bluuebunny/crossref_metadata_2025 huggingface dataset:
An evolutionary model of glacial dispersal and till genesis in Maritime Canada
Authors: Stea Rudolph R. , Finck Phillip W.
Published: April 2008

Glacier process models of till genesis cannot fully explain the properties of tills in Maritime Canada. A succession of local ice caps, called the Appalachian Ice Complex, developed during the last glaciation and were drained by ice streams into the submarine channels bordering the region. The migration of these centres produced areas with widely differing flow patterns, landform assemblages and deposits. Early regional phases of ice flow were characterized by wide, rapidly-flowing ice-streams that formed thick exotic, silty tills. In later phases, ice divides developed over highland areas underlain by metamorphic and igneous rocks, forming stony local tills. Terrain zones characterized by distinct transport histories and depositional sequences were produced by the interplay and migration of regional ice sheets and local ice caps. The interaction of local glaciers and previously deposited tills formed hybrid tills through two reworking processes: inheritance and overprinting. Inheritance is incorporation of till components and/or fabric into a younger till by erosion and entrainment of material from an older till. Overprinting is the injection or imprint of matrix, clasts or fabric on older tills by overriding ice. Glacial dispersal of rocks, minerals and trace elements in this complex glaciated terrain is controlled by the location of former ice divides. Simple unidirectional trains are preserved in relict terrains under divides. In ice marginal areas, reworking processes result in complex dispersal fans produced by smearing and widening of previously formed trains and fans. These dispersal fans can be modelled by vector addition of discrete flow events within each dispersal zone. A simple empirical model of glacier dispersal is presented using exponential decay and uptake algorithms, and incorporating the reworking of older till material.
Permeability variation across an active low-angle detachment fault, western Woodlark Basin (ODP Leg 180), and its implication for fault activation
Authors: Kopf Achim
Published: April 2008

In the western Woodlark Basin, off Papua New Guinea, the variation from continental rifting to sea-floor spreading has profound effects on the mechanical response of the lithosphere. The extension is well expressed in a seismically active, shallow-dipping detachment fault. Recent Ocean Drilling Program drilling (ODP Leg 180) in the area obtained cores from the hanging wall, detachment fault gouge, and footwall, of which samples underwent permeability testing in the laboratory. Permeability variation was found to be critically dependent on (1) flow direction, i.e. fabric anisotropy of the rocks, and (2) deformational structures in the hanging wall to the fault. Regarding the first, a slight but distinct increase in permeability has been recorded parallel to the fabric (compared with flow normal to this, as indicated by anisotropy indices ofkhorizontal/kverticalof >1.7). This phenomenon appears most profound directly above fault zones in the hanging-wall block, which are interpreted to represent splays to the main detachment fault plane at depth. Here, shear-enhanced compaction seals fluid flow to the sea floor, so that conductive flow parallel to the fault plane is favoured (in general one order of magnitude higher). The fault gouge, mainly consisting of highly serpentinized basalt and chlorite, exhibits an increase in permeability relative to the clay- and siltstones of the hanging-wall block. In the metamorphic basalt from the tectonic footwall, permeability decreases again by three orders of magnitude (kisc.6e—17 to 5e—18 m2). Consequently, the detachment and synthetic splays related to it are zones of enhanced fluid migration in the fault plane direction. Fluid overpressure, and hence fault activity, is suggested to be trigered by seal of the top of the fault zone, owing to both shear fabrics and cementation processes.
Deformation microfabrics of clay gouge, Lewis Thrust, Canada: a case for fault weakening from clay transformation
Authors: Yan Yonghong , van der Pluijm Ben A. , Peacor Donald R.
Published: April 2008

A sequence of bentonite and shale samples in a gouge zone of the Lewis Thrust (Alberta, Canada) that display increasing degree of transformation of clay minerals toward the hanging wall of the thrust has been studied by X-ray diffraction (XRD), X-ray texture goniometry (XTG), scanning electron microscopy (SEM), and transmission and analytical electron microscopy (TEM-AEM), to examine the relations among mineral transformations, microfabrics and fault zone properties. TEM images of authigenic clays show abundant smectite in shale away from the hanging wall, characterized by anastomosing layers with an average orientation that parallels bedding, coexisting with uncommon
R
1 illite-smectite (I-S). In the sample nearest the hanging wall, by contrast, the dominant clay is mixed-layered, illite-rich ilite-smectite (
R
1 I-S), coexisting with discrete illite, occurring in individual packets of relatively straight layers with well-defined boundaries. Deformed clay packets are common. Pore space, where packets intesect at high angles to one another and to bedding, is abundant (
c.
25%). The microfabric and proportion of illite of intermediate samples are transitional to these end-members. Inter-layered bentonite samples show properties that are similar to those of shale. TEM observations are supported by quantification of the fabrics using XTG, which shows that the intensity of clay preferred orientation decreases significantly with increasing illitization. These relations imply that faulting was the cause of mineral transformations and formation of secondary pore space. The illitization reaction rate was enhanced both by stress-induced defects in clays, and by increased water/rock ratio resulting from deformation-related pore space, resulting in lowering of the effective stress. The deformation-enhanced reaction thus created a positive feedback for further faulting in clay gouge, leading to enhanced weakening of the fault zone.
Lithospheric and crustal reactivation of an ancient plate boundary: the assembly and disassembly of the Salmon River suture zone, Idaho, USA
Authors: Tikoff B. , Kelso P. , Manduca C. , Markley M. J. , Gillaspy J.
Published: April 2008

The Salmon River suture zone, western Idaho, is a fundamental lithospheric boundary between the North American craton and the accreted terranes of the Cordilleran margin. The initial juxtaposition along this north-south-oriented structure occurred during Early Cretaceous time. This zone was potentially reactivated twice by subsequent tectonism, once during Cretaceous time and once during Miocene time. The Late Cretaceous western Idaho shear zone formed along the Salmon River suture zone, as denoted by a sharp gradient in the isotopic signature of the granitoids that intruded the lithospheric boundary zone. The reconstructed Late Cretaceous orientation of the western Idaho shear zone contains subvertical fabrics (lineation, foliation). The same boundary also acted as a locus for subsequent Miocene Basin and Range extensional deformation. Domino-style normal faulting and deep (2100 m) basin formation accommodated the motion between the extending accreted terranes to the west and the unextended Idaho batholith to the east. Whereas either the mantle boundary or a crustal-scale structuring controls the regional extent of the extensionally reactivated zone, locally crustal basement faults and lithological contacts control the orientation and precise location of faults that accommodate reactivation. The multiple reactivation of the Salmon River suture zone is critical for several reasons. The Early Cretaceous suture zone apparently created a fundamental lithospheric flaw, which was reactivated after terrane accretion. Whether this zone was a fracture or a shear zone, the fabric in the mantle lithosphere was apparently not ‘healed’ during orogenesis. Thus, juxtaposition of mantle lithosphere, which is inferred to occur by faulting in the uppermost mantle, acts as a weakness during later tectonism. Second, the paucity of strike-slip plate boundaries in the geological record makes sense in the context of reactivation. The vertical, lithospheric-scale nature of these structures makes them particularly susceptible to lithospheric-scale reactivation during both transcurrent and/or extensional deformation. These reactivations both overprint the earlier deformation and modify the original geometry. Steeply dipping fabrics, rather than vertical fabrics, may be the general signature of major, ancient strike-slip faults.
Rheological partitioning during multiple reactivation of the Palaeozoic Brevard Fault Zone, Southern Appalachians, USA
Authors: Hatcher Robert D.
Published: April 2008

The Brevard Fault Zone is a linear, NE-trending, gently to moderately SE-dipping fault zone traceable some 750km from Alabama to Virginia in the crystalline southern Appalachians. It ranges from 1 to 3 km wide and contains a mappable lithostratigraphy. The Brevard Fault Zone has been interpreted as a thrust, strike-slip fault (both dextral and sinistral), a suture and terrane boundary, and a fundamental crustal tectonic boundary. Deformation was partitioned in space and time, and motion was both strikeslip (dextral) and dip-slip (thrust). Early strike-slip and thrust movement was coupled to map-scale structures in the deep Inner Piedmont, late Palaeozoic dextral motion was confined to a zone of 1–3 km width, and the latest reactivation consisted of brittle thrusting confined to a zone of 100m width. The fault zone is cut by undeformed NW-trending Mesozoic dolerite dykes. The Brevard Fault Zone is characterized by the presence of a prominent retrograde (chlorite-muscovite stable) S-C fabric that indicates dextral motion. This fabric is related to late Palaeozoic (Alleghanian) dextral reactivation of the fault zone, with an unknown displacement at a time when huge volumes of fluid were fluxed through the zone. The deformation overprints an earlier (Acadian) high-temperature (garnet-staurolite-kyanite) fabric that also yields a dextral motion sense, and involved a component of thrusting. This mid-Palaeozoic deformation was coupled with west-directed, near-metamorphic peak thrusting and flow from the deep Inner Piedmont (to the east) that was buttressed against the primordial Brevard Fault Zone so that the motion became SW directed, and plastic flow became constricted in this narrow 1—3 km zone. Both of these plastic deformations were overprinted by late Alleghanian NW-directed dip-slip brittle deformation confined to the NW side of the Brevard Fault Zone. This last deformation involved at least 10 km of displacement and was related to reactivation of this block of crust as part of the late Alleghanian, NW-directed Blue Ridge-Piedmont megathrust sheet, and formed out of sequence with respect to the megathrust sheet. The Brevard Fault Zone was clearly a zone of crustal weakness that had a suitable mechanical stratigraphy that imparted sufficient anisotropy to localize the initial Acadian fault(s). Early Alleghanian fluid fluxing weakened the already strongly anisotropic fault zone and probably focused ductile reactivation at a shallower crustal depth during the early Alleghanian event. Late Alleghanian reactivation occurred even shallower as an almost discrete boundary in the brittle regime. This is one of the few faults in the Appalachians to have undergone deformational partitioning to permit multiple reactivation during Palaeozoic time.
The role of fault zones and melts as agents of weakening, hardening and differentiation of the continental crust: a synthesis
Authors: Handy M. R. , Mulch A. , Rosenau M. , Rosenberg C. L.
Published: April 2008

The rheology of crustal fault zones containing melts is governed primarily by two strain-dependent mechanical discontinuities: (1) a strength minimum parallel to mylonitic foliation just below the active brittle-viscous (b-v) transition; (2) the anatectic front, which marks the upper depth limit of anatectic flow. The mode of syntectonic melt segregation in fault zones is determined by the scale of strain localization and melt-space connectivity, to an extent dependent on strain, strain rate and melt fraction in the rock. Melt drains from the mylonitic wall rock into dilatant shear surfaces, which propagate sporadically as veins. Anatectic flow at natural strain rates therefore involves melt-assisted creep punctuated by melt-induced veining. On the crustal scale, dilatant shear surfaces and vein networks serve as conduits for the rapid, buoyancy-driven ascent of transiently overpressured melt from melt-source rocks at or just below the anatectic front to sinks higher in the crust. Strength estimates for natural rocks that experienced anatectic flow indicate that melts weaken the continental crust, particularly in depth intervals where they spread laterally beneath low-permeability layers or along active shear zones with a pronounced mylonitic foliation. However, acute weakening associated wit h strength drops of more than an order of magnitude occurs only during short periods (103–105a) of crustal-scale veining. Cooling and crystallization at the end of these veining episodes is fast and hardens the crust to strengths at least as great as, and in some cases greater than, its pre-melting strength. Repeated melt-induced weakening then hardening of fault zones may be linked to other orogenic processes that occur episodically (shifting centres of clastic sedimentation and volcanism) and has implications for stress transmission across orogenic wedges and magmatic arcs.
Propagation of continental break-up in the southwestern South China Sea
Authors: Huchon P. , Nguyen T. N. H. , Chamot-Rooke N.
Published: April 2008

We present new bathymetric, seismic and gravity data on the southwestern tip of the South China Sea oceanic basin, where propagation of continental break-up occurred before
c.
15 Ma. The oceanic domain has a V-shape typical of oceanic propagating rifts. The tectonic fabric of its margins shows that the main stretching direction was slightly oblique to that of the rift axis. A 2D gravity anomaly inversion, corrected for the thermal effect, is used to estimate the crustal structure. At the continent-ocean boundary, the continental crust is stretched by a factor of about four, rapidly decreasing to about two over a few tens of kilometres, a distance corresponding to just over 1 Ma of break-up propagation. Thus, strain localization occurs at the tip of the propagating oceanic crust just before break-up. The along-axis variation in continental crustal stretching is in good agreement with the kinematics of the oceanic crust derived from magnetic anomalies. This analysis suggests that break-up propagates toward the pole of relative rotation and is primarily controlled by the amount of stretching of the continental crust before oceanization.
Nature of the continent-ocean transition on the non-volcanic rifted margin of the central Great Australian Bight
Authors: Sayers Jacques , Symonds Philip A. , Direen Nicholas G. , Bernardel George
Published: April 2008

A region of 50–120 km width defines the continent-ocean transition (COT) in the central Great Australian Bight. It is characterized by a thin apron of post-break-up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement. Recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the COT and basement ridge. Modelled gravity and magnetic data, and features interpreted from seismic data, are consistent with aspects of extensional and break-up models proposed for the West Iberia margin. Many of the features and relationships observed beneath the outer margin of the central Great Australian Bight can be explained by extension within a lithosphere-scale ‘pure-shear’ environment involving four layers: brittle upper crust and upper mantle, and ductile lower crust and lower lithospheric mantle. The COT is interpreted to be underlain by extended continental lithosphere. Thus, the continent-ocean boundary is unequivocally defined between oceanic crust and the COT and appears to be associated with sea-floor spreading magnetic anomaly 33, indicating that break-up and sea-floor spreading did not commence until
c.
83 Ma (early Campanian time), later than the currently accepted 95 Ma age. The major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting. The magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly, but one that does not relate to break-up and sea-floor spreading.
Deformation fabrics of faulted rocks, and some syntectonic stress estimates from the active Woodlark Basin detachment zone
Authors: Roller Sybille , Behrmann Jan H. , Kopf Achim
Published: April 2008

Ocean Drilling Program (ODP) Leg 180 investigated, in the western Woodlark Basin off Papua New Guinea, the nature and evolution of continental extension, eventually leading to crustal break-up and sea-floor spreading. At Moresby Seamount, the rift-related extension is localized at a recently active low-angle (30°) detachment fault, partly buried beneath a Pliocene-Pleistocene sedimentary synrift sequence. Data from three drillsites sample the detachment fault itself, secondary faults in its hanging wall and a steep normal fault cutting the footwall. The fault plane itself is manifested as a strongly altered fault gouge. Deformation of turbiditic sediments in several fault zones in the hanging wall is dominated by brittle mechanisms, and accompanied by intensive veining and pervasive diagenetic cementation. The metabasic rocks of the footwall below the detachment show an unusual transition from ductile to brittle deformation fabrics with increasing depth. Many fracture systems show evidence of repeated opening and healing during multistage hydrothermal mineralization. Syn-mylonitic microstructures and vein fill mineralogy suggest exhumation of the detachment footwall from considerable depth in the crust. Two palaeo-piezometers were applied to calcite-filled veins that show evidence of plastic deformation. Differential stress values of similar magnitude and probably close to the rock failure strength are found in both the hanging wall and footwall.
Micropalaeontological and palaeomagnetic approaches to stratigraphic anomalies in rift basins: ODP Site 1109, Woodlark Basin
Authors: Resig Johanna M. , Frost Gina M. , Ishikawa Naoto , Perembo Russell C.B.
Published: April 2008

The stratigraphic succession of the western Woodlark Basin is examined in detail relative to ODP Site 1109, where
c.
55 m of Pliocene sediment lies anomalously shallow owing to slumping between
c.
1.10 and 0.65 Ma in the tectonically active rift basin. Palaeomagnetic reversals and varying percentages of the characteristic microfossils,
Globigerinoides fistulosus
and discoasters, within the deformed sediment defining the slump indicate that the Pliocene sediment was periodically introduced by a number of slumps rather than being emplaced by a single slump event. Palaeomagnetic and biostratigraphic events in the remainder of the hemipelagic section of Site 1109 to
c.
4 Ma appear undisturbed and consistent with those at adjoining sites.
Globorotalia truncatulinoides
first appeared between 2.65 and 2.71 Ma at these low-latitude sites, which extends the previously reported area of evolution of the species in the southwestern Pacific toward the Equator. Seven of the nine coiling changes in
Pulleniatina
through time are recognized and dated using sedimentation rates. Along with palaeomagnetic events and microfossil species datum levels, these coiling changes can be used to correlate between sites in the area.
The role of detachment faulting in the formation of an ocean-continent transition: insights from the Iberia Abyssal Plain
Authors: Manatschal G. , Froitzheim N. , Rubenach M. , Turrin B.D.
Published: April 2008

The Iberia Abyssal Plain segment of the West Iberia margin was drilled during Ocean Drilling Program Legs 149 and 173 and has been extensively studied geophysically. We present new microstructural investigations and new age data. These, together with observed distribution of upper- and lower-crustal and mantle rocks along the ocean-continent transition suggest the existence of three detachment faults, one of which was previously unrecognized. This information, together with a simple kinematic inversion of the reinterpreted seismic section Lusigal 12, allows discussion of the kinematic evolution of detachment faulting in terms of the temporal sequence of faulting, offset along individual faults, and thinning of the crust during faulting. Our study shows that the detachment structures recognized in the seismic profile became active only during a final stage of rifting when the crust was already considerably thinned to
c.
12 km. The total amount of extension accommodated by the detachment faults is of the order of 32.6 km corresponding to a β factor of about two. During rifting, the mode of deformation changed oceanwards. Initial listric faulting led to asymmetric basins, accommodating low amounts of extension, and was followed by a situation in which the footwall was pulled out from underneath a relatively stable hanging wall accommodating high amounts of extension. Deformation along the latter faults resulted in a conveyor-belt type sediment accumulation in which the exhumed footwall rocks were exposed, eroded and redeposited along the same active fault system.
Geodynamic models of continental extension and the formation of non-volcanic rifted continental margins
Authors: Bowling Jerry C. , Harry Dennis L.
Published: April 2008

Finite-element models of continental rifting show that formation of non-volcanic rifted margins may be the result of extension of a rheologically homogeneous crust. In such circumstances lithosphere necking does not become well developed until late in the rift history, delaying the onset of decompression melting in the asthenosphere until the last 10% of the rifting episode. This result is robust over a broad range of mantle temperatures, margin geometries, and extension rates. A cool mantle is not required, so the models are able to account for the production of oceanic crust at the end of amagmatic rifting episodes. The duration of the syn-rift melting episode is most sensitive to changes in extension rate, with higher extension rates leading to shorter periods of melt production. The duration of the rifting episode is controlled by extension rate and initial crustal thickness, and the geometry of the margin after continental break-up is controlled by initial crustal thickness and the distribution of pre-existing rheological heterogeneity in the crust. The model results are generally compatible with the dimensions and extension rates of rifted continental margins across the globe, and provide a particularly good fit to the evolution of the Iberia Abyssal Plain margin.
Palaeogroundwater of glacial origin in the Cambrian-Vendian aquifer of northern Estonia
Authors: Vaikmäe R. , Vallner L. , Loosli H. H. , Blaser P. C. , Juillard-Tardent M.
Published: April 2008

A strongly depleted stable isotope composition, absence of
3
H and a low radiocarbon concentration are the main indicators of glacial origin of groundwater in the Cambrian-Vendian aquifer in northern Estonia. It is concluded from noble gas analyses that palaeorecharge occurred at temperatures
c.
0°C. In some wells unexpectedly high gas concentrations have been found. Excess air, up to
c.
50 %, is common but two-five times oversaturation is very unusual, requiring special processes and explanations, e.g. oversaturation may indicate recharge under highpressure conditions, perhaps by subglacial meltwater recharge through the aquifers. Analyses of the gas composition in some groundwater samples also showed a rather high concentration of CH
4
, indicating the influence of biogenic reactions in the subsurface that could cause the rather negative δ
13
C values. Results of δ
13
C analyses in two CH
4
samples also show that the CH
4
is most likely of a biogenic origin. Based on the isotope data, the results of noble gas analyses, and considering the palaeoclimatic and palaeoenvironmental situation in Estonia during the late Weichselian time, it is concluded that palaeorecharge of Cambrian-Vendian aquifer most probably occurred during the last glaciation, probably by subglacial drainage through the tunnel valleys.
The Ribe Formation in western Denmark — Holocene and Pleistocene groundwaters in a coastal Miocene sand aquifer
Authors: Hinsby K. , Harrar W. G. , Nyegaard P. , Konradi P. B. , Rasmussen E. S. , Bidstrup T. , Gregersen U. , Boaretto E.
Published: April 2008

The Ribe Formation is a regionally extensive Miocene sand aquifer that is present in western Denmark at depths ranging from 100 to 300 m below ground surface. Groundwater chemistry and isotope data collected from more than 40 wells show that the Ribe Formation mainly contains high quality Cabi-carbonate type groundwater of Holocene age (100–10 000 a
bp
). Pleistocene age groundwaters, identified on the basis of stable isotopes, noble gases and corrected
14
C values, are present below the island of Rømø, in discharge areas near the coast, and in hydraulically isolated inland areas. The groundwater age distribution in the Ribe Formation was successfully simulated with a numerical groundwater flow model and particle tracking only when the
14
C content in groundwater was corrected for both geochemical reactions and diffusion. The results indicate that geochemical and physical processes significantly influence the
14
C content of groundwater and that the correction factors required for the two processes are of the same magnitude. Flow modelling results indicate that Pleistocene groundwaters were emplaced at depth within the Ribe Fromation under low base-level conditions that prevailed throughout the late Pleistocene — near the coast these waters are essentially isolated from the present flow system, and Pleistocene freshwater may be present offshore. Seismic surveys show that conditions offshore are favourable for the presence of Pleistocene freshwater within the Ribe Formation and other aquifers.
Palaeowaters in the aquifers of the coastal regions of southern and eastern England
Authors: Edmunds W. M. , Buckley D. K. , Darling W. G. , Milne C. J. , Smedley P. L. , Williams A. T.
Published: April 2008

The marked climatic changes that occurred during the Late Quaternary and Holocene have had a significant impact on the evolution of the groundwater systems at and near the English coastline. Lowered sea levels and the emergence of a much larger landmass over most of the past 100 ka have also ensured deeper groundwater circulation in the vicinity of the modern coastline. The impacts on the Chalk and Lower Greensand (Albian) aquifers along the English Channel and North Sea coasts are examined, using mainly geochemical and isotopic evidence, especially from borehole depth profiles and interstitial waters.

Along the south coast, fresh groundwaters are found to depths of 250–300 m below OD (ordnance datum) in the Brighton-Worthing area, as well as beneath Poole Harbour, which are related to deeper circulation during lowered sea levels, controlled by the central palaeovalley of the English Channel. In contrast, pockets of saline groundwater are found, protected in east-west structures, which are considered to be little-modified Chalk formation waters. In the Albian sands, near Worthing, freshwaters dating to 7 ka are found at a depth of −450 m OD, suggesting that movement of groundwater towards the shoreline and possibly beyond is still occurring. The east-west structures also influence groundwater migration in north Kent, where fresh palaeowaters can be identified beneath saline water which invaded during the Holocene sea-level rise. In the East Midlands Sherwood Sandstone aquifer, freshwater is found to a depth of −500 m OD, showing continuous geochemical evolution probably over a period of 100 ka, although an ‘age gap’ of between
c.
20 and 10 ka
c.
corresponds to permafrost cover. These palaeowaters in coastal and near-coastal areas remain effectively isolated from the active present-day meteoric flow system but represent high-value resources that may, in some cases, extend offshore.
Isotopic methods and their hydrogeochemical context in the investigation of palaeowaters
Authors: Loosli H. H. , Aeschbach-Hertig W. , Barbecot F. , Blaser P. , Darling W. G. , Dever L. , Edmunds W. M. , Kipfer R. , Purtschert R. , Walraevens K.
Published: April 2008

Isotope and geochemical techniques are the primary way in which the residence time, recharge conditions and subsequent evolution of palaeowaters can be determined. Isotopic species and noble gas concentrations are used as residence time and palaeoclimate indicators. Among the former,
14
C is pre-eminent in late Quaternary studies because of an age range which covers the Pleistocene-Holocene transition. However, its use is constrained by frequent difficulties in determining the dilution of dissolved
14
C due to water-rock interaction. A combination of
14
C data with
226
Ra and
4
He results may be useful for Holocene waters but they can also be used to validate the carbon systematics assumed for
14
C dating. For waters beyond the range of
14
C dating,
81
Kr,
36
Cl,
4
He and chemical tracers can be applied.

Stable isotope ratios and noble gas concentrations primarily reflect climatic conditions at the time of recharge. While the noble gases provide absolute values for recharge temperatures, stable isotopes are only relative indicators that vary regionally. The PALAEAUX programme has examined these aspects in some detail by looking at the δ
18
O shift between Pleistocene and Holocene waters on the European scale, and by calculating δ
18
O/Δ
T
ratios from δ
18
O v. recharge temperature plots for aquifers at different distances from the Atlantic Ocean. Indications are that the more positive δ
18
O value of ocean water during the Pleistocene dominates in the more westerly European countries over the negative δ
18
O shift during cooler conditions. There are also indications that air-mass circulation during the Pleistocene was similar to the present day.

The evolution of a palaeowater can best be studied by measuring chemical tracers; this is possible in freshwater aquifers, where a clear trend of geochemical reactions is observed, and in freshening marine aquifers. Chemical and isotopic tracers can also be used to study the movement of the front between palaeowater and younger components that must be identified in coastal aquifers to guarantee a sustainable water use.
Management of coastal palaeowaters
Authors: Custodio E. , Edmunds W. M. , Travi Y.
Published: April 2008

Coastal regions of Europe have special water supply problems due to the population pressure, competing demands and the ever-present risk of saline intrusion from modern and old sea water. This is especially the case in southern Europe where touristic demands exacerbate water supplies, often in semi-arid regions. Palaeowaters emplaced at times of lowered sea level offer potential high-quality, high-value reserves in many areas, although a lack of understanding of the nature of the resource, together with exploitation for non-drinking purposes and indiscriminate drilling, may already have damaged the underground reservoirs and the reserves within them. These aquifers may, however, offer sites that are attractive for seasonal water storage.

Palaeowaters generally are of high quality and are demonstrably free of human impacts. Good drilling practice and operation are required to avoid contamination, the mixing of palaeowaters with more saline waters and avoidance of marine intrusion. Two case studies illustrating the management practice in areas containing palaeowaters — in the French Mediterranean coast and the Llobregat Delta area of Catalonia, Spain — are given. These demonstrate, above all, the need for integrated development, observation and planning, which involves all the stakeholders, especially the beneficiaries and end-users. There is a need for improved regulation for the protection, use and management of aquifers containing palaeowaters at both the national and European scale, to consider the intrinsic value of uncontaminated palaeowaters as a unique, non-renewable source of drinking water. The value of such aquifers for subsequent freshwater storage and also for use as a brackish water source for desalination may also be considered.
European views on terrestrial chronology from Descartes to the mid-eighteenth century
Authors: Vaccari Ezio
Published: April 2008

The Theories of the Earth formulated by the English scholars Thomas Burnet, William Whiston and John Woodward at the end of the seventeenth century circulated widely within the continent of Europe during the first decades of the eighteenth century. These theories established a sequence of physical conditions of the Earth according to the chronology outlined in the Book of Genesis, emphasizing two main stages: the Creation and the Deluge. Although the authority of the Biblical account of the age and early history of the Earth was normally accepted at the beginning of the eighteenth century, the continental reception of English Theories of the Earth varied. This was due to the complexity of the European context which since the 1660s had produced the theories of René Descartes, Gottfried Wilhelm Leibniz and Athanasius Kircher, as well as Nicolaus Steno’s dynamic view on the development of the Earth’s surface. Steno emphasized the importance of the interpretation of rock strata in the field for reconstruction of the Earth’s history. He also carefully avoided contradicting the Biblical account and associated the Deluge with one of the geological stages identified in his history. Nevertheless, the Stenonian heritage stimulated some Italian scientists — such as Antonio Vallisneri, Luigi Ferdinando Marsili, and later Giovanni Targioni Tozzetti and Giovanni Arduino — to presuppose, within the results of their researches, an indefinitely great antiquity of the Earth. Theoretical models linked to Biblical chronology included those of Emanuel Swedenborg in Sweden and Johann Jakob Scheuchzer in Switzerland, while in France, Benoît De Maillet proposed a Theory of the Earth which was censured by the Church because of its possible implications regarding the eternity of matter. Among European scholars of the first decades of the eighteenth century, the Stenonian heritage (notably the necessity of fieldwork in a regional context) and the global Theories of the Earth were equally influential.
Buffon, Desmarest and the ordering of geological events in
époques
Authors: Taylor Kenneth L.
Published: April 2008

During the eighteenth century many naturalists and philosophers became persuaded of the great antiquity of the Earth, and of the promise that knowledge of the Earth’s past and development could be built up through investigations of natural terrestrial features. In common with most geological issues of the time, these opinions rose to prominence to a considerable degree in connection with the so-called Theories of the Earth. This paper discusses some interconnections between Theories of the Earth and the emerging enterprise of geological field investigation, as they related to efforts toward establishing relative ages of geological phenomena. It considers in particular the two rather different Theories of the Earth offered by Buffon in 1749 and 1778, respectively. While the earlier one (
Théorie de la Terre
) emphasized principles for extracting physical knowledge of the Earth’s configuration through empirical investigation, the latter theory (
Époques de la Nature
) drew attention to the project of organizing knowledge about the Earth around a directional sequence of periods. The central impulses of Buffon’s two conceptions of the Earth were combined in actualistic field investigations by geologists of the late eighteenth century, Nicolas Desmarest in particular, which contributed significantly to the establishment of methods for determining distinct stages or sequences of the Earth’s past.
Timeless order: William Smith (1769–1839) and the search for raw materials 1800–1820
Authors: Torrens Hugh S.
Published: April 2008

Smith first described himself as ‘land surveyor and drainer’ in his 1801
Prospectus
but then as ‘engineer and mineralogist’ in his first book of 1806. His several careers are discussed with an attempt to shed new light on his pioneering career as ‘mineral surveyor’ (a term invented by his pupil, John Farey, in 1808). The trials for coal with which he was involved can be divided into two: those in which he used his new stratigraphic knowledge in positive searches for new coal deposits; and those where his stratigraphic science could often negatively demonstrate that many such searches were doomed to failure. These latter attempts were being made in, and misled by, repetitious clay lithologies, which resembled, but were not, Coal Measures. Smith was the first to show how unfortunate it was for such coal hunters that the British stratigraphic column abounded in repetitious clay lithologies. It was also unfortunate for Smith that many of the founding fathers of the Geological Society were unconvinced of the reality or the utility of Smith’s discoveries. Its leaders at first did not believe he had uncovered anything of significance and then simply stole much of it. The development of Smith’s stratigraphic science in the world of practical geology remains poorly understood, but the legacy of his method for unravelling relative geological time and space was one of the most significant of the nineteenth century.
The age of the Earth in the United States (1891–1931): from the geological viewpoint
Authors: Yochelson Ellis L. , Lewis Cherry L. E.
Published: April 2008

In North America, prior to the Second World War, discussions on the age of the Earth were a minuscule part of the geological literature, as demonstrated by the small number of papers indexed to the subject in bibliographies. Indeed, during the first quarter of the twentieth century, there were few general papers on this topic circulating among those geologists who dealt with sedimentary rocks and fossils; nevertheless, evidence is provided that many geologists were aware of the ‘debate’ going on in Britain.

As the methodology for determining the length of geological time dramatically changed during the four decades represented here, so too did the evolution of ideas about the age of the Earth. These can conveniently be divided into three time periods: before, during and after the discovery that radioactivity could be applied to the dating of rocks. The first section reviews the attitudes of geologists in America to the age of the Earth in the 1890s. It is followed by their reactions to the discovery of radioactivity. The third part discusses two major publications on the age of the Earth which reflect the ultimate acceptance, by geologists, of the long timescale revealed by radioactivity. Because much of the early work on radioactivity was being done in Europe, American geologists were marginally later than their British counterparts in accepting the concept of radiometric dating, but by the end of the period under consideration they led the field in geochronology.
The oldest rocks on Earth: time constraints and geological controversies
Authors: Kamber Balz S. , Moorbath Stephen , Whitehouse Martin J.
Published: April 2008

Ages in the range 3.6–4.0 Ga (billion years) have been reported for the oldest, continental, granitoid orthogeneisses, whose magmatic precursors were probably formed by partial melting or differentiation from a mafic, mantle-derived source. The geological interpretation of some of the oldest ages in this range is still strongly disputed.

The oldest known supracrustal (i.e. volcanic and sedimentary) rocks, with an age of 3.7–3.8 Ga, occur in West Greenland. They were deposited in water, and several of the sediments contain
13
C-depleted graphite microparticles, which have been claimed to be biogenic.

Ancient sediments (
c.
3 Ga) in western Australia contain much older detrital zircons with dates ranging up to 4.4 Ga. The nature and origin of their source is highly debatable. Some ancient (magmatic) orthogneisses (
c.
3.65–3.75 Ga) contain inherited zircons with dates up to
c.
4.0 Ga. To clarify whether zircons in orthogneisses are inherited from an older source region or cogenetic with their host rock, it is desirable to combine imaging studies and U-Pb dating of single zircon grains with independent dating of the host rock by other methods, including Sm-Nd, Lu-Hf and Pb/Pb.

Initial Nd, Hf and Pb isotopic ratios of ancient orthogneisses are essential parameters for investigating the degree of heterogeneity of early Archaean mantle. The simplest interpretation of existing isotopic data is for a slightly depleted, close-to-chondritic, essentially homogeneous early Archaean mantle; this does not favour the existence of a sizeable, permanent continental crust in the early Archaean.

By analogy with the moon, massive bolide impacts probably terminated on Earth by
c.
3.8–3.9 Ga, although no evidence for them has yet been found. By
c.
3.65 Ga production of continental crust was well underway, and global tectonic and petrogenetic regimes increasingly resembled those of later epochs.
Lead isotopes and the age of the Earth — a geochemical accident
Authors: Hofmann Albrecht W.
Published: April 2008

The assumptions underlying the models used in the literature for obtaining the age of the Earth from terrestrial lead isotopes are severely violated by the complex evolution of the Earth, particularly the extreme chemical fractionation occurring during crust-mantle differentiation. Young conformable lead deposits are isotopically very similar to young sediments, the erosion products derived from the Earth’s most highly fractionated large-scale reservoir, the upper continental crust. Therefore, ancient conformable lead deposits are also likely to track continental compositions rather than the composition of any truly primitive reservoir.

Although the specific enrichment mechanisms during crust formation are both extreme and quite different for U and Pb, the net enrichments in the crust, as well as the corresponding depletions in the residual mantle, are on average very similar for the two elements. It is because of this geochemical coincidence that the time-integrated U/Pb ratios of conformable lead deposits, which integrate and average large volumes of crustal lead, are very close to average mantle values. For the same reason, the isotopic evolution of these conformable lead deposits follows an apparently (nearly) closed system evolution path of a 4.4 to 4.5 Ga-old U-Pb system rather closely, even though that system was actually very far from remaining chemically closed during its history. From these considerations I conclude that terrestrial Pb isotopes do not furnish a suitable tool for determining a refined estimate of the age of the Earth within the broad bounds of 4.4 and 4.56 Ga limits, which are given by other types of evidence, such as the ages of meteorites, the Moon, and the formation intervals of the Earth’s core and atmosphere derived from the decay products of short-lived, now-extinct nuclides.
Understanding the beginning and the end
Authors: Rees Martin J.
Published: April 2008

This paper attempts to set the Earth in a cosmic perspective. It discusses the Sun’s life cycle in the context of stellar evolution, and the ideas of stellar nucleosynthesis, as an explanation of the origin of the atoms on the Earth. Current ideas on how planetary systems form are mentioned, along with data on recently discovered planets around other stars. The origin of matter itself can be traced back to a ‘Big Bang’: corroboration of this model comes from the microwave background and from observed helium and deuterium abundances. There is now a concordance between stellar ages and the cosmic evolutionary timescale inferred from cosmology, from which we derive an age for the universe. Recent progress brings into focus a new set of questions about the ultra-early universe. Until these can be answered, it will remain a mystery why the universe is expanding in the observed fashion, and why it contains the measured mix of atoms, radiation and dark matter.
Compaction creep of quartz-muscovite mixtures at 500°C: Preliminary results on the influence of muscovite on pressure solution
Authors: Niemeijer A. R. , Spiers C. J.
Published: April 2008

It is widely claimed that the presence of phyllosilicates in sandstones increases intergranular pressure solution (IPS) rates in these rocks. However, this has not been experimentally confirmed. This study reports the results of isostatic hot-pressing compaction experiments at a temperature of 500°C and an effective pressure of 100 MPa on mixtures of quartz and muscovite. Previous work has shown that under these conditions dissolution is rate controlling in pure quartz. No acceleration of compaction rates of quartz by the addition of muscovite was observed. Instead, a modest decrease in compaction rates was observed (factor 3–10), which we infer was due to a decrease in IPS rate. The effect of muscovite in slowing IPS may be due to the influence of dissolved aluminum (Al
3+
) dominating over any accelerating effects of alkali-metal cations. From the geochemical literature, Al
3+
in solution is expected to decrease the solubility, dissolution rates and precipitation rates of quartz. However, the effect of the addition of muscovite on IPS rates in quartz when controlled by diffusion or precipitation may be different. Experiments should be conducted on quartz sand under conditions where diffusion or precipitation is rate controlling to investigate these possible effects.
The origin of fibrous veins: constraints from geochemistry
Authors: Elburg Marlina A. , Bons Paul D. , Foden John , Passchier Cees W.
Published: April 2008

Several recent studies have suggested that antitaxial fibrous veins may form without fracturing, and not by the commonly invoked crack-seal mechanism. It has also been suggested that such veins would derive their nutrients locally by diffusional transport. This hypothesis was tested on carbonaceous shale-hosted antitaxial fibrous calcite veins from Oppaminda Creek in the northern Flinders Ranges, South Australia. Apart from their fibrous texture, these veins lack the classical features of crack-seal veins, such as wallrock-parallel inclusion bands.

Diffusional transport of locally derived calcite cannot explain all major and trace element data of the veins and their adjacent wallrock and indicate that part of the calcite was transported over distances of at least >decimetres, probably ≫100m. Sr isotopic fingerprinting shows that an external fluid that carried radiogenic Sr must have percolated through the system. Fluid flow was pervasive as there is no evidence that this fluid preferentially percolated through the veins. Our data support the view that antitaxial fibrous veins of the type found at Oppaminda Creek grew in the absence of fractures, but show that such veins do not necessarily indicate local diffusional transport. Our data confirm a recently postulated basin-wide fluid flow event around 586 Ma that is probably related to copper mineralization in the area.