bluuebunny/crossref_metadata_2025 huggingface dataset:
New grounds for reassessing palaeoclimate of the Sirius Group, Antarctica
Authors: RETALLACK G. J. , KRULL E. S. , BOCKHEIM J. G.
Published: December 2007

Fossil
Nothofagus
leaves from the Meyer Desert Formation of the Sirius Group in the central Transantarctic Mountains have been found with recycled marine diatoms indicating that they are no older than 4.1–3.1 Ma; they have been interpreted as evidence for Pliocene warming and diminution of the East Antarctic Ice Cap. In contrast, Plio-Pleistocene ice-cap stability and sustained polar palaeoclimate has been argued from landforms in Victoria Land and isotopic data from the Southern Ocean. New evidence on this question comes from fossil soils in the Meyer Desert Formation. One of these, the Siesta palaeosol, has a gypsic horizon at a depth of 85 cm as in soils of polar deserts with a mean annual precipitation (MAP) of 120–220 mm. Clastic dykes from a 60–80 cm thick permafrost active layer in the palaeosols are evidence of a mean annual temperature (MAT) of −3 to −11°C. This is warmer and wetter than the Dominion Range today (MAP 36 mm, MAT −39°C) but still a periglacial climate, cooler and drier than southern Chilean moorland and krummholz (MAP 600–7500 mm, MAT 5–8°C), or subantarctic tundra (MAP 400–2500 mm, MAT −5 to +5°C). A Pliocene age for the
Nothofagus
fossils and Siesta palaeosol is compatible with soil development on surfaces that bracket their enclosing deposits. The Dominion Range was significantly warmer and wetter than it is today during Pliocene (
c
. 3.5 Ma) growth of
Nothofagus
and formation of the Siesta palaeosol, but the Beardmore Glacier was still large at that time. Surface soils and palaeosols of the Meyer Desert Formation are evidence of another warmer and wetter episode earlier during the Pliocene (
c.
5 Ma). Both warm intervals were separated by intervening times of glacial expansion and frigid palaeoclimate.
Decapod crustaceans from the Eocene La Meseta Formation, Seymour Island, Antarctica: a model for preservation of decapods
Authors: Feldmann R.M. , Schweitzer C.E. , Marenssi S.A.
Published: December 2007

Thirteen species of fossil decapod crustaceans collected from 43 localities in the La Meseta Formation (Eocene), Seymour Island, Antarctica, have been located precisely using global positioning system techniques and accurately placed in their stratigraphic context using an allostratigraphic scheme. Three decapod species are congeneric with extant species known from outer shelf and slope habitats documenting an onshore–offshore pattern of ecological preference. Functional morphological analysis of the decapods confirms the environmental interpretations based upon sedimentological studies. Species diversity is greatest in the lower and upper parts of the section, in the Acantilados and Submeseta allomembers, respectively. However, numerical abundance of specimens is greatest near the top of the coarsening-upward sequence in the Cucullaea I Allomember. This allomember and the underlying Campamento Allomember are overwhelmingly dominated by a single species,
Lyreidus antarcticus
. The relatively high diversity of decapods in the lower and upper parts of the La Meseta Formation is interpreted as resulting from favourable preservational environments in delta-front and nearshore environments where burial was rapid and sediment reworking was minimal. In the middle part of the La Meseta Formation, sediment reworking was probably high and fragile arthropod cuticular material was destroyed, except in the case of
Lyreidus
, which is a burrower and was probably preserved within its burrow. The pattern of diversity documented by the arthropods differs markedly from that of the molluscs, probably because of the presence of more durable shell material in the pelecypods and gastropods. The La Meseta Formation record of decapods may serve as an important model for arthropod preservation against which other occurrences can be tested.
Superposed deformations and their hybrid effects: the Rhoscolyn Anticline unravelled
Authors: Treagus Susan H. , Treagus Jack E. , Droop Giles T. R.
Published: December 2007

This study of the controversial structures of the Rhoscolyn Anticline suggests a different result of two-phase coaxial deformation from Ramsay's Type 3 interference fold patterns. From detailed field observations of the sequence of bedded quartzites, psammites, pelites and oblique quartz veins, with their strong competence contrasts, we conclude that the Rhoscolyn Anticline was an original tight, upright F
1
anticline that has undergone modification and distortion in a second deformation (D
2
). This second deformation is an oblique, but near-vertical, pure shear, with a quantifiable strain ratio (
R
=3) that altered the Rhoscolyn Anticline and its minor structures into a more open, SE-overturned antiform, with
c
. 260 m hinge migration. Refolded folds are rare, but hybrid F
1
+ F
2
minor folds and their fabrics, especially in the region between old and new hinges, provide clues to the two-stage history. Oblique distortion of originally NW-verging F
1
minor folds has resulted in their apparent neutral vergence in the present-day hinge of the Rhoscolyn Anticline. We regard the structures and fabrics in quartzites and psammites as more reliable indicators of the region's deformation history than those in pelites or quartz veins, and this may prove true for other regions of polyphase deformation.
Fractionation of carbon and oxygen isotopes in
13
C-rich Palaeoproterozoic dolostones in the transition from medium-grade to high-grade greenschist facies: a case study from the Kola Superdeep Drillhole
Authors: Melezhik Victor A. , Fallick Anthony E. , Smirnov Yury P. , Yakovlev Yury N.
Published: December 2007

Samples from the Kola Superdeep Drillhole (12 262 m), a deep drillhole (1060 m), and from the surface, seaprated by only around 10 km, provided a unique opportunity for direct tracing of
δ
13
C and
δ
18
O changes through a low- to high-grade greenschist-facies transition within impure,
13
C-rich Palaeoproterozoic dolostones. The least-altered dolostones have
δ
13
C of +9‰ and
δ
18
O of 22‰. The metamorphic transition is expressed by dolomite + calcite
1
+ quartz ± K-feldspar ← tremolite + calcite
2
± dolomite ± calcite
1
and defined by
13
C depletion of calcite
2
(
c
. 3.0‰), calcite
1
(1.0–2.0‰) and dolomite (<1‰) which is associated with a Rayleigh distillation process.
δ
18
O shows a considerable resetting in all carbonate components by around 6‰ caused by a Rayleigh distillation process coupled with isotopic exchange between the carbonates and fluids with an external source of oxygen. The retrograde alteration is expressed by the formation of quartz–chlorite veinlets within tectonically bound zones of brecciated and sheared dolostones. The maximum
18
O depletion in dolomite (9‰) and calcite
1
(
c
. 4‰) were probably controlled by infiltration into permeable zones of external fluids associated with retrograde alteration;
δ
13
C remains largely unaffected.
Carbon and U–Pb evidence for a Palaeoproterozoic crustal component in the Central Zone of the Limpopo Belt, South Africa
Authors: Buick I.S. , Williams I.S. , Gibson R.L. , Cartwright I. , Miller J.A.
Published: December 2007

Supposedly mid-Archaean (
c
. 3.3 Ga) granulite-grade marbles from the Gumbu Group, Central Zone, Limpopo Belt (South Africa) have anomalously high
δ
13
C values (+4.6 to +7‰) interpreted as minimum values for their limestone protoliths. Such elevated
δ
13
C values are unknown in any Archaean carbonate worldwide, but occur in Palaeoproterozoic (
c
. 2.4–2.1 Ga) carbonates; for example, on the adjacent Zimbabwe and Kaapvaal cratons. This suggests that the Central Zone contains a previously unrecognized Palaeoproterozoic cover sequence, contrary to the prevailing view. This conclusion is supported by zircon U–Pb sensitive high-resolution ion microprobe ages from two metasediments, which, in addition to
c
. 2.02 Ga metamorphic zircon overgrowths, contain detrital zircons no older than
c
. 2.68 Ga, and some possibly as young as
c
. 2.2 Ga. The recognition of post-3.3 Ga metasediments in the Central Zone requires a major revision of models of the tectonic evolution of the Limpopo Belt.
Combined tide and wave influence on sedimentation of Lower Gondwana coal measures of central India: Barakar Formation (Permian), Satpura basin
Authors: Kumar Ghosh Sanjoy , Chakraborty Chandan , Chakraborty Tapan
Published: December 2007

The coal-bearing Barakar succession of the Satpura basin is typical of the Gondwanan coal basins of peninsular India, in that it has previously been interpreted as continental in origin. The succession comprises three main facies associations, which are documented within this paper. Medium- to fine-grained muddy sandstone deposits of 5–75 m thickness are reinterpreted as tidally influenced delta deposits. Mudstone deposits of 3–20 m thickness with subordinate sandstones, coals and carbonaceous shales are reinterpreted as delta top deposits, and medium to coarse sandstones of 3–38 m thickness are interpreted as braided delta-top channels. The evidence for tidal influence arises from documentation of bidirectional cross-strata, tidal bundles, tidal rhythmites and periodic variation in foreset thickness. The recognition of tidal deposits indicates marine depositional conditions and significantly changes existing palaeogeographical models. This in turn has important implications for our understanding of the depositional setting and distribution of the Permian coals that occur across much of the southern supercontinent. Furthermore, to the best of the authors' knowledge, coal-bearing tidal-delta deposits have not previously been described from continental interior basins.
Andean uplift and climate change
Authors: HARTLEY ADRIANJ.
Published: December 2007

Sedimentological data indicate that a semi-arid/arid climate prevailed across the Central Andes from 15 Ma to 4 Ma. Between 4 and 3 Ma a switch to hyperaridity occurred along the western margin of South America. Palaeoaltitude data suggest that a substantial proto-Central Andean mountain range was in place between 15 and 9 Ma. These data support the idea that the Andean rain shadow existed by 15 Ma and that it reinforced the pre-existing climatic regime rather than changing it. The change to hyperaridity in western South America is attributed to a combination of global climate cooling and enhanced upwelling of the Humboldt current generated by closure of the Central American Seaway between 3.5 and 3 Ma, and not to the Andean rain shadow.
A cryptic Mesoarchaean terrane in the basement to the Central African Copperbelt
Authors: RAINAUD C. , MASTER S. , ARMSTRONG R.A. , ROBB L.J.
Published: December 2007

In a study of the geochronology of the Katangan Sequence and its basement in the Central African Copperbelt, detrital and xenocrystic zircons from Muva quartzites and Katangan lapilli tuffs, were dated using the Sensitive High-Resolution Ion Microprobe (SHRIMP). A detrital population (dated between 3007 and 3031 Ma) and a group of xenocrystic zircons aged between 3169 and 3225 Ma provide the first evidence for the existence of a Mesoarchaean basement beneath the Central African Copperbelt.
Precise radiolarian age constraints on the timing of ophiolite generation and sedimentation in the Dazhuqu terrane, Yarlung–Tsangpo suture zone, Tibet
Authors: Ziabrev SergeyV. , Aitchison JonathanC. , Abrajevitch AlexandraV. , Badengzhu  , Davis AileenM. , Luo Hui
Published: December 2007

Well-preserved, abundant radiolarians provide high-precision biostratigraphic age constraints on the timing of the eruption of ophiolitic basalts exposed along the Yarlung–Tsangpo suture zone in southern Tibet. Dazhuqu terrane ophiolites were generated in an intra-oceanic supra-subduction zone setting within a relatively short (<10 Ma) interval from late Barremian to late Aptian. Accumulation of sediments upon the newly generated ophiolite initially occurred in a series of discrete rift-controlled sub-basins associated with various spreading centres. An increasing flux of arc-derived volcaniclastic sediment up-section indicates nearby volcanic arc activity. The Dazhuqu terrane developed in an intra-oceanic setting within Tethys where it was isolated from any continental influence.
Exhumation of the Ronda peridotite and its crustal envelope: constraints from thermal modelling of a
P
–
T
–time array
Authors: Platt J.P. , Argles T.W. , Carter A. , Kelley S.P. , Whitehouse M.J. , Lonergan L.
Published: December 2007

The Ronda peridotite in the Betic Cordillera of southern Spain is a relic of the sub-orogenic lithospheric mantle that was exhumed during earliest Miocene time from about 66 km depth. Overlying crustal rocks show an apparently coherent metamorphic zonation from high-pressure granulite-facies rocks at the contact to unmetamorphosed rocks 5 km higher in the structural sequence, indicating drastic tectonic thinning of the whole orogenic crust during exhumation.
P
–
T
paths from the peridotite and its crustal envelope indicate decompression with rising temperature to shallow depths. U–Pb ion microprobe dating of zircon, Ar/Ar dating of hornblende, Ar/Ar laserprobe dating of muscovite and biotite, and fission-track analysis of zircon and apatite reveal that cooling was extremely rapid in the interval 21.2–20.4 Ma. One-dimensional thermal modelling of the array of
P
–
T
–time paths indicates that an asthenospheric heat source at an initial depth of about 67.5 km is required to explain heating during exhumation, and that the main period of exhumation lasted 5 Ma, starting at around 25 Ma. Exhumation must therefore have directly followed removal of most, but not all, of the lithospheric mantle beneath the Betic orogen, and was coeval with a period of late orogenic extension that profoundly modified the crustal structure and created the present-day Alboran Sea in the western Mediterranean.
Spherule deposits in Cretaceous–Tertiary boundary sediments in Belize and Guatemala
Authors: Keller G. , Stinnesbeck W. , Adatte T. , Holland B. , StÜben D. , Harting M. , Leon C.de , Cruz J.dela
Published: December 2007

Large spheroid deposits at Albion Island and Armenia in northern and central Belize and the spherule deposits of southern Belize and eastern Guatemala have the same glass origin based on the presence of almost pure Cheto smectite derived from alteration of impact glass from the Chicxulub impact on Yucatan, Mexico. The same origin has also been determined for altered glass spherules in Mexico, Haiti and the Caribbean. However, the spherule layers have variable ages as a result of erosion and redeposition, with an early Danian (
Parvularugoglobigerina eugubina
) zone Pla(1) age in southern Belize, Guatemala, Haiti, southern Mexico and the Caribbean, and a pre-K–T (
Plummerita hantkeninoides
) zone CF1 age of 65.27 ± 0.03 Ma in NE Mexico. A pre-K–T age for the Chicxulub impact has now also been determined from the new Yaxcopoil 1 core drilled in the impact crater. These data show that Chicxulub was not the K–T impact that caused the end-Cretaceous mass extinction, but an earlier impact event. A multiple impact hypothesis, volcanism and climate change appears the likely scenario for the end-Cretaceous mass extinction.
SIMS U–Pb zircon ages for the Upper Devonian Snobs Creek and Cerberean Volcanics from Victoria, with age uncertainty based on UO
2
/UO v. UO/U precision
Authors: Compston William
Published: December 2007

Sensitive high-resolution ion microprobe (SHRIMP) zircon
206
Pb/
238
U ages for the Snobs Creek Volcanics and the overlying Cerberean Volcanics in central Victoria are analytically indistinguishable at 373.2 ± 1.8 and 375.0 ± 2.0 Ma (2σ). The SHRIMP data provide a refined numerical age for interbedded freshwater fish fauna of the Taggerty Formation and, together with its recently revised Givetian age based on independent faunal correlations, provide a new calibration point on the Devonian time scale. The use of Pb
+
/UO
2
+
rather than Pb
+
/U
+
in secondary ionization mass spectrometry (SIMS) dating reduces the range of secondary ion discrimination from zircon. Between-spot correlations observed between UO/U and UO
2
/UO ratios give quantitative estimates for external SIMS uncertainty per spot age that are independent of assumed uniformity in zircon Pb/U. They can exceed internal uncertainties by up to 1.5% dependent on the analytical session. This has important effects on the calibration of SIMS ages at the sub-percent level using imperfect reference zircons subject to small-scale perturbations of the U/Pb system.
Sr–Nd isotopic characteristics of the Mesozoic magmatism in the Taihang–Yanshan orogen, North China craton, and implications for Archaean lithosphere thinning
Authors: Chen Bin , Jahn Bor-ming , Zhai Mingguo
Published: December 2007

Voluminous felsic rocks (mainly monzonitic) and coeval mafic rocks (mainly monzogabbro–diorites) were emplaced in the Taihang–Yanshan orogen of eastern North China craton in Mesozoic time. The monzogabbro–diorites have high Sr (mostly >1300 ppm) and low
ε
Nd
(t) values (−9.5 to −15), indicating a long-term incompatible element enriched subcontinental lithospheric mantle source for their genesis. The monzonitic rocks show elemental geochemistry (e.g. high Sr, and REE patterns) and isotopic compositions similar to the monzogabbro–diorites, which leaves little doubt that the two rock suites share a similar origin. These mafic and felsic rocks thus represent a significant addition of juvenile continental crust from an enriched lithospheric mantle source in the Mesozoic, and their generation via melting of enriched portions of the subcontinental lithospheric mantle is probably an important mechanism responsible for the lithosphere thinning beneath eastern North China craton.
The Acraman asteroid impact, South Australia: magnitude and implications for the late Vendian environment
Authors: Williams GeorgeE. , Wallace MalcolmW.
Published: December 2007

Acraman, located in the 1.59 Ga Gawler Range Volcanics on the Gawler Craton, South Australia, is a complex impact structure that is now eroded ≥2.5 km below the original crater floor. The geology, geomorphology, apatite fission-track geochronology, and geophysical signature of Acraman suggest that the original crater comprised highly disturbed rocks of a central uplift, a transient cavity up to
c
. 40 km in diameter, and a possible final structural rim at 85–90 km diameter. Radial unfolded distance from the centre of Acraman, versus decompacted thickness for the Acraman ejecta horizon identified in late Vendian (
c
. 580 Ma) mudstone in the Adelaide fold belt, Torrens Hinge Zone and Officer Basin up to 540 km from the impact site, accords with a transient cavity diameter of
c
. 40 km. The estimated impact energy for Acraman exceeds the threshold of 10
6
Mt set by earlier workers for global catastrophe. The impact occurred at a low palaeolatitude (
c
. 12.5°) and probably perturbed the atmosphere in both the northern and southern hemispheres. The Acraman impact probably caused a severe perturbation of the late Vendian environment, a finding consistent with independent data from the Vendian palynology of Australia that the Acraman impact induced a biotic crisis.
The elastic thickness of the British Isles
Authors: TILEY RICHARD , MCKENZIE DAN , WHITE NICKY
Published: December 2007

Free-air gravity and topography data from the British Isles have been analysed in the frequency domain to determine the mechanisms of topographic support. First, we calculate how the admittance between measured free-air gravity and topography varies as a function of wavelength. A simple model, which consists of a crust with two layers of different densities overlying a higher density mantle, was then used to calculate admittance functions. The misfit between observed and calculated admittance was minimized by varying elastic thickness and the proportion of the total load due to internal loading. At short wavelengths λ < 200 km), the fit between observed and calculated admittance is consistent with an elastic thickness of 5 ± 2 km and a small proportion of internal loading (

c.

0.2). The general behaviour of the observed admittance suggests that topography is primarily supported by elastic stresses in the crust. A small departure between observed and calculated admittance at the longest wavelengths (400< λ <1000 km) is consistent with modest dynamic support which is probably convective in origin.
Structural features of the July–August 2001 Mount Etna eruption: evidence for a complex magma supply system
Authors: Lanzafame G. , Neri M. , Acocella V. , Billi A. , Funiciello R. , Giordano G.
Published: December 2007

We describe the evolution of the volcanic activity and deformation patterns observed at Mount Etna during the July–August 2001 eruption. Seismicity started at 3000 m below sea level on 13 July, accompanied by moderate ground swelling. Ground deformation culminated on 16 July with the development of a NE–SW graben
c
. 500 m wide and
c
. 1 m deep in the Cisternazza area at 2600–2500 m above sea level on the southern slope of the volcano. On 17 July, the eruption started at the summit of Mount Etna from the SE Crater (central–lateral eruptive system), from which two radial,
c
. 30 m wide,
c
. 3000 m long fracture zones, associated with eruptive fissures, propagated both southward (17 July) and northeastward (20 July). On 18 July, a new vent formed at 2100 m elevation, at the southern base of the Montagnola, followed on the next day by the opening of a vent further upslope, at 2550 m (eccentric eruptive system). The eruption lasted for 3 weeks. Approximately 80% of the total lava volume was erupted from the 2100 m and the 2550 m vents. The collected structural data suggest that the Cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north–south eccentric dyke, which eventually reached the ground surface in the Montagnola area (18–19 July). In contrast, the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation, from the conduit of the SE Crater, of north–south- and NE–SW-oriented shallow dykes, 2–3 m wide. The evolution of the fracture pattern together with other volcanological data (magma ascent and effusion rate, eruptive style, petrochemical characteristics of the erupted products, and petrology of xenoliths within magma) suggest that the eccentric and central–lateral eruptions were fed by two distinct magmatic systems. Examples of eccentric activity accompanied by central–lateral events have never been described before at Etna.
The October–November 2002 Molise seismic sequence (southern Italy): an expression of Adria intraplate deformation
Authors: DI BUCCI DANIELA , MAZZOLI STEFANO
Published: December 2007

A new seismotectonic model for the outer Central-Southern Apennines, including the epicentral area of the 2002 Molise seismic sequence, and adjacent foreland is proposed. The seismic sequence is related to foreland deformation affecting the Adriatic lithosphere. Such deformation is characterized by active NW–SE compression, resulting in the reactivation, mainly as dextral strike-slip faults, of pre-existing east–west oriented structures, both offshore and onshore. One of these structures is interpreted to extend westward and to reach the epicentral area of the recent earthquakes. NW–SE compression, ultimately related with Africa–Europe plate convergence, and uplift would essentially control the active tectonics of the analysed region.
Some palaeontological implications of putative, long-term, gene reactivation
Authors: Dingle R.V.
Published: December 2007

The reactivation of dormant genes in fossil lineages after long time periods is considered a likely evolutionary mechanism. This would not violate Dollo's law on evolutionary irreversibility in a genetic sense, but the law might appear to be contradicted by certain intra- and inter-cladogenic phenotypic variations to at least the generic level. Practical effects would include potential complications for unravelling palaeontological phylogenies, and the recognition of the true status of some so-called Lazarus taxa.
U–Pb chronology and duration of late Ordovician magmatism in the English Lake District
Authors: Millward D. , Evans J.A.
Published: December 2007

U–Pb zircon ages are presented from igneous rocks in the English Lake District for which a wide range of ages had been obtained previously by other methods. The Little Stand and Crinkle tuffs, from the Borrowdale Volcanic Group, have ages of 451.6 ± 1.4 and 452.8 ± 0.7 Ma (2σ), respectively, the Threlkeld Microgranite 451.0 ± 1.1 Ma (2σ) and the Carrock Microgranite 452.4 ± 4.1 Ma (2σ). These dates are identical to the previously published dates for the Ennerdale and Eskdale granites and together are considered to be a good estimate for both the age and length of Caradoc magmatism in the Lake District. This is the first of three magmatic events recognized in the Lake District, the other two occurring during Ashgill and Early Devonian times. Regional comparisons with the Leinster Terrane in SE Ireland and the largely concealed English Midlands basement emphasize the magnitude and significance of the Caradoc event along the Eastern Avalonia margin.
87
Sr/
86
Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales
Authors: Thomas ChristopherW. , Graham ColinM. , Ellam RobertM. , Fallick AnthonyE.
Published: December 2007

New calcite
87
Sr/
86
Sr data for 47 limestones from the metamorphosed and deformed Neoproterozoic–Cambrian Dalradian Supergroup of Scotland and Ireland are used to identify secular trends in seawater
87
Sr/
86
Sr through the Dalradian succession and to constrain its depositional age. Dalradian limestones commonly have Sr >1000 ppm, indicating primary aragonite and marine diagenesis. Low Mn, Mn/Sr <0.6, δ
18
O and trace element data indicate that many
87
Sr/
86
Sr ratios are unaltered since diagenesis despite greenschist- to amphibolite-facies metamorphism, consistent with the documented behaviour of Sr and O during metamorphic fluid–rock interaction. Thus, the
87
Sr/
86
Sr data are interpreted largely to reflect
87
Sr/
86
Sr of coeval seawater. Currently available data show that Neoproterozoic seawater
87
Sr/
86
Sr rose from
c
. 0.7052 at 850–900 Ma to
c
. 0.7085 or higher in the latest Neoproterozoic. Temporal changes at
c
. 800 Ma and
c
. 600 Ma bracket the range in
87
Sr/
86
Sr values of calcite in Grampian, Appin and lowest Argyll Group (
c
. 0.7064–0.7072) and middle and uppermost Argyll Group (
c
. 0.7082–0.7095) limestones, consistent with a rise in seawater
87
Sr/
86
Sr around 600 Ma.
87
Sr/
86
Sr data are consistent with the sedimentary affinity of the Islay Subgroup with the underlying Appin Group, and with a possible time interval between deposition of Islay and Easdale Subgroup rocks. They indicate that the Dalradian, as a whole, is younger than
c
. 800 Ma.
Deglacial chronology from County Donegal, Ireland: implications for deglaciation of the British–Irish ice sheet
Authors: McCabe A.M. , Clark Peter U.
Published: December 2007

In the north of Ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum. We constrain the timing of three subsequent events by accelerator mass spectrometry
14
C dating of marine microfaunas from muds at Corvish, County Donegal. Early and rapid deglaciation of the continental shelf off northwestern Ireland occurred before 17.1 k
14
C years bp when marine muds formed in Trawbreaga Bay. Ice subsequently readvanced into the bay some time between 15.0 and 14.0 k
14
C years bp and compressed contemporary sea stacks and beach cobbles into a ridge at Ballycrampsey. Early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted
14
C ages between 16.0 and 15.2 k
14
C years bp. The deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14.1 k
14
C years bp. The early deglaciation in the north at
c
. 17 k
14
C years bp is correlative with deglaciation recorded in the Irish Sea Basin, western Ireland and northeastern Scotland, indicating a response of the entire British–Irish ice sheet to early warming of the North Atlantic Ocean that resulted in a loss of up to two-thirds of its mass. Subsequent ice-sheet readvance between 15.0 and 14.1 k
14
C years bp in the north is part of a widespread response of the British–Irish ice sheet to Heinrich event 1 during the Killard Point Stadial. High relative sea levels that accompanied deglaciation at 17 k
14
C years bp and again at 14.1 k
14
C years bp indicate substantial loading and attendant isostatic depression by the British–Irish ice sheet.
Fossil seaward-dipping reflector sequences preserved in southeastern Australia: a 600 Ma volcanic passive margin in eastern Gondwanaland
Authors: Direen Nicholas G. , Crawford Anthony J.
Published: December 2007

Evidence for a
c
. 600 Ma rifted passive margin in eastern Australia exists in the form of multiple belts of mafic volcanic rocks preserved along the western margin of the Tasman Fold Belt System, and giving rise to elongate magnetic anomalies. Outcrop, drillhole and geophysical evidence points to piles of lavas, volcaniclastic and intrusive rocks up to 6 km thick, extending for strike lengths of hundreds of kilometres in individual segments. The distinctive, unifying characteristics of these piles are apparent common formation ages (600–580 Ma), presence of early more landward transitional alkaline basalts, and more seaward abundant rift tholeiites, with high-temperature picrites and olivine-rich basalts at most localities. Despite later structural reorganization, these belts have close geochemical, geometric and lithological affinities with Mesozoic seaward-dipping reflector sequences along the North Atlantic, and northwestern Australian volcanic passive margins, and strongly imply the formation of a volcanic passive margin in eastern Gondwanaland at the close of the Neoproterozoic. Recognition of this event has implications for the position of an implied earlier rifted margin related to the break-up of Rodinia around 780 Ma. A rifting event at 600 Ma in eastern Gondwanaland helps explain both the lack of evidence for volcanism from Rodinia break-up, and a widespread 600 Ma population of inherited zircons within rocks of the Lachlan Orogen, which developed outboard of the passive margin in earliest Palaeozoic time.
The Cenozoic uplift and earthquake belt of mainland Britain as a response to an underlying hot, low-density upper mantle
Authors: Bott Martin H.P. , Bott Jacqueline D.J.
Published: December 2007

A belt of hot, low-density uppermost mantle underlying mainland Britain down to at least 200 km depth, revealed by seismic tomography, may be the prime cause of the Cenozoic uplift and exhumation. We use finite-element modelling to demonstrate how isostatic uplift can occur in response to such a low-density hotspot beneath continental crust. To explain the narrow width of the uplift of northern Britain, the lower crust must be ductile (power-law rheology assumed) and the asymmetrical uplift may be bounded at least on the west side by a pre-existing fault or faults of appropriate polarity. Faulting has probably been reverse under NW–SE regional compression since the onset of the Cenozoic. With the assistance of continuing denudation, inferred gross Cenozoic exhumation of up to 3000 m can be explained. British earthquakes concentrate along a similar north–south belt, with the strongest events in the west. We suggest that the earthquakes result from the continuing tectonics associated with the hot upper mantle, the uplift it causes, and the weakened crust. The underlying low-density region gives rise to tensional loading stress in all directions and bending stresses are associated with the upper-crustal flexuring accompanying uplift. These large stresses supplement NW–SE regional compression. Available earthquake mechanisms are approximately consistent with this stress environment.
Diagenetic effects on the oxygen isotope composition of bones of dinosaurs and other vertebrates recovered from terrestrial and marine sediments
Authors: Trueman Clive , Chenery Carolyn , Eberth David A. , Spiro Baruch
Published: December 2007

Assessing effects of diagenesis on oxygen isotope composition of bone is essential to its use in reconstructing habitats and lifestyles of ancient vertebrates. These effects are a matter of controversy, particularly in the case of extinct animals such as dinosaurs. To investigate the effects of diagenesis on isotopic composition of fossil bone, bone samples from both marine and terrestrial Campanian sediments from Alberta, Canada, have been analysed. The isotopic compositions of oxygen (
δ
18
O
SMOW
) were determined in bones sampled from articulated skeletons of exclusively terrestrial animals recovered from the terrestrial Dinosaur Park Formation, and compared with bones from the marine Bearpaw Formation. The articulated skeleton of an exclusively terrestrial dinosaur (hadrosaur) found in marine sediments yielded similar
δ
18
O values for both structural carbonate and phosphate fractions (mean
δ
18
O
SMOW
values 22.6‰ and 16.9‰, respectively) in bone to marine reptiles (mosasaurs) recovered from the same locality (mean
δ
18
O
SMOW
values 24.2‰ and 17.3‰, respectively). The isotopic composition of both skeletons recovered from marine sediments was significantly more positive than that of articulated hadrosaur skeletons recovered from contemporaneous terrestrial sediments (mean phosphate
δ
18
O
SMOW
value 12.9‰), and outside the range of phosphate
δ
18
O
SMOW
values previously reported for terrestrial dinosaur skeletons (
c
. 9–14‰). These data suggest that the isotopic composition of oxygen in the phosphate and structural carbonate ions in the bone apatite was altered during diagenesis and can be used for neither palaeoclimate nor physiological reconstruction.
Early-stage orogenesis in the Timor Sea region, NW Australia
Authors: Harrowfield Mat , Cunneen J. , Keep M. , Crowe W.
Published: December 2007

Neogene collision between the Australian, Eurasia and Pacific plates was coeval with the growth of major depocentres in the Timor Sea. Seismic cross-sections across these troughs identify a characteristic architecture: all three lie inboard of diffuse horst-like structural highs and all mimic older depressions in the top-Permian and upper-Jurassic surfaces. Distortion of pre-tectonic (Aptian–Oligo-Miocene) sequences indicates apparent trough subsidence was coupled to uplift of outboard highs. Rudimentary cross-section restoration identifies negligible strike-normal length change. We interpret apparent Neogene subsidence to reflect amplification of basement topography. This was not accommodated by discrete structural inversion. Rather, landward propagation of contractional strain caused continuous vertical amplification of basement topography. At shallow levels, normal faulting accommodated flexure and thin-skinned collapse of detached sedimentary cover, permitting it to shed away from structural highs and pond in adjacent troughs. We infer that shortening of the North West Shelf accommodated oblique convergence between Australia and the Eurasia–Pacific arc and speculate that the transcurrent component of this deformation was partitioned well outboard. Neogene modification is interpreted to reflect the earliest stages of collisional orogenesis.
Microstructure and lattice preferred orientation of calcite mylonites at the base of the southern Urals accretionary prism
Authors: FernÁndez F.J. , Brown D. , Álvarez-MarrÓn J. , Prior D.J. , PÉrez-EstaÚn A.
Published: December 2007

Emplacement of the southern Urals accretionary complex onto the East European Craton involved off-scraping of shallow marine limestones from the continental margin and their underplating to the base of the accretionary complex during the final stages of arc–continent collision. These limestones underwent localized ductile to semi-brittle deformation at upper-crustal levels, at temperatures close to 200 °C. Field observations, macroscopic fabric elements and crystallographic preferred orientations indicate a heterogeneous distribution of the deformation. Measurements from twinned calcite grains indicate that peak differential stress conditions during deformation attained
c
. 230 ± 40 MPa. These differential stress conditions are further supported by the small size of both recrystallized and twinned calcite grains. Twinning and intracrystalline slip were the major contributors to the bulk deformation and lattice preferred orientation (LPO) formation. LPO evolved with progressive strain, from an initial constrictional fabric that is consistent with the macroscopic mineral lineation as the dominant macroscopic fabric element to a
c
-axis maximum normal to foliation as the rock underwent dynamic recrystallization and grain refinement during progressive simple shear.
Structure and timing of transpressional deformation in the Shackleton Glacier area, Ross orogen, Antarctica
Authors: Paulsen T.S. , EncarnaciÓn J. , Grunow A.M.
Published: December 2007

Basement of the Transantarctic Mountains comprises the Ross orogenic belt, a Neoproterozoic to Ordovician mobile belt located along the palaeo-Pacific margin of Gondwana. Our structural analysis of deformation in the Liv Group, a sequence of Cambrian volcanic, volcaniclastic, clastic and carbonate rocks, and nearby plutonic rocks indicates that the Shackleton Glacier area has a polyphase deformation history that includes development of both contractional and strike-slip structures. We describe evidence for synchronous contraction and strike-slip movement, and suggest that the structural suite in this area developed, at least in part, within a sinistral transpressive kinematic regime. Deformation in the Shackleton Glacier area is inferred to be at least in part younger than 505 Ma, based on the deformation of the well-dated Taylor Formation. New
40
Ar/
39
Ar cooling ages from metamorphosed igneous and sedimentary rocks range from c. 500 to 470 Ma and are interpreted to date orogenic cooling. Based on our structural results, and on consideration of the tectonic environment represented by the Liv Group, we propose that shortening across a subduction-related volcanic arc system caused deformation of the Liv Group and associated plutonic rocks. Oblique convergence and thus, transpression, may have ultimately been related to left-oblique plate subduction.
The development and seismic expression of synsedimentary features within the Chalk of southern England
Authors: Evans D.J. , Hopson P.M. , Kirby G.A. , Bristow C.R.
Published: December 2007

Seismic reflection data acquired onshore to the north of Bournemouth, southern England, image clearly a series of prominent concave-up (troughs or depressions) and concave-down (mounded) structures within the White Chalk Subgroup. The Chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations. These correlations then provide calibration of the seismic reflection data, indicating that the structures are concentrated at levels between the Lewes Nodular Chalk Formation and Tarrant Chalk Member, and towards the base of the Portsdown Chalk Formation. Onlap, downlap and truncation of reflectors are observed, with the most dramatic features forming a stacked series directly overlying faulting of Jurassic strata. Similar stratal geometries have been described from comparable levels in the Chalk of the North Sea, and in outcrop in Britain and France. To many they represent channels formed by submarine erosion and redeposition of the Chalk during relative sea-level falls, linked to tectonics. We also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin. The slumping and the close association of these features with underlying faults, and proximity to nearby major crustal faults, may be indicative of submarine erosion of the Chalk caused by sea-level changes linked to syndepositional fault movements. However, evidence of toplap–downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts. The presence of any such structures implies rapid lateral variations in the Chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the Chalk across southern Britain.
North Atlantic marine rifting in the Early Triassic: new evidence from East Greenland
Authors: Seidler Lars , Steel RonJ. , Stemmerik Lars , Surlyk Finn
Published: December 2007

Two Early Triassic marine rifting events have been recognized in new outcrop data from East Greenland, increasing our understanding of this important tectonic episode in the development of the NE Atlantic (Norwegian–Greenland Sea). A detailed ammonoid stratigraphy, together with stratigraphic and radiometric evidence, show that the first rifting event took place in the Early Griesbachian. This event was largely confined to major basin-margin faults. The second rifting event, which involved splay-faulting and intra-basinal fault-block tilt, is dated as late Griesbachian. Deposition in East Greenland took place in half-grabens dominated by deep-water gravity flow sandstones and mudstones as well as shallow marine conglomerates and sandstones. Similarly, recent core data from offshore Mid-Norway show that deposition on the eastern margin of the Norwegian–Greenland Sea took place in deep marine settings dominated by gravity flows. This suggests that the Early Triassic marine realm extended from East Greenland to the present-day Norwegian coastline and that the marine rift-basin was significantly wider than previously thought.
U–Pb (LA–ICP-MS) dating of detrital zircons from Cambrian clastic rocks in Avalonia: erosion of a Neoproterozoic arc along the northern Gondwanan margin
Authors: Murphy J.Brendan , FernÁndez-SuÁrez Javier , Jeffries TeresaE. , Strachan RobinA.
Published: December 2007

Most Neoproterozoic and Early Palaeozoic tectonic syntheses place Avalonia and related peri-Gondwanan terranes facing an open ocean along the northern margin of Gondwana, thereby providing important constraints for palaeocontinental reconstructions during that time interval. However, the precise location of Avalonia along the margin and its position relative to other peri-Gondwanan terranes is controversial. We present laser ablation–inductively coupled plasma mass spectrometry U–Pb data for detrital zircons from Cambrian clastic rocks in two localities in Avalonia: the Antigonish Highlands of Nova Scotia (62 analyses) and the British Midlands (55 analyses). The data from both samples are very similar, and taken together indicate an overwhelming dominance of Neoproterozoic (
c
. 580–680 Ma) or Early Cambrian source rocks with minor older Neoproterozoic clusters at
c
. 710 Ma or of Mesoproterozoic age, three Palaeoproterozoic zircons and one Archaean zircon. The zircons can all be derived from local Avalonian sources. The Neoproterozoic zircons are attributed to erosion of the underlying Avalonian arc. Mesoproterozoic and Palaeoproterozoic zircons of similar ages are also found in Avalonian Neoproterozoic clastic rocks and their presence in the Cambrian clastic rocks could represent recycling of Neoproterozoic strata and do not necessarily imply the presence of Mesoproterozoic or Palaeoproterozoic basement rocks within their respective drainage basins. Comparison with the data from the Neoproterozoic arc-related clastic sequences suggests significant differences between their respective drainage systems. Whereas the Neoproterozoic data require extensive drainage systems, the Cambrian data can be attributed to localized drainage systems. The change in drainage patterns could reflect rifting and isolation of Avalonia from Amazonia between
c
. 585 and 540 Ma. Alternatively, it might reflect the creation of topographical barriers along the northern Gondwanan margin, in a manner analogous to the Cenozoic rise of the Andes or the creation of the Basin-and-Range topography in the Western USA.
Vertical density currents: a review of their potential role in the deposition and interpretation of deep-sea ash layers
Authors: Manville V. , Wilson C.J.N.
Published: December 2007

Marine tephra layers form important chronostratigraphic markers and may also provide information on eruption dynamics and chronology. Recent experiments, and field data from the 1991 Pinatubo eruption, challenge tacit assumptions that, following atmospheric fallout on the ocean surface, marine sedimentation of ash-grade material occurs by Stokes Law settling of individual grains. Laboratory experiments have demonstrated that vertical density currents can be initiated at representative mass flux rates: further experiments, described herein, involving sustained particle fluxes entering stratified environments, demonstrate that ash particles can decouple from the transporting fluid, whose vertical motions are limited by the stable density gradient. In the ocean, vertical density currents generated by ash-loading and gravitational destabilization of the water column can overcome the strong stable density gradients in the ocean and transport ash particles vertically 1–3 orders of magnitude faster than possible by Stokesian settling, greatly reducing their residence time. Sea-bed sedimentation is inferred to involve settling of individual coarse or dense grains through the entire water column, plus suspension fallout from the polydisperse turbid layer delivered by convective plumes, yielding normal distribution grading. The turbid layer may continue laterally as a (nepheloid) current under the influence of bottom slopes and/or geostrophic forces, either mechanism possibly modifying the grain-size distribution of the suspension and hence the resulting ash layer by transporting selected fractions into different depositional locations. Consequently, and regardless of any subsequent reworking, deep-sea ash isopachs may not directly reflect an eruptive signal, and the ash layers may not directly record the order, rate, or location of arrival of ash particles at the ocean surface.
Phytoplankton evidence for the timing and correlation of palaeoceanographical changes during the early Toarcian oceanic anoxic event (Early Jurassic)
Authors: Mattioli Emanuela , Pittet Bernard , Palliani RaffaellaBucefalo , RÖhl Hans-Joachim , Schmid-RÖhl Annette , Morettini Elena
Published: December 2007

The causes and duration of the early Toarcian anoxic event are controversial. Integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western Tethys. In particular, the
Carinolithus superbus
nannofossil Zone can be used to correlate the levels enriched in organic matter and the related
δ
13
C negative excursion. Although a variable duration is given in the literature for this negative excursion, it is likely that it lasted between 520 and 650 ka. Increased atmospheric
p
CO
2
, related to excess volcanic emissions (magmatic activity in the Karoo and Ferrar Provinces), had an impact on climate and ocean chemistry, and marked the inception of a biotic crisis affecting many organisms. The beginning of the crisis within shallow carbonate platforms, documented at southern latitudes, predates the levels enriched in organic matter. Dinoflagellate cysts experienced a decrease in abundance in the
C. superbus
Zone, until they temporarily disappeared. The nannoplankton crisis was twofold: a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance. The increased atmospheric
p
CO
2
, as a result of the magmatic activity and temporarily amplified by transient methane release, could have been the trigger for the biocalcification crisis, which first affected the probably more reactive neritic system, and eventually the nannoplankton community.