bluuebunny/crossref_metadata_2025_split huggingface dataset:
Normal fault geometry and fault reactivation in tectonic inversion experiments
Authors: Krantz Robert W. 
Published: April 2008

Abstract
Scaled physical models of extensional structures associated with fault reactivation were achieved in sand by superimposing extensional tectonics on thrust faults created during prior episodes of horizontal shortening. The extension produced three distinct responses: selective reactivation of pre-existing thrusts, favouring the steepest thrusts and those dipping more than a critical value; development of new normal faults that were linked to or developed within the zone of thrust faults; or generation of new normal faults in previously unfaulted domains. Linked normal faults showed a wide range of orientations and most dipped less steeply than the unlinked faults, which had dips clustered about the value predicted from the internal friction coefficient of sand. During extension of a distributed fault model, reactivation of existing thrusts influenced the location, dip direction, and dip magnitude of linked normal fualts. Compared to natural fault systems, the models showed many geometric similarities especially regarding linked normal faults.
Physical and seismic modelling of listric normal fault geometries
Authors: McClay K. R. , Waltham D. A. , Scott A. D. , Abousetta A. 
Published: April 2008

Abstract
Scaled analogue models of listric fault systems display a characteristic rollover anticline and crestal collapse graben features. Faults nucleate in sequence into the hangingwalls of the crestal collapse graben and towards the footwall of the master fault. Superposition of crestal collapse grabens produces complex fault arrays. When the basal detachment surface is tilted a characteristic panel of unfaulted synfault stratigraphy forms adjacent to the detachment. These experiments produce structures with close similarities to listric growth fault systems on prograding delta slopes. Synthetic seismic sections of the experimental models have been produced using Kirchhoff integral techniques. These illustrate the complexities in trying to image complex structures in listric fault systems but also show good agreement with natural seismic examples.
Geochemistry and provenance of Rhenohercynian synorogenic sandstones: implications for tectonic environment discrimination
Authors: Floyd P. A. , Shail R. , Leveridge B. E. , Franke W. 
Published: April 2008

Abstract
The provenance of synorogenic greywackes from Devonian flysch successions occupying structurally similar positions at opposite ends of the Rhenohercynian zone in SW England and Germany is evaluated. Greywackes from both regions are petrographically and chemically similar, although minor differences are seen in the relative proportions of lithics; the Gramscatho group being richer in volcanic and metavolcanic clasts, whereas the Giessen group is richer in metasedimentary clasts. Absolute abundances of Ni-Cr-V and Zr-Hf-Y vary to a limited extent in each group and reflect variable mafic detritus and heavy mineral inputs respectively. Framework mode parameters and chemical data indicate the Rhenohercynian greywackes were derived mainly from a calc-alkali, acidic, dissected continental arc source, with minor MORB-like and argillaceous metasedimentary components. Upper continental crust-normalized multi-element patterns for the greywackes are characteristic of the continental arc/active margin tectonic environment. However, ‘Mid-Proterozoic’ model Nd ages for the Gramscatho greywackes suggest that an active Devonian arc source is unlikely. Instead the range of chemical and isotopic composition displayed mainly reflects mixing between acidic arc terranes of Proterozoic age and Devonian (Lizard-type) oceanic crust. Petrographic and geochemical discrimination diagrams alone cannot resolve the temporal decoupling between source and basin and may lead to an erroneous interpretation of tectonic setting.
Anoxia in the Northern Adriatic Sea: rapid death, slow recovery
Authors: Stachowitsch Michael 
Published: April 2008

Abstract
The Northern Adriatic Sea is characterized by the full range of features associated with sensitive marine ecosystems. In the Gulf of Trieste, mortalities due to anoxia have been reported in 1974, 1983 and 1988. The anoxic event in September 1983 led to mass mortality in a highly developed and wide-ranging community in the Gulf. This destroyed over 50% of the epifaunal biomass in only two days, and over 90% within four days.
The increased frequency, severity, and range of recent oxygen deficiencies suggest that, in addition to meteorological and hydrographic factors, anthropogenic influences are a contributing or enhancing factor in the onset of anoxic conditions and associated mass mortalities. These anthropogenic influences may be subsumed under the heading eutrophication. If eutrophication only slightly increases the rate of oxygen decrease below the thermocline, it may advance the point at which critical oxygen levels are attained by several days. Since only a few days of anoxic conditions are required to destroy this benthic community (with an equally short time required for reoxygenation) the degree of eutrophication may determine whether an ecological catastrophe occurs or not.
The recolonization process between 1984 and 1987 has been slow: the total biomass and the relative contribution of the designating species have remained distinctly below previously recorded values. Additional anthropogenic influences (intensive dredging) may further impede recolonization. A further, small-scale mortality was registered in 1988.
Sedimentary and geochemical expressions of oxic and anoxic conditions on the Peru Shelf
Authors: Emeis Kay-Christian , Whelan Jean K. , Tarafa Martha 
Published: April 2008

Abstract
Sediments from drill hole transects across the Peru shelf and upper slope show that the extent and intensity of the oxygen minimum zone (OMZ) has varied considerably from the early Pleistocene to the present. Primary sedimentary features, such as laminations and bioturbation, and the hydrogen index of sedimentary organic matter, appear to covary with the presence and intensity of the OMZ. Sediments deposited under dysoxic to anoxic bottom-water conditions are significantly more hydrogen-rich relative to bulk TOC. The molecular composition of pyrolytic hydrocarbons and heterocompounds, however, is surprisingly uniform, and is indicative of neither oxic nor anoxic degradation at either the sediment-water interface or in the water column. The concept of better preservation of organic matter under anoxic conditions in the bottom water is reflected in the bulk parameter of pyrolyzable organic matter content relative to TOC, but not in individual compound classes incorporated into kerogen. The most important control on the hydrogen-richness of organic matter appears to be sediment reworking and redeposition.
Pelletal black shale fabrics: their origin and significance
Authors: Cuomo M. Carmela , Bartholomew Paul R. 
Published: April 2008

Abstract
Recent work has demonstrated that, under certain conditions, laminated mudstones may be produced from the compaction of highly pelletized, organic-rich sediments occupied by populations of marine benthic worms. Such sediments can be found at the most developed part of the dysoxic region in many modern minimum zones. In order to reconstruct this facies accurately in the rock record, it is necessary to discern the true origin of pellets (benthic or planktonic) present in black, laminated shales.
Petrographic techniques, electron microscopy and microprobe analysis were employed on modern benthic and planktonic faecal pellets in order to arrive at inorganic geochemical criteria useful for discriminating between them. Benthic pellets contained more of those elements found in the fine fraction of the sediments (Al, Mg, K) while planktonic pellets contained high amounts of those elements (Si) representing the inorganic remains of the food they consume.
These criteria were successfully applied to pellets and their enclosing sedimentary matrices in ancient laminated black shales. Systematic identification of the origins of pellets found in laminated black shales should allow for detailed identification of palaeooxygen gradients within ancient depositional environments and may reveal that truly anoxic and azoic marine conditions were much less widespread than is commonly thought.
Thin widespread Pennsylvanian black shales of Midcontinent North America: a record of a cyclic succession of widespread pycnoclines in a fluctuating epeiric sea
Authors: Heckel P. H. 
Published: April 2008

Abstract
Within the Middle-Upper Pennsylvanian cyclic sequence of Midcontinent North America (Iowa, Nebraska, Missouri, Kansas, Oklahoma), there are at least 20 horizons of thin (<1 m) phosphatic black shales that extend up to 600 km along outcrop. They overlie transgressive limestones that range from very thin (1–5 cm) shell beds where they lie above coals, to thin (1 m or less) skeletal calcilutites where they lie above fluviodeltaic deposits and palaeosols. The black shales underlie thicker (2–10 m) regressive limestones that are characterized by various types of shallowing-upward sequences and are typically capped by palaeosols on the northern shelf (Iowa to central Kansas). The black shales represent the deepest-water deposits within the succession of widespread eustatic inundations that were responsible for the major cyclothems. Their frequency in the cyclic sequence is estimated to be close to that of the longer of the earth’s orbital parameters that are considered to control the wax and wane of continental glaciation. They apparently formed beneath pycnoclines that were established during interglacial high-stands of sea level when the water was both warm enough (at the surface) and deep enough to maintain a thermocline for perhaps several thousand years. These thermoclines were probably augmented by haloclines in areas of greater fresh-water run-off and possibly in areas accessible to more saline bottom water.
Biofacies, stratigraphic distribution and depositional models of British onshore Jurassic black shales
Authors: Wignall Paul B. , Hallam Anthony 
Published: April 2008

Abstract
The majority of British Jurassic dysaerobic and anaerobic facies (black shales) accumulated in rapidly subsiding basinal areas. Exceptionally, during the earliest stages of transgression, organic-rich facies expanded their distribution into more marginal areas. The biofacies of the black shales display a range of species richness values which, when ranked, record an oxygen gradient that is also reflected by gradients in geochemical and sedimentological data. Truly anaerobic facies (no benthic taxa present) are very rare in the British Jurassic. More common are fissile organic-rich shales with discrete, low-diversity horizons of benthos here defined as lower dysaerobic biofacies. These are interpreted to have formed in a generally anoxic environment punctuated by benthic colonization events in response to ephemeral improvements of oxygen levels. Upper dysaerobic biofacies are characterized by slightly higher diversity faunas scattered throughout poorly fissile strata.
The favoured depositional model for the British Jurassic black shales attributes the high preservational values of organic carbon to accumulation in oxygen-deficient waters trapped beneath a stratified water column in the deepest, basinal areas. We propose an ‘expanding puddle’ model for transgressive black shales. Deep water conditions are envisaged to become proportionally more extensive during early transgression due to the combined effects of subsidence, a rapid rate of sea-level rise and, unique to this portion of the sea-level curve, sediment starvation.
Organic matter and palynomorphs in the ‘Posidonienschiefer’ (Toarcian, Lower Jurassic) of southern Germany
Authors: Prauss Michael , Ligouis Bertrand , Luterbacher Hanspeter 
Published: April 2008

Abstract

The low δ
13
C values observed in beds with high TOC and high hydrogen index in the Toarcian oil shales of the ‘Posidonienschiefer’ (Lower Jurassic) correlate with palynomorph assemblages composed largely by prasinophyte phycomata and sphaeroidal, coccal palynomorphs of ambiguous affinity (‘sphaericals’). The macerals of the same beds are dominated by lamalginite and bituminite. The liptodetrinite content is very variable. Vitrinite, inertinite and sporinite macerals are rare. This correlation is consistent with the model proposed by Riegel
et al.
for the ‘Posidonienschiefer’ of northwestern Germany. The accumulation and preservation of the organic matter were favoured by a density stratification of the water column caused by the influx of low-salinity water. The paleogeographic setting and the affinity of dinocyst assemblages in the Proto-Arctic and in W Europe during Pliensbachian/Toarcian times suggest a high-latitude origin of this lowsalinity water.

Hydrogen indices obtained from Rock—Eval analyses indicate Type-II kerogen for most of the ‘Posidonienschiefer’ oil shale. Reflectance values of vitrinite and bitumen in oil shales are significantly suppressed by the presence of high amounts of liptinite.
The maturity of the organic matter determined by vitrinite reflectance and by Rock—Eval pyrolysis corresponds to the start of the oil window.
Glauconitization episodes in marginal settings as echoes of mid-Cretaceous anoxic events in the Vocontian basin (SE France)
Authors: Bréhéret Jean-G. 
Published: April 2008

Abstract
The formation of mid-Cretaceous glaucony-rich beds on the margins of the Vocontian (SE France) is correlated with the black shales intervals in the adjacent basinal facies. These black shales are a local expression of widespread oceanic anoxic events during the late Lower Aptian, Lower and Middle Albian, and late Upper Albian. An interfingering of glaucony-rich beds and black shales may be seen in some Lower Albian sections in outer shelf facies. Furthermore, one of the most important black shale horizons (the Paquier Level) contains numerous thin layers rich in glaucony grains that often developed at the expense of in situ faecal pellets. This autochthonous origin implies a direct relationship between the laminated black shale facies deposited under anoxic conditions, and glaucony as a subsequent diagenetic product formed under the influence of slightly oxygenated waters. Mineralogical and chemical data acquired on green grains characterize ‘evolved’ assemblages rich in micaceous glauconite, suggesting that the Paquier Level represents a condensed interval. These observations may have considerable significance for mid-Cretaceous sequence stratigraphy and palaeoceanographic investigations.
Micropalaeontological and geochemical evidence of mid-Cretaceous dysoxic-anoxic palaeoenvironments in the Sergipe Basin, northeastern Brazil
Authors: Koutsoukos E. A. M. , Mello M. R. , de Azambuja Filho N. C. 
Published: April 2008

Abstract
Combined micropalaeontological, geochemical and sedimentological studies of the mid-Cretaceous (upper Aptian to Turonian) succession of the Sergipe Basin, northeastern Brazil, indicate that intermittent dysoxic-anoxic events occurred in the basin, most likely associated with the interplay of processes such as restricted physiography in the deep basin, salinity-stratified water masses, increased epipelagic primary productivity and high sea levels. Three maxima in oxygen depletion are recorded in the succession from middle neritic to upper bathyal environments: the late Aptian-earliest Albian, the early Cenomanian, and the latest Cenomanian-earliest Turonian. Improving oxidizing conditions (dysoxic to oxic) are apparent during middle-late Albian and early-middle Turonian times. The existence of a rich and diverse planktonic biota throughout the mid-Cretaceous succession suggests widespread oxygenated epipelagic layers of variable thickness in space and time in the basin.
Modelling of secondary migration and entrapment of a multicomponent hydrocarbon mixture using equation of state and ray-tracing modelling techniques
Authors: Sylta Øyvind 
Published: April 2008

Abstract
Equation of state modelling of multicomponent hydrocarbon mixtures has been incorporated into a program which models the secondary migration of oil and gas. Migration is modelled by means of a ray-tracing technique which operates on backstripped depth maps of a carrier bed. Reservoir beds are represented as rectangular grids (arrays) in the computer, ensuring the high resolution required for proper secondary migration modelling. The resulting software, named SEMI, can be calibrated against the hydrocarbon composition in drilled traps and then used to compute the composition in undrilled prospects. This is especially useful in moderately explored basins where some discoveries have already been made. A model for the loss of hydrocarbons during secondary migration is utilized and, by modelling secondary migration within a synthetic basin, it is shown that compositional differences in traps may result from differences in loss of the vapour and liquid phases. Using a simple model for primary migration, it is shown that the primary and secondary migration losses influence the hydrocarbon composition in traps differently. Thus it is hoped that the proposed methodology can be used to quantify some of the unknown effects of migration and that a decrease in the quantified uncertainty in exploration for oil and gas may result.
Structural controls on fluid migration through the Rencurel thrust zone, Vercors, French Sub-Alpine Chains
Authors: Roberts Gerald 
Published: April 2008

Abstract
The Vercors, French Sub-Alpine Chains, is part of a classic foreland thrust belt which accommodates the last few kilometres of WNW-directed shortening in the Alps. The Rencurel thrust zone locally emplaces Barremian limestones onto Miocene sandstones. The thrust zone is well exposed allowing detailed structural logging and sample collection to be carried out. Calcite veins occur within gouge zones along minor faults occurring pervasively throughout the fault zone. However, at the base of the exposed fault zone, where a large displacement thrust has developed, the dominant vein fill is ferroan calcite, locally accompanied by bitumen. Cross-cutting relationships indicate that the pervasive set of minor faults developed early in the deformation sequence. The lack of ferroan calcite and bitumen within the early set of faults suggests that they were impermeable during later faulting. Fluid migration during deformation along the large displacement thrust was confined to underneath the impermeable zone of early minor faults. This study indicates that the style and location of deformation changes during the incremental development of a foreland thrust zone. Distributed deformation by mesoscale faulting or folding may be characteristic of deformation which occurs before the localization of displacement onto a major fault zone. Deformation probably occurs episodically with diffusive mass transfer and cataclasis as the dominant deformation mechanisms. Microstructures evolve during progressive deformation and this may induce changes in the permeability along a fault zone through time. These changes in the nature of fault zones during incremental deformation must be considered in order to assess fully the role of faulting in controlling syn-tectonic fluid migration.
Updoming, rifting and continental margin development during the Late Palaeozoic in northern Oman
Authors: Blendinger W. , van Vliet A. , Hughes Clarke M. W. 
Published: April 2008

Abstract
Subsurface data from northern interior Oman and new surface data from the Oman Mountains imply that the north Oman passive continental margin developed in the Permian. Late Carboniferous and Permian updoming of an area roughly overlapping the present Oman Mountains is indicated by the northward thinning of the continental clastics of the Haushi Group (Late Carboniferous and Early Permian) in the sub-surface. Well correlations show the thinning as cutouts at internal unconformities proving contemporary uplift along a roughly E-W strike. Deep water sedimentation off northern Oman commenced already in the early Late Permian. Permian deep water sediments of the Hawasina nappes consist of reef-derived sediment gravity flow deposits, cephalopod limestones and radiolarites that were deposited in a slope and basin floor environment north of a coralgal reef tract. Mafic volcanics underlying these deposits show locally tholeiitic characters suggesting that incipient drifting of the Hawasina ocean occurred as early as the Late Permian. Penecontemporaneous flooding of the Arabian shield occurred on an almost unfaulted substratum even in areas close to the inferred shelf edge.
The interpretation of these data in terms of models for continental rifting suggests that north Oman developed on the little faulted side of an asymmetrical rift produced by Permo-Carboniferous low-angle normal faulting of the lithosphere.
Sedimentary aspects of the Eo-Alpine cycle on the northeast edge of the Arabian Platform (Oman Mountains)
Authors: Rabu D. , Le Metour J. , Bechennec F. , Beurrier M. , Villey M. , Bourdillon-Jeudy de Grissac C. 
Published: April 2008

Abstract
The northeast edge of the Arabian Platform in the Oman Mountains is represented by the autochthonous unit that crops out in the two windows of Jabal Akhdar and Saih Hatat, beneath and in front of the Hawasina and Samail nappes.
The Eo-Alpine orogenic cycle began in the Late Permian with extension on the margin of Gondwana and ended in the Campanian with the formation of a subduction-obduction-type mountain range, the Oman Mountains of the Late Cretaceous. During this cycle, long periods of stable shelf sedimentation were interrupted by tensional tectonic episodes, often accompanied by volcanism and subsidence of the platform, passing into the bathyal domain.
Deposition during the Permian to Campanian occurred during five main sedimentary cycles. In the Late Permian (Murghabian), a widespread marine transgression covered the edge of Gondwana in a tensional setting. The ‘Fusulinid Sea’ transgression was followed by the deposition, lasting until the Triassic, of a thick regressive sequence, the Akhdar Group, which was terminated by emergence and weathering in a continental environment. The next sedimentary cycle, represented by the Sahtan Group, began in the Pliensbachian, when the Oman Mountains area formed an inner carbonate shelf, and ended in the early Tithonian. The entire margin of the platform was profoundly affected, in the late Tithonian, by extension, listric faulting and foundering into the bathyal domain, with deposition of the Kahmah Group (Maiolica-type deposits: calpionellid-bearing micrite), and rapid retreat of the continental slope by about 250 km. Renewed carbonate shelf deposition then prograded SSW-NNE across the foundered part, though this was still incomplete when the latest Aptian-Albian transgression took place. At the Cenomanian-Turonian boundary, the shelf underwent profound reorganization with the development of the Muti (intrashelf) Basin, in which the Aruma Group was deposited, and the Masqat-Musandam High which provided the detritus filling the Muti Basin on the continentward side and the Hawasina Basin on the oceanic side. Fragments from the advancing nappe were redeposited in the Muti Basin only from the Campanian on, and it was only during this period that a flysch trough became superimposed on part of the Muti Basin. The closure of the Muti Basin was affected with the emplacement of the nappes on the platform and the subsequent deposition of cover formations over both nappes and the autochthon from the late Maastrichtian onward.