bluuebunny/crossref_metadata_2025 huggingface dataset:
The terrane concept and its manifestation by deep reflection studies in the Variscides
Authors: Meissner R. , Sadowiak P.
Published: July 2007

The terrane concept is understood as an important extension of plate tectonics and is based on the recognition of allochthonous, mobile geological units. The concept is successfully applied to the Variscides with their wide range of collisional belts. It is mainly supported by the dense deep‐seismic network of DEKORP, which reveals certain reflectivity patterns and succeeds in mapping old and new deep fault zones between the terranes. Variscan terranes are rooted in the ductile lower crust and seem to consist of continental crust only, partly exclusively of rigid upper crust. Oceanic terranes, on the other hand, are always rooted in the asthenosphere. The development of continental terranes and their boundaries depends strongly on their thermal and rheological history. In the case of post‐orogenic collapse with heating and extension of the lower crust, seismic lamellae develop and often truncate former thrust faults.
Earliest stegosaur dinosaur
Authors: Boneham Brian F.W. , Forsey George F.
Published: July 2007

Re‐excavation of the type site of the Sharp's Hill Formation (Bathonian, Middle Jurassic) in Oxfordshire, England, has revealed several horizons with disarticulated remains of a species of stegosaurian dinosaur, here considered to be the earliest stegosaur. It is suggested that stegosaurs radiated out from northern Europe in the Middle and Upper Jurassic to the rest of the world. The general stratigraphy of the type site is described, and it is concluded that the stegosaur remains are possibly of earliest Lower Bathonian age. The sediment in which the remains accumulated is considered to represent a drought‐controlled environment.
The palaeobiogeography of Permian anomodonts
Authors: King Gillian M.
Published: July 2007

It is generally considered that the oldest anomodont mammal‐like reptiles are known from Late Permian sediments of the USSR and that during the rest of the Late Permian distribution of these fossils widens to encompass nearly all geographical areas by the end of the Period.

This study reviews the occurrence of anomodont genera in Permian sediments and reassesses the conventionally accepted distribution pattern. A broad correlation of terrestrial Permian rocks from different continents is attempted. Using recent reconstructions of Permian continental positions the effect of latitude on anomodont distribution is investigated. Some explanations for the restrictions operating on anomodont distribution are suggested.
Palaeogeographic and geodynamic evolution of the Gondwana continental margins during the Cambrian
Authors: Courjault‐Radé Pierre , Debrenne Françoise , Gandin Anna
Published: July 2007

During the Cambrian, two types of continental margins occurred around Gondwana. The eastern margin (Antarctica, Australia and southern South America) was characterized by a narrow continental shelf with a steep slope separating the shallow water environment from a deep‐oceanic one accompanied by mafidultramafic volcanics. The western margin was characterized by a wider continental shelf, probably passing gradually to an unknown outer basin. This comprised three main domains: the Asiatic shelf, composed of distinct cratonic blocks, presumably separated from each other by deeper‐water/ volcanic intracontinental basins; the European shelf, characterized by the development of shallow intracontinental siliciclastic basins; and the Americanc‐African shelf, morphologically and depositionally uniform. The distinction of these two Gondwana continental margins expresses their different geodynamic behaviour during Cambrian extensional tectonics. In fact, the sedimentary/palaeogeographic evolution, suggests the establishment of an active Pacific‐like margin in the eastern domain, and the tentative establishment of a divergent Atlantic‐like margin, in the westem one.
Infrared spectroscopy of Triassic conodonts: a new tool for assessing conodont diagenesis
Authors: Nöth Sheila , Richter Detlev K.
Published: July 2007

The Fourier transform infrared spectra of individual conodonts with various CAI values indicate definite changes in conodont francolite during diagenesis. Steady decarbonation can be observed in the increasing intensity of the band with the wavenumber 2340 an‐1, which is assigned to trapped molecular CO2. Carbon dioxide originates from decomposing CO2‐3‐ions occupying the B‐site in francolite. Furthermore, the intensity of the water‐deformation band at 1644 cm‐1 decreases with higher CAI values. These changes of intensity can be quantified by calculating the maximum extinction (Emax) for the corresponding absorption maxima and correlated with the CAI. Unaltered conodonts have a relative variable water ‘content’ and very little CO2. Up to a CAI value of 4 conodont francolite continuously expells water and carbon dioxide is trapped. Conodonts with CAI = 5 have similar water ‘contents’ to CAI = 4 conodonts, but decarbonation continues to take place during this stage of diagenesis.
On the migration of precursors of strong earthquakes
Authors: Bella F. , Biag P.F. , Caputo M. , Monica G. Della , Ermini A. , Sgrigna V.
Published: July 2007

It is found that perturbations presumedly associated with swarms, the B patterns and the BG pattern precursors of strong earthquakes in New Zealand, California and Apennines, propagate in the crust of the Earth with a velocity of the order of cm1. The hypothesis that a single travelling elastic perturbation causes a set of precursors of the same strong earthquake is discussed and it is concluded that each precursor is associated with a different perturbation.
Seismic imaging of Pleistocene deep‐sea cyclothems: implications for sequence stratigraphy
Authors: Carter R.M. , Cartef L.
Published: July 2007

Plate collision along the New Zealand Alpine Fault since the late Miocene has resulted in an abundant supply of temgenous sediment to an adjacent starved late Cretaceous rift‐basin, the Bounty Trough. During the late Neogene, alternating pulses of temgenous (glacial) and biogenic (interglacial) sediment were deposited in the trough in the form of deep‐sea cyclothems, in sympathy with glacio‐eustatic sea‐level fluctuations. Individual cyclothems ranging up to 15 m in thickness have been directly imaged by both 3.5 kHz and single channel airgun profiling. They are particularly conspicuous on the continental slope and in areas of the trough under the influence of overbank turbidite deposition from the Bounty Channel. On the abyssal Bounty Fan, approximately 50 cyclothems have been deposited since the late Pliocene, i.e. each cyclothem corresponds to two contiguous oxygen isotope stages. Each cyclothem also corresponds to the offshore conformity of a single 5th or 6th order seismic sequence, with the lower, temgenous portion marking a lowstand systems tract, and the upper, biopelagic part representing the transgressive and highstand systems tracts. Therefore, as a single continental margin sequence is traced seawards it passes from unconformity‐bounded shelf and shelf‐margin cyclothems, to slope sediments which include thick conformity‐bounded cyclothems or autocyclic canyon deposits, to thin conformity‐bounded deep‐sea cyclothems on the distal rise, and finally to cryptically cyclic biopelagic sediment andor red clay on the abyssal plain.
Stable isotope differences among morphotypes of Neogloboquadrina pachyderma (Ehrenberg): implications for high‐latitude palaeoceanographic studies
Authors: Healy‐Williams Nancy
Published: July 2007

The stable isotopic composition of planktonic foraminifera plays a paramount role in interpretations of past oceanographic and environmental conditions; thus an accurate understanding of the factors which influence their isotopic composition is essential. In order to increase the palaeoceanographic utility of the high‐latitude planktonic foraminifera Neogloboquadrina pachyderma, its shape and oxygen and carbon isotopic variability are quantitatively described in this study. Over 8200 specimens of N. pachyderma from 36 gravity and piston core tops from surface sediments of the North Atlantic and southern Indian Oceans were digitized and analysed via Fourier series in closed form. The morphological results are presented in detail elsewhere and are utilized in this study to select specimens for isotopic analyses. Significant isotopic differences exist between morphological variants of this important high‐latitude speaes. Specimens become depleted in both oxygen and carbon isotopes as the test shape becomes more pentagonal and less quadrate. The isotopic differences cannot be attributed to test thickening nor to size or coiling direction. This observation has important implications in the use of this speaes as a tracer in high‐latitude palaeoceanographic investigations. In particular, future isotopic investigations utilizing this species should analyse single forms to allow for clear interpretation of palaeoceanographic signals.
Tectonic episodes of cratons: conflicting North American concepts
Authors: Sloss L.L.
Published: July 2007

Over the past one hundred years North American geologists have been influenced by concepts of Earth history based on periodic events involving marked (‘Neocatastrophic’) changes and competing concepts involving steady‐state (‘Uniformitanan’) behaviour. T.C. Chamberlin, a late 19th‐/early 20th‐Century exponent of a nonuniformitarian scenario of earth history, proclaimed ‘diastrophism as the ultimate basis of correlation’ ‐ meaning that geological history is punctuated by orogenic paroxysms causing retreat of epicontinental waters to oceanic basins, creating segmentation of the stratigraphic and chronological record. At mid‐Century James Gilluly gained wide support for the proposition that orogeny has followed a Uniformitarian, near‐steady‐state course. Accordingly, episodic diastrophism is a myth and cannot be the basis for periodic eustatic sea‐level change, interregional unconformities, etc.

In more recent decades two powerful new influences on geological thought have emerged. The global tectonic paradigm has forced upon us the realization that rearrangements of lithospheric plates are capable of changing the freeboard of continents. At the same time technological advances in the acquisition and processing of seismic‐reflection data have been seized by receptive minds to organize the newly available stratigraphic imagery for application to the discipline of seismic stratigraphy which emphasizes the identification and correlation of unconformity‐bounded successions of strata. Expansion of the methodology to the outcrop, beyond the limitations of seismic resolution, has brought about the flowering of the New Sequence Stratigraphy, doctrine that has deservedlyachieved wide application and acclaim. Practitioners of sequence stratigraphy, impressed by the distances over which unconformity‐bounded stratal units can be correlated, hew to the belief that eustatic (commonly glacially engendered) sea‐level change is the control.

This paper examines evidence of tectonic episodes affecting cratons and their margins. These offer promise of a more satisfactory understanding of stratigraphic sequences and of the Earth history they represent. Consideration of these matters makes it inescapable that the elevation and subsidence of cratons (and their component basins and arches) reflect tectonic phenomena of the continental lithosphere quite independent of eustatic events.
From high plateaux to marginal basins: the active role of the mantle
Authors: Wezel Forese‐Carlo
Published: July 2007

Current geodynamic models pose many serious problems for the description of continental tectonic processes, Serious difficulties arise also in the description of some of the ocean basins.

Deformation of the Earth's crust appears to be concentrated along several mobile megashear belts. It is proposed that these could be the surficial expression of ‘mantle chimneys’ which extend to great depths. Within these structures, post orogenic high plateaux form, and as time passes these develop a central depression enclosed within arcs or indeed full‐scale rings of mountains. The enlargement and deepening over time of the back‐arc depression occurs in concert with the radial migration of a ‘topographic wave’. In this respect, the following structures represent different phases in an evolutionary sequence: (a) the Tibetan Plateau, (b) the North American Cordillera, and (c) the Tyrrhenian Basin and Calabrian Arc. The development of this succession reflects a particularly high degree of activity in the mantle, in which diapiric rising of asthenospheric matter elevates the land and causes tensional rifting. The resulting centrifugal movement of the mantle melt results in crustal foundering and engulfment of the area behind the arc, which thus becomes susceptible to the subsequent processes of com‐pressional deformation.
Geophysiology of mineral deposits ‐ a model for a biological driving force of global changes through Earth history
Authors: Krumbein W.E. , Schellnhuber H.‐J.
Published: July 2007

The upper mantle, crust, hydrosphere and atmosphere of Earth are kept in a geophysical, geochemical and thermodynamical state far from astrophysical and planetary equilibrium. The system oscillates around a quasi‐stable centre following laws governing dissipative or dynamic systems. The energy and materials necessary for such global pseudo‐equilibria are fed in, stored and released on a geological time‐scale by (a) the energy and electron channelling processes of photosynthesis, respiration and fermentation, (b) biologically controlled accumulation of energy and matter into crustal reservoirs and much later (c) release of the latter from crust and upper mantle into surface‐related geotectonical and geochemical cycles. Phototrophic and chemorganotrophic bacterial microorganisms of microbial mats, potential stromatolites or microbialites are capable of anoxygenic and oxygenic photosynthesis, of aerobic and anaerobic respiration and of organic and inorganic fermentation, i.e. disproportioning of energy‐rich molecules. In this way large amounts of photosynthate are transformed on a global scale into hydrocarbons and sulphides (sulphate serving as electron acceptor for anaerobic respiration or fermentation). Inorganic reduced compounds produced by the same processes of photosynthesis followed by respiration and fermentation are stored as sulphides of iron, lead, zinc, silver, gold etc. All the aforementioned microbial processes can transfer energies and matter at a global scale. Thus disparities of the Earth's crust and mantle from the geochemical equilibrium may not be caused solely by internal temperature, radioactivity and gravity gradients, but increasingly by life processes. The biogenic formation of energy‐rich compounds on a global scale delivers huge amounts of energy and electrons to the crust, which are recycled through geological time. The quantities of energy involved appear in themselves to be sufficient to provide the driving force for geotectonic processes. Thus, a model of geophysiological equilibration of geochemical cycles and geotectonics is proposed in which the biota play the role of energy and matter transmitters for geodynamic processes. Living matter controls and transfers more than 10% of the Earth's mass in this system with turnover times of up to 500 million years. The transfer speed of each individual atom according to the model must have gradually decreased since the Precambrian, while the amounts of energy and matter stored and cycled have in turn increased, as also witnessed by the increase in the thickness of the crust. Earth as a bioplanet has come of age.
Carbon sources in arc volcanism, with implications for the carbon cycle
Authors: Varekamp J.C. , Kreulen R. , Poorter R.P.E. , Van Bergen M.J.
Published: July 2007

New CO2/3 He data from the East Sunda Arc (Indonesia) confirm earlier observations that arc volcanic gases have higher CO2/3 He ratios than MOR environments.On average, > 80% of arc volcanic CO2 is recycled, exogene carbon. Addition of a few percent of carbonate‐bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases, but can not explain the He isotope observations. The CO2/3He in arc volcanoes is not strongly dependent on the composition of modem trough sediments (e.g. deep sea clays vs carbonate‐rich sequences), and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of, arcs. The sum of globally deep‐subducted sediment and slab carbon exceeds the estimated arc CO2 flux, and approximately 3.5 teramole of carbon may return annually to the mantle in convergent zones. The modem combined processes of MOR volcanism, slab alteration, and subduction volcanism do not produce a substantial carbon flux into the exosphere, and rate‐changes in ocean floor spreading are unlikely to cause major changes in atmospheric CO2 as a result of changes in the volcanic CO2 fluxes. Intense pulses of flood basalt volcanism, however, may alter the CO2 contents of the atmosphere over the course of a millenium or so, and influence global climate.
An investigation by transmission electron microscopy of planar deformation features in naturally shocked quartz
Authors: Goltrant Olivier , Doukhan Jean‐Claude , Cordier Patrick , Courtillot Vincent
Published: July 2007

We have investigated by Transmission Electron Microscopy (TEM) the planar deformation features(PDF) in quartz from various sites where shock metamorphism has been detected optically: impact sites; the Vredefort complex (South Africa) and the K/T boundary at Raton Basin (Colorado). PDFs are straight narrow bands of glass or microtwins or huge densities of dislocations. Such contrasting microstructures must reflect different shock scenarios. In the Vredefort complex the post‐shock thermal history has strongly overprinted the shock‐induced defects. In the Raton Basin samples very tiny bubbles have precipitated on the dislocations, strongly suggesting a lengthy annealing at moderate pressure and temperature. This new information should be taken into account in any model of the origin of the K/T transition. In any case, observation of PDFs by optical microscopy alone is not sufficient to unambiguously conclude on their origin.
Investigations on geomagnetic reversals in Icelandic lavas, 1953–78
Authors: Kristjansson Leo
Published: July 2007

Recent reviews of the development of palaeomagnetic techniques in geology have shown that palaeomagnetism has contributed significantly to the acceptance of new concepts in global tectonics. The present paper extends Frankel's (1987) review of palaeomagnetic work on the basalt lava sequences of Iceland in the early 1950s. These lavas provide some of the most complete series of reliable ‘spot readings’ of the geomagnetic field available. It is shown that research on Icelandic basalts has continued to be of importance in improving our understanding of palaeomagnetism and its applications.
Eocene age of eclogite metamorphism in Pakistan Himalaya: implications for India‐Eurasia collision
Authors: Tonarini Sonia , Villa Igor M. , Oberli Felix , Meier Martin , Spencer David A. , Pognante Ugo , Ramsay John G.
Published: July 2007

A geochronological investigation of two rocks with an eclogitic assemblage (omphacite‐garnet‐quartz‐rutile) from the High Himalaya using the Sm/Nd, Rb/Sr, U/Pb and Ar/Ar methods is presented here. The first three methods outline a cooling history from the time of peak metamorphism at 49±6 Ma recorded by Sm/Nd in garnet‐clinopyroxene to the closure of Rb/Sr in phengite at 43±1 Ma and U/Pb in rutile at 39–40 Ma. The Sm/Nd isotopic system was fully equilibrated during eclogitization and has not been disturbed since; its mineral ages may date the peak metamorphic conditions (650±50°C at 13–18 kbar: Pognante and Spencer, 1991). The Ar/Ar data reveal the presence of substantial amounts of excess 40Ar in hornblende, and yield a statistically acceptable but geologically meaningless phengite plateau age of 81.4±0.2 Ma, inconsistent with Sm/Nd, Rb/Sr and U/Pb. This questions the use of such a chronometer for the dating of high‐pressure assemblages. The results imply a Late Palaeocene or Early Eocene subduction of the northern Indian plate margin in NW Himalaya. The fact that eclogites are restricted to NW Himalaya may be the result of a peculiar p‐T‐t path associated with a high convergence rate during the first indentation, in contrast to the later and slow subduction in Central and Eastern Himalaya.
Hydrothermal alteration of basic island‐arc volcanic rocks north and south of Mytilini Town, Lesvos Island, Greece
Authors: Kelepertsis A.E.
Published: July 2007

The mobilities of major and trace elements have been investigated in hydrothermally altered volcanic rocks of Pliocene age on the island of Lesvos. One type of hydrothermal assemblage, montmorillonite‐K‐feldspar‐goethite, was recognized in outcrops north of Mytilini town.

The alteration occurs a few metres under the surface of unaltered volcanic rocks of high‐K andesite and high‐K basaltic andesite composition. The unaltered latite‐andesite consists of plagioclase, clinopyroxene, sanidine and magnetite with quartz, calcite, pumpellyite and montmorillonite as subordinate secondary minerals.

The main control over major oxide distribution appears to be the extent of conversion of plagioclase to K‐feldspar.

Three distinct groups of elements were revealed to be positively correlated:

Si, Mg, Ca, Na, Mn, Sr and Ba, which are leached during the alteration process. This group of elements reflects their association with plagioclase feldspar and clinopyroxene.

Fe, K, Ti, P, Nb, Zr, Y, Rb, Ni, Cr, V. This group includes elements which are enriched relative to the unaltered volcanic rock, reflecting their association with K‐feldspar, iron hydroxides and Ti and P‐bearing minerals.

Ti, P, Nd, La, Ce. From this group of elements it is indicated that Nd, La and Ce are associated with Ti‐ and P‐bearing minerals.

There is no evidence of Cu or Zn addition to the system by hydrothermal fluids since there are no correlations between these base metals and elements enriched in the K‐feldspar, montmorillonite‐rich zone. This potassic rich zone may be connected with hidden epithermal sulphide mineralization with gold.
Taxonomy and stratigraphic occurrence of Thalassiosira tetraoestrupii sp. nov. and related species in upper Miocene and lower Pliocene sediments from the Norwegian Sea, North Atlantic and North West Pacific
Authors: Bodén Per
Published: July 2007

Three new Thalassiosira species are described. Thalassiosira baldaufii and T. labimarginata have previously never been reported whereas specimens of T. tetraoestrupii have probably often been assigned to T. oestrupii (Ostenfeld) Hasle (Fryxell and Hasle) in previous studies. The description of Thalassiosira praeoestrupii Dumont Baldauf and Barren is emended.

Quantitative analysis of these Thalassiosira species has been completed for upper Miocene and lower Pliocene sediments from three different regions in the northern hemisphere. The material used is from DSDP Hole 552A in the North Atlantic, Site 578 in the NW Pacific and ODP Site 642 in the Norwegian Sea. The abundance patterns (number of valves per gram dry sediment) obtained allow the assessment of the biostratigraphic significance and precision of specific diatom events. Levels of reliability are estimated based on the degree of abundance change at the critical stratigraphic interval, level of abundance, consistency of occurrence and duration of consistency. The chronology of the events is obtained through direct correlation to the established magnetic polarity history.

The following four first‐order reliability (R1) diatom datums are proposed: in the North Atlantic the first abundant occurrence (FAO) of T. praeoestrupii (5.34 Ma), in the Norwegian Sea, first consistent occurrence (FCO) of T. tetraoestrupii (5.00 Ma), FCO of T. praeoestrupii (5.00 Ma) and last consistent occurrence (LCO) of T. baldaufii (4.30 Ma). Two R2 diatom datums are proposed: in the Norwegian Sea, FCO of T. baldaufii (5.13 Ma), LCO of T. praeoestrupii (4.87 Ma). Three R3 diatom datums are proposed: in the NW Pacific, FCO of T. tetraoestrupii (5.02 Ma) and FCO of T. praeoestrupii (5.54 Ma): in the Norwegian Sea, the first occurrence (FO) of T. labimarginata (5.83 Ma).
Ocean Bottom Seismographs used in a crustal study of an area covered with flood‐basalt off Lofoten, N. Norway
Authors: Mjelde R. , Sellevoll M.A. , Shimamura H. , Iwasaki T. , Kanazawa T.
Published: July 2007

Seismic refraction measurements were made in August 1988 to study the crustal structure off Lofoten, Northern Norway. Twenty‐four 3‐component Ocean Bottom Seismographs (OBS) were used, of which seven were deployed in the area covered by landward‐flowing basalt deposited during the early Eocene break‐up between Norway and Greenland. The main purpose of the OBS survey was to investigate whether this method can be used to map structures below the basalt, which is not easy to penetrate with conventional seismic reflection techniques. The records obtained showed that the OBS data contain considerable information about structures below the flood‐basalt; preopening sediments up to 4.0 km thick is indicated below the 1.0–2.5 km‐thick landward‐flowing basalt. The success of the OBS survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and, potentially, in other areas where highly reflective boundaries make the reflection technique difficult to apply.
Exhumation of high‐pressure rocks: a review of concepts and processes
Authors: Platt J.P.
Published: July 2007

The exhumation of high‐pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures, or the transport of the metamorphic rocks through the overburden. Exhumation cannot be achieved simply by thrusting or strike‐slip faulting. It may be caused by erosion of shortened and thickened crust, but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km. One or more of the following additional mechanisms may be involved.

1 Corner flow of low‐viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock, and may explain some occurrences of high‐pressure tectonic blocks in mélange. This process does not, however, appear to be adequate to explain the exhumation of regional high‐pressure terrains.

2 Buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings. This is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle, but cannot explain the emplacement of coherent tracts of high‐density metamorphic rock into shallow crustal levels. Some high‐pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low‐density mud or serpentinite.

3 Extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high‐pressure terrains. Extension may occur in the upper part of an accretionary wedge thickened by underplating; or it may affect the whole lithosphere in a region of intracontinental convergence, if surface elevation has been increased by the removal of a lithospheric root. In the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain.
Temperature logs in deep wells—a useful tool for past climatic reconstruction
Authors: Cermak V. , Kukkonen I.T. , Safanda J.
Published: July 2007

According to the theory of heat conduction in a semi‐infinite body, temperature changes at the surface propagate into the subsurface with the amplitude attenuation and time delay that increase with depth. Temperature changes on the earth's surface, reflecting the past climatic history, can thus be evaluated by analysing the curvature they have caused in the present temperature‐depth distribution. As a rule, temperature profiles to depths of 200–300 m record surface temperature trends accurately over the last two centuries or so; deeper holes may reveal climate history farther back but with decreasing resolution.

We present several synthetic temperature‐depth profiles to demonstrate the expected signature of past surface temperature changes in the subsurface, the analysis of which may help better identify the climate of the past. Examples of extracted climate recollections from holes in North America and Europe are discussed. While inconspicuous underground records may correspond to the postglacial warming 8–11 kyr ago, reasonably well‐documented borehole logging data have confirmed climate excursions in the past millenium, namely the Little Climate Optimum and the Little Ice Age. Traces of recent warming are generally common in many temperature records, evidencing the temperature rise by 1–2 K over the past 100 years.
Heat flow in rift basins above a hot asthenosphere
Authors: Pedersen Tom
Published: July 2007

When continental rifting takes place above a hot asthenosphere, pressure‐release melting of adiabatically upwelling mantle may generate large volumes of basaltic melts which subsequently are emplaced at crustal levels and cool. To correctly estimate the heat flow from tectonic subsidence and crustal thinning, it is necessary to account for the melt volumes. A simple physical model of heat flow that incorporates a crustal growth correction on lithospheric extension estimates, as well as the heat in the emplaced magma, has been developed. The principal result is that heat flow may be substantially increased for several million years after rifting, even for a moderately heated asthenosphere.
Dipping basement reflectors along volcanic passive margins—new insight using data from the Kerguelen Plateau
Authors: Schlich Roland , Rotstein Yair , Schaming Marc
Published: July 2007

Multichannel seismic reflection data from the Southern Kerguelen Plateau show many dipping basement reflectors associated with volcanic flows. These reflectors are quite similar in their shape to seaward‐dipping basement reflectors observed along volcanic passive margins. On the Kerguelen Plateau the sources are updip of the basement reflectors, in the presently extinct and eroded volcanoes. We suggest that the same source/reflector geometry may also apply to the seaward‐dipping basement reflectors observed along passive margins. We interpret these reflectors to be the result of volcanism on the passive margin which flowed in all directions into the newly created ocean basin at an early spreading stage.
Salt insertions in sedimentary sequences: impacts on temperature and thermal maturation with depth
Authors: Zhao K. , Lerche I.
Published: July 2007

Due to the contrast in thermal conductivity between salt and typical sedimentary formations the presence of salt in various shapes in the sub‐surface can have a significant impact on the sub‐surface temperature distribution and thermal maturation of source rocks.

Using a thermal indicator tomography 1‐D modelling system, which deals with salt insertion, the thermal and excess maturity anomalies caused solely by the presence of a salt layer are investigated. Two cases, salt ‘plug’ and ‘lens’, illuminate the different patterns of vitrinite reflectance variation with depth that would be recorded by borehole sampling. Salt can be inserted either as a primary depositional layer or by secondary intrusion at depth.

The effects of salt are more dominant on the subsalt layers because: 1 salt insertion changes the burial paths of subsalt sediments. Thus the compaction‐driven fluid flow of subsalt sediments, and also basement subsidence, are altered;

2 iso‐temperature lines are modified by the presence of the salt and the variation depends on the thickness of the salt layer.

The model was also designed to estimate the time of salt insertion and the variation of salt thickness in an inverse sense using present day data on temperature with depth and measured thermal indicators. An investigation is given of the degree to which inverse procedures resolve parameters associated with salt insertion. The sensitivity of those parameters is also discussed.
The Erzincan earthquake of 13 March 1992 in Eastern Turkey
Authors: Barka Aykut , Eyidoǧan Haluk
Published: July 2007

The 13 March 1992 Erzincan earthquake, M=6.8, occurred in the eastern half of the Erzincan basin. The largest aftershock took place near Pülümür on 15 March 1992. No clear surface breaks were observed, although teleseismic studies suggested that it was a strike‐slip earthquake striking parallel to the North Anatolian fault, with a focus of approximately 10±2 km depth, 30 km rupture length, 95 cm of slip, and a 1.16×1026 dyn.cm seismic moment. The aftershock distribution concentrated at an area of the intersection between the North Anatolian fault and the Ovacik fault. These results indicate that the previously suggested seismic gap along the North Anatolian fault, east of Erzincan, still remains unruptured.
Tertiary tectonic evolution along the Arne‐Elin Trend in the Danish Central Trough
Authors: Clausen Ole Rønø , Korstgård John A.
Published: July 2007

Tertiary sequence boundaries are mapped on reflection seismic sections in the northern part of the Danish Central Trough, North Sea. The geometry of the sequence boundaries and the isopach maps of the sequences are used as indicators of differential subsidence.

The Tertiary tectonic evolution is subdivided into: (i) Late Palaeocene and Early Oligocene episodes of inversion along the NNW–SSE striking Arne–Elin Trend (ii) Early Oligocene to Pliocene episodes of differential subsidence across pre‐Tertiary fault trends.

The observed differential subsidence and inversion is related to pre‐Tertiary faults and fault trends, and dating of the sequences shows that the tectonic phases were contemporaneous with tectonic events in NW Europe. It is suggested that the differential subsidence‐inversion is controlled by reactivation of pre‐Tertiary faults/fault‐trends by block movements due to an interaction of the Alpine collision and the opening of the Atlantic.
Origin and role of major strike‐slip transfers during plate collision in the central Mediterranean
Authors: Reuther Claus‐Dieter , Ben‐Avraham Zvi , Grasso Mario
Published: July 2007

Variations in the crustal structure along the northern African plate margin have caused different modes of collision with Eurasia. Lateral density variations along the central Mediterranean collision zone are expressed in a change of the angle of the downbending African Plate and lead to the formation of strike‐slip transfers in these transition zones that are roughly perpendicular to the trend of the collisional zone. In some cases these transfer zones are developed into hinge faults, while in others they can be developed into transform faults. This process governs the segmentation of the collision zone in the central Mediterranean region south of the Maghrebian thrust belt in Tunisia and Sicily through the Calabrian Arc to the northeastern Hellenic Arc, extending further to the Cyprian Arc and to the Taurus‐Zagros chain.
Mesozoic neo‐tethyan pre‐orogenic deep marine sediments along the Indus–Yarlung Suture, Himalaya
Authors: Sinha Anshu K. , Upadhyay Rajeev
Published: July 2007

Shelf, forereef and basin margin (slope) olistoliths (Exotic blocks of limestone) of Permian–Jurassic age are tectonically juxtaposed within the Triassic to Eocene age pre‐orogenic, deep abyssal plain turbidites of the Lamayuru. The pre‐collision tectonic setting and depositional environment of the limestone olistoliths can be reconstructed from within the neighbouring Zanskar range. The disorganized Ophiolitic Melange Zone, an association of different tectonic rock slivers of Jurassic–Eocene age, is tectonically underlain by the overthrusted Lamayuru Formation and tectonically overlain by the Nindam Formation. Tectonic slivers of Late Jurassic–Early Cretaceous age red radiolarian cherts represent a characteristic lithotectonic unit of the Ophiolitic Melange Zone, those occurring near the contact zone with the Lamayuru Formation, were deposited within the neo‐Tethyan deep‐ocean floor of the Indian passive margin below the carbonate compensation depth. These tectonic slivers accumulated along the northern margin of the Indus–Yarlung Suture Zone of the Ladakh Indian Himalaya during subduction accretion associated with the initial convergence of the Indian plate beneath the Eurasian plate.
THE EUROPEAN MACROSEISMIC SCALE (MSK‐92)
Authors: Gunthal G. , Musson R.M.W. , Schwarz J. , Stucchi M.
Published: July 2007

A new updated version of the MSK macroseismic intensity scale has been prepared by a Working Group of the European Seismological Commission and has been published in April 1993 (European Macroseismic Scale 1992: updated MSK scale, 1993, ed. by G. Grünthal, Cahiers du Centre Européen de Geodynamique et de Séismologie, no. 7).
High‐resolution correlations between Gotland and Estonia near the base of the Wenlock
Authors: Jeppsson Lennart , Männik Peep
Published: July 2007

The strata of the Ireviken Event can be correlated between Gotland, Sweden and the Viki core on Saaremaa, Estonia, with a high degree of precision. Most of the ten datum planes are found with a precision of better than 0.1 m in the Lower and upper Visby Beds on Gotland and high in the Mustjala Member of the Jaani Formation on Saaremaa. Five of the latest Llandovery–early Wenlock units defined by these datum planes are between c. 0.12 and 1.77 m thick on Gotland and 0.12 and 0.67 m in Estonia. The duration of each was between a few thousand and c. 31 000 years. The stratigraphic resolution achieved in the interval of the Ireviken Event is 10,000 years. Ultimate range ends are lacking within a preceding, slightly longer interval, but the pattern of intermittent presence of some taxa agrees well with an unchanged relative rate of sedimentation. Their coeval presence in different places indicates ecological, regional or more widespread changes.
Seismostratigraphy and structural framework of the SW Baltic Sea
Authors: Thomas Stefan A. , Sivhed Ulf , Erlström Mikael , Seifert Manfred
Published: July 2007

The SW part of the Baltic Sea between Scania, Rügen, Bornholm and Mön constitutes a complex crustal transition between the Baltic Shield and the accreted Phanerozoic provinces of the West European Platform. An integrated interpretation of marine reflection seismic data sets from the BABEL AC line and two commercial surveys offshore NE Germany and S Sweden have resulted in a complete view of the structural framework in the area. The general seismic picture can best be detected by two characteristic sets of reflection phases. The lower set is dominated by slightly dipping and vertically displaced prominent reflectors corresponding to downfaulted Lower Palaeozoic strata on top of the Precambrian basement. The upper set represents Mesozoic and Cenozoic coherent reflection phases including a thick Upper Cretaceous unit. The Caledonian deformation front is identified in the southern part of the investigated area as the border against which basement rocks have been affected by Caledonian metamorphism and deformation. Major structural elements also include the N–S trending Agricola–Svedala Fault and North Rügen‐Skurup Fault. Several NW–SE trending faults are also identified including the Nordadler–Kamien Fault, Jutland–Mön Fault, Carlsberg Fault, Romeleåsen Fault Zone and the Fyledalen Fault Zone. The sedimentary record from NE German offshore wells and Scanian boreholes is compared with the seismic data. The Cambro‐Silurian strata are composed mainly of quartzitic sandstones, shales and biomicritic limestones. The Silurian is dominated by grey, micaceous shale and micaceous siltstone deposited in a marginal basin. Upper Palaeozoic strata are merely encountered in the southernmost part of the investigated area. These include Zechstein strata. The Mesozoic deposits are dominated by a thick Cretaceous sequence of mainly limestones with interbedded sandstones.
Vertical variation of heat flow density in the continental crust
Authors: Kukkonen I.T. , Čermák V. , Hurtig E.
Published: July 2007

Terrestrial heat flow density is a key parameter in understanding the past, present and future development of our planet. Most phenomena studied in deep crustal geophysics are temperature dependent and therefore reliable assesments of deep temperatures are necessary. Most heat flow measurements have been made in drill holes which are shallow (< 1 km) in comparison to the thicknesses of the crust and lithosphere. The recent findings in deep drilling projects (e.g. the Kola deep hole in Russia and the KTB hole in Germany) have yielded results which suggest that there is a distinct contrast between heat flow densities measured in the uppermost 1 km and values measured at deeper levels. The factors contributing to the vertical variation in the uppermost few kilometres are discussed with special emphasis on palaeoclimatic ground surface temperature changes and groundwater circulation in the bedrock.
The 20 March 1992 South Aegean, Greece, earthquake (Ms= 5.3): possible anomalous effects
Authors: Papadopoulos Gerassimos A.
Published: July 2007

The earthquake (Ms= 5.3) of 20 March 1992 and its aftershocks, which occurred near the volcanic island complex of Milos, South Aegean, Greece, are studied on the basis of filed observations and instrumental data. The mainshock caused some building damage, the maximum intensity of VI+ (MM) being assigned to Triovasalos, Milos. Ground cracks, liquefaction in soil, landslides and rockfalls were observed in Milos. Liquefaction took place at an apparently anomalously long epicentral distance (D= 12 km) and is associated with unusually small earthquake magnitude. Abnormal animal behaviour was reported no longer than twelve hours before the mainshock. The b‐value (= 1.02) of the G–R relation for the aftershock sequence, the exponentially decreasing number of aftershocks with time, and the difference (= 0.5) in magnitude between the mainshock and its largest aftershock imply that the origin of these earthquakes is tectonic and not associated with the volcanic field of Milos.
Fractal damage mechanics of geomaterials
Authors: Chelidze Tamaz
Published: July 2007

Recent progress in a new field of mechanics of diluted solids is reviewed ‐ the fractal mechanics of geomaterials. It has become clear that the mechanics of geomaterials should take into consideration the influence of the fracture delocalization process on fundamental fracture characteristics such as the strength, the fractal dimension of a network of cracks, the surface energy of fracture and the elastic properties of fragmented media.

The percolation model of fracture proposed by this author in 1979, in accordance with experimental data, treats the destruction process as a sequence of nucleation and coalescence of microcracks caused by their interaction. This approach enables the mathematical description of the entire process of fracturing. Many aspects of the fracture of heterogeneous solids ‐ the magnitude‐frequency distribution of seismic activity and acoustic emission, the high‐surface energy of fracture in composite materials and rocks, the geometrical peculiarities of a crack network, the appearance of forerunners of mechanical collapse, and the intermittency of the fracture process in the time domain ‐ find quantitative explanation in the percolation model. The process of determining the elasticity of fractured media, which is the object of the elastic percolation theory, also reveals some unusual features that can affect the process of geophysical interpretation. For example, the elastic modulus M and the velocity of elastic waves v become scale‐dependent in the fractal regime. It is shown that the fractal dimension of the elastic modulus of a depleted solid differs significantly for ‘refilled’ and ‘hollow’ voids.

Several implications of fractal mechanics for seismology are considered, namely the generalized form of the magnitude‐frequency relationship, the phenomenon of anomalous tensosensitivity, the scale‐dependence of the elastic moduli of massively faulted rocks and the possibility of apparent seismic boundaries.
Precession‐punctuated growth of a late Miocene submarine‐fan lobe on Gavdos (Greece)
Authors: Postma G. , Hilgen F. J. , Zachariasse W. J.
Published: July 2007

Sedimentary cycles in an upper Miocene succession of hemipelagic sediments (marls) and laminites (sapropels) were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity. Individual marl‐laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr. The lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences. The turbidite sequences occur within or substitute entirely the laminite beds, so that turbidite deposition is similarly precession punctuated.

The turbidite facies is characteristic for small, prograding fan lobes fed by small‐volume turbidites. The abundant plant remains, the local palaeogeographic setting and the association with laminites (related to wet climate) suggest a river‐fed submarine fan‐lobe, where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run‐off. The onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief. Sea‐level changes seem least important for the triggering of turbidites, which is in contrast with current beliefs.
Evidence against the core/cover interpretation of the southern sector of the Menderes Massif, west Turkey
Authors: Bozkurt Erdin , Park R. Graham , Winchester John A.
Published: July 2007

The Menderes Massif, in western Anatolia, has been described as a lithological succession comprising a basal ‘Precambrian gneissic core of sedimentary origin’ overlain in sequence by ‘Palaeozoic schist’ and ‘Mesozoic‐Cenozoic marble’ forming the envelope. The boundary between core and schist envelope was interpreted as a major unconformity, the ‘Supra‐Pan‐African unconformity’. By contrast, our field observations and geochemical data show that around the southern side of Besparmak Mountain, north of Selimiye (Milas), the protoliths of highly deformed, mylonitized augen gneisses are granitoid rocks intrusive into the adjacent Palaeozoic metasedimentary schists. The field relationships indicate the age of intrusion to be younger than late Permian and there is no evidence for the existence of either an exposed Precambrian basement or the ‘Supra‐Pan‐African unconformity’ in this sector of the Menderes Massif.
Problems in assessing macroseismic intensity from historical earthquake records
Authors: Monachesi G. , Moroni A.
Published: July 2007

This paper tackles the problems connected with the use of macroseismic scales, with particular attention to MSK. Intensity estimates are in principle affected by uncertainties which are seldom quantified in practice. In the case of two localities (Scisciano and Orciano) damaged by two Italian earthquakes (1741, Fabriano and 1846, Orciano), which have a good historical documentation, the difficulties of obtaining the data necessary for MSK evaluation have been analysed. In order to assess the maximum range of uncertainty the data have been analysed in two extreme scenarios. Finally a comparison between intensity assigned using the MSK and MCS scales is analysed.