bluuebunny/crossref_metadata_2025 huggingface dataset:
Ancient vent chimney structures in the Silurian massive sulphides of the Urals
Authors: Herrington R. J. , Maslennikov V. V. , Spiro B. , Zaykov V. V. , Little C. T. S.
Published: April 2008

Exceptionally well preserved volcanogenic massive sulphide ores at Yaman Kasy in the Silurian of the southern Urals have yielded not only well-preserved sulphidized vent macrofauna but also fragments of vent chimneys. All fragments show a broad 3-fold mineralogical zonation. An outer zone which forms the chimney/conduit wall comprises largely pyrite and marcasite which is laminated or collomorphic and is commonly porous. In one fragment this zone is characterized by a honeycomb-like structure in the pyrite, infilled by barite, sphalerite and chalcopyrite. Dendrite growth textures branch outwards towards the chimney wall. The middle of the three zones comprises largely pyrite with chalcopyrite and sphalerite as thin veinlets and infillings. The innermost zone is dominated by chalcopyrite. Minor gold and bismuth tellurides occur at the boundary between the middle and the inner zones. The inner zone is interpreted as the hydrothermal conduit lining and in all cases is defined by bladed chalcopyrite, which shows a texture consistent with growth toward an inner open space. The central part of the conduit is now infilled with sphalerite or in one case pyrite, chalcopyrite, silica and minor barite. Fluid inclusion studies indicate the presence of high-temperature (> 350°C) fluids of around 3.5 0.000000e+00quivalent NaCl in the basal parts of the massive sulphide mound with cooler temperatures (< 100°C) recorded in barite from the upper part of the mound. Barite is associated with chimney fragments, as worm tube infillings and as later cross-cutting veins. Preliminary S and Sr isotope data from sulphides and sulphates supports both igneous and seawater sources for sulphur in the hydrothermal system with evidence for seawater circulation and sulphate precipitation beneath the sulphide mound. The results are consistent with a similar model of chimney growth to that proposed for modern vent sites. It is proposed that a high temperature fluid flux through open conduits fed black smoker activity accompanied by lateral fluid diffusion through the chimney wall which mixed with seawater. The result of this is a combination of conductive cooling and fluid mixing leading to precipitation of distinctively zoned mineral assemblages across the vent conduit wall. The occurrence of tellurium, bismuth and precious metal-bearing phases indicates some similarities with the geochemistry of sulphides from other Palaeozoic massive sulphide deposits associated with felsic volcanic centres.
Relics and antiquity revisited in the modern vent fauna
Authors: McArthur A. G. , Tunnicliffe V.
Published: April 2008

A total of 464 species is currently known from hydrothermal vents, with 820eing endemic. More strikingly, endemicity at hydrothermal vents reaches high taxonomic levels with 18 families, 4 superfamilies, 2 suborders, and 1 order endemic. It has been proposed that this magnitude of endemicity is reflective of an ancient, refugial fauna. A review of the many endemic groups reveals that hydrothermal vent communities have mosaic origins. Many endemic groups have recent origins while some appear to reflect ancient faunal elements that have survived in hydrothermal vent refugia. Some may be members of groups surviving refugially throughout the deep-sea while others may have survived refugially in a variety of sulphide-rich habitats, such as hydrothermal vents, hydrocarbon seeps and sunken whale bones. Evolution of sulphide tolerance and especially symbioses with chemoautotrophic bacteria may be threshold adaptations for invasion of multiple sulphide-rich environments. These environments may provide protection from certain causes of extinction. In addition to reviewing current views on endemic taxa, a molecular systematic investigation of the evolutionary origins of vent endemic neomphalinid gastropods is presented.
Decoupling post-glacial tectonism and eustasy at Huon Peninsula, Papua New Guinea
Authors: Chappell John , Ota Yoko , Campbell Colin
Published: April 2008

Late Quaternary uplift of coral terraces varies along the coast at northeast Huon Peninsula, Papua New Guinea, but the uplift rate has been assumed to be constant at any given locality in previous studies. Measurements indicate that rates for the last 7000 and 120 000 years were similar but this may be coincidence, because uplift at Huon Peninsula is dominated by isolated, metre-scale events with recurrence intervals around 1000 years. Using age-height data from 54 corals from the post-glacial reef, we examine the uplift rate over the last 13 000 years near Kwambu, where facies changes in a drill core indicate several uplift events before 7 ka
bp
. To separate uplift from sea level, a eustatic curve for Kwambu was generated by the global sea-level model described by Lambeck, recalibrated to new, Late Pleistocene sea-level data. With Barbados as a test case, predictions compare well with observations reported earlier, but predicted sea levels for Kwambu cannot be reconciled with the coral data unless the water depth of coral growth at the site was greater than estimated previously.
Neotectonic implications of a lineament-coplanarity analysis in southern Calabria, Italy
Authors: Cornet Yves , Demoulin Alain
Published: April 2008

A synthesis of the geodynamical interpretations proposed in the literature shows that the respective role of different possible driving mechanisms in the Neogene and Quaternary tectonic evolution of southern Calabria is still under discussion. Owing to different methodological approaches and scales of observation, the same holds true for marine terrace levels recognized in the area of Reggio Calabria. Their number, elevation, spatial correlation and age, as well as their tectonic significance, are still debated, resulting in some uncertainty about the timing and rate of the regional uplift and its local variations. To complete the mapping of fault zones potentially dislocating the marine terraces, a three-dimensional (3D) morphometrical analysis of lineaments has been carried out. From a data-set composed of linear structures recognized on an illuminated digital elevation model (17 km × 18 km in size) centred on Reggio Calabria, the method aims at identifying lineaments pertaining to a single plane. Assuming that faults may be assimilated to planes at the local scale, the coplanar lineaments allow the 3D attitude and location of fault or fracture planes to be determined. The planes retained as tectonically significant (on the dip value and number of coplanar lineaments) have been successfully compared with the existing faults as well as with geomorphological data (long river profiles) of southern Calabria. Beyond mapping the main faults of the study area, the coplanarity analysis highlights the existence of conjugate faults within the NW-SE fault zone of Terreti-Monte Embrisi. It also locates some E-W striking faults which were previously known only at the outcrop scale.
Ancient coastal installations and the tectonic stability of the Israeli coast in historical times
Authors: Galili Ehud , Sharvit Jacob
Published: April 2008

Coastal archaeological structures are often used to identify coastal displacements and relative land-sea changes. Settlement of foundations and collapse of coastal stone-built structures, however, can sometimes lead to misinterpretations of sea-level changes or neotectonic activity. Coastal rock-cut installations, on the other hand, because they are cut into the bedrock, are not threatened by settlement or collapse and can serve as reliable indicators for detecting land-sea changes. A detailed survey of rock-cut installations along the Israeli coast shows that coastal pools, channels and quarries cut within the last 2500 years are today found at present-day sea level or very close to it and are still able to function. Archaeological and geological indications of major neotectonic activity along the Israeli coast during historical times were re-examined in this study, and were found to be inconsistent with the new data presented. The study concludes that the Israeli coast is relatively stable and that no significant neotectonic movement (> 0.2 m per 1000 years) has occurred during historical times.
Regional vertical motion in Iceland 1987–1992, determined using GPS surveying
Authors: Foulger G. R. , Hofton M. A.
Published: April 2008

Vertical motion in Iceland may arise from tectonic sources, e.g. large earthquakes and spreading episodes, isostatic movements owing to the change in mass of icecaps, and secular sinking of the volcanic pile under its own weight. Regional Global Positioning System (GPS) surveys covering the eastern half of Iceland have revealed the vertical motion for the period 1987–1992. Although the errors associated with the vertical component are large, exceptionally good agreement between independent data processing and agreement with isolated terrestrial measurements lends credence to the somewhat surprising results. These are dominated by relative uplift ofc.12 cm in the northern part of the Northern Volcanic Zone and subsidence of up toc.12 cm elsewhere. This motion can be partially explained by recent tectonic and glacio-isostatic events. The most significant of these are the 1975–1984 Krafla spreading episode and isostatic uplift around the currently melting Vatnajökull icecap ofc.1 cm/year. However, a substantial amount of the observed motion cannot be explained by any known processes. It is concluded that hitherto unknown, largescale processes associated with the hotspot and plume, possibly continuing at depths ofc.75 km, may be responsible. Behaviour of this kind has been observed associated with the Yellowstone hotspot, which is broadly comparable with the Iceland hotspot. Future remeasurements of the GPS network in Iceland will be valuable for refining these observations.
Convergent-margin deformation of Pleistocene strata on the Olympic coast of Washington, USA
Authors: Thackray Glenn D.
Published: April 2008

Quaternary tectonism on the central Olympic coast is dominated by the Kalaloch syncline, a broad (>32 km wavelength), low-amplitude (
c.
45 m) fold deforming the Pleistocene glacial-nonglacial stratigraphic sequence. The stratigraphy includes two sequences of glacial and nonglacial sediments, one overlying and one underlying a prominent wave-cut surface. Stratigraphic and chronological data indicate that the buried wave-cut surface formed during isotope stage 7 or 5 sea-level highstands, probably during substage 5e or 5c. The elevation pattern of the wave-cut surface expresses the syncline most clearly. The outcrop patterns of overlying strata also reflect the syncline, as does outcrop-scale deformation in the underlying strata. Geological uplift rates for the wave-cut surface on the syncline’s north limb contrast in magnitude with, but are similar in pattern to, geodetically measured 1931–1974 uplift rates. Geological uplift rates range from −0.03 to 0.7 mm/year. The difference at each location between geological and geodetic uplift rates ranges from 0.4 to 1.0 mm/year, and is inferred to reflect interseismic strain accumulation. For each assumed age for the wave-cut surface, the inferred interseismic strain accumulation is nearly constant across the syncline’s north limb. Thus, the syncline accounts for most of the spatial variability in the 1931–1974 uplift rates. Comparison of the geological uplift rates with alternative representations of 1931–1974 uplift does not result in the same patterns, but does reveal a significant component of interseismic strain accumulation.
Variable rates of Late Quaternary surface uplift along the Banda Arc-Australian plate collision zone, eastern Indonesia
Authors: Merritts Dorothy , Eby Rebecca , Harris Ron , Edwards R. Lawrence , Chang Hai
Published: April 2008

Radiometrically dated emergent coral terraces from southeastern Indonesia provide estimates of differential vertical strain in the Banda Arc-continent collision complex. At Semau island, two samples from the lowest emergent reef (5–7 m) yield
230
Th dates that correspond to the 5a (
c.
83 ka) sea-level highstand and a low surface uplift rate of 0.2–0.3 m per 1000 years. At Rote island, samples from the lowest emergent reef (
c.
1–2 m) on both north and south sides of the island yield late Holocene ages and an average short-term uplift rate of
c.
1–1.5 m per 1000 years. Similarity of ages from different samples on the north coast of Rote suggests possible coseismic emergence. Survey data from nine emergent reefs and marine notches up to 170 m in altitude on the south side of Rote indicate that uplift rates may have been
c.
1–1.5 m per 1000 years for
c.
120 000–130 000 years. Combined with previous studies, these results indicate that late Quaternary surface uplift rates vary an order of magnitude along the strike of the Banda orogen. Vertical displacement rates are greatest in young parts of the orogen where the shelf-slope break recently has been underthrust beneath the orogenic wedge, as at Rote, and in older parts of the orogen where retroarc thrust faulting occurs, as at Alor island.
Quaternary marine terraces and tectonic uplift rates on the south coast of Iran
Authors: Reyss J. L. , Pirazzoli P. A. , Haghipour A. , Hatté C. , Fontugne M.
Published: April 2008

A survey of 1500 km of the Iranian coastline, from Bushehr (Persian Gulf) to the Pakistani border, made it possible to visit several sequences of raised marine terraces, some of which (especially on the Makran coast) had already been described by previous workers. As many as 18 marine terraces, up to 220 m in altitude, were identified on Qeshm Island and as many as 19 levels, up to 246 m in altitude, near Chah Bahar. Though
in situ
coral heads and fossilized marine shell deposits exist in many uplifted areas, only a few samples, mainly from elevations lower than 30m, appeared to be unrecrystallized and thus suitable for radiometric dating. Six uranium-series analyses of aragonitic corals from Haleh, Jazeh and Qeshm Is. gave apparent ages between 100 and 140 ka
bp
, in some cases demonstrating that previous radiocarbon dates between 20 and 40 ka
bp
had to be considered minimum ages. This made it possible to estimate that average uplift rates since the last Interglacial period had been about 0.2 mm/year, i.e. one order of magnitude less than most previous estimates. Radiocarbon dates suggest almost uniform emergence of 2–4 m since mid-Holocene times along most of the coastal sectors investigated. This is in agreement with the 2–3 m emergence predicted by glacio-hydro-isostatic models in this area if an uplift rate of about 0.2 mm/year is also taken into account. Near a salt dome on Qeshm Is., however, a much faster uplift rate of about 6 mm/year was documented for the period between 6 and 5 ka
bp
but only over a limited area.
Coastal Tectonics across the South Atlas Thrust Front and the Agadir Active Zone, Morocco
Authors: Meghraoui Mustapha , Outtani Fatima , Choukri Abdelmajid , De Lamotte Dominique Frizon
Published: April 2008

Quaternary marine terraces of the South Atlas Thrust Front near the Agadir seismogenic region are investigated by detailed geological mapping, precise height measurement and tectonic analysis. A coastal step-like morphology with four main benches (Q
1
-Q
4
) crosses the Ait Lamine-Kasbah anticlines, 10 km north of Agadir. U-Th dating of 12 fossil samples (mainly molluscs) yields two main groups of ages for marine terraces Q
4
and Q
3
and can be correlated with oxygen-isotope stages 5 and 7 respectively. Terrace height changes significantly near the Kasbah fold, and attains a maximum of 18–28 m for Q
4
and 35.5 m for Q
3
. Estimates and measurements of terrace elevation yield an average late Quaternary uplift rate of 0.1–0.2 mm/year. Modelling of anticlinal structures suggests that the Kasbah fold may have developed as a fault-propagation fold with a low dip angle of 25° or a listric geometry as implied by flexural slip faulting. Surface ruptures associated with the 1960 (
M
s
5.9) earthquake coincide with flexural slip faulting showing 4–5 m offset of terrace Q
3
. Incremental movements and uplifted marine terraces on the Kasbah fold are likely to occur during large earthquakes related to the 25 km long flexural slip fault.
The effects of upper plate deformation on records of prehistoric Cascadia subduction zone earthquakes
Authors: McNeill Lisa C. , Goldfinger Chris , Yeats Robert S. , Kulm Laverne D.
Published: April 2008

Geophysical data from the offshore Cascadia forearc reveal many Quaternary upper-plate faults and folds. Most active structures are within the accretionary wedge, but significant deformation is also found on the continental shelf. Several faults and synclines project into adjacent coastal bays where deformation of Pleistocene marine terraces is reported. Rapidly buried marsh deposits and drowned forests in these coastal lowlands are interpreted to record coseismic deformation by prehistoric subduction zone earthquakes. The extent and amount of such coastal subsidence has been used to infer characteristic magnitudes and recurrence intervals. However, the record may incorporate both elastic strain release on the subduction zone and localized permanent upper-plate deformation. Movement on upper-plate structures may be triggered by a subduction zone earthquake, as observed in the Nankai and Alaskan forearcs. Alternatively, they may deform independently of subduction zone earthquakes. Regardless of which style of deformation predominates, the record of coseismic subsidence is likely to be affected. Crustal deformation may also contribute to the preservation of subsided marshes. Modelling of subduction zone earthquake characteristics based on coastal marsh stratigraphy is likely to be inaccurate in terms of: (a) total apparent rupture length and earthquake magnitude; (b) amount of subsidence and hence the position of the locked zone; (c) recurrence interval. Most of these shelf and coastal structures respond to N-S compression, in contrast to convergence-related northeasterly compression in the accretionary prism, but in agreement with the regional stress field. Despite low historical coastal and continental shelf seismicity, upper-plate faults may also pose an independent seismic hazard.
Carbonate ramps, 1973–1996: a historical review
Authors: Ahr W. M.
Published: April 2008

The carbonate ramp as a type of sedimentary depositional platform was conceived after failed attempts to fit some carbonate facies patterns to shelf models. Ramps were first defined as two-dimensional (2D) depositional surfaces along which facies variations reflect differences in the oceanographic environment from shore to basin. Shelves and ramps were placed at opposite poles without definitions of intermediate platform configurations or environmental subdivisions between shore and basin. The 2D ramp is of limited use in determining slope and surface configuration in the rock record where stacked depositional surfaces are separated by beds of different age and thickness, and the original definition did not anticipate the complexities that would develop as high- v. low-energy and tropical v. temperate carbonate systems became better known. Though the original definition is flexible, modifications were inevitable. Refinements of the concept introduced distal steepening, among other intermediate styles of platform geometry. Environmental subdivisions were proposed for shallow, intermediate, and deeper-water ramp segments. Further studies of ramps and shelves brought to light differences in sediment production and retention on ramps, response of ramps to sea-level change, and the variety of tectonic settings in which ramps occur. Sequence stratigraphic analysis of ramps resolved most of the problems in reconstructing depositional surfaces from 3D sequences in the rock record, high- v. low-energy and temperate v. tropical ramps became well known, and studies on hydrocarbon reservoir characterization focused on diagenesis in a carbonate ramp sequence stratigraphic context. From a paper in a rather obscure regional journal, the ‘carbonate ramp’ has grown to become a world-wide standard.
Phanerozoic carbonate ramps from greenhouse, transitional and ice-house worlds: clues from field and modelling studies
Authors: Read J. Fred
Published: April 2008

During times of continental glaciation (e.g. Pennsylvanian-Early Permian, Miocene-Pleistocene), parasequences on carbonate platforms appear to be dominated by 400, 100 and possibly 40 ka Milankovitch climatic and eustatic changes with 50–100 m shifts in sea level. Carbonate cycles have conspicuous regional disconformities and associated aeolianites, lack tidal-flat facies except near the continental shoreline, commonly have deeper-water facies sandwiched between shallow-water deposits, and there is much unfilled accommodation. The large changes in sea level in ice-house times causes ramps to have significant gradients, thus on high-energy ramps, there can be widespread grainstone sheets. Platform tops have much depositional relief (pinnacle reefs and mounds) and erosional topography. Cycles may be highly shingled and show major lateral shifts on the ramp from cycle to cycle.

During times with moderate continental ice sheets (e.g. late Mid- to Late Ordovician, Early Carboniferous), ramp cycles lack deeper-water facies, rarely have regional tidal flats but instead show widespread disconformities updip and some aeolianites. The only tidal-flat facies are developed within third-order highstand systems tracts (perhaps reflecting decreased amplitude, higher-frequency eustasy) or in downdip positions during fourth-order lowstands. Margins show moderate shingling. Grainy reservoir facies are regionally extensive, as a result of moderately large shifts of grainstone belts. Grainy facies in downslope build-ups are compartmentalized by muddy incipient drowning facies. Storm beds on the deep ramp are arranged in upward-coarsening units because of high-frequency eustasy.

During global greenhouse times and little global ice (e.g. Late Cambrian-Early Ordovician, Devonian, Triassic, Cretaceous), parasequences updip on aggraded ramps are dominated by roughly 20 ka precessional cycles that formed under small (possibly <10 m or so) sea-level fluctuations, possibly coupled with an autocyclic component. The cycles typically consist of very shallow-water facies, with regional tidal flat caps and minor disconformities; cycles form layer-cake successions on the shallow ramp, and may be bundled into 100 and 400 ka sets, although ‘missing beats’ on the platform commonly obscure simple ratios typical of Milankovitch forcing. The ramps commonly have very low gradients and platforms tend to be aggraded with little topography, unless sedimentation rates are low, which results in poorly cyclic, subtidal skeletal facies over much of the ramp. Any compartmentalization of downslope subtidal build-ups is due to long-term incipient drowning events.
The Middle Cretaceous carbonate ramp of the northern Sinai: sequence stratigraphy and facies distribution
Authors: Bachmann Martina , Kuss Jochen
Published: April 2008

The Middle Cretaceous carbonate ramp of the northern Sinai developed in two stages on a passive continental margin overlying basal rift suites. The lower delta-dominated ramp (Upper Aptian-Lower Albian) in the north evolved into the upper carbonate-dominated ramp (Middle Albian-Cenomanian) which covered the central and southeastern parts of the Sinai. The transition between the two ramp settings took place during a period of a second-order sea-level rise and a major change in climatic conditions. The sedimentary patterns are superimposed upon by higher-frequency relative sea-level changes. The influence of the third-order relative sea-level changes on the ramp deposition was reconstructed on the basis of facies patterns, sedimentary geometries, and the distribution of microfacies types. As regional tectonic movements were of subordinate importance, a sequence stratigraphic interpretation allows a fine-scale estimation of the changing ramp settings and their characteristics. The combined use of semiquantitative microfacies analysis and sequence stratigraphy allows study of the factors controlling deposition during the different systems tracts, including the respective microfacies distributions. These factors indicate that third-order sea-level fluctuations result not only in simple shifts of facies belts up and down the ramp but also in changing environmental factors such as water circulation, carbonate production and siliciclastic input.
Geometry and facies dynamics of Middle Jurassic carbonate ramp sandbodies, West-Central Portugal
Authors: Azerêdo Ana C.
Published: April 2008

The Middle Jurassic succession of the Lusitanian Basin (Portugal) represents a carbonate ramp depositional system. For most of the time, the shallow-water facies defined a microtidal barrier-island complex, where prominent oolite-dominated sandbodies developed. Detailed facies analysis of these sandbodies allowed the recognition of their elementary depositional facies, which are described and whose relative importance is estimated. Sandbody geometry, hydrodynamic controls and ramp evolution are discussed. Carbonate sediment production and redistribution, coupled with inner ramp aggradational and progradational trends, have interacted in a such a way that ramp geometry persisted for a longer period of time than usually recorded in these systems.
Ramp facies and sequence stratigraphic models in an epeiric sea: the Upper Ordovician mixed carbonate-siliciclastic Glenwood and Platteville Formations, Wisconsin, USA
Authors: Choi Yong Seok , Simo J. A.
Published: April 2008

Variability in lithofacies and depositional environments of the Upper Ordovician mixed carbonate-siliciclastic Glenwood and Platteville Formations in Wisconsin are studied and analysed within a sequence framework. Two depositional sequences are identified in these strata. Sequence boundaries correspond to identified and interpreted exposure surfaces with or without angular discordance. These surfaces mark an abrupt upward increase in shale, and correspond to widespread discontinuity surfaces interpreted to represent time-stratigraphic breaks. Sequences show a base with either sandstones or shales grading upward into carbonate lithologies devoid of terrigenous clastic deposits. Cycles are the smallest stratigraphic packages of regional significance (tens to hundreds of kilometres) and correspond to interpreted upward-shallowing successions. Cycle attributes change from sequence to sequence.

Depositional environments are interpreted similarly to many ancient carbonate ramps. Sequence S1 contains diverse facies indicating deposition in wide palaeowater depth ranges from tidal-flat to deep subtidal outer ramp environments. Rapid lateral facies change with irregular spatial distribution observed in sequence S1 is interpreted to be related to the high ramp gradient and irregular antecedent topography during deposition of sequence S1. Facies succession in sequence S2 shows upward changes from storm-dominated mid-ramp to low-energy inner ramp environments without intervening high-energy shallow-water shoal belts. This differs from most storm-dominated carbonate ramp facies models in the geological record, in which storm bed rich mid-ramp deposits show transition to inner ramp successions that contain shoreface barrier sediments such as ooid-skeletal grainstone and boundstone. This model is interpreted as a consequence of infrequency of significant wave activity, in which incoming oceanic waves lost their energy very gradually over a wide area. Without inherited topography, the broad epeiric sea modified circulation and the overall result is a decrease in energy landward. A low wave-energy, microtidal, storm-dominated ramp model is postulated for such successions.
James Hutton’s Edinburgh: a précis
Authors: Mcintyre Donald B.
Published: April 2008

James Hutton (1726–1797) was born and bred in Edinburgh. Having decided to be a farmer, he went to Norfolk aged 24 to learn new methods of husbandry. From that base, he travelled widely and developed an interest in geology. In 1767 he left his Berwickshire farm and returned to Edinburgh, where he became a valued member of the remarkable group of men who founded the Royal Society of Edinburgh and made the city the unrivalled intellectual centre of the age.

Edinburgh was a capital without the distractions of king and parliament. When the Industrial Revolution began, many disciplines were already represented by men of world renown who knew each other — many, indeed, were related. There were still no boundaries between narrowly defined disciplines; there was shared interest in all knowledge.

Geological structure had constricted Edinburgh’s growth, keeping the compact Old Town on its ancient defensive ridge. The North Bridge, completed soon after Hutton’s return to Edinburgh, made possible the planned New Town, in dramatic architectural and intellectual contrast to the mediaeval city. The beauty and interest of Edinburgh’s scenery is the result of an active geological past. Consequently, in a small and accessible space, rocks of different character are exposed in a natural geological laboratory.

James Hutton did not live in an ivory tower. War, rebellion and revolution, both political and industrial, all had their influence. In a turbulent world, a decade of peace (1783–1793) was another factor making possible Hutton’s great contribution to modern geology.
High-pressure experiments and the varying depths of rock metamorphism
Authors: Schreyer Werner
Published: April 2008

Hutton’s visions of 1785 included burial and metamorphism of rocks and their reincorporation into the continental crust. As a result of changing environmental conditions, mainly of pressure (
P
) and temperature (
T
), rocks change their mineral assemblages during metamorphism. High-pressure experimentation has now provided geoscientists with quantitative data on the behaviour of rock systems under varying
PT
conditions, so that depths of burial or subduction and pathways of exhumation can be reconstructed, and the metamorphic histories of rocks can be used to gauge the internal dynamics of our globe during geological time. An important prerequisite is the knowledge of the states of chemical equilibrium as a function of
P, T
and rock composition. Several simple chemical model systems are chosen here to demonstrate characteristic mineralogical and petrological behaviour during metamorphism and to identify some important and unusual minerals that typify high- or ultrahigh-pressure metamorphism taking place at depths of up to 150 km, e.g. the dense forms of carbon (diamond) and of SiO
2
(coesite). Low-pressure metamorphism within the normal (∼35 km) crust of the Earth, on the other hand, is typified by less dense minerals such as tridymite or cordierite. In this way, deep and very deep subduction of former rocks of the Earth’s crust was recognized. This required new geodynamic concepts involving the participation of crustal materials in the overall secular convection processes within the Earth’s mantle.
Preliminary investigations into the acquisition of remanence in archaeological sediments
Authors: Batt C. M.
Published: April 2008

Investigations of magnetic remanence, anisotropy of magnetic susceptibility and magnetic mineralogy of sediments from over 30 depositional environments within British archaeological excavations are compared with archaeological evidence provided by excavation and analysis of associated artefacts and ecofacts. The sites include canals, wells, river floods, ditches, moats and estuarine deposits. A comparison of the magnetic and archaeomagnetic determinations allows the characterization of those deposits that appear to retain a record of the past magnetic field and are therefore datable by comparison with the UK archaeomagnetic calibration curve. Most water-lain sediments have a measurable magnetization, but finer grain sizes tend to have higher intensities, although there is no relationship between depositional environment and intensity of magnetization. The sediments with a higher organic content have a lower consistency index probably as they were more likely to have been bioturbated. Although the magnetic fabrics did not always correspond to the expected ‘primary depositional style’, almost all sites seemed to have directions of remanence that corresponded well to the dates indicated by the archaeological evidence.
Viscous remanent magnetization of high thermal stability in limestone
Authors: Borradaile Graham J.
Published: April 2008

Undisturbed Mesozoic limestones of eastern England show univectorial magnetizations of high thermal stability that appear, on first inspection, to be primary geological remanences. However, viscous remanent magnetization (VRM) of anomalously high thermal stability is an alternative possibility. VRM acquired elsewhere in laboratory experiments, or in a few hundred years as in the examples studied here, may require unblocking temperatures >300°C to demagnetize. Normally, such demagnetization temperatures are required to remove only very ancient geological remanences. The classical ‘conglomerate test’ of palaeomagnetism fails to discriminate between a VRM and a primary remanence. Any lithology sensitive to VRM will yield a negative result, suggesting that the remanence is secondary. However, tests of physical phenomena that caused multiple reorientations of clasts, at rotation rates comparable with the viscous remagnetization rate, provide a more suitable field test for VRM. In this study, these latter kinds of test reveal that some
in situ
Mesozoic limestones of eastern England have VRM, despite stability to temperatures >300°C. The high thermal stability VRM of the bedrock must have been acquired in the last 0.7 Ma, since the last geomagnetic reversal. Two new field tests detected the viscous nature of the high stability remanence. The first was a ‘debris flow test’, in which limestone blocks spin slowly with respect to the geomagnetic field. The blocks record variably tilted or helicoidal, multicomponent vectors. The second was a ‘masonry test’, in which samples of limestone from buildings of known age were exposed to the geomagnetic field for known periods, up to 1600 years in this study. This shows that unusually stable VRM may be common in carbonates. Finally, the masonry test permits an empirical estimate of viscous remagnetization rates over hundreds of years. This established chronometric curves that date ground disturbances of geotechnical or geomorphological interest, and archaeological features of unknown age.
Diagenesis and remanence acquisition in the Lower Pliocene Trubi marls at Punta di Maiata (southern Sicily): palaeomagnetic and rock magnetic observations
Authors: Dinarès-Turell J. , Dekkers M. J.
Published: April 2008

Three new profiles (LCM, PMD and CMD) through the lower Cochiti polarity zone allow comparison of the effects of weathering and diagenesis on the magnetic properties of the Lower Pliocene Trubi marls. These marls have been well dated, by means of astronomical calibration, and are of particular interest in terms of polarity zonation and regional tectonics. The freshest exposures (LCM profile) carry a remanence associated with pyrrhotite, which is particularly enhanced in some grey layers. This is the first time that pyrrhotite has been documented as the main remanence carrier in these marls. Previously, single-domain (SD) magnetite was recognized as the fundamental ferromagnetic phase. The mean characteristic remanent magnetization (ChRM) direction from the LCM record does not show the expected 30–35° clockwise rotation found in other studies, nor does it record the normal Cochiti interval (i.e. the sampled interval is entirely reverse polarity), suggesting a relatively late origin for the natural remanent magnetization (NRM). Standard rock magnetic techniques are used to investigate the nature of the magnetization in the three laterally equivalent profiles at Punta di Maiata. The entire dataset seems to be better explained by a complex diagenetic history involving a multistage redox history that invokes a ‘late’ anoxia event. The previously postulated iron migration model was put forward for the ‘suboxic situation’ and does not take into account the presence of magnetic sulphides, which are clearly demonstrated in the zone under study. The ‘extended diagenetic model’ inferred here proposes a pathway that accounts for most of the new observations. The salient feature is the postulated existence of a diagenetic phase that has altered the original NRM in some areas (dissolution of magnetite) resulting in a later-stage acquisition of chemical remanence that does not date to the timing of deposition of the sediments. The extension and the detailed mechanisms by which such a process has taken place deserve further research. None the less, the present investigation accounts for previously unrecognized features in the Trubi marls from Sicily and outlines how intricate the nature of the mechanisms contributing to the blocking of remanence in sediments can be.
The isolation of diagenetic groups in marine sediments using fuzzy
c
-means cluster analyses
Authors: Urbat Michael , Dekkers Mark J. , Vriend Simon P.
Published: April 2008

The evaluation of large rock magnetic datasets may benefit from the application of multivariate statistical methods. The combined use of fuzzy
c
-means clustering (FCM) and non-linear mapping (NLM) have considerable merit over conventional multivariate techniques and appear to provide a more logical choice. An example of the method of identification and characterization of early diagenetic effects on marine sediments is given using samples drilled at Ocean Drilling Program (ODP) Site 904. This confirms the clusters previously identified more laboriously by multi-variable analyses and detects clusters (diagenetic, detrital, etc.) that may only be recognized by the consideration of an array of rock magnetic data. In another example of a complex diagenetic signal the link is expanded between two papers on a long piston core (KC-01B) from the Calabrian Ridge (Central Mediterranean), where FCM and NLM provide a clue as to why the record of the lower Jaramillo Subchron is delayed in this core.
Remanence acquisition and magnetostratigraphy of the Leman Sandstone Formation: Jupiter Fields, southern North Sea
Authors: Turner P. , Chandler P. , Ellis D. , Leveille G. P. , Heywood M. L.
Published: April 2008

The Leman Sandstone Formation, which forms part of the unfossiliferous Rotliegend sediments in the Jupiter Fields, has been cored at various location in the southern North Sea. Samples from the finer-grained sediments have measurable remanences that were classified into four main types. Some of these characteristics can be related to the petrological features that demonstrate that they are likely to have originated during deposition or very early diagenesis. This allows the age of the sediments to be determined using magnetostratigraphy, indicating that the sediments are of post-Kiaman age as they contain both normal and reversed polarities. This magnetostratigraphy can also be used to determine different rates of deposition in different areas.
Diagenesis in platform carbonate rocks: a palaeomagnetic study of an upper Triassic-lower Jurassic section, Tata (Hungary)
Authors: Márton Emő
Published: April 2008

The upper Triassic platform carbonate rocks at Tata are penetrated by three generations of neptunean dykes and cut by strike-slip faults connected to the platform’s break-up in early Jurassic time. These platform carbonate rocks are conformably overlain by lower Jurassic pelagic carbonate rocks, with a clear change in sedimentation type at the Triassic-Jurassic boundary. Openings within the Triassic platform, including bedding-conformable cavities and
Megalodon
shells, are filled with Jurassic material showing late ‘diagenetic’ features with respect to the Triassic platform facies. The Triassic platform carbonate rocks were examined in a 10m high outcrop and in a 200m core, which commenced 40 m below the surface. The Triassic rock commonly has a weak initial natural remanent magnetization (NRM) and diamagnetic susceptibilities, in both outcrop and within the core, and has the same kind of magnetic mineralogy as in the ‘diagenetic’ material and stratified Jurassic rock, but the magnetic mineral content is higher in the Jurassic materials. The core has mixed polarity, whereas the Triassic outcrop and Jurassic materials have only normal polarity. The overall mean palaeomagnetic direction for the core is similar to those in two large quarries of similar age in the same area (the Gerecse Hills), but differs significantly from the overall mean directions of both the Jurassic ‘diagenetic’ material and the Jurassic beds, which are practically identical to each other. Some sites and individual samples in the Triassic outcrop carbonate rocks show Jurassic directions, but others show remagnetization circle distributions between this Jurassic direction and the present-day Earth’s magnetic field. These observations suggest that the remanence of the latest Triassic time was reset during the early Jurassic diagenesis, but this was not associated with chemical changes as the mineralogies in all groups are the same.
The influence of dolomitization on the magnetic properties of Lower Palaeozoic carbonate rocks in Estonia
Authors: Shogenova Alla
Published: April 2008

The low-field magnetic susceptibility and saturation isothermal remanent magnetization of Estonian Lower Palaeozoic carbonate core and outcrop samples were studied, together with their chemical composition. Dolomites of different age and genesis were found to be of different chemical composition and different magnetic properties. The dolomitization of the Lower and Middle Ordovician sequences is diagenetic and is represented by widespread dolomitized layers as well as dolomitization associated with tectonic disturbances. All studied dolomites have an increasing total iron content. In Upper Ordovician and Silurian dolomites this increase is not enough to change magnetic properties significantly. In the rocks, sampled from a fracture zone and from a dolomite layer of the Väo Formation in the Middle Ordovician sequence and another widespread, several metres thick dolomite layer of the Volkhov stage from the Lower Ordovician sequence, the magnetic susceptibility of dolomites was found to be several times higher than that of limestones of the same age. Changes in magnetic susceptibility were found to be associated with substitution of Fe
2+
for Mg
2+
in the crystalline lattice of dolomites.
Alteration of magnetic properties of Palaeozoic platform carbonate rocks during burial diagenesis (Lower Ordovician sequence, Texas, USA)
Authors: Haubold Herbert
Published: April 2008

Palaeomagnetic and sedimentological investigations of samples from two sections of correlative Iapetan platform carbonate rocks from Texas, USA, were made to test whether their magnetic properties reflect diagenetic alteration associated with regional and local tectonism. The Honeycut Formation (Llano Uplift area, central Texas), in close proximity to the late Palaeozoic Ouachita orogenic belt, exhibits a distinct correlation between magnetization intensity, magnetization age (direction) and lithofacies. Mudstones preserve their weak primary Early Ordovician magnetization, whereas dolo-grainstones carry a strong Pennsylvanian magnetization residing in authigenic magnetite. Fluid migration associated with the Ouachita Orogeny has been focused in lithofacies with high permeability and caused dolomite recrystallization and pervasive remagnetization. Magnetization intensity trends covary with fluid/rock ratios. However, aquitards were either not affected or less affected by these fluids. Unlike the Honeycut Formation, permeable rocks of the El Paso Group (Franklin Mountains, west Texas) carry only a non-pervasive Pennsylvanian magnetization. Therefore, a larger percentage of El Paso Group samples retain a primary Early Ordovician signature. This area is further removed from the Ouachita front, and, thus, the influence by Pennsylvanian orogenic fluids was less pronounced.
The role and value of ‘high-impact biostratigraphy’ in reservoir appraisal and development
Authors: Payne S. N. J. , Ewen D. F. , Bowman M. J.
Published: April 2008

Over recent years changes in the application of biostratigraphy in the reservoir appraisal and development arena have greatly increased the impact and value of the discipline, giving it a central role in integrated reservoir description. These changes include placing emphasis on local field-scale bioevents to erect a reservoir framework of time slices through which reservoir heterogeneity can be modelled and the application of biosteering to maximize reservoir penetration. In addition, palaeoenvironmentally diagnostic benthonic microfacies are used to model the lateral continuity of intra-reservoir mudstones in an attempt to understand their potential as baffles/barriers to fluid flow. The evolution of this cost-effective methodology is discussed by reference to three Palaeocene turbidite reservoirs from the North Sea UK continental shelf (UKCS); the Donan, Forties and Andrew fields.
Chalk palaeoenvironments and depositional model, Valhall-Hod fields, southern Norwegian North Sea
Authors: Sikora P. J. , Bergen J. A. , Farmer C. L.
Published: April 2008

Palaeoenvironmental analysis in the North Sea chalk is hampered by the prevalence of widespread allochthonous units, intervals of massive reworking of microfossils and an often monotonous lithology of massive chalks of uncertain depositional history. Most difficult of all is devising precise regional biostratigraphic correlations in a complex section with large, but very subtly expressed, disconformities and condensed zones. Facies change quickly both laterally and vertically. Without very precise regional correlations, it is impossible to formulate any detailed palaeoenvironmental model.

Through a multidisciplinary palaeontological approach, employing graphic correlation methodology and a composite standard database, a highly accurate and detailed regional chronostratigraphy was generated. Biofacies recognized within the section were then scaled in absolute time, allowing for more reliable recognition of facies trends at any one time horizon. Biofacies were formulated based upon recovered benthic foraminifera, planktic foraminifera, calcispheres, siliceous microfossils and macrofossil debris.

Biofacies mapping for several higher-order sequences recognized in the Upper Cretaceous chalks has allowed recognition of four major periods of deposition: (1) early Turonian-early Santonian high pelagic productivity and rapid deposition of chalks over a relatively continuous ridge from the Valhall to Hod fields; (2) early Campanian-earliest Maastrichtian deep-water autochthonous chalk deposition off-structure with structural crests mantled by submarine hardgrounds; (3) very heterogeneous autochthonous and allochthonous middle Maastrichtian chalk deposition controlled by local grabens formed from crestal collapse; and (4) widespread sediment flows and redeposition of sediments with crestal shoaling and winnowing in the latest Maastrichtian culminating in crestal erosion of Cretaceous chalks in the early Danian.