bluuebunny/crossref_metadata_2025 huggingface dataset:
‘Verrucano’ and ‘Pseudoverrucano’ in the Central-Western Mediterranean Alpine Chains: palaeogeographical evolution and geodynamic significance
Authors: Perrone V. , Martín-Algarra A. , Critelli S. , Decandia F. A. , D’Errico M. , Estevez A. , Iannace A. , Lazzarotto A. , Martín-Martín M. , Martín-Rojas I. , Mazzoli S. , Messina A. , Mongelli G. , Vitale S. , Zaghloul M. N.
Published: April 2008

The Anisian-Carnian Verrucano Group of the Tuscan Metamorphic Units and the Triassic-Hettangian Pseudoverrucano Formation of the homonymous unit are mainly continental redbeds occurring in Tuscany at the base of the Alpine orogenic cycle. A study carried out throughout the Apennine, Maghrebian and Betic Chains emphasized the presence in all these orogenic belts of deposits more or less coeval and similar both to the metamorphic Verrucano and to the unmetamorphosed Pseudoverrucano. Thus, the distinction of Verrucano and Pseudoverrucano successions has a palaeogeographical and geodynamic importance at the scale of the Western Mediterranean. Both successions developed during the continental rift stage of Pangaea, which led to later break-up at the edges of a future microplate, interposed between the Europe, Africa and Adria-Apulia plates, but they are characterized by different tectonometamorphic evolution. Pseudoverrucano-like deposits, devoid of Alpine metamorphism, characterize the highest tectonic units of the nappe stack and they overthrust units bearing Verrucano-like deposits. These latter show an Alpine tectonometamorphic history marked during the Miocene by intense deformation and HP/LT metamorphism (at pressures in the range of 0.8–2 GPa), followed by a retrograde phase associated with decompression, suggesting subduction and subsequent exhumation of continental crust. Intriguing palaeogeographical problems arise from the analysis of Verrucanobearing units, because the same evolution seems to characterize both units considered to belong to a realm similar to that of the north-verging Austroalpine nappe system and some units referred to the south-verging fold-thrust belt derived from the Adria-Apulia palaeomargin.
Recent palaeostresses from striated pebbles related to fold development in a mountain front: the Prerif Ridges (Rif Cordillera, Morocco)
Authors: Ruano P. , Bargach K. , Galindo-Zaldívar J. , Chalouan A. , Ahmamou M.
Published: April 2008

The southern mountain front of the Rif Cordillera (Morocco) provides impressive geological evidence of the most recent deformations related to the activity of the Eurasian-African plate boundary in the Western Mediterranean. In this region, striated and pitted pebbles are analysed from Pliocene-Quaternary rocks located in the southern front of the Prerif Ridges, which have been deformed by south-vergent folds of decametre to hectometre sizes. Striated and pitted pebbles represent a tectonic deformation structure which, although very scarce in nature, is revealed as one of the most complete for determining palaeostresses. In Jbel Trhat and Jbel Zerhoun of the Rif mountain front, north-south to NNW-SSE prolate compression stress ellipsoids are related to an initial stage of south-vergent fold development during the progressive tilting of conglomerate layers. Finally, oblate stress ellipsoids indicate extension parallel to the fold axes. The north-south trend of the determined compression is compatible with a tectonic setting where the NW-SE convergence of the Eurasian and African plates is modified by the westward motion of large crustal blocks such as the Alboran Domain or the southwestward motion of blocks in the Rif Cordillera.
Geophysical and geological interpretation of discrepancies in site residuals in northern Morocco: a simple qualitative approach
Authors: Ait Brahim L. , Mouayn I. , Abdelouafi A. , Benhalima M. , Tadili B.
Published: April 2008

Surface geology, gravimetric, and heat flow data are used to explain discrepancies between

M
D

site residuals, using the average magnitude site residuals (

AMSR
j

) which are opposite of the station corrections (

cSta
j

) calculated for the 25 selected short-period seismic stations of the Moroccan seismological network.

M
D

site residuals range from −0.29 to +0.32, and appear to be the result of the complex interaction of the predominant near-station geophysical and geological parameters. With this simple qualitative approach, we found that high negative residuals are obtained for older well-consolidated Precambrian crystalline rocks with low surface heat flow, and high positive residuals are attributed to recent unconsolidated sediments with high heat flow. The explanation for the intermediate residual values remains more complex and requires more accuracy and better quality data, and may not be fully justified in this study.
Factorial correspondence analysis: a useful tool in palaeogeographical reconstructions; example from late Cretaceous calciturbidites of the northwestern External Rif (Morocco)
Authors: El Kadiri Kh. , El Kadiri K. , Chalouan A. , Bahmad A. , Salhi F. , Liemlahi H.
Published: April 2008

Factorial correspondence analysis proved to be a useful statistical tool when comparing the clastic input of distinct deposits and searching for their source area. Here we analyse and compare the reworked carbonate clastic material in the late Cretaceous calciturbidites of the Béni Ider area (Rifian External Domain) and the Internal Dorsale Calcaire (Internal Domain). The main result is that the source area for the Béni Ider calciturbidites was a neighbouring, isolated, shallow carbonate platform, the basement of which consists of a Jurassic succession of the Internal Dorsale Calcaire type. However, statistical comparison with the coeval pelagic deposits of to the latter domain leads us to exclude the Dorsale Calcaire as a possible origin of these Béni Ider calciturbidites. The source area was probably a lost carbonate platform, which should be located in the open External Domain. This result appears to be consistent with the Tariquide Ridge hypothesis and gives new insights into the palaeogeographical scheme of the flysch trough.
Fault and fold interaction during the development of the Neogene-Quaternary Almería-Níjar basin (SE Betic Cordilleras)
Authors: Pedrera Antonio , Marín-Lechado Carlos , Galindo-Zaldívar Jesús , Rodríguez-Fernández Luis Roberto , Ruiz-Constán Ana
Published: April 2008

The Neogene-Quaternary Almería-Níjar basin includes the Carboneras Fault, which constitutes a major left-lateral feature of the Betic Cordilleras. New gravity data help to determine the geometry of the sedimentary infill. The region underwent NE-SW extension during the Tortonian and local NW-SE compression during the first stages of Sierra Alhamilla uplift. During the Messinian, the sinistral strike-slip motion along the Carboneras Fault Zone, the dextral strike-slip motion along NW-SE-oriented faults, and the development of large folds such as the Sierra Alhamilla antiform, suggest clockwise rotation (towards the north) of the maximum stress axis (σ
1
). During the Pliocene, a NNW-SSE-oriented compression also contributes to fold development. Finally, during the Quaternary, an ENE-WSW-directed extension controls the development of NW-SE-oriented normal oblique faults. The most recent local normal activity of the Carboneras Fault is related to this extension, whereas its behaviour as a left-lateral strike-slip fault may be a consequence of the accommodation of NW-SE normal fault displacements. Basic rock bodies, recognized by means of a detailed study of the magnetic anomalies, are related to the volcanic activity known to have occurred in the area in Late Miocene times.
The Upper Cretaceous in the Tagus Basin (Central Spain): sequential analysis based on oil-well data and outcrop correlation
Authors: Segura Manuel , Polo Teresa , García-Hidalgo José F. , Gil Javier , Carenas Beatriz , García Álvaro
Published: April 2008

The logs from six oil wells drilled between 1960 and 1980 in the Upper Cretaceous succession of the Tagus Basin were analysed and correlated with surface outcrops, to estimate sedimentary environments and to detect cyclicity in sedimentation. Log interpretation has been carefully checked with outcrop data, because high peaks in gamma-ray logs, usually considered to represent open marine facies, may correspond either to open marine or to muddy coastal deposits. The former correspond to the maximum flooding surfaces of depositional sequences, whereas the latter correspond to sequence boundaries. Three second-order depositional megasequences have been recognized (MS-2, MS-3 and MS-4). The basal megasequence onlaps older rocks, grading upwards from continental to marine deposits. The megasequence MS-3 shows a basal marly transgressive interval and a thick carbonate pile at the top, grading to the SE to sabkha environments. The top megasequence is hardly recognized in surface outcrops, but in well logs it is a thick evaporite — claystone unit of mainly sabkha environments that grade westwards to coastal deposits. Sedimentation of megasequences MS-3 and MS-4 extended farther west than previously considered, covering areas considered as part of the exposed Hesperian Massif. These were areas of marine and coastal sedimentation where organic matter accumulation could be potentially high, and can be considered potential areas for oil or gas exploration.
Palaeogeography of the Upper Cretaceous-Eocene carbonate turbidites of the Northern Apennines from provenance studies
Authors: Argnani Andrea , Fontana Daniela , Stefani Cristina , Zuffa Gian G.
Published: April 2008

The Upper Cretaceous Helminthoid Flysch (HF) of the Northern Apennines consists of thick and regionally widespread deep-water carbonate turbidite successions, deposited during the initial stages of Alpine collision. The HF spans the time from Turonian to Early Eocene and is mainly composed of intrabasinal carbonate ooze mixed with clay; siliciclastic terrigenous beds are also present, but they are a volumetrically minor component of the successions. Petrographic and sedimentological signatures indicate that the HF was deposited in distinct basins located below the carbonate compensation depth. Bulk composition and heavy minerals of terrigenous beds indicate provenance from different crustal levels of the European and Adria plates. The petrographic and palaeobathymetric characteristics of these turbidites indicate the coexistence of an active-margin tectonic setting, a palaeogeographical position suitable for carbonate ooze production and storage, and limited supply of terrigenous detritus into the basin. Palaeotectonic reconstructions and stratigraphic data suggest that Adria represented a vast repository of penecon-temporaneous carbonate mud; the presumably intense seismic activity related to the pre-collisional Alpine orogeny promoted large-scale failures of shelf and/or slope biogenic muddy sediments, resulting in the deposition of a large volume of carbonate turbidites. Only occasionally, turbidity currents probably linked to exceptional fluvial floods generated pure terrigenous beds with different petrographic signatures for each HF succession.
High-resolution petrophysical characterization of samples from an aeolian sandstone: the Permian Penrith sandstone of NW England
Authors: Lovell M. A. , Jackson P. D. , Harvey P. K. , Flint R. C.
Published: April 2008

The Penrith Sandstone is an orange/red, mainly homogeneous, friable rock made up of well-rounded, highly spherical quartz grains, often showing euhedral overgrowths of quartz. Sandstone samples from Stoneraise Quarry, NW England, exhibit a remarkable degree of rounding and very high sphericity, along with frosted textures typical of aeolian deposits. Chemically, the rock is predominantly SiO
2
(>95%), with no evidence of carbonate cements. Quartz predominates with a small proportion (10%) of feldspar. The grain size across heterogeneous zones varies from very fine (100 µm) to coarse sand (700 µm). There is no evidence of the presence of clay minerals. Petrophysically, based on the measurements made in this study, the Penrith Sandstone is a typical clean sandstone characterized by moderate porosity (12%) and core-plug permeability (10
−14
−10
−12
m
2
), and Archie ‘
m
’ exponents between 1.90 and 1.91, suggesting a reasonably clean ‘Archie’ rock with no excess conductivity associated with clays or bound water. Capillary pressure curves for four samples demonstrate unimodal pore-size distributions with a single modal range that varies between 25–50 and 70–80 µm. Because of the relative simplicity of its petrophysics, the sandstone is thus potentially very useful in fundamental studies, and also in the trialling of new techniques.

We use imaging techniques to investigate the degree of heterogeneity and the fabric of the Penrith Sandstone. Conventional optical images are complemented by electrical resistivity, porosity and mini-permeametry images. These two-dimensional maps of resolution of approximately 5 mm show a spatial similarity determined by the rock fabric. The detailed images show a wider degree of variation and heterogeneity than the plug-averaged values. The success of the resistivity imaging method suggests that the technique could be used in deriving correlations that could be used to interpret borehole resistivity imaging logs. However, in the present study, correlations of property values derived from the imaging do show considerable scatter: this suggests that heterogeneity even below the scale of the imaging is also important, a conclusion supported by thin-section and electronmicroscope data.
Petrophysical characterization of the Sherwood Sandstone from East Yorkshire, UK
Authors: Pokar Magdeline , West L. J. , Odling N. E.
Published: April 2008

Petrophysical tests were conducted on core samples from the unsaturated zone of the Sherwood Sandstone Group in East Yorkshire. Tests were conducted to determine which physical parameters most influenced its hydraulic conductivity values. The main parameters analysed were grain-size distribution, pore-throat size distribution, clay content, mineralogy and porosity. A constant flow rate permeameter was used to measure saturated hydraulic conductivity values in the vertical direction (perpendicular to lamination),
K
v
, and horizontal direction (parallel to lamination),
K
h
. Hydraulic conductivity values in the vertical direction,
K
v
, ranged from 0.004 to 0.12 m day
−1
while values in the horizontal direction,
K
h
, ranged from 0.01 to 0.17 m day
−1
. Hydraulic conductivity anisotropy,
K
h
/
K
v
, varied from 0.6 to 35. Scanning electron microscope analysis showed this anisotropy to be caused mainly by millimetre-scale laminations. Representative bulk hydraulic conductivity values were estimated from the core data; bulk horizontal hydraulic conductivity,
K
hb
, was estimated as 0.1 m day
−1
, and bulk vertical hydraulic conductivity,
K
vb
, as 0.01 m day
−1
. Principal components analysis and multiple regression analysis were used to determine parameters that affect hydraulic conductivity most. Grain sorting is established to be the most important parameter to influence
K
v
values; samples with fine laminations have relatively low
K
v
.
Calcrete as a source of heterogeneity in Triassic fluvial sandstone aquifers (Otter Sandstone Formation, SW England)
Authors: Newell Andrew J.
Published: April 2008

Carbonate is not generally considered as a potential source of large-scale heterogeneity in Permo-Triassic sandstone aquifers. This study shows that carbonate, in the form of early diagenetic calcrete, forms an abundant component of the Triassic Otter Sandstone Formation in south Devon. Three types of calcrete are described from the outcrop of this fluvial sandstone dominated aquifer: rhizocretions; calcrete sheets; and calcrete conglomerates. Data obtained from core plugs show that calcrete reduces sandstone permeability to less than 10
−15
m
2
and porosity to less than 12%. Calcrete can be sufficiently abundant to produce a significant (up to 30%) reduction in the total effective porosity of the aquifer. Moreover, calcrete conglomerates can form laterally extensive (up to 1 km) low-permeability sheets that will represent major baffles to vertical flow.
Investigating rising nitrate concentrations in groundwater in the Permo-Triassic aquifer, Eden Valley, Cumbria, UK
Authors: Butcher Andrew , Lawrence Adrian , Jackson Chris , Cullis Emma , Cunningham Jennifer , Hasan Kamrul , Ingram John J. A.
Published: April 2008

Groundwater nitrate concentrations in the Permo-Triassic aquifer of the Eden Valley vary from less than 4 mg l
−1
to in excess of 100 mg l
−1
(as NO
3
). A significant number of boreholes exhibit rising trends in nitrate concentration that either approach or exceed the CEC Directive 80/778 Maximum Admissible Concentration (MAC) of 50 mg l
−1
. The main source of the nitrate is believed to be the nitrogen applied to grassland, both as slurry and as inorganic fertilizers.

The variability in groundwater nitrate concentrations is thought to be due in part to land use, particularly where low-yielding boreholes derive their water from a limited/localized area, and in part due to the variability in the travel times for water and solutes to migrate from the soil to the water table and then to the borehole. This variability in travel times is a function of surficial geology, depth to water table, depth of borehole and superficial deposit thickness, amongst other factors.

It is surprising, given the considerable storage within the saturated zone of the aquifer and the slow groundwater movement, that some relatively deep boreholes pump groundwater with nitrate concentrations in excess of 20 mgl
−1
. Simple numerical modelling suggests that the fraction of modern water pumped is sensitive to the presence of fissures close to the abstraction boreholes and the location of the boreholes relative to superficial deposits. For some scenarios, using realistic superficial deposit geometries and aquifer hydraulic parameters, the proportion of modern water (water that is derived from infiltration that reached the water table since pumping started) could exceed 40% within 15 years of pumping.
Investigation and management of a kerosene leakage into a Permo-Triassic sandstone aquifer in the UK
Authors: Rees S. B.
Published: April 2008

Leakage over a 35-year period, starting in the 1960s, of approximately 9 × 10
6
l of kerosene from an industrial complex located above fractured Permo-Triassic sandstone aquifer resulted in the potential for a significant dissolved phase. However, a phased, risk-based approach identified no significant risks in terms of dissolved-phase petroleum hydrocarbons, BTEX, or volatile or semi-volatile organic compounds. This is considered to be due to biodegradation of potential contaminants via metabolic pathways using electron acceptors primarily provided by the groundwater recharge (oxygen, nitrate and sulphate). Contaminant concentrations have remained below regulatory limits for protection of the receptor since monitoring was initiated in 2000. This case study demonstrates the potential for biodegradation within the Permo-Triassic sandstone aquifer of the UK: the risk-based approach described and the management plan developed could be applicable at other sites.
Compositional data and their analysis: an introduction
Authors: Pawlowsky-Glahn V. , Egozcue J. J.
Published: April 2008

Compositional data are those which contain only relative information. They are parts of some whole. In most cases they are recorded as closed data, i.e. data summing to a constant, such as 100% — whole-rock geochemical data being classic examples. Compositional data have important and particular properties that preclude the application of standard statistical techniques on such data in
raw
form. Standard techniques are designed to be used with data that are free to range from − ∞ to + ∞. Compositional data are always positive and range only from 0 to 100, or any other constant, when given in closed form. If one component increases, others must, perforce, decrease, whether or not there is a genetic link between these components. This means that the results of standard statistical analysis of the relationships between
raw
components or parts in a compositional dataset are clouded by spurious effects. Although such analyses may give apparently interpretable results, they are, at best, approximations and need to be treated with considerable circumspection. The methods outlined in this volume are based on the premise that it is the relative variation of components which is of interest, rather than absolute variation. Log-ratios of components provide the natural means of studying compositional data. In this contribution the basic terms and operations are introduced using simple numerical examples to illustrate their computation and to familiarize the reader with their use.
On stability of compositional canonical variate vector components
Authors: Reyment R. A.
Published: April 2008

Canonical variate analysis (aka discriminant coordinates) is viewed from the aspect of Aitchisonian compositional data analysis and the concept of stability in canonical vectors examined in relation to their refication (i.e. providing canonical vector components with a practical interpretation). The log-ratio transformation was found to have computational and interpretational advantages over the centred log-ratio transformation. The
ad hoc
application of N. A. Campbell’s application of the method of shrinkage estimators to multiple discrimination, and the optimal retention of discrimination power, is exemplified by two cases, one drawn from quantitative sedimentology, the other from biomolecular palaeontology, with the intention of probing the effect of instability on interpreting the relative importance of standardized canonical variate coefficients in relation to the suppression of near-redundant directions of within-groups variation. Pronounced instability in canonical vectors may endanger the validity of an analysis.
Detailed guide to CoDaPack: a freeware compositional software
Authors: Thió-Henestrosa S. , Martín-Fernández J. A.
Published: April 2008

Suitable statistical methods for compositional data based on log-ratio methodology are not included in standard statistical packages. This work presents a detailed guide to freeware Excel for Windows-based package, named CoDaPack, which implements most of the basic statistical methods of this methodology. The web site Data Package contains this freeware package and to install it users need only to have Excel installed on their computers. The guide starts with an example in order to show how to work with this software and ends with a description of all features of CoDaPack.
Visualization of three- and four-part (sub)compositions with R
Authors: Bren M. , Batagelj V.
Published: April 2008

In 2003 the MixeR (Mixtures with R) project was started and work began to develop a library of functions written in R to support the analysis of compositional data, i.e. mixtures. This paper presents the ‘mix’ object in R, reading different data file formats and some MixeR routines for graphical presentation of three- and four-part (sub)compositions in ternary diagrams and tetrahedrons. Additional graphical features and use of parameters are applied on real data — a glacial dataset and dataset of the researcher’s daily activities, both from Aitchison’s (1986) book. All these routines and datasets are available at
http://vlado.fmf.uni-lj.si/pub/MixeR
Frequency distributions and natural laws in geochemistry
Authors: Buccianti A. , Mateu-Figueras G. , Pawlowsky-Glahn V.
Published: April 2008

The chemical composition of natural waters is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and effects resulting from human activities. The chemical composition of the crustal rocks of the Earth, as well as the composition of the ocean and the atmosphere, are important in evaluating sources of solutes. Data used in the investigation of natural and non-natural contributions are obtained usually from chemical analysis of water samples, which may be statistically evaluated with the aim of summarizing the contained information. However, as these data are compositional and thus constrained to move in the simplex, application of usual statistical methodologies may lead to incorrect evaluations and/or interpretations. This paper focuses on how to draw information on natural processes by modelling univariate and multivariate frequency distributions using water data. The chemical composition of 977 samples collected in wells from Vulcano island (Italy) are used as a case study. The methodological approach can be transferred to the investigation of other geochemical or constrained data.
Is the simplex open or closed? (some topological concepts)
Authors: Barrabés E. , Mateu-Figueras G.
Published: April 2008

The simplex is the natural space to work with when compositional data are considered. Sometimes, the concepts of
open
simplex and
closed
simplex are used, although most of the time they are not well defined. The objective of this contribution is to expose some of the mathematical concepts related to the simplex and its structure in order to make clear when the terms
open
and
closed
are mathematically appropriate. Moreover, these concepts sometimes generate discussion about the proper representation of the simplex. It will be shown that this discussion makes no sense when considering the simplex as a Euclidean vector space.
Non-marine Permian biostratigraphy and biochronology: an introduction
Authors: Lucas Spencer G. , Schneider Joerg W. , Cassinis Giussepe
Published: April 2008

The Permian time scale based on marine rocks and fossils is well defined and of global utility, but non-marine Permian biostratigraphy and chronology is in an early phase of development. Non-marine Permian strata are best known from western Europe and the western United States, but significant records are also known from Russia, South Africa, China and Brazil. Global time terms based on non-marine Permian strata, such as Rotliegend, Zechstein, Autunian, Saxonian and Thuringian, are either inadequately defined or poorly characterized and should only be used as lithostratigraphic terms. Macro- and microfloras have long been important in non-marine Permian correlations, but are subject to limitations based on palaeoprovinciality and facies/climatic controls. Charophytes, conchostracans, ostracodes and freshwater bivalves have a potential use in non-marine Permian biostratigraphy but are limited by their over-split taxonomy and lack of well-established stratigraphic distributions of low-level taxa. Tetrapod footprints provide poor biostratigraphic resolution during the Permian, but tetrapod body fossils and insects provide more detailed biostratigraphic zonations, especially in the Lower Permian. Numerous radioisotopic ages are available from non-marine Permian sections and need to be more precisely correlated to the global time scale. The Middle Permian Illawarra reversal and subsequent magnetic polarity shifts are also of value to correlation. There needs to be a concerted effort to develop non-marine Permian biostratigraphy, to correlate it to radio-isotopic and magnetostratigraphic data, and to cross-correlate it to the marine time scale.
Tetrapod footprint ichno-associations from French Permian basins. Comparisons with other Euramerican ichnofaunas
Authors: Gand Georges , Durand Marc
Published: April 2008

In order to take into account the studies of the European and American (USA) collections carried out by one of the authors, and of the recent nomenclatural revisions from new footprint discoveries, which have occurred during the last decade, the authors present a critical review of the French Permian palichnofauna. The distribution of the ichnospecies in the stratigraphy of the Lodève Basin, taken as a reference, is outlined. The ichno-associations are then compared with those of other French (Provence), European (Italy, Germany) and USA basins. Based on the ages of different ichnofossiliferous formations, three successive ichnofaunal units can be distinguished in the Permian of Europe. The first developed in the Cisuralian (Asselian to Kungurian). The second is found in the south of France in Kazanian to Lower Tatarian strata, equivalent to the Roadian-Wordian. The third and youngest, dated as Lopingian, is only found in Italy, in the Bolzano Basin. Because of sedimentary gaps, limited observations, sometimes erroneous determinations, and ichnospecies with great vertical distribution, it currently appears that footprints have a low utility for biochronological resolution. Nevertheless, they allow us to discriminate three time intervals in the Permian, as is also the case for skeletal remains.
Permian tetrapod footprints: biostratigraphy and biochronology
Authors: Lucas Spencer G. , Hunt Adrian P.
Published: April 2008

Permian tetrapod footprints are known from localities in North America, South America, Europe and Africa. These footprints comprise four ichnofacies, theChelichnusichnofacies from aeolianites and theBatrachichnus, BrontopodusandCharacichnosichnofacies from water-laid (mostly red-bed) strata. Permian track assemblages of theChelichnusichnofacies are of uniform ichnogeneric composition and low diversity, range in age from Early to Late Permian, and thus are of no biostratigraphic significance. Footprints of theBatrachichnusandBrontopodusichnofacies represent two biostratigraphically distinct assemblages: (1) Early Permian assemblages characterized byAmphisauropus, Batrachichnus, Dimetropus, Dromopus, Hyloidichnus, LimnopusandVaranopus; and (2) Middle to Late Permian assemblages characterized byBrontopus, Dicynodontipus, Lunaepes, Pachypes, Planipes, and/orRhynchosauroides. Few Permian footprint assemblages are demonstrably of Middle Permian (Guadalupian) age, and there is a global gap in the footprint record equivalent to at least Roadian time. Permian tetrapod footprints represent only two biostratigraphically distinct assemblages, an Early Permian pelycosaur assemblage and a Middle to Late Permian therapsid assemblage. Therefore, footprints provide a global Permian biochronology of only two time intervals, much less than the ten time intervals that can be distinguished with tetrapod body fossils.
Carboniferous-Permian actinopterygian fishes of the continental basins of the Bohemian Massif, Czech Republic: an overview
Authors: Štamberg Stanislav
Published: April 2008

The actinopterygian fishes from the continental Westphalian to the Lower Permian basins in the Czech Republic are reviewed and compared with those of deposits of equivalent age in some central and western European Basins. Nine genera of actinopterygians belonging to eight families are known from the Westphalian-Stephanian sediments, and five genera belonging to four families are known from the Early Permian sediments of the Bohemian Massif. The new family Sceletophoridae is erected for the genus
Sceletophorus
from the Westphalian D. Very close relationships of the actinopterygian fauna between the Bohemian Massif and especially the basins of the French Massif Central are discussed.
Late Permian to Early Triassic transition in central and NE Spain: biotic and sedimentary characteristics
Authors: Arche Alfredo , López-Gómez Jose
Published: April 2008

The Late Permian to Early Triassic (P/T) transition represents one of the most important Phanerozoic mass extinction episodes. Data from this transitional period are very scarce in continental basins, and reliable correlation with marine series is still a matter of debate. In this paper, information on the P/T transition in the continental series of central and NE Spain and the Balearic Islands is presented and compared with some coeval western European basins. The Iberian Ranges sections contain detailed information on the P/T transition, with sediments interpreted as alluvial fans, sandy and gravelly braided rivers and high sinuosity rivers with extensive floodplains, dated by means of pollen and spore assemblages. However, the fossil record contains two barren intervals throughout the study area, one in the Late Permian (Thuringian) and another during the latest Permian to Early Triassic. The possible causes of these gaps include the very likely relationship with the emplacement of the basaltic large igneous provinces (LIP) of SE China and western Siberia during this period of time.
The problem of the transition from the Permian to the Triassic Series in southeastern France: comparison with other Peritethyan regions
Authors: Durand Marc
Published: April 2008

In the French sedimentary basins, widespread alluvial deposits sealing narrow Permian troughs are referred to as ‘Buntsandstein’. An Early Triassic age is generally put forward despite a lack of any Scythian biochronological elements. In Provence (Southeast Basin) some doubts remain about the age of the latest Permian deposits, and the oldest Triassic fossils (Anisian palynomorphs) appear in the upper ‘Buntsandstein’. Three types of contact occur: disconformity overlain by a quartz-conglomerate, apparent transition, and angular unconformity, according to an increasing basal incompleteness of the ‘Buntsandstein’. Whereas the conglomerate was deposited under arid conditions, the overlying fluvial deposits indicate a marked climate change. A transect from France up to the Germanic Basin centre shows that the ‘French Buntsandstein’ cycle might begin considerably before the end of the Permian; the Early Triassic arid ‘event’ is Dienerian/Smithian in age; and the Provençal ‘basal’ conglomerate corresponds to the uppermost part of a coeval subordinate cycle, and thus the underlying sub-Triassic unconformity represents a hiatus estimated at 10–15 Ma. Works in progress confirm that sedimentary climate indicators constitute powerful tools for correlations within non-marine formations devoid of biostratigraphical marker that straddle the Permian-Triassic boundary, at least on the scale of the Western European Plate.
The Eagle III BKA system, a novel sediment core X-ray fluorescence analyser with very high spatial resolution
Authors: Haschke M.
Published: April 2008

Sediment cores contain valuable information on geological history and palaeoclimate, and it is necessary to study cores at high spatial resolution to recover useful palaeoenvironmental data. This paper describes an innovative micro-X-ray fluorescence spectrometer that can measure spot sizes in the range of 50 μm, with incremental step sizes down to 10 μm. The analysis is non-destructive so the sediment core is preserved and available for other investigations. This paper describes the new instrument, the Eagle III BKA system, which employs some novel features such as a polycapillary lens, moveable sample stage and X-ray head, a Varispot focusing system and an environmental sample cabinet. Some examples of recent applications are described.
The Avaatech XRF Core Scanner: technical description and applications to NE Atlantic sediments
Authors: Richter Thomas O. , van der Gaast Sjerry , Koster Bob , Vaars Aad , Gieles Rineke , de Stigter Henko C. , De Haas Henk , van Weering Tjeerd C. E.
Published: April 2008

X-ray fluorescence (XRF) core scanning provides rapid high-resolution (down to 1 mm) records of chemical composition on split sediment cores. The measurements are non-destructive and require very limited sample preparation. The new Avaatech XRF Core Scanner, operational since 2002, covers the atomic mass range from Al to U. Instrument parameters, especially tube voltage, can be adjusted to provide optimum settings for selected elements or sets thereof. Owing to the nature of the surface of split sediment cores, particularly effects resulting from sample inhomogeneity and surface roughness, results are semiquantitative, yet provide reliable records of the relative variability in elemental composition downcore. Selected case studies from diverse sedimentary settings in the NE Atlantic Ocean illustrate a range of applications of XRF logging data. These include preliminary stratigraphic interpretations (glacial-interglacial cycles), provenance studies of the terrigenous sediment fraction, lithological characterization, early diagenetic processes and distinction between carbonate phases (aragonite v. calcite).
Turbidite emplacement on the southern Balearic Abyssal Plain (western Mediterranean Sea) during Marine Isotope Stages 1–3: an application of ITRAX XRF scanning of sediment cores to lithostratigraphic analysis
Authors: Rothwell R. Guy , Hoogakker Babette , Thomson John , Croudace Ian W. , Frenz Michael
Published: April 2008

The upper part (0–20 m) of a long piston core from the SE Balearic Abyssal Plain — spanning the past 50 ka — has been studied using the ITRAX micro-XRF core scanner to obtain downcore elemental profiles. The Ca/Fe ratio was found to be an effective parameter to distinguish between turbidites and pelagites, because turbidites generally have higher Fe contents and lower Ca contents compared with pelagic intervals. Beds that were obscure when visually logged could be identified as turbidites or pelagites on their geochemical characteristics, allowing more complete subdivision of the sequence into genetic units. The ITRAX XRF data also provide useful information on textural grading, bioturbative mixing, identification of geochemically distinctive marker beds, indications of differences in provenance, and confirm or query the presence of early arrivals during turbidite emplacement. A chronostratigraphic framework for the core based on accelerator mass spectrometry (AMS) radiocarbon dating and correlation with oxygen isotope stages of pelagic intervals in other cores (using calcium carbonate stratigraphy) was also established. This shows that turbidite emplacement on this part of the Balearic Abyssal Plain has been modulated strongly by climate and sea-level change, with turbidite emplacement most frequent during the early Holocene when the rate of post-glacial sea-level rise was greatest. Deposition of the coarsest (i.e. sand and silt-based) turbidites at the core site was restricted to the full and Late Glacial (11–25 ka). Turbidite emplacement during Oxygen Isotope Stage 3 was rare. Most of the turbidites at the site are distal, but some coarse-grained-based turbidites are characterized by higher Sr/Ca ratios (possibly indicating a higher aragonite content), higher Ca and lower Fe contents compared to other turbidites, and are interpreted as having a more proximal shelf source. Such turbidites are generally rare, however, and restricted to full Glacial and Younger Dryas time. There is little evidence for large-scale seismogenic turbidites (expected to be seen as randomly timed emplacement, seemingly independent of eustatic control) at the core site, despite proximity to the seismically active Algerian margin 100 km to the south. This suggests that seismogenic turbidites must largely bypass this part of the plain. Although the ITRAX core scanner provides a rapid and non-destructive means of characterizing downcore geochemical distributions in great detail, interpretation of the data requires caution and assessment from an informed standpoint. Analytical artefacts such as those caused by water or organic content, degree of compaction, grain-size and mineral effects, unevenness of the cut core surface and poor discrimination of closely spaced element XRF peaks need identification and elimination.
Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction
Authors: Godin L. , Grujic D. , Law R. D. , Searle M. P.
Published: April 2008

The channel flow model aims to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya-Tibet system. Channel flow describes a protracted flow of a weak, viscous crustal layer between relatively rigid yet deformable bounding crustal slabs. Once a critical low viscosity is attained (due to partial melting), the weak layer flows laterally due to a horizontal gradient in lithostatic pressure. In the Himalaya-Tibet system, this lithostatic pressure gradient is created by the high crustal thicknesses beneath the Tibetan Plateau and ‘normal’ crustal thickness in the foreland. Focused denudation can result in exhumation of the channel material within a narrow, nearly symmetric zone. If channel flow is operating at the same time as focused denudation, this can result in extrusion of the mid-crust between an upper normal-sense boundary and a lower thrust-sense boundary. The bounding shear zones of the extruding channel may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or thrust sense, depending on the relative velocity between the upper crust and the underlying extruding material. This introductory chapter addresses the historical, theoretical, geological and modelling aspects of channel flow, emphasizing its applicability to the Himalaya-Tibet orogen. Critical tests for channel flow in the Himalaya, and possible applications to other orogenic belts, are also presented.
A synthesis of the Channel Flow-Extrusion hypothesis as developed for the Himalayan-Tibetan orogenic system
Authors: Hodges K. V.
Published: April 2008

Surface and subsurface geological features of the Himalayan-Tibetan orogenic system may be explained by three sets of processes: those related to plate convergence, those related to the gravitational spreading of a fluid middle crust beneath the Tibetan Plateau, and those related to aggressive erosion along the southern margin of the plateau. In this paper, the possible relationships among the last two of these—and their tectonic manifestations—are presented in the form of a ‘Channel Flow-Extrusion’ hypothesis. This hypothesis, deriving from a series of ideas advanced by many geologists and geophysicists over the past two decades, suggests the definition of three phases in the Early Miocene-Recent history of the orogenic system. During Phase I (Early Miocene), the crust of southern Tibet was sufficiently hot and thick to enable lateral flow of a weak middle crust. To the north and east, this flow resulted in the expansion of the Tibetan Plateau. To the south, erosion at the Himalayan front permitted the mid-crustal channel to breach the surface; this process is recorded in the deformational history of the Himalayan metamorphic core and the Main Central and South Tibetan fault systems that bound it. While the lateral expansion of the plateau by mid-crustal flow has continued throughout Neogene time, some evidence suggests that extrusion across the Himalayan front waned substantially during the Middle Miocene-Early Pliocene interval (Phase II). In Middle Miocene time, large magnitude extension of the decoupled upper crust of southern Tibet led to the development of a subsidiary channel; its extrusion explains the existence of the North Himalayan gneiss domes. Phase III (Late Pliocene-Recent) has involved renewed southward extrusion of the main channel due to climatically induced increases in the erosion rate at the Himalayan range front.
Kinematic dilatancy effects on orogenic extrusion
Authors: Grasemann B. , Edwards M. A. , Wiesmayr G.
Published: April 2008

We undertake kinematic modelling to explore the role of volume increase in a slab extruding froman orogenic wedge with constant or decreasing slab width. Using a dilatancy term, we modify the velocity gradient tensor dependent on the stretching-rate factor, kinematic dilatancy and vorticity number. We use this to explore the previously largely ignored role of volume change in kinematic evolution of extrusive flow, considering area change for non-isochoric flow types with no deformation in the intermediate direction. By keeping individual parameters constant for geologically simple scenarios (e.g. finite strain, steady-state flow) we examine the interdependence of the reciprocal parameters (kinematic vorticity and dilatancy number) and note model situations where degrees of freedom are limited. These interdependent parameters thereby provide a set of rules for integrating and modelling real field data. In particular we observe that for extrusion flow with a constant slab (or ‘channel’) width, degrees of freedom in kinematic vorticity and volume change at given finite strains are very restricted. We compare scenarios of low and high strain and low and high volume change on anatexis (related to partial melting of fertile sedimentary rocks and release of water upon crystallization) for different parts of the Himalaya.
Interpretation of deformation fabrics of infrastructure zone rocks in the context of channel flow and other tectonic models
Authors: Williams P. F. , Jiang D. , Lin S.
Published: April 2008

Infrastructure zones are essentially horizontal to shallowly dipping crustal-scale zones of non-coaxial flow, with two possible interpretations: (a) a crustal-scale shear zone, transporting upper crust over lower crust and/or mantle (transport flow); or (b) a zone of channel flow in which there is a flux of weak crust between relatively strong upper and lower crust and/or mantle, away from the centre of the orogen. Transport flow has a constant shear sense across the zone, whereas in channel flow the sense of shear reverses across the zone. Channel flow may be driven by extrusion (extrusive channel flow), due to the two channel walls approaching one another, or by a pressure gradient along the channel (normal channel flow), with no convergence of the walls necessary. Arguments based on strain compatibility and mechanics suggest that extrusive channel flow is unlikely. Kinematic vorticity numbers have been used to show that infrastructure and other shear zones have undergone flattening strains, but we show that the numbers are incompatible with extrusion. We also show that in addition to the problems inherent in determining kinematic vorticity numbers from fabric, the numbers cannot be related to bulk flow in mechanically heterogeneous zones, because of flow partitioning. Drag folds are a better indication, albeit qualitative, of whether a zone is thinning or not. They also give a conservative estimate of the minimum accumulated shear strains, and may inhibit strain localization. Like snowball garnets, they indicate shear strains that are so large that the pure-shear-thinning component for a steady-shear zone has to be small.
Structural evolution and vorticity of flow during extrusion and exhumation of the Greater Himalayan Slab, Mount Everest Massif, Tibet/Nepal: implications for orogen-scale flow partitioning
Authors: Jessup M. J. , Law R. D. , Searle M. P. , Hubbard M. S.
Published: April 2008

The Greater Himalayan Slab (GHS) is composed of a north-dipping anatectic core, bounded above by the South Tibetan detachment system (STDS) and below by the Main Central thrust zone (MCTZ). Assuming simultaneous movement on the MCTZ and STDS, the GHS can be modelled as a southward-extruding wedge or channel. New insights into extrusion-related flow within the GHS emerge from detailed kinematic and vorticity analyses in the Everest region. At the highest structural levels, mean kinematic vorticity number (
Wm
) estimates of 0.74–0.91 (
c.
45–287fb3e69cure shear) were obtained from sheared Tethyan limestone and marble from the Yellow Band on Mount Everest. Underlying amphibolite-facies schists and gneisses, exposed in Rongbuk valley, yield
Wm
estimates of 0.57–0.85 (
c.
62–357fb3e69cure shear) and associated microstructures indicate that flow occurred at close to peak metamorphic conditions. Vorticity analysis becomes progressively more problematic as deformation temperatures increase towards the anatectic core. Within the MCTZ, rigid elongate garnet grains yield
Wm
estimates of 0.63–0.77 (
c.
58–447fb3e69cure shear). We attribute flow partitioning in the GHS to spatial and temporal variations that resulted in the juxtaposition of amphibolite-facies rocks, which record early stages of extrusion, with greenschist to unmetamorphosed samples that record later stages of exhumation.