bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential restoration of the external Alpine Digne thrust system, SE France, constrained by kinematic data and synorogenic sediments
Authors: Lickorish W. Henry , Ford Mary
Published: September 2007

The Tertiary foreland basin of the southern Subalpine chains preserves a stratigraphic record of late Alpine deformation, both ahead of the thrust front in the Valensole basin, and in a series of thrust-sheet-top basin remnants. Stratigraphy and growth structures in these basin remnants have been used to identify the location and timing of deformation and hence to constrain the sequential restoration of a cross section through the region.

The thrust belt developed as a single large thrust sheet riding on a weak Triassic evaporite layer. Minor breaching thrusts occur, in particular at Mesozoic normal faults. Kinematic studies of the Digne thrust sheet show a dominantly SW direction of tectonic transport. Where reactivated structures lie at a slightly oblique angle to the transport direction there has been a partitioning of deformation into SW-directed thrusting and a component of dextral strike-slip taken up on minor faults. The total shortening across the fold and thrust belt is 21.5 km, a much lower value than previously estimated but more in line with regional tectonics.

The foreland basin stratigraphy demonstrates that deformation within the Digne sheet occurred in three stages. Firstly, during the late Eocene, Alpine collision in the hinterland caused flexure of the foreland plate to generate a simple broad marine foredeep. Slight detachment above the Triassic evaporites allowed gentle buckling of the floor of the foredeep. Secondly, in the Early to Mid-Oligocene overthrust shear associated with the SW emplacement of the internally derived Embrunais-Ubaye nappes into the foredeep caused substantial deformation in the underlying Digne sheet. A component of flattening strain was associated with overthrust shear beneath the nappes, but ahead of the nappe front gentle, upright folding and thrusting continued. Sedimentation stepped westward, became dominated by continental facies and confined to small thrust sheet top basins (e.g. Barrême). The Mio-Pliocene stage of deformation involved a change from thin-skinned to a thick-skinned out-of-sequence deformation when basement blocks were uplifted on deepseated structures across the region (e.g. dôme de Chateauredon). Shortening associated with the uplift of the main Argentera basement massif at the internal boundary of the external fold and thrust belt was transferred onto the Triassic detachment from below, and transferred forward to reactivate the frontal edge of the Digne sheet, which was thrust out over the Valensole basin.
History and deformation rates of a thrust sheet top basin: the Barrême basin, western Alps, SE France
Authors: Artoni Andrea , Meckel Lawrence D.
Published: September 2007

The geometrical evolution of the 2 km wide Barrême thrust-sheet-top basin has been established over a time interval of 10 Ma. The Barrême basin developed during the late Eocene-Oligocene, during the migration from east to west of the western Alpine orogenic front in SE France. Unlike in other orogenic belts, where foreland basins are often buried and observable only on seismic profiles, the outcrop conditions at Barrême allow the detailed analysis of this basin fragment. The syntectonic sedimentation and growth strata preserved on the east flank of the Barrême basin, on the Clumanc Anticline, are used to restore sequentially a balanced cross-section, thereby constraining the progressive steps of basin development. Numerical ages, obtained by correlating biozones and chronostratigraphy with most recent geochronological calibrations, are assigned to the bases of the mappable growth strata in order to obtain an indication of deformation rates. Shortening rates vary from 0.003 to 0.2 (±0.083) mm a
−1
, while uplift rates vary from 0 to 0.37 mm a
−1
. These rates are comparable to those recorded in recently active mountain belts, and represent a significant refinement of previously published rates for the Barrême basin.
Thin-skinned inversion tectonics at oblique basin margins: example of the western Vercors and Chartreuse Subalpine massifs (SE France)
Authors: Philippe Yann , Deville Eric , Mascle Alain
Published: September 2007

The western Vercors and Chartreuse Subalpine fold-and-thrust belts form part of the western Alpine foreland that wa sinvolved in Neogene compressive tectonics. The deformation front of the two massifs is superimposed on the western margin of the Mesozoic Southeast Basin, which was inverted in the Late Miocene. Obliquity between this NE-SW-directed basin margin and the WNW-ESE Alpine tectonic transport resulted in the development of en-échelon folds and thrusts at the leading edge of the massifs. The gradual change of the tectonic style from the Chartreuse to the southern Vercors belts denotes that the initial configuration of the basin as well as the rheological properties of the basal detachment layer strongly influenced the geometry and the kinematic evolution of the two fold belts. This paper presents the geometry of the inverted western Tethyan palaeomargin through a series of balanced cross-sections and attempts to evaluate the possible boundary conditions that controlled the development of the western Chartreuse and Vercors massifs and the lateral variations of the tectonic style in the study area. Results of an analogue modelling experiment simulating a thin-skinned inversion of an oblique platform-basin transition zone are compared with those of the field study and used to discuss the role of the palaeogeographic inheritance on both the initiation and orientation of thrust faults in décollement tectonics.
Tectono-stratigraphy and hydrocarbons in the Molasse Foredeep of Salzburg, Upper and Lower Austria
Authors: Wagner Ludwig R.
Published: September 2007

The evolution of the sedimentary record and the tectonic setting of the Molasse Basin at the margin of the European platform from the Bavarian border across Salzburg, Upper and Lower Austria to the border of the Tschech Republic provides the possibility of unravelling the history of the Alpine - Carpathian Foredeep. The marine ingressions and the sedimentary processes reflect the dynamic process of the plate tectonics and the Alpine Orogeny. At present the outcrop of the passive margin of the Bohemian Massif and the northern edge of the active Molasse thrust front approach each other within a distance of a few kilometres. The basement is broken into several fault blocks. Tectonic activities within the thrust sheets as well as lateral movements of the basement along the flanks of the craton are ongoing.

The hydrocarbon generation and trapping is based on the interaction of synsedimentary tectonism, erosion and deposition.

This study is based on surface and subsurface data acquired by Rohöl Aufsuchungs AG (RAG) and Österreichische Mineralöl Verwaltungs AG (OMV) during its exploration in Salzburg, Upper and Lower Austria.
Flexure and ‘unflexure’ of the North Alpine German-Austrian Molasse Basin: constraints from forward tectonic modelling
Authors: Andeweg B. , Cloetingh S.
Published: September 2007

We present the results of forward modelling of the Northern Alpine German-Austrian Molasse Basin, which forms part of the Northern Alpine Foreland Basin (NAFB) extending from Lake Geneva in the west to Lower Austria in the east. The observed deflection of the European plate under the NAFB has been modelled along five profiles perpendicular to the basin axis. Models treating the deflection of the NAFB as a flexural response to loading only, require a set of loading parameters (bending moment, vertical force) which would imply bending stresses exceeding the strength of the subsiding plate. Moreover, this approach would not take into account the significant post-Molasse uplift experienced by the Alpine chain and its northern foreland basins. We modelled the deflection as the response to two distinct processes: (1) flexure of an elastic plate with lateral variations (EET-values of 7–26 km from east to west) loaded with surface and limited subsurface loads and (2) the Late Cenozoic (post-molasse) phase of ‘unflexing’, significant uplift observed in the Alps and its northern foreland. Our study provides a first attempt to separate these two processes in order to model the deflection by an elastic plate-model, adopting flexural parameters that will not exceed the strength of the lithosphere.
A primer on the geological occurrence of gas hydrate
Authors: Kvenvolden K. A.
Published: September 2007

Natural gas hydrates occur world-wide in polar regions, usually associated with onshore and offshore permafrost, and in sediment of outer continental and insular margins. The total amount of methane in gas hydrates probably exceeds 10
19
g of methane carbon. Three aspects of gas hydrates are important: their fossil fuel resource potential; their role as a submarine geohazard; and their effects on global climate change. Because gas hydrates represent a large amount of methane within 2000 m of the Earth’s surface, they are considered to be an unconventional, unproven source of fossil fuel. Because gas hydrates are metastable, changes of pressure and temperature affect their stability. Destabilized gas hydrates beneath the sea floor lead to geological hazards such as submarine slumps and slides, examples of which are found world-wide. Destabilized gas hydrates may also affect climate through the release of methane, a ‘greenhouse’ gas, which may enhance global warming and be a factor in global climate change.
Physical/chemical properties of gas hydrates and application to world margin stability and climatic change
Authors: Sloan E. D.
Published: September 2007

The major points in this paper concern: (a) physical and chemical properties and (b) applications of those properties. Three questions are addressed: What are hydrates? What is our knowledge about their thermodynamic and kinetic properties? What are the applications to the environment and climate stability?

The physical and chemical characteristics of hydrates are approximated by three heuristics: (1) physical properties approximate those of ice, (2) phase equilibrium characteristics are set by the size ratio of guest within host cages, and (3) thermal properties are set by hydrogenbonded crystals with cavity size ratios. Knowledge of hydrate kinetics is substantially lacking, but it appears that formation kinetics derive from aggregation of water clusters at interfaces. A significant future challenge is to characterize hydrates directly (through NMR, Raman, diffraction, etc.) for both thermodynamics and kinetics.

Hydrocarbons in natural hydrates represent twice the amount of all combined fossil fuels. Most recovered samples have been small, dispersed (even dissociated) particles with isolated examples of massive hydrates. Hydrates probably will not contribute significant methane to the atmosphere in the near future. Ocean hydrates and air hydrates from Antarctic ice are indicators of ancient climatic changes.
Gas hydrate accumulation in deep-water marine sediments
Authors: Ginsburg G. D.
Published: September 2007

The accumulation of gas hydrates largely depends on the spatial variability of gas solubility in pore waters. Within the submarine gas hydrate stability zone the solubility of methane in water significantly decreases towards the sea floor in response to temperature lowering. Gas hydrates can precipitate from methane-saturated water seeping up. They also accumulate from diffusing gas and segregated pore water within diffusion aureoles associated with the ascending fluid flows and with the zones where biochemical methane is generated at high rates. Hydrates more readily form in sediments where pore waters are relatively fresh and pores are rather large. The thermobaric gas hydrate stability zone is a geochemical barrier for hydrocarbon gases migrating from sediments into the sea water. However, the rising gas is not completely preserved in the hydrate.
The occurrence of gas hydrates in Eastern Mediterranean mud dome structures as indicated by pore-water composition
Authors: De Lange G. J. , Brumsack H.-J.
Published: September 2007

During ODP Leg 160 to the Eastern Mediterranean, two mud dome structures have been sampled. The massive presence of gas hydrates at relatively shallow depths in the sediment of one of these, Milano Dome, contrasts to that of the other, Napoli Dome, where gas hydrates are unlikely to be present at depths greater than 1 m below the sea floor (mbsf). Some observations from very shallow pore-waters at Napoli Dome, however, suggest that some gas hydrates must be present above 1 mbsf. In the case of Milano Dome, it is likely that a massive cap of gas hydrates is overlying natural gas that cannot escape due to this cap and its shape. In this report, some of the mud dome pore-water results of Ocean Drilling Program Leg 160 to the Eastern Mediterranean are discussed in relation to the inferred presence of gas hydrates. In addition, the total quantity of methane, including gas hydrates and ‘free gas’, has been estimated for Milano Dome (∼5 × 10
9
m
3
CH
4
) and for the Eastern Mediterranean Ridge mud dome structures (∼1 × 10
14
m
3
CH
4
).
Shallow gas and gas hydrates in the Anaximander Mountains region, eastern Mediterranean Sea
Authors: Woodside J. M. , Ivanov M. K. , Limonov A. F.
Published: September 2007

Gas hydrates have been sampled from a mud volcano in the eastern Mediterranean for the first time, during a recent expedition to study the nature and origin of the Anaximander Mountains offshore from southwest Turkey. Seven mud volcanoes were sampled as part of a successful strategy to obtain rocks which had been brought up from the deeper parts of the mountains themselves. The mud volcanoes seem to be associated with cross-cutting strike-slip faults defining individual blocks in this mountain complex, and may permit overpressured fluids from thrusts in this compression zone to be expelled at the surface. There is ample evidence in many parts of the area studied for the widespread presence of gas in the sediments, such as pockmarks, acoustic turbidity and acoustic wipeouts in sub-bottom profiles, gas in sediment samples, and mud volcanoes with carbonate crusts and benthic communities typical of those found elsewhere near gas seeps and fluid vents (e.g. vestimentifera worms, bivalves). It is postulated that the high mobility of some of the sediments is promoted by excess fluids possibly released in part from gas hydrates in the Plio-Pleistocene sediments. A good example of the sediment deformation is shown by a large area of moving sediments.
Possible hydrate mounds within large sea-floor craters in the Barents Sea
Authors: Long D. , Lammers S. , Linke P.
Published: September 2007

Interpretation of several surveys across a ‘crater field’ in the Barents Sea provide further evidence that the craters (large depressions, 300–500 m diameter, 10–30 m deep) are related to gas escape after deglaciation some 15 000 years BP. The disposition of the craters suggests that the flow of gas was controlled by fractures within the Triassic siltstone bedrock. Topographic highs within several craters, comprising angular blocks of rock locally rising above the level of surrounding crater walls, are interpreted as hydrate mounds indicating that gas flow continued after the formation of the craters. This may be the first reported occurrence of hydrate mounds in lithified sediments. Assuming the gas was methane and seabed temperature was similar to that at present then the hydrate mounds were formed at a time when the sea-bed was between 280 and 340 metres below sea level (mbsl)(i.e. 10–80 m lower than at present). Geochemical studies provide evidence that gas hydrates in the sub-bottom adjacent to the crater field are presently decomposing in accordance with seasonal temperature variations.
Gas hydrates along the northeastern Atlantic margin: possible hydrate-bound margin instabilities and possible release of methane
Authors: Mienert J. , Posewang J. , Baumann M.
Published: September 2007

The presence of gas hydrates and free gas in oceanic sediments along the northeastern European Margin is documented in high-frequency near-vertical and wide-angle seismic reflection data. Shallow-water and deep-water gas hydrate instabilities can cause free gas to escape from oceanic sediments. Particularly, methane from shallow-water gas hydrate destabilization may then get transferred from the sediments into the water column, and eventually into the atmosphere. Deep-water gas hydrates are coincident with areas and depths of slope failures in continental margin sediments. Comparisons between seismicity and the potential hydrate distributions suggest a correlation between hydrate instability and margin instabilities along the north-eastern Atlantic Margin.
Evidence for faulting related to dissociation of gas hydrate and release of methane off the southeastern United States
Authors: Dillon W. P. , Danforth W. W. , Hutchinson D. R. , Drury R. M. , Taylor M. H. , Booth J. S.
Published: September 2007

An irregular, faulted, collapse depression about 38 × 18 km in extent is located on the crest of the Blake Ridge offshore from the south-eastern United States. Faults disrupt the sea floor and terminate or sole out about 40–500 m below the sea floor at the base of the gas hydrate stable zone, which is identified from the location of the bottom simulating reflection (BSR). Normal faults are common but reverse faults and folds also are widespread. Folds commonly convert upward into faults. Sediment diapirs and deposits of sediments that were erupted onto the sea floor are also present. Sea-floor depressions at faults may represent locations of liquid/gas vents. The collapse was probably caused by overpressures and by the decoupling of the overlying sediments by gassy muds that existed just beneath the zone of gas hydrate stability.
Natural gas hydrates: searching for the long-term climatic and slope-stability records
Authors: Haq B. U.
Published: September 2007

The recent revival of interest in gas hydrates has grown from the awareness that they may play significant roles in several global and regional processes, including global carbon recycling, rapid climate change through emission of methane from marine sediments into the atmosphere, and as a cause for massive transport of sediments and structural changes on the continental slope. Their estimated large volumes are also considered to be a potential resource for future exploitation. Here the long-term record of gas hydrate behaviour is examined in terms of climatic, oceanographic, stratigraphic and slope-stability changes of the past. Various intriguing hypotheses recently offered to explain the observed record also highlight the numerous unknowns and our relative ignorance about these widespread features of the continental margins. The paper identifies some of these gaps and poses several relevant questions that will need to be answered before we can appreciate their full potential and cause-effect relationship of hydrate dissociation with climate change and slope stability.
What does the ice-core record imply concerning the maximum climatic impact of possible gas hydrate release at Termination 1A?
Authors: Thorpe R. B. , Pyle J. A. , Nisbet E.G.
Published: September 2007

The rapid climate changes at the terminations marking the end of the last glaciation are poorly understood. CH
4
hydrate decomposition has been suggested as a possible trigger of deglaciation. This would imply that there was a large pulse of atmospheric CH
4
contemporaneous with Termination 1A. This implication is tested here in a two-stage process using an adapted version of the Cambridge 2-D model. Firstly, the ice-core record was used to place an upper limit on the magnitude of possible CH
4
release at Termination 1A. Secondly, the climatic impact of this realistic maximum (RM) pulse was estimated and compared with the actual climate change occurring at deglaciation. It was found that the maximum pulse that could readily be squared with the ice-core record was around 4000 Tg. Its climatic impact was modelled for a range of scenarios covering climate sensitivities from 1.5 to 5.2°C, and involving possible changes in atmospheric CO
2
and latitudinal heat transport. The direct radiative effects of this pulse were too small to account for the deglaciation alone, but, for certain combinations of CH
4
, CO
2
, and heat transport changes, coupled with high climate sensitivity, it was possible to simulate changes of the same magnitude as those observed.
Ice-core record of atmospheric methane changes: relevance to climatic changes and possible gas hydrate sources
Authors: Raynaud D. , Chappellaz J. , Blünier T.
Published: September 2007

The Antarctic and Greenland ice contains an almost direct record of past atmospheric CH
4
. The record over the last 200 years reveals a spectacular 150% increase of the CH
4
atmospheric mixing ratio since pre-industrial times. At the scale of a glacial-interglacial cycle the record shows a remarkable correlation with climatic changes, with high (low) CH
4
levels during warm (cold) periods. A striking feature of the glacial-interglacial CH
4
record is the presence of large and abrupt (at the scale of a century or less) changes during the last glaciation and glacial-interglacial transition. The classical interpretation for the origin of CH
4
changes prior to the industrial era involves mainly the wetland source. In the context of gas hydrates the question is to know whether the past ice-core record contains fingerprints of catastrophic hydrate release (CHR). We currently conclude that the available record shows no evidence for CHR but additional ice-core analyses are necessary to reach a more definitive conclusion.
Galactic periodicity and the geological record
Authors: Napier W. M.
Published: September 2007

Precisely dated impact craters, major geological disturbances and mass extinction peaks were used to investigate statistically the hypothesis that global terrestrial phenomena are triggered by the Galactic environment through bombardment episodes. Strong temporal correlations were found between events in these datasets, and in aggregate they were found to have a periodicity of
c.
27 ± 1 Ma corresponding to the half-period of the Sun’s vertical oscillations within the Galactic disc. Global disturbances appear to be forced in quasi-periodic fashion through a combination of impacts and prolonged climatic stress, the latter as a result of stratospheric dusting by debris from very large short-period comets.
Meteorite flux on the Nullarbor Region, Australia
Authors: Bevan A. W. R. , Bland P. A. , Jull A. J. T.
Published: September 2007

The Nullarbor Region of Australia is one of the most prolific sites for meteorite recoveries outside of Antarctica. Reported
14
C terrestrial ages for chondritic meteorites from the Nullarbor indicate an age range from present day to
c.
35 ka. There is good evidence to suggest that meteorites are lying on, or close to the surfaces on which they fell and that, physiographically, the region has remained essentially undisturbed for at least the last 30 ka. The Nullarbor can thus provide important data on the flux of meteorites over the period of accumulation. One significant factor influencing flux calculations based on meteorite accumulation sites is the determination of the number of falls represented in the recovered population. In the case of the Nullarbor, a general lack of transportation processes in the region and careful documentation of the distribution of finds allows confident ‘pairing’ of meteorites. For example, strewn fields of showers that have remained undisturbed for thousands of years are easily recognized and mapped today. Mass distribution statistics confirm that there are few undetected pairs in the population of meteorites so far described from the Nullarbor, and there is no evidence of selection of meteorites of a specific terrestrial age. The Nullarbor is the largest accumulation of meteorites nearest to Antarctica with a terrestrial age range (0–35 ka) that overlaps the Antarctic population (0 to >1 Ma). Analysis of the well-documented population of meteorites from the Nullarbor compared with Antarctica suggests that there are many unrecognized paired meteorites in the Antarctic population and the abundance of small meteorites at that site can be accounted for, at least in part, by the presence of large shower falls of common chondrites. The data suggest that there may also be many unrecognized paired meteorites in collections from the Sahara.
Mapping Chicxulub crater structure with gravity and seismic reflection data
Authors: Hildebrand A. R. , Pilkington M. , Ortiz-Aleman C. , Chavez R. E. , Urrutia-Fucugauchi J. , Connors M. , Graniel-Castro E. , Camara-Zi A. , Halpenny J. F. , Niehaus D.
Published: September 2007

Aside from its significance in establishing the impact-mass extinction paradigm, the Chicxulub crater will probably come to exemplify the structure of large complex craters. Much of Chicxulub’s structure may be ‘mapped’ by tying its gravity expression to seismic-reflection profiles revealing an ∼180 km diameter for the now-buried crater. The distribution of karst topography aids in outlining the peripheral crater structure as also revealed by the horizontal gradient of the gravity anomaly. The fracturing inferred to control groundwater flow is apparently related to subsidence of the crater fill. Modelling the crater’s gravity expression based on a schematic structural model reveals that the crater fill is also responsible for the majority of the negative anomaly. The crater’s melt sheet and central structural uplift are the other significant contributors to its gravity expression. The Chicxulub impact released ∼1.2 × 10
31
ergs based on the observed collapsed disruption cavity of ∼86 km diameter reconstructed to an apparent disruption cavity (
D
ad
) of ∼94 km diameter (equivalent to the excavation cavity) and an apparent transient cavity (
D
at
) of ∼80 km diameter. This impact energy, together with the observed ∼2 × 10
11
g global Ir fluence in the Cretaceous-Tertiary (K-T) fireball layer indicates that the impactor was a comet estimated as massing ∼1.8 × 10
18
g of ∼16.5 km diameter assuming a 0.6 gcm
−3
density. Dust-induced darkness and cold, wind, giant waves, thermal pulses from the impact fireball and re-entering ejecta, acid rain, ozone-layer depletion, cooling from stratospheric aerosols, H
2
O greenhouse, CO
2
greenhouse, poisons and mutagens, and oscillatory climate have been proposed as deleterious environmental effects of the Chicxulub impact with durations ranging from a few minutes to a million years. This succession of effects defines a temperature curve that is characteristic of large impacts. Although some patterns may be recognized in the K-T extinctions, and the survivorship rules changed across the boundary, relating specific environmental effects to species’ extinctions is not yet possible. Geochemical records across the boundary support the occurrence a prompt thermal pulse, acid rain and a ∼5000 year-long greenhouse. The period of extinctions seems to extend into the earliest Tertiary.
Geochemistry of carbon in terrestrial impact processes
Authors: Gilmour Iain
Published: September 2007

Terrestrial impact craters appear to be unique in the geological environment in that they contain evidence for the presence of all four carbon allotropes: graphite, diamond, C
60
and carbynes. This diversity appears to reflect the wide range of physical and chemical conditions that occur during impact processes including shock-induced alterations and vapour-phase chemistry. Impact-produced diamonds are known from several impact craters around the world, and their ability to survive over immense periods of geological time makes the presence of diamonds an important criterion for the identification of terrestrial impact structures.
Impacts and marine invertebrate extinctions
Authors: MacLeod Norman
Published: September 2007

The Phanerozoic history of life has been interrupted by at least 17 different stage-level episodes of elevated extinction intensity. These range from major turnovers that affected the majority of the Earth’s extant biota (e.g. the Tatarian, Ashgill, and Maastrichtian events) to much smaller and perhaps more geographically localized disruptions. Review of available stage-level stratigraphic evidence suggests that bolide impacts do not exhibit a compelling correspondence to the Phanerozoic record of marine invertebrate extinctions. A much stronger case can be made for the repeated association of extinction events and episodes of long-term eustatic sea-level fall and/or major episodes of continental flood basalt volcanism. Moreover, during the last 250 Ma particularly severe extinction events have occurred during times of simultaneous continental flood basalt eruption and eustatic sea-level fall (e.g. Tatarian, Norian, Maastrichtian). Attempts to employ patterns of extinction selectivity to infer the physical cause of extinction events have foundered on the non-specificity of biological predictions as well as the seemingly unique biotic nature of each event. Although a few high-resolution biostratigraphic analyses have demonstrated that largely progressive patterns of faunal turnovers are consistent with co-extinction models under certain assumptions, this does not constitute a strong confirmation of the co-extinction model as a necessary or sufficient general explanation for Phanerozoic extinction events. In all likelihood, the nature of the fossil record precludes precise identification of extinction causal mechanisms. Nevertheless, comparative studies are able to evaluate the role both large and small extinction events have played in altering the long-term course of Earth’s biological history.
Timing and causes of vertebrate extinction across the Cretaceous-Tertiary boundary
Authors: Milner A. C.
Published: September 2007

A continuous sequence of terrestrial sediments bracketing the Cretaceous-Tertiary (K-T) boundary is known only in the western interior of North America. Documentation of terrestrial faunal diversity, and patterns of survival and extinction, demonstrate that dinosaurs (i.e. non-avian dinosaurs) declined in the Late Maastrichtian and were the only major terrestrial vertebrate group, along with the pterosaurs, that became extinct at or near the K-T boundary. There was a varying degree of turnover but no mass extinction in other vertebrate groups. Both gradualist and catastrophe scenarios have been advocated as the main cause. There is much less evidence in other parts of the world that can be brought to bear on the timing and nature of dinosaur extinction. None the less, there are dinosaur remains from Maastrichtian horizons on every continent and none are recorded from overlying Paleocene strata. This supports the axiom that dinosaurs died out world-wide at the end of the Cretaceous although there is no means of determining whether the extinction pattern in western North America was a local or global phenomenon. The disruption of reproductive patterns in herbivorous dinosaurs by trace element contamination derived from an impact, volcanic activity or both events is one factor which might correlate with their global extinction.
Lyell and the
Principles of Geology
Authors: Rudwick M. J. S.
Published: September 2007

Lyell’s
Principles of Geology
is still treated more often as an icon to be revered than as the embodiment of a complex scientific argument rooted in its own time and place. This paper describes briefly the origins of Lyell’s project, in the international geological debates of the 1820s and in his own early research; the structure of argument of the first edition (1830–1833), and its relation to its intended readership; and the modification of the work in subsequent editions, and the transformation of its strategy in response to its critical evaluation by other geologists. The fluidity of the
Principles
(and its offshoot the
Elements of Geology
) reflects the ever-changing interaction between Lyell and his fellow geologists, and between them and a much wider public, during one of the most creative periods in the history of geological science. Lyell’s scientific stature is best appreciated if he is placed not on a pedestal but among his peers, in debates at the Geological Society and elsewhere.
Lyell: the man and his times
Authors: Wilson Leonard G.
Published: September 2007

Born in Scotland at the end of the eighteenth century, Charles Lyell spent his early life in Hampshire in the midst of the kind of comfortable rural society described in Jane Austen’s novels. Influenced by his father, who was a keen botanist, the young Lyell collected butterflies and studied natural hisory. As a student at Oxford, he attended the Revd William Buckland’s lectures on geology and continued to pursue geology while studying for the bar at Lincoln’s Inn. In 1824 Lyell wrote his first scientific paper on the freshwater limestones and marls of Scottish lakes, demonstrating their detailed similarity to ancient freshwater formations among the Tertiary strata of the Paris Basin. Throughout his life Lyell remained an active field geologist, travelling throughout Europe from Sicily to Scandinavia. He made repeated geological tours through the Swiss and Austrian Alps and studied intensely the Tertiary strata of France, Belgium and England. He examined the geology of North America from Nova Scotia to the Mississippi Delta, working in the field in all weather. In 1853–1854 he spent several months studying the volcanic geology of Madeira and the Canary Islands and in 1857 and 1858 revisited Sicily to spend arduous weeks studying Mount Etna. In his seventy-fifth year and nearly blind, he travelled to the south of France to examine the caves of Aurignac and the Dordogne.

In 1830 in thePrinciples of GeologyLyell challenged the assumption of a cooling Earth and of the greater former intensity of volcanic action and other geological forces. He separated geology from cosmology, pointing out that the crust of the Earth told nothing of its origin. What geology did reveal was an unending cycle of changes such as were still going on. In his metamorphic theory developed in theElements of Geology, Lyell showed how the various classes of igneous and metamorphic rocks were formed in the gradual elevation of mountains. Lyell’s theories brought about a revolution in geology, changing the meaning of geological data. In successive editions of thePrinciplesand theElements, two books of American travel, and theAntiquity of Man, Lyell’s stature as an author and as a scientist grew steadily throughout his lifetime, the sale of his books often exceeding the publisher’s expectations. Liberal in his sympathies, Lyell worked effectively for the reform of English university education and during the American Civil War defended the Union against its British critics.
Lyell’s reception on the continent of Europe: a contribution to an open historiographical problem
Authors: Vaccari Ezio
Published: September 2007

After the publication of the
Principles of Geology
the name of Charles Lyell became well known among European geologists. However, the diffusion of his works and the intensity of the debates on his ideas varied throughout the continent. This paper attempts to analyse some aspects of Lyell’s reception in Continental Europe, emphasizing the role of the translations of fundamental works such as the
Principles of Geology
and the
Elements of Geology
, as well as their influence on the first textbooks of geology published in Europe, especially from the 1840s onwards. Some significant examples of nineteenth-century European reactions to Lyell’s geology, and in particular to his uniformitarian statements, will be pointed out, in order to show the extent of Lyell’s influence.
Charles Lyell’s debt to North America: his lectures and travels from 1841 to 1853
Authors: Dott Robert H.
Published: September 2007

Charles and Mary Lyell visited North America four times from 1841 to 1853. During the first three visits, Lyell lectured and they travelled widely. The lectures were great successes with the American public in spite of Lyell’s poor elocutionary skills. Comparisons of lecture topics covered over a decade provide insights into the rapid development of the young science of geology and of Lyell’s changing preoccupations. Included were crustal movements; uniformity of causes through time; coral reefs and oceanic subsidence; Carboniferous conditions; the early appearance of reptiles; palaeoclimate; the submergence of land and the origin of drift; biogeography; and a uniform organic plan with arguments against transmutation and historical progression.

The Lyells saw more of the United States and Canada than had most citizens. Their conveyances included horseback, stagecoach, train, railroad handcar, and steamboat. Accommodation varied from elegant hostelries to dirt-floored shacks. Their travels took them from the Atlantic coast to the Ohio and Mississippi Rivers and from the St Lawrence valley to the Gulf Coast. America gained from Lyell the enhancement of the stature of geology, several original contributions to the understanding of its geology, and a positive impression of the New World conveyed back to Britain. Lyell’s reward was greater, however, thanks to the generosity of American guidance in his field work. He gained many fresh geological examples for his books, published two travel journals and more than 30 journal articles and presented at least eight lectures in Britain about American geology, making him the local British authority on America. He especially gained new evidence for his opposition to biological progression and for his submergence theory for the drift. Besides enhancing his geological reputation, Lyell also made an incisive comparison of British and American education, which drew him into public reforms at home sponsored by Prince Albert. Finally, his exposure to American Unitarianism, coupled with disenchantment with the Anglican Church, caused Lyell to shift his religious allegiance.
Charles Lyell and climatic change: speculation and certainty
Authors: Fleming James Rodger
Published: September 2007

In the first edition of the
Principles of Geology
, Charles Lyell announced his theory of the geographical determination of climate and speculated on possible climatic changes during the geological and historical past. In light of the subsequent discovery of ice ages, the proliferation of theories of climatic change, and the great climate debates of his time. Lyell’s theory remained remarkably stable. This paper examines Lyell’s appropriation, modification and rejection of the views of his contemporaries. It provides perspectives on elite and popular ideas of climate and climatic change from the late eighteenth century to 1875, examines Lyell’s position on climatic change in geological and historical times, and explores in some detail the mutual influences of Lyell and James Croll, the proponent of an astronomical theory of ice ages.
Sequence stratigraphy: a revolution without a cause?
Authors: Wilson R. C. L.
Published: September 2007

The paper presents personal reflections on the origins and utility of sequence stratigraphic models. These focus on two questions: (1) does sequence stratigraphy represent a revolution in our understanding of the stratigraphic record, and (2) does it provide a new means of global correlation? The first question is answered in the affirmative, at least insofar as sequence stratigraphy enables us to integrate a wide range of data and interpretations across a huge range of spatial and temporal scales. The recognition of the importance of stratal surfaces has led to a greater understanding of the response by sedimentary to climatic, tectonic and eustatic changes. But it has yet to be shown that eustatic signals can be detected unequivocally in the stratigraphic record. Therefore this ‘new global stratigraphy’, based on the premise that sequence boundaries are primarily controlled by eustatic changes, is not yet a reality. Testing this hypothesis is beyond the resolution of current biostratigraphic and chronostratigraphic techniques.
Earthquakes and Earth structure: a perspective since Hutton and Lyell
Authors: Bolt Bruce A.
Published: September 2007

Lyell’s interest in earthquakes as part of the
Principles of Geology
continues to be justified many fold. A quarter century after Lyell’s death, seismology began to open the window on the contemporary structure and tectonic deformation of the Earth. Detailed non-biased observations of the global distribution of earthquakes played a crucial role in the attack on preplate theories of Earth dynamics. There were three critical seismological assault tools: reliable hypocentre catalogues, uniform magnitude estimates, and fault source mechanisms. Previously used as evidence for plate tectonics, seismicity is now often taken as predicted by it. Nevertheless, earthquake occurrence remains unforecastable in definite temporal terms. Interplate and intraplate spatial patterns show complexity in macro-crustal and micro-crustal structures. In particular, the mechanism and dynamic implications of deep-focus earthquakes and subduction remain a challenge.

Local and global seismographic networks are increasingly enhanced by broadband digital seismometry. This modern instrumentation provides high resolution of strong ground shaking and crustal and deeper interior structure. Second-order structural variations are now being mapped in the upper mantle and more detailed boundary conditions for convection models are being resolved in the lithosphere and in the D″ mantle-core layer. Recently, seismological evidence for scattering anomalies throughout the mantle has become persuasive.
Humanity and the modern environment
Authors: Knill John
Published: September 2007

The geological record is a chronicle of change in which long periods of apparent climatic stability were successively replaced by new environmental conditions. These broad cycles of change were punctuated by shorter-term events, some of which had catastrophic implications. Lyell recognized that this menu of environmental scenarios recorded in the past was well reflected by the range of environmental conditions which occur at the present day.

It is now recognized that human influence on climate and the environment is engendering a new event which has all the hallmarks of a phase which might, if preserved in the geological record, be interpreted as cataclysmic. However, the Earth system has proved remarkably effective in recovering from extremes of climate or devastating reductions in biodiversity.

Humankind has two alternatives. To accept the inevitable, adapting to such changes as can occur, whether of human or natural origin, and facing the possibility of ultimate extinction as a species, thereby leaving the Earth ultimately to recover. Or to attempt to control man-made change so effectively that eventually it will be possible to manage the Earth’s natural processes. Our understanding of the past is therefore central to our ability to survive in the future.
Spatiotemporal Differences in CXCL12 Expression and Cyclic AMP Underlie the Unique Pattern of Optic Glioma Growth in Neurofibromatosis Type 1
Authors: Warrington Nicole M. , Woerner B. Mark , Daginakatte Girish C. , Dasgupta Biplab , Perry Arie , Gutmann David H. , Rubin Joshua B.
Published: September 2007

Astrocytoma (glioma) formation in neurofibromatosis type 1 (NF1) occurs preferentially along the optic pathway during the first decade of life. The molecular basis for this unique pattern of gliomagenesis is unknown. Previous studies in mouse Nf1 optic glioma models suggest that this patterning results from cooperative effects of Nf1 loss in glial cells and the action of factors derived from the surrounding Nf1+/− brain. Because CXCL12 is a stroma-derived growth factor for malignant brain tumors, we tested the hypothesis that CXCL12 functions in concert with Nf1 loss to facilitate NF1-associated glioma growth. Whereas CXCL12 promoted cell death in wild-type astrocytes, it increased Nf1−/− astrocyte survival. This increase in Nf1−/− astrocyte survival in response to CXCL12 was due to sustained suppression of intracellular cyclic AMP (cAMP) levels. Moreover, the ability of CXCL12 to suppress cAMP and increase Nf1−/− astrocyte survival was a consequence of mitogen-activated protein/extracellular signal-regulated kinase kinase–dependent inhibition of CXCL12 receptor (CXCR4) desensitization. In support of an instructive role for CXCL12 in facilitating optic glioma growth, we also show that CXCL12 expression along the optic pathway is higher in infant children and young mice and is associated with low levels of cAMP. CXCL12 expression declines in multiple brain regions with increasing age, correlating with the age-dependent decline in glioma growth in children with NF1. Collectively, these studies provide a mechanism for the unique pattern of NF1-associated glioma growth. [Cancer Res 2007;67(18):8588–95]
Semaphorin SEMA3F Affects Multiple Signaling Pathways in Lung Cancer Cells
Authors: Potiron Vincent A. , Sharma Girish , Nasarre Patrick , Clarhaut Jonathan A. , Augustin Hellmut G. , Gemmill Robert M. , Roche Joëlle , Drabkin Harry A.
Published: September 2007

Loss of SEMA3F occurs frequently in lung cancer and correlates with advanced stage of disease. We previously reported that SEMA3F blocked tumor formation by H157 lung cancer cells in a rat orthotopic model. This was associated with loss of activated αVβ3 integrin, impaired cell adhesion to extracellular matrix components, and down-regulation of phospho-extracellular signal-regulated kinase 1/2 (ERK1/2). These results suggested that SEMA3F might interfere with integrin outside-in signaling. In the present report, we found that SEMA3F decreased adhesion to vitronectin, whereas integrin-linked kinase (ILK) kinase activity was down-regulated in SEMA3F-expressing H157 cells. Exposure to SEMA3F-conditioned medium led to diminution of phospho-ERK1/2 in four of eight lung cancer cell lines, and ILK silencing by small interfering RNA led to similar loss of phospho-ERK1/2 in H157 cells. Moreover, SEMA3F expression (with constitutive and inducible systems) also reduced AKT and signal transducer and activator of transcription 3 (STAT3) phosphorylation independently of ILK-ERK1/2. These signaling changes extended downstream to hypoxia-inducible factor-1α (HIF-1α) protein and vascular endothelial growth factor (VEGF) mRNA levels, which were both reduced in three of four SEMA3F-transfected cell lines. Mechanistically, the effects on HIF-1α were consistent with inhibition of its AKT-driven protein translation initiation, with no effect on HIF-1α mRNA level or protein degradation. Furthermore, when H157 cells were injected s.c. in nude mice, tumors derived from SEMA3F-expressing cells showed lower microvessel density and tumor growth. These results show that SEMA3F negatively affects ILK-ERK1/2 and AKT-STAT3 signaling, along with inhibition of HIF-1α and VEGF. These changes would be anticipated to contribute significantly to the observed antitumor activity of SEMA3F. [Cancer Res 2007;67(18):8708–15]