bluuebunny/crossref_metadata_2025 huggingface dataset:
The Valanginian carbon isotope event: a first episode of greenhouse climate conditions during the Cretaceous
Authors: Lini Andrea , Weissert Helmut , Erba Elisabetta
Published: July 2007

Lower Cretaceous pelagic carbonates outcropping along the Southern Alps of northern Italy provide a record of Tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle. The carbonate C‐isotope stratigraphy established at five selected localities in the Southern Alps allows an accurate picture to be drawn of the duration and amplitude of the Valanginian C‐isotope event. δ13C values near 1.25–1.50% determined in Berriasian and lower Valanginian sediments are replaced by more pdsitive δ13C values near 3% in the late Valanginian. The carbonate C‐isotope excursion ends in the early Hauterivian with values fluctuating between 1.5% and 2%. The carbonate C‐isotope excursion is accompanied by a positive excursion in the total organic carbon C‐isotope curve. The Valanginian C‐isotope excursion identified in Tethyan sediments correlates with a C‐isotope excursion recorded in the western North Atlantic, in the Gulf of Mexico, and in the Central Pacific (DSDP Sites 534,391,535 and 167). By analogy with the Aptian stage, also marked by a significant positive C‐isotope excursion, the time of positive δ13C values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments. A warm and humid climate, possiblycoupled with a high atmospheric CO2 content and a high global sea‐level, may have triggered the acceleration of the global carbon cycling. In this case the Valanginian C‐isotope event would reflect a first episode of Greenhouse Earth conditions during the Cretaceous.
Strontium isotope stratigraphy in the Late Cretaceous: intercontinentaI correlation of the Campanian/ Maastrichtian boundary
Authors: McArthur J.M. , Kennedy W.J. , Gale A.S. , Thirlwall M.F. , Chen M. , Burnett J. , Hancock J.M.
Published: July 2007

In the Boreal Chalk of northwestern Europe the base of the Maastrichtian Stage is defined by entry of the belemnite Belemnella. In the Kronsmoor section, in northwestern Germany, which is a standard section for the European Chalk, 87Sr/86Sr at the Campanian/ Maastrichtian (C/M) boundary is 0.707723±9 (10). An isotopic correlation of this boundary to the US Western Interior, for which a highly refined cephalopod biostratigraphy exists, suggests that this boundary, as defined at Kronsmoor, occurs within the Baculites jenseni zone. This correlationagrees with the latest placement based on biostratigraphic criteria. On87Sr/86Srcriteria the boundary at Kronsmoor correlates to the English Chalk at Trunch, Norfolk, UK, at a level 3.5 m lower than its position based on biostratigraphic criteria.

At Kronsmoor, 87Sr/86Sr increases in a quasi‐linear manner through much of the section, suggesting that, averaged over intervals of 1 Myr, the gross sedimentation rate and temporal rate of change of 87Sr/86Sr were approximately constant through the section. For US samples, zonally‐plotted values of 87Sr/86Sr define a quasi‐linear trend, which suggests a moderate uniformity of zonal duration from the Baculites compressus zone (73.2±0.7 Ma, 10) to the Baculites grandis zone (70.1±0.7 Ma, 10).
The relevance of iridium and microscopic dynamic deformation features toward understanding the Cretaceous/Tertiary transition
Authors: Officer Charles B.
Published: July 2007

Iridium enhancements are associated with the fine particle emanations from present day basaltic and acidic volcanic eruptions but are not associated with impact craters, with one possible exception of Precambrian age. Microscopic dynamic deformation features are associated with structures originating from a meteorite impact, volcanic and internal explosion event(s), and high tectonic strain‐rate(s). The Cretaceous/Tertiary (K/T) distributions of inidium and shocked minerals extend over a stratigraphic interval of a few hundred thousand years, in agreement with the known record of intense volcanism at K/T time but not in accord with the signature expected from a single meteorite impact. The recently studied K/T sections in Haiti add further information on the associations of shocked minerals and iridium enhancements.
Ground temperature changes in eastern Canada: borehole temperature evidence compared with proxy data
Authors: Beltrami Hugo , Mareschal Jean‐Claude
Published: July 2007

Borehole temperature logs have been inverted to infer ground temperature histories (GTH) in eastern and central Canada. Regional ground temperature histories were obtained by simultaneous inversion of several temperature profiles from the same areas. Simultaneous inversion of 21 temperature logs sampled across all of eastern and central Canada yielded an average solution for this region. All but three of the studied sites show signs of warming in the last 150 years. This period of warming, which started after 1800 AD, was found throughout this part of Canada. The warming followed a cooler period corresponding to the little Ice Age. The inferred ground temperature histories exhibit long‐term trends similar to those obtained from treering growth indices in nearby regions and stable isotope data in the southern hemisphere. The modern warming appears correlated with the atmospheric concentration of CO2 as measured in ice cores.
Time as an independent variable for current ripples developing towards linguoid equilibrium morphology
Authors: Baas Jaco H. , Oost Albert P. , Sztano Orsolya K. , de Boer Poppe L. , Postma George
Published: July 2007

Flume experiments show that current ripples on very fine sand surfaces always develop towards a linguoid shape with constant height and wavelength provided that sufficient time is allowed for their formation. Straight and sinuous current ripples only reflect intermediate stages in ripple development and may be regarded as non‐equilibrium bedforms. The time period which current ripples require to reach linguoid equilibrium morphology is related to an inverse power of flow velocity. In the transitional stage from current ripples to upper stage plane bed (i.e. washed‐out ripple stage) only the equilibrium wavelength remains constant, whereas equilibrium height rapidly decreases to zero.

Our observations imply that bed‐roughness parameters in sediment transport calculations can be simplified when equilibrium conditions are attained, and that inferences about flow energy from the dimensions of current ripples in very fine sand need to be regarded with caution.
The occurrence and significance of beekite in Palaeocene alluvial‐fan deposits in central Anatolia, Turkey
Authors: Kazanci Nizamettin , Varol Baki
Published: July 2007

The Palaeocene alluvial‐fan succession in central Anatolia, Turkey, contains three isolated zones of beekite‐encrusted clasts. Each zone is 3–5 m thick and c. 1 km long. Beekite is developed as thin (1–5 mm), concentric silica rings formed by replacement and encrustation of carbonate clasts. The formation of beekites requires a relatively long time, with non‐deposition and fluctuating arid/semiarid conditions. The significance of beekite is thus analogous to that of silcrete. The presence of beekite encrustation within the Palaeocene alluvial‐fan succession indicates considerable breaks in sedimentation in the eastern part of the basin, and this inference is supported by the lower thickness of the alluvium in the east.
Analysis of the Kodiak Shelf Basin using 1D and 2D fluid flow/compaction models
Authors: Liu J. , Lerche I. , Wei Z.
Published: July 2007

The Kodiak Shelf Basin is one of the undeveloped basins in Alaska. In surrounding areas, hydrocarbon accumulations have been found. It is of interest to investigate whether there might also be hydrocarbons generated in the Kodiak Shelf Basin.

Using both one‐ and two‐dimensional fluid flow/compaction models, together with geological, geophysical and geochemical data from the Kodiak Shelf Basin, we simulate the development with time and depth of sedimentary compaction, porosity, permeability, pressure, palaeoheat flux variation and palaeotemperature variation. We then evaluate quantitatively the maturation of organic matter in the basin. The model results indicate that there was only a low likelihood of hydrocarbon generation in the basin due mainly to the combined effects of a cool palaeothermal history and low organic carbon content.
Seismicity of the Cyprus region
Authors: Ambraseys N.N. , Adams R.D.
Published: July 2007

We have used a combination of macroseismic and instrumental techniques to re‐evaluate the seismicity of Cyprus and the surrounding region for the period 1890–1900. We identified 56 events which we believe to have a surface‐wave magnitude (Ms) of 4.5 or greater. Early events are located by felt effects alone, and macroseismic information is used to improve the location of many later events. We find the broad pattern of seismicity follows that given by standard listings: an area of weak seismicity to the north‐west of Cyprus in the Gulf of Antalia includes intermediate‐depth events as are found in the Hellenic Arc to the west; a gap of reduced activity separates this activity from that of the main region of Cyprus, where we could find no evidence for sub‐crustal foci; there appears to be no present seismological connection along the presumed plate boundary to the north‐east to the junction of the East Anatolian fault and the extension of the Dead Sea rift system. We find a much greater level of activity in the first part of this century than is given in the standard listings, such as that of the ISC. Up to 1963 we identified 47 events of Ms > 4.5, compared with only 10 given in the ISC files. Recent improved station coverage locates more events in the region, but these have not been of large magnitude, and the moment release in recent decades has been appreciably less than earlier in the century. For the events in our list the total moment release is 2.7x 1019 Nm with 75% of this originating in the main Cyprus region. We reaffirm the danger of uncritical use of standard earthquake listings for tectonic interpretation and in particular for hazard evaluation in areas such as this, where neither the historical nor the instrumental seismicity record is complete.
Extension of global creepex definition (Ms‐mb) to local studies (Md‐ML): the case of the Italian region
Authors: Panza G.F. , Prozorov A.G. , Pazzi G.
Published: July 2007

Creepex, defined as the systematic deviation of the magnitude of a single earthquake from the linear orthogonal regression between local magnitude ML and coda duration magnitude Md, calculated for the whole region, is used as a measure of the frequency content of the seismic sources in the Italian region. Predominantly high‐frequency events are found in the two areas of Quaternary tectonic shortening in North‐Central Italy and in the Calabrian Arc. This result, confirmed by two independent statistical tests, is in agreement with the global pattern obtained from the study of the regression between body‐wave magnitude, mb, and surface‐wave magnitude Ms: systematic shift to high frequencies in the energy release of seismic sources located in subduction zones and to low frequencies in zones of spreading. The analysis of the correlation between the patterns of heat flow and of seismic source spectral properties indicates that these source properties, in general, do not reflect thermal conditions in the lithosphere, but rather represent the result of tectonic processes.
The MARMARA Poly‐Project: tectonics and recent crustal movements revealed by space‐geodesy and their interaction with the circulation of groundwater, heat flow and seismicity in Northwestern Turkey
Authors: Schindler C.
Published: July 2007

An interdisciplinary project of ETH Zurich, in collaboration with Turkish universities, is described. The research area of NW Turkey was chosen because it exhibits active crustal movements, pronounced seismicity, elevated heat flow, and characteristic deep groundwater circulation patterns. In order to elucidate the interrelations between these features the collaboration of different specialists is required. Among the disciplines employed are geology, tectonics, seismology, geodesy, hydrogeology, and geothermics.
The Erzincan earthquake of 13 March 1992 in Eastern Turkey: tectonic aspects
Authors: Trifonov Vladimir G. , Bayractutan M. Salih , Karakhanian Arkadiy S. , Ivanova Tamara P.
Published: July 2007

The tectonic significance of the Erzincan earthquake of 13 March, 1992 in Eastern Turkey is discussed. The intersection of the North Anatolian and The East Anatolian strike‐slip fault zones has resulted in formation of the Erzincan pull‐apart basin and new seismically active fault branches on its northeastern side. Local concentrations of surface ruptures strike along the most active branches of the North Anatolian fault zone (N300W) for 62 km. They are usually open fractures with northeastern sides uplifted up to 20 cm and rarely with dextral offset up to 10 cm. These secondary ruptures manifest indirectly oblique seismic fault displacement corresponding to the Late Quaternary motion on the fault zone, although at the surface the dextral component has been suppressed relative to the vertical one.
On the structure and formation of fracture zones
Authors: Gudmundsson Agust
Published: July 2007

Studies of the oceanic fracture zones, as well as field observations of the on‐land parts of a fracture zone in Iceland, show that there are numerous tension fractures, normal faults, small‐scale grabens and dykes within, and trending subparallel with, the fracture zones. These structures indicate that, in addition to the shear displacement, there is considerable extension associated with the development of fracture zones and that many of them may be regarded as complex graben structures. The ridges surrounding the continents of Africa and Antarctica are examples of mid‐ocean ridges that are moving away from the continental margins where they originated and therefore expanding. Here it is suggested that as the perimeter of an expanding ridge increases, the tensile stresses associated with the ridge extension may contribute to the formation of fracture zones.
Stable isotopic calibration of the earliest skeletal fossil assemblages in eastern Siberia (Precambrian‐Cambrian boundary)
Authors: Brasier M.D. , Khomentovsky V.V. , Corfield R.M.
Published: July 2007

Sections from the eastern margin of the Siberian Platform provide important reference sections for stable isotopic correlation of the newly defined Precambrian–Cambrian boundary level since they contain some of the earliest pre‐Tommotian shelly fossil assemblages known, and are amenable to δ13C stratigraphy. Stable isotopes are examined from the Dvortsy and Ulakhan–Sulugur sections (River Aldan), where sparse pre‐Tommotian assemblages occur, and from the Uchur River region, where the putative Anabarites trisulcatus and Purella antiqua Zones of the Nemakit–Daldynian Stage are well‐developed. Diagenetic resetting of δ18O and δ13C must be taken into account when comparing such sections. Simple corrections allow for stable isotopic correlation of basal Nemakit–Daldynian and Tommotian strata across eastern Siberia.
Possible reasons for the δ13C anomaly of Lower Proterozoic sedimentary carbonates
Authors: Tikhomirova M. , Makarikhin V.V.
Published: July 2007

Detailed isotopic study (δ13C, δ18O) of Lower Proterozoic sedimentary carbonates from biostratigraphically dated successions in Karelia (Russia) revealed a large positive δ13C anomaly (average δ13C‐value constitutes approximately +10‰ PDB) at 2.3 Byr ago and a huge drop of δ13C‐values in the subsequent ‘black shale period’(2.2 Byr ago). These data are interpreted to be a result of large‐scale changes in the oxygen content of the atmosphere. According to this model the positive carbon isotopic anomaly of sedimentary carbonates at about 2.3 Byr ago reflects a very high O2‐content of the atmosphere at this time; the subsequent drop in δ13C‐values equates with a sharp decrease of the O2‐content of the atmosphere.
Prognosis of pool phase state and hydrocarbon fluid composition for the Pre‐Caspian OGP
Authors: Nechaeva O.L. , Graizer E.M.
Published: July 2007

The results of detailed studies and interpretations are presented for composition variations, structural properties and the phase state of hydrocarbon fluids from subsalt pools of the Pre‐Caspian depression. These data serve as a basis for substantiating the existence of several types of condensate, and identifying the locations of the main centres of fluid generation. The basic geological‐geochemical conditions controlling the composition of condensate and free gases have been determined as well as their present phase state. A set of basic criteria is proposed as well as prognostic maps for the condensate and free gas composition, and the pool phase states.
Topography, climate and ice masses: a review
Authors: Kerr Andrew
Published: July 2007

Topography acts as a filter between regional climate and the consequent response of a glacier or ice sheet. It influences the mass and energy inputs and modifies the ice dynamics. The evolution of the ice sheet surface and, over longer time scales, of the bed topography modulates the climatic forcing.

Until we have a better understanding of these topographic linkages, the use of geophysical signals from former ice masses to determine palaeoclimates must be regarded as fundamentally flawed.
On the emergence of life via catalytic iron‐sulphide membranes
Authors: Russell Michael J. , Daniel Roy M. , Hall Allan J.
Published: July 2007

We propose that the precipitation of a gelatinous iron‐sulphide membrane is the necessary first step towards life. Membrane vesicles were inflated with alkaline, sulphide‐bearing hydrothermal (<200°C) solution and grew on a submarine sulphide mound in acid iron‐bearing Hadean seawater. Once a critical size had been reached (0.1–1 mm) vesicles would have budded contiguous self‐similar daughters. We assume that the membrane was rendered insulating by the adsorption and/or oxidative precipitation of organic and organosulphur compounds. As a consequence of the naturally induced proton‐motive (chemiosmotic) force, and the activity of the iron monosulphide redox catalysts within the membrane, organic compounds would have accumulated within the vesicle. Osmotically driven growth therefore became more significant with time. The geochemical environment envisaged as responsible for this first step towards life is consistent with that widely accepted for the early Earth.
Search for solar periodicities in Miocene tree ring widths
Authors: Kurths J. , Spiering Ch. , Müller‐Stoll W. , Striegler U.
Published: July 2007

We have analysed ring‐width records of two Miocene coniferous trees with an absolute age of 15–20 million years. Such data may reflect solar periodicities from the prehistoric past. Evidence for a main period of ∼ 12.5 years has been found. This is near the present basic solar activity period of ∼ 11 years. Other periodic components appear at 220, 150 and 53 years, respectively, which may also be related to solar variations.
Contemporary state of stress and neotectonic deformation in the Carpathian‐Pannonian region
Authors: Becker Arnfried
Published: July 2007

The Carpathian‐Pannonian region has been characterized by a two‐stage tectonic evolution since the beginning of the Neogene. During early and mid‐Miocene the lateral eastward escape of the Pannonian Fragment caused thrusting and folding in the Outer Carpathian Mountains, south‐ and westward directed subduction of the Eurasian lithosphere, calc‐alkaline volcanism along the Inner Carpathian bend, and localized fault‐controlled subsidence of basins in the Pannonian region. This style of tectonic deformation ceased by the end of the mid‐Miocene. The neotectonic stage began in the late Miocene. It is characterized by differential regional subsidence with maximum rates in the west and east and minimum rates in the centre of the Pannonian Basin. Further characteristics of the central Pannonian Basin are the anomalous high heat flow values, the thin crust and lithosphere.

The neotectonic stress field has been determined by in situ stress measurements, the analyses of borehole breakouts and fault‐plane solutions of earthquakes. In situ stress measurements by the doorstopper and triaxial strain cell methods indicate high compressional stresses in the western Pannonian Basin with its maximum in WNW‐ESE to NW‐SE direction. In contrast to its western part, the central Pannonian Basin shows tensional stresses near the Earth's surface with maximum tension in the same WNW‐ESE direction. Borehole breakout data indicate a general WNW‐ESE orientation of maximum horizontal stress in the western part of the Pannonian Basin and in the eastern part as well, whereas in the central Pannonian Basin this direction is the preferred azimuth of minimum horizontal stress.

It is suggested that the neotectonic deformations and stresses in the Carpathian‐Pannonian region have a sublithospheric origin.

Asthenospheric convection with an upwelling mantle flow below the centre of the Pannonian Basin and downwelling flows along the cold lithospheric roots below the eastern Carpathians and the Alps seems to be most plausible. Accordingly, the relative uplift of the central

Pannonian Basin, the high heat flow and also the tensional stresses are explained as the surface expression of an upstreaming branch of a localized convection cell below the Pannonian Basin.
Reassessing intensity of some Friuli earthquakes at the turn of the eighteenth century
Authors: Barbano M.S.
Published: July 2007

During 1770–1820 Northeastern Italy was hit by a series of high intensity earthquakes affecting the Piedmont area of Friuli from Maniago to Tolmezzo. Greater knowledge of these events, which seem to be extremely circumscribed and to have damaged only a small number of localities (1776, 1789, 1794: Tramonti; 1788, 1790: Tolmezzo; 1812: Cavasso), could make a significant contribution towards defining better the potential seismic hazard in Northern Friuli. A review of these shocks has been undertaken within the framework of activities organized by the macroseismic working group of the National Group for Protection against Earthquakes (GNDT). The critical revision of the information gathered by the programme ‘analysis through the compilations’, has stressed the need for a new interpretative method and for great caution to be exercised when assessing reliable intensity degrees, to avoid possible inconsistencies in their values. This preliminary investigation allowed us to identify both doubtful and some misestimated shocks. A rough macroseismic intensity distribution pattern of each event, showing that the earthquakes were felt over an area (including Italian, Slovene and Austrian territories) coherent with the epicentre intensity, has been also delineated.
Fake quakes in Italy through parametric catalogues and seismological compilations: case histories and typologies
Authors: Bellettati Daniela , Camassi Romano , Molin Diego
Published: July 2007

The Italian catalogue contains many earthquakes of moderate to high epicentral intensity which are located in areas of low seismicity and near big cities. Some of them have been inserted in the catalogue after one historical record only. This study investigates many such events in the 1000–1690 time‐window showing that a great number of them are fake.

Starting by an operational definition of ‘fake quake’, this paper shows the procedures adopted, and the main results which contribute in a significant way to the reassessment of seismicity and seismic hazard.
A ‘cluster’ of earthquakes in the Apennines at the end of XIII century
Authors: Castelli Viviana
Published: July 2007

The assessment of seismicity in many areas of Italy hinges on poorly known earthquakes listed by the seismic catalogue on the grounds of single, poor quality data taken from seismological compilations which, in most cases, did not adopt a consistently critical outlook in processing their miscellaneous information. Starting from such datasets it was easy to misunderstand, lose and duplicate evidence and events. This study was initiated to see whether better results might be attained by a more careful reprocessing of the same data already gathered by compilations. Six important, but poorly known, earthquakes were listed by the Italian catalogue in the selected time‐window (1292–1294): according to the results of the study one of them is to be back‐dated by a century, three others should be reduced to one, another can be confirmed and the last one is a fake.

The author is indebted to Paola Albini, Romano Camassi, Magda Minoli, Laura Mucci and Massimiliano Stucchi for moral and material support.
Monsoon‐induced sea surface temperature changes recorded in Indian corals
Authors: Chakraborty S. , Ramesh R.
Published: July 2007

The South Asian Summer Monsoon induces vertical mixing in the surface Arabian Sea, leading to a reduction in the Sea Surface Temperature (SST) of the order of 3–4°C. This reduction in temperature is recorded by modern corals (Porites) that grow in the Lakshadweep Islands (coralline islands located at about 350 km off the south‐west coast of India) in their stable oxygen isotope ratios (denoted by δ18O). As large coral colonies of this genus are available, our results show that palaeomonsoon records for a few centuries back in time, a crucial input for climatic models aimed at predicting the Asian Monsoon, can be obtained from these corals. We also show that two corals separated by ˜ 60 km show similar (518O variations as does a giant clam (Tridacna maximus) that grew near one end of the coral colonies. As this clam is known to precipitate CaCO3 in isotopic equilibrium with the ambient sea‐water, it is possible to estimate the isotopic offset of coralline δ18O from that of the CaCO3 precipitated in isotopic equilibrium. This ‘disequilibrium effect’ appears to be constant around 4.5±0.2%0. Our calculations show that SST (t, °C) is related to the coral δ18O (δc) and the sea‐water δ18O (δw) by the equation t = 3.0–4.68 (δc ‐ δw), which is in good agreement with such relationships for corals from the Pacific and Atlantic.
Epibiont shadowing: a hitherto unrecognized way of preserving soft‐bodied fossils
Authors: Palmer Timothy J. , Taylor Paul D. , Todd Jon A.
Published: July 2007

Outlines of soft‐bodied sessile epibionts that grew attached to the surfaces of calcareous shells in ancient seas are sometimes preserved by a process termed ‘Epibiont Shadowing’. Processes that altered the surface of the shell were prevented from happening immediately beneath the attached epibiont, leaving a shadow of its attachment site following its death and decay. Microboring around the perimeter of the epibiont by presumed endolithic cyanobacteria gave rise to Endolithic Shadows, and dissolution of the calcareous substrate, maybe beneath larger smothering organisms, produced Solution Shadows of smaller organisms that protected their sites of attachment from such etching effects. Recognition of this type of preservation allows the stratigraphic range of certain soft‐bodied groups to be extended. Details of the shadows may yield information about the morphological construction of the groups in question.
Structural and lithological controls on coastline profiles in Fife, Eastern Britain
Authors: Ringrose Philip S.
Published: July 2007

The coastline of southern Fife on the east coast of the British Isles is presented here as an illustration of geological influences on spatial variability at different lengthscales. The coastline profile of Britain is widely referred to as an example of fractal geometry, as presented in Mandelbrot's (1967) original paper on statistical self‐similarity. I show here that at different lengthscales, different geological processes dominate the character of the coastline profile, and that estimates of the fractal dimension are strongly dependant on the scale and choice of sample. Significant periodic components in the tortuosity of the coastline are evident, and can be related to the causative, scale‐specific, geological processes.
High‐temperature geothermal reservoir possibilities in Hungary
Authors: Stegena L. , Horváth F. , Landy K. , Nagy Z. , Rumpler J.
Published: July 2007

Theoretical studies have shown the possibility of high‐temperature (‘high enthalpy’) geothermal reservoirs in the pre‐Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén‐4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica‐thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations.
Recent trends in strontium isotope stratigraphy
Authors: McArthur J.M.
Published: July 2007

An introduction to Sr‐isotope stratigraphy can be obtained from several recent reviews (Elderfield, 1986; Veizer, 1989; McArthur, 1991, 1992a). The purpose of this article is not to repeat these reviews but to give to those not expert in the field, but who may be prospective users, a summary of aspects of the method not covered elsewhere, and some examples of recent applications of the technique and the problems that affect it. Highlighting problems inevitably means highlighting the publications in which they occur; I hope the authors will forgive me for spotlighting their work. Neither is this article intended to be a review of all that has been written on the use of Sr isotopes in low‐temperature geochemistry; it concentrates on their use in stratigraphy and dating, rather than how they may be used to elucidate geochemical processes. Many excellent papers are thereby excluded from consideration. Implicit in this article is the view that the successful application of strontium isotope stratigraphy requires an application of good methodology in both geochemistry and stratigraphy.
Closing‐up structures, alternatives to pull‐apart basins; the effect of bends in the North Anatolian Fault, Turkey
Authors: Neugebauer Joachim
Published: July 2007

Fault blocks passing bends or stepovers in a fault zone must adapt their margins to the uneven fault trace. Two cases of adaption are distinguished for extensional bends or stepovers (transtension): (1) The fault margins close up behind a single bend ('knickpoint') of a strike‐slip fault and a ‘closing‐up structure’ (new term) arises or (2) fault‐block margins are extended behind a releasing bend (double bend) or stepover parallel to the displacement and a pull‐apart basin originates. The dosing up described here is accomplished by acute‐angled synthetic strike‐slip faults that dissect the straight fault in front of a knickpoint to form a zig‐zag block boundary behind it. Crustal extension is also involved in the closing‐up structure, but in a different way from typical pull‐apart basins.

The closing‐up structure illustrated was developed behind an extensional knickpoint in the North Anatolian Fault west of Lake Abant, NW Turkey, where the process of closing up continues to this day. The kinematic model of this closing‐up structure is supported by displacements and ruptures observed during the 1967 Mudurnu valley earthquake and the 1957 Abant earthquake.
Ground effects in intensity scales
Authors: Serva Leonello
Published: July 2007

The use of ground effects for the evaluation of earthquake intensity is described and discussed. The importance of such effects, and the problems that arise when they are not properly considered, are analysed in particular. The opinions of many experts in the field, regarding the uselessness of such data because of their great variability, are refuted.
Mafic enclaves in granitoid intrusions: a catastrophic model of rheological behaviour
Authors: Pesquera A.
Published: July 2007

The significance of mafic enclaves as indicators of magma mixing processes between juxtaposed felsic and mafic magmas is evaluated from a rheological point of view. A qualitative model for explaining strain and morphological changes in the enclaves has been developed on the basis of the catastrophe theory.

Mafic enclaves in intrusive granitoids commonly behave as physical systems that can be described using a cusp catastrophe model. Their behaviour is characterized by bimodality, divergence and sudden changes, which are properties typical of this model. Accordingly, the presence of mafic enclaves showing variable strain and morphology within the same granitoid intrusion would be indicarive of mutual interaction and mingling between mafic and felsic magmas. Due to the characteristics of these processes, it is not possible to establish unambiguous age relationships between the two magmatic components.
Palaeozoic sequences and evolution of the Calabrian‐Peloritan Arc (Southern Italy)
Authors: Acquafredda P. , Lorenzoni S. , Lorenzoni E. Zanettin
Published: July 2007

Three Palaeozoic sequences belonging to three different basins crop out in the Calabrian–Peloritan Arc. Their age covers the time span from middle (?) Cambrian to early Carboniferous. The sequences comprise terrigenous, volcanic and carbonate rocks, and show low‐grade metamorphism. The basement is of pre‐middle Cambrian age, crops out in the Calabrian–Peloritan Arc, and was metamorphosed prior to the opening to the Palaeozoic basins.

The Palaeozoic basins existed no later than the middle Carboniferous, with inferred maximum crustal extension in the Cambro‐Ordovician. By Devonian time, the tectonic regime was compressional overall with middle Devonian island‐arc type volcanic activity that continued until the closure of the basins. Approximately 330 Myr, the Palaeozoic sequences experienced low‐pressure greenschist facies metamorphism and continuing subduction controlled the Variscan tectonogenesis with 280 Myr island‐arc type intrusive magmas. Subduction ceased and late‐stage 280–270 Myr granitic magmas were emplaced during continental collision.

The crustal sector carrying the Palaeozoic basins is interpreted as comprising fragments of an active continental margin, one of the several microplates, located at the southern margin of the Euro‐Asia continent which faced a large (at least 1500 km in width) ocean basin.
Palynological dating (Arenig) of the sedimentary sequence overlying the Ishkarwaz Granite (upper Yarkhun valley, Chitral, Pakistan)
Authors: Tongiorgi Marco , Di Milia Anna , Le Fort Patrick , Gaetani Maurizio
Published: July 2007

A sedimentary sequence overlying a granite pluton near Ishkarwaz (upper Yarkhun valley, Chitral, Pakistan; Karakorum Microplate) contains abundant, but poorly preserved, acritarchs probably referable to the late early Arenig‐early late Arenig interval. The palynological assemblages of Karakorum show a marked similarity to the cold water Peri‐Gondwana assemblages; i.e. to those of Li Jun's Arbusculidium‐Coryphidium‐Striatotheca‘Mediterranean’ Bioprovince. Biogeographical and geological comparisons suggest that, before the accretion of Cimmerian microplates to the Eurasian continent, the Karakorum Microplate was located along the northern margin of Gondwana in a latitude intermediate between the Mediterranean region and South China (Yangtze Platform).
Early Proterozoic regolith at Pasvik, NE Norway: palaeoenvironmental implications for the Baltic Shield
Authors: Sturt Brian A. , Melezhik Victor A. , Ramsay Donald M.
Published: July 2007

Regolith occurs at a number of localities along the northern margin of the early Proterozoic Pechenga Greenstone Belt marking a profound stratigraphic unconformity at the base of the 10 km thick Petsamo Supergroup. The age of regolith formation can be bracketed between 2.453 ± 42 Ga (Sm‐Nd) and 2.330 ± 36 Ga (Rb‐Sr). Regolith is developed on a varied substrate of Archaean rocks including early Proterozoic layered gabbros (2.45 Ga). The best example of the regolith occurs in the Pasvik valley at Brattli, Norway. Analogues are widespread on the Baltic Shield at the base of early Proterozoic ‘greenstone belts’ showing a low degree of chemical weathering and carbonatisation. Fluviatile deposits overlying the Brattli regolith preserve unweathered pyrite‐magnetite boulders and terrigenous pyrite grains. These features are considered to relate an arid or semi‐arid palaeoenvironment, possibly with some deficiency of oxygen in the atmosphere‐hydrosphere system. A systematic and well‐preserved regolith or palaeosaprolite at the base of the Petsamo Supergroup is proof that the northern boundary of the Pechenga Greenstone Belt is a fundamental first‐order unconformity. This places constraints on geotectonic modelling of this early Proterozoic rift‐basin.
THE IMPACT‐FLOOD CONNECTION: DOES IT EXIST?*
Authors: Deutsch Alexander , Koeberl Christian , Blum Joel D. , French Bevan M. , Glass Billy P. , Grieve Richard , Horn Peter , Jessberger Elmar K. , Kurat Gero , Reimold Wolf Uwe , Smit Jan , Stöffler Dieter , Taylor Stuart Ross
Published: July 2007

In a recent article inTerra Nova, Kristan‐Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research.
The geologist's dilemma: predicting the future behaviour of buried radioactive wastes
Authors: Chapman Neil A.
Published: July 2007

The last 10–15 years have produced a considerable amount of research into the geological disposal of radioactive wastes. This has had some very beneficial spin‐offs for the geosciences. There are, however, a number of areas where it is difficult for earth scientists to provide quantitative information required for the types of long‐term safety assessment being performed at present. With the likely increased stringency with which we may begin to treat other industrial wastes, much is to be learned from the radioactive waste experience. This article reviews some of the geological issues in constraining long‐term predictions, discusses how geological data are used, and questions exactly what it is that we are trying to achieve in the management of these wastes and in the regulations concerning their disposal.
Geophysical interpretation of a high‐resolution seismic refraction profile in the Northern Apennines
Authors: Biella Giancarlo , De Franco Roberto , Demartin Martina , Barzaghi Riccardo , Sanso Fernando , Sguerso Domenico
Published: July 2007

A combined seismic and gravimetric interpretation in the Northern Apennines area (Italy) is presented. To the knowledge of the authors, this is one of the few attempts to apply tomographic methodology to a seismic refraction profile. This procedure, together with the classical interpretation for defining lower reflectors, led to the formulation of quite an accurate model of the upper crust. A gravity analysis was performed concurrently taking into account the seismic results at different depths which correspond to different frequency domains in the gravity signal. While the medium‐ and high‐frequency patterns have been solved by trial‐and‐error, the regional trend has been modelled applying the collocation procedure to the gravity data.
Collision tectonics in the late Precambrian Eastern Ghats Mobile Belt: mesoscopic to satellite‐scale structural observations
Authors: Chetty T.R.K. , Murthy D.S.N.
Published: July 2007

Regional mapping of a section across the Eastern Ghats Mobile Belt (EGMB) north of the Godavari graben in Eastern Peninsular India by using Landsat Thematic Mapper data enables recognition of a number of shear zones, lineaments, and structural domes and basins. A conspicuous megashear occurs at the western boundary of the granulite facies rocks of the EGMB adjacent to the Archean granite‐greenstone craton. The confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature. The strike extensions of this shear belt extend through to the Elchuru alkaline complex, Prakasam District, Andhra Pradesh, and the syenite plutons of Koraput district, Orissa. The contrasting lithologies, metamorphism and structural history on either side of the shear zone suggests that it might be a Precambrian suture zone.

The mesoscopic structural features in the EGMB include prominent foliation with moderate to steep dips, folds, faults/shears, S‐C fabrics, pinch and swell structures and other linear fabric elements. These observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence. The major rock units in this part of EGMB comprise garnetiferous sillimanite gneisses, quartzites and calc‐granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks. The contact of the two rock units is generally sheared and often migmatised.

The structural fabric suggests two major tectonic events: an essentially horizontal tectonic regime resulting in thrust systems and associated structures, subsequently followed by strike‐slip tectonics characterized by high shear strains. Features such as westward‐verging thrusts, large‐scale recumbent folds, major shear zones, structural domes and basins, indications of tectonic crustal shortening, extensive calc‐alkali magmatism and widespread migmatization in the region are attributed to collisional processes during Proterozoic times. The spatial disposition of the EGMB and its linkage with the distribution of similar rock units during the late Precambrian time in a global tectonic scenario are discussed.
Seismotectonics of the 20 October 1991 Uttarkashi earthquake in Garhwal, Himalaya, North India
Authors: Thakur V. C. , Kumar Sushil
Published: July 2007

The 20 October 1991 Uttarkashi earthquake killed over a thousand people and caused extensive damage to property in the Garhwal Himalaya region. The body wave magnitude of the earthquake was 6.6, and the fault plane solution indicates reverse faulting. The hypocenrre was located at a focal depth of about 12 km between the Chail and Jutogh Thrusts, but movement propagated southward along the Jamak–Gangori Fault (JGF) and Dunda fault (DF) which are developed as blind faults related to the growing Uttarkashi antiform.
The Uttarkashi earthquake of 20 October 1991: field observations
Authors: Kumar Surendar , Mahajan A. K.
Published: July 2007

The epicentre of the destructive 20 October 1991 earthquake is in the north‐east of the Uttarkashi region of the Higher Himalaya. The earthquake was felt up to 250–350 km away from Poh and Keylong in the north to Delhi in the south and beyond Chandigarh in the west. Seismologists of the Seismotectonic Group of Wadia Institute of Himalayan Geology studied fissures, surface breaks, and the foreshock and aftershock activity caused by this event. Land fissures show normal dislocations of 0.06–1 m, run E‐W and NE‐SW in the epicentral region and could be followed for 30–40 km.
Debate about ironstone: has solute supply been surficial weathering, hydrothermal convection, or exhalation of deep fluids?
Authors: Kimberley Michael M.
Published: July 2007

Ironstone is any chemical sedimentary rock with > 15% Fe. An iron formation is a stratigraphic unit which is composed largely of ironstone. The solutes which have precipitated to become ironstone have dissolved from the Earth's surface, from the upper crust, e.g. the basaltic layer of oceanic crust, or from deeper within the Earth. Genetic modellers generally choose between surficial weathering, e.g. soil formation, and hydrothermal fluids which have convected through the upper kilometre of oceanic crust. Most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering. However, both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater. Evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal Venezuela. A deep‐source origin for ironstone has wide‐ranging implications for the origins of other chemical sedimentary ores, e.g. phosphorite, manganostone, bedded magnesite, sedimentary uranium ore, various karst‐filling ores, and even petroleum. Preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models.
Role of melt during deformation in the deep crust
Authors: Davidson Cameron , Schmid Stefan M. , Hollister Lincoln S.
Published: July 2007

Deformation in the deep crust is strongly influenced by the presence of melt. Injected melt (or magma) weakens the crust because strain will tend to localize where melt is present. The amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate. For plutons that intrude into rocks which are near the solidus temperature of the melt, crystallization times can be quite long (> 1Myr).

Partial melting of deep crustal rocks can lead to melt‐enhanced embrittlement. This occurs because the volume change for most melting reactions is positive. Therefore, when the rate of melt production outpaces the rate at which melt can leave the system, the melt pressure increases. Eventually, the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture.

Conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the Central Gneiss belt (Canada); this suggests that melt‐enhanced embrittlement occurred in these rocks. An expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived. Assuming that migmatite has a small tensile strength, differential stresses are ≤ 20 MPa in migmatitic rocks at the time melt‐enhanced embrittlement occurs. The occurrence of melt‐enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting. Furthermore, repeated episodes of melt‐enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains.