bluuebunny/crossref_metadata_2025 huggingface dataset:
Size: all it’s shaped up to be? Evolution of shape through the lifespan of the Cenozoic bivalve
Spissatella
(Crassatellidae)
Authors: Crampton James S. , Maxwell Phillip A.
Published: April 2008

Outline shape is a key morphological character of infaunal bivalves that reflects both phylogenetic history and function. A new method of Fourier shape analysis has been used here to study the evolution of shape and size in the Cenozoic genus
Spissatella
(Crassatellidae), using material from New Zealand. The Fourier method can be used to construct a map of morphological ‘geography’, to generate synthetic average or extreme morphologies, and to visualize marginal growth fields and allometries. The results demonstrate that growth in
Spissatella
was strongly allometric and that differences between individual growth stages are commonly far greater than evolutionary changes in shape spanning 20 Ma. In all taxa, allometry was dominated by the relative elongation of the posterior margin with growth, an inferred functional adaptation for life in relatively high-energy environments. Heterochrony was the dominant evolutionary mechanism and, following an initial peramorphic expansion into morphospace, both paedomorphosis and peramorphosis probably occurred in approximately equal proportions. In general, it is not possible to decouple patterns of shape and size evolution. The data reveal no directional trends in evolution of these traits. The ontogenetic pathway followed by
Spissatella
may be a key genus-level taxonomic character and apparently represents a developmental constraint that largely controlled evolution within the genus.
Diversity, growth forms and taphonomy: key factors controlling the fabric of coralline algae dominated shelf carbonates
Authors: Nebelsick James H. , Bassi Davide
Published: April 2008

The fabric of biogenic carbonate sediments can be differentiated (1) with respect to diversity of constituent components, (2) using features pertaining to their growth forms and (3) upon consideration of taphonomic aspects. These not only determine limestone fabrics, but also form the basis for facies differentiation and palaeoecological interpretation.

This study is based on coralline algae dominated Lower Oligocene shelf carbonates from northern Slovenia from which seven facies (nummulitic, bivalve, foraminiferal-coralline algal, coralline algal, coralline algal-coral, coral and grainstone) are differentiated. The role of diversity, growth forms and taphonomy of coralline algae in each facies is discussed. Nine species from seven genera of coralline algae including geniculates and non-geniculates were recognized. Numerous different growth forms ranging from crusts, protuberances, lamellae to arborescent types are present. A wide range of taphonomic features including disarticulation, encrustation, fragmentation and abrasion can be observed.

The determination of diversity is dependent on taxonomic identification using preserved diagnostic characters relevant to palaeontological and botanical systematics. Growth-form determination in thin section is influenced by orientation and sectioning effects. The taphonomy of red algae is highly dependent on initial growth form and the specific environment in which they are found. A number of taphonomic processes described in Recent environments (e.g. disease, shallow grazing) cannot be ascertained in fossil material, while others are readily observable. Some taphonomic processes are detrimental (e.g. fragmentation, abrasion) to the preservation and recognition of vegetative and growth-form features, while others have positive effects (e.g. encrustation).
Factors regulating the development of elevator rudist congregations
Authors: Gili Eulàlia , Skelton Peter W.
Published: April 2008

Upper Cretaceous carbonate platform deposits show a widespread development of distinctive lenticular to tabular bodies of rock (lithosomes) formed by congregations of upright tubular (‘elevator’) rudist bivalves. Here we discuss the factors that regulated the initiation, consolidation and termination of such lithosomes, based on examples in the Santonian of the southern Central Pyrenees.

In the study area, rudist congregations developed between phases of sediment influx from neighbouring source areas. For the initiation of settlement, sedimentation rate evidently had to be very low or nil. The first rudist settlers both provided more hard substrates for subsequent recruitment, and fuelled the in situ formation of bioclastic sediment, leading to the embedding and consolidation of the congregation (both positive feedbacks to establishment). Thereafter, rudist density correlated with inferred sediment destabilization at the benthic boundary layer, which in turn affected rudist recruitment. Thus, successful rudist larval settlement declined with increasing numerical density of individuals in the congregation — a crucial negative feedback mechanism. The density of the rudist congregations could then have been maintained at more or less the same level through time by this stabilizing process. Finally, development of the rudist congregations ceased with progressive shallowing, usually involving reworking of their upper parts and/or burial by renewed influxes of sediment.
Geochemistry and provenance of Devono-Carboniferous volcano-sedimentary sequences from the Southern Vosges Basin and the geodynamic implications for the western Moldanubian Zone
Authors: Eisele Jürgen , Gertisser Ralf , Montenari Michael
Published: April 2008

The Southern Vosges host a volcano-sedimentary basin subdivided into a Lower Unit of Late Devonian age containing marine greywackes associated with bimodal volcanism, a marine Middle Unit (of Early Carboniferous age) and a terrestrial Upper Unit (of Late Carboniferous age), both accompanied by volcanism of intermediate to evolved composition. Petrographically and geochemically, sediments from the Lower Unit are characterized by mafic volcanic, sedimentary and metamorphic components and a positive Cr-Ni anomaly. A negative Nb anomaly weakens in the Middle and Upper Units. These units are dominated by intermediate to felsic volcanic detritus, and exhibit an enrichment in incompatible trace elements and disappearance of the Cr-Ni anomaly. The facies and composition of the volcano-sedimentary sequences indicate that an extensional basin existed in Late Devonian time (
c.
360 Ma). Subduction-related volcanism and successive closure of the basin occurred in the Lower Carboniferous (
c.
330 to
c.
325 Ma). Sedimentation graded from flysch into molasse in Late Carboniferous time, where terrestrial conditions indicate that continental collision had occurred. The volcanism reported here coincides with arc magmatism in the Mid-German Crystalline High and closure of the Rheno-Hercynian Ocean, which was possibly responsible for the geodynamic evolution of the Southern Vosges Basin.
Depositional and structural setting of the (?)Lower Old Red Sandstone sediments of Ballymastocker, Co. Donegal
Authors: McSherry M. , Parnell J. , Leslie A. G. , Haggan T.
Published: April 2008

Approximately 250 m of unfossiliferous sediments attributed to the Old Red Sandstone outcrop onshore at Ballymastocker, Donegal in northwest Ireland. Massive sandstones and trough cross-bedded sandstones pass upwards into coarse purple-brown basal conglomerates. The majority of the clast types, which include quartzite, marble, pelite, schist, vein quartz and metadolerite, are derived from the local Dalradian basement. Acid to intermediate porphyry clasts have no local source and may indicate a source to the northeast in the vicinity of the Devonian Lorne Plateau volcanic rocks in Argyll. The rocks are believed to represent an intermontane alluvial fan environment. The sediments occur in an outcrop of 3 km length against the northern flank of Knockalla Mountain, bounded to the southeast by the NE-SW-trending Caledonian Leannan Fault and resting on fractured Argyll Group Dalradian basement. No unconformable contact is observed and all contacts may be tectonic. Coarsening-up cycles within the sediments may reflect syn-sedimentary tectonic activity. The Devonian rocks are transected by a fracture system implying dextral transpressional activity on the Leannan Fault. The Dalradian basement rocks preserve evidence of sinistral strike-slip movement in late Caledonian times. Slickenfibres observed within the sediments and Dalradian rocks provide evidence for oblique dip-slip movement to the northwest. It is considered that these structures represent the last movement of the ORS basin, dropping it below denudation level, which resulted in its preservation. Movement along the Leannan Fault played a major role in the preservation of the offshore basins in the Islay-Donegal Platform region.
Palaeoenvironment of the plant bearing horizons of the Devonian-Carboniferous Kiltorcan Formation, Kiltorcan Hill, Co. Kilkenny, Ireland
Authors: Jarvis D. E.
Published: April 2008

The environment of deposition of the plant-bearing horizons of the Devonian-Carboniferous Kiltorcan Formation in Co. Kilkenny is poorly known. Previous studies suggested a possible lacustrine palaeoenvironment with plant material being swept in and fluvial conditions. Reinvestigation of the plant-rich localities on Kiltorcan Hill using both sedimentological facies and palynofacies suggests that there were high-sinuosity streams carrying fine-grained sediments with the plant fossils preserved on point bars, and marginal back-swamp conditions with plant material deposited close to the growth site.
Sedimentology, cyclicity and floodplain architecture in the Lower Old Red Sandstone of SW Wales
Authors: Love Susan E. , Williams Brian P. J.
Published: April 2008

The high-quality, laterally continuous coastal exposures of the Moor Cliffs Formation have allowed a highly detailed 2D reconstruction of the floodplain sediments and their contained pedogenic horizons to be made. The thick siltstone packages were actively deposited as finely laminated and rippled sheets, or as intraformational clasts forming larger bedforms. It is proposed that the unusual sediment geometries preserved are intimately related to the timing of land plant colonization of the Old Red Sandstone continent. Channels were extremely broad with low relief and flow over interfluvial areas was common. Evidence for ephemerality and regular desiccation is also closely related to the lack of rooted vegetation and not to palaeoclimate, which is postulated to be warm and seasonally wet. The low net sandstone (<10%) fluvial sediments are the product of deposition by shallow, high width to depth fluvial ‘channels’ flanked by broad, low-relief silty plains on which Vertisols formed. The reconstructions of this fluvial system reveal distinctive and systematic vertical and lateral variations in floodplain architecture and palaeosol development. Pedogenic maturity consistently increases with distance both vertically and laterally from channels. The vertical patterns of palaeosol development and maturity suggest that autocyclic processes of aggradation and avulsion predominated.
Introduction
Authors: Hart Malcolm B.
Published: April 2008

In recent years media attention has focused on global climate change and the impacts on the human experience that this may cause. This interest has stimulated earth scientists into a re-appraisal of the rates of change seen in the geological record and which, for years, had been taken for granted. Climatic modelling and other palaeoclimate assessments have reversed the geological adage that the ‘present is the key to the past’ into ‘the past may be the key to the future’. This renewed interest was the driving force behind the European Palaeontological Association’s Congress in Vienna.
Palaeoclimatic evolution in the Miocene from the Transylvanian Depression reflected in the fossil record
Authors: Chira Carmen , Filipescu Sorin , Codrea Vlad
Published: April 2008

The palaeoclimate during the Miocene of the Transylvanian Depression (Romania) is interpreted mainly by the response of calcareous nannoplankton, microfauna (foraminifera), molluscs and mammals (rhinoceros) assemblages.

The first significant palaeoclimatic event is recorded during the early Miocene. The climatic warming at the level of the Vima Formation was followed by a more important warming during the Eggenburgian, which is preserved in the fossil record of the Corus Formation. During the Ottnangian, a cooling episode is recorded in the Hida Formation, probably related to Atlantic and Boreal influences. The climate on land was probably subtropical, humid, but much cooler than the Eggenburgian, as the remains of rhinoceros from this formation indicate.

The Middle Miocene marine sub-tropical assemblages are present in the Dej Formation (early Badenian), but towards its upper part sub-tropical species become scarce. The endemic elements, with boreal influences, are recognized in Kossovian strata. On land, the Moravian rhinoceros also suggest a sub-tropical climate, with marshy, densely afforested areas. Another rhinoceros found in the upper part of the Moravian, indicates a tendency to the continentalization of the climate. The early Sarmatian began with short period of warming, followed again by a cooling episode (Feleac Formation).

The last significant warming is recorded in the Late Miocene, during the Pannonian (Lopadea Formation). The small aceratheres from the Pannonian suggest marshy areas with a relatively warm climate.
Late Miocene climatic cycles and their effect on sedimentation (west Hungary)
Authors: Korpás-Hódi M. , Nagy E. , Nagy-Bodor E. , Székvölgyi K. , Kovács L. Ó.
Published: April 2008

On the basis of sedimentological, well-log, palaeontological and pedological analyses of three Upper Miocene borehole sections from Hungary, a cyclic change of sediments from deltaic and alluvial depositional systems is presented, which is considered to have been driven by a cyclical change of the climate (temperature and precipitation). A delayed but positive correlation between the sedimentary cyclicity linked with fourth order sedimentary sequences, and a long-term cyclicity in temperature have been observed. Within this cyclicity, higher-order sedimentary changes are seen. They are interpreted as fifth order sedimentary cycles related, in turn, to short-term climate phases. Within a long-term cycle, four short-term climate phases are defined as a result of changes in temperature and precipitation: semi-arid, turning from warm-temperate to cold-temperate; humid, cold-temperate; warm-temperate with a warming trend, with average but decreasing precipitation; and warm-temperate, with average precipitation.
‘
Uisge Mèinne
’: mine water hydrogeology in the Celtic lands, from
Kernow
(Cornwall, UK) to
Ceap Breattain
(Cape Breton, Canada)
Authors: Younger Paul L. , LaPierre Anthony B.
Published: April 2008

Mining has historically made a major contribution to the economies of all the contemporary Celtic lands. At the start of the third Millennium, the bulk of mining activity has ceased, and problems associated with hydrogeological changes in abandoned mines are now common to all these lands. In global terms an unusually high proportion of mining in the Celtic lands has been by underground methods, a fact which is reflected in the range of hydrogeological problems encountered in these countries. Recent experiences in these countries offer insights which should be useful elsewhere when currently-active deep mines are eventually abandoned. Particular lessons are drawn from case studies and analyses of previously unpublished data from
Alba
(Scotland),
Ceap Breattain
(Cape Breton, Canada),
Cymru
(Wales) and
Kernow
(Cornwall). These lessons are:

(1)

The importance of recognizing the predominance of mined features in the post-closure hydrogeology of abandoned mines.

(2)

Dynamic temporal changes in hydrogeological behaviour arise from collapse of mined voids, caused by fluvial erosion by rapidly-flowing mine waters and/or by pneumatic fracturing by mine gases compressed in pockets during mine water rebound; these changes can have significant implications for human safety and environmental protection.

(3)

Net-acidic mine waters are generally restricted to situations in which high-sulphur strata are present in (i) recently-flooded deep-mine workings (ii) shallow partially flooded mine workings and (iii) perched groundwater systems in spoil heaps and opencast backfill.

(4)

Net-alkaline mine waters are associated with (i) low-sulphur strata in any hydrogeological setting and (ii) high-sulphur strata at depth in long-flooded workings. In practice, this means that the net-alkaline mine waters are far more abundant than the net-acidic.

(5)

The presence of limestone in a mined sequence is not on its own a guarantee that mine waters will be net-alkaline; the patterns of groundwater flow (which determine the transport of limestone dissolution products through the mined system) must also be favourable.

(6)

Mine water often becomes hydrochemically stratified during rebound. However, when discharge from a mined system commences, this stratification can break down, resulting in discharges considerably poorer in quality than would have been inferred by sampling the uppermost waters alone.
Groundwater protection in Scotland
Authors: Fox I. A.
Published: April 2008

The way in which groundwater protection policy is implemented in Scotland is briefly reviewed, before the current status (July 1999) is examined. Imminent changing circumstances, particularly the advent of the Scottish Parliament and the implications of the forthcoming Water Framework Directive are discussed and related to a review of current and proposed groundwater research and development projects which should take forward the protection of Scottish groundwaters in the new millennium.
Public water supplies from alluvial and glacial deposits in northern Scotland
Authors: Jones C. R. C. , Singleton A. J.
Published: April 2008

Surface runoff from upland areas in northern Scotland can be excessively coloured and turbid, making water treatment costs high. In contrast, groundwater has little colour or suspended solids, and has a more stable water quality, therefore treatment needs can be minimal. A number of public water supply schemes based on the development of groundwater in alluvial and glacial deposits are reviewed. These supplies range from major projects such as the 27 Ml/d Spey and 10 Ml/d Fort William schemes to the 0.16 Ml/d supply for Dalwhinnie. It has been demonstrated that yields of up to 2 Ml/d can be achieved from dug wells or boreholes even where the aquifer thickness is limited. Larger yields have been obtained from infiltration galleries and Ranney wells. Future challenges include improved siting techniques to locate thicker and more productive sediments and the avoidance of groundwater containing high iron and/or manganese concentrations.
QSC graphs: an aid to classification of data-poor aquifers in Ireland
Authors: Wright G. R.
Published: April 2008

The Geological Survey of Ireland’s aquifer classification system recognizes three main categories: Regionally Important, Locally Important and Poor Aquifers. This system is increasingly used to assist local authorities and state agencies to make decisions on planning applications and integrated pollution control licences, by prioritizing areas according to the value of their underlying groundwater resources. Most aquifers in Ireland are unconfined fractured hard rock aquifers, often of limited extent, which can exhibit a wide range of properties. Pumping test data are scarce, patchy and often of uncertain quality, and reliable transmissivity or permeability values are unavailable for many aquifers. Under these circumstances, the classification of a given geological formation in a given region can be difficult. The ‘QSC Graph’ compares the specific capacity (SC) for a borehole, determined by a pumping test, with the abstraction rate during the test (Q), and indicates a ‘borehole productivity index’, in five classes (I, II, III, IV and V from highest to lowest). From the relative frequency of productivity classes for a given aquifer, the appropriate aquifer category can be inferred. However, other types of information for the aquifer should also be considered. The current QSC data set comprises about 1100 boreholes, and for individual formations up to 150 boreholes. The minimum data set required for an aquifer, depending on the diversity or compactness of the data, is between 20 and 50. Examples are given of the application of the approach to a number of Irish aquifers.
Groundwater exploration in rural Scotland using geophysical techniques
Authors: Macdonald A. M. , Ball D. F. , McCann D. M.
Published: April 2008

Identifying the location, size, and characteristics of small aquifers is becoming increasingly important in Scotland with the growing demand for groundwater to supply isolated rural communities. These small, localized aquifers are found within superficial deposits, such as alluvium, blown sands and raised beach deposits, and in fracture zones in the underlying bedrock. Geophysical techniques offer a rapid and inexpensive method of characterizing these aquifers. Electromagnetic techniques using EM34 and EM31 instruments have proved useful in identifying variations in the thickness of superficial deposits and detecting buried channels, for example, at Palnure, SW Scotland. Ground penetrating radar has been used at several locations, including the island of Coll, to detect the boundary between bedrock and alluvium or blown sand. More detailed techniques, such as resistivity soundings, seismic refraction and resistivity tomography have been used to identify fractures in basement rocks and help calibrate the other methods, for example at Foyers, near Loch Ness. Magnetic profiling has also been used to locate dykes (acting as hydraulic barriers) within Permian aquifers in the west of Scotland.
Role of geographical information systems and groundwater modelling in water resource management for small islands: a case study from St Martin’s and St Agnes, Isles of Scilly, UK
Authors: Watkins David C.
Published: April 2008

Common to other small islands, water resource management is a critical issue on the Isles of Scilly, UK. This study examined the current practice of water management on the islands of St Martin’s and St Agnes in the Isles of Scilly so that a local water management plan could be formulated. The study commenced with a survey of water supplies which included locating wells, rainwater tanks and septic tanks and determining their connections and utility. Wellheads were level surveyed with respect to UK Ordnance Datum, allowing reduced groundwater levels to be monitored. Groundwater is abstracted from shallow dug wells in blown sand or Head deposits and deep wells bored into fractured granite. Hydraulic tests were conducted in seven wells to determine well and aquifer characteristics, although these tests were limited by the low yields of the wells. A geographical information system was used to collate and process information. MODFLOW and MODPATH models were constructed to help interpret the hydrogeology; to determine the impact and sustainability of groundwater abstractions; and to determine the possible extent of source protection zones around wells. The present rate of abstraction is sustainable but, due to large natural variations in the water table level, groundwater resources will always be vulnerable during periods of dry weather. The main threats to existing groundwater supplies are saline intrusion, elevated nutrient levels from agriculture and bacterial contamination from septic tanks.
North Atlantic climate variability in early Palaeogene time: a climate modelling sensitivity study
Authors: Sloan Lisa Cirbus , Huber Matthew
Published: April 2008

Understanding the nature and causes of the variability associated with past warm, high
p
CO
2
climates presents a significant challenge to palaeoclimate research. In this paper we investigate the early Eocene climatic response in the North Atlantic region to forcing from an indirect effect of atmospheric methane (via polar stratospheric clouds (PSCs)), and we investigate the response of the climate system to forcing from a combination of orbital insolation changes and high atmospheric
p
CO
2
concentration. We find that sea surface temperatures (SSTs), sea ice extent, net surface moisture, continental runoff and upwelling in the North Atlantic Ocean are all sensitive to those forcing factors, and that the degree of sensitivity is a function of location and season. Our results suggest that high-latitude SST values can vary by as much as 20 °C during the winter season in response to precessional and polar cloud forcing, whereas in contrast summer temperature varies by 4 °C or less. Model predictions of net surface moisture balance also vary substantially with our prescribed forcing. There is a large difference in variability between the localized net surface moisture results and the mean North Atlantic Ocean results, which suggests that large-scale assumptions about past surface ocean salinities and seawater δ
18
O may need to be reassessed. According to model results, the influx of terrigenous material via continental runoff to the North Atlantic Ocean should be highly seasonal, with greatest runoff occurring in spring. Our model results also indicate that changes in wind-driven upwelling and in continental runoff on a precessional time scale should be seen in regions of the central North Atlantic.
The role of deep basement during continent-continent collision: a review
Authors: Ryan Paul D.
Published: April 2008

Structural, geophysical and metamorphic studies show that collisional orogeny thickens the crust by a factor of two or more. A large volume of continental material at the base of the orogen is, therefore, subject to eclogite facies conditions. Phase equilibration results in a loss of buoyancy and thermodynamic heating of this crustal root. This dense crustal material may be partially subducted, as in the Alps or the Himalayas, and lost to the system. Alternatively, it may rest isostatically below the Moho until it is partially exhumed during orogenic collapse, as in the Scandinavian Caledonides or the Tonbai-Dabie Mountains. Remnant orogenic roots may exist as seismically reflective mantle and provide a locus for subsequent Wilson Cycle rifting. The rate at which these phase transformations take place may have a profound buffering effect on the amount and duration of orogenic contraction. Isostatically compensated transient 2-dimensional finite element thermal models are presented, which seek to place some limits on these processes. It is interesting to speculate whether more is learnt about the process of orogeny from a single exhumed eclogitic boudin or from mapping nappe complexes.
Thermal-rheological controls on deformation within oceanic transforms
Authors: Furlong Kevin P. , Sheaffer Steven D. , Malservisi Rocco
Published: April 2008

Transform faults that offset mid-ocean ridge (MOR) segments accommodate plate motion through deformations that involve complex thermal and mechanical feedbacks involving both brittle and temperature-dependent ductile rheologies. Through the implementation of a 3D coupled thermal-mechanical modelling approach, we have developed a more detailed picture of the geometry of plate boundary deformation and its dependence on plate velocity and the age offset of MOR transforms. The modelling results show that cooling of near-ridge lithosphere (lateral heat transfer) has significant effects in the ductile mantle lithosphere for both the location and style of deformation. The region where strain is accommodated in the subjacent mantle lithosphere is systematically offset from the position of the overlying linear transform fault in the brittle crust. This offset causes the boundary to be oblique to plate motions along much of the transform’s length, producing extension in regions of significant obliquity modifying the location of the surface fault segments. An implication of this complex plate-boundary geometry is that in the near-ridge region, the older (cooler) lithosphere will extend beneath the ridge tip, restricting the upwelling of mantle to the MOR. The melt to generate the oceanic crust adjacent to the transform must migrate laterally from its offset source, resulting in a reduced volume and thinner crust. This near-ridge plate boundary structure also matches the pattern of core-complex extension observed at inside corners of many slow-spreading ridges. The oblique extensional structure may also explain magmatism that is observed along ‘leaky’ transforms, which could ultimately result in the generation of new ridge segments that effectively ‘split’ large transforms.
Clay mineral transformations and weakening mechanisms along the Alpine Fault, New Zealand
Authors: Warr Laurence N. , Cox Simon
Published: April 2008

The formation of clay minerals within active fault zones, which results from the infiltration of aqueous fluids, often leads to important changes in mechanical behaviour. These hydrous phyllosilicates can (1) enhance anisotropy and reduce shear strength, (2) modify porosity and permeability, (3) store or release significant volumes of water, and (4) increase fluid pressures during shearing. The varying interplay between faulting, fluid migration, and hydrous clay mineral transformations along the central Alpine Fault of New Zealand is suggested to constitute an important weakening mechanism within the upper section of this crustal discontinuity. Well-developed zones of cataclasite and compacted clay gouge show successive stages of hydrothermal alteration, driven by the cyclic, coseismic influx of meteoric fluids into exhumed amphibolite-facies rocks that are relatively Mg rich. Three modes of deformation and alteration are recognized within the mylonite-derived clay gouge, which occurred during various stages of the fault’s exhumation history. Following initial strain-hardening and frictional melting during anhydrous cataclastic breakdown of the mylonite fabric, reaction weakening began with formation of Mg-chlorite at sub-greenschist conditions (<320 °C) and continued at lower temperatures (<120 °C) by growth of swelling clays in the matrix. The low permeability and low strength of clay-rich shears are suitable for generating high pore-fluid pressures during faulting. Despite the apparent weakening of the
c.
6 km upper segment of the Alpine Fault, the upper crust beneath the Southern Alps is known to be actively releasing elastic strain, with small (<M 5) earthquakes occurring to 12 km depth. We predict that larger events will nucleate at
c.
6–12 km along an anhydrous, strain-hardened portion of the fault.
Petrology and geochemistry of exhumed peridotites and gabbros at non-volcanic margins: ODP Leg 173 West Iberia ocena-continent transition zone
Authors: Hébert Réjean , Gueddari K. , LaFlèche M.R. , Beslier M.-O. , Gardien V.
Published: April 2008

Ultramafic and mafic rocks recovered at Holes 1068A and 1070A were drilled during Leg 173 of the Ocean Drilling Program (ODP) in the ocean-continent transition zone of the Iberia Abyssal Plain. Peridotites show contrasting petrographic characteristics. Hole 1068A peridotites are fine grained and show a well-defined high-temperature foliation marked by elongated pyroxene as well as aligned spinels. Hole 1068A peridotites are strongly serpentinized. Hole 1070A peridotites are coarse grained and show little evidence of high-temperature foliation. The degree of serpentinization is lower and relicts of silicate minerals are preserved. In both sets of recovered material, spinels show a wide range of composition and suggest a complex magmatic evolution. Gabbros dykes, which are found only in Hole 1070A, are very coarse grained and are locally sheared and/or crushed. Magmatic amphiboles are kaersutites and Ti-rich tschermakites that are partially replaced by hornblende and actinolite, and are associated with plagioclase of intermediate composition. Peridotites and pyroxenite have low TiO
2
, Al
2
O
3
and CaO contents in carbonate-free samples. Ni and Cr contents fall into the upper-mantle array. On the other hand, gabbros have relatively high TiO
2
and V contents reflecting modal ilmenite, and suggesting that they are relatively differentiated. This paper presents the very first geochemical data on platinum group elements (PGE) of peridotites and gabbros from passive margins. Peridotites and gabbros show low PGE (25.83 ppb and 1.44 ppb), Pd (2.75 ppb and 0.15 ppb), Pd/Ir ratios (1.45 and 1.3) and mafic index. Pyroxenite has the highest PGE (27.97 ppb), Pd/Ir (19.87) and Pt/Ir (10.25). Interelemental correlation and observation of PGE-bearing sulphide phases suggest that the PGE are hosted by single sulphide phases. From a PGE point of view, extraction of magmas involved very PGE-depleted liquids similar to gabbroic veins cutting the peridotites at Hole 1070A. Partial melting is interpreted as occurring just before oceanic accretion. Geochemical attributes suggest that the peridotites belong to the Ronda and Beni Bousera peridotitic depleted end-member clan. Thus they are believed to be of subcontinental origin. Deformation and retrograde metamorphism of peridotites and gabbros are consistent with exhumation in a rift environment post-dating the 120 Ma magmatic stage.
Palaeomagnetic and rock magnetic results from serpentinized peridotites beneath the Iberia Abyssal Plain
Authors: Zhao Xixi
Published: April 2008

A palaeomagnetic and rock magnetic study has been performed on serpentinized peridotite rocks recovered at Ocean Drilling Program (ODP) Leg 149 and 173 sites, off the west coast of Portugal (Sites 897, 899 and 1070). Stable components of magnetization are revealed after detailed thermal and alternating field demagnetization. Results from a series of rock magnetic measurements with advanced instrumentation all corroborate the demagnetization behaviour and show that (titano)magnetites and maghemite are present in the peridotites. At Leg 149 and 173 sites, the inclinations of characteristic magnetization in the ‘fresher’ lower part of the serpentinized peridotite section show a predominantly reversed polarity in a depth zone ofc.25 m, which is compatible with a reversed event (probably correlated with marine Anomaly M0 atc.121 Ma) before the Cretaceous Long Normal Superchron (83–120 Ma) and is incompatible with a Holocene field direction. In contrast, the inclinations of samples from the more ‘altered’ upper part are predominantly normal. In view of the polarity of magnetization identified from the overlying Cretaceous and Tertiary sediments and the newest interpretation of the drilling results for the Iberia margin, our results suggest that the Iberian peridotites were emplaced during Aptian-Barremian time and recorded the middle Cretaceous geomagnetic field during Anomaly M0 time (c.121 Ma). Our data are consistent with new radiometric dates for the Iberian peridotites at Leg 173 drill sites.
Palaeowaters in European coastal aquifers — the goals and main conclusions of the PALAEAUX project
Authors: Edmunds W. M.
Published: April 2008

The PALAEAUX project has brought together up-to-date geochemical, isotopic and hydrogeological information on coastal groundwaters across Europe in a transect from the Baltic to the Canary Islands. These data have been interpreted in relation to past climatic and environmental conditions, as well as extending and challenging concepts about the evolution of groundwater near the present day coastlines. Groundwater movement beyond the present coastline as well as emplacement on shore to greater depths (up to 500 m) than allowed by the present-day flow regime has occurred, hence offshore freshwater reserves are inferred in some coastal areas. The main attributes of palaeowaters, in terms of water quality, are their high bacterial purity, total mineralization that is often less than that of modern waters and being demonstrably free of anthropogenic chemicals. However, in the Mediterranean coastal areas, lower recharge leads to higher salinity conditions in both palaeo- and modern waters.

Freshwater of high quality originating from different climatic conditions to the present day, when the sea level was much lower, is found at depth beneath the present-day coastline in several countries. Recharge is shown to have been more or less continuous during the past 100 ka, even beneath the ice, as demonstrated by groundwaters from Estonia, having δO values of c. −22%o. However, elsewhere (UK and Belgium) an age gap can be recognized indicating that no recharge took place at the time of the last glacial maximum. Devensian recharge temperatures (soil air temperatures) were some 6°C colder across Europe than at the present day.

The development of aquifers in Europe during the past 50–100 a, by abstraction from boreholes, has generally disturbed flow systems that have evolved over varying geological timescales, especially those derived from the Late Pleistocene and Holocene. Hydrogeophysical logging has demonstrated time and quality stratified aquifers resulting in mixed waters being produced on pumping. A range of specific indicators, including
3
H,
3
H/
3
He,
85
Kr, chlorofluoro-carbons and pollutants, have been used to recognize the extent to which waters from the modern (industrial) era have penetrated into the aquifers, often replacing the natural palaeogroundwaters.

In the coastal regions, many problems for management are identified, including issues relating to quantity and quality of water, seasonal demand, pollution risks and ecosystem damage, requiring a new look at legislation.
Evidence for palaeowaters in the coastal aquifers of France
Authors: Dever L. , Travi Y. , Barbecot F. , Marlin C. , Gibert E.
Published: April 2008

Over time, coastal aquifers, which constitute a great part of available freshwater resources from sedimentary basins in France, have been subjected to changes in hydraulic gradients and hydrodynamic properties, mainly due to discharge-recharge phases in response to sea-level variations and/or human influences. This work aims to understand the salinization process originating from the recharge-discharge conditions as recognized at three sites: the calcareous Dogger aquifers along the English Channel (Caen area); along the Atlantic coast (Marais Poitevin), and the Astian sandy aquifer (Cap d’Agde). In addition to conventional hydrogeological and hydrochemical techniques, the main tools used for investigation are those of isotope geochemistry.

For the three study sites, the evolution of isotopic signatures along a flow path, depending on the mineralogy of the aquifer matrix, is linked to water-rock interactions such as cation exchange and equilibrium with aluminosilicates. Residence times of these fresh groundwaters are from Modern (Atlantic site) up to the
14
C detection limit (English Channel site). Groundwater of the Astian aquifer (Mediterranean) belongs to the Holocene, as determined by
14
C analyses.

The saline waters identified in the three study sites have a marine origin and were modified either by interaction with organic-rich layers, by cation exchange, or by deep carbon input. The salinization process has been associated with marine overflow onto a plain and to an upward leakage of water rich in CO
2
. The marine intrusion registered in the English Channel and Atlantic aquifers is associated with the Flandrian transgression; for the Astian aquifer, the salinization is related to mixing with older water.
Hydrochemical modelling as a tool for understanding palaeowaters
Authors: Van Der Kemp W. J. M. , Appelo C. A. J. , Condesso De Melo M. T. , Gaus I. , Milne C. J. , Walraevens K.
Published: April 2008

Hydrogeochemical modelling was used to interpret water-sample analyses of three European aquifers: the East Midlands Triassic Sandstone (UK), the Tertiary Ledo-Paniselian (Belgium) and the Aveiro Cretaceous aquifer (Portugal). Soil CO
2
pressures at recharge,derived from inverse chemical modelling, correlate well with δ
18
O of the water. Higher soil CO
2
pressures correspond to less negative δ
18
O of the recharge water, indicating higher recharge temperatures. This trend is confirmed by noble gas temperatures from the East Midlands aquifer. Cation exchange and carbonate reactions were the most important chemical processes that contributed to the groundwater composition of all three aquifers. Transport modelling of the water quality of the Ledo-Paniselian aquifer confirmed the importance of cation exchange and elucidated that recharge of this aquifer occurs through preferential pathways.
‘Had Lord Kelvin a right?’: John Perry, natural selection and the age of the Earth, 1894–1895
Authors: Shipley Brian C.
Published: April 2008

The Marquis of Salisbury’s 1894 address to the British Association for the Advancement of Science sparked an important development in the debate on the age of the Earth. It led John Perry, a physicist, to produce the first mathematical rebuttal of Lord Kelvin’s calculations, which had since 1862 functioned as an argument against the theory of evolution by natural selection. Perry wished to affirm the independence of geology from physics, keeping each branch of science to its proper domain. With the support of his mathematical friends, Perry tried privately to induce Kelvin to modify his views. This effort failed, however, and the discussion became public in
Nature
. Perry supported his calculations with Heaviside’s new mathematical methods, and also with empirical data, though these were later undermined by Kelvin’s experiments. Perry was uncomfortable with his position as Kelvin’s critic, however, because he held his old teacher in great esteem. Although Kelvin never stopped believing that the Earth was too young for natural selection to have taken place, geologists and biologists responded very positively to Perry’s results, and no longer felt they had to justify their conclusions to physicists. The answer to ‘Had Lord Kelvin a right?’, ultimately depended on one’s scientific politics.
Arthur Holmes’ vision of a geological timescale
Authors: Lewis Cherry L. E.
Published: April 2008

Arthur Holmes (1890–1965) was a British geoscientist who devoted much of his academic life to trying to further the understanding of geology by developing a radiometric timescale. From an early age he held in his mind a clear vision of how such a timescale would correlate and unify all geological events and processes. He pioneered the uranium-lead dating technique before the discovery of isotopes; he developed the principle of ‘initial ratios’ thirty years before it became recognized as the key to petrogenesis, and he wrote the most widely read and influential geology book of the twentieth century. But despite all this, much of his contribution to geology has gone unrecognized in the historical literature. This paper attempts to redress this omission, to dispel some of the myths about Holmes’ life, and to trace his contribution to the development of the geological timescale.
Fossils as geological clocks
Authors: Callomon John H.
Published: April 2008

To reconstruct the history of the Earth we need to know
what
happened and
when — events
and their
dates
— and we should like to know
how
it happened and
why — processes
and their
rates
. To date a historical event we need a timescale for reference — a
calendar
— and a means of placing events in this timescale — a
clock
. Direct access to the primary physical calendar, of time measured in years by means of elemental radiometry as clock, is possible in only a minority of geological problems. By far the richest historical source in the Phanerozoic Eon has been the stratigraphical analysis of sedimentary rocks by means of fossils, the approach pioneered by William Smith. The succession of fossil biotae found in the rocks is used to construct the calendar of
relative
time, the familiar geological calendar defining the standard chronostratigraphical timescale still in process of refinement today. Rocks are then dated through time correlations with this scale by means of their
guide
fossils (von Buch) as clocks. The power to measure the rates of geological processes then depends on the time
resolution
achievable by means of fossils, the time
intervals
between distinguishable events, the
finesse
of the calendar.

The present-day state of play is reviewed, both in the refinement of the geological calendar and the finesse that has been attained. Comparison of the geological calendar with our familiar human historical calendar reveals some illuminating parallels as well as some important differences. Illustrative examples are taken from the Jurassic Period (170 Ma BP) and its ammonites as clocks.
Time, life and the Earth
Authors: Manning Aubrey
Published: April 2008

Modern developments in the Earth sciences have revealed, for the first time, how our planet actually ‘works.’ For biologists, they have brought a fresh understanding of the interwoven histories of the physical and the living worlds. In turn, new biological discoveries show how early in Earth’s history life arose and how it was able to flourish even under the apparently hostile conditions of the young solar system. In particular the high ocean temperatures following meteor impacts would not have precluded the successful progress of so-called hyperthermophilic prokaryotic organisms.

The early problems which evolutionary biologists faced, when presented with estimates of the age of the Earth as a few tens of millions of years, have now been replaced by arguments concerning mechanisms underlying the variable rates and patterns of evolution.

Life and the Earth have reciprocally interacted over billions of years and repeatedly planetary processes have led to mass extinctions whose dramatic results can be seen in the fossil record even though the details of such events remain problematical. So far mass extinctions have resulted in increased opportunities for the survivors; the current human-induced extinction is unlikely to do so.
Dating the origin of modern humans
Authors: Stringer Christopher B.
Published: April 2008

One of the most serious past difficulties facing realistic tests of evolutionary models for modern human origins was the lack of widely applicable dating procedures that could reach beyond the practical limits of radiocarbon dating. Moreover, the amount of fossil material that had to be sacrificed to obtain a conventional radiocarbon date meant that human fossils could generally only be dated indirectly through supposedly associated materials. Because of these limitations, the transition from Neanderthals to modern humans in Europe was believed to have occurred about 35 000 radiocarbon years ago, but detailed reconstruction of the processes involved (for example, evolution or population replacement) was not practicable. In the Levant, the transition period from Neanderthals to modern humans was believed to lie only slightly beyond this 35 000-year watershed. Elsewhere, in Africa, east Asia and Australasia, the chronology for modern human origins was even more difficult to establish. However, over the last fifteen years, radiocarbon and non-radiocarbon physical dating techniques such as luminescence and electron spin resonance have been increasingly refined, leading to a revolution in our understanding of the timescale for human evolution, particularly for the last 200 000 years. Although each dating method has its own strengths and weaknesses, the picture that now emerges is one of a gradual evolution of Neanderthal morphology in Europe, in parallel with a similar evolution of modern humans in Africa. Modern humans also appear surprisingly early in the Levant (
c.
100 ka ago) and Australia (
c.
60 ka ago). However, many uncertainties still surround the process of establishment of our species globally.