debris flow facies. Detailed mapping of these dominantly gas charged erosional remnants shows little to no fit of seismic amplitude effects to structure and the hydrocarbon accumulations often appear as amplitude anomalies ‘floating in space’.

This work was done to provide an analogue study, as well as to document any remaining prospects that were initially overlooked. Almost every discovery and dry hole in the trend was interpreted and included in this study. Integrating the well control into the geological model by using detailed seismic stratigraphy, whole core description, dipmeter logs, seismic to well tie synthetics, Gassmann fluid substitution and AvO analysis, provided the necessary insight to prosecute this play.

Within the play area, seismic velocities of sands and shales are very similar. As a consequence of this, seismic reflections are generally weak and, due to the stratigraphic variability, they are discontinuous. Hence, standard sequence stratigraphic mapping techniques alone are not enough to define these subtle traps. The key to successful exploration is a complete understanding of the rock properties. All of the fields examined displayed subtle amplitude anomalies associated with the presence of hydrocarbons. The ability to understand and quantify both the amplitude is essential to increasing the probability of success in this play.
The geological exploration techniques applied by BG in evaluation of the Buzzard Field prior to discovery
Authors: Moore Richard M. , Blight Richard D.
Published: April 2008

Substantial technical studies were undertaken by BG in the exploration effort which preceded the discovery of the Buzzard oil field. These studies were of value in forming BG’s perception of prospect risk and reward and confirming the company’s commitment to drill the prospect. Studies ranged from standard evaluation techniques to application of cutting edge technology of the time to innovative applications of software to address specific uncertainties or risks. BG perceived the prospect to be of moderate to high value, with a substantial upside reward, and since acquisition of 3D seismic to have moderate risk. This perception derived from several factors that may be peculiar to this particular prospect:

•

an existing well with an oil accumulation, located down dip, proving a migration path from oil mature source and the presence of thick sandstone units of excellent reservoir quality, logged and cored

•

tectonic tilting had both accentuated trap relief significantly increasing trap volume, and aided migration direction

•

the abundance of offset well data allowing an understanding of basin history and a robust geological model

Furthermore the BG evaluation benefited from:

•

involvement of in-house specialists in sedimentology, basin analysis and geophysical modelling

•

application of the findings of research projects at Edinburgh and Leeds Universities in the fields of Moray Firth structural development and Turbidite Sedimentation respectively
West of Shetland revisited: the search for stratigraphic traps
Authors: Loizou N. , Andrews I. J. , Stoker S. J. , Cameron D.
Published: April 2008

The West of Shetland area has scope for the stratigraphic entrapment of hydrocarbons at various Jurassic to Palaeogene stratigraphic levels. Mapping and identification of such traps requires a fundamental understanding of the regional geology, the study of analogues and source kitchens, and a thorough approach to trap validation. Since 1982, 47 exploration wells have been positioned on Paleocene prospects with a significant stratigraphic component, but few have found hydrocarbons — many failing as a result of poor trap definition and overconfidence in the predictive use of amplitude anomalies. Hydrocarbon sourcing of many of the failed prospects was also poorly constrained. Few amplitude-related stratigraphic features could be tied with confidence to a viable source kitchen. The presence of a regional seal is a prerequisite ingredient for a successful Paleocene play. Many remaining undrilled, subtle prospects rely on a stratigraphic trapping component, and high-quality 3D seismic data are seen as an essential search tool. Examples of undrilled prospects are presented from the Paleocene of the northern Faroe-Shetland Basin and the Mesozoic of the East Solan Basin and Corona Ridge.
Shallow-marine carbonates of the tropical-temperature transition zone: effects of hinterland climate and basin physiography (late Miocene, Crete, Greece)
Authors: Reuter Markus , Brachert Thomas C. , Kroeger Karsten F.
Published: April 2008

In modern oceans, the transition zone between the tropical and temperature carbonate province is gradual and covers a wide latitudinal belt. Little knowledge exists regarding the geological signatures of this zone. This paper describes a late Miocene (early Tortonian-early Messinian) transitional carbonate system that combines elements of the tropical and cool-water carbonate systems (Iraklion Basin, island of Crete, Greece). As documented in stratal geometries, the submarine topography of the basin was controlled by tilting blocks. Coral reefs formed by
Porites
and occurred in a narrow clastic coastal belt along a central Cretan landmass and steep escarpments formed by faulting. On the gentle dip-slope ramps of those blocks having the widest geographical distribution within the basin, extensive covers of level-bottom communities existed in a low-energy environment. Isolated colonial corals were present in the shallow segments of the ramps. Consistent patterns of landward and basinward shift of coastal onlap in all outcrop studies reveal an overriding control of third- and fourth-order sea-level changes on sediment dynamics and facies distributions over block movements. An increasingly dry climate and the complex submarine topography of the fault-block mosaic kept sediment and nutrient discharge from a central Cretan landmass at a minimum. The skeletal limestone facies therefore reflects oligotrophic conditions and sea surface temperatures near the lower threshold temperature of coral reefs in a climatic position transitional between the tropical coral reef belt and the temperate zone. It is suggested that the recognition of an overall late Miocene aridification trend helps to explain the Mediterranean-wide distribution of shallow-marine carbonates, both cool-water and warm-water, in settings adjacent to uplifting mountain ranges (intramontane basins).
The Southern Marion Platform (Marion Plateau, NE Australia) during the early Pliocene: a lowstand-producing, temperate-water carbonate factory
Authors: Kindler Pascal , Ruchonnet Cyril , White Tim
Published: April 2008

The Southern Marion Platform (Marion Plateau, offshore NE Australia) is a drowned, isolated carbonate platform of Neogene age that was drilled during ODP Leg 194 in January–March 2001. Initial results from the Leg suggested that temperate-water carbonate production was terminated by a phase of subaerial exposure during the late Miocene, and did not resume during the ensuing Pliocene transgression. New petrographic, geochemical, isotopic and biostratigraphical data obtained from samples collected during the cruise show that the Southern Marion Platform was not subaerially exposed during the late Miocene, and further remained intermittently active during the early Pliocene. At that time, its mode of functioning was probably the reverse of that of classical, Bahamian-type, isolated platforms: sediment production occurred during sea-level lowstands and was shut off during highstands.
Chemostratigraphy in Miocene heterozoan carbonate settings: applications, limitations and perspectives
Authors: Mutti Maria , John Cédric M. , Knoerich Andrea C.
Published: April 2008

The temporal variability of geochemical proxies can be used in time intervals characterized by global changes in marine chemistry to achieve improved stratigraphic correlation. The application of this approach in rocks lithified by cementation requires particular attention, as the original isotopic signature may have been modified by diagenetic processes and, when bulk samples are used, could reflect facies-specific compositional changes as opposed to primary changes in the water column. This paper examines sedimentological and chemostratigraphic records from outcrops in the central Mediterranean and cores drilled on the Marion Plateau by the Ocean Drilling Program (ODP) Leg 194, where heterozoan carbonates accumulated during the Miocene. Specifically, the paper addresses how facies and preservation of original marine signatures differentially affect the quality of the dataset. The analysis indicates that, in general, heterozoan systems, relative to their tropical counterparts, show good preservation of marine signatures. Chemostratigraphy offers a viable low-resolution alternative for dating platform sediments considering the general lack of biostratigraphic markers in these settings. It is stressed, however, that care must be taken when interpreting these values, especially when the dataset is at a low resolution or when post-depositional dolomitization took place. Furthermore, chemostratigraphy in shallow-water environments cannot be done without detailed facies analysis, as facies changes may impact bulk-rock stable isotope values.
Archaeometry:
quo vadis
?
Authors: Maggetti Marino
Published: April 2008

First, a brief overview of the tasks and the historical development of archaeometry will be given. Although archaeometry is generally doing well, a few issues currently faced by this discipline will be outlined. These include: (1) funding for projects and research positions; (2) the appeal of archaeometry to a new generation of academics; (3) the standard of publications; (4) the safeguarding of and the immediate access to scientific data.
Fibre-tempered pottery of the Stallings Island Culture from the Crescent site, Beaufort County, South Carolina: a mineralogical and petrographical study
Authors: Smith Michael S. , Trinkley Michael B.
Published: April 2008

Late Archaic to Early Woodland (4500–3000 years
bp
) Stallings Island Culture fibre-tempered plainware pottery is found from northern North Carolina to NW Florida and is often separated into two temper groups (Stalling and Orange series) based upon fibre type. Thirty-four sherds were studied to determine textural or mineralogical characteristics to assist in form and type separation. This study finds that only a few of the sherds were dominated by fibre. The fibre is visible as secondary porosity (voids) with some carbonized remains and exhibits specific shape and orientation at different locations within the sherd. Only two sherds had carbonized stem fragments that allowed identification of the Spanish moss (
Tillandsia usnedoides
). The remainder of the Crescent site plainware pottery has such low (to no) fibre contents as to be indistinguishable from similar age sand-tempered Thom’s Creek wares. The identity and textural features of the fine-grained aplastic minerals (quartz, feldspar, biotite and opaque minerals) in the paste are similar in both fibre- and non-fibre-tempered sherds, and this suggests that the materials used are consistent with sediment extraction from a fluvial coastal plain or estuarine setting. These observations indicate that the degree of fibre incorporation in these sherds may be related to the specific clay source (or manufacturing location) or represent examples of an evolving pottery manufacturing process within the Stallings Island Culture.
Islamic and Hispano-Moresque (múdejar) lead glazes in Spain: a technical approach
Authors: Vendrell-Saz M. , Molera J. , Roqué J. , Pérez-Arantegui J.
Published: April 2008

Islamic and Hispano-Moresque glazes from the 10th to 15th centuries found in various archaeological sites, most of them workshops, are studied to show the technical evolution of the medieval glazing process. The technology seems to show a simplification: the early Islamic glazes were applied on prefired bodies and after fritting a lead-silica mixture, whereas for the later Islamic productions the raw materials for the lead glazes were not fritted and they were applied over unfired bodies. The same simplified technology was used in the Hispano-Moresque workshops. In the Islamic workshops lead glazes were coloured by adding elements (Fe, Cu, Mn), whereas the múdejar technology simplified the process by using only one recipe to produce pots of different colour. This was achieved by applying the glaze in a different manner (on one side of the pot to obtain yellow or on both sides to obtain green), or using different pastes (already used to produce pottery for different uses). Finally, there are differences between Islamic and Hispano-Moresque tin glazes related to the crystal size of the opacifier (tin oxide crystals), which should indicate some technological differences in temperature, glaze composition and the process to obtain the frits because of the high dependence between viscosity, temperature and crystal nucleation and growth.
Archaeometric analyses of game counters from Pompeii
Authors: Arletti R. , Ciarallo A. , Quartieri S. , Sabatino G. , Vezzalini G.
Published: April 2008

Among the glass finds of the Pompeii excavations, numerous objects of opaque and transparent glassy material of different colours were recovered and classified as game counters. The main aims of this work were to characterize these samples so as to identify the materials used as colorants and opacifying agents, and subsequently to deduce the technology used for their production. The results of the chemical and mineralogical analyses obtained for game counters were also compared with those obtained for transparent and opaque glass artefacts. The chemical analyses were carried out, using only 300 mg of sample, by both wavelength-dispersive electron microprobe and X-ray fluorescence analysis. The crystalline phases present in the opaque glass were identified using both an automatic X-ray powder diffractometer and a Gandolfi camera. Secondary and backscattered electron images were obtained to study the distribution and morphology of the opacifier particles, and qualitative chemical analyses were obtained with an energy-dispersive system. All the game counters analysed can be classified as silica-soda-lime glass. Two calcium antimonates (CaSb
2
O
6
and Ca
2
Sb
2
O
7
) were identified in the opaque white, green and blue glass, and Pb
2
Sb
2
O
7
particles were detected in the opaque yellow glass. Particles of metallic copper were detected by both energy-dispersive system and X-ray powder diffraction. These results support the hypothesis that transparent game counters were obtained by remelting of fragments of common transparent artefacts. In contrast, opaque finds were probably produced using the glassy paste employed in the production of mosaic tesserae.
Medieval stained glass windows from Pavia Carthusian monastery (northern Italy)
Authors: Marchesi Valeria , Negri Elisabetta , Messiga Bruno , Riccardi Maria Pia
Published: April 2008

Stained glass windows of the Carthusian monastery (Certosa) of Pavia (15th century) were investigated during a recent restoration campaign, to define chemical compositions and to understand manufacture techniques. Analyses were performed on six stained glass windows, representing S. Caterina (St. Catherine), S. Gregorio (St. Gregory), S. Agostino (St. Augustine), la Natività (the Nativity), S. Bernardo (St. Bernard) and S. Girolamo (St. Jerome), and on two undecorated windows. The methodological approach couples micro-sampling with micro-analyses. The detailed chemical analysis reveals four compositionally distinct glass-types: mixed alkali, soda and two potash glass types. These last two types display a rather constant MgO content but variable CaO content and define two main compositional clusters, CaO rich (Type II) and CaO poor (Type III), that have been ascribed to the pristine glass. The compositional boundary of Type II and Type III glass fits those already defined in recent literature. The mixed alkali and soda glass are considered to be related to later repairs. The narrow compositional cluster represents a good statistical result defining the composition of the pristine glass panes and allows compositional comparisons with stained glass from coeval cathedrals of Northern Europe (Germany, Switzerland and France). Close similarities are found to stained glass from Rouen and St. Maur des Fosses.
Textural analysis of ancient plasters and mortars: reliability of image analysis approaches
Authors: Carò F. , Di Giulio A. , Marmo R.
Published: April 2008

Different image analysis (IA) methods have been developed to compute textural parameters of ancient plasters and mortars using standard petrographic thin sections. These IA routines were applied to samples of materials with different technological characteristics from three historical buildings in the city of Pavia (Northern Italy), covering a period from the 12th to the 19th century. The IA techniques tested in this study belong both to classical digital image processing and to neural network modelling. In the first case, analyses were performed by commercial IA software whereas in the second case a Multi-Layer Perceptron neural network (MLP) was tested. Digital image analysis was performed on images taken by means of a petrographic microscope; additionally, analysis of back-scattered electron (BSE) images was performed. Textural data obtained through the IA applied to thin sections were compared with the data from traditional point counting and mechanical sieve analysis of disaggregated samples of the same materials. The results show that the IA of thin sections provides robust results in a fast and easy way. However, the reliability of the analyses can be prejudiced by textural and compositional heterogeneity of the samples.
Marine volcaniclastics of the Hidden Lake Formation (Coniacian) of James Ross Island, Antarctica: an enigmatic element in the history of a back-arc basin
Authors: Whitham Andrew G. , Ineson Jon R. , Pirrie Duncan
Published: April 2008

The Coniacian Hidden Lake Formation of James Ross Island, Antarctica is a 300–400 m-thick succession of marine volcaniclastic conglomerates, sandstones and mudstones. It occurs at a point of transition in the evolution of the James Ross Basin, as it is underlain by deep-marine strata and overlain by shallow-marine strata. The succession reflects the two main factors controlling the deposition of the formation: (1) the influx of large quantities of volcaniclastic sediment; and (2) a pronounced inversion event in the early Coniacian heralding the cessation of transpressive tectonic activity in the James Ross Basin. The succession is dominated by a range of sediment density-flow deposits, which, combined with the limited faunas and the lack of wave-induced structures, suggest deposition in a relatively deep-marine environment below storm-wave base. Three main facies associations are recorded representing base-of-slope, fan-delta and basin-floor depositional environments. The volcaniclastic fan-delta association is dominated by fresh pyroclastic detritus and was deposited in response to volcanic eruptions on the adjacent arc. Thick beds of parallel-stratified sandstone record deposition from sustained, concentrated sediment density flows. The conditions immediately following pyroclastic eruptions lend themselves to the deposition of such deposits, as vegetation cover is destroyed and large amounts of poorly consolidated sediment are available for reworking. An enigmatic feature of the succession is the presence of units of cross-bedded sandstones thought to be of tidal origin that are locally abundant and are intimately interbedded with sediment density-flow deposits. The occurrence of tidal sediments in a substorm-wave base setting is explained by appealing to partial basin inversion during the final phases of strike-slip tectonic activity in the basin creating an irregular basin floor that focused and amplified tidal currents. The infilling of this basin topography by sediment and waning intrabasinal tectonism during the Coniacian resulted in the progressive elimination of this basin-floor topography and the onset of shallow-marine shelf sedimentation.
A new ‘South American ungulate’ (Mammalia: Litopterna) from the Eocene of the Antarctic Peninsula
Authors: Bond M. , Reguero M. A. , Vizcaíno S. F. , Marenssi S. A.
Published: April 2008

Notolophus arquinotiensis
, a new genus and species of the family Sparnotheriodontidae (Mammalia, Litopterna), is represented by several isolated teeth from the shallow-marine sediments of the La Meseta Formation (late Early-Late Eocene) of Seymour Island, Antarctic Peninsula, which have also yielded the youngest known sudamericids and marsupials. The new taxon belongs to the extinct order of ‘South American native ungulate’ Litopterna characterized by the convergence of the later forms with the equids and camelids.
Notolophus arquinotiensis
shows closest relationships with
Victorlemoinea
from the Itaboraian (middle Palaeocene) of Brazil and Riochican-Vacan (late Palaeocene-early Eocene) of Patagonia, Argentina. Although still poorly documented, this new taxon shows that the early Palaeogene Antarctic faunas might provide key data concerning the problems of the origin, diversity and basal phylogeny of some of the ‘South American ungulates’ (Litopterna). This new taxon shows the importance of Antarctica in the early evolution of the ungulates and illustrates our poor state of knowledge.
The Carboniferous to Jurassic evolution of the pre-Alpine basement of Crete: constraints from U-Pb and U-(Th)-Pb dating of orthogneiss, fission-track dating of zircon, structural and petrological data
Authors: Romano S. S. , Brix M. R. , Dörr W. , Fiala J. , Krenn E. , Zulauf G.
Published: April 2008

The pre-Alpine evolution of the external Hellenides is poorly constrained because of the Alpine impact which largely erased the older orogenic imprints. Only a few outcrops with pre-Alpine basement exist, one of which is located in eastern Crete. The pre-Alpine basement, part of the Phyllite-Quartzite Unit, is composed of four sub-complexes, which are different in protolith age, type and age of metamorphism, and postmetamorphic cooling history. The lowermost, Kalavros crystalline complex (KCC) underwent Permian amphibolite-facies metamorphism related to top-to-the-NE shearing. The KCC exhibits a four-stage garnet zonation and a late, high-temperature event associated with the growth of K-feldspar. The KCC is overlain by the Myrsini crystalline complex (MCC), which underwent Carboniferous amphibolite facies metamorphism associated with top-to-the-north shearing. Late cooling of the MCC is documented by Jurassic fission track ages of zircon. The Chamezí crystalline complex underwent upper greenschist-facies metamorphism related to top-to-the-north shearing. In addition, the Vaí crystalline complex, in an uncertain structural position, is characterized by Triassic emplacement of granite, followed by amphibolite-facies top-to-the-NW shearing and cooling, as is indicated by Jurassic fission-track ages of zircon. A preliminary tectonic model is presented, which invokes south-directed subduction, collision and accretion of the crystalline complexes to the northern margin of Gondwana.
Neotethyan ophiolites: formation and obduction within the life cycle of the host basins
Authors: Garfunkel Zvi
Published: April 2008

To understand the Neotethyan ophiolites better, their place in the history of the host basins is explored, using the Jurassic Hellenic-Dinaric and some Cretaceous (mainly peri-Arabian) ophiolites as examples. These formed in mature (
c.
60 Ma and 100 Ma old) seaways by spreading at rates that apparently were too high to persist for more than a fraction of the basin history. Each ophiolite group formed in a short time interval, about 10 Ma, soon after changes in the motions of plates in the host basins. Therefore, these ophiolites do not seem to have formed by normal long-term spreading along mid-ocean ridges, but their formation signifies special ‘ophiolite events’. This fits well the widely accepted origin in a supra-subduction zone (SSZ) setting that was inferred from geochemical data. The ophiolites studied here are thus interpreted as having formed in new subduction zones that originated during changes in plate motions. The spreading during their accretion was driven by fast retreat (roll-back) of the subducting slabs. The western ophiolites of the Hellenic-Dinaric belt, dominated by mid-ocean ridge basalt (MORB)-like rocks but invaded by SSZ magmas, could have formed along ridges just before they failed (collapsed), but the age data fit better formation in a proto-back-arc setting alongside the more eastern ophiolites with the typical SSZ signature. The construction of the ophiolites examined here ended when they were detached from their substrate and pushed over the adjacent basins. At that stage they were underplated by metamorphic soles, but how the latter were emplaced still needs clarification. Continuing retreat of the subducting slabs consumed the host basins and pushed the ophiolites hundreds of kilometres until they were obducted over the nearby margins 15–20 Ma after formation. This framework seems to apply to many ophiolites and allows us to interpret them in terms of known processes, but also highlights problematic issues that still need to be resolved.
Nature and significance of Late Cretaceous ophiolitic rocks and their relation to the Baskil granitic intrusions of the Elazığ region, SE Turkey
Authors: Rizaoğlu Tamer , Parlak Osman , Hoeck Volker , İşler Fİkret
Published: April 2008

The Elazığ region in SE Turkey comprises, in descending order, the Palaeozoic-Mesozoic Malatya-Keban platform, an ensimatic island arc unit (i.e. Elazığ magmatic rocks-Yüksekova complex), and ophiolitic rocks (i.e. Kömürhan) of Late Cretaceous age. All of these were intruded by the Baskil granitic rocks. These tectonomagmatic-stratigraphic assemblages were emplaced over the Middle Eocene volcano-sedimentary Maden complex to the south during the evolution of the SE Anatolian orogen. The Kömürhan ophiolite exhibits an intact ophiolite pseudostratigraphy. The base of this has been metamorphosed to amphibolite facies during intraoceanic subduction-thrusting. The amphibolitic rocks were intruded by synkinematic granitic rocks (Baskil magmatic rocks). The ensimatic island arc volcanic rocks are widely distributed in the region. The contact of the volcano-sedimentary unit with the underlying Kömürhan ophiolite is a thrust dipping to the north. The rock assemblages of the volcano-sedimentary unit suggest formation of small volcanic edifices above a subduction zone, coupled with debris-flow deposits and volcaniclastic turbidites. The whole-rock and mineral chemistry of the Kömürhan ophiolite and the ensimatic island arc volcanic rocks suggests that they represent a comagmatic tholeiitic suite, formed in the Late Cretaceous in a suprasubduction zone (SSZ) setting. The amphibolites beneath the Kömürhan ophiolite indicate derivation from an island arc tholeiite (IAT) protolith. The geological and geochemical evidence from the Elazığ region suggests the following evolutionary scenario. The Kömürhan ophiolite was formed above a north-dipping subduction zone between the Arabian platform to the south and the Tauride platform to the north in Late Cretaceous (
c.
90 Ma). An ensimatic island arc assemblage was then built on the SSZ-type crust. The metamorphic sole was formed by metamoprhism of IAT-type basalts that were detached from the front of the overriding Kömürhan ophiolite and then underplated. These units were then accreted to the base of the Tauride active margin to the north, where both units were cut by the Baskil granitic rocks around 85 Ma.
Synthesis of the tectonic-sedimentary evolution of the Mesozoic-Early Cenozoic Pindos ocean: evidence from the NW Peloponnese, Greece
Authors: Degnan Paul J. , Robertson Alastair H. F.
Published: April 2008

The tectonic development of the western part of the Pindos ocean in southern Greece is exemplified by the mountainous Pindos thrust belt in the NW Peloponnese. A Late Triassic-Early Cenozoic succession exposed within imbricate thrust sheets records a range of deep-water siliciclastic, redeposited carbonate and siliceous sediments, which in general become more distal oceanwards towards the east. Igneous rocks, locally dated as Triassic, occur within a mélange that is entrained beneath and within the Pindos thrust stack; these igneous rocks and related sediments are interpreted as remnants of a continent-ocean transition zone. ‘Immobile’ element geochemistry is explicable by rifting of a compositionally heterogeneous subcontinental mantle, possibly related to pre-existing Hercynian subduction, although coeval Triassic subduction cannot be excluded based on evidence from this area alone. Localized, ‘enriched’ basalts are interpreted as fragments of oceanic seamounts formed in a relatively distal setting. Late Paleocene-Early Eocene (locally Mid-Eocene) siliciclastic turbidites, derived from the north, record the latest deposition prior to incorporation of the sedimentary succession into a westward-migrating accretionary wedge during post-Early Eocene time in the NW Peloponnese. Structural restoration of the well-ordered thrust stack indicates a minimum of 201 km (55%) of shortening at an average rate of 5.8 mm a
−1
. As the Pindos allochthon approached the Apulian continent, the Gavrovo-Tripolitza foreland underwent flexural upwarp during the Mid-Eocene, followed by collapse to create a foreland basin by the Late Eocene. This basin was infilled with generally upward-thickening and -coarsening deep-water turbiditic sediments of Late Eocene-Early Oligocene age. The foreland was, in turn, overthrust by the Pindos accretionary prism during post-Early Paleocene time, and was then imbricated and thrust over the Ionian foreland basin to the west by Pliocene time.
Sedimentology and tectonic setting of the Pindos Flysch of the Peloponnese, Greece
Authors: Piper David J. W.
Published: April 2008

The Palaeogene Pindos Flysch of the Peloponnese shows important differences from the flysch of northern Greece. Stratigraphic sections and palaeocurrent indicators were measured in the Pindos Flysch Formation and the underlying Kataraktis Passage Member throughout the Peloponnese. The Kataraktis Passage Member records carbonate-dominated sedimentation from the Apulian continental margin to the west, with intercalated terrigenous sediment also derived from the west. Variations in thickness and turbidite facies show that the overlying Pindos Flysch Formation was deposited in channels with levees and in channel-termination lobes in the western Peloponnese and in a distal basin plain, locally ponded, in the east. At least in the central Peloponnese, facies variation, palaeocurrents and detrital petrology show that the Pindos Flysch was derived from the Apulian margin. The Pindos Flysch of northern Greece, of late Paleocene to Oligocene age, was deposited in a foreland basin and derived from the rising Pelagonian nappes to the east. A younger microcontinental collision south of the Gulf of Corinth line resulted in the Pindos Flysch of the Peloponnese being incorporated in the accretionary prism by Mid-Eocene time.
Late Cenozoic extension in SW Bulgaria: a synthesis
Authors: Westaway Rob
Published: April 2008

Southwest Bulgaria forms the northern margin of the Aegean extensional province. Since the Early Pliocene (
c.
4 Ma), this region has accommodated southward or SSE extension at several millimetres per year, superimposed on
c.
400 m of post-Early Pliocene regional uplift. This sense of deformation superseded earlier extension, oriented ENE-WSW, which is estimated to have begun in the early Late Miocene (
c.
10–9 Ma) and lasted until
c.
4 Ma. The regional topography is dominated by NNW-SSE-striking grabens and normal fault escarpments, relics from this time. Normal faults that are now active cut across these older structures, although in some localities normal faults that were oriented obliquely to the earlier extension have remained active, also oblique to the modern extension sense. It is suggested that this present phase of extension relates to the modern sense of deformation throughout the Aegean region and to the modern geometry of the North Anatolian Fault Zone (NAFZ), which is independently inferred to have existed since
c.
4 Ma. The earlier ENE-WSW extension is inferred to have involved two phases, the first predating the NAFZ and the second synkinematic with its initial phase of slip during
c.
7–4 Ma, when its geometry and the overall sense of deformation in the Aegean region were different from at present. Some previous studies have inferred that SW Bulgaria experienced large-scale extension on low-angle normal faults in the Mid-Miocene or earlier. However, the limited evidence in support of this view is open to other interpretations, and after due consideration can be discounted.
Neotectonic development of the Çameli Basin, southwestern Anatolia, Turkey
Authors: Alçiçek Mehmet Cihat , Ten Veen Johan H. , Özkul Mehmet
Published: April 2008

This study of the Çameli Basin presents a detailed basin evolution combined with structural analysis and provides the first detailed time-stratigraphic framework for the neotectonic development of Neogene grabens along the Fethiye-Burdur Fault Zone in southwestern Anatolia. During the Early Tortonian, the Çameli Basin was established as a broad fault-bounded fluviolacustrine basin that experienced NW-SE extension. By Mid-Pliocene time, continued NW-SE extension resulted in the formation of a new intrabasinal fault zone that split the basin longitudinally into two compartments. The development of a new generation of normal faults further split the basin into four narrow half-graben compartments at the end of the Late Pliocene. Structural analysis of basin-bounding and intrabasinal faults related to this three-stage basin development shows that NW-SE extension apparently persisted from Late Miocene to early Quaternary time. The youngest (i.e. Holocene), deformation is characterized by dextral shear along NE-SW-trending strikeslip faults and continuing NW-SE extension. The Late Miocene foundering of the basin was related to extension in the northerly hinterland zone of the still-emplacing Lycian nappes, whereas outward growth of the Hellenic Arc in response to the westward Anatolian extrusion is the main cause for NW-SE extension from the Pliocene onward. Dextral strike-slip faulting is localized and is associated with the activity of NW-SE-trending faults that accommodated NE-SW extension. The simultaneous activity of these faults suggests the existence of biaxial extensional tectonics, as initially proposed for the Burdur-Dinar area. Sinistral strike-slip faulting, continuing along the eastern Hellenic Arc, penetrated the southernmost part of Turkey but has not yet reached the Çameli Basin area. Our biostratigraphically well-constrained tectonosedimentary model for the evolution of the Çameli Basin provides a reliable time-stratigraphic framework for NE-SW extension in the ‘Fethiye-Burdur Fault Zone’ of SW Anatolia. We believe that this fault zone represents a broad zone of isolated or interconnected NE-SW-trending basins that formed under prevailing NW-SE extension, rather than being a significant strike-slip fault zone.
Neotectonic and seismological data concerning major active faults, and the stress regimes of Northern Greece
Authors: Mountrakis D. , Tranos M. , Papazachos C. , Thomaidou E. , Karagianni E. , Vamvakaris D.
Published: April 2008

Northern Greece is an intracontinental region behind the Hellenic subduction zone, with widespread seismic activity (ranging from low to high), with strong destructive earthquakes of M ≥ 6.0 in historical to recent times. Geological and seismological data indicate that recent seismic activity is mainly localized along large, inherited, fault zones, which have transected Northern Greece since Oligocene-Miocene times. The main active fault zones in Thrace, and Eastern and Central Macedonia strike approximately east-west, with lengths of 40–120 km. Fault segments strike WNW-ESE to ENE-WSW and range from 10 to 30 km in length. In Western Macedonia the main active fault zones strike NE-SW to ENE-WSW with lengths of 40–60 km and consist of 10–30 km segments. The region’s strong earthquakes are usually associated with reactivation of these fault segments and are estimated at M = 5.6–6.5. Focal mechanisms and fault-slip data from the fault zones indicate a change in the trend of extension axes from NNE-SSW in Eastern Macedonia-Thrace to NNW-SSE in Western Macedonia. Thus, neotectonic and seismological data suggest that variations in fault patterns, as determined from the large inherited fault zones transecting Northern Greece, are the major factor governing this change in the trend of maximum extension. This interpretation is consistent with the long-lived arcuate shape of the Hellenic subduction zone.