bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cooling evidence from Pleistocene shelf assemblages in SE Sicily
Authors: Di Geronimo I. , Di Geronimo R. , La Perna R. , Rosso A. , Sanfilippo R. 
Published: April 2008

Abstract

A short Lower Pleistocene section, cropping out in SE Sicily, is studied. The sequence mainly consists of richly fossiliferous sandy layers with
Arctica islandica
, deposited in mid-shelf environments. Molluscs, bryozoans, serpuloideans and calcareous algae are investigated, to identify species with palaeoclimatological implications. Apart from some well-known North Atlantic molluscs, other species are identified as palaeoclimatological tools. Cooling evidence is provided by such palaeoclimatological indicators and by the increasing shell size in some species.
Palaeoceanography and numerical modelling: the Mediterranean Sea at times of sapropel formation
Authors: Rohling E. J. , De Rijk S. , Myers P. G. , Haines K. 
Published: April 2008

Abstract

Palaeo-circulation concepts based on (micro-)palaeontological records are compared with results of a general circulation model (GCM), in a review of the eastern Mediterranean conditions during sapropel S1 deposition (7–8ka
bp
). We discuss two conceptual models, based on proxy data, which integrate bottom water anoxia and high productivity during sapropel formation. One infers a weakened version of the present-day anti-estuarine circulation, whereas the other invokes a reversal of the circulation to an estuarine type. Although both seem reasonable, in view of the available palaeoceanographic proxy data, they imply completely different states of the Mediterranean fresh-water budget. Numerical modelling has been based on three available reconstructions of changes in the west-east salinity gradient compared with present-day conditions (small decrease, intermediate decrease and reversing). The three scenarios give surprisingly similar results. The interface between the surface and intermediate water has shoaled significantly compared with the present, which fuels a deep chlorophyll maximum. All three simulations show stagnant deep waters, which could cause bottom water anoxia. Reversal of circulation is not observed, not even in the reconstruction of most extreme salinity changes. The combined approach of palaeoceanographic and numerical modelling reviewed in this paper shows that modelling provides an indispensable feedback on the viability of the various proxy-based conceptual models.
The contribution of Quaternary vertebrates to palaeoenvironmental and palaeoclimatological reconstructions in Sicily
Authors: Bonfiglio Laura , Marra Antonella C. , Masini Federico 
Published: April 2008

Abstract

In Sicily few studies have been devoted to the climatic-environmental changes of the Pleistocene and Holocene period. Most of the studies on Quaternary vertebrates in Sicily have been focused on the evolutionary-taxonomic aspects of the fauna. Sicily experienced at least four vertebrate dispersal events during Quaternary time, which are of different provenence (African and/or European) and have been controlled by filtering barriers of different intensities. The marked endemism and the extremely low diversity of the fossil assemblages of early and early-mid-Pleistocene time do not allow detailed interpretations. By way at contrast, younger assemblages are more diverse and, although they display some endemic characters, are similar to those of southern peninsular Italy. The late mid-Pleistocene and early Late Pleistocene assemblages (
Elephas mnaidriensis
faunal complex) are characterized by the occurrence of a red deer (
Cervus elaphus siciliae
), a dwarf fallow deer-like endemic megalocerine (
Megaceroides carburangelensis
), auroch (
Bos primigenius siciliae
), bison (
Bison priscus siciliae
), elephant (
Elephas mnaidriensis
), hippopotamus (
Hippopotamus pentlandi
), boar (
Sus scrofa
), brown bear (
Ursus
cf.
arctos
) and three large social carnivores (
Panthera leo, Crocuta crocuta
and
Canis lupus
). Most of these taxa, except for the megalocerine, are characterized by slightly reduced body size compared with the same taxa from mainland Europe. These assemblages are indicative of a climate with temperate, Mediterranean affinity and of landscapes in which forested areas were associated with more open environments. The relatively low abundance of the red deer and the dominance of the megalocerine in several assemblages suggests that a Mediterranean-type forest locally dominated some of the climatic phases. The assemblages of the youngest Late Pleistocene period on Sicily are characterized by a dramatic drop in diversity, with the disappearance of elephant, hippopotamus, bison, the endemic megalocerine, and the largest predators. This would indicate an environmental crisis probably linked to the drier climatic oscillations of late Pleniglacial time, as is suggested also by the spread of the ground vole, which is the dominant small mammal in several assemblages. The Late Glacial period is characterized by the spread of equids (horse and wild ass), which are indicators of open landscapes and of xerophytic steppe-like cover. The beginning of the Holocene period is characterized by the expansion of forested areas and by a more humid climate, as suggested by the abundance of red deer, and by the dispersal of the common dormouse (
Glis glis
) and water vole (
Arvicola
sp.).
Groundwater protection in a Celtic region: the Irish example
Authors: Misstear Bruce D. , Daly Donal 
Published: April 2008

Abstract
One of the key environmental objectives of the proposed EU Water Framework Directive is that Member States must prevent the deterioration of groundwater quality. A national groundwater protection scheme for Ireland has been published recently. This scheme shows certain broad similarities to the groundwater protection policy for England and Wales, incorporating the concepts of groundwater vulnerability, source protection zones and responses to potentially polluting activities. However, the Irish scheme is different in several important respects, reflecting the different hydrogeological conditions and pollution concerns in Ireland. Some of these hydrogeological conditions and pollution concerns are common to the other Celtic regions. A major feature of the Irish scheme is the importance given to subsoil permeability in defining groundwater vulnerability. At present, the subsoil permeability is classified in qualitative terms as high, moderate or low. For the protection scheme to be defensible, it is essential to adopt a systematic and consistent approach for assigning subsoil units to these permeability categories. In mapping groundwater vulnerability, it is also useful to take account of secondary indicators such as groundwater recharge potential, natural and artificial drainage density and vegetation characteristics. Another important issue in Ireland is the protection of groundwater in karst areas, since these areas are especially vulnerable to contamination.
The Triassic Sherwood Sandstone aquifer in Northern Ireland: constraint of a groundwater flow model for resource management
Authors: McNeill G. W. , Cronin A. A. , Yang Y. , Elliot T. , Kalin R. M. 
Published: April 2008

Abstract

The most important aquifer in Northern Ireland is the Triassic Sherwood Sandstone formation that lies under the urban area of Belfast and the areas to the east (Newtownards) and south (Lagan Valley) of the city. The management of this groundwater resource is important in providing a sustainable supply for both public and industrial users. A groundwater flow model that collated relevant meteorological, hydrological and hydrogeological information for the Lagan Valley and Newtownards areas was developed. This conceptual model was coupled with geochemical and isotopic data (using inverse modelling) to constrain the groundwater flow parameters. The results of
14
C-dating suggest some of the groundwater in the aquifer may be up to 4000 years old, and that structural controls play a major role in both the flow rate and the spatial distribution of groundwater within the Sherwood Sandstone aquifer.
Modelling the potential impact of climate change on a shallow coastal aquifer in northern Scotland
Authors: Malcolm R. , Soulsby C. 
Published: April 2008

Abstract
The potential impact of climate change on a freshwater wetland in a coastal dune system at St. Fergus, north-east Scotland, was assessed using hydrogeological modelling techniques. A range of climate change scenarios were input into a numerical model (MODFLOW) that had been calibrated for the site using contemporary field data. The combination of parameter and hydrogeological uncertainty in models, together with uncertainty over likely site-specific climate change in the future, dictates that such modelling studies are often inconclusive. Nevertheless, a range of scenarios was forecast which indicates that future average recharge and flooding of the wetland is likely to fall within the range of interannual variation observed at the site, regardless of whether recharge increases or decreases. It is therefore likely that any resulting ecological impacts will be limited and reflect subtle hydrological changes that will affect different species in different ways. The utility of such a modelling approach is in providing environmental managers with a range of likely scenarios that can be incorporated into future management plans and policies to maximize flexibility of response.
Mid- to Late Eocene organic-walled dinoflagellate cysts from ODP Leg 171B, offshore Florida
Authors: Van Mourik Caroline A. , Brinkhuis Henk , Williams Graham L. 
Published: April 2008

Abstract

The well-calibrated mid- to late Eocene sediment record of ODP Leg 171B (Site 1053A, Blake Nose) allows a detailed stratigraphic and palaeoenvironmental analysis of the dinoflagellate cyst (dinocyst) content. The recovered assemblages are a mixture of inner neritic, outer neritic and oceanic species. The autochthonous dinoflagellates, principally those of the
Impagidinium
group, indicate an oceanic milieu, with possibly some shallowing of water depth towards the top of the section. This trend is also indicated by a corresponding increase of inner neritic dinocysts. The close agreement in the abundance peaks of inner neritic dinocysts and terrestrial palynomorphs indicats that both are allochthonous. This is confirmed by the much higher number of neritic species found in JOIDES Holes 1 and 2, on the continental shelf of eastern Florida, immediately to the west of the Blake Nose. Lower-latitude species found in Hole 1053A, but not occurring at higher latitudes during late Eocene time, are
Diphyes colligerum
and
Thalassiphora delicata
. The presence of these, and other lower-latitude species, confirms that warmer-water conditions persisted during mid- to early late Eocene time in the vicinity of Site 1053. Eighteen new taxa are described, two of them formally:
Charlesdowniea proserpina
sp. nov. and
Oligosphaeridium anapetum
sp. nov.
Long-term thermal consequences of tectonic activity at Mount Isa, Australia: Implications for polyphase tectonism in the Proterozoic
Authors: McLaren S. , Sandiford M. 
Published: April 2008

Abstract

Mount Isa is a Palaeo-Mesoproterozoic terrane in Northern Australia characterized by >300 Ma of episodic tectonic activity prior to effective cratonization. This tectonic activity has resulted in dramatic changes in the heat production distribution in the crust and must have been accompanied by long-term changes in thermal regimes. Primary differentiation of crust initially enriched in heat producing elements has been achieved by felsic magmatism over much of the 300 Ma history, often associated with extensional deformation. The flux of heat producing elements from lower to mid-upper crustal levels associated with this magmatism was sufficient to cause long-term lower crustal cooling of at least 200°C. The accumulation of the radiogenic intrusives (which comprise
c.
230f surface outcrop and have heat production rates averaging 5.2 µWm
−3
) in the mid-upper crust resulted in a highly stratified heat production distribution. One consequence of this distribution is that small changes in the depth to this heat production, through processes such as deformation, erosion and the deposition of sediments, lead to significant changes in deep crustal temperatures (up to 100°C) and consequently lithospheric strength. These considerations suggest that the long-term evolution of the Mount Isa region partly reflects the progressive concentration of heat-producing elements in the upper crust leading to a long-term increase in lithospheric strength, and eventually to effective cratonization. The long-term cooling and strengthening trend was locally countered by the role of subsidence during basin formation which, through burial of heat producing elements in the existing crust and the accumulation of more heat production in insulating sediments, helped to localize subsequent contractional deformation.
The response of mineral chronometers to metamorphism and deformation in orogenic belts
Authors: Parrish Randall R. 
Published: April 2008

Abstract
Mineral chronometers, especially accessory minerals using the U-Pb decay system, can reveal important information regarding the environmental conditions and duration of metamorphic-deformation events during the re-working of older rocks. Minerals such as zircon can newly grow during amphibolite facies or granulite facies events, providing direct ages of metamorphism. Pre-existing minerals like monazite, allanite, and titanite can preserve a component of their original age in spite of upper amphibolite facies re-working and very thorough recrystallization of the rock fabric during mylonite development. The degree of Pb loss can be used to deduce, at least semi-quantitatively, the temperature and duration of the subsequent event. In well-studied examples, the relative retentivity of Pb is highly predictable, and this helps place strong constraints on relative closure temperatures, even when laboratory experimental data are lacking or inconclusive. A number of examples are presented from a wide variety of geological environments to illustrate the response of U-Pb isotope systematics within accessory minerals to superimposed deformation, metamorphism and/or mineral growth.
The effects of early Cambrian metamorphism in western Dronning Maud Land, East Antarctica: a carbon and oxygen isotope study of fluid-rock interaction in the Sverdrupfjella Group
Authors: Johnstone Warren P. , Harris Chris 
Published: April 2008

Abstract

The Sverdrupfjella Group in western Dronning Maud Land is a 1200 to 900 Ma orogenic belt that experienced a thermal overprint in the early Cambrian. Evidence for distinct episodes of fluid-rock interaction is found in calc-silicate rocks, veins and retrograde mineral assemblages. A sequence of altered but undeformed basalts exhibit extreme
18
O depletion (
δ
18
O as low as −1.8%) apparently due to interaction with meteoric water during regional (possibly early Cambrian) metamorphism. In the central Kirwanveggen, metasomatic calc-silicates, and retrograde mineral assemblages are associated with late high-strain zones of probable Cambrian age. The former have δ
13
C values which overlap those of massive metacarbonate units 150 km to the NE, and imply regional scale movement of fluids. The latter record
18
O depletion relative to unretrogressed equivalent rocks and suggest interaction with externally derived fluids.
The glacial transport and physical partitioning of mercury and gold in till: implications for mineral exploration with examples from central British Columbia, Canada
Authors: Plouffe A. 
Published: April 2008

Abstract

Mercury glacial dispersal was measured in the clay-sized fraction (< 0.002 mm) and heavy mineral concentrate (0.063–0.250 mm, specific gravity > 3.3 g/cm
3
) of till in a region of bedrock cinnabar occurrences, in central British Columbia, Canada. Most of the Hg in till occurs as sand-sized cinnabar (HgS) grains. A longer dispersal train was measured with the heavy mineral concentrates because Hg concentrations in heavy minerals yielded a higher ratio between anomalous and background concentrations when compared to the clay-sized material. It is proposed that geochemical or mineralogical analyses on a specific grain size fraction or density fraction of till, where the desired metal resides, result in a higher contrast between anomalous and background concentrations. Such a great contrast translates into a longer detectable dispersal train and hence, a larger target for mineral exploration. Therefore, in drift exploration programs, it is crucial to identify the mode of occurrence of a sought commodity in till; this can be achieved in part with a simple partitioning study whereby metal concentrations are measured in specific grain size fractions of till. Physical partitioning results for Au in the study area indicate that close to the bedrock source, large metal concentrations in some cases are present in the sand- (0.063–2 mm) and granule-sized (2–4 mm) fractions. Therefore, the significance of a regional Au anomaly, commonly defined in the silt plus clay-sized fraction of till could be evaluated by further determining the Au content of coarser size fractions (sand and granule).
The nature and tectonic significance of fault-zone weakening: an introduction
Authors: Rutter E. H. , Holdsworth R. E. , Knipe R. J. 
Published: April 2008

Abstract
Fault zones control the location, architecture and evolution of a broad range of geological features, act as conduits for the focused migration of economically important fluids and, as most seismicity is associated with active faults, they also constitute one of the most important global geological hazards. In general, the repeated localization of displacements along faults and shear zones, often over very long time scales, strongly suggests that they are weak relative to their surrounding wall rocks. Geophysical observations from plate boundary faults such as the San Andreas fault additionally suggest that this fault zone is weak in an absolute sense, although this remains a controversial issue. Our understanding of fault-zone structure and mechanical behaviour derive from three main sources of information: (1) studies of natural fault zones and their deformation products (fault rocks); (2) seismological and neotectonic studies of currently active natural fault systems; (3) laboratory-based deformation experiments using rocks or rock-analogue materials. These provide us with a basic understanding of brittle faulting in the upper crust of the Earth where the stress state is limited by the frictional strength of networks of faults under the prevailing fluid-pressure conditions. Under the long-term loading conditions typical of geological fault zones, poorly understood phenomena such as subcritical crack growth in fracture process zones are likely to be of major importance in controlling both fault growth and strength. Grain-size reduction in highly strained fault rocks produced in the plastic-viscous and deeper parts of frictional regime can lead to changes in deformation mechanisms and relative weakening that can account for the localization of deformation and repeated reactivation of crustal faults. Our understanding the interactions between deformation mechanisms, metamorphic processes and the flow of chemically active fluids is a key area for future study. An improved understanding of how fault- or shear-zone linkages, strength and microstructure evolve over large changes in finite strain will ultimately lead to the development of geologically more realistic numerical models of lithosphere deformation that incorporate displacements concentrated into narrow, weaker fault zones.
Implications of earthquake focal mechanisms for the frictional strength of the San Andreas fault system
Authors: Townend John , Zoback Mark D. 
Published: April 2008

Abstract
Analysis of stress orientation data from earthquake focal plane mechanisms adjacent to the San Andreas fault in the San Francisco Bay area and throughout southern California indicates that the San Andreas fault has low frictional strength. In both regions, available stress orientation data indicate low levels of shear stress on planes parallel to the San Andreas fault. In the San Francisco Bay area, focal plane mechanisms from within 5 km of the San Andreas and Calaveras fault zones indicate a direction of maximum horizontal compression nearly orthogonal to both subvertical, right-lateral strike-slip faults, a result consistent with those obtained previously from studies of aftershocks of the 1989 Loma Prieta earthquake. In southern California, the direction of maximum horizontal stress near the San Andreas fault is nearly everywhere at a high angle to it, similarly indicating that the fault has low frictional strength. Thus, along these two major sections of the San Andreas fault (which produced great earthquakes in southern California in 1857 and central and northern California in 1906), the frictional strength of the fault is much lower than expected for virtually any common rock type if near-hydrostatic pore pressure exists at depth, and so low as to produce no discernible shear-heating anomaly.

Our findings in southern California are in marked contrast to recent suggestions by Hardebeck & Hauksson that stress orientations rotate systematically within
c.
25 km of the fault, which prompted a high frictional strength model of the San Andreas fault. As we utilize the same stress data and inversion technique as Hardebeck & Hauksson, we interpret the difference in our findings as being related to the way in which we group focal plane mechanisms to find the best-fitting stress tensor. We suggest that the Hardebeck & Hauksson gridding scheme may not be consistent with the requisite
a priori
assumption of stress homogeneity for each set of earthquakes.

Finally, we find no evidence of regional stress changes associated with the occurrence of the 1992 M7.4 Landers earthquake, again in apparent contradiction with the findings of Hardebeck & Hauksson.
Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions
Authors: Boillot G. , Froitzheim N. 
Published: April 2008

Abstract
During the last 20 years, regional studies on the West Iberia margin and on the former margins of the Tethys have considerably advanced the understanding of processes related to continental break-up and the onset of sea-floor spreading. However, some questions remain outstanding. To tentatively answer these, a coherent interpretation of available data is proposed, based on the detachment fault concept applied to the continental as well as the oceanic lithosphere, and on the hypothesis of a multi-staged rifting process. The interpretation addresses the nature of the lower crust beneath non-volcanic passive margins, the origin of ophicalcites, the probable time gap between syn- or post-rift crystallization of gabbros and extrusion of basalts on the sea floor, and the significance of dipping reflectors within oceanic lithosphere adjacent to non-volcanic passive margins. The interpretation also considers the symmetry v. asymmetry of continental rifting and break-up, the location of the ocean-continent boundary, and the possible association of magnetic quiet zones with ultramafic sea floor (serpentinized peridotite) bordering non-volcanic passive margins.