bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical modelling of fold and fracture geometries associated with salt diapirism
Authors: Alsop G. Ian 
Published: April 2008

Abstract
The generation of salt diapirs is associated with a protracted deformation history in the surrounding overburden, which may be difficult to image seismically due to the highly inclined and fractured nature of sediments adjacent to the salt. To further the understanding of overburden deformation related to diapir development, a series of physical models has been produced incorporating a viscous SGM polymer source layer which is overlain by a granular, glass bead overburden. Model diapirs are initially triggered (to the pillow stage) via a basal indentor, but subsequently develop by a passive downbuilding process. The maximum widths of withdrawal basins and diapir-related upturn are approximately equivalent to one another. Experiments in which the salt analogue is allowed to extend laterally result in listric normal faulting of the overburden, to define graben structures centred on the diapir. Injection of the source layer into the footwall of normal faults results in reactive dispirism on the flanks of the major structure, whilst the adjacent central sections illustrate geometries which could be attributed to both active and passive diapirism. Multiple generations of normal faults produce graben with an inward-stepping sequence of fault propagation towards the central block. Complete evacuation of the source material at the keel of the normal fault simulates localized salt welds and results in extensional displacement being transferred into the hangingwall block. Sand-clay mix layers act as relatively competent horizons and display radial fracture patterns which may also be associated with a central ring fault and circular collapse graben above the diapir. Normal faults defining graben structures converge on the radial fracture pattern overlying the diapir. Circular thrust faults surrounding the diapir are developed when more competent horizons temporarily arrest vertical growth resulting in diapiric ‘ballooning’.
Palaeoenvironments in the North Sea Basin around the Paleocene-Eocene boundary: evidence from diatoms and other siliceous microfossils
Authors: Mitlehner Alexander G. 
Published: April 2008

Abstract

Assemblages of siliceous microfossils (diatoms, silicoflagellates, radiolaria, and ebridians) have been examined from calcareous concretions (cementstones) in the Fur Formation, an ash-bearing diatomite which crops out around the Limfjorden region of Jutland, northern Denmark. Although microfossil assemblages (particularly diatoms) change character through the deposit, only one major turnover occurs that is reflected by all of the microfossil groups examined. This biotic event indicates a marked increase in marine influence, and probably climatic warming. It appears to mark the beginning of the early Eocene transgressive phase that affected the whole of the North Sea Basin and eventually re-established this isolated basin’s links with the North Atlantic and Tethys. Other diatom assemblages examined from offshore samples towards the centre of the basin show strong similarities with those from the Fur Formation and confirm that the lower part of this deposit correlates to the Sele Formation, whilst the upper part correlates to the Balder Formation. The lowest occurrence of the widely occurring diatom
Fenestrella antiqua
is suggested as a practical marker for the base of the Eocene in both offshore and onshore sediments in the North Sea Basin. Restricted circulation processes involving seasonal, monsoon-driven upwelling leading to sporadic basin eutrophication and water-column stratification, are considered to account for the widespread proliferation of siliceous microfossils in the North Sea Basin during the late Paleocene to early Eocene.
Deep water circulation in the Paleocene Ocean
Authors: Corfield Richard M. , Norris Richard D. 
Published: April 2008

Abstract

We have compiled deep water benthic δ
13
C data from the Paleocene portions of several DSDP and ODP holes and present it using the new timescale of Berggren et al. (1995).

Our data show that the north Atlantic hole DSDP 384 was the most positive site for δ
13
C in the late Cretaceous and the earliest Paleocene, suggesting that the sub-tropical north Atlantic was an important locus of deep water production during these intervals. Salinity and temperature comparisons do not support unequivocal deep water production by halothermal means in this region so we prefer to avoid the term Warm Saline Deep Water (WSDW) and employ instead the more neutral term ‘palaeo-North Atlantic Deep Water’ (palaeo-NADW). During K/T boundary time, the southern ocean apparently became the major producer of deep waters. Based on δ
13
C comparisons both the North Atlantic and Southern Ocean were deep water producers during the early Paleocene to the late Paleocene interval. In the latest Paleocene (during the ‘Paleocene carbon isotope maximum’) Southern Ocean δ
13
C was most positive, supporting a Southern Ocean deep water source. The earliest Eocene ocean was characterized by deep water production in the high southern latitudes with well developed interbasinal δ
13
C gradients.

δ
18
O data show an overall decrease from the late Cretaceous into the Early Eocene interrupted by an increase between 64 and 57 Ma. This is interpreted as an overall warming trend with a superimposed, previously undocumented, cooling phase in the early to late Paleocene.
Use of palaeosols in sequence stratigraphy of peritidal carbonates
Authors: Wright V. P. 
Published: April 2008

Abstract
Palaeosols (fossil soils) are common in ancient shallow marine carbonate successions. The degree of development exhibited by the palaeosol reflects the duration of subaerial exposure, with palaeosols occurring at lower order sequence boundaries commonly showing complex, polygenetic histories, and those at higher order boundaries showing less development. Palaeosols in parasequence sets commonly display systematic variations in their degrees of development reflecting the varying lengths of subaerial exposure related to changes in accommodation space creation. These properties of palaeosols can be used to reappraise the sequence stratigraphical positions of peritidal carbonates in the Lower Carboniferous of southwest Britain, serving to illustrate the dangers of assigning facies units to systems tracts based solely on simple facies relationships. The palaeosols and associated sequences do not support the view that high frequency, moderate amplitude eustatic sea-level fluctuations of Milankovitch-type were operating during the Tournaisian or early Viséan.
Slump and debris-flow dominated basin-floor fans in the North Sea: an evaluation of conceptual sequence-stratigraphical models based on conventional core data
Authors: Shanmugam G. , Bloch R. B. , Mitchell S. M. , Damuth J. E. , Beamish G. W. J. , Hodgkinson R. J. , Straume T. , Syvertsen S. E. , Shields K. E. 
Published: April 2008

Abstract
The sequence-stratigraphical concept of the basin-floor fan within the Vail/Exxon conceptual sea-level model is popular in hydrocarbon exploration because this model predicts that basin-floor fans are composed of sand-rich turbidites with laterally extensive reservoir geometries. Many producing deep-marine facies in the Palaeogene and Cretaceous of the North Sea have been interpreted as basin-floor fans based on their seismic (e.g. mounded forms) and wire-line log signatures (e.g. blocky log motifs). We have examined nearly 3700 m (12000 feet) of conventional core from features interpreted as basin-floor fans in the North Sea and adjacent regions to determine the sedimentary facies, which actually comprise these features. Our study reveals that basin-floor fans are predominantly composed of mass-transport deposits (mainly slumps and debris flows); turbidites are extremely rare. Sedimentary features indicative of slump and debris-flow origin include sand units with sharp upper contacts, slump folds, discordant, steeply dipping layers (up to 60°), glide planes, shear zones, brecciated clasts, clastic injections, floating mudstone clasts, planar clast fabric, inverse size grading, and moderate to high matrix content (5–30%). Calibration of these facies in long cores (120–210 m or 400–700 ft) with seismic and wire-line log signatures suggests that seismic mounds and blocky log motifs are actually a manifestation of amalgamated sand units emplaced by these mass-transport processes. The cores show that in some cases, sequence boundaries on seismic profiles actually correspond to primary glide planes (decollement) between slump sheets in cores examined. Unlike laterally continuous turbidites, slump- and debris-flow-emplaced sands are often laterally discontinuous, thus making reservoir geometry and continuity much harder to predict. Nevertheless, these mass-transport deposits still form important hydrocarbon-producing reservoirs (e.g. the Frigg Field). Because both sands and muds deposited by slumps and debris flows form features that are routinely interpreted as basin-floor fans on seismic and log data, process-sedimentological interpretation of conventional core is critical to the establishment of the true origin and distribution of sands contained in such features and thereby evaluate their hydrocarbon potential.
A sequence stratigraphical approach to the understanding of basin history in orogenic Neoproterozoic successions: an example from the central Highlands of Scotland
Authors: Glover B. W. , McKie T. 
Published: April 2008

Abstract
Sequence stratigraphical principles, developed largely in Phanerozoic basins, are applied here to a Neoproterozoic metasedimentary succession. The Grampian and Appin groups of the southern Monadhliath represent clastic and carbonate deposition within a multiphase rift basin. Subsequent polyphase deformation has resulted in considerable crustal shortening so that, within a comparatively small area, there is significant lateral variation in basinal settings. The succession is rationalized into a number of transgressive-regressive cycles. The northwestern area is dominated by shelfal metasedimentary rocks which exhibit a hierarchy of sequence boundaries distinguished by abrupt basinward shifts (southwards and southeastwards) in the proximality of marine facies, and onlap. The surfaces between the sequences provide the objective criteria for correlation into the basinal succession of the southeast. This sequence stratigraphical approach gives new insight into Neoproterozoic basin dynamics. Although rifting is confirmed as having a dominant role in creating accommodation for the deposition of at least two ‘supersequences’ thousands of metres thick, the basin depocentre is reinterpreted to have lain to the south and east throughout deposition of the Grampian and Appin groups. The upwards trend towards ‘cleaner’ sand from Grampian to Appin group deposition is suggested to reflect increasing sediment reworking by tides during a second-order transgression. The scale of major sequences means that patterns of deposition are likely to have been basin-wide or greater, so that it may be possible to identify similar transgressive-regressive stratal architectures in structurally isolated and disparate successions. This approach may help resolve the status of some suspect terranes.
Influence of relative sea-level on facies and reservoir geometry of the Middle Jurassic lower Brent Group, UK North Viking Graben
Authors: Jennette David C. , Riley Cheyenne O. 
Published: April 2008

Abstract
Detailed sequence stratigraphy of several neighbouring fields in the East Shetland basin indicates that a higher order of cyclicity is superimposed onto the lower Brent Group. Both relative falls and rises in sea-level affected the strongly progradational nearshore/barrier-island system and induced important variations in the geometry, distribution and stacking patterns of the reservoir facies. The majority of the shallow marine strata belong to the transgressive and highstand systems tract and consist of the lower-shoreface Rannoch, the upper shoreface and strand-plain Etive and the back-barrier and lagoonal Lower Ness. High frequency increments of shoreline progradation are preserved in the Rannoch as gently seaward-dipping bedsets. The small-scale units mark asymmetric cycles in grain size and mica content and together, with stratiform cement, impart a strong permeability anisotropy on the Rannoch. The nearshore Etive Formation represents a sediment-laden, barred nearshore complex and is subdivided into (1) a uniformly thick upper shoreface and (2) an overlying emergent strand plain. The two subfacies are commonly separated by a thin interval of foreshore which is locally enriched in heavy minerals. The shoreface deposits show systematic variations in stacking geometries ranging from strongly progradational to aggradational.
Two relative falls in sea-level led to the subaerial erosion of nearshore Etive deposits and the juxtaposition of coastal-plain mudstones, coals and fluvial deposits with shale-clast lags on lower shoreface Rannoch strata. Although lithostratigraphically part of the Etive, these deposits bear no resemblance to the well ordered nearshore-Etive deposits. The channel complexes are vertically and laterally heterogeneous and are confined to incised valleys separated by non-depositional interfluves. In Cormorant and Tern fields, well-performance anomalies such as early water breakthrough and unpredictable water injection and oil production rates are associated with these lowstand incised valley deposits. An enigmatic coarse-grained unit occurs in the lower Rannoch in Eider field and is provisionally interpreted as the distal expression of the lowstand shoreface deposits associated with the older incised valley. Following the lowstand deposition nearshore-marine sedimentation reestablished during the transgressive/early highstand systems tract. Under the influence of rising relative sea-level the barrier complex aggraded in place with minimal landward translation of the shoreline position. The volume of sediment supplied to the Etive shoreface was sufficiently high to keep pace with phases of increased accommodation. The shoreline system subsequently stacked with a strongly progradational geometry as the high sediment supply filled the available accommodation space during the latter part of the highstand systems tract.
A model for high resolution sequence stratigraphy within extensional basins
Authors: Howell John A. , Flint Stephen S. 
Published: April 2008

Abstract
Existing sequence stratigraphic models imply that for any given time period in a sedimentary basin, the interplay between rates of eustatic sea-level change and subsidence will dictate the type of sequence boundary formed (type-1 boundary if rate of sea-level fall exceeds subsidence and type-2 if it does not). Basin margin profile will dictate whether lowstand fluvial systems feed submarine fans (shelf-slope break profile) or detached shorelines (forced regressions on ramp margin). A conceptual model presented here, proposes that in structurally active extensional domains the expressions of eustatic sea-level change are still present in the stratigraphic record. These expressions are modified by complex basin margin topography and by significant, along strike variations in subsidence and accommodation creation. This model also illustrates that tectonically complex basins can host a spectrum of time equivalent lowstand deposits previously considered to be spatially and mutually exclusive. This model is illustrated by an example from the Oxfordian of the UK North Sea Central Graben.
Hierarchical stratigraphic cycles in the non-marine Clair Group (Devonian) UKCS
Authors: McKie T. , Garden I. R. 
Published: April 2008

Abstract

The Devonian lower Clair Group (
c.
300–800 m thick) is dominantly composed of fluviatile sandstones and conglomerates, aeolian sandstones and minor floodplain and lacustrine shales. These facies are organized into stratigraphical cycles which have a three-fold hierarchy: an unconformity bounded cycle representing first order retreat and advance of the fluvial drainage system; three subsidiary second order cycles bounded by minor unconformities, and numerous third order cycles. These stratigraphical cycles exhibit common characteristics: they are bounded by sharp, commonly erosive surfaces; they are composed of a fining-upwards succession overlain by a variably developed coarsening-upward element; the fining-upward element records a progressive decrease in the fluvial component, and increasing proportion of aeolian, floodplain or lacustrine facies (this trend is reversed in the upper, coarsening-upward section). The grain size of the fluvial facies, and nature of the non-fluvial facies (aeolian vs floodplain/lacustrine) within any order of cycle is dependent on it’s position within a lower order (larger scale) cycle.

The cycles are areally extensive, and are present in all wells within the Clair Basin, although spatial changes in internal facies make-up occur. The second order cycles show progressive onlap followed by offlap of the basin margin.
These hierarchical cycles are interpreted to be the product of changes in the accommodation:supply ratio of the depositional system. An increasing accommodation:supply ratio provided space to preserve the record of waning fluvial influence, enhanced aeolian reworking, preserved floodplain fines or lacustrine mudrocks. In contrast, a reducing accommodation:supply ratio resulted in filling of accommodation space and sediment bypassing. Accommodation space variations were dictated by tectonic variations in strain rate, which caused incremental uplift of the basin margin and subsidence of the basin. Sediment supply changes were influenced by source area uplift, which changed sediment yield, and climate change which affected runoff. Climatic changes are detectable within the non-fluvial elements of the Clair Group by stratigraphic variations between aeolian, floodplain and lacustrine facies. These vary systematically within and between second order unconformity bounded units, suggesting a tectonic influence on climate.
Within the second and third order cycles, those which were evolving towards, or were occurring within, semi-arid to arid climatic conditions are commonly (but not exclusively) biased towards fining-upward successions, whilst the more humid systems show a better developed coarsening-upward element. This may be the result of the changing impact of discharge versus sediment supply variations when one of these parameters became suppressed or enhanced under varying climatic conditions.
Interfluve sequence boundaries in the Grassy Member, Book Cliffs, Utah: criteria for recognition and implications for subsurface correlation
Authors: O’Byrne Ciaran J. , Flint Stephen 
Published: April 2008

Abstract
The Late Campanian Grassy Member of the Blackhawk Formation, Mesaverde Group, Utah consists of two unconformity-bounded fourth-order sequences within a third-order highstand sequence set. Several orders of bounding surface define the internal architecture of each sequence and component parasequences. Incised valley fill deposits, dominated by braided channel-fills updip and laterally accreted fluvial and estuarine channel-fills down dip, overlie the fourth-order sequence boundaries, truncating shoreface and shelf facies of underlying sequences. Incised valleys are separated by extensive interfluves with evidence of subaerial exposure and minor tributary channel systems. The interfluve gullies are interpreted to have transported very little bedload during lowstand and acted primarily as rainwater run-off or bypass channels lateral to the main incised valley system. They are filled with bioturbated fine-grained sandstone and siltstone and capped by marine shale. Interfluve areas provide subtle but crucial evidence for base level falls, including rare examples of roots penetrating formerly offshore marine shale, partially eroded hematitic hardpan sediments and sand or silt filled gullies containing coal and shell debris. Interfluve sequence boundaries have powerful predictive application in respect to recognition of along-strike incised valley fills. Recognition of these surfaces is commonly hampered by removal of subaerial indicators as a result of subsequent transgressive erosion. There is indirect stratigraphic evidence of an emerging salt or basement fault driven structural high, orthogonal to the Late Campanian palaeoshoreline, which controlled the locus of valley incision and associated interfluves in two successive high frequency sequences.
Consequences of post-collisional deformation on the reconstruction of the East Pyrenees
Authors: Keller P. , Gehring U. 
Published: April 2008

Abstract
Post-collisional structures are generally ignored in tectonic reconstructions of the Pyrenees. The South Pyrenean thrust belt is characterized by different tectonic rotations about vertical axes. A new statistical analysis of palaeomagnetic data shows that the observed rotations are homogeneous within discrete zones which only partly coincide with the tectonic units of the thrust belt. The combination of the palaeomagnetic information with structural and sedimentological data demonstrates that the actual structure of the southeastern Pyrenees is due to interference of Palaeogene (collisional) and Neogene (post-collisional) deformations. Accounting for this structural interference leads to significantly less shortening than calculated by earlier reconstructions of the southeastern Pyrenees. This example clearly shows that the small contribution made by post-collisional tectonics to the overall deformation can strongly influence the structure of orogenic belts.
Palaeomagnetic evidence of block rotations in the Matese Mountains, Southern Apennines, Italy
Authors: Iorio M. , Nardi G. , Pierattini D. , Tarling D. H. 
Published: April 2008

Abstract
After rigorous geological and petrological study to exclude all Miocene rock samples that may have been affected by post-deposition disturbances and selecting only sites where the Miocene rocks appear to be rigidly attached to their Mesozoic substrate, over 100 samples were collected from the Monte Matese region. Over 200 oriented specimens, cut from these samples, were subjected to rigorous thermal and alternating field demagnetization. Strict criteria for the definition and within-site consistency of remanent vectors showed that most sites were dominated below 200°C or 20 mT by a magnetization associated with the present geomagnetic field direction. In almost all sites, any higher coercivity or blocking temperature components were inconsistent with the exception of one locality near Pescorosito. Re-sampling of two outcrops at this locality, 100 m apart, provided 26 samples that met all of the geological, petrological and palaeomagnetic criteria. The low temperature/coercivity component is the same as the present geomagnetic field in the locality, but all samples from eight of the nine sites have identical remanence vectors between 200 and 400/450°C. Petrological and tectonic considerations imply that this remanence must be associated with very early diagenesis and is thus probably of Mid-Miocene but possibly Early Miocene age. As these sites are autochthonous relative to their Mesozoic basement, they indicate a 40° anticlockwise rotation of the Monte Matese block, relative to Apulia, since Mid-Miocene times. Thus most of the post-Early Cretaceous rotation of this block has occurred since Mid-Miocene times. It is suggested that similar age constraints may also apply to other rotated blocks within the Southern Apennines.