bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative sea‐level change and carbon isotopes: data from the Upper Jurassic (Oxfordian) of central and Southern Europe
Authors: Jenkyns Hugh C. 
Published: July 2007

ABSTRACTStudies on Cretaceous pelagic limestones have shown a close correspondence between putative sea‐level curves and the carbon‐isotope profile, suggesting a possible relationship between the two phenomena. Such a relationship could relate to shelf‐sea area governing the global burial rate of organic carbon which, in turn, controls the13C/12C ratio of dissolved inorganic carbon in the oceanic reservoir. In order to see whether or not this relationship might be of more general applicability, the major mid‐Oxfordian (Jurassic) transgression is documented to zonal level and appropriate carbon‐isotope data are presented. Although the applicability of ammonite zonation to the mid Oxfordian is problematic on a regional scale, a clear δ13C excursion is present in thetrunsversariurnZone, which is coincident with regional overstep and/or evidence of shoreline retreat and/or evidence of bathymetric deepening in Europe and elsewhere. The use of the carbon‐isotope curve as a proxy for shelf‐sea area or relative sea level is worthy of further exploration.
Solid bitumens: an assessment of their characteristics, genesis, and role in geological processes
Authors: Mossman David J. , Nagy Bartholomew 
Published: July 2007

ABSTRACTFamiliar since antiquity, and subject in contemporary times to various characterization schemes, the exact nature of solid bitumen is not yet fully known. Bitumens have ‘random polymer‐like’ molecular structures, are mobile as highly viscous fluids or were once fluids but have since turned into solids. Solid bitumens consist mainly of large moieties, of polyclyclic aromatic hydrocarbons, occasionally with finely admixed, fine‐grained cryptocrystalline graphite. Solid bitumens are distinguished from kerogen, which is the syngenetic and generally finely dispersed particulate organic matter in sedimentary rock that virtually does not migrate following its deposition.Occurrences of solid bitumens are relevant to petroleum exploration as well as the search for, and evaluation of, a variety of metallic mineral deposits. Genesis of bitumen is in many cases linked to the thermal and hydrothermal history of organic matter in sedimentary rock. Apparently bitumen, or more specifically organic acids generated along with bitumen during diagenesis, may alter porosity of reservoir rocks or otherwise prepare the ground for ore deposition. Bitumen is also relatively sensitive to alteration processes, some of which, such as oxidative weathering, water leaching, biodegradation (contact) metamorphism and ionizing radiation may likewise affect its nature.Elemental composition of bitumen commonly reflects the nature of mineral deposits. Is is possible that in petroleum exploration, trace metal abundances of bitumen may eventually allow prediction of crude oil types and volumes anticipated from a given source rock? Beside transition elements, notably Ni and V, highly anomalous concentrations of U, Pt and Au occur in some solid bitumens.During the generation of petroleum from kerogen, the trend in δ13C is toward lighter values. The opposite seems to occur when liquid petroleum is subjected to thermal cracking (and /or related processes) yielding solid bitumen enriched in 13C, and isotopically light methane. In fact, except for deasphalting and possibly some irradiation processes, the result of thermal cracking, oxidation, water leaching, inspissation (drying) and bacterial degradation of crude oil is that lower molecular weight hydrocarbons are removed leaving bitumen residues enriched in aromatic hydrocarbons, heteroatomic compounds (NSO) and 13C. Such phenomena are relevant to bitumen paragenesis in petroleum reservoir rocks, to certain Phanerozoic occurrences of multiple generations of bitumens, and to bitumens in mineral deposits.
A widespread positive δ13Ccarb anomaly at around 2.33–2.06 Ga on the Fennoscandian Shield: a paradox?
Authors: Melezhik Victor A. , Fallick Anthony E. 
Published: July 2007

ABSTRACTCarbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ13C (PDB) spanning ‐ 20.5% to + 11%. A general δ13C secular trend shows that prior to 2.33 Ga values are typically ‘normal’ marine, averaging around ‐ 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ13C of around + 6%. Post‐Jatulian time is characterized by δ13C of sedimentary carbonates fluctuating between ‐ 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ13C between ‐ 14% and ‐ 6%. The c. 6% positive δ13C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of ‘red beds’, but does not coincide with the maximum of buried Corg mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ13C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the ‘Ronov ratio’, and/or ‘Broecker ratio’ and other possible models are discussed as the target for future investigations.
Global cooling inferred from dropstones in the Cretaceous: fact or wishful thinking?
Authors: Bennett Matthew R. , Doyle Peter 
Published: July 2007

ABSTRACTTraditionally, the Cretaceous has been considered as a long period of global warmth, a ‘greenhouse’ world. This view has been challenged in recent years by several lines of evidence; palaeobotany, stable isotopes, and palaeoclimatic modelling in particular. However, although these data demonstrate that cooling is likely, the only first‐hand evidence which demonstrates the presence of substantial ice build‐up in Cretaceous high palaeolatititudes are dropstones. These outsized or exotic clasts set in a fine‐grained sediment are often interpreted as a direct result of ice rafting. The reliability of this dropstone evidence and particularly its validity is questioned in demonstrating ice age interludes within the Cretaceous greenhouse.
Late Quaternary relative sea‐level changes and the role of glaciation upon continental shelves
Authors: Plag H.‐P. , Austin W.E.N. , Belknap D.F. , Devoy R.J.N. , England J. , Josenhans H. , Peacock J.D. , Petersen K.S. , Rokoengen K. , Scourse J.D. , Smith D.E. , Wingfield R.T.R. 
Published: July 2007

ABSTRACTSea levels of the past 20 kyr are largely determined by the response of the Earth to the last ice age. Consequently, sea‐level indicators are an important source of information about the interaction between cryosphere and hydrosphere and the solid Earth. Based on the material presented at a recent European Science Foundation conference, the present paper pin‐points some of the topics currently under discussion with respect to sea‐level evidence found on continental shelves. These topics include possible effects of erosion and changes in palaeotidal ranges on indicators of former relative sea levels as well as the problems involved in the determination of palaeo‐water depth in addition to former sea levels. More evidence is being gathered for substantial small‐scale patterns in the sea‐level changes at or nearby to the former ice margins. These patterns are not reproduced by the available geophysical models, which reconcile on first‐order level only the large‐scale pattern.
The Irish Variscides: problems, perspectives and some solutions
Authors: Keeley Martin L. 
Published: July 2007

ABSTRACTA review is presented of interpretations made to date of the Irish Variscides, and the various models of Late Palaeozoic crustal evolution. An examination is then made of the factors controlling Variscan strain in Ireland, including lithological competence, basement fabric and basement‐cover thickness. From this, the difficulties of recognizing Variscan ‘fronts’ and ‘fold belts’ are emphasized.In order to determine whether all putative Variscan strain is indeed Variscan. in age, new time‐temperature data (vitrinite reflectance; apatite fission track populations) are discussed, along with offshore data. A case is then presented for recognizing quite distinct episodes of both Variscan and post‐Variscan heating and deformation. Some of the implications for the Variscides to the east are briefly examined, and the suitability of a regional ‘escape tectonics’ model is tested.
Metamorphic decarbonation, silicate weathering and the long‐term carbon cycle
Authors: Bickle M.J. 
Published: July 2007

ABSTRACTThe seawater87Sr/86Sr curve implies a 50–100 Myr episodicity in weathering rate which requires a corresponding variation in CO2degassing from the solid earth to the atmosphere. It is proposed that this is caused by orogenesis, which both produces CO2as a result of metamorphic decarbonation reactions, and consumes extra CO2as a consequence of erosion‐enhanced weathering. Global climate on the geological time‐scale is therefore contTolled by the difference between the relatively large and variable orogenic‐moderated degassing and weathering CO2fluxes.
Magnification of undamped seismographs and the analysis of the 1906 San Francisco earthquake record obtained on the Vicentini seismograph in Zagreb (Croatia)
Authors: Herak Marijan , Allegretti Ivo , Duda Seweryn J. 
Published: July 2007

ABSTRACTA method to estimate the dynamic magnification of nonlinear seismographs is presented. The method was tested by applying it to the record of the 1906 San Francisco earthquake seismogram obtained on the Vicentini seismograph in Zagreb, in order to reconstruct the ground motion amplitudes. The magnitudes inferred from the corrected Vicentini recording of P‐ and surface waves are internally consistent (mb= 7.74, Ms= 8.48) and agree with the values published in various catalogues, within the error limits of magnitude determination for individual events. The corrected P‐waveform is compatible with a rupture slip profile exhibiting several distinct maxima along the 300 km‐long section of the San Andreas fault, in accordance with recent studies and contemporary geodetic measurements.
Magmatic and hydrothermal processes in the Bouvet Triple Junction Region (South Atlantic)
Authors: Simonov V.A. , Peyve A.A. , Kolobov V.Yu. , Milosnov A.A. , Kovyazin S.V. 
Published: July 2007

ABSTRACTResults of electron microprobe and microthermometric studies of samples collected from the Bouvet Triple Junction Region (BTJR) during a joint Russian‐Italian geological expedition on the R/V Academician Nikolaj Strakhov (1994) have revealed new data on the composition of basaltic magmas and oceanic hydrothermal fluids connected with magmatic processes. Detailed analysis of basaltic glasses shows that the modem Mid‐Atlantic Ridge (MAR) rift valley is composed of normal mid‐ocean ridge basalts with low concentrations of K2 O and TiOz (N‐MORB), while its flanks are more enriched with these components approaching E‐MORB. A marked influence of the Bouvet hot spot volcanism on magma generation on the South‐West Indian Ridge (SWIR) near Bouvet Island is observed. Basaltic melts in this area belong to alkalic and transitional series and have maximum contents of K2O, TiO2, H2O.Microthermometric analyses of fluid inclusions in the samples from the BTJR have revealed major differences in the oceanic hydrothermal fluid systems on the MAR and near SWIR, which depends on the peculiarities of magma. In the area of the MAR (with dry melts) only H2O solution inclusions in quartz were found; thus, seawater is probably the only primary source of hydrothermal fluids (NaCl + MgCl2+ H2O; T= 170–200°C). In the SWIR area (with the high content of water in melts) syngenetic liquid CO2 and H2O solution inclusions in quartz indicate the influence of the magmatic fluid component on the ore‐forming water/carbon dioxide solutions (NaCl + CaC12+ H2O + CO2; T= 200–310 °C; P= 900–1700 bar).
The 1 October 1995 Dinar earthquake, SW Turkey
Authors: Eyidoǧan Haluk , Barka Aykut 
Published: July 2007

ABSTRACTThe Dinar earthquake (Ms= 6.1, USGS‐PDE) of 1 October 1995 occurred on the NWSE‐trending Dinar Fault. The earthquake is associated with a 10‐km‐long surface rupture with predominantly normal faulting. The mainshock was preceded by a series of foreshocks that started 6 days before the mainshock and included two Md= 4.5 events. The mainshock source mechanism derived from the inversion of broad‐band P waves revealed that two sub‐events occurred on a NW‐SE trending normal fault with a small strike‐slip component. According to the source model estimated in this study, the first rupture started at a depth of about 8 km and reached to a depth of about 12 km propagating north‐west. The total seismic moment found from the inversion of P waveforms is 2.0 times 10 18 Nm. The seismic moment of the second sub‐event was about four times larger than the first one. Field observations, GPS measurements and slip vector obtained from the inversion of broad‐band P waveforms suggest that the NW‐SE trending Dinar Fault is due to the internal deformation of SW Anatolia moving south‐westwards.
History of the stereographic projection and its early use in geology
Authors: Howarth Richard J. 
Published: July 2007

ABSTRACTThe origin of the polar and equatorial stereographic projections can be traced back to Hipparchos (d. 125 bc). The equatorial projection became an essential tool in astronomy and from the 2nd to mid‐17th Century it enabled the development of the astrolabe as a navigational tool and later became important in mapmaking. Examples of equatorial stereographic nets by the astronomer al‐Zarqua&#x030c;la&#x030c; (ad, 10701 and the cartographer Blaeu (1624) are illustrated. By the early 19th Century, mathematics was beginning to be applied outside the fields of astronomy, physics and mechanics. The stereographic net was first applied to mineralogy by Neumann (1823) and its use was subsequently popularized by Federov (1892), inventor of the universal microscope stage, and by the introduction of the Wulff net (1902). It also proved of considerable use in the correct interpretation by W.L. Bragg of Laue X‐ray diffraction patterns of crystals which led to the development of X‐ray crystallography. The Lambert (1772) equal‐area projection, developed for cartographic use and subsequently termed the Schmidt net by Sander in 1925, was essential to the development of petrofabric analysis in the late 1920s. The transition to macroscopic structural analysis, which largely took place over the period 1930–55 is briefly touched upon.
A revised estimation of the steady‐state geotherm for the continental lithosphere and its implication for mantle melting
Authors: Zhou Shaohua 
Published: July 2007

ABSTRACTAn analytical solution has been derived for the steady‐state geotherm of the continental lithosphere, using an empirical thermal conductivity model that incorporates the experimentally observed temperature and pressure effect. Based on recent global compilations of crustal thickness and heat flow data, a standard continental lithosphere is re‐defined by a global mean model with total crustal thickness of 40 km and surface heat flow of 55 mWm‐2 (within which 28 mWm‐2 is assumed to be derived from deep mantle source). The thickness of the continental lithosphere (≅125 km), consistent with previous models, is given by the depth at which the geotherm intersects the potential asthenosphere temperature of 1280°C. It is shown that the new steady‐state geotherm is much hotter than that based on the previously adopted model where material thermal conductivity is assumed to be constant (≅3.14 W/m/k) throughout the lithosphere. The consequence of this re‐evaluation of pre‐extension thermal structure in the lithosphere is that the minimum stretching factor required to cause the onset of dry mantle partial melting can be 15–20% lower than the previous estimate. Also, if minor amounts of water or other volatile element or dry basalt are present in the upper mantle, melting of the subcontirfental mantle is very likely to occur for any geotherms constructed using surface heat flows > 30 mWm‐2.
The kinematic paradox of the San Andreas Fault
Authors: Doglioni C. , Harabaglia P. 
Published: July 2007

ABSTRACTThe Pacific‐North America plate boundary along the San Andreas fault system is notoriously a right‐lateral transpressive margin where both almost pure thrust and strike‐slip tectonics take place. The Pacific plate travels WNW, forming an angle of about 25° with the boundary. Since the Pacific is moving WNW faster than North America, right lateral transtension should result along the San Andreas system. North America, in turn, travels westward obliquely to the boundary and a left‐lateral transpressive component would be expected along the same margin. Therefore, the right‐lateral transpression of the San Andreas system can be partitioned into (i) a sinistral transpression along the southwestern margin of the North America plate obliquely overriding (ii) a faster right lateral transtension occurring along the transfer margin of the Pacific plate between the East Pacific rise in the California Gulf and the Gorda ridge to the north‐west. This is due to the oblique trend of the Pacific and North America plate margins with respect to their motion in a absolute reference frame.The geodynamics of California is marked by a unique setting in which there is a special subduction where, in contrast with classic subduction zones, the footwall of the subduction plane is obliquely diverging from the hanging wall in an E‐W section, while it is converging at slower rates in a NE‐SW direction. The extensional E‐W component is absorbed into the Basin and Range rifting, whereas the compressive NE‐SW component is mainly expressed in the Coast Ranges and California offshore. The compression perpendicular to the San Andreas is then not intrinsic in the strike‐slip movement, but it is rather an independent tectonic factor. Therefore, the San Andreas system cannot be considered as an archetype of a pure strike slip fault.
Evolution of the Archean‐Palaeoproterozoic Bundelkhand Massif, central India—evidence from granitoid geochemistry
Authors: Mondal M.E.A. , Zainuddin Syed M. 
Published: July 2007

ABSTRACTThe Bundelkhand massif of Archean‐Palaeoproterozoic age is primarily a granite‐gneiss complex. Three distinct granitoid suites have been identified within the massif hornblende granitoids, biotite granitoids and leucogranitoids, in order of decreasing age. These granitoids were emplaced in previously deformed basement consisting of gneisses, banded iron formations and other metasediments, mafic to felsic volcanics.The granitoids exhibit a large compositional range from quartz diorite to syenogranite and show a calc‐alkaline trend. They are metaluminous to peraluminous and have I‐type characteristics. The SiO2content ranges from 49 to 77 wt%. Low K2O/Na2O characterizes the granitoids. The oldest hornblende granitoids have low Rb and Yb contents compared to the younger biotite granitoids and leucogranitoids. Rb/Sr values for most of the granitoids are low (< 1). K/Rb ratios range from 95 to 373 which is, in general, comparable with other calc‐alkaline suites. Y/Nb ratios of the granitoids are > 1.2 which is a characteristic feature of magmas derived from sources chemically similar to island arc or continental margin basalts.The features mentioned above coupled with concentrations of Rb, Y, Nb, Yb, Ta and Th indicate a volcanic‐arc tectonic setting for the granitoids. It is proposed that the massif represents subduction‐related magmatism of an ocean in the southern part of the massif (an Andean plate margin).
A flow‐foliated ignimbrite related to the Åland rapakivi granite in SW Finland
Authors: Eklund Olav , Shebanov Alexey , Fröjdö Soren , Yli‐kyyny Kari , Andersson Ulf B. 
Published: July 2007

ABSTRACTA flow‐foliated felsic ignimbrite constitutes the uppermost lithological unit of the 1.58 Gyr anorogenic magmatic rocks in SW Finland. The ignimbrite is derived from an explosive eruption of hot (≅ 950 °C) phenocryst‐bearing A‐type (rapakivi‐type granite magma.The ignimbrite is close in composition to subvolcanic rapakivi granites that occur in the margins of the kand rapakivi batholith. The subvolcanic granites crystallized under a pressure of ≅ 1 kbar and at temperatures of about 650–700 °C. However, both major and rare earth elements show that the ignimbrite‐ forming magma was more fractionated than the magma forming the subvolcanic varieties.Supported by evidence of mafic‐felsic magma mingling, it is suggested that injection of hot mafic magma into a shallow magma chamber produced the high temperature of the ignimbrite‐forming magma. This injection increased the magmatic and the volatile pressure that caused the eruption of the dry felsic magma.
Tectonic setting of post‐orogenic granites within SW Fennoscandia based on deep seismic and gravity data
Authors: Andersson M. , Lie J. E. , Husebye E. S. 
Published: July 2007

ABSTRACTWithin the Svecononvegian Province of SW Scandinavia granite intrusions are abundant. Prominent ones are the Bohus‐Iddefjord and the Flå granites, the so‐ called Bohus‐Flå Granite belt. The age of these granites, consistent at ≅ 900 Ma, coincides with the late extensional stage of the Svecononvegian‐Grenvillian orogen. Gravity observations and deep seismic profiling lines are presented that also cover the Skagerrak Sea. The geophysical data suggest that the Bohus granite continues seaward for at least 80 km and its thickness, offshore, is estimated to be 2–4 km. Where the seismic profiling lines intersect the inferred seaward extension of the Bohus granite, a distinct reflection pattern is observed at ≅ 1.6 s. TWT. This coincides with a gravity modelled thickness of ≅ 4 km. The seismic profiles also show a large Moho offset beneath the modelled granite. It is proposed that this offset is related to Svecononvegian crustal underthrusting and that the granite melt could have formed by anatexis of mid‐crustal rocks downthrusted to greater depths in the vicinity of the seismically observed Moho offset.
Late‐orogenic Svecofennian deformation in SW Finland constrained by pegmatite emplacement ages
Authors: Lindroos Alf , Romer Rolf L. , Ehlers Carl , Alviola Reijo 
Published: July 2007

ABSTRACTLate stages of the Svecofennian orogeny in SW Finland were related to a tranpressional stress field and dextral movements along crustal scale shear zones under decreasing temperature and pressure conditions. In the Kemiö area, a minimum estimate for the time span of movements along one of these shear zones is obtained from the ages of 1840 to 1830 Myr‐old microcline granite sheets, related to early ductile deformation, and by dating structurally late rare‐mineral granite pegmatites, related to brittle deformation. One pegmatite was emplaced when the rheological conditions in the gabbro changed from ductile to semi‐ductile and brittle. It has U‐Pb ferrotapiolite ages ranging between 1807.0 ± 2.9 Myr (2 s̀) and 1803.1 + 2.9/ ‐2.0 Myr (2 s̀). Another pegmatite emplaced under brittle conditions has an U‐Pb ferrotapiolite age of 1802.9 ± 1.3 Myr (2 s̀). These pegmatites were emplaced preferentially in gabbroic rocks, that showed brittle to semi‐ductile deformation at a time when their more felsic host‐rocks still showed ductile deformation. The age range bracketed by the microcline granite sheets and the structurally late pegmatites indicates that ductile deformation related to the transpressional Late Svecofennian tectonic regime in southwestern Finland, persisted for at least 30–40 Myr.