bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract
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

Abstract

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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract

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).