bluuebunny/crossref_metadata_2025 huggingface dataset:
The nature of data on a geological map
Authors: Giles J. R. A. , Bain K. A.
Published: April 2008

The primary purpose of the traditional geological map is to convey the map maker’s understanding of the geology of an area to the user of the map. A second, and less well understood role is as the
de facto
repository for much of the recorded geological data of an area. With the advent of digital geological map production, geographic information systems and digital geological databases, these traditional roles are changing. The data from which a map is constructed can reside in geological databases and the maps produced from these databases can concentrate on conveying information to the map user.

The design and construction of the digital geological databases used to store the information collected by geologists requires a detailed understanding of the elements of a geological map. This paper attempts to describe those elements and discusses some of the problems caused by the conventions used on geological maps.
Database design and data management on the Swansea-Llanelli Earth Science Mapping Project
Authors: Power S. , Scott M. , Robinson G. , Statham I.
Published: April 2008

Earth science, environmental and planning information was collected for a 200 km
2
area centred around Swansea and Llanelli, South Wales. The aim was to use this data to produce development advice maps for use in the planning process. To ensure efficiency of data storage and retrieval, a relational database was used, combined with a geographic information system (GIS), the GIS helping with data collection and data entry. This required the design of a logical model for data storage and manipulation, together with customized database forms for input and reporting. Information was captured in a variety of forms, ranging from reports and maps to text and existing databases, and often required different input techniques. The resulting comprehensive database was therefore stored in a structured way which has enabled effective interrogation and querying of the data to produce the information around which the final maps can be drawn. These, and the data, have already proved to be of importance and interest within the study area.
Hydrocarbon seepage dating through chemical remagnetization
Authors: Perroud Hervé , Chauvin Annick , Rebelle Michel
Published: April 2008

A magnetostratigraphic study of Permian red sandstones from the Van Dyck well, offshore the Netherlands, revealed an anomalous magnetization, with normal polarity and a high inclination (+47°), interpreted as a Jurassic chemical remagnetization. An extensive investigation of the magnetic mineralogy indicated that, in addition to the main carrier (hematite), minor magnetic phases were present (magnetite, maghemite or pyrrhotite). This last phase is unstable with temperature and has a Curie point of 350°C. As an interpretation, late hematite precipitation (200–150 Ma ago) is proposed, following an initial dissolution of the original hematite and precipitation of magnetite and/or other low coercivity minerals, possibly in association with seepage of reducing fluids such as hydrocarbons. This model allows the proposition of a Jurassic age for the end of the hydrocarbon migration, giving new constraints to the origin of the fossil products in this basin.
Palaeomagnetic implications for the timing of hematite precipitation and remagnetization in the Carboniferous Barren Red Measures, UK southern North Sea
Authors: Johnson S. A. , Turner P. , Hartley A. , Rey D.
Published: April 2008

Although rocks of the Carboniferous Barren Red Measures in the UK southern North Sea are often primarily reddened, they also show secondary reddening by fine-grained hematite precipitated as a result of deep weathering below the Permian unconformity. However, palaeomagnetic and petrographic analyses of samples from wells 49/1–3 and 49/2–3 have shown that a third phase of hematite was precipitated in the Triassic. The specularite grains associated with this magnetization are larger than those precipitated in the Permian and also contain a more dominant magnetic signature. Although Permian hematite precipitation was largely produced as a result of oxidation through vertical percolation, the occurrence of Triassic hematite grains appears to be related to distinct fluvial channels. It is suggested that lateral fluid flow is responsible for the precipitation of hematite in the Triassic and that this is associated with fluvial channel sandstones which have the best permeabilities and interconnectivities. The palaeomagnetic technique is therefore useful for assessing the degree of lateral communication in reservoir sandstones.
Magnetostratigraphic correlations in two cores from the late Triassic Lunde Formation, Beryl Field, northern North Sea, UK
Authors: Hounslow Mark W. , Maher Barbara A. , Thistlewood Laurence , Dean Kevin
Published: April 2008

The magnetostratigraphy of two cores from the late Triassic Lunde Formation of the northern North Sea are compatible with the calibrated magnetostratigraphy for the Norian stage determined by Gallet
et al.
(1993) from Tethyan carbonates. The polarities of the cores indicate a lower to upper Norian age for core 9/13A–36 and lower to middle Norian age for core 9/13A–A45. The isolated characteristic magnetizations are due to a Triassic detrital remanent magnetization, which is partially overprinted with a drilling-induced remanence of two origins. The drilling-induced remanences are associated with (1) the main coring procedure, producing an overprint which is oriented downcore and (2) the subsample coring procedure, which produces an overprint parallel to the subsample core axis and directed outwards from the main core axis. The elimination of those specimens with a significant drilling-induced remanence is important for the determination of the magnetostratigraphy in these cores.
Phenotypic experiments into new pelagic niches in early Danian planktonic foraminifera: aftermath of the K/T boundary event
Authors: Koutsoukos Eduardo A. M.
Published: April 2008

In the aftermath of the Cretaceous-Tertiary (K/T) boundary event it appears that unusual phytoplankton blooms were boosted by the abundant nutrient levels left over from a short-lived ‘Strangelove Ocean’ period, which possibly gave rise to the negative-to-positive δ
13
C surface-to-bottom gradient in the Danian.

The highly plastic morphology of the planktonic foraminifera at the base of the Palaeocene appeared, most likely, as an adaptive response of functional morphology to the pelagic habitat of the species and its mode of life. The diversification episodes of Danian planktonic foraminifera appear to correspond to times of reduced oceanic mixing, stratified water masses, recovery of the surface water productivity and a progressive expansion of the trophic-resource continuum, with periods of maximum diversity corresponding to widespread oceanic surface-water oligotrophic conditions. These suggest a parallel adaptive trend of feeding strategies caused by the changing availability of nutrients in the water column, with probable increasing reliance in symbiosis under low nutrient conditions later in the Danian.

Guembelitria cretacea
, one of the few Cretaceous survivors, has been recorded in northeastern Brazil up to the lower part of the P2 Zone. A triserially coiled planktonic morphotype, this species started to diversify immediately after the K/T transition. After only a few thousand years, in the earliest Danian, the first Tertiary taxa (the
Guembelitria- Woodringina
lineage) appeared; these are microperforate nonspinose forms that were probably restricted to shallow epipelagic waters. There is a trend towards uncoiling of the triserial pattern by progressively changing the positioning of the aperture, without any detectable ecophenotypic preference at first.

The first specimens of the
Eoglobigerina-Pseudosubbotina, Eoglobigerina-Subbotina
and
Praemurica
lineages, cancellate spinose and non-spinose forms, also evolved in the Danian in a nearly coeval and parallel evolutionary trend from a probably ancestral Hedbergella stock.

A revised phylogeny is suggested for the early Palaeocene planktonic foraminifera based on recorded stratigraphic ranges and morphological affinities (chamber arrangement and surface texture ornamentation).
Recovery of North Caucasus foraminiferal assemblages after the pre-Danian extinctions
Authors: Bugrova E. M.
Published: April 2008

The planktonic changes associated with the Maastrichtian-Danian boundary are described from successions in the North Caucasus, Russia. The extinctions recorded in the benthonic fauna are less sudden than those recorded in the plankton, with many pre-dating the end of the Maastrichtian. The Danian benthonic fauna contains a number of survivor taxa with few new species. The recovery interval for the benthonic fauna was much shorter and the increase in diversity occurred earlier than that of the planktonic fauna. Within the
Globorotalia angulata
Zone the recovery of the foraminiferal assemblage was almost complete.
A critique of techniques for modelling normal-fault and rollover geometries
Authors: Hauge T. A. , Gray G. G.
Published: April 2008

A review of the published literature indicates that antithetic oblique shear, at an angle of 30 ± 10° measured from the vertical, is the most appropriate algorithm for quantitative modelling of geometric relationships between downward-flattening normal faults and the strata in their hanging walls. This conclusion is based on 2D analysis of 11 natural examples (listric normal faults without apparent salt involvement, shale mobility, or footwall deformation) and selected laboratory physical models. It may not apply where mobile salt, mobile shale, or significant footwall tilting or deformation is present. Antithetic oblique shear, like all modelling algorithms, does not accurately simulate natural deformation processes, which are significantly more complex.
Analysis of fault geometry and displacement patterns
Authors: Needham D. T. , Yielding G. , Freeman B.
Published: April 2008

Interpretation of the subsurface is still often performed on suites of vertical seismic sections with structures being correlated from line to line to build up a map view at a particular horizon. The advent of 3D seismic surveys and routine use of interpretation software has made it common to produce ‘horizon-based’ interpretations, using auto-tracking techniques. Neither of these approaches guarantees a three-dimensionally consistent interpretation because of ambiguities in lateral and vertical correlation of structures. More reliable descriptions of a faulted surface can be obtained if the three-dimensional properties of a fault network are observed directly. Fault traces picked on vertical sections can be used to model the fault surfaces, which are then viewed in perspective to give an immediate assessment of the plausibility of the interpreted fault geometry. By associating horizon terminations with their respective fault segments this cut-off information can be shown on the perspective view of the fault surface, allowing the interpreter to examine in detail how reservoir layers are disrupted and juxtaposed by the fault network. The horizon cut-off information can also be used to calculate displacement-related values (throw, heave, separation) which may be gridded over the entire picked surface in order to produce displacement maps, also in the perspective view. Isolated single faults have simple displacement patterns with a maximum near the fault centre. Fault arrays show partitioning of displacement between the various splays, with relatively abrupt changes in the displacement at branchlines. Long ‘single faults’ are frequently shown to be segmented into en-echelon arrays rather than being simple continuous structures. Antithetic faults exhibit a downward decrease in displacement towards a tip line near their master fault. In areas of cross-cutting fault trends, displacement patterns can discriminate between different possible kinematic histories. Fault displacement can also be used to calculate other attributes such as fault seal potential, which can also be posted onto the perspective view of the fault surface. These analyses of fault geometry and displacement allow a more objective assessment of subsurface interpretation. They do not rely on particular assumptions about deformation mechanisms, only on the observation that displacement variation on individual fault surfaces is systematic.
Crustal fault reactivation facilitating lithospheric folding/buckling in the central Indian Ocean
Authors: Beekman F. , Bull J. M. , Cloetingh S. , Scrutton R. A.
Published: April 2008

High-quality, normal-incidence seismic reflection data confirm that tectonic deformation in the central Indian Ocean occurs at two spatial scales: whole lithosphere folding with wavelengths varying between 100 and 300 km, and compressional reactivation of crustal faults with a characteristic spacing of
c.
5 km. Faults penetrate through the crust and probably into the upper mantle. Both types of deformation are driven by regional large intraplate stresses originating from the Indo-Eurasian collision. Numerical modelling of the spatial and temporal relationships between these two modes of deformations shows that, in agreement with geophysical observations, crustal faults are reactivated first with stick-slip behaviour. Subsequent lithospheric folding does not start until horizontal loading has significantly reduced the mechanical strength of the lithosphere, as predicted by elasto-plastic buckling theory. Modelling suggests that lithospheric folding does not develop in the absence of fault reactivation. Crustal fault reactivation, therefore, appears to be a key facilitating mechanism for oceanic lithospheric buckling in the central Indian Ocean.
Internal structure of a detachment horizon in the most external part of the Pyrenean fold and thrust belt (northern Spain)
Authors: Sans M. , Sánchez A. L. , Santanach P.
Published: April 2008

The thick Eocene Cardona salt forms the detachment horizon of the most external part of the Pyrenean fold and thrust belt. This salt horizon forms the cores of anticlines and is intensively mined for potash. The study of the structure of the salt layer at three sites (Cabanasses, Súria-Shaft IV and Balsareny underground mines) reveals that the metric and decametric scale structures are consistent with deformation in a shear zone (detachment horizon) with a shear sense of top-to-the-south and not related to compressional or diapiric folding. A further study shows that these structures are later modified by larger wavelength folds and thrusts which have a surface expression. The total horizontal shortening in the two anticlines studied (Súria and El Guix) is a minimum of 750 m. All the folds developed in the detachment horizon have horizontal axes which are normal to the shear direction. This contrasts with folds developed in detachment horizons with intense shearing, where folds with axes parallel to shear direction are common.
Influence of salt on fault geometry: examples from the UK salt basins
Authors: Stewart S. A. , Harvey M. J. , Otto S. C. , Weston P. J.
Published: April 2008

The influence of salt layers on cover faulting during thick-skinned extensional faulting is examined using seismic examples from the salt basins offshore UK. The ratio of salt layer thickness to basement fault displacement is a key geometric parameter governing spatial offset between cover and basement fault segments. The influence of geological factors such as stratigraphic variation in salt thickness, basement fault zone geometry and basement fault growth through time on this parameter are individually examined. 3D models are constructed to illustrate the spectra of possible fault geometries which result from variations in these factors. Lateral stratigraphic variations within individual ‘salt’ layers are also considered, as are complications introduced by the addition of further salt layers into cover stratigraphy. Since diapiric intrusions occur after cover fault geometries are established and are localized by such faulting, an understanding of basement-cover fault relationships also illuminates salt diapir-basement fault relationships. An example from the Central North Sea diapir province is subject to such a genetic analysis, relating the diapir and its location to an underlying basement fault. The influence of salt on cover fault reactivation during basin inversion is discussed, focusin on the southern North Sea, where inhibition of reverse fault propagation from basement to cover is noted. It is suggested that analysis of local basement-cover relationships should form a first step in any attempt at a genetic classification of salt bodies.
Genesis of large counter-regional normal fault by flow of Cretaceous salt in the South Atlantic Santos Basin, Brazil
Authors: Szatmari P. , Guerra M. C. M. , Pequeno M. A.
Published: April 2008

The outstanding feature of the Santos Basin is a gigantic landward-dipping listric fault, about 300 km long, which trends NE parallel to the coast and is soled in the Aptian salt. This fault forms the seaward limit of a half-graben, up to 50 km wide and restricted to the post-salt sediments. In the present work we show, by physical modelling, that such a fault can result from the flow of salt in response to progradation of sediments over a spreading salt layer.
Global δ
13
C changes across the Paleocene-Eocene boundary: criteria for terrestrial-marine correlations
Authors: Stott Lowell D. , Sinha Ashish , Thiry Medard , Aubry Marie-Pierre , Berggren William A.
Published: April 2008

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high δ
13
C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of
12
C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic ‘events’ near the Paleocene-Eocene boundary provide stratigraphic information that can facilitate intersite correlations between marine and non-marine sequences.

Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera biostratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean’s carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO
2
. As a consequence of this exchange of
12
C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.
Fluvial incision and sequence stratigraphy: alluvial responses to relative sea-level fall and their detection in the geological record
Authors: Leeder M. R. , Stewart M. D.
Published: April 2008

A critical question in sequence stratigraphy is whether or not a falling or lowered sea level will cause a river or delta distributary channel to incise and thus help to initiate an Exxon type-1 unconformable surface. River adjustment to relative sea-level fall was quantitatively modelled by linear diffusion. Although not a new approach to the general problem of river incision, these numerical experiments illustrate the rates and magnitudes of channel incision expected for various combinations of river slope, shelf slope and sediment transport coefficient. The results of the modelling broadly agree with, admittedly uncertain, field observations from the Gulf Coastal Plain of the USA. Incised valleys have limited lateral extent because of the slowness of valley side slope retreat. Successive nodal avulsions upstream of the highest point of channel incision may progressively neutralize the effects of sea-level fall in younger channel courses. It is also possible that incision is reduced or eliminated by rivers with high sediment transfer coefficients: it is shown that rivers may ‘keep up’ with sea-level fall under certain circumstances, constructing a prograding alluvial plain over a previous ramp-like shelf with little slope differential. These conclusions apply to the recognition of geologically ancient incision and thus to the existence or otherwise of local and regional sequence stratigraphical boundaries caused by relative sea-level fall. We briefly discuss examples from the stratigraphical record and conclude that much exciting work remains to be done in the field and on the computer.
Unconformities within the Portlandian Stage of the Wessex Basin and their sequence-stratigraphical significance
Authors: Coe Angela L.
Published: April 2008

At outcrop, the Portlandian Stage of the western Wessex Basin, southern England comprises a complex series of marine and non-marine carbonates deposited in moderate to shallow water depth, with the occasional development of siliciclastic deposits near to the basin margins. The strata record part of a marked overall long-term regression on which are superimposed four shorter term relative sea-level cycles. The base of each of these short-term cycles is marked by a major unconformity or its correlative conformity (sequence boundary) formed during the maximum rate of relative sea-level fall; these are denoted P1 to P4. The south Dorset exposures are each in slightly different tectonic settings within the Central Channel Sub-basin. The Isle of Purbeck sections are stratigraphically the most complete, but the sections on the Isle of Portland, previously assumed to be complete, contain at least two significant stratal gaps. The sections at Ringstead Bay and Dungy Head are thin, condensed and in part incomplete. Proximally, in the Vale of Wardour (Mere Sub-basin), Vale of Pewsey (Pewsey Sub-basin) and on the London Platform at Swindon, in Oxfordshire and in Buckinghamshire the succession becomes condensed, the major unconformities are frequently angular and there is at least one incised valley.
Gamma-ray spectrometry as a tool for stratigraphical interpretation: examples from the western European Lower Jurassic
Authors: Parkinson D. N.
Published: April 2008

Portable gamma-ray spectrometry provides an objective and quantitative method of studying sedimentary cyclicity in otherwise-cryptic mudrock successions. Spectral gamma-ray data are presented from the Lower Jurassic sections of the Yorkshire and Dorset Coasts (England), from Peniche (Portugal) and from inland exposures in southern Germany, including a recent road-cut. In Yorkshire, where proximal-distal relationships are readily demonstrated from sedimentological evidence, there is good correspondence between more proximal facies and elevated Th/K ratios. This relationship may be extended to the Dorset succession where the sequence-stratigraphical interpretation of Lower Lias mudrocks has been a source of some controversy. Th/K ratio data here suggest a distal, starved, Hettangian-earliest Sinemurian (Blue Lias) and a prograding Sinemurian interval (Black Ven Marls and Shales-with-‘Beef’). Flooding and further progradation in the Early Pliensbachian (Belemnite Marls) is also suggested. These results provide support for common ‘second order’ stratigraphical forcing mechanisms between the Dorset and Yorkshire successions. Data from mainland Europe suggest that there are systematic regional variations in Th/K ratio, upon which local temporal variations are superimposed. These may reflect climatic or regional sediment transport effects.
Impact of sequence-based correlation style on reservoir model behaviour, lower Brent Group, North Cormorant Field, UK North Sea
Authors: Wehr F. L. , Brasher L. D.
Published: April 2008

An increasing percentage of remaining reserves in mature Brent Group producing fields is found in the Rannoch Formation, a lower shoreface succession characterized by low permeabilities, abundant mica and stratabound carbonate cements. The high contrast in permeability between the Rannoch and overlying Etive formations has resulted in severe water overrunning of oil-bearing Rannoch sandstones in a number of fields. Remaining Rannoch reserves will be difficult to recover and will require sophisticated reservoir management techniques. Differences in log correlation style which in the past may have been dismissed as inconsequential may now be important to consider in field depletion planning.

The objective of this study was to assess whether, in a high net-to-gross shoreface section such as the lower Brent Group at Cormorant Field, a sequence-based correlation would result in a significant difference in reservoir model behaviour, particularly in oil displacement patterns in lower shoreface sandstones of the Rannoch Formation. The modelled interval includes the prograding shoreline succession of the Rannoch (lower shoreface), Etive (upper shoreface-strandplain) and Ness (coastal plain) formations. There is a significant amount of facies interfingering between the Etive and Rannoch within the modelled area. Permeability models were constructed from both sequence-based and lithostratigraphic well-log correlations and used as input for 2-D reservoir simulations.

The results show a divergence in oil displacement behaviour between the two models, depending upon the degree of permeability anisotropy assumed. The principal reason for the difference lies in how the Rannoch layers are correlated. In the lithostratigraphic model, the Rannoch is treated as a tabular unit with layer boundaries parallel to the formation boundaries. Water injection into the upper Rannoch sweeps the upper Rannoch across the length of the model. In contrast, the sequence-stratigraphic approach treats the Rannoch-Etive as a series of clinoforms with layers offlapping toward the north in the direction of progradation. In this scenario, water injected into the upper Rannoch in the downdip area migrates parallel to layering into the lower Etive in the updip direction. The oil-bearing upper Rannoch in the updip areas correlates downdip to low-permeability facies which do not take water on injection; thus, the upper Rannoch remains unswept.

Predicted recovery efficiencies from the Rannoch lower shoreface sandstones are consistently lower in the sequence stratigraphic model, and more closely match observed reservoir behaviour at Cormorant Field than predictions based on lithostratigraphic correlation. This study suggests that, even in sand-rich systems such as the Rannoch-Etive, a sequence-based approach to reservoir zonation can improve predictions of reservoir performance.
Marine and nonmarine systems tracts in fourth-order sequences in the Early-Middle Cenomanian, Dunvegan Alloformation, northeastern British Columbia, Canada
Authors: Plint A. Guy
Published: April 2008

The Early to Middle Cenomanian Dunvegan Alloformation is a 3rd-order clastic sequence that was deposited on the western margin of the Alberta foreland basin. The alloformation, comprising ten allomembers (A-J) has been mapped over 33 000 km
2
using 1500 well logs and 40 outcrops. Regional flooding surfaces are used to define allomembers because they are more reliably identified in well logs than are Exxon-type unconformities (although in many instances unconformities and flooding surfaces are coplanar). The Dunvegan records episodic deltaic progradation from NW to SE along the axis of the foreland basin. This paper focuses on an 800 km
2
study area in NE British Columbia where both shallow marine and coastal plain strata are exposed in the valleys of the Peace and Beatton rivers. Marine strata comprise sandier-upward successions that grade from platy mudstone through cm-scale interbeds of wave rippled fine sandstone to dm-scale beds of HCS, commonly including large gutter casts. Successions may be capped by SCS and cross-bedded, fine-grained sandstone, sometimes with a rooted top. The succession of facies suggests a strongly wave-influenced deltaic shoreline. Gutter casts are consistently orientated shore-normal and appear to have been formed by oscillatory wave scour during storms. Sandstone distribution varies between successive progradational packages (‘shingles’) in allomember J, suggesting that delta switching was an important control on depositional cyclicity. Coastal plain deposits include small-scale (few metres) coarsening-upward successions of carbonaceous mudstone, siltstone and fine sandstone interpreted as lake and bay-fill deposits. Decimetre scale sharp-based sandstones may represent crevasse splays whereas lenticular, rippled and crossbedded sandstones were probably deposited in distributary channels. Rooted palaeosols are abundant. Both coastal plain and marine strata are locally replaced by erosive-based bodies of cross-bedded sandstone up to 25 m thick and 0.5–3 km wide, interpreted as incised valley fills underlain by type 1 sequence boundaries. Additional evidence of relative sea-level fall is provided by regressive surfaces of marine erosion beneath sharp-based shoreface sandstones. If attached to highstand deposits, these sandstones are assigned to the falling stage systems tract, whereas detached sandstones are assigned to the lowstand systems tract. During the early part of the transgressive systems tract, sedimentation was confined to incised valleys but later, interfluves were buried by sediments that locally contain dense
Thalassinoides
burrow systems,
Teredolites
and well-developed mud drapes, suggestive of brackish, tidally-influenced conditions. Overlying coastal plain strata lack evidence of marine influence and are attributed to the highstand systems tract.
Variable expressions of interfluvial sequence boundaries in the Breathitt Group (Pennsylvanian), eastern Kentucky, USA
Authors: Aitken John F. , Flint Stephen S.
Published: April 2008

Interfluvial sequence boundaries are a largely neglected aspect of sequence stratigraphy. They are subtle lowstand exposure surfaces which in marginal and nonmarine environments are often difficult to distinguish from exposure surfaces developed during the transgressive and highstand systems tracts. Three examples of interfluvial sequence boundaries, correlated with incised valley fills along strike, are described from Pennsylvanian delta plain deposits of the Breathitt Group of eastern Kentucky. The most common interfluvial palaeosols in the Breathitt Group are gleys developed under poorly drained conditions. This is in contrast to much of the published literature which suggests that soils on interfluves ought to be freely drained. Previously published geochemical analyses suggest that interfluvial palaeosols within the Breathitt Group are composite, forming initially under freely drained conditions and subsequently becoming gleyed due to a rise in the water table during the late lowstand and early transgressive systems tracts. This is a good criterion for differentiating lowstand palaeosols from those developed during the transgressive and highstand systems tracts.

Interfluvial sequence boundaries in the Breathitt Group have low preservation potential, being readily eroded by fluvial activity in the transgressive systems tract, which may totally remove all evidence of their former existence. In addition, if incised valleys overspill their margins during major flood events, interfluves may be represented by aggradational successions comprising thin coal seams, rootlet horizons and mature palaeoforests interbedded with crevasse splay sandstone. In such circumstances the presence of an interfluve can only be determined by the presence of correlative incised valley fills along strike.
The Neogene remagnetization in the western Betics: a brief comment on the reliability of palaeomagnetic directions
Authors: Villalaín J. J. , Osete M. L. , Vegas R. , García-Dueñas V. , Heller F.
Published: April 2008

Recent palaeomagnetic investigations in the western Subbetics have shown the existence of a widespread pervasive magnetic overprint of Neogene age in Upper Jurassic rocks. This remagnetization is coeval with the folding deformation in the area. We describe three examples in which the fold test result indicates that the remagnetization is pre-folding, post-folding and synfolding. An evaluation of the consequences of an incorrect interpretation of the remagnetization is presented. Heterogeneous rotational patterns can be explained as a consequence of incorrect evaluation of the timing between folding and overprint acquisition.
Palaeomagnetic studies in Morocco: tectonic implications for the Meseta and Anti-Atlas since the Permian
Authors: Khattach D. , Najid D. , Hamoumi N. , Tarling D. H.
Published: April 2008

Most Palaeozoic rocks studied in Morocco show evidence of partial or complete remagnetization that occurred towards the end of Hercynian times (late Carboniferous and Permian). The age of remagnetization can be established by direct comparisons with other Permian palaeomagnetic directions. The late Carboniferous and Permian rocks, and the remagnetizations of this age, show essentially identical directions throughout the Meseta and Anti-Atlas regions of Morocco and suggest that there have been few significant rotations of blocks within the Meseta domain since Permian times. This implies that most later motions in this region have not involved significant rotations about vertical axes or large scale changes in the latitude.
Palaeomagnetic study of Jurassic limestones from the Iberian Range (Spain): tectonic implications
Authors: Juárez M. T. , Osete M. L. , Vegas R. , Langereis C. G. , Meléndez G.
Published: April 2008

A palaeomagnetic investigation has been carried out in the Iberian Range (Spain). Seven localities have been sampled. Two stable magnetization components have been found in all investigated sections. A high-temperature primary component of Oxfordian age shows alternatively normal and reversed polarities. A consistent low-temperature component appears in all the studied sites; it has normal polarity and passes the fold test indicating its pre-Oligocene-Miocene age. Six localities show counterclockwise declinations for both components, the high-temperature component having a Jurassic direction and the low-temperature component an early Cretaceous direction. Only the southernmost section shows a clockwise rotation for both components. This indicates that the whole Iberian Range can not be considered as a part of Stable Iberia. The angular difference (
c.
15°) between both components is the same in all investigated sites. This implies that: (1) based on the palaeomagnetic direction of both components, the low-temperature remagnetization was probably acquired in the Cretaceous during the rotation of the Iberian Plate; (2) the clockwise rotation observed in the southernmost section took place after the acquisition of the remagnetization.
Palaeomagnetic dating and determination of tectonic tilting: a study of Mesozoic-Cenozoic igneous rocks in central West Portugal
Authors: Pereira J. L. , Rapalini A. , Tarling D. H. , Fonseca J.
Published: April 2008

Samples of igneous rocks (36 sites, 218 samples) associated with two main phases of the evolution of the Lusitanian Basin can be dated magnetically to latest Jurassic-early Cretaceous or late Cretaceous-Eocene. Directions of remanence in rocks belonging to the older phase require a 35° rotation to become consistent with directions from stable Europe, while those of younger age do not require such rotation. On a finer scale, the remanent directions can be used to ascertain the probable tectonic tilt at different times of the igneous activity and hence provide intermediate evidence on the tectonic evolution of this area, including rotations of individual tectonic blocks about both vertical and horizontal axes.
Magnetostratigraphy of Jurassic-Cretaceous limestones in the Western Carpathians
Authors: Houša Václav , Krs Miroslav , Krsová Marta , Pruner Petr
Published: April 2008

Magnetostratigraphic studies were carried out on limestones spanning the Tithonian-Berriasian boundary at Brodno (near the town of Žilina, west Slovakia) and Štramberk (north Moravia) in the Western Carpathians. The magnetic carrier in both sections was found to be magnetite. The observed pattern of normal and reverse polarity magnetozones corresponds well to magnetostratigraphic profiles in other areas of the Tethyan realm. Calpionellids are abundant in both profiles, while ammonites are almost completely missing. The base of the
Calpionella
zone, provisionally considered to represent the Jurassic-Cretaceous boundary in the Tethyan realm, was established in magnetozone M19n. The palaeolatitude of 27°N derived from the Brodno profile corresponds well to those derived from Jurassic rocks of the Križná nappe, on the northern rim of the Inner Carpathians. A pronounced anticlockwise tectonic rotation of 124° is established.
The Sumatra margin: oblique subduction and lateral displacement of the accretionary prism
Authors: Malod Jacques André , Kemal Badrul Mustafa
Published: April 2008

The Sumatra active margin extends more than 1600 km from northwest to southeast. The almost north-south direction of subduction is normal in front of Java and oblique in front of Sumatra. The transition between the two regimes of subduction occurs south of the Sunda Strait. A structural and stratigraphical study of the forearc domain, based on data collected during a French-Indonesian programme of cooperation in oceanography, confirms that the convergent motion is partitioned into a convergent motion, more or less perpendicular to the trench, and a strike-slip motion parallel to the trench. This latter motion is taken up along two major faults, the Sumatra and the Mentawai faults. At its northern end, the Mentawai fault is attenuated and seems to terminate within the accretionary prism. It is relayed and connected to the Sumatra fault by the Batee fault. This pattern can be explained by a simple model with two sliver plates: the Mentawai and Aceh sliver plates, on the top of which the forearc basin has developed. The accretionary prism itself is moving northwestwards along the Mentawai fault. Because there is no major evidence of extension within the Mentawai plate, we conclude that the motion along the Sumatra fault may occur at a uniform rate south of latitude 3°N. Strike-slip motion along the Mentawai fault may be explained by relatively better coupling between the subducting slab and the upper plate beneath the accretionary prism compared to that beneath the forearc, perhaps because of the large oceanic structures entering the subduction zone.
Extension, collision and curvature in the eastern Banda arc
Authors: Milsom John , Kaye Steve , Sardjono
Published: April 2008

The Kai Islands occupy the region of maximum curvature in the east of the Banda arc, where the Aru trough has been regarded as the surface trace of past subduction and present arc-continent collision. Eocene to Pleistocene sediments on Kai Besar, the easternmost island, have not been deeply buried or imbricated but have experienced large-scale extensional faulting. The associated Bouguer gravity high of more than +200 mGal requires upfaulting of the accretionary complex, the attenuated Australian continental crust on which it rests and the underlying mantle at the western side of the Aru trough. Seismic reflection surveys show the deformation front within the Aru trough SE of the Kai Islands but entirely to its west further north. Instead of continuing NNE to an offset near the coast of New Guinea, the collision trace passes through the narrow and shallow strait between Kai Besar and the other islands, and thus mimics the relatively smooth curve of the Bouguer gravity contours, rather than the discontinuities of the bathymetric troughs. The continuity in deep and shallow structures is strong evidence for the existence of the outer arc as a single geological unit prior to the present phase of arc-continent collision.
SE Sundaland accretion: palaeomagnetic evidence of large Plio-Pleistocene thin-skin rotations in Buton
Authors: Ali Jason R. , Milsom John , Finch Edward M. , Mubroto Bundan
Published: April 2008

The Tukang Besi Platform, an Australian microcontinental fragment, began docking with Sundaland in the Pliocene, impacting on east Buton (SE Sulawesi). Fortuin
et al.
(1989;
Journal of SE Asian Earth Sciences
,
4
, 107–124) postulated that south Buton had rotated clockwise through about 60° relative to central/north Buton in response to the Tukang Besi collision. A palaeomagnetic investigation was carried out to test this model. Some 41 (of 72) palaeomagnetic sites from the upper Neogene Tondo and Sampolakosa Formations on Buton yielded interpretable data. Sites from south Buton record locally consistent directions, but at sampling localities < 25 km apart deflections are between 0° and 35° clockwise. There is no trend in these data with respect to the broad geotectonic setting. In central Buton declination offsets are negligible. In north Buton localized (kilometre scale) large (30–60°) clockwise and counter-clockwise declination offsets are observed. Effectively the Buton data provide spot markers on cover sequences that have been locally deformed as ‘thin-skin’ sheets. The underlying basement may have experienced the large relative motions proposed by Fortuin
et al.
(1989) but the upper Cenozoic cover has not been deformed in such a simple way. This study demonstrates that thin-skin sheets associated with continental collision may undergo 30–60° rotations within very short intervals (< 2–3 Ma).
Docking and post-docking escape tectonics in the southern Philippines
Authors: Pubellier M. , Quebral R. , Aurelio M. , Rangin C.
Published: April 2008

The structure of the Philippine archipelago results from the juxtaposition, between the Late Miocene and the present, of a volcanic belt against fragments of the Eurasian margin and associated marginal basins. The southern Philippines offers the opportunity of studying the mechanics of the deformation from active contraction to a more complex post-docking setting. The docking period is characterized by a compression which began during the early Late Miocene in the central Philippines and has been recently studied in the island of Mindanao. There, deformation initiated in the Late Miocene-Early Pliocene on a NW-trending wrench zone, and continued until the Late Pliocene with thrusting on west-verging flats and ramps within the arc and east-verging thrusts within the Sangihe forearc. This deformation is still active to the south in the Molucca Sea. The post-docking period began in the Early Pleistocene in northern Mindanao and is represented by a new geodynamic framework with a paired subduction zone and strike-slip fault. However, convergence is still active in the Manila and the Negros trenches, although the Philippine fault is not offset. Large wrench faults, which reactivate the ramp faults of the collision stage, transfer strain from the Philippine fault to the Manila and Negros trenches. These observations imply active intra-arc extension and fragmentation within the Philippine mobile belt.
Basement structural controls on Carboniferous-hosted base metal mineral deposits in Ireland
Authors: Johnston J. D. , Coller D. , Millar G. , Critchley M. F.
Published: April 2008

Explorationists have long recognized the importance of structural control of Irish base metal deposits, but the kinematics and timing of the structures relative to the mineralization are subject to wildly differing interpretations. This paper presents a combination of structural, magnetic and gravity data that show that the fundamental structural controls are easterly to northeasterly-trending basement (Caledonian) structures which have been reactivated in dextral transtension by northeasterly to north-northeasterly extension during the Dinantian. In general, in the north of the country the ore-controlling faults dip south, while in the south of the country they dip north. The structures have evolved through a temporal kinematic history of early normal faulting, later oblique slip, and some show evidence of later reverse movements. Part of this evolution may reflect burial history, although it also reflects the transition from Dinantian transtension to Variscan (Hercynian) compression. The bulk of the mineralization appears to post-date the normal faulting, and pre-date Variscan compression. Mineralization is thought to be post-compactional and could have occurred during the dextral transtension, although some of the sulphides could post-date most of the transtensional movement.
Cyclic emersion surfaces and channels within Dinantian limestones hosting the giant Navan Zn-Pb deposit, Ireland
Authors: Rizzi Giancarlo , Braithwaite Colin J. R. , Rizzi Giancarlo
Published: April 2008

The Carboniferous succession in the Navan Mine area, which lies near the northern margin of the Dublin Basin, rests unconformably on folded Lower Palaeozoic rocks. The informal stratigraphic nomenclature of the mine is used throughout. Sedimentation began in the late Devonian-early Courceyan with Red Beds reflecting deposition in braided streams and alluvial fans. The overlying Laminated Beds consist of shallow-marine barrier sandstones, tidal-flat/lagoonal mudstones, and sabkha evaporites. The Muddy Limestone is a mud-dominated carbonate sequence reflecting deposition in an open clastic-influenced lagoon. The Pale Beds that follow, and on which attention is focused here, contain at least 44 peritidal and shallow-shelf depositional cycles. The overlying Shaley Pale and Argillaceous Bioclastic Limestones reflect deeper water open-sea conditions. This sequence is truncated by a conspicuous erosion surface overlain by Chadian submarine debris-flows and limestone turbidites.

The succession reflects a progressive deepening of the waters as subsidence outpaced sediment accumulation, but emersion surfaces capping cycles indicate that neither deposition nor relative sea-level rise were continuous. Cyclicity and emergence are believed to reflect the interaction of regional subsidence, glacio-eustatic sea-level oscillation, and sediment supply.

Emersion surfaces occur in the Laminated Beds and throughout the Pale Beds, and include palaeosols,
in situ
breccias, pinnacled and hummocky surfaces, and karst-modified topography. Deeply incised channels at four intervals point to larger-scale incision. The lithoclast-bearing conglomerates which they contain indicate extensive emergence nearby. The distribution of these features may be related to the margins of outcrops of Old Red Sandstone and Lower Palaeozoic rocks.

The Dinantian limestones in this region host several Zn-Pb ore deposits including Europe’s largest at Navan. The results of this study suggest a relationship to the margins of former emergent carbonate terrains.