bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural implications of compactional strain caused by fault block rotation: evidence from two-dimensional numerical analogues
Authors: Iliffe J. E. , Lerche I. , Nakayama K. 
Published: April 2008

Abstract
The effects of compaction on tilted fault blocks are assessed using a two dimensional mathematical model which assumes homogeneous non-rigid blocks. Lithology is described by a depth-dependent porosity function.
Compaction is restricted to the upper parts of the hangingwalls of blocks and is greater in blocks bounded by sub-vertical faults rotated by 30° or more. The fault planes are unaffected.
Significant sub-vertical lines of maximum compaction are noted directly below block crests. Since secondary faults occur in similar orientations in rigid blocks, rotation in the Earth’s gravitational field is proposed as a mechanism for secondary faulting.
Fluid migration from the compressed hangingwall to the undeformed footwall has implications for shale diapir formation.
Alpine deformation on Naxos (Greece)
Authors: Urai J. L. , Schuiling R. D. , Jansen J. B. H. 
Published: April 2008

AbstractA detailed structural study of Naxos (Attic-Cycladic massif, Greece) reveals two major deformation events. The first one is associated with large scale thrusting and high-pressure-low-temperature metamorphism during an early Alpine subduction episode. The second event occurred during continental extension and the associated development of localized thermal domes, where lower crustal rocks were brought into contact with upper crustal units along a major shallow dipping shear zone. We agree with a model of Naxos as a Cordilleran type Metamorphic Core Complex. However, our observations show that the sense of shear was ‘upper plate moving North’ during the second event, calling for a reinterpretation of existing tectonic models of the Cyclades.
Timing, style and sedimentary evolution of Late Palaeozoic-Mesozoic extensional basins of East Greenland
Authors: Surlyk Finn 
Published: April 2008

AbstractThe late Palaeozoic-Mesozoic sedimentary basins of East Greenland record a complex series of events which eventually led to the successful opening of the Norwegian-Greenland Sea in the late Palaeocene. Major tectonic events and regional sea-level changes caused by plate movements and reorganizations, overprinted by the effects of local tectonics and associated sea-level changes are reflected in thick, unconformity bounded sequences. Caledonian crustal shortening and thickening culminated in the Silurian, and was succeeded by extensional collapse, vulcanism and intrusion of post-tectonic granites in the Devonian. Large, transtensional pull-apart basins were formed and became filled with continental red beds. Basin margins underwent repeated episodes of thrusting. A change to rifting took place in the latest Devonian. Rapid subsidence and continental deposition punctuated by episodes of igneous activity and contractional deformation continued from the Devonian until early Permian times for about 120 Ma leaving a record of alluvial fan and flood plain siliciclastics alternating with rhyolitic and alkaline basaltic intrusions and extrusions. Later basin subsidence reflected thermal cooling and contraction following the prolonged late Palaeozoic period of crustal thinning. Important phases of block faulting occurred at several intervals during Mesozoic times climaxing in the Volgian-Valanginian interval. Cenozoic basin inversions resulted in dramatic decoupled uplift and tilting of large blocks. The degree of Devonian extensional collapse, the position and orientation of Caledonian thrust planes, and the localization of mid- and late Palaeozoic transtensional strike-slip basins exerted a profound control on localization and style of the compartmentalized Mesozoic rift. The importance of pre-Mesozoic history, timing of Mesozoic tectonic events and the interplay of tectonism, and rates of subsidence, sea-level change and sediment influx have close parallels in the North Sea area. Examples from the exposed Mesozoic succession of East Greenland may thus serve as excellent predictive guides for subsurface geology around the British Isles.
The significance of normal faults in the exploration and production of North Sea hydrocarbons
Authors: Hardman R. F. P. , Booth J. E. 
Published: April 2008

Abstract
The Mesozoic geological history of the northern North Sea was dominated by extensional faulting. In addition to forming the most important hydrocarbon traps, such faults can be shown to exert a significant degree of control over the distribution of mature source rocks, and the deposition and erosion of reservoir rocks. As exploration and production have progressed the importance of small normal faults has been increasingly recognized. Although they do not totally offset reservoir formations, such small faults may provide lateral seals, thus disrupting hydrocarbon migration routes, forming subtle traps and causing technical problems during production by unanticipated compartmentalization of fields. Consequently, as the commercial size of fields is reduced by improving production technology and the North Sea matures as a hydrocarbon province, a thorough understanding of the origins and characteristics of normal faults as well as a command of the increasingly sophisticated techniques for analysing the behaviour of these faults will be vital to successful exploration programmes.
Mechanisms generating normal fault curvature: a review illustrated by physical models
Authors: Vendeville Bruno 
Published: April 2008

Abstract
This paper briefly reviews the mechanisms generating fault curvature during extension, illustrates them using physical models, and discusses their applicability at different scales and for specific extensional styles. These mechanisms are in two groups. In the first, initially curved fault planes are essentially of mechanical origin. They commonly result from marked vertical changes in stress orientation and rheology within the faulted layer. Experiments suggest that such mechanisms are more likely to influence secondary faults that form where deformation and displacements are severely constrained. The second group includes faults that become curved after they form, either by volume loss due to compaction, by internal deformation of fault blocks, or by interacting sedimentation and faulting. Fault curvature due to compaction is mainly restricted to growth-faulted areas. Internal deformation of blocks affects fault shapes at the transition zone between continuous and discontinuous deformation. Block rotation during rapid deposition can lead to strongly curved fault profiles. Blocks or faults are distorted during block rotation to maintain geometric compatibility within and between the blocks. This review suggests that normal growth faults in deltaic areas are more likely to be listric than crustal-scale normal faults.
Provenance research: Torridonian and Wealden
Authors: Allen P. 
Published: April 2008

Abstract
Torridonian regional flow-directions are indicated unequivocally by sediment geometries and palaeocurrent structures. In the Wealden more reliance has to be placed on textural and compositional gradients. Flow directions in both guide the search for sourcemassif ‘stumps’: uncovered, covered or inferred. ‘Putting back’ the detritus on to the stumps leads to broad palaeogeographies; but erosional histories, recycling, basin budgets and changes in basinal configuration are major uncertainties. Diagenetic interference with the evidence is minimal. Overlapping opposing flows are consistent with extensional tectonic regimes.
Torridonian waste provides evidence on the timing of mantle contributions to the Laurentian crust. Refreshingly new Hercynian petrographies in the Wealden may bear on a similar problem in European Gondwana.
Single-grain dating (perhaps to include quartz) and rapid and ultra-precise geochemical and isotopic analysis (including whole-rock) make the prospects for provenance research exciting. Tourmaline, zircon and glauconite have considerable potential for dating and justify fuller investigation of their isotopic and mineral chemistries.
On the use of turbidite arenites in provenance studies: critical remarks
Authors: Zuffa Gian Gaspare 
Published: April 2008

Abstract
When we determine framework petrography of deep-sea arenites for provenance studies we should concentrate not only on what particles make up sedimentary beds but also when, where and how they form. Taking such information into account, grains can be classified according to their temporal, spatial and compositional characteristics. This will allow a better understanding of palaeogeography and palaeotectonics of the basin/source system. Two examples from the literature that support this approach are reported.
Organic carbon flux and development of oxygen deficiency on the modern Benguela continential shelf south of 22°S: spatial and temporal variability
Authors: Bailey Geoffrey W. 
Published: April 2008

Abstract
Anoxia in continental shelf waters has previously been ascribed to lack of circulation, advection from a remote source and in situ formation. It appears that in situ formation resulting from degradation of organic-rich material derived from phytoplankton blooms is generally the controlling factor in coastal upwelling ecosystems such as the Benguela system. Here, spatial variation in accumulation of organic-rich shelf sediments and associated anoxia is closely related to the degree to which primary production is enhanced at sites ‘downstream’ of coastal upwelling centres. Consequently, at sites where there is strong seasonal variation in the input of recently upwelled water, there is temporal variability in the incidence of oxygen-deficient waters overlying the shelf and anoxic sediments.
The extent of phytoplankton blooms is also dependent on coupling between the benthic and pelagic zones and physical characteristics of the water column. This is supported by observations of phytoplankton abundance, sedimentation of particulate organic matter and benthic oxygen deficiency in the Benguela upwelling system, where the continental shelf is marked by oxygen-deficient bottom waters and anoxic sediments equatorward of three of the major upwelling centres where such coupling occurs.
This work reaffirms the view that primary production rather than anoxia exerts direct control on the accumulation of organic-rich sediments.
The dysaerobic zone revisited: a magnetic facies?
Authors: Rhoads Donald C. , Mulsow Sandor G. , Gutschick Raymond , Baldwin Christopher T. , Stolz John F. 
Published: April 2008

Abstract
The original dysaerobic zone concept defined a unique assemblage of benthic organisms and sedimentary fabrics associated with dissolved oxygen concentrations ranging between 0.3 and 1.0 ml/l. Subsequent studies of the Santa Barbara Basin and oxygen minimum zone (OMZ) off the California coast suggest that this facies is bounded by dissolved oxygen in the range 0.1 to 0.5 ml/l.
This range of dissolved oxygen is optimal for the growth of magnetotactic bacteria. We present a hypothesis predicting that the dysaerobic zone should be associated with a high inventory of biogenic magnetite and that this magnetite can be used as a palaeo-oxygen indicator.
We have tested this hypothesis with a magnetic analysis of samples from aerobic, anaerobic, and dysaerobic sediments taken off the Peruvian coast. The mean magnetic susceptibility of the dysaerobic zone is 3 to 5 times higher than the aerobic and anaerobic parts of the Peruvian oxygen minimum zone (OMZ). Micrographs (TEM) of these sediment samples indicate that only the dysaerobic zone contains appreciable amounts of fine-grained magnetite.
Oxygen-related biofacies in marine strata: an overview and update
Authors: Savrda Charles E. , Bottjer David J. 
Published: April 2008

Abstract

Recent studies of contemporary basins and ancient strata have provided a basis for expanding and refining early oxygen-related marine biofacies models. New observations permit higher resolution in palaeoecological, palaeoceanographic, and basin analyses. Five oxygen-related biofacies are currently recognized. (1) Anaerobic biofacies: well-laminated strata lacking in situ macro- and microbenthic body fossils and microbioturbation; may contain well-preserved remains of nektonic vertebrates, epiplanktonic or otherwise transported invertebrates, and faecal material of planktonic and/or nektonic origin. (2) Quasi-anaerobic biofacies: laminated strata, subtly disrupted by microbioturbation, containing microbenthic body fossils but lacking in situ macrobenthic body fossils; allochthonous body fossils and recognizable planktonic faecal material may be common. (3) Exaerobic biofacies: laminated strata similar to that of anaerobic or quasianaerobic biofacies but containing in situ epibenthic macroinvertebrate body fossils. (4) Dysaerobic biofacies: bioturbated strata characterized by low-diversity assemblages of relatively small, poorly calcified macrobenthic body fossils or absence of body fossils altogether. (5) Aerobic biofacies: bioturbated strata (where physical processes do not dominate) containing diverse assemblages of relatively large, heavily calcified macrobenthic body fossils. Recognition of these biofacies facilitates the recognition of relative palaeo-oxygenation gradients along the seafloor, vertically across the sediment-water interface, and through time. Application of sensitive trace-fossil models permits even more detailed reconstructions of benthic oxygenation histories for bioturbated strata, particularly those that fall
within
the previously defined dysaerobic realm.
Submarine erosion on the anoxic sea floor: stratinomic, palaeoenvironmental, and temporal significance of reworked pyritebone deposits
Authors: Baird Gordon C. , Brett Carlton E. 
Published: April 2008

Abstract
Numerous black (organic-rich) shale units in the Palaeozoic of North America are marked by discontinuities along their bases which are characterized by acid-insoluble lag concentrations of reworked pyrite, phosphatic debris, and siliceous material. These contacts, ranging in magnitude from widespread disconformities (typically marine flooding surfaces) to local, within-outcrop-scale, scour features, were produced by submarine erosion under anoxic to lower dysoxic conditions. Dissolution of carbonate debris under conditions of carbonate undersaturation and/or low pH in bottom waters, was generally complete. Hydraulic transport coupled with dissolution led to the formation of laterally discontinuous and current-sorted lenses of pyritic grains, fish bones, condonts, quartz sand, chert nodules, and glauconite. Lags of reworked pyritic tubes and small spherules are typical of finely interbedded black and green shale successions (‘zebra facies’) observed in the Upper Devonian (Famennian). Under anoxic conditions pyrite was chemically stable, while carbonate debris was not.
Herein, we examine lag deposits associated with a variety of black-shale-roofed discontinuities ranging in age from Middle Ordovician to Mississippian. Possible erosion mechanisms for producing these discontinuities and associated lags include deep-stormwaves, density currents and internal waves. In each case erosion occurred following an interval of condensation associated with flooding surfaces, particularly those timed with the beginning of highstand intervals.
Keys to the depositional history of the Posidonia Shale (Toarcian) in the Hils Syncline, northern Germany
Authors: Littke R. , Leythaeuser D. , Rullkötter J. , Baker D. R. 
Published: April 2008

Abstract
The Posidonia Shale from northwest Germany displays a threefold stratigraphic subdivision: lower marlstone, middle calcareous shale with bivalve shells, and upper calcareous shale. Deposition commenced after transgression over a disconformity on the Pliensbachian. Absence of current features indicates depositional conditions below wave base. Sediment infilling to water depths coincident with wave base probably caused cessation of Posidonia Shale deposition.
Calcitic carbonate, organic matter and detrital clay are principal primary components. TOC values are 2–15%. Macerals are mostly from marine phytoplankton; terrigenous macerals are minor. HI values are high (500–800). Detailed sampling reveals a thin (4.5 m) low carbon zone within the middle shale; water column oxidation and bacterial alteration may account for this facies. Clay and organic matter relationships suggest that land-derived nutrients controlled phytoplankton productivity; carbonate constituents were a diluent to organic matter accumulation.
Absence of burrowing, abundance of organic matter, and pervasive diagenetic pyrite demonstrate continual anoxia below the sediment-water interface. However, C/S relationships suggest that a euxinic water layer did not extend far above the depositional surface. The occurrence of benthic bivalves in the middle shale indicates that bottomwater tolerable to epibenthos sometimes prevailed. Sulphate-reducing bacteria modified the primary organic matter causing a 20–30% loss.
Inorganic geochemistry of the German ‘Posidonia Shale’: palaeoenvironmental consequences
Authors: Brumsack Hans-J. 
Published: April 2008

Abstract
42 samples of the SW and NW German ‘Posidonia Shale’ have been analysed for their major element and sulphur isotopic composition, as well as the trace metals Ag, As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sr, V, and Zn. Several of these trace metals are found enriched in the TOC-rich ‘bituminous’ layers. A comparison of the enrichment of specific metals in the Toarcian shales with black shales from the Cenomanian/Turonian anoxic event and Recent TOC-rich sediments from the Black Sea and the Gulf of California reveals a strong similarity of the ‘Posidonia Shale’ with Black Sea sapropels. The origin of the trace metals found enriched in this rock type predominantly seems to be fluvial input. Seawater alone fails to explain the high Co, Mn, and Pb concentrations of the ‘Posidonia Shale’. The environment of deposition therefore seems to be characterized by less saline surface waters overlying intermittently anoxic, more saline water masses of this epicontinental sea. Anoxic conditions must have persisted during the deposition of some bituminous layers and probably during the ‘falciferum’ Subzone.
Fate of organic carbon and reduced sulphur in dysoxic-anoxic Oligocene facies of the Central Paratethys (Carpathian Mountains and Hungary)
Authors: Vetö István , Hetényi Magdolna 
Published: April 2008

Abstract
The fate of organic carbon and reduced sulphur has been studied in two laminated and organic-rich formations of the Oligocene Central Paratethys. The Menilite Beds (Carpathian Flysch Belt) contrast with the Tard Clay (Hungarian Paleogene Basin) and are characterized by a high rate of sedimentation and biogenic silica enrichment.
About 80 core and outcrop samples were analyzed for their TOC, total sulphur, sulphate sulphur and pyrite iron content. Rock-Eval pyrolysis was carried out on more than half the samples.
On the basis of C/S relationships, the Menilite Beds are believed to have been deposited under sulphidic bottom water, while the existence of a sulphidic water at the bottom of the ‘Tard Sea’ cannot be documented.

C/S relationships, organic maturity data, and knowledge of anaerobic bacterial processes, especially the mechanisms and extent of the early diagenetic escape of reduced sulphur from recent sediments, permit assessment of the rates of organic carbon deposition. The obtained values of 10.8 t m
−2
Ma
−1
for the Menilite Beds and 1.4–1.8 t m
−2
Ma
−1
for the Tard Clay fit reasonably with geological settings and reflect the intensity of the corresponding planktonic productivities. The significant differences observed in TOC content between the two studied Tard Clay sections were caused by difference in the intensity of sulphate supply.
Expulsion of petroleum from type III kerogen source rocks in gaseous solution: modelling of solubility fractionation
Authors: Leythaeuser D. , Poelchau H. S. 
Published: April 2008

Abstract

The composition of n-alkane mixtures expelled from type III kerogen-bearing source rocks at moderate maturity levels shows strong signs of fractionation according to molecular chain length. This effect is attributed to the process of expulsion in gaseous solution. The degree of fractionation varies with the pressure and temperature conditions of primary migration. Fractionation effects for C
15+
-n-alkanes have been simulated with the help of equations developed from experimental data of Price
et al.
(1983) for gaseous solution of oil. For known compositions of expelled n-alkanes our simulation model allows the estimation of pressure and temperature conditions during primary migration. Expulsion of petroleum in gaseous solution is a particularly effective migration mechanism for overpressured type III kerogen-bearing source rocks.

Two geological case histories are presented which demonstrate the compositional effects of petroleum expulsion in gaseous solution from such source beds. The observed n-alkane distributions expelled can be closely matched by simulated distributions, which were calculated for
P-T
conditions estimated from reconstructions of the burial histories of both case histories.
Numerical modelling of petroleum expulsion in two areas of the Lower Saxony Basin, Northern Germany
Authors: Düppenbecker S. J. , Dohmen L. , Welte D. H. 
Published: April 2008

Abstract
The process of petroleum expulsion is mainly determined by the initial quality of the source rock and its sedimentary facies and by the temperature and pressure histories during burial. A numerical model of the complex processes of expulsion was developed based on observations of expulsion phenomena, detailed petrophysical and organic geochemical investigations and data provided by basin modelling. In this model petroleum expulsion is treated as a pressure driven transport in a separate phase using the existing pore system and newly formed microfractures as migration pathways. Microfracturing predominantly parallel to the bedding plane, as it is observed in oil generating source rocks, is initiated when the pore pressure build-up exceeds the rock strength. Major sources of overpressure in source rocks are considered to be volume expansion of organic matter during petroleum generation and compaction disequilibrium. Experimental data were obtained from detailed investigations of the Posidonia Shale source rock of the Lower Saxony Basin. An application of expulsion modelling is presented for two regions of the Lower Saxony Basin, where timing and quantity of petroleum generation and expulsion from Posidonia shale was studied with respect to different heating rates. The efficiency of transport mechanisms and migration pathways through both the pore network and newly-formed fractures could be determined by this quantitative treatment. The modelling results were in good agreement with geological observations and a mass balance based on organic geochemical analysis.