bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inversion-controlled uplift of an outer-arc ridge: Nias Island, offshore Sumatra
Authors: Samuel M. A. , Harbury N. A. , Jones M. E. , Matthews S. J. 
Published: April 2008

Abstract
This study presents data from Nias Island which lies on an outerarc ridge 150 km to the west of mainland Sumatra. A new stratigraphy, geological map and cross-section of Nias have been produced from field data collected over all the island supplemented with aerial photography, LANDSAT and SAR (synthetic aperture radar) studies and these data form the basis for a new interpretation of the island. Where exposed the basement consists of ophiolitic rocks, originating from a variety of tectonic settings, and with a thin sedimentary cover. Three main sub-basins are identified on Nias. Late Paleogene-Neogene sedimentation in these basins was controlled primarily by major extensional faults though deposition within sub-basins was influenced by the presence of sub-basin transecting faults with significant vertical throws. Two phases of inversion are recognized: the first occurred during the Early Miocene, was limited to western regions and is identified by the presence of a localized unconformity and vitrinite and apatite fission track data. The second inversion initiated in Pliocene times and affected all the sub-basins on Nias. Latest Pliocene-Pleistocene rocks unconformably overlie the Miocene strata. Deformational styles within separate fault-bounded segments vary markedly; structural mapping demonstrates uplift and deformation has been largely controlled by reactivation of sub-basin extensional faults and oblique-slip movements on transecting faults. Diapiric melanges developed during inversion suggesting an intimate relationship between uplift and remobilization of overpressured mudrocks. This study concludes that the uplift of the sub-basins on Nias resulted from inversion of basin successions by reactivation of original major extensional faults rather than on thrust-slices developed in an accretionary prism. Nias does not form part of an accretionary complex; the accretionary prism has developed to the southwest of Nias.
Fold growth during basin inversion — example from the East China Sea Basin
Authors: Wang Guang Ming , Coward Mike P. , Yuan Wenguang , Liu Shenshu , Wang Wenqiang 
Published: April 2008

Abstract
Understanding the progressive growth of fold structures during basin inversion is an important part of basin analysis. To achieve this, a complex inversion-related anticline in the East China Sea Basin has been studied to examine variations in the growth rate and growth kinematics during the Miocene inversion of the basin. Detailed studies of onlaps and truncations of seismic reflections, particularly within the syn-growth package, indicate that different parts of the anticlinal structure grew at slightly different times, i.e. the start and cessation of growth vary along and across the structure. Growth was related to the reactivation of the pre-existing, dominantly W-dipping early normal faults. The reactivation of these early normal faults and the development of new reverse faults progressed laterally and transversely across the structure. Sections have been depth-converted, back-stripped and reconstructed to restore the progressive development of the fold. The concept of this study may be applied to many other basins with a similar evolutionary history.
Correlation of sandstones using heavy minerals: an example from the Statfjord Formation of the Snorre Field, northern North Sea
Authors: Morton Andrew , Hurst Andrew 
Published: April 2008

Abstract
Correlation of sandstones using heavy minerals is dependent on the recognition and quantification of provenance-sensitive parameters. Suitable criteria include ratios of minerals that have similar hydraulic and diagenetic behaviour, and properties of populations of individual mineral species. Sandstones of the Statfjord Formation in the Snorre Field display marked variations in their heavy mineral assemblages. Although hydraulic and diagenetic processes have played some part in generating these variations, major changes in the nature of the source material can be detected on the basis of heavy mineral ratio and varietal data. These changes in sand provenance can be used to produce a detailed stratigraphic breakdown of the sequence and to correlate from well to well. Eleven heavy mineral zones have been recognized on the basis of variations in monazite/zircon, garnet/zircon and rutile/zircon ratios, on the incoming of chloritoid, and on the composition of garnet populations. The marked changes in provenance result from the proximity of the depositional location to the hinterland and it is considered unlikely that the detailed correlation made in the Snorre Field area applies to Statfjord sandstones in other parts of the northern North Sea. However, there is evidence for some degree of allogenic control on the heavy mineral variations and therefore some events may have regional significance.
Direct Pb/Pb dating of Silurian macrofossils from Gotland, Sweden
Authors: Russell Jonathan 
Published: April 2008

Abstract

Pb/Pb and U-Pb methods of direct isotopic dating, characteristically associated with igneous and metamorphic rocks, have been applied successfully to well-preserved stromatoporoidal carbonates from Gotland, Sweden. A Pb/Pb date of 432 ± 15 Ma for Wenlock-Ludlow boundary carbonates is in good agreement with independent chronometric estimates and is interpreted as the age of deposition/early diagenesis. A Pb/Pb date of 326 ± 11 Ma for older Middle Wenlock samples is
c.
100 Ma too young for its stratigraphic position and is interpreted as a late diagenetic age associated with fluid movement along sub-surface faults. U-Pb systematics in both samples have been disturbed by U remobilization in response to recent weathering associated with post-glacial uplift in the Baltic.

For many years, the direct age determination of sediments has been an irritating problem to earth scientists. Direct Pb/Pb dating of carbonates should be considered a credible source of chronometric information. Application of the method to poorly constrained Precambrian stromatolitic carbonates is potentially powerful since host sediment ages may be only poorly constrained through indirect reference to basement and intrusive rocks. A broad geochemical review is presented to explain the suitability of certain carbonates for this method of isotopic investigation.
Wireline log-cyclicity analysis as a tool for dating and correlating barren strata: an example from the Upper Rotliegend of The Netherlands
Authors: Yang Chang-Shu , Kouwe Wim F. P. 
Published: April 2008

Abstract
The stratigraphic subdivision and correlation of the Upper Rotliegend Group in The Netherlands offshore is difficult due to lack of biostratigraphic data. A regional study of 150 released wells and core data has revealed the preservation of five supersequences, 12 sequences and short-term cyclicities in the Upper Rotliegend deposits. They are interpreted to reflect long- and short-term climate changes, which controlled the deposition of Rotliegend sequences.
The supersequences (second order) serve best for regional correlation and prediction of sand distribution. The sequences (third order) are best suited for detailed block- or field-scale correlation and distribution of (un)favourable lithofacies. The short-term (higher order) cycles represent orbital-forcing (Milankovitch) cycles and are used as quantitative parameters in wireline log cyclicity analysis. This includes the calibration of sequence boundaries and maximum flooding surfaces, the determination of the absolute age, the estimation of the duration time and the net accumulation rate of the preserved rock succession, and the pattern recognition of the trend of net accumulation rate variations within the third-order sequence. The method has revealed a new possibility of dating and correlating strata such as the Upper Rotliegend.
Detachment tectonics during Atlantic rifting: analysis and interpretation of the S reflection, the west Galicia margin
Authors: Reston T. J. , Krawczyk C. M. , Hoffmann H.-J. 
Published: April 2008

Abstract
Beneath the tilted fault blocks of the western Galicia rifted margin an unusually bright reflection, the S reflection, is observed. The waveform, polarity and amplitude of S indicate that it is a reflection from a seismic interface across which the acoustic impedance increases sharply. This result is consistent with its interpretation as a detachment fault juxtaposing a low velocity and density upper plate and a high velocity and density lower plate. The lower plate may represent partially serpentinized mantle material, brought into contact with pre-rift sediments and upper crustal basement by tectonic denudation.
Pre-stack depth migration is applied to determine the true geometry of S, and its relationships with the overlying faults. It is found that S passes continuously beneath the upper crustal faults, which detach onto S. However, S does appear to be truncated westwards by east-dipping reflections associated with the peridotites exposed at the seafloor. We interpret these reflections as the continuation of the top-to-the-east extensional shear zone sampled within the peridotite, and suggest that S is either antithetic to a master mantle detachment, or that S is cut by a later mantle shear zone.
Evolution of a major oceanographic pathway: the equatorial atlantic
Authors: Jones E. J. W. , Cande S. C. , Spathopoulos F. 
Published: April 2008

Abstract

The history of continental separation in the equatorial Atlantic is important to our understanding of the events which have led to the establishment of the present patterns of water circulation. Orientations of oceanic basement lineaments determined from bathymetric, seismic, magnetic and satellite altimetry data, and the distribution of seismic reflectors in deep-water sediments indicate that during its early opening stages the Atlantic was bounded to the south by the Guinea Fracture Zone. Using stage poles obtained from South Atlantic spreading patterns, basement ages and the palaeobathymetry of the equatorial region have been derived. The proximity of magnetic anomaly M0 to the present continental slopes suggests that the deep-water basins began to form in the Aptian. During the early stages of basin development water circulation was greatly restricted by fracture zone ridges, leading to the formation of thick sequences of carbonaceous shales. Outflow of dense, saline water from the equatorial basins may have been an important factor in controlling deposition along the Atlantic margins, contributing to the development of unconformities within the Cretaceous sedimentary record. By Santonian time the equatorial rift had reached a width of
c.
1200 km, water depths close to the continental margins exceeded 5000 m and the transfer of surface water between the North and South Atlantic was well established. The conjugate Sierra Leone and Ceara Rises were built up during the late Cretaceous and existed as separate features by Early Oligocene time. Both the Romanche and Vema Fracture Zones have acted as important conduits for the transfer of bottom-water from the western to the eastern equatorial basins, with seismic profiles providing evidence for vigorous bottom water flow during the Eocene and later Tertiary. In the Sierra Leone Basin the circulation of bottom water may have reversed during the late Tertiary as a result of the movement of the eastern portion of the Romanche Fracture Zone north of the equator.
The tephrochronology and radiocarbon dating of North Atlantic, Late-Quaternary sediments: an example from the St. Kilda Basin
Authors: Hunt John B. , Fannin Nigel G. T. , Hill Peter G. , Peacock J. Douglas 
Published: April 2008

Abstract

A sequence of disseminated basaltic tephras of Icelandic provenance has been investigated in sediments of Late Quaternary age recovered from the St Kilda Basin, on the Scottish continental shelf. The tephras were deposited from gradually melting rafted pack ice, transported on an anti-clockwise surface current originating to the north of Iceland. The presence of these ice-rafted tephras extends the zone of this current activity well beyond its previously documented western limit, demonstrating current impingement on the UK continental shelf. The evidence of ice-rafting, together with the biostratigraphy and a series of AMS
14
C dates, confirm that this deposition occurred during the Younger Dryas chronozone. Electron probe microanalysis (EPMA) of glass-shard geochemistry is used to ralate the St Kilda tephras to tephras found in marine and terrestrial deposits throughout the North Atlantic area, and to possible volcanic centres in Iceland. The joint role of tephrochronology and radiocarbon dating is discussed in relation to the comparative reliability of marine and terrestrial timescales. Problems with the chronology of the terrestrial equivalents of these tephras in Northern Iceland are highlighted.
Palaeobathymetric reconstruction on a gridded database: the northern North Atlantic and southern Greenland-Iceland-Norwegian sea
Authors: Wold C. N. 
Published: April 2008

AbstractA computer program combining backstripping with plate tectonics has been used to reconstruct the palaeobathymetry of the region between the Charlie Gibbs and Jan Mayen Fracture Zones from the East Greenland margin to the European shelf for the past 50 Ma. Two different models were tested, one assuming that continental extension and rifting opened the Rockall Trough and Faeroe-Shetland Channel during the Cretaceous and that the area has subsided ever since. The second model assumes that the Rockall-Faeroe region rifted in the Cretaceous and was uniformly uplifted in the late Palaeocene due to heating of the lithosphere by the mantle plume of the Iceland Hotspot. The alternative assumptions about the thermal age of the lithosphere produce very different results with implications for the palaeoceanography and sedimentation in the region. The isostatic model presented here predicts crustal thicknesses along the Iceland-Faeroe Ridge and in the Rockall-Faeroe region that are in close agreement with estimates using seismic and gravity techniques.
Triassic correlation and stratigraphy in the South Central Graben, UK North Sea
Authors: Goldsmith P. J. , Rich B. , Standring J. 
Published: April 2008

Abstract
Triassic strata in the South Central Graben of the North Sea have yielded moderate to good recoveries of palynofloral assemblages and have sufficiently distinct petrophysical responses to enable the subdivision of the succession into between seven and eleven units. The Triassic succession of the Amoco well, 30/12b-3, is proposed as the type section for the Skagerrak Formation of the area. Despite lacking good biostratigraphic control, typical log character for the sequences is well displayed. The mainly Scythian (early Triassic) red mudstones of the Smith Bank Formation can locally be divided into three units, but generally only one is recognized. A new lithostratigraphic nomenclature for the middle to late Triassic Skagerrak Formation is proposed. Six members, with eight units, are recognized over UK Quadrants 29 and 30, and may possibly continue into the southern part of Quadrant 22 and into Norway Quadrant 7. The member names are partly derived from the Phillips fields in which they were first recognized. The basal Judy Sandstone Member is named after the Judy Field discovery well 30/7a-4A, and is overlain by the petrophysically distinct Julius Mudstone Member. The Joanne Sandstone Member is named after the Joanne Field well 30/7a-3, and is overlain by the Jonathan Mudstone Member, which can be further subdivided into upper, middle and lower units on log character. The uppermost members are the Josephine Sandstone Member, from the type well on the Josephine structure, 30/13-1 (Deegan & Scull 1977), which is overlain by the Joshua Mudstone Member. The upper members are rarely preserved, due to extensive early to middle Jurassic uplift and erosion.
Distinction between fault and salt control of Mesozoic sedimentation on the southern margin of the Mid-North Sea High
Authors: Griffiths P. A. , Allen M. R. , Craig J. , Fitches W. R. , Whittington R. J. 
Published: April 2008

Abstract
The North Dogger Fault Zone (NDFZ) is situated at the northern margin of the UK Southern North Sea Basin at the northern limit of the mobile Zechstein Supergroup. This fault zone underwent movement during late Triassic and probably early Jurassic times. The NDFZ is comparable with the southern part of the Dowsing Fault Zone (SDFZ), which was initiated during late Scythian times and continued to move until at least mid-Carnian times. The SDFZ is located at the southwestern edge of mobile salt. Both fault zones form part of the basin-bounding fault system, which is proposed to have been initiated as a response to the growth of salt swells in the centre of the Southern North Sea Basin. The fault formation is due to folding of the Triassic strata over the swells and overall shortening of the Triassic cover. The shortening was taken up as extension at the basin margins, corresponding to the edge of the mobile Zechstein salt.
The timing and direction of Permo-Triassic extension in southern Britain
Authors: Chadwick R. A. , Evans D. J. 
Published: April 2008

Abstract
The Permo-Triassic sedimentary basins of southern Britain form a roughly N-S-trending linear rift system which extends more than 400 km from the northern English Channel to the Irish Sea. The component basins of the rift system typically contain 1000–4000m of dominantly continental red-beds. The basin margins are clearly imaged by seismic reflection data, and typically comprise a major syndepositional normal fault or faults lying in the hanging-wall block of a reactivated basement thrust. In southern England, basin-controlling faults have a dominant E-W (Variscoid) trend, in the Midlands the faults have a dominant N-S (Malvernoid) trend and in northern England NE-SW (Caledonoid) basin fault trends are prominent. Thus the rift system can be structurally divided into three segments, dependent on the structural gain of the underlying basement. Because the orientations of the basin-margin faults were controlled by basement structures, they did not develop perpendicular to the extension direction and consequently suffered varying degrees of oblique-normal displacements. An analytical model is developed which relates the displacement components of a set of variably oriented faults to a single regional extension direction. Application of the model to the rift basin-margin faults indicates that faults trending N-S had displacements which most closely approximated to dip-slip. Conversely, faults trending E-W suffered strongly oblique-slip displacements. This is consistent with a cumulative Permo-Triassic extension vector oriented 060°–240°, roughly ENE-WSW. Analysis of thickness changes across the basin-margin faults, and backstripped burial history plots from the basin depocentres, indicate at least two phases of crustal extension. The first occurred in late Permian times, with a second major episode in early Triassic times. They were characterized by rapid fault-controlled basin subsidence and coarse clastic sedimentation. Each was followed by a period of more gradual, regional subsidence, depositional overlap of the basin margins and a tendency towards finer-grained sedimentation.
Diagenetic history and reservoir potential of Permo-Triassic sandstones in the Rathlin Basin
Authors: Fitzsimons Steven , Parnell John 
Published: April 2008

Abstract
Exploration prospects in the Rathlin Basin depend in part upon the reservoir potential of sandstones in the Permo-Triassic. The sandstones are the deposits of alluvial fan, channel and floodplain environments; aeolian deposits may occur in the basal (Permian) part of the succession. Scattered outcrops around the basin margin in Ireland and Scotland, and boreholes in the deep part of the basin onshore Northern Ireland, allow determination of diagenetic history and reservoir quality.
Cementation is dominated by very early pore-filling sulphate/carbonate, illite-smectite grain-coatings, and overgrowths of potassium feldspar. Other cements are haematite graincoatings, quartz overgrowths and kaolinite pore-fillings. The sulphates/carbonates occlude porosity, and the clays/feldspars reduce permeability by bridging pore throats. Even in the deepest parts of boreholes, porosities can be high owing to dissolution of cements and unstable grains. This secondary porosity has in some cases been occluded by kaolinite, particularly in shallow-buried marginal parts of the basin.
Thick, coal-bearing Carboniferous and gypsiferous Mercia Mudstone Group sections onshore suggest that adequate source and seal rocks exist below and above the sandstones, respectively, thus enhancing the exploration potential of the basin.
Shallow gas accumulation and migration in the western Irish Sea
Authors: Croker Peter F. 
Published: April 2008

Abstract
The Irish Sea has long been known to contain extensive areas of shallow gas accumulation, particularly in the area southwest of the Isle of Man. More limited occurrences of seabed features associated with shallow gas migration, such as columnar disturbances, seabed doming and pockmarks, have also been reported. Until now this gas was generally assumed to be of biogenic origin.
Recently acquired route survey data have provided new insights into the distribution of both gas accumulation and gas migration in this area, as well as identifying areas of active seepage. It is proposed that the gas originates as coalbed methane or thermogenic gas in the extensive Carboniferous deposits underlying the region. This has considerable significance for hydrocarbon exploration in the area.