bluuebunny/crossref_metadata_2025_split huggingface dataset:
The tectonics of the southern Alps and the Austro-Alpine nappes: a comparison
Authors: Laubscher H. P. 
Published: April 2008

Summary
The southern Alps as well as the Austro-Alpine nappes originate from the southern margin of Tethys with close analogies both in basement petrography and stratigraphic sequence. Although they played vastly different roles in Alpine orogeny they developed similar tectonic features. In both domains there is a ramp-flat geometry with associated folds, analogous to those found in thrust belts worldwide, and the basement consists of thrust plates not more than 5 km thick with a conspicuous frontal ramp fold, complicated by imbrications. Regional décollement levels are at the base of the middle Triassic, the Carnian, and the Rhaetian. Both the southern Alps generally and at least the western end of the Upper Austro-Alpine Lechtal nappe are affected by transverse segmentation which in the southern Alps is demonstrably due to reactivation of Jurassic normal fault zones. Tectonic wedging into the regional décollement layers was a frequent phenomenon. In contrast to the southern Alps, the Silvretta-Lechtal nappe forms part of the Alpine nappe system with total translations of many hundreds of kilometres. It now overlies nappes deriving from different palaeogeographic domains (Lower Austro-Alpine, south Pennine, mid-Pennine, and north Pennine nappes in the Rätikon). Reactivation of the equivalent of the original Lechtal sole thrust, although at a somewhat deeper level within the south Pennine Arosa zone, led to the introduction of exotic Arosa masses into the Carnian interval of the Lechtal nappe, and reactivation of the transverse faults and their propagation to deeper levels resulted in non-cylindrical kinematics of Penninic nappes along the Rhine line.
Concentrated and lean oolites: examples from the Nubia Formation at Aswan, Egypt, and significance of the oolite types in ironstone genesis
Authors: Bhattacharyya D. P. 
Published: April 2008

Summary
Two textural types of oolitic ironstones occur in the Late Cretaceous Nubia Formation at Aswan, Egypt. These are: (1) relatively thin bedded (5–20 cm) muddy or ‘lean’ oolites containing up to 300oids, proto-ooids and peloids scattered in a matrix of ferruginous mud, and (2) thicker beds (as much as 2.5 m thick) of ‘rich’ or ‘concentrated’ oolites comprising 60–800oids.
Sedimentologic and textural attributes of the ‘concentrated’ oolites suggest that these represent ooids transported and redeposited away from their site of formation. In fact, in ironstone-bearing successions elsewhere the concentrated oolites are either associated with winnowed sandstones or, in sand-poor deposits, they substitute for sandstone. Together the ooids and the detrital sand form bar and sand wave complexes in upward shoaling marginal marine sediments. In unbioturbated or less bioturbated occurrences these sandbodies of ferruginous ooids are replete with primary sedimentary structures indicative of strong current transport. Thin beds of similar ferruginous ooids in sequences of off-shore carbonate or argillaceous basinal mudstone, such as those in the Silurian Clinton Group of eastern United States, are storm deposits characterized by basal scours and hummocky cross-stratification. The muddy or ‘lean’ oolites, on the other hand, are commonly associated with prograding subtidal mudflat deposits. Textural characteristics of these ironstones suggest that they probably represent the primary sites of ooid formation. Different stages of ooid formation preserved in these ‘lean’ ironstones and their relationship with the concentrated oolites provide information which is significant for a more realistic and comprehensive genetic modelling for the Aswan ironstones.
In the model proposed here the deposition of muddy, ferruginous sediments on prograding, near-shore, subtidal mudflats begins during the waning stages of detrital sediment supply. The ooids are formed on these shallow-water mudflats by mechanical accretion of detrital kaolinitic clay and precipitated iron hydroxide minerals, mostly around faecal pellets or flocculated peloids, under the influence of gentle wave or current agitation. Periodic high-energy events, such as storm-generated or tidal currents, transport the ooids to off-shore areas to be reworked there into oolitic sand bar and shoal complexes. Following deposition, the kaolinitic ooids, peloids and matrix are transformed into berthierine under a chemically reducing diagenetic environment.
Oolitization processes in Palaeozoic ironstones of France, Algeria and Libya
Authors: Chauvel J-J. , Guerrak S. 
Published: April 2008

Summary
On the basis of the study of Palaeozoic ironstones from France, Algeria and Libya, some oolitization processes are documented, particularly intrasedimentary accretion and ‘snow-ball’ type accretion. In a single ooid, successive layers of the cortex can have been formed by different processes. Chemical analysis of an ooid cortex can help to reconstruct its history. Chamositic layers are always weathered in their outer part, with the leaching of aluminium and magnesium. Haematitic layers result from iron, and often titanium concentration in the weathered outer parts of primary chamositic layers. Crystallization of siderite appears to be late diagenetic, and often took place at the same time as, or after, the development of quartz overgrowths.
Time and space distribution of Palaeozoic oolitic ironstones in the Tindouf Basin, Algerian Sahara
Authors: Guerrak S. 
Published: April 2008

Summary
The Tindouf Basin is located, mainly in Algeria, in the SW part of the Saharan Platform. It comprises Cambro-Ordovician to Carboniferous marine formations overlain by the continental Cretaceous and Pliocene Hamada cover. On the southern limb of the Tindouf Basin several oolitic ironstone deposits occur within Silurian and Devonian sediments. They occupy an area of 500 × 40 km and have an east — west trend. These oolitic ironstone deposits are part of the major North African oolitic ironstone belt, extending more than 3000 km, from Zemmour to Libya. These occurrences are of the LOID type (Local Ironstone Deposition), and contain more than 10000 million tonnes of ironstone reserves (1500 million tonnes in the Silurian and 9200 million tonnes in the Devonian).
The various ironstones were formed in shallow marine environments such as barriers and deltas. The major features of these deposits are: (i) a palaeogeographical control of the sediment which was mainly formed on the flanks of uplifts; (ii) the occurrence of the ironstones at the top of coarsening-upward sequences, mostly located towards the end of major regressive cycles, particularly in the Pragian and Famennian; (iii) ooids developed in quiet environments such as lagoons or embayments, within an iron-rich mud; (iv) a southern, relatively close, iron source area and; (v) a palaeolatitudinal distribution giving successively cold and temperate climates.
The Palaeozoic history of the basin involved pericratonic sedimentation on the borders of a large epicontinental sea.
The Aztec fish fauna (Devonian) of Southern Victoria Land: Evolutionary and biogeographic significance
Authors: Young G. C. 
Published: April 2008

Abstract

The Aztec fauna is one of the most diverse fossil vertebrate faunas from Antarctica, with over 30 taxa belonging to the four major groups of jawed fishes (acanthodians, placoderms, osteichthyans, chondrichthyans), and one group of agnathans (thelodontids). Biogeographically the strongest affinity is with eastern Australia, as part of the East Gondwana Province. Biostratigraphically the Aztec succession includes probably the youngest known non-marine thelodont agnathans at the base, and the oldest known phyllolepids at the top. This transition, and an association of species of
Turinia
and
Bothriolepis
, is not seen in any other sequence. Most or all of the Aztec sequence is regarded as Givetian (late Middle Devonian) in age. The Aztec fauna contains older and/or more primitive representatives of several groups typical of younger (late Palaeozoic) strata in Euramerica, suggesting a biotic dispersal episode between Gondwana and Euramerica in the Late Devonian. Centres of origin and dispersal hypotheses in Palaeozoic biogeography can be related to disappearance of faunal barriers as manifested in different stratigraphic ranges in different areas. The change for Devonian vertebrates from the endemic patterns seen in the Early Devonian to the close similarity of Famennian faunas between East Gondwana and Euramerica suggests disappearance of a major faunal barrier in the Late Devonian, presumably the ocean between Gondwana and Euramerica.
Patterns of evolution in the Dicynodontia, with special reference to austral taxa
Authors: DeFauw Sherri L. 
Published: April 2008

Abstract

Dicynodonts were the dominant primary consumers of the latest Palaeozoic and early Mesozoic ecosystems. Of the 66 currently accepted genera of dicynodonts, three (possibly four) of these occur in the Fremouw Formation of Antarctica (i.e.
Kingoria, Lystrosaurus, Myosaurus
and ?
Kannemeyeria
). Modifications to the basic shearing mechanism of the jaws as well as postcranial morphology presumably reflect differences in the physical nature of the food consumed and foraging techniques used by dicynodonts. To date, five dicynodont feeding types have been recognized: invertebrate specialists, grubbers, browsers, forest litter foragers and flexible foragers. Three out of the five ‘central’ dicynodont feeding types are represented among the members of the early Mesozoic Antarctic palaeofauna. In order to more accurately assess systematic and ecomorphic relationships among dicynodonts, comprehensive generic diagnoses (that incorporate postcranial characters) are warranted; suggested revisions to the generic diagnoses of Antarctic dicynodonts are provided. Dicynodont distributions are evaluated in light of ecomorphic considerations, tectonic-orogenic events, sea-level fluctuations, palaeoclimates and floral changes. Available evidence, pertaining to austral taxa, suggests that: (1) Antarctica served as a refugium for kingoriamorphs in the Early Triassic, and (2) the informal members of the Fremouw Formation are correlated with more than one African biozone.
The relevance of dip profiles from outcrops as reference for the interpretation of SHDT dips
Authors: Herweijer J. C. , Höcker C. F. W. , Williams H. , Eastwood K. M. 
Published: April 2008

Abstract
The ability of SHDT processing techniques to produce detailed sedimentological information has been evaluated by comparing the data with 3000 ft of cores covering shallow marine, deltaic, lacustrine, fluvial and aeolian sedimentary environments. It has been shown previously that, by using side-by-side processing, realistic sedimentary dip sequences through sedimentary bodies can be obtained from SHDT data under normal conditions. However, optimum results require processing parameters to be chosen compatible with the scale of the sedimentary structures present. Furthermore, post-processing selection procedures are required to remove noise and to identify dips representing foreset inclination which can be interpreted in terms of flow direction and sand body orientation.
The sedimentological interpretation of downhole dips is often difficult. It may be improved by comparison with vertical dip sequences from outcrops. Sedimentary dip profiles have been measured as part of field work carried out in the Pocahontas Basin of Kentucky. Extensive roadcuts not only enable an unambiguous sedimentological interpretation, but also exhibit numerous relict blast-boreholes, in which vertical dip profiles can be measured under conditions similar to downhole logging. The data now available show that even contradictory dip sequences may be a proper representation of the reality. Systematic collection of sedimentary dip sequences will provide guidelines for a realistic interpretation of downhole records of sedimentary dips.
Geological applications of geochemical well logging
Authors: Herron M. M. , Herron S. L. 
Published: April 2008

Abstract
Recent advances in geochemical logging and interpretation have made it possible to obtain in situ concentration logs for at least ten of the chemical elements present in sedimentary formations: Al, Si, Ca, Fe, S, Ti, K, Th, U, Gd and possibly Mg. Each of these elements is concentrated in the solid portion of the formation as opposed to the pore fluids, and together these elements provide an array of measurements with a large dynamic range and tremendous diagnostic strength for geological interpretation.

The combination of a few diagnostic elements, such as silicon, aluminum, and calcium, provides sufficient information for a rapid but accurate lithological description. In the case of siliciclastic reservoir rocks, it is possible to discriminate between sand and shales and to determine types of sandstones using the ratios of SiO
2
/Al
2
O
3
and Fe
2
O
3
/K
2
O. Calcium is used in conjunction with these ratios to differentiate between non-calcareous, calcareous, and carbonate rocks. On a more sophisticated level, a set of chemical abundances can be incorporated into a sedimentary normative analysis to determine quantitatively both the framework and clay mineralogy of siliciclastic formations. Derived mineral assemblages can provide valuable information for the interpretation of depositional environments and diagenesis. In shales, elemental data can be used alone or in conjunction with derived mineralogy to derive total organic carbon and thereby begin to evaluate source rock potential. By using individual elemental concentration logs or any of the interpreted formation units it is possible to enhance the characterization of vertical sequences and the recognition of well-to-well correlations.
Circumferential acoustic logs detect natural fractures and determine their orientation
Authors: Fertl W. H. 
Published: April 2008

Abstract
As the direction of fractures shifts from horizontal/near-horizontal toward the vertical plane with respect to the intersecting wellbore, conventional acoustic logging devices become unreliable for fracture detection purposes. Under these circumstances, circumferential acoustic logging technology has already proven to be an excellent technique to determine vertical and/or near-vertical open fracture systems that intersect a wellbore and to measure the directional subsurface trends of these detected fractures. In addition to visual ‘quick-look’ interpretation of the recorded acoustic waveform data, novel digital interpretive techniques enhance the fracture evaluation.
The Venezuelan hydrocarbon habitat
Authors: James K. H. 
Published: April 2008

Abstract
Venezuela has produced some 40 billion barrels of oil. Remaining recoverable reserves are currently in the order of 60 billion barrels of oil and 92 trillion cubic feet of gas. The Orinoco Heavy Oil Belt, the world’s largest known oil accumulation, has some 1.2 trillion barrels of oil-in-place. Only part of the 267 billion barrel, ultimate recoverable of this belt is included in the current reserves.
Most of Venezuela’s hydrocarbon reserves are located in the Maracaibo, Eastern Venezuela, and Barinas—Apure Basins, and most are derived from Upper Cretaceous, marine source rocks. Tertiary, terrestrial source rocks have also contributed hydrocarbons in the Maracaibo and Eastern Venezuela basins, and Tertiary marine and terrestrial source rocks have generated hydrocarbons in the Falcon and offshore Venezuelan basins.
The hydrocarbon habitat has been profoundly influenced by Mesozoic—Recent platetectonics. Many of the structural traps are the consequence of Carribbean—South America dextral relative movements. Some of these structures, mainly in the northwest, were enhanced by stress generated in the Pacific. The northern part of the country has suffered considerable shortening and inversion. The resultant mountain chains limit the modern hydrocarbon basins. Reconstruction of late Cretaceous source rock palaeogeography, of Late Cretaceous to Palaeocene kitchens (now metamorphosed), and of Eocene to Recent kitchens, shows that the latter are remnants of a much larger petroliferous province and provides an explanation for the great abundance of hydrocarbons in the area.
Significant volumes of hydrocarbons remain to be discovered in extrapolations of traditional and developing plays.
Structural styles of growth faults in the U.S. Gulf Coast Basin
Authors: Lopez J. A. 
Published: April 2008

Abstract
Structure and sediments related to shelf margin growth faults are an important exploration objective in the Cenozoic in the U.S. Gulf Coast basin. The syndepositional nature of these fault systems has been recognized for decades with well control and seismic. Recent seismic of higher quality and deeper penetration has begun to reveal more clearly the variety of structural styles of the ‘typical’ Gulf Coast shelf margin growth fault.
Generally five different shelf margin growth fault types are recognized: (1) listric faults which detach above undeformed older section, (2) listric faults which detach on mobile, overpressured shales above older undeformed sediments, (3) faults which sole into autochthonous salt withdrawal basins, (4) faults which detach along allochthonous salt sill intrusions, and (5) non-detached faults caused by differential compaction of thick shale intervals or basement faulting. The first four are the dominant structural types and their different structural styles reflect various modes of accommodation of fault offset within the sedimentary section. The fifth structural type, although not as commonly recognized, may be obscured by other structural complexities.
These five fault types have different structural and stratigraphic characteristics which create different trap-source-reservoir relationships for each type. By understanding and identifying the distribution of these structural types one may better understand the complex production trends established in the Gulf Coast basin and more accurately assess potential production on prospective traps.
The Middle East Basin: a summary overview
Authors: Stoneley R. 
Published: April 2008

Abstract
In a review of classic petroleum provinces, it is instructive to consider the most prolific of them all and once again to ask ourselves why it is that the Middle East is so rich in oil and gas. The question has been addressed many times (e.g. see the discussion by Beydoun) but, as new data become available, it will continue to be asked and new insights may be gained by fresh attempts to provide the answer.
The part of the region considered in this brief overview surrounds the Arabian/Persian Gulf, and does not extend either northwest far into Iraq or southeast into Oman, where much of the oil is Palaeozoic in age. Neither is the abundant gas in the Permian Khuff Formation included, since little information about it is available — and even less on its source. We are therefore concerned with the Mesozoic and Tertiary accumulations in a limited part of the basin.
Niger Delta reservoir geology: historical growth of the sedimentological model and its application to field development
Authors: Weber K. J. 
Published: April 2008

Abstract
In 1953 when the exploration in Nigeria moved towards the Niger Delta, it was realised that the recent delta could be used as a guide to the past. Consequently many studies were carried out between 1953 and 1964, ranging from surveys of the shallow offshore, the coastal zone and the rivers to an extensive shallow coring campaign (1960–62).
The studies of the recent delta were soon augmented by the analysis of cores from several newly discovered fields (1963–69) and also by the description and grain size analysis of numerous side-wall samples. Around 1970 the basic facies types comprising the individual deltaic cycles of the hc-bearing paralic sequence were well established. The facies types occur in a very repetitive pattern of combinations and successions which facilitates recognition and correlation. A fairly reliable system of diagnostic criteria was worked out based on petrophysical logs and side-wall samples and calibrated by the cores and the recent delta.
With the sequencial introduction of new logging tools the diagnostic methods are being refined while additional cored wells continuously enlarge the data base. Detailed seismic analysis at reservoir level is showing considerable promise for sand body delineation. For each facies a representative data base of sand body geometry could be compiled based on detailed reservoir correlations and recent examples. There is a good understanding of typical permeability and grain-size distributions. Knowledge on shale intercalation continuity is particularly useful in the planning of well completions to retard gas or water breakthrough to the well bore. It was shown that permeability can be computed from log derived porosity and grain-size distribution measured on side-wall samples.
The practical value of the reservoir geological research lies in the possibility to correlate and model reservoirs in a reliable and consistent manner. Reservoir and well behaviour can be predicted and where necessary reservoir simulation models can be constructed. Continuous updating of reservoir studies has demonstrated the validity of this approach by checking past predictions and analysis of infill wells. In this way the production planning and reserve estimation is given a solid base.
Hydrocarbon generation and migration in the Western Canada sedimentary basin
Authors: Creaney S. , Allan J. 
Published: April 2008

Abstract

A total of ten marine, petroleum source rocks ranging in age from Middle Devonian to Late Cretaceous exist within the Western Canada Basin. Principal hydrocarbon reserves occur in the Lower Cretaceous Mannville Group and subcropping Paleozoic carbonates, where 270 × 10
9
m
3
(1.7 trillion barrels) of heavy oil form one of the largest deposits of oil on Earth. Biomarker analyses of these heavy oils, many conventional oils and most source rocks in the basin have been combined with basic geology to establish the source and migration history of the Western Canada Basin. Several pre-Cretaceous source rocks (principally the Lower Jurassic Nordegg Formation, the Mississippian Exshaw/Bakken Formation, the Triassic Doig/Phosphate Formation and the Upper Devonian Duvernay Formation) have contributed to the Mannville accumulations. The Joli Fou shale, overlying the Mannville, is a regional seal for the Mannville and older section. Oils present in the overlying Viking, Cardium, and Belly River sands are all of a single family, sourced from the Colorado Shale section and are quite distinct from the oils in the Mannville and older section.

Meteoric water incursion at the eastern limb of the basin permitted biodegradation, which converted the conventional Mannville crude oil to heavy oil. The Western Canada Basin also contains an estimated 5 × 10
12
m
3
(180 TCF) of gas. Gas sources are the marine, oil-prone source rocks where overmature, as well as Lower Cretaceous Mannville coals and coaly shales. Hydrogen sulphide is contributed from overmature Paleozoic evaporites/carbonates with an estimated 36% of the total in-place gas reserves being classified as sour.