bluuebunny/crossref_metadata_2025_split huggingface dataset:
40
Ar/
39
Ar ages of fallout tephra layers and volcaniclastic deposits in the sedimentary succession of the western Woodlark Basin, Papua New Guinea: the marine record of Miocene-Pleistocene volcanism
Authors: Lackschewitz K.S. , Bogaard P.V.D. , Mertz D.F. 
Published: April 2008

Abstract

Five fallout tephra layers and 13 heterolithological volcaniclastic deposits drilled at Holes 1115A, 1115B, 1115C, 1109C, 1109D and 1118A, during Leg 180 on the downflexed northern margin of the western Woodlark Basin, have been dated by single-crystal laser
40
Ar/
39
Ar analyses. The fallout tephra layers range in age from 0.135 ± 0.008 Ma to 2.84 ± 0.03 Ma. Sedimentation ages determined for the volcaniclastic deposits range from 1.75 ± 0.29 Ma to 3.79 ± 0.01 Ma, closely matching the nannofossil, planktonic foraminifer and palaeomagnetic chronostratigraphies of the holes. However, two volcaniclastic deposits from 516.91 m below seafloor (mbsf) and 632.5 mbsf in Hole 1118A are significantly older than indicated by biostratigraphic and palaeomagnetic data, probably because of the presence of older reworked volcanic crystals. The youngest ash layer is derived from explosive eruptions in the Dawson Strait area of the D’Entrecasteaux Islands, whereas the four older tephra layers are attributed to explosive eruptions in the Moresby Strait area of the D’Entrecasteaux Islands. The
40
Ar/
39
Ar ages of volcaniclastic sand layers in Holes 1115C and 1118A indicate a transition from a shallow-water succession (<150m) to a deeper-water succession (150–500m) with rapid deposition of volcaniclastic sands, mainly by turbiditic currents, at 3.8 Ma. This transition is related to the subsidence of the margin during rifting of the Woodlark Basin. Two volcaniclastic deposits with ages of 13.84 ± 0.02 Ma and 14.04 ± 0.03 Ma, respectively, provide important time markers in the middle Miocene sedimentary sequence at Hole 1115C, where biostratigraphic ages are scarce. Our
40
Ar/
39
Ar ages represent the first marine record of Miocene to Pleistocene volcanism in the area of eastern Papua.
Tectonic evolution of the NW Red Sea-Gulf of Suez rift system
Authors: Khalil S.M. , McClay K.R. 
Published: April 2008

Abstract
The NW Red Sea-Gulf of Suez rift system was initiated during Late Oligocene time and underwent extension in a N65°E direction, almost orthogonal to pre-existing WNW-trending Pan African shear-zone fabrics in the crystalline basement of the Sinai-African plate. Earliest syn-rift sediments are Upper Oligocene continental clastic deposits with minor syn-rift basalts. Early Miocene sedimentation was dominated by shallow marine clastic deposits, which developed variable stratigraphic architectures as a response to the interaction of extensional faulting, sea-level changes, sediment supply and dispersal. Analysis of fault geometries, fault kinematics and sedimentation patterns indicates that rift-normal extension predominated throughout the Late Oligocene-Early Mid-Miocene evolution of the rift. Reactivation of the Precambrian basement fabrics was the main factor controlling the fault architecture, fault linkage and evolution of the NW Red Sea-Gulf of Suez rift. Individual faults were initially strongly segmented and offset across ‘soft-linked’ relay structures. With increased extension these faults became linked by breaking down relay structures with the development of local ‘hard-linked’ transfer faults, thus giving rise to the rhomboidal fault pattern of the rift system. In Mid-Miocene time, the Levant-Gulf of Aqaba transform boundary was established, linking the Red Sea rift plate boundary to the convergent Bitlis-Zagros plate boundary. This resulted in a dramatic decrease in extension rates within the Gulf of Suez whereas the northern Red Sea continued to extend, with significant syn-rift sediments deposited in Late Miocene-Pliocene time in offshore fault-bounded basins.
Transfer zones normal and oblique to rift trend: examples from the Perth Basin, Western Australia
Authors: Song Tingguang , Cawood Peter A. , Middleton Mike 
Published: April 2008

Abstract
The Perth Basin is a major tectonic province along the western margin of the Australian continent. Basin morphology is controlled by north-striking faults formed during Permian rifting and reactivated during later tectonic events, notably during continental break-up in Late Jurassic-Early Cretaceous time. Transfer structures, including those normal and oblique to the major faults, compartmentalized the basin into segments of distinctive character. East-west transfer faults, perpendicular to the basin trend, were active throughout the rift stage of basin development and are recognized only in the northernmost onshore part of the Perth Basin, corresponding to the depocentre for Permian sediment accumulation. Northerly trending normal faults change in character and/or terminate at these east-west structures. The NW-striking transfer zones influenced deformational features formed during the Late Jurassic-Early Cretaceous break-up. No continuous fault plane has been identified with these zones in the sedimentary sequences. They are characterized by the termination and/or swing of major normal faults at the transfer zones. Sinistral strike-slip movement of at least 16 km is recognized across the Abrolhos Transfer Zone on the basis of offset in the trend of the Beagle Fault system. The orientation, age of activation, and position of these zones are similar to those of transform faults in the adjoining Indian Ocean, suggesting that the two structures are contiguous.
Patterns of extension and magmatism along the continent-ocean boundary, South China margin
Authors: Clift Peter D. , Lin Jian ,   Odp Leg 184 Scientific Party
Published: April 2008

Abstract

Early Oligocene sea-floor spreading in the South China Sea was preceded by at least two episodes (in Maastrichtian and Mid-Eocene time) of continental extension that generated a series of rift basins on the South China margin, which are separated from the continent-ocean boundary (COB) by an outer structural high. Regional multichannel seismic profiles showing faulting of the pre-rift basement allow the amount of extension in the upper crust to be measured. The total subsidence across the South China margin is far in excess of that predicted using a forward flexural-cantilever model of extension and the degree of faulting measured seismically in the upper crust. This mismatch suggests preferential extension of the lower crust, increasing towards the COB to account for the subsidence. The same feature is seen in the Nam Con Som Basin, which is located close to the southwest end of an extinct propagating spreading ridge offshore from Vietnam. However, in the Beibu Gulf Basin, which is not adjacent to the COB, subsidence is approximately compatible with uniform extension in the upper and lower crust across the entire basin, if not at all locations. We predict that extension of the lower crust exceeds that in the lithospheric mantle along the COB. Heat-flow measurements at Ocean Drilling Program (ODP) sites on the Chinese continental slope and on the conjugate Dangerous Grounds margin yield values consistent with, or slightly higher than, those predicted by models of uniform extension in the lithosphere. Although there is no magmatism comparable with the seaward-dipping volcanic rocks of rifted volcanic margins, there is seismic evidence of rift-related volcanic rocks spanning a width of
c.
25 km landward of the COB. Simple adiabatic melting models do not predict magmatism, and we suggest that the presence of water in the mantle lithosphere, together with residual pre-rift heat, may instead be responsible for increasing melting here. Deep-water syn-rift sediments recovered by the ODP near the COB indicate that volcanism was submarine and that rifting culminated in a mass wasting event that marks a break-up unconformity. The average extension in South China Sea is much less than that seen in the extreme ‘non-volcanic’ Iberian margin. The South China margin may represent an intermediary form of continental extension between the end member extremes of the Iberia-type non-volcanic and the Greenland-type volcanic margin.
Anomalous melt production after continental break-up in the southern Iberia Abyssal Plain
Authors: Minshull T.A. , Dean S.M. , White R.S. , Whitmarsh R.B. 
Published: April 2008

Abstract

Recent geophysical work and Ocean Drilling Program drilling in the southern Iberia Abyssal Plain have indicated that, in a transition zone up to 170 km wide between thinned continental crust and oceanic crust, the basement consists of serpentinized peridotite mantle with sparse mafic intrusive or extrusive rocks. There is no evidence for the addition of significant magmatic material to the stretched continental crust landward of this zone during the last phase of rifting, whereas seaward of this zone, where the half-spreading rate is about 10 mm a
−1
, the crust rapidly reaches a thickness of
c.
6 km, which is normal for Atlantic oceanic crust. Models of melt generation during pure shear, finite-duration continental rifting can successfully reproduce the observed absence of significant syn-rift magmatism on, within and beneath the thinned continental crust if the rifting episode is longer than 10–20 Ma. However, for normal mantle potential temperatures, such models predict significant melt generation in the transition zone seaward of the thinned continental crust even for rift durations longer than 20 Ma. Restricted melting beneath the transition zone might be explained partly by lateral heat loss to the adjacent continental lithosphere, by anomalously low mantle potential temperatures at break-up time, or by depth-dependent stretching such that the observed infinite stretching factor for the crust is not representative of the lithosphere as a whole. An additional mechanism for restricted melt production involves a transitional state between the end of continental extension and the onset of steady-state sea-floor spreading, during which mantle upwelling is less focused than at normal oceanic spreading centres.
Palaeowater in coastal aquifers of Spain
Authors: Manzano M. , Custodio E. , Loosli H. , Cabrera M. C. , Riera X. , Custodio J. 
Published: April 2008

Abstract

In the framework of the PALAEAUX project, three coastal aquifers have been studied in Spain, looking at the possible existence of Pleistocene or Early Holocene fresh groundwater, in addition to the formerly studied Llobregat Delta. They constitute representative situations of the most common coastal aquifers. The main characteristics of these four areas are:

The Llobregat Delta system, studied since 1965, is placed to the southwest of Barcelona (NE Mediterranean coast of the Iberian Peninsula). It is a sedimentary fluvial formation of Pleistocene to recent age, which is representative of small size coastal alluvial formations with the deep confined aquifer open to the sea offshore. Marine sea water penetrated the deep Pleistocene layer during the Flandrian sea-level rise but afterwards relatively high freshwater heads upstream allowed its progressive flushing to the sea through the submarine outlet since 6000–8000 a ago. Freshwater turnover time is shorter than the Holocene duration and it has been renovated due to natural discharge of the aquifer to the sea. The renovation process has recently been accelerated due to intensive groundwater exploitation during the past century.
Nowadays, only freshwater a few centuries old remains in low permeability areas of the
confined Pleistocene aquifer.

The Doñana sedimentary aquifer system corresponds to the ancient estuary of the Guadalquivir
River (SW Spain). It contains old saline groundwater that has not been flushed away due to the
low freshwater head. In this aquifer
39
At,
85
Kr,
3
H,
14
C and
13
C measurements have been used
to ascertain the age structure of several mixed groundwater samples. After correction, the
oldest fresh groundwater
14
C age is
c.
12–15 ka but
39
Ar ages point to somewhat younger
water. Neither the stable isotope contents nor the recharge temperature calculated from noble
gases show a climatic signature for these waters.

The Inca-Sa Pobla carbonate system is the northeast sector of the island of Mallorca. Brackish
and salt groundwater in the coastal area has been found along the coastal strip of S’Albufera,
displaying what seems a convective-like flow pattern inside the up to 200 m thick aquifer. The
most consistent estimated average
14
C ages of the mixed water vary between 9 and 13 ka, i.e.
Early Holocene-Late Pleistocene. Water
18
O and
2
H contents do not show a clear climatic
signature.

The Amurga volcanic Massif is on the southeast of the island of Gran Canaria. Brackish
groundwater is found in the thick phonolite rock sequence. The unsaturated zone can be up to
200 m thick. Groundwater salinity is due to recharge under arid conditions and the influence
of marine airborne salts. Groundwater
14
C age is possibly
c.
11 ka, indicating a Late
Pleistocene age water mixture. The small recharge due to aridity and the thick unsaturated zone
explains this. Stable-water isotopes show no clear climatic signature
Palaeowaters from the Glatt Valley, Switzerland
Authors: Purtschert R. , Beyerle U. , Aeschbach-Hertig W. , Kipfer R. , Loosli H. H. 
Published: April 2008

Abstract

Isotopic and noble gas data from a confined gravel aquifer in the Swiss Plateau has been investigated. From glaciomorphological studies it is well known that the Glatt Valley was repeatedly ice covered during the last glacial period. Corrected radiocarbon ages range from 0 to >28 ka
bp
and reveal a gap of between 25 and 17 ka
bp
, indicating an interruption of groundwater recharge during the last glacial maximum. Based on
39
Ar measurements, a contribution of younger water components with residence times of a few hundred years have been identified in some waters. Recharge temperatures, estimated by analysis of noble gas contents, suggest a temperature difference of
c.
5°C at the Holocene-Pleistocene transition at 12 ka
bp
. The long-term temporal δ
18
O-recharge temperature relation over the last 30 ka has a slope of
c.
0.49‰ °C
−1
, consistent with the modern seasonal relation.
Weichselian palaeoclimate and palaeoenvironment in Europe: background for palaeogroundwater formation
Authors: Vaikmäe R. , Edmunds W. M. , Manzano M. 
Published: April 2008

Abstract

A review is given of palaeoclimatic and palaeoenvironmental evidence across Europe for the Weichselian period relevant to interpreting the emplacement and circulation of groundwaters. In addition, this provides the background against which the evidence of past climates and environments contained in groundwaters in coastal areas of Europe, from the Baltic to the Atlantic Ocean may be compared. For much of the Weichselian, although significantly colder than at present, conditions were favourable for the recharge of groundwater, as shown, for example, by periods of speleothem growth. During the last glacial maximum (LGM) recharge is likely to have ceased over much of permafrost-covered Europe, although shallow groundwater recharge from meltwater (generated by the geothermal gradients) could have taken place beneath the ice where pressure relief through tunnel valleys may have occurred. Modern recharge could have started as early as 13
14
C ka
BP
, but probably interrupted by the Younger Dryas between 11 and 10
14
C ka
BP
. In the Baltic areas, ice-dammed lakes inhibited the start of the modern hydrogeological regimes until
c.
10.3
14
C ka
BP
. Tundra conditions prevailed over most of ice-free southern Europe at the time of the LGM. At this time the area south of the Portuguese-Spanish border retained a generally warm and relatively humid climate due to the maintenance of warmer sea-surface temperatures derived from Atlantic Ocean circulation. For most of coastal Europe, however, the most significant impact on groundwater circulation is likely to have been the lowering of sea levels that drained large areas of the shelf, such as the North Sea and the English Channel, and also had a significant impact on the Atlantic coast of the Iberian Peninsula where the maximum lowering of up to 130 m would have been experienced. This, together with the general changes in climate, would also have reorganized the atmospheric chemistry over sites in Europe that is likely to be recorded in the groundwater’s chemical and isotopic signatures.
Modelling scenarios for the emplacement of palaeowaters in aquifer systems
Authors: Harrar W. G. , Williams A. T. , Barker J. A. , Van Camp M. 
Published: April 2008

Abstract
The response of coastal aquifer systems to global sea-level rise, the presence of permafrost and glaciation has been analysed using analytical and numerical models. The hydraulic connectivity between confined coastal aquifers and the sea largely controls their response to global sea-level rise. Open aquifer systems have direct hydraulic contact with the sea where they sub crop along the continental slope and base-level history for the aquifer is defined by sea-level history. In these systems, hydraulic heads equilibrate quickly to sea-level change at rates controlled by the aquifer hydraulic diffusivity. Interface movement lags behind the equilibration of the hydraulic heads and is controlled largely by the rate at which freshwater can be flushed from the aquifer through overlying semi-confining units. Interface movement occurs over time periods of tens of thousands of years. In contrast, closed aquifer systems lack direct hydraulic connectivity with the sea, which is controlled by the thickness and permeability of overlying semi-confining layers. During the Late Pleistocene-Early Holocene the base-level history for closed aquifer systems underlying the North Sea Basin was defined by the location of rivers and lakes in areas that are now offshore. These aquifers became coastal aquifers during the Holocene when rivers and lakes were inundated by rising sea levels. Salinization of closed aquifer systems may occur due to the downward diffusion of salts through overlying semi-confining layers in the presence of upward freshwater seepage. Aquifers overridden by glaciers respond in a manner that is largely controlled by aquifer transmissivity and geometry. The presence of permafrost inhibits recharge resulting in lower hydraulic heads and a reduction in aquifer fluxes.
Application of geophysical borehole logging techniques to examine coastal aquifer palaeohydrogeology
Authors: Buckley David K. , Hinsby Klaus , Manzano Marisol 
Published: April 2008

Abstract
Geophysical logging is shown to be a useful technique to support investigations of coastal aquifer hydrogeology. Formation logging can identify the geological layering and fluid logging can characterize the salinity distribution. The measurements also reveal wellbore flow to be common in coastal boreholes, which can mask the salinity stratification in the aquifer matrix. Geophysical logging can be used to guide water sampling and to provide information on the palaeohydrogeology. In combination with water sampling and age determinations, it has shown modern groundwaters overlying Holocene age groundwaters, in turn overlying groundwaters of Pleistocene age, within 150 m of the surface in some of the aquifers studied. Sea-level change in response to Pleistocene glaciations and deglaciations is recognized as a major control on the salinity of groundwaters and on the development of permeable flow routes in coastal aquifers. The permeable routes that developed by groundwater circulation to older and deeper base levels are now partly or wholly occupied by groundwaters of modern flow systems, and can be the focus for saline intrusion. The effects of Pleistocene sea-level change on aquifer development appear to be worldwide and are being increasingly recognized. Examples are described to illustrate the development of flow horizons in relation to rock layering, structure and base levels.
The modern water interface: recognition, protection and development — advance of modern waters in European aquifer systems
Authors: Hinsby K. , Edmunds W. M. , Loosli H. H. , Manzano M. , Condesso De Melo M. T. , Barbecot F. 
Published: April 2008

Abstract

Modern groundwater that has recharged aquifers within the past 50 a shows the influence of humans globally, either by the presence of small concentrations of environmental tracers or in some cases by severe pollution. This study describes important environmental tracers (e.g.
3
H,
85
Kr, chlorofluorocarbons, SF
6
) and contaminants (e.g. NO
3
−
}, pesticides, chlorinated solvents) for modern groundwater dating and recognition of human impacts. Some applications of the described tracers in aquifers investigated in the PALAEAUX study are presented in order to illustrate the advance of modern waters in European aquifer systems. The study shows that the location of the modern water interface varies within a range of between
c
. 10 and
c
. 100 m in the investigated aquifers due to variations in hydrogeological setting, climate and exploitation of the groundwater resource. The subsurface distribution of the modern water indicators and contaminants demonstrate that the advance of modern groundwaters and the fate of harmful substances in them have important implications for protection and development of the water resources. Contaminants that do not degrade or degrade only very slowly will advance further into the aquifers and may eventually contaminate even deep groundwater systems.
Evolution of groundwater systems at the European coastline
Authors: Edmunds W. M. , Hinsby K. , Marlin C. , Condesso de Melo M. T. , Manzano M. , Vaikmae R. , Travi Y. 
Published: April 2008

Abstract

An overview is given of the status and origin of fresh and saline groundwaters in the sedimentary aquifers at or near the present European coastline. Results are presented as six regional maps summarizing, as far as possible, the conditions likely to have existed at the end of the Pleistocene, after the impact of glaciation, when groundwaters might be expected to have reached their maximum offshore evolution prior to the encroachment of sea water during the Holocene marine transgression. In the eastern Baltic, the groundwater evolution was different to other European regions in that freshwater heads were
higher
than the present day, promoting recharge during much of the Late Pleistocene. Near the North Sea coasts, there is generally evidence of freshwater movement to depths of 100–150 m but the absence of deeper freshwater (palaeowater) storage may relate to the low hydraulic gradients in the North Sea Basin. In the southeastern part of the North Sea brackish palaeowater is found between Tertiary marine sediments
c
. 300 m below the island of Rømø, 10 km off the Danish west coast. Freshwater of Pleistocene and Holocene ages is found in aquifers at the English Channel coast in several areas, to depths in excess of −300 m; offshore flow in the Late Pleistocene took place towards the central palaeovalley and some of this groundwater may be preserved off the present coastline. In the two Atlantic coastal areas of France and Portugal-Spain a contrast exists due to the proximity of the continental margin and different hydraulic gradients. In Portugal, freshwaters are found at the coastline, and probably offshore, that contain evidence of recharge during the lowered sea levels. In most of the southwestern Atlantic coast of Spain, fresh recent groundwater discharges along and beyond the coastline, while in the old estuary of the Guadalquivir River, saline Holocene water still encroaches the sediments. On the Mediterranean coast of France and Spain some salinity encroachment took place during sea-level rise. In most of the Spanish aquifers fresh recent groundwater has substituted for palaeowater, except for the low-lying areas (Ebro Delta, Inca-Sa Pobla Plain) where brackish Holocene water is still present.