bluuebunny/crossref_metadata_2025 huggingface dataset:
Major active faults of SW Bulgaria: implications of their geometry, kinematics and the regional active stress regime
Authors: Tranos Markos D. , Karakostas Vassilis G. , Papadimitriou Eleftheria E. , Kachev Vladislav N. , Ranguelov Boyko K. , Gospodinov Dragomir K.
Published: April 2008

Southwest Bulgaria is an intracontinental region between the Dinaro-Hellenic and Balkan mountain ranges that has experienced infrequent, but strong and destructive earthquakes. The general geometric and kinematic characteristics of the major faults, mainly the active ones, are investigated, as the seismic activity is insufficient to describe thoroughly the active crustal deformation associated with the faulting. The results suggest a major rupture zone with a length of more than 50 km. The east-west-striking Kochani-Kroupnik-Bansko ‘rupture zone’ was potentially associated with the large 1904 Kroupnik earthquakes, and has been found to transect the region joining the Kochani, Kroupnik and Bansko faults. In addition, a long-term slip rate ranging from 0.14 to 0.7 mm a
−1
has been estimated for some large faults in the region using morphotectonic features. The most active faults are normal ones striking WNW-ESE to ENE-WSW, whereas the NNW-SSE- to NW-SE-striking faults tended to act as barriers to the growth of the former faults, as they do not exhibit much indication of recent reactivation. The stress regime determined is extensional with the least principal stress axis (σ
3
) subhorizontal and oriented north-south. The fact that the active faults show geometric and kinematic characteristics, as well as estimated long-term slip rates, similar to those of the active faults of central and eastern Macedonia and Thrace (Northern Greece) suggests that both of these regions share a single contemporary stress field.
Scaling properties of the dimensional and spatial characteristics of fault and fracture systems in the Majella Mountain, central Italy
Authors: Marchegiani L. , Van Dijk J. P. , Gillespie P. A. , Tondi E. , Cello G.
Published: April 2008

In this paper we report on the results of a systematic study carried out on the fault and fracture systems exposed in the Majella Mountain, in the central Apennines fold and thrust belt of mainland Italy. The focus of our work was to assess the dimensional, spatial, and scaling properties of fault and fractures in carbonate rocks, in order to set up appropriate flow models for these types of potential geofluid reservoirs. The results provide information on (1) orientation, size distribution, density variations, and fractal characteristics of the fault and fracture networks affecting the Majella anticline; (2) the scaling properties and the overall architecture of different fault zone components; (3) the overprinting relationships between fault and fracture sets and the Majella fold structure. These data were used to elaborate a three-dimensional discrete fault and fracture model (DFFN model) of a ∼100 m
3
geological volume, and for this to (1) evaluate the transport and storage properties of the reservoir; and (2) assess the degree of vulnerability and any possible hazard related to the exploitation and management of geofluids hosted in carbonate rock volumes.
Evidence for the existence of a simple relation between earthquake magnitude and the fractal dimension of seismogenic faults: a case study from central Italy
Authors: Cello G. , Marchegiani L. , Tondi E.
Published: April 2008

Fault data from the central Apennines (Italy) were integrated with earthquake information from seismic catalogues in order to derive an empirical relation between the magnitude of the strongest historical earthquake and the fractal dimension of active fault patterns. We show that the assessment of earthquake magnitude from fault data has given good results, hence suggesting that the relation may be used to evaluate the potential hazard of seismic source areas in the Apennines using a low-cost methodology. We also suggest that a similar approach may be used in other seismic belts worldwide, provided that the basic seismological and geological information needed is adequate to constrain the appropriate relation between these two size parameters.
Synsedimentary tectonics of the Triassic Carbonate Formation of the Oujda Mountains (Eastern Meseta, Morocco): geodynamic implications
Authors: Oujidi M. , Azzouz O. , Elmi S.
Published: April 2008

The Ladinian-Carnian tectonic instability is well recorded within the Carbonate Formation of the Oujda Mountains (Eastern Meseta, Morocco). It was induced by a bidirectional extensional palaeo-state of stress (ENE-WSW and NNW-SSE) resulting in the development of the Oujda Mountains Triassic basins that open towards the Western Tethyan domain. This extensional event correlates with an early episode of Tethyan rifting, which is coeval with the Ladinian-Carnian extensional episode of the Alpine domain. The structural development of these basins was controlled by an extensional reactivation of Hercynian faults, with N70°E and N160°E fault trends predominating over the N35°E and N120°E ones. Therefore, the Ladinian-Carnian palaeo-state of stress of the Oujda Mountains is fundamentally different from that of the Triassic-Liassic basins to the west, in Central Morocco and the Atlas belts, where the N45°E-trending, sinistral fault trend predominates over the N70°E and N90°E fault trends.
Tectonic wedge escape in the southwestern front of the Rif Cordillera (Morocco)
Authors: Chalouan A. , Galindo-Zaldívar J. , Akil M. , Marín C. , Chabli A. , Ruano P. , Bargach K. , Sanz de Galdeano C. , Benmakhlouf M. , Ahmamou M. , Gourari L.
Published: April 2008

The Rif Cordillera is a part of the Alpine orogenic arc in the Western Mediterranean, which was developed by the interaction of the westward motion of the Alboran Domain between the converging Eurasian and African plates. The Prerif Ridges, located along the southwestern front of the Rif, are south-vergent folds that are in places associated with faults affecting Jurassic to Quaternary sedimentary rocks and slope breccias that evidence the deformations that were active over the Neogene-Quaternary period. The different southward or southwestward displacement of each Prerif Ridge is related to the development of frontal and lateral ramps, which may or may not reach the surface. Oblique shortening may be explained by southwestward escape of large tectonic wedges, bounded by large strike-slip faults: the North-Middle Atlas fault which extends northward into the Alboran Sea, the Fez-Tissa-Taïneste fault, the Bou Draa-Sidi Fili fault, the Jebha fault and the Fahies fault. The relative displacement of these tectonic wedges toward the SW may explain the NNE-SSW to ENE-WSW compression observed in the Rif front and in the northern part of its Meseta-Atlas foreland.
Transgressive-regressive facies cycles in late Cretaceous calciturbidites from the Mauretanian Series, Béni Ider thrust sheet, northwestern External Rif, Morocco: application of the ‘facies tract-facies sequence’ concept
Authors: El Kadiri Kh. , El Kadiri K. , Chalouan A. , Bahmad A. , Salhi F. , Liemlahi H. , Hlila R.
Published: April 2008

Late Cretaceous mixed carbonate-siliciclastic, thin-bedded turbidites occur between the two great sandstone packages of the Mauretanian Series (the Tisirène and the Béni Ider sandstone flyschs, of early Cretaceous and late Oligocene-early Burdigalian age, respectively). The application of the facies tract-facies sequence model allows subdivision of the studied calciturbidites into five distinct facies sequences (FS.1–5), which equal five transgressive-regressive facies cycles. These cycles mainly consist of thinning upward calciturbidites, which almost all start with coarse-grained carbonate breccias, and passing upward into a shale-dominated interval. Fe-stained discontinuities, together with sedimentological and ichnological evidence, lead us to assign these two lithological components to a transgressive and a regressive trend, respectively. This result provides new insights into the sequence-stratigraphic interpretation of turbiditic successions.
Regional correlations across the Internides-Externides front (northwestern Rif Belt, Morocco) during the Late Cretaceous-Early Burdigalian times: palaeogeographical and palaeotectonic implications
Authors: El Kadiri Kh. , Hlila R. , Sanz de Galdeano C. , López-Garrido A. C. , Chalouan A. , Serrano F. , Bahmad A. , Guerra-Merchán A. , Liemlahi H.
Published: April 2008

New insights into the palaeogeographical evolution of the Rifian Internides and their external surroundings are inferred from six key stratigraphic successions selected across the Internides-Externides front. These successions span a time interval ranging from the late Cretaceous to the early Burdigalian. The main results are: (1) important lost palaeogeographical domains should be located during the late Cretaceous-Eocene between the present-day Ghomarides and the Dorsale Calcaire, on one hand, and between the Predorsalian units and the Flysch Trough as isolated carbonate platforms, on the other hand; (2) during the late Eocene-early Oligocene an extensional tectonic event, well marked in the Dorsale Calcaire, caused the collapse of these platforms and resulted in olistostromes and coarse-grained breccias in both the Predorsalian and the Béni Ider areas; (3) by the beginning of mid-Oligocene, an overturning contractional event in the Ghomarides resulted in the regional onset of the siliciclastic depositional regime throughout these palaeogeographical areas; (4) during the Aquitanian-early Burdigalian, the stepwise return of pelagic deposition in the Ghomarides indicates extensional phases, whereas the homogenization of the same pelagic facies over the Dorsale Calcaire and its external surroundings may indicate that the previously distant palaeogeographical areas were brought nearer (i.e. just before large-scale thrusting).
The Argille Varicolori unit in Lucania (Italy): a record of tectonic offscraping and gravity sliding in the Mesozoic-Tertiary Lagonegro Basin, southern Apennines
Authors: Mattioni L. , Tondi E. , Shiner P. , Renda P. , Vitale S. , Cello G.
Published: April 2008

Detailed geological mapping and new stratigraphic and structural data collected in the Lucania area of the southern Apennines allowed us to assess the deformation history of Il Monte-Corleto Perticara zone, in the High Agri Valley (Lucanian Apennines, southern Italy) where red and green shales (known as Argille Varicolori or Argille scagliose) crop out. Our observations suggest that: (1) ‘chaotic’ facies within the Argille Varicolori may be attributed to a broken formation generated by overthrusting of Apenninic Platform units onto already deformed Lagonegro basin strata; (2) gravity sliding phenomena at the thrust front enhanced the development of debris flow and the emplacement of olistostromes at distances of up to tens of kilometres from the leading edge of the Apenninic Platform thrust; (3) the above processes probably ended in mid-Miocene time, as suggested by observed structural and stratigraphic relationships among accreted terranes and synorogenic deposits. The evolutionary model envisaged here could also be relevant in other active convergent zones, where seismic and drilling data are sparse, and in subaerial fossil margins where broken formations occur.
Pore geometry of Permo-Triassic sandstone from measurements of electrical spectroscopy
Authors: Scott Julian B. T. , Barker R. D.
Published: April 2008

In order to provide an indirect method of estimating the hydraulic properties of sandstone aquifer rocks, electrical spectroscopy measurements were made on Permo-Triassic Sandstone over the frequency range 0.0001–1000 Hz. Samples from several boreholes across Britain are shown to exhibit a phenomenon called electrical relaxation, which we have modelled using a generalized Cole-Cole equation. The Cole-Cole parameters correlate well with other hydrogeologically important parameters determined using mercury injection capillary pressure and nitrogen adsorption techniques. Of greatest importance is that the relaxation time, τ, is strongly related to the dominant pore-throat size from which intergranular permeability may be estimated. A normalized version of the chargeability appears to be related to the surface conductivity and this gives the possibility of estimating the pore surface area to volume ratio, a value that is important in determining both permeability and sorption. The potential uses of electrical spectroscopy in hydrogeology and many other fields, including geology and petroleum petrophysics, are only now becoming apparent, and further advances are certain.
Estimation of vertical diffusivity from seasonal fluctuations in groundwater pressures in deep boreholes near Sellafield, NW England
Authors: Streetly M. J. , Heathcote J. A. , Degnan P. J.
Published: April 2008

In 1998, as part of the process to assess the suitability of a site near Sellafield, Cumbria, for a deep geological repository for solid intermediate level and some solid low-level radioactive waste, United Kingdom Nirex Limited (Nirex) commissioned a study into the seasonal fluctuations in groundwater pressure observed in many of the monitoring boreholes in the area. Many of the monitoring zones in the deep boreholes at Sellafield show some response in groundwater pressure to annual variations in recharge. These seasonal fluctuations were quantified in terms of amplitude and lag over two full recharge cycles (1994–1996). The extremely detailed monitoring array installed by Nirex at the potential repository zone gives a unique opportunity to observe in detail the attenuation of the recharge signal, as it is propagated vertically downwards through the Sherwood Sandstone Group and into the underlying basement rocks. Use of an analytical approach to model the data provides constraints on values of the vertical diffusivity of the strata. The values of hydraulic formation parameters derived by this methodology are broadly consistent with results from borehole testing, though somewhat higher. This may in part be due to the large scale associated with the cyclic recharge signal. The attenuation of the seasonal fluctuations in three dimensions (3D) throughout the study area provides information at a scale suitable for use in constraining regional flow models.
Structural controls on groundwater flow in the Permo-Triassic sandstones of NW England
Authors: Seymour K. J. , Ingram J. A. , Gebbett S. J.
Published: April 2008

There is increasing evidence that groundwater flow in many parts of the major Permo-Triassic sandstone aquifers of NW England is influenced strongly by predominantly N-S-trending faults. These structural controls on groundwater flow may only become apparent when the aquifers are subject to abstraction stress. A series of case examples are presented, from the Fylde Sandstone aquifer north of Preston, and from the sandstone aquifers of the Lower Mersey Basin, Manchester and Wirral areas. In these studies the ‘compartmentalization’ of the aquifers by faults has been recognized in field investigations and also in numerical modelling studies related to groundwater resources development on both local and aquifer-wide scales.
Controls on dense non-aqueous-phase liquid transport in Permo-Triassic sandstones, UK
Authors: Gooddy D. C. , Bloomfield J. P.
Published: April 2008

The Permo-Triassic sandstones are geographically and lithologically diverse, and exhibit large variations in porosity (ф), pore-throat size, gas permeability (
k
) and mineral phases. These parameters influence considerably the flow and transport of contaminants. The aquifer is susceptible to contamination by a range of pollutants from both contemporary and historic sources as it outcrops in a number of large industrial towns. One such class of pollutants are chlorinated hydrocarbons, which have been used extensively for years in dry-cleaning and metal degreasing. The physical, chemical and biological properties of these dense non-aqueous-phase liquids (DNAPLs) make them a particular cause of groundwater contamination. Standard physical property measurements, along with a weak nitric acid extraction to determine dominant minerals, were carried out on consolidated sandstones. A laboratory method was developed to produce pressure-saturation curves for a DNAPL-water-sandstone system. Entry pressures were found to be lower than predicted from theoretical considerations, which could be explained in part by the relative amounts of calcite and dolomite present in the pore space. Calculations on relative permeability show that at roughly 60% DNAPL saturation no water flow occurs. Understanding the controls on DNAPL transport can greatly assist the need for appropriate remedial action.
The capillary characteristic model of petroleum hydrocarbon saturation in the Permo-Triassic sandstone and its implications for remediation
Authors: Privett K. D.
Published: April 2008

Up to 9 × 10
6
l of light non-aqueous-phase liquid (LNAPL) is present in a 400 m-wide zone in the Permo-Triassic sandstone 30 m below a working industrial site. Remediation by skimmer wells failed to meet the expectations of the regulatory authorities. A detailed study has concluded that this form of remediation is not possible in this formation.

Initial estimates of the volume of LNAPL in the sandstone had been made by applying the concept of correcting for an ‘exaggerated thickness’ in the wells and multiplying by the porosity. Regulatory requirements were to remove most, preferably all, of the LNAPL. Site observations and measurements from high-quality core samples showed that the fine pores of the rock obey the capillary characteristic model. This was derived some 50 years ago in the oil production industry but has, in the opinion of the author, not been fully appreciated by the contaminated groundwater remediation sector in the UK. The model has been used to make a more reliable estimate of LNAPL volume and to demonstrate to the regulatory authorities the processes involved and how these control the ability to clean the site.

The concept of ‘apparent volume’ is introduced as an overall measure of apparent thickness in the site-wide monitoring borehole network. Apparent volume is shown to be broadly negatively correlated with groundwater-level fluctuations and so the measure of changes in apparent thickness is not a sound basis for regulatory compliance. It was found that LNAPL thickness in wells is less than the thickness of the contaminated zone in the sandstone and, importantly, the degree of saturation is no more than 30%. This leads to a reduction in effective permeability of two orders of magnitude (from the fully saturated condition), which has serious implications for remediation. Most of the LNAPL is immobile and so pumping is ineffective; it does not reduce the volume of aquifer impacted nor does it have any significant effect on reducing the source zone for dissolved-phase generation, the size of any dissolved phase plume or the longevity of such a plume.
Combined isotopic and modelling approach to determing the source of saline groundwaters in the Selby Triassic sandstone aquifer, UK
Authors: Bottrell S. H. , West L. J. , Yoshida K.
Published: April 2008

Groundwater abstraction from the Triassic Sherwood Sandstone aquifer in the Selby area, Yorkshire, UK, has caused decline of the water level in the aquifer and groundwater quality problems such as high chloride and sulphate concentrations. Geochemical and isotopic analysis of groundwaters and groundwater modelling of an approximately 25 × 30 km area around Selby was carried out to understand the groundwater flow conditions and identify the source of saline water. Isotopic compositions (δ
34
S and δ
18
O) of seawater sulphate, Coal Measures brine and Permian evaporite sources do not match that associated with salinity in the Selby wellfield. Rather, the source of saline groundwater in the Selby wellfield matches the isotopic composition of Triassic evaporites in the overlying Mercia Mudstones.

Steady-state groundwater flow modelling demonstrates that that majority of water abstracted from the Selby wellfield is balanced by recharge from the west of Selby at Brayton Barff, and from the Escrick and York moraines to the north. A small proportion of the abstracted water originates from leakage from the River Ouse through the confining layer as a result of drawdown in the Selby area. The development of a cone of drawdown centred on Selby has created a new E-W hydraulic gradient to the east of Selby, allowing water ingress from the east. Capture-zone analysis indicates that the four abstraction boreholes contaminated by saline water collect groundwater from the north to NE (i.e. from the direction of the boundary between the Sherwood Sandstone and the Mercia Mudstone), confirming that the source of salinity is likely to be the Mercia Mudstone evaporites.
Simplicial geometry for compositional data
Authors: Egozcue J. J. , Pawlowsky-Glahn V.
Published: April 2008

The main features of the Aitchison geometry of the simplex of
D
parts are reviewed. Compositions are positive vectors in which the relevant information is contained in the ratios between their components or parts. They can be represented in the simplex of
D
parts by closing them to a constant sum, e.g. percentages, or parts per million. Perturbation and powering in the simplex of
D
parts are respectively an internal operation, playing the role of a sum, and of an external product by real numbers or scalars. These operations impose the structure of (
D
− 1)-dimensional vector space to the simplex of
D
parts. An inner product, norm and distance, compatible with perturbation and powering, complete the structure of the simplex, a structure known in mathematical terms as a Euclidean space. This general structure allows the representation of compositions by coordinates with respect to a basis of the space, particularly, an orthonormal basis. The interpretation of the so-called balances, coordinates with respect to orthonormal bases associated with groups of parts, is stressed. Subcompositions and balances are interpreted as orthogonal projections. Finally, log-ratio transformations (alr, clr and ilr) are considered in this geometric context.
The magnetic polarity time scale across the Permian-Triassic boundary
Authors: Steiner Maureen B.
Published: April 2008

Early Triassic and Late to Middle Permian magnetostratigraphic investigations are numerous and span the globe. More than 20 magnetostratigraphic sequences have documented all or part of the Early Triassic geomagnetic field polarity, and > 27 have examined the Late and Middle Permian; 13 span the Permian-Triassic boundary. In order to assess the exact polarity sequence in the time period surrounding the Permian-Triassic boundary, the sequences have been compared diagrammatically. Four distinctive intervals of geomagnetic polarity characterize the Early Triassic, and have been named for discussion purposes: Gries N, Diener R-N, Smith N, and Spath N. A polarity pattern for the Mid- and Late Permian is also recognizable. The Mid- and Late Permian are characterized by two normal polarity intervals (Chang N and Capitan N) of greater apparent duration than those of the Early Triassic. Below the Permo-Triassic Gries N, a distinctive short duration reversed-normal-reversed polarity pattern characterizes the uppermost Changhsingian. The oldest normal polarity in the Middle Permian occurred during the Wordian Stage, established by results from three global sequences. Therefore, the geomagnetic field resumed reversing behaviour after the ∼50 Ma-long constant polarity of the Kiaman Reversed Polarity Superchron (‘Illawarra reversals’) during the Mid- to Late Wordian, or ∼267 Ma.

Very significantly, the magnetostratigraphic summary from this work indicates that the Siberian Traps were active in the Late Permian and spanned the Permian-Triassic boundary. This new geomagnetic polarity dating of the massive Siberian flood basalt activity suggests long-term eruption and environmental degradation, therefore making this igneous activity the most likely cause of the end-Permian mass extinctions. Magnetostratigraphy suggests that eruptions probably commenced in the Late Guadalupian; therefore, the eruptions of two large igneous provinces, Emishan and Siberian, were probably partly simultaneous during part of the Mid- to Late Permian. Environmental havoc throughout the late Mid- and Late Permian is easy to imagine, stressing the environment prior to probably more voluminous eruptions at the end of the Guadalupian and Permian. Siberian eruptions continued through the early Early Triassic, and probably contributed to the slow biotic recovery.
Global Permian tetrapod biostratigraphy and biochronology
Authors: Lucas Spencer G.
Published: April 2008

The most extensive Permian tetrapod (amphibian and reptile) fossil records from the western United States (New Mexico-Texas) and South Africa provide the basis for definition of 10 land-vertebrate faunachrons that encompass Permian time. These are (in ascending order): the Coyotean, Seymouran, Mitchellcreekian, Redtankian, Littlecrotonian, Kapteinskraalian, Gamkan, Hoedemakeran, Steilkransian and Platbergian. These faunachrons provide a biochronological framework with which to determine and discuss the age relationships of Permian tetrapod faunas. Their correlation to the marine time scale and its numerical calibrations indicate that the Coyotean is a relatively long time interval of about 20 Ma, whereas most of the other faunachrons are much shorter, about 1–2 Ma long each. The Platbergian may also be relatively long, 14 Ma, although this is not certain. This suggests slow rates of terrestrial tetrapod faunal turnover during most of the Early Permian and late Middle to Late Permian, but more rapid rates of turnover during the latest Early and most of the Middle Permian, especially during the explosive initial diversification of therapsids.
Permian to Triassic sequences from selected continental areas of southwestern Europe
Authors: Virgili C. , Cassinis G. , Broutin J.
Published: April 2008

This contribution is a tentative reconstruction of the still-debated geological history in the primarily continental domains now represented in various parts of southwestern Europe, between the end of the Variscan diastrophism and the beginning of the Alpine sedimentary evolution. Data and interpretations vary from one region of terrestrial rocks to another. Despite this, we have tried to highlight the most typical and significant geological features. From the Carboniferous to Triassic, palaeontological investigations of the macroflora, microflora and tetrapod footprints, as well as radiometric data, generally point out the presence of three main ‘tectono-stratigraphic units’ (TSUs), separated by marked unconformities and gaps of as yet uncertain duration. The most important geological episode generally started about the Early/Middle Permian boundary and later spanned discontinuously and intensely throughout Middle Permian (Guadalupian) time. It was characterized by specific tectonic, magmatic, thermal and basinal features, which could mark the presumed change suggested by some authors from a Pangaea B to a Pangaea A. In this context, it is worth mentioning that the unconformable Middle?-Upper Permian higher TSU in Spain consists of ‘Buntsandstein’-type red beds, sometimes yielding a Thuringian flora; differently, in southern France, such as in the Lodève area, the Buntsandstein is Anisian and thus constitutes a later Triassic sequence, which rests unconformably above the as yet undefined (Mid-Late) Permian age assessment of the ‘La Lieude fossil site’; in the Southern Alps, the ‘Second tectono-sedimentary Cycle’ emphasized from the recent literature, which is initially made up of the Verrucano Lombardo-Val Gardena Sandstone red clastics, is in part laterally and upwardly replaced, east of the Adige Valley, by the sulphate evaporite to shallow-marine Bellerophon Formation. It is thus represented by continental and marine sediments generally pertaining to Late Permian (post-‘Lower Tatarian’) time and can be interpreted, in the light of the geological context of the region, as an Upper Permian and Lower Triassic TSU of a slightly younger numerical order (i.e. TSU 3 in place of TSU 2).
New continental Carboniferous and Permian faunas of Morocco: implications for biostratigraphy, palaeobiogeography and palaeoclimate
Authors: Hmich D. , Schneider J. W. , Saber H. , Voigt S. , El Wartiti M.
Published: April 2008

Late Palaeozoic sediments in central Morocco and the High Atlas Mountains document the development of this area during the formation of the Mauretanide part of the Hercynian orogeny. Continental basins formed during the Stephanian and Permian. Although scattered in time, they provide valuable biogeographical and climatic information for the Mauretanides as a link between the Variscides in the east, the Appalachians in the west and the Karoo in the south. New blattid insects in the Souss Basin enable correlation to Early Stephanian B. Furthermore, we document the oldest African tetrapod tracks (
Batrachichnus, Dromopus
). Litho- and biofacies indicate seasonally wet and dry phases. Wet red beds of the Khenifra Basin have produced tetrapod bones and the tracks
Limnopus, Batrachichnus
and
Dromopus
. Macrofloras give a transitional Autunian/Saxonian age. This fits well into the Artinskian wet phase. Similar facies pattern in the Tiddas Basin are correlated by tetrapod tracks as transitional Artinskian to Kungurian. Advanced tetrapod tracks of
Synaptichnium
and
Rhynchosauroides
were discovered in the Ikakern Formation of the Argana Basin, dated by pareiasaur remains as Wuchiapingian. Red beds of similar type are known in Europe, for example, from the Late Permian of the Lodève Basin. They originated during the Wuchiapingian wet phase.
Insect biostratigraphy of the Euramerican continental Late Pennsylvanian and Early Permian
Authors: Schneider Joerg W. , Werneburg Ralf
Published: April 2008

An insect zonation with a time resolution of 1.5–2 Ma for Late Pennsylvanian to Early Permian (Kasimovian to Artinskian) non-marine deposits is presented. The zonation is based on the directed morphogenetic evolution of colour pattern in the forewings of the blattid (cockroach) family Spiloblattinidae. This evolution is observed in lineages of succeeding species of three genera. All three genera are widely distributed in the palaeo-equatorial zone from Europe to North America, that is, in the Euramerican biota province. Increasing reports of spiloblattinid zone species in condont-bearing, interfingered marine/continental strata of North American Appalachian, Mid-Continent and West Texas basins could be the key to direct biostratigraphical correlations of pure continental profiles, as are present in the most parts of the Hercynides, to the global marine scale.
Sediment colour analysis from digital images and correlation with sediment composition
Authors: Nederbragt Alexandra J. , Dunbar Robert B. , Osborn Anthony T. , Palmer Adrian , Thurow Jürgen W. , Wagner Thomas
Published: April 2008

Sediment colour records can be extracted from digital images of sediment core surfaces, which provide the spatial resolution needed to measure colour in laminated sediments. Digital cameras sample colour in three broad wavelengths, red, green and blue, which are subsequently translated into the CIE
L*a*b*
colour space. Methods to extract calibrated colour values are discussed in this paper.
L*, a*
and
b*
values are correlated with geochemical analyses of cm-scale bulk sediment samples. The sediments are from a suite of laminated and homogenous sections containing organic matter, carbonate, biogenic opal and lithogenic material in variable proportions. Total organic carbon (TOC) content has the dominant effect on sediment colour. Results show that there is a strong correlation with lightness (
L*
) for TOC values between 0.5 and 10%, but that sediment lightness becomes saturated at higher TOC concentrations. Biogenic opal content cannot be resolved using the
L*a*b*
colour space. Biogenic opal in itself has a light colour but it tends to occur in darker coloured sediments because of a positive correlation between opal and TOC content. Carbonate content in the measured sections is generally less than 25%, at which values its effect on colour is obscured by the other sediment components.
Applications of confocal macroscope-microscope luminescence imaging to sediment cores
Authors: Ribes A. C. , Rack F. R. , Tsintzouras G. , Damaskinos S. , Dixon A. E.
Published: April 2008

We demonstrate the successful application of a novel, confocal scanning laser macroscope-microscope (cslM/m) system for non-invasive imaging of samples taken from lake and ocean sediment cores. Advantages of the macroscope-microscope system over other macroscopic luminescence imaging techniques, such as scanning electron microscopy-based cathodoluminescence and scanning-stage laser imaging, are highlighted and the implications for new core analysis techniques are explored.

The macroscope-microscope can image specimens ranging from 25 × 25 μm up to 7.5 × 7.5 cm in under 10 s using reflected light or photoluminescence as contrast mechanisms. Macroscope mode is used to rapidly survey the specimen and provide a photoluminescence ‘roadmap’. Microscope mode is used to provide ultra-high-resolution images of microfossils or areas of interest. Laser scanning is non-invasive and does not require any preparation of the specimen. Photoluminescence and fluorescence imaging results are shown for an entire core section recovered from Lake Huron by the Geological Survey of Canada (GSC). Photoluminescence images are shown for Ocean Drilling Program samples of a diatom mat and a radiolarian microfossil within the sample, a laminated interval of sediment from the Santa Barbara Basin (Site 893) and specimens from the Scotian Shelf (collected by the GSC).
On-site geological core analysis using a portable X-ray computed tomographic system
Authors: Freifeld Barry M. , Kneafsey Timothy J. , Rack Frank R.
Published: April 2008

X-ray computed tomography (CT) is an established technique for non-destructively characterizing geological cores. CT provides information on sediment structure, diagenetic alteration, fractures, flow channels and barriers, porosity and fluid-phase saturation. A portable CT imaging system has been developed specifically for imaging whole-round cores at the drilling site. The new system relies upon carefully designed radiological shielding to minimize the size and weight of the resulting instrument. Specialized X-ray beam collimators and filters maximize system sensitivity and performance. The system has been successfully deployed on the research vessel
JOIDES Resolution
for Ocean Drilling Program’s legs 204 and 210, at the Ocean Drilling Program’s refrigerated Gulf Coast Core Repository, as well as on the Hot Ice #1 drilling platform located near the Kuparuk Field, Alaska. A methodology for performing simple densiometry measurements, as well as scanning for gross structural features, is presented using radiographs from ODP Leg 204. Reconstructed CT images from Hot Ice #1 demonstrate the use of CT for discerning core textural features. To demonstrate the use of CT to quantitatively interpret dynamic processes, we calculate 95% confidence intervals for density changes occurring during a laboratory methane hydrate dissociation experiment. The field deployment of a CT represents a paradigm shift in core characterization, opening up the possibility for rapid systematic characterization of three-dimensional structural features, and leading to improved subsampling and core-processing procedures.
Nuclear magnetic resonance pore-scale investigation of permafrost and gas hydrate sediments
Authors: Kleinberg R. L.
Published: April 2008

Permafrost is a ubiquitous feature of arctic landmasses, and natural gas hydrate occurrence is widespread in the arctic and beneath the sea floor on continental slopes at all latitudes. The mechanical, thermal and hydraulic properties of the subsurface are profoundly modified by ice and hydrate. Nuclear magnetic resonance is a relatively recent addition to the measurement methods used to characterize recovered samples. This review shows how magnetic resonance has been used in two field studies to quantify frozen and unfrozen components of the sediment pore space, to understand the growth habit of ice and hydrate in rock and sediments, and to estimate hydraulic permeability.
Integration of the stratigraphic aspects of very large sea-floor databases using information processing
Authors: Jenkins Chris , Flocks Jim , Kulp Mark
Published: April 2008

Information-processing methods are described that integrate the stratigraphic aspects of large and diverse collections of sea-floor sample data. They efficiently convert common types of sea-floor data into database and GIS (geographical information system) tables, visual core logs, stratigraphic fence diagrams and sophisticated stratigraphic statistics. The input data are held in structured documents, essentially written core logs that are particularly efficient to create from raw input datasets. Techniques are described that permit efficient construction of regional databases consisting of hundreds of cores. The sedimentological observations in each core are located by their downhole depths (metres below sea floor — mbsf) and also by a verbal term that describes the sample ‘situation’ — a special fraction of the sediment or position in the core. The main processing creates a separate output event for each instance of top, bottom and situation, assigning top-base mbsf values from numeric or, where possible, from word-based relative locational information such as ‘core catcher’ in reference to sampler device, and recovery or penetration length. The processing outputs represent the sub-bottom as a sparse matrix of over 20 sediment properties of interest, such as grain size, porosity and colour. They can be plotted in a range of core-log programs including an in-built facility that better suits the requirements of sea-floor data. Finally, a suite of stratigraphic statistics are computed, including volumetric grades, overburdens, thicknesses and degrees of layering.
Crustal flow in Tibet: geophysical evidence for the physical state of Tibetan lithosphere, and inferred patterns of active flow
Authors: Klemperer S. L.
Published: April 2008

Many seismic and magnetotelluric experiments within Tibet provide proxies for lithospheric temperature and lithology, and hence rheology. Most data have been collected between
c.
88°E and 95°E in a corridor around the Lhasa-Golmud highway, but newer experiments in western Tibet, and inversions of seismic data utilizing wave-paths transiting the Tibetan Plateau, support a substantial uniformity of properties broadly parallel to the principal Cenozoic and Mesozoic sutures, and perpendicular to the modern NNE convergence direction. These data require unusually weak zones in the crust at different depths throughout Tibet at the present day. In southern Tibet these weak zones are in the upper crust of the Tethyan Himalaya, the middle crust in the southern Lhasa terrane, and the middle and lower crust in the northern Lhasa terrane. In northern Tibet, north of the Banggong-Nujiang suture, the middle and probably the lower crust of both the Qiangtang and Songpan-Ganzi terranes are unusually weak. The Indian uppermost mantle is cold and seismogenic beneath the Tethyan Himalaya and the southernmost Lhasa terrane, but is probably overlain by a northward thickening zone of Asian mantle beneath the northern Lhasa terrane. Beneath northern Tibet the upper mantle has not been replaced by subducting Indian and Asian lithospheres, and is warmer than to the south. These inferred vertical strength profiles all have minima in the crust, thereby permitting, though not actually requiring, some form of channelized flow at the present day. Using the simplest parameterization of channel-flow models, I infer that a Poiseuille-type flow (flow between stationary boundaries) parallel to India-Asia convergence is occurring throughout much of southern Tibet, and a combination of Couette (top-driven, between moving boundaries) and Poiseuille lithospheric flow, perpendicular to lithospheric shortening, is active in northern Tibet. Explicit channel-flow models that successfully replicate much of the large-scale geophysical behaviour of Tibet need refinement and additional model complexity to capture the full details of the temporal and spatial variation of the India-Asia collision.
Crustal flow modes in large hot orogens
Authors: Beaumont C. , Nguyen M. H. , Jamieson R. A. , Ellis S.
Published: April 2008

Crustal-scale channel flow numerical models support recent interpretations of Himalayan—Tibetan tectonics proposing that gravitationally driven channel flows of low-viscosity, melt-weakened, middle crust can explain both outward growth of the Tibetan Plateau and ductile extrusion of the Greater Himalayan Sequence. We broaden the numerical model investigation to explore three flow modes: homogeneous channel flow (involving laterally homogeneous crust); heterogeneous channel flow (involving laterally heterogeneous lower crust that is expelled and incorporated into the mid-crustal channel flow); and the hot fold nappes style of flow (in which mid-/lower crust is forcibly expelled outward over a lower crustal indentor to create fold nappes that are inserted into the mid-crust). The three flow modes are members of a continuum in which the homogeneous mode is driven by gravitational forces but requires very weak channel material. The hot fold nappe mode is driven tectonically by, for example, collision with a strong crustal indentor and can occur in crust that is subcritical for homogeneous flows. The heterogeneous mode combines tectonic and gravitationally driven flows. Preliminary results also demonstrate the existence and behaviour of mid-crustal channels during advancing and retreating dynamical mantle lithosphere subduction. An orogen temperature—magnitude (T-M) diagram is proposed and the positions of orogens in T-M space that may exhibit the flow modes are described, together with the characteristic positions of a range of other orogen types.
Provenance of the Greater Himalayan Sequence and associated rocks: predictions of channel flow models
Authors: Jamieson R. A. , Beaumont C. , Nguyen M. H. , Grujic D.
Published: April 2008

Numerical models for channel flow in the Himalayan—Tibetan system are compatible with many tectonic and metamorphic features of the orogen. Here we compare the provenance of crustal material in two channel flow models (HT1 and HT111) with observations from the Himalaya and southern Tibet. Thirty million years after the onset of channel flow, the entire model crust south of the India—Asia suture still consists only of ‘Indian’ material. The model Greater Himalayan Sequence (‘GHS’) is derived from Indian middle crust originating ≤1000 km south of the initial position of the suture, whereas the Lesser Himalayan Sequence (‘LHS’) is derived mainly from crust originating ≥1400 km south of the suture. Material tracking indicates little or no mixing of diverse crustal elements in the exhumed region of the model ‘GHS’, which is derived from originally contiguous materials that are transported together in the top of the channel flow zone. These results are compatible with provenance data indicating a clear distinction between GHS and LHS protoliths, with the GHS originating from a more distal position (relative to cratonic India) than the LHS. In model HT111, domes formed between the suture and the orogenic front are cored by ‘Indian’ middle crust similar to the ‘GHS’, consistent with data from the north Himalayan gneiss domes. Material tracking shows that plutons generated south of the suture should have ‘Indian’ crustal signatures, also compatible with observations. Model ‘GHS’ pressure—temperature—time (P-T-t) paths pass through the dehydration melting field between 30 and 15 Ma, consistent with observed leucogranite ages. Finally, exposure of midcrustal ‘GHS’ and ‘LHS’ material at the model erosion front is consistent with the observed appearance of sedimentary detritus in the Lesser Himalaya. We conclude that channel flow model results are compatible with provenance data from the Himalaya and southern Tibet.
Exhumation of Greater Himalayan rock along the Main Central Thrust in Nepal: implications for channel flow
Authors: Robinson D. M. , Pearson O. N.
Published: April 2008

South-vergent channel flow from beneath the Tibetan Plateau may have played an important role in forming the Himalaya. The possibility that Greater Himalayan rocks currently exposed in the Himalayan Fold-Thrust Belt flowed at mid-crustal depths before being exhumed is intriguing, and may suggest a natural link between orogenic processes operating under the Tibetan Plateau and in the fold-thrust belt. Conceptual and numeric models for the Himalayan-Tibetan Orogen currently reported in the literature do an admirable job of replicating many of the observable primary geological features and relationships. However, detailed observations from Greater Himalayan rocks exposed in the fold-thrust belt’s external klippen, and from Lesser Himalayan rocks in the proximal footwall of the Main Central Thrust, suggest that since Early Miocene time, it may be more appropriate to model the evolution of the fold-thrust belt using the critical taper paradigm. This does not exclude the possibility that channel flow and linked extrusion of Greater Himalayan rocks may have occurred, but it places important boundaries on a permissible time frame during which these processes may have operated.
Thermal evolution of leucogranites in extensional faults: implications for Miocene denudation rates in the Himalaya
Authors: Annen C. , Scaillet B.
Published: April 2008

The crustally derived High Himalayan leucogranites (HHL) are characterized by strong isotopic heterogeneity and occurrence of magmatic muscovite. Such attributes indicate that the HHL were non-convecting magma bodies and crystallized at pressure-equivalent depths of more than 8.5 km. We have performed one-dimensional thermal modelling in order to simulate the process of incremental growth of a laccolith whose roof is tectonically removed during intrusion, in a context of crustal exhumation due to channel flow. The objective is to define under what conditions HHL laccoliths emplaced close to active normal faults may be built without convecting while crystallizing muscovite. The results indicate that for a HHL thickness in the range 5–10 km, denudation rates cannot be higher than 4 mm a
−1
, and are more likely below 3 mm a
−1
. At such denudation rates, the intrusion process needs to start at depths of
c.
22 km, except when the final laccolith thickness is 10 km, in which case the depth of first-emplaced magmas cannot exceed 18 km. Thick HHL laccoliths (>7 km) may require a minimum denudation rate, on the order of 1 mm a
−1
, to prevent wholesale convection and allow muscovite crystallization. Yet, emplacement of such thick HHL laccoliths during normal faulting implies that the top part of the leucogranite nearly reaches the surface while its base is still fed by active intrusions. Overall, such relatively low denudation rates suggest that, when HHL were intruded, the overlying crustal column was not undergoing vigorous erosion. Within the framework of a crustal channel flow, this suggests that the zone of focused erosion during the Miocene was located to the south of the current exposures of the HHL belt. Our results also show that to explain the steep cooling histories documented in many HHL, denudation must have been active after HHL solidification, especially when they were intruded close to their source region. However, to preserve the HHL from exhumation and erosion until the present time, the average denudation rate after emplacement cannot have exceeded 0.5 mm a
−1
.