bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permian to Triassic sequences from selected continental areas of southwestern Europe
Authors: Virgili C. , Cassinis G. , Broutin J. 
Published: April 2008

Abstract
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

Abstract

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

Abstract
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

Abstract

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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract
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

Abstract

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
.