bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanics of layer-bound polygonal faulting in fine-grained sediments
Authors: GOULTY N. R.
Published: December 2007

Abstract: Extensive polygonal networks of normal faults have reportedly been identified within layer-bound sequences in about 28 sedimentary basins worldwide. The gentle regional dips, passive tectonic settings and geometry of the fault networks have led to the conclusion that faulting must have resulted from gravity-driven mechanical compaction. The faulted sequences comprise very fine-grained sediments, with lithofacies that range from smectitic claystones to almost pure chalks. In most, if not all, cases it is clear that volumetric contraction has occurred with horizontal contraction of the sediments complementing the heave of the faults. One explanation which has previously been offered is that the fine-grained sediments have shrunk due to syneresis, a process that involves spontaneous contraction of the solid network with expulsion of the pore fluid. However, syneresis is an implausible mechanism because it does not explain the observed lithological variation in the sediments concerned, why the initiation of faulting occurs in the depth range 100–1000 m, and why faulting continues for millions of years. A much simpler explanation is that shear failure inevitably results from one-dimensional compaction if the coefficient of friction is sufficiently low; and there is some evidence from laboratory measurements that the coefficient of friction is likely to be exceptionally low in these fine-grained sediments. Qualitatively, low coefficients of friction also explain why these compaction faults preferentially dip towards the basin margin where the regional dip of the bedding is greater than 1˚. Furthermore, they help to explain the origin of a polygonal fault system in the Eromanga Basin, South Australia, where the situation is complicated by the presence of a low velocity, ductile layer at the base of the faulted sequence.
Relations between granitoid magmatism and migmatization: U–Pb geochronological evidence from the Western Gneiss Complex, Norway
Authors: SkÅr Øyvind , Pedersen Rolf B.
Published: December 2007

Gneiss and migmatite samples from the southern part of the Western Gneiss Complex of Norway define a single U–Pb zircon discordia line with lower and upper intercepts at 1633 ± 8 Ma and 969 ± 8 Ma. The upper intercept is interpreted as the magmatic age of the protoliths, showing that the basement rocks were generated during the Gothian orogeny (1750–1500 Ma). The migmatites yield titanite ages that are similar to the lower intercept zircon age, and we interpret this to be the age of migmatization during the Sveconorwegian orogeny. U-rich titanite cores yield an age of 973 ± 3 Ma whereas less U-rich rims gave a slightly younger age of 961 ± 4 Ma. A granitoid batholith in the area gave a U–Pb zircon age that is coeval with the migmatite age (966 ± 2 Ma). The metaluminous granitic magma of the pluton formed by melting at relatively high temperatures in the lower crust. In contrast, the migmatites formed during upper amphibolite-facies conditions at relative high crustal levels. The close temporal and spatial relations between the migmatites and the granite batholith suggest that migmatite formation in the lower parts of the upper crust was related to the heat and mass flux linked to the rise of granitic magma from the lower crust.
Single-zircon geochronology and Nd isotopic systematics of Proterozoic high-grade rocks from the Mozambique belt of southern Tanzania (Masasi area): implications for Gondwana assembly
Authors: KrÖner A. , Muhongo S. , Hegner E. , Wingate M.T.D.
Published: December 2007

The Mozambique belt of southern Tanzania is underlain by locally restricted 1100–950 Ma (late Kibaran) granitoid gneisses that were derived from remelting of Archaean continental crust, as suggested by Nd isotopic systematics. These rocks were deformed and metamorphosed during an intense Neoproterozoic (Pan-African) event at around 630 Ma together with tectonically interlayered and widespread 800–650 Ma granitoid gneisses and minor clastic metasediments. The 800–650 Ma granitoids were derived predominantly from Neoproterozoic juvenile melts. There is no evidence for pre-800 Ma deformation. The 630 Ma event led to extensive migmatization in all gneisses and caused local melting. Similarities in age and tectonometamorphic evolution between these rocks and similar gneisses in northern Mozambique and southern Malawi suggest a similar geological evolution. However, distinctly different ages for the peak of metamorphism in Tanzania, Malawi and Mozambique indicate diachronous high-grade events that may be associated with terrane accretion and continental collision during orogenesis and favour the view that East Gondwana was not a coherent block during formation of the Gondwana supercontinent.
The transition from sedimentation to flood volcanism in the Kangerlussuaq Basin, East Greenland: basaltic pyroclastic volcanism during initial Palaeogene continental break-up
Authors: Peate IngridUkstins , Larsen Michael , Lesher CharlesE.
Published: December 2007

Primary basaltic pyroclastic deposits compose volumetrically
c
. 35–50% of the Lower Palaeogene Vandfaldsdalen, Mikis and Haengefjeldet Formations within the lower volcanic series of the East Greenland flood basalt province. The eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break-up and initiation of flood basalt volcanism. We present a revised stratigraphy for the pre-volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the Kangerlussuaq Basin, East Greenland. Primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds, surge deposits and vent sites with cinder cones. Early volcanism was apparently restricted to localized basins and formed shield volcano structures 30–40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites, sediments, pyroclastic deposits and lavas. The lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the NE, paired with continued down-dropping of inactive volcanic centres. The complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting.
Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland
Authors: Tanner P.W.G. , Evans J.A.
Published: December 2007

There has been controversy over the number and timing of orogenies in the Precambrian Moine block in the Scottish Caledonides since the earliest radiometric dating in the 1960s. This work challenges a recent hypothesis, that this sector of the Laurentian margin was subjected to continuous crustal extension between >900 and 470 Ma. U–Pb dating (thermal ionization mass spectrometry) of titanite from a calc-silicate pod in the Moine (Morar Group) of the western Highlands gives an age of 737 ± 5 Ma. The titanite grew from Fe–Ti-bearing detrital minerals during the main progressive, syn-D
2
, amphibolite-facies (sillimanite zone) regional metamorphism, thus demonstrating that a Neoproterozoic contractional tectonothermal event (Knoydartian orogeny) affected the Moine block following the rift-related emplacement of the West Highland granite gneiss at 873 Ma. We conclude that the Sgurr Beag Thrust, a major tectonic break separating the Morar and Glenfinnan groups of the Moine, is mainly of Neoproterozoic, not Caledonian, age. The early tectonothermal event was succeeded by the Grampian Phase (Caledonian orogeny) at 460–470 Ma.
A tectonostratigraphic synthesis of the Sub-Andean basins: inferences on the position of South American intraplate accommodation zones and their control on South Atlantic opening
Authors: Jacques JohnM.
Published: December 2007

It has been shown in the accompanying paper that the Sub-Andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains. To test the hypothesis that changes in palaeo-depositional setting rely on the presence of a series of transverse zones of structural accommodation, data have been digitally compiled from across the South American continent. Spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries (structural accommodation zones), and patterns of subsidence and intraplate deformation. The results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which, on a regional scale, interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization. Their strong spatial relationship with Mesozoic, intraplate, alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during Gondwana breakup. These localized zones of high heat flow have important implications for source rock maturity in the interior, Phanerozoic intracratonic basins of South America. On the South Atlantic margin, the majority of these crustal lineaments correlate with failed arms of triple-junction rifts and define the boundaries to tectonostratigraphic domains recognized along the South Atlantic Rift System.
Response of Late Carboniferous tropical vegetation to transgressive–regressive rhythms at Joggins, Nova Scotia
Authors: Falcon-Lang H.J.
Published: December 2007

Fossil plant assemblages are described in their sequence stratigraphic context from the Upper Carboniferous (Langsettian) Joggins Formation of Nova Scotia to elucidate ecosystem response to transgressive–regressive rhythms. Results show that rising base level resulted in retrograding submerged coastal mires co-dominated by
Lepidodendron
and
Lepidophloios
, which were replaced by short-lived
Paralycopodites
communities immediately following mire drowning. Extensive brackish bays existed during early highstand, distally fringed by gymnospermous and putative progymnospermous coastal and/or upland vegetation. Late highstand bay filling generated prograding distributary wetlands dominated by flood-disturbed lycopsid–pteridosperm–sphenopsid communities, and locally by cordaite mangroves. As base level fell, well-drained alluvial plains were dominated by fire-prone cordaite and/or
Sigillaria
communities, which persisted until the next phase of base-level rise. This rhythmic ecosystem succession repeatedly occurred on a
c
. 50–200 ka time scale, and was probably driven by glacial–interglacial climate rhythms.
Structural framework of a major intracontinental orogenic termination zone: the easternmost Tien Shan, China
Authors: Cunningham Dickson , Owen LewisA. , Snee LarryW. , Jiliang Li
Published: December 2007

The Barkol Tagh and Karlik Tagh ranges of the easternmost Tien Shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range. Barkol and Karlik Tagh and lesser ranges to the north are bounded by active thrust faults that locally deform Quaternary sediments. Major thrusts in Karlik Tagh connect along strike to the east with the left-lateral Gobi–Tien Shan Fault System in SW Mongolia. From a Mongolian perspective, Karlik Tagh represents a large restraining bend for this regional strike-slip fault system, and the entire system of thrusts and strike-slip faults in the Karlik Tagh region defines a horsetail splay fault geometry. Regionally, there appears to be a kinematic transition from thrust-dominated deformation in the central Tien Shan to left-lateral transpressional deformation in the easternmost Tien Shan. This transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the NNE-directed maximum horizontal stress in the region and the pre-existing basement structural grain, which is northwesterly in the central Tien Shan (orthogonal to SH
max
) but more east–west in the eastern Tien Shan (acute angular relationship with SH
max
). Ar–Ar ages indicate that major range-bounding thrusts in Barkol and Karlik Tagh are latest Permian–Triassic ductile thrust zones that underwent brittle reactivation in the Late Cenozoic. It is estimated that the modern mountain ranges of the extreme easternmost Tien Shan could have been constructed by only 10–15 km of Late Cenozoic horizontal shortening.
Neotethyan ophiolitic rocks of the Anatolides of NW Turkey and comparison with Tauride ophiolites
Authors: Önen A. Piril
Published: December 2007

The I2zmir–Ankara–Erzincan zone in Turkey is part of the Anatolide belt. In NW Anatolia, near Kütahya, the ophiolitic rocks within the I2zmir–Ankara–Erzincan suture zone have a tholeiitic character and oceanic back-arc chemistry. Amphibolites form a metamorphic sole to part of the ophiolite in the Kütahya region and yield an
40
Ar/
39
Ar age of 93 ± 2 Ma, interpreted to record high-grade metamorphism and intra-oceanic thrusting of pre-existing ocean crust. Gabbros and dykes yield
40
Ar/
39
Ar ages of 94 ± 13 Ma and 48 ± 12 Ma. The first is suggested to be the ophiolite formation age, and the second a regional metamorphic event. The ophiolitic rocks of the Kütahya region are composite and record several events in the evolution of a Neotethyan seaway situated in north–central Anatolia and farther east. They are interpreted to have formed in a small ocean basin marginal to the subducting I2zmir–Ankara–Erzincan ocean. The Kütahya ophiolites of the Anatolide belt are similar in age to the Tauride ophiolites, and the sub-ophiolite metamorphic rocks and dykes in the ultramafic parts of the ophiolites in the Anatolide–Tauride Block formed at the same intraoceanic subduction zone within the same Neotethyan ocean.
Estimating hydrogeological conditions over the last 120 ka: an example from the Sellafield area, UK
Authors: Heathcote J.A. , Michie U.McL.
Published: December 2007

For a number of years, United Kingdom Nirex Limited investigated the suitability of the area around Sellafield in NW England to assess its suitability to host a deep repository for intermediate-level and some low-level radioactive wastes resulting from Britain's nuclear programme. The investigation programme collected a large amount of lithological, hydrogeological and hydrochemical data from 18 boreholes up to 2000 m deep. A potential route by which radionuclides may leave the repository and return to surface is the groundwater pathway. It was recognized that the groundwater regime could be disturbed significantly by major climate changes, particularly glacial–interglacial cycles, over the very long time scales considered in the assessment of the radiological safety of a repository. Available geological and hydrogeological data for the Sellafield area are reviewed in the context of current thinking on glacial hydrogeology, showing that disturbance of the hydrogeological regime is possible during glaciation, and that there are significant uncertainties in determining the timing and magnitude of the effects caused by glaciation. However, the evidence available, both from Quaternary fracture-filling minerals and from the chemistry of groundwater now present, suggests that any disturbance to the deeper hydrogeological regime was relatively minor and that any subglacial recharge has been removed by the present flow regime. There is a possibility that high hydraulic heads at depth in the low-permeability basement rock considered as a host for the repository, the Borrowdale Volcanic Group of Ordovician age beneath a cover of Triassic sandstones, may be residual.
U–Pb geochronology of Lewisian orthogneisses in the Outer Hebrides, Scotland: implications for the tectonic setting and correlation of the South Harris Complex
Authors: Mason A.J. , Parrish R.R. , Brewer T.S.
Published: December 2007

The South Harris Complex of the Scottish Outer Hebrides forms a distinctive component of the Lewisian Complex and contains three supposedly co-magmatic meta-igneous bodies, a diorite, a ‘norite’ and an anorthosite, believed to be part of a Palaeoproterozoic arc. New U–Pb zircon ages obtained from these bodies of 1888 ± 2 Ma, 1890 +2/−1 Ma, and 2491 +31/−27 Ma, respectively, demonstrate that the anorthosite cannot be related to the younger calc-alkaline diorite and ‘norite’. The diorite and ‘norite’, however, probably are related products of arc magmatism. The spatial association of the diorite and ‘norite’ with the substantially older anorthosite suggests that the younger intrusions were emplaced into continental crust. Any suture associated with the South Harris Complex remains cryptic, and is not marked by an obvious change in protolith ages in the adjacent tonalitic gneisses.
Tectonic evolution of the NE Palmyride mountain belt, Syria: the Bishri crustal block
Authors: Brew Graham , Best John , Barazangi Muawia , Sawaf Tarif
Published: December 2007

Investigation of the Bishri block, centrally positioned amid the diverse tectonic and structural zones of Syria, reveals details of the intraplate Phanerozoic development of the northern Arabian platform. The Bishri block is a broad NE-plunging inverted basin located at the NE portion of the Palmyride mountain belt where the mountains intersect the Euphrates fault system. Well and seismic data show that subsidence and sedimentation in the Bishri area was generally continuous from Carboniferous to Paleocene time, with the Bishri block part of the extensive Palmyride–Sinjar trough. Major bounding faults and a rift-type environment are documented in the Permo-Triassic, Jurassic and Cretaceous. The present Bishri structural and topographic high has been formed through transpressive structural inversion since the Mid-Miocene; high-angle Mesozoic bounding normal faults now have net reverse offsets with a significant dextral strike-slip component. East of the Bishri block, towards the Euphrates fault system, NNW–SSE-striking normal faults exhibit less reverse movement. This deformation history correlates with the opening and closing of the nearby NeoTethys ocean that has driven the evolution of intracontinental Syria.
Non-destructive multiple approaches to interpret the preservation of plant fossils: implications for calcium-rich permineralizations
Authors: Scott Andrew C. , Collinson Margaret E.
Published: December 2007

Permineralized fossil coniferous woods from the Pliocene of Dunarobba, Umbria, Italy, and the Jurassic of Swindon, Wiltshire, England, were studied using non-destructive techniques on uncoated polished thin sections to elucidate their preservational history. Specimens were observed using transmitted light, polarized light, reflected light under oil, and cathodoluminescence. Selected areas were studied using a variable pressure SEM in backscattered electron mode. This allowed uncoated specimens to be examined and elemental distributions to be determined using an energy dispersive X-ray microanalyser. The data were used to interpret details of the permineralization history. Results reveal that anatomical interpretations based merely on observations of thin sections in transmitted light can be very misleading and could potentially affect the application of permineralized plant fossils, for example, in evolutionary biology, palaeoclimate analysis and isotope geochemistry.
55 million years of continuous anatexis in Central Iberia: single-zircon dating of the Peña Negra Complex
Authors: Montero P. , Bea F. , Zinger T.F. , Scarrow J.H. , Molina J.F. , Whitehouse M.
Published: December 2007

Single-zircon evaporation and ion-microprobe dating of migmatites and anatectic granites in the Peña Negra Complex of Central Iberia reveal that the Variscan anatexis occurred continuously from 352 to 297 Ma, with a maximum at 335–305 Ma. Anatexis began coeval with the main collision of continental masses. A limited melting event, probably related to syncollision crustal-scale shear zones, produced a population of zircons with ages of
c
. 350 Ma. The production of new zircons decreased to a minimum at
c
. 343 Ma but then increased swiftly as the internal thermal evolution of the thickened Central Iberian crust led to widespread anatexis in the Peña Negra region at 332 Ma. Shortly after this, the melt resident in the migmatites was locally segregated into small bodies that crystallized as cordierite leucogranites at 321 Ma. Simultaneously, extensional subhorizontal shear zones were preferentially developed over layers of the migmatite series that, owing to their elevated heat production and fertility, had the highest melt fraction. Shearing provoked further anatexis and contributed significantly to the
in situ
production of high melt-fraction granodiorites and adamellites from the migmatites. This process occurred from 325 to 305 Ma, with a maximum at 309 Ma marking the peak of the Variscan extensional collapse in Central Iberia. After
c
. 305 Ma the melt fraction decreased quickly, so that the production of new zircons was insignificant at 300 Ma and had stopped completely by 297 Ma.
Sr isotope evidence for population movement within the Hebridean Norse community of NW Scotland
Authors: MONTGOMERY JANET , EVANS JANE A. , NEIGHBOUR TIM
Published: December 2007

The excavation at Cnip, Isle of Lewis, Scotland, of the largest, and only known family cemetery from the early Norse period in the Hebrides, provided a unique opportunity to use Sr isotope analysis to examine the origins of people who may have been Norwegian Vikings. Sr isotope analysis permits direct investigation of a person's place of origin rather than indirectly through acquired cultural and artefactual affiliations. Sr isotope data suggest that the Norse group at Cnip was of mixed origins. The majority were consistent with indigenous origins but two individuals, of middle-age and different sex, were immigrants. They were, however, not from Norway but were raised separately, most probably on Tertiary volcanic rocks (e.g. the Inner Hebrides or NE Ireland) or, for the female, on marine carbonate rocks.
Unconformities related to the Jurassic–Cretaceous synrift–post-rift transition of the northern North Sea
Authors: KyrkjebØ Rune , Gabrielsen R.H. , Faleide J.I.
Published: December 2007

In the Jurassic–Cretaceous North Sea basin, the synrift sequence is separated from the post-rift sequence by the ‘base Cretaceous’ or ‘late Cimmerian’ unconformity. The unconformity covers almost the entire basin, has a distinct character in seismic reflection data and wireline logs, and hence, is easily identified and correlated, making it the most important marker horizon in the area. The unconformity displays great local complexity (in many localities) and great variability on a regional scale (from one locality to another). Thus the unconformity is classified as a nonconformity, a disconformity and an angular unconformity. We suggest that these variations basically reflect different structural position within the basin, so that the short-wavelength variation is dominated by local structural development (e.g. the rotational history of a fault block), whereas the long-wavelength variation reflects basin-scale tectonic, thermal and isostatic processes. The merging of this unconformity with younger erosional surfaces, its complex configuration and polychronous character makes the general term ‘base Cretaceous unconformity’ inadequate. Thus, the term ‘northern North Sea Unconformity Complex’ is used here.
Mid-Ordovician U–Pb ages of porphyroids in the Peloritan Mountains (NE Sicily): palaeogeographical implications for the evolution of the Alboran microplate
Authors: Trombetta Antonella , Cirrincione Rosolino , Corfu Fernando , Mazzoleni Paolo , Pezzino Antonio
Published: December 2007

Petrographic, geochemical and geochronological work on a metavolcanic suite interbedded in a metapelitic sequence of the Palaeozoic basement in the Peloritan Mountains (Sicily) is used to contribute to a better understanding of the pre-Variscan geodynamic evolution of the former Alboran microplate. Major and trace element data show that the volcanic suite consists of two main groups: an Intermediate Unit of andesites and dacites with volcanic arc affinity and a Felsic Porphyroid Unit of rhyolites with peraluminous composition. Isotope dilution thermal ionization mass spectrometry U–Pb analyses for single- and multigrain zircon fractions from four samples of the felsic porphyroids yield results that are tightly clustered on or near concordia giving Caradoc ages in the range of 456–452 Ma. The consistent morphological characteristics and oscillatory zoning of the zircons indicate single-stage magmatic crystallization. Xenocrystic zircon grains with ages of 1150 and 2015 Ma indicate that these rocks were developed upon a cratonic basement with Grenvillian and Transamazonian components, hence supporting a peri-Gondwanan origin. From the combined evidence we conclude that this portion of the Alboran microplate formed as a Mid-Ordovician volcanic arc in a sector of the peri-Gondwanan terranes that was affected by a tectonothermal Caradoc event.
Carbon-isotope stratigraphy recorded by the Cenomanian–Turonian Oceanic Anoxic Event: correlation and implications based on three key localities
Authors: Tsikos H. , Jenkyns H.C. , Walsworth-Bell B. , Petrizzo M.R. , Forster A. , Kolonic S. , Erba E. , Premoli Silva I. , Baas M. , Wagner T. , Sinninghe DamstÉ J.S.
Published: December 2007

We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian–Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of
c
. 4‰ for TOC and phytane and
c
. 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak
δ
13
C values for all components are followed by intervals of high, near-constant
δ
13
C in the form of an isotopic plateau. Recognition of an unambiguous return to background
δ
13
C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil
Quadrum gartneri
at or near the Cenomanian–Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the
δ
13
C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.
Eocene–Oligocene mammalian faunal turnover in the Hampshire Basin, UK: calibration to the global time scale and the major cooling event
Authors: Hooker J.J. , Collinson M.E. , Sille N.P.
Published: December 2007

A new high-resolution,
c
. 1 Ma mammalian record in continental Eocene–Oligocene strata in the Hampshire Basin is used to investigate the nature and timing of the major Europe-wide mammalian faunal turnover termed the Grande Coupure. Whether this was caused by climate change or by competition with taxa dispersing from Asia is controversial. The mammalian faunas in this record, after rarefaction analysis, show a sharp reduction in diversity only after the Grande Coupure. Improved correlation of NW European successions to global events confirms the Grande Coupure as earliest Oligocene. It shows that a
c
. 350 ka hiatus interrupts the Hampshire and Paris Basin sequences prior to the first record of post-Grande Coupure Asian taxa. Hiatus-bridging faunas from elsewhere in Europe record mainly post-Grande Coupure taxa, suggesting that the turnover occurred early in the hiatus, minimizing bias to the turnover pattern. A previously unrecorded, second, smaller turnover, involving European mammals only, immediately precedes the Grande Coupure in the Hampshire Basin, coinciding with vegetational change. This turnover is judged not to represent cooling. It is concluded that the Grande Coupure coincides with the earliest Oligocene Oi-1 glaciation and that climate change combined with competition to produce the turnover.
Palaeocene–Eocene paratropical floral change in North America: responses to climate change and plant immigration
Authors: Harrington GuyJ. , Kemp SimonJ. , Koch PaulL.
Published: December 2007

The Initial Eocene Thermal Maximum (IETM) at
c
. 55 Ma represents a period of rapid global warming that lasted less than 200 ka. The response of vegetation to such an event, and particularly warm-adapted highly diverse vegetation types, is poorly understood. Using pollen floral, clay mineral and stable carbon isotope analyses of sediments from the upper Tuscahoma Formation on the eastern US Gulf Coast (eastern Mississippi and western Alabama), we document paratropical floral changes across the Palaeocene–Eocene boundary from the Wahalak #2 and lower Harrell cores. Data indicate strong changes in the abundance of kaolinite that correlate with changes in relative abundance of native pollen taxa. There is no evidence for a transient, extra-tropical flora on the US Gulf Coast that may characterize the IETM. Immigration and extinction are not associated with this event. Instead, Early Eocene plant immigration occurs in pulses and therefore is not associated directly with climate change during the IETM. The two cores share the same regional species pool but compositional differences are stronger between cores than they are either through changes in environment, increased soil erosion or chemical weathering, or through the introduction of non-native plants. Our data suggest that vegetation change across the Palaeocene–Eocene boundary is not a single event but rather a sequence of cascading events.
The foreland-propagating thrust architecture of the East Greenland Caledonides 72°–75°N
Authors: Higgins A.K. , Elvevold S. , Escher J.C. , Frederiksen K.S. , Gilotti J.A. , Henriksen N. , Jepsen H.F. , Jones K.A. , Kalsbeek F. , Kinny P.D. , Leslie A.G. , Smith M.P. , Thrane K. , Watt G.R.
Published: December 2007

Systematic geological mapping of the East Greenland Caledonides demonstrates that the orogen is built up of WNW-directed thrust sheets displaced across foreland windows. The foreland windows in the southern half of the orogen are characterized by a thin (220–400 m) Neoproterozoic to Lower Palaeozoic succession, structurally overlain by two major Caledonian thrust sheets (Niggli Spids and Hagar Bjerg Thrust Sheets). The metasediments of the upper-level Hagar Bjerg Thrust Sheet host 940–910 Ma granites and migmatites formed during an early Neoproterozoic thermal or orogenic event, as well as Caledonian 435–425 Ma granites and migmatites. The uppermost unit of the thrust pile, the Franz Joseph Allochthon, comprises a very thick (18.5 km) Neoproterozoic to lower Palaeozoic sedimentary succession (Eleonore Bay Supergroup, Tillite Group, Kong Oscar Fjord Group). Total westward displacement of the thrust sheets was about 200–400 km, with shortening estimated at 40–60%. Major extensional faults post-date thrusting. Restoration of the thrust sheets indicates that the sequence of Caledonian orogenic events now preserved in East Greenland was initiated several hundred kilometres ESE of present-day East Greenland, as Baltica and its marginal assemblage of Early Palaeozoic accretions began to impinge on the Laurentian margin.
New palaeomagnetic results from the Whin Sill complex: evidence for a multiple intrusion event and revised virtual geomagnetic poles for the late Carboniferous for the British Isles
Authors: Liss D. , Owens W.H. , Hutton D.H.W.
Published: December 2007

A large-scale palaeomagnetic study (125 specimens from 88 sampling localities) has been carried out on the Whin Sill complex and its associated dykes in northern England. The dominant carrier of remanent magnetization of the doleritic rocks is relatively pure magnetite of pseudo-single domain size, and the characteristic remanent magnetizations are typically well defined and unidirectional. Regionally consistent palaeomagnetic directions are obtained from three geographically distinct parts of the Whin Sill complex, here named as the Holy Island Sill (Declination/Inclination (
D
/
I
)=189.5/−2.8, α
95
=6.3), the Alnwick Sill (
D
/
I
=194.6/−25.6, α
95
=8.1) and the Hadrian's Wall–Pennines Sill (
D
/
I
=189.2/3.3, α
95
=3.5). Although the Holy Island Sill and the Hadrian's Wall–Pennines Sill are of similar age (
c
. 296 Ma) and indistinguishable on palaeomagnetic grounds, the difference in palaeomagnetic directions between them and the Alnwick Sill demonstrates the multi-component nature of the complex; magma-flow indicators suggest that the Holy Island Sill and the Hadrian's Wall–Pennines Sill may also represent separate intrusion events. Dykes local to the three sills have remanence directions corresponding to their respective sills and can tentatively be identified as their feeder dykes. Virtual geomagnetic poles for the three palaeomagnetic sites are: Holy Island Sill and Holy Island Dyke, 346.8E, 35.4S; Alnwick Sill, High Green Dyke and St. Oswald's Chapel Dyke, 337.1E, 47.1S; Hadrian's Wall–Pennines Sill and Hett Dyke, 347.1E, 32.9S.
Volcanic rock-mass properties from Snowdonia and Tenerife: implications for volcano edifice strength
Authors: Thomas Mark E. , Petford Nick , Bromhead Edward N.
Published: December 2007

Although volcano instability is increasingly recognized as a societal hazard, numerical data on the relevant mechanical properties remain sparse. We report new field data on the rock-mass properties of volcanic materials from Snowdonia (North Wales, UK) and Tenerife (Canary Islands). Using rock types that range in composition from phonolite to rhyolite, we summarize a method for estimating the overall strength of a volcanic edifice based on the rock-mass rating index (RMR) and the Hoek–Brown criterion. We show that the average rock-mass compressive (
σ
cm
) and cohesive (
c
) strengths decrease exponentially with RMR according to σ
cm
=0.652
(0.0559RMR)
and
c
=0.035
(0.0669RMR)
, respectively, and appear insensitive to both initial magma composition and relative age. This exponential relationship provides a new predictive tool for directly estimating rock-mass strength from the RMR. Our analysis further predicts a marked reduction of up to 96% in the rock-mass compressive strength relative to the intact rock value based on laboratory tests and that, overall, the combined results from both study areas yield cohesive strength values from 4.8 to 0.44 MPa. Estimated values of rock-mass angle of friction range from 28° to
c
. 38°. Recent modifications to the Hoek–Brown criterion, in particular the inclusion of the disturbance factor
D
, suggest that even these low values of rock-mass strength and cohesion may be optimistic, and the true values of rock parameters relevant for accurate predictions of volcano edifice strength may be up to 30% weaker still.
Microbial silicification in Iodine Pool, Waimangu geothermal area, North Island, New Zealand: implications for recognition and identification of ancient silicified microbes
Authors: Jones Brian , Konhauser Kurt O. , Renaut Robin W. , Wheeler Raymond S.
Published: December 2007

Silicified microbes provide evidence for some of the earliest life forms on Earth. They are extremely important to understanding the early development of life and the conditions that allowed its development. Such discussions commonly rely on comparisons with extant taxa and therefore depend upon the preservation style of the microbes and, in particular, the preservation of the taxonomically important features. Silicified microbes are deceptive: they commonly appear to be well preserved even though their taxonomically critical features have been destroyed by silicification. An understanding of the early taphonomic processes that influence microbial silicification can be obtained by studying extant microbes that are being silicified in modern hot spring pools. Iodine Pool, located in the Waimangu geothermal area on the North Island of New Zealand, is ideal for this purpose. The spring water has a temperature of 69–100 °C, a pH of 8.3–9.0, and 440–457 ppm SiO
2
. Glass slides left in the shallow marginal waters of this pool for 90 h became covered with thin layers of opaline silica, discrete opal-A spheres, unsilicified microbes, pseudofilaments, partly silicified microbes and silicified microbes. The rapidly silicified microbes appear well preserved with their general morphology, diameter, length, and presence or absence of septa being readily apparent. Most of the silicified microbes, however, lack the key features that would allow accurate comparisons with extant taxa. Only two of the silicified microbes can be tentatively allied with the unsilicified forms, despite being found side by side on the same glass slide. These problems in identifying modern, rapidly silicified microbes suggest that identifications of ancient silicified microbes can be problematic and must be treated with caution.
Lateral ramps and thrust terminations: an example from the Moine Thrust Zone, NW Scotland
Authors: KRABBENDAM MAARTEN , LESLIE GRAHAM
Published: December 2007

Detailed remapping within the Assynt Culmination in NW Scotland shows that the Ben More Thrust joins the Glencoul Thrust along a lateral branch line positioned in Loch Glencoul. This branch line marks the northern lateral termination of the Glencoul Thrust. The thrust on the northern shore of Loch Glencoul (‘the famous view’) is thus the Ben More Thrust. The Ben More Thrust Sheet is therefore much larger than previously thought. The lateral terminations of the Ben More Thrust to the north and the south are of two distinct types. This reinterpretation negates the existence of ‘surge’ zones in Assynt.
Geochemical and size variations in inhalable UK airborne particles: the limitations of mass measurements
Authors: MORENO TERESA , GIBBONS WES , JONES TIM , RICHARDS ROY
Published: December 2007

Current European Union legislation limits acceptable levels of inhalable particulate matter <10 μm based only on measurements of mass (currently 50 μg m
3
of PM
10
per day), without considering particle shape, size or chemistry. However, SEM and inductively coupled plasma mass spectrometry data on airborne particle samples from five UK sites (Port Talbot, London, Sheffield, Birmingham and the Lizard, Cornwall) show huge variations in PM
2.5
/PM
10
ratios and particle chemistry, irrespective of mass. Local geology, as well illustrated by the abundance of silicate particles of ophiolitic derivation from the Lizard, can be an important factor in particle variation. Thus a consideration of mass alone provides inadequate information about an airborne dust sample and any potential health effects linked to that sample.
Provenance and age constraints of the South Stack Group, Anglesey, UK: U–Pb SIMS detrital zircon data.
Authors: COLLINS ALANS. , BUCHAN CRAIG
Published: December 2007

U–Th–Pb Secondary Ion Mass Spectrometry (SIMS) data from detrital zircons extracted from the South Stack Group, Anglesey, UK, indicate that: (1) the maximum depositional age of the Holyhead Formation (South Stack Group, Monian Supergroup) is 501 ± 10 Ma; (2) the Monian Supergroup was deposited between

c.

500 and 475 Ma and is part of the Cambrian–Lower Ordovician succession found in southern Britain and Ireland; (3) Avalonia was a major sediment source (age maxima at 543–552 and 604–627 Ma); (4) Amazonia probably also provided zircons (common Neoarchaean–Mesoproterozoic grains) weakening suggestions that Avalonia had rifted off Gondwana by Cambrian times.
Organic maturation, thermal history and hydrocarbon generation in the Orcadian Basin, Scotland
Authors: HILLIER S. , MARSHALL J. E. A.
Published: December 2007

The Devonian Orcadian Basin contains thick sequences of organic-rich lacustrine sediments of interest as hydrocarbon source rocks. Throughout the basin the range of organic maturation is large, spore colours vary from yellow-orange to black, and vitrinite reflectance for Type
III
kerogens ranges from 0.7 to 10.5%. Maximum palaeotemperatures are estimated to range from those typical of moderate burial diagenesis (100°C) to those characteristic of greenschist facies metamorphism (400°C). The highest maturities are related to contact metamorphism by Devonian plutons, and it is postulated that a large pluton underlies much of Caithness. High and low maturity regions are often juxtaposed across major faults which were active during Variscan inversion. Regionally, the lowest maturity is about 0.8%
R

o

, implying uplift and erosion of 2–3 km of cover, basin wide. This cover was probably a sequence of Late Devonian and Carboniferous rocks removed largely during Variscan uplift.

Geothermal gradients were high but variable during Devonian extension. This, together with the contact metamorphic affects of the Devonian plutons, resulted in early maturation/metamorphism of large areas of the basin. Most of the onshore sequence entered the oil window during Devonian and Carboniferous times. Significant generation of hydrocarbons from Orcadian lacustrine facies offshore during subsequent Mesozoic burial will have occurred only in those areas which escaped maturation during the Palaeozoic.
Timing of Cenozoic extensional tectonics in west Turkey
Authors: SEYITOǴLU G. , SCOTT B. C. , RUNDLE C. C.
Published: December 2007

The timing of the transition from compressional to extensional tectonics in the late Cenozoic evolution of west Turkey has been constrained by K-Ar geochronology from acidic volcanic rocks and tourmaline leucogranite dykes in the central and east margin respectively of the Gördes basin.

Dacites and rhyolites in the centre of the Gördes Neogene sedimentary basin cut both the basement ophiolites of the Izmir-Ankara suture zone and the Neogene sediments. On the basin’s eastern margin the leucogranites cut metamorphic basement along a major NE-SW-trending normal fault that controls the regional structure of the basin. Pebbles of these leucogranites occur in adjacent Neogene turfites and conglomerates.

K-Ar dates on biotites from the central volcanic rocks vary from 18.4 ± 0.8 Ma to 16.3 + 0.5 Ma (early Miocene) whilst muscovite from a leucogranite on the eastern margin of the basin provides ages of 24.2 ± 0.8 Ma and 21.1 ± 1.1 Ma (latest Oligocene to early Miocene).

Geochronological data and field relationships demonstrate that the earlier compressional regime had been replaced by extensional tectonics by latest Oligocene-early Miocene.
Geology of the northern part of the Nanga Parbat massif, northern Pakistan, and its implications for Himalayan tectonics
Authors: BUTLER R. W. H. , GEORGE M. , HARRIS N. B.W. , JONES C. , PRIOR D. J. , TRELOAR P. J. , WHEELER J.
Published: December 2007

The northern outcrop termination of Indian continental crust lies at the Nanga Parbat massif, from where this contribution presents new field data. The tectonic contact with the structurally overlying Kohistan island arc is concordant and ductile, is associated with interleaving of Nanga Parbat and Kohistan lithologies, and may be correlated with the Main Mantle thrust found elsewhere in the NW Himalayas. This ductile shear zone is locally overprinted by cataclastic faults associated with exhumation of the massif but overall, the northern outcrop termination of the massif is controlled by erosion through a gently, northward-plunging antiformal structure. This folds both the Main Mantle thrust and the underlying, concordant 'Layered Unit' of the Nanga Parbat basement. Thus there is no indication that the massif acted as a promontory to the Indian continent during collision nor that it is a structure entirely bound by neotectonic faults. Ductile shear fabrics associated with the 'Main Mantle thrust' are cross-cut by leucogranite sheets and pegmatites. These may represent the stockwork to a significant crustal-melt granite body described here in the northern massif. This Jutial granite shows many geochemical characteristics in common with similar bodies in the High Himalayas which are consistent with anatexis of the buried Indian continental basement rocks. However, the granite is enriched in heat producing elements (particularly Th: 22 ppm) and shows extremely high
87
Sr/
86
Sr ratios (>0.88). The high concentrations of radiogenic Sr are also an attribute of a suite of hitherto enigmatic leucogranitic pegmatites that laces the Nanga Parbat massif, suggesting that these may represent a stockwork to a largely buried body of which the Jutial granite is a small exposure. The enrichment in heat-producing elements within the granite may reflect similarly high heat production in the source Indian continental crust requiring in turn a fundamental re-examination of the thermal evolution of this crust during Himalayan metamorphism and exhumation.
A reinterpretation of the genesis of the Cae Coch pyrite deposit, North Wales
Authors: BOTTRELL S. H. , MORTON M. D. B.
Published: December 2007

Data are presented on sulphur isotope ratios and Co/Ni ratios of samples from both the Cae Coch massive pyrite body and the adjacent lithologies in North Wales. The majority of the pyrite has light δ
34
S (-20 to -24‰
CDT
) indicative of a predominantly biogenic sulphur source; a minority of heavier values are interpreted as the result of sulphate depletion during the last stages of bacterial sulphide production. These values are far lighter than from volcanic-associated, exhalative massive sulphide deposits found in similar geological settings elsewhere, and Co/Ni ratios at Cae Coch (0.2-0.5) are also far lower than usual for such deposits. An alternative syn-diagenetic inhalative origin is proposed for the sulphide mineralization at Cae Coch.
Background to the Cambrian Explosion
Authors: BRASIER M. D.
Published: December 2007

This thematic set brings together invited papers given at the Lyell Meeting on 14 February 1991. Despite the Siberian weather, over 60 scientists descended on Burlington House from 12 different countries to attend this meeting, which brought together a wide range of specialists. A major aim of the meeting was to discuss the background to the ‘Cambrian Explosion’ by focussing on various aspects of ‘Geological and biological changes across the Proterozoic-Phanerozoic transition’.

This interval (Fig. 1) marked a major turning point in the geological record, during which the major invertebrate groups appeared. Rapid evolutionary diversification (Fig. 2) is clear from data presented in the following papers. Decline in the abundance and diversity of the soft-bodied Ediacara fauna during the Kotlinian Crisis was followed by an adaptive radiation that included trace fossils, acritarch phytoplankton and a variety of early skeletal fossils. The rise and subsequent fall of the early Cambrian biota is most dramatically picked out by the history of archaeocyathan sponges (Fig. 2) which largely became extinct during the Toyonian Crisis.

No biostratigraphical framework existed for this remote part of the scale prior to 1960.
J. W. Cowie
gives the background to the last two decades of steady progress by members of IGCP Project 29 on the Precambrian-Cambrian boundary, leading up to a vote on the boundary stratotypes at about the time of the Lyell Meeting. In the interval between the meeting and going to press, a majority vote has favoured placing the Precambrian-Cambrian boundary at a point marked by