bluuebunny/crossref_metadata_2025 huggingface dataset:
Palaeomagnetism of some Tertiary sedimentary rocks, southwest Sinai, Egypt, in the tectonic framework of the SE Mediterranean
Authors: Abdeldayem A. L. , Tarling D. H.
Published: April 2008

Two hundred and fifteen limestone core samples of Palaeocene (nine sites), Lower Eocene (ten sites) and Miocene (nine sites) ages were collected from the Wadi Feiran area, southwest Sinai. The majority of samples contained magnetic vectors that were consistent in direction during thermal and alternating field demagnetization. Normal and reversed polarities were identified that passed a reversal test, but the bedding tilts were too small to enable an adequate fold test to be undertaken. When compared to coeval palaeomagnetic poles for stable Africa, the Sinai palaeomagnetic poles are consistently displaced by some 30°. This is unlikely to be due to crustal translation between Sinai and Africa, but is attributed to local tectonic rotations of fault blocks in a similar way as for other areas in the SE Mediterranean. In the Suez area, the rotation has been mainly about horizontal axes and is associated with the opening of the Gulf of Suez.
Archaeomagnetic results from the Mediterranean region: an overview
Authors: Evans M. E.
Published: April 2008

Palaeomagnetic methods were first applied to archaeological materials and very young geological formations in the Mediterranean region a century and a half ago. Although the pioneering work established the general validity of the method, the data remained sparse and permitted only limited conclusions. By the mid-1920s, thorough investigations of the lava flows of Mt. Etna demonstrated how geomagnetic secular variation could be traced back into pre-observatory epochs. In the following decade, systematic study of archaeological features commenced, but it was not until the 1960s that the database had grown to the point where useful geomagnetic inferences could be drawn. For the Mediterranean region, there are currently available two extensive data sets (one for France, the other for Bulgaria) containing a total of
c.
400 directional results. For Italy and Greece, a useful start has been made (
c.
100 results); for other countries (Morocco, Tunisia, Turkey) only a handful of results have been published. Collectively these data enable us to trace back the directional behaviour of the geomagnetic field with resonable confidence for the last 2000 years, but with less certainty for earlier times. Nevertheless, a picture is emerging in which static flux bundles and flux spots undergoing zonal retrograde drift can be recognized. Since the determination of geomagnetic field strength does not require
in situ
material, the investigator is freed of the need for accurately oriented samples and the scope of archaeomagnetic research is therefore enlarged. Many results have been published, but their status remains questionable due to the on-going debate concerning the validity of the different experimental procedures. Intensity and directional results have potential for archaeological dating both in an absolute and in a relative sense. Some authors claim the possibility of achieving a precision approaching ±50 years, but this depends strongly on the region and time interval in question. One example of particular interest is the application of archaeomagnetic data to the demise of the Minoan civilization.
Collision and strike-slip faulting in the northern Molucca Sea (Philippines and Indonesia): preliminary results of a morphotectonic study
Authors: Rangin Claude , Dahrin Daharta , Quebral Ray ,   The Modec Scientific Party
Published: April 2008

A swath mapping, gravity and single channel seismic survey was carried out in the northern Molucca Sea with R.V.
L’Atalante
. Preliminary interpretation of these data reveals the presence of an almost complete Sangihe arc and forearc. The Miangas-Pujada-Talaud ridge in the central part of the Molucca Sea appears to be a backstop within the Sangihe forearc. East of the ridge very contrasting terranes are separated by a major NW-SE crustal discontinuity interpreted as a left-lateral strike-slip fault. North of 6°N the Philippine Trench inner wall is dissected by NW-SE trending left-lateral strike-slip faults, resulting from the dominantly oblique convergence between colliding arcs. South of 6°N the westward subduction of the buoyant Snellius volcanic plateau, a fragment of the Halmahera arc terrane, has induced the formation of a new plate boundary, the Philippine Trench along what is interpreted as a former strike-slip fault zone. East of the Miangas-Pujada-Talaud ridge there is a wide sedimentary wedge separated from the Snellius Ridge to the south by the major NW-SE crustal discontinuity. The thickness of this wedge cannot be explained by subduction along the very young Philippine Trench. It could be either an accretionary wedge developed at the deformed leading edge of the Sangihe forearc or be part of a former intra-arc basin which was part of the colliding Halmahera arc terrane. There is no clear evidence for accreted oceanic crust belonging to the recently subducted Molucca Sea. The Miangas-Pujada-Talaud ridge is part of the Sangihe forearc, and the ophiolites could represent its basement, uplifted along the outer arc ridge. The dog-leg-shaped Philippine Trench is propagating southward across the fragmented Halmahera arc terrane and its southern segment could reactivate a former strike-slip fault zone.
Detailed processing of seismic reflection data from the frontal part of the Timor trough accretionary wedge, eastern Indonesia
Authors: Hughes B. D. , Baxter K. , Clark R. A. , Snyder D. B.
Published: April 2008

The DAMAR deep seismic line across the Banda arc in Indonesia provides a valuable insight into the Late Cenozoic collision between the northward-moving Australian plate and the Southeast Asian plate. Previous geophysical investigations across the accretionary wedge have only imaged relatively shallow structures due to the complex structure of the wedge which remains poorly resolved following conventional processing techniques. The design of a detailed processing sequence and its application to a 35 km section of the DAMAR line to include the Australian Northwest shelf, the Timor trough and the frontal part of the accretionary wedge, has allowed an improvement in resolution of structures both within and below the frontal part of the wedge. The Australian margin to the south of the trough contains a number of normal faults which show inversion features. The reprocessing of the accretionary wedge has allowed an improved interpretation of the internal structure in the frontal part of the collision zone and this consists of a number of high angle thrust structures. This has shown that shortening in the frontal part of the accretionary wedge has developed coherent thrust slices imbricated from the subducting Australian margin, rather than an incoherent melange.
Cenozoic SE Asia: reconstructing its aggregation and reorganization
Authors: Packham Gordon
Published: April 2008

Reconstructing SE Asia in the Cenozoic is dependent on being able to model three major tectonic events and their consequences. They are the collision of India with Eurasia, the rotational history of the Philippine Sea plate and the ongoing collision of Australia with eastern Indonesia. Models of the Eocene India-Eurasia collision imply extrusion along major strike-slip faults or crustal thickening and block rotation. Kinematic modelling of the present day tectonics of central Asia indicates rotations and strike-slip faulting and an eastward displacement of crust. Prior to middle Miocene time tectonic activity was closely associated with the collision zone and extrusion of Indochina was supposed to have occurred. Analysis of the volume of the topography formed by the collision indicates eastward displacement and the loss of some crust by expulsion or into the mantle. Palaeomagnetic measurements have found northward displacement of Tibet and strong clockwise rotation east of the eastern syntaxis but unequivocal evidence of southward displacement is rare. Large Palaeogene to early Neogene displacements on strike-slip faults have been documented and related with confidence to the rotations that formed at least the Oligocene South China Sea floor. Early Oligocene docking of the Indoburman Flysch belt south of the eastern syntaxis is difficult to explain in extrusion models. Whether the rotations that have been documented are a response by internal deformation or block rotation is unresolved, as is the amount of extrusion of SE Asia to the south. In the eastern region, rotation and associated northward motion of the Philippine SEa plate as it developed puts constraints on possible models because of a maintained close proximity of its southern margin to the northern edge of the Australian craton. Assembling of continental fragments now in the Banda Sea and derived from eastern New Guinea appears to have occurred by Late Cretaceous time. Formation of the Banda arc may have isolated the Banda Sea from the Australia plate then collision of the Australian margin possibly rotated the Banda Sea counter-clockwise. Although westward movement of the Philippine Sea plate relative to Australia commenced in the early Miocene, convergent left-lateral shear was not possible until the late Miocene thus limiting westward tectonic transport of terranes and the transmission of the shear into the region west of the Banda Sea.
Timing of the Shan-Thai-Indochina collision: new evidence from the Pak Lay Foldbelt of the Lao PDR
Authors: Stokes Robert B. , Lovatt Smith Paul F. , Soumphonphakdy Ko
Published: April 2008

The Pak Lay Foldbelt in the northwest of the Lao PDR is a product of the Indosinian orogeny, resulting from the collision of Shan-Thai and Indochina along a suture now marked by the Nan-Uttaradit ophiolite zone. Current hypotheses place the timing of this collision in either the Permian or the Triassic. Recent field work and subsequent laboratory analyses suggest that, in the area to the south of Pak Lay: pre-collision sediments are as young as Middle to Upper Jurassic; arc-related volcanism continued from the Triassic into the Late Jurassic; all these sediments and volcanic rocks form an imbricate zone; and the Cretaceous Khorat Group rests with marked unconformity above the imbricate wedge. From this we conclude that the Shan-Thai-Indochina suturing occurred in the Late Jurassic.
Mid-Cretaceous inversion in the Northern Khorat Plateau of Lao PDR and Thailand
Authors: Lovatt Smith Paul F. , Stokes Robert B. , Bristow Charlie , Carter Andrew
Published: April 2008

Evidence is presented from the study area for the occurrence of a regional compressive tectonic event in the mid-Cretaceous (Aptian-Cenomanian). This is tentatively attributed to the effects of a distant continent-continent collision to the west. Pre-existing structural trends were reactivated parallel to palaeo-continental sutures to the northeast (Song Ma and Song Da) and west (Nan). The event interrupted the latest Jurassic to earliest Palaeocene subsidence and continental sedimentation of the Khorat Plateau Basin. The primary effects are shown by seismic data to be regional tilting, compressive folding, reverse faulting and inversion of the basin subsidence pattern. The data do not support the current view that such structuring was initiated during the Tertiary. However they do show that there was some reactivation of mid-Cretaceous structures during regional uplift in the Tertiary. This revision of timing of structuring suggests the hydrocarbon potential of the area may be greater than previously anticipated.
Origin and tectonic significance of the metamorphic rocks associated with the Darvel Bay Ophiolite, Sabah, Malaysia
Authors: Omang Shariff A. K. , Barber A. J.
Published: April 2008

Banded hornblende gneiss, foliated amphibolite, hornblende, chlorite and siliceous schist form lenses in an 8 km wide belt within the Darvel Bay Ophiolite Complex. Foliation in the belt is generally steep to vertical, striking parallel to the trend of the belt and lineations are sub-horizontal. Mineral and geochemical studies show that the metamorphic rocks represent banded and isotropic gabbros, plagiogranites, doleritic and basaltic dykes, basaltic volcanics and cherts formed at a spreading ridge in a supra-subduction zone environment, which were deformed at high temperatures but low pressures along a transform fault. Incorporation of supracrustal cherts indicates that the transform extended for hundreds of kilometres between spreading centres. Garnet pyroxenites and amphibolites found as clasts in Miocene volcanic agglomerates formed at high pressures, and temperatures are interpreted as derived from a metamorphic sole underlying the complex, formed during subduction of ocean crust and the emplacement of the ophiolite complex on Sabah.
The Tertiary evolution of South Sulawesi: a record in redeposited carbonates of the Tonasa Limestone Formation
Authors: Wilson Moyra E. J. , Bosence Dan W. J.
Published: April 2008

South Sulawesi, situated at the junction of three major plates and with an almost complete Tertiary sequence, is an ideal location in which to study syntectonic sedimentation. Redeposited carbonate facies of the lower/middle Eocene to middle Miocene Tonasa Limestone Formation in the Barru area prove to be reliable indicators of tectonic activity. South of the Barru area contemporaneous carbonate sediments formed on a relatively stable shallow-water platform, known as the Tonasa Carbonate Platform. Redeposited carbonate facies and interbedded marls from the Barru area are described and interpreted in this study. The immaturity and provenance of clasts indicate that the redeposited facies were derived from the faulted northern margin of the Tonasa Carbonate Platform. A relay ramp between at least two major NW-SE trending faults is the inferred configuration of this margin. Three main phases of faulting are indicated by the redeposited facies: late Eocene to early Oligocene, middle Oligocene and early to middle Miocene. This is consistent with other outcrop and seismic data from the region and with the inferred plate tectonic situation during the Tertiary.
40
Ar/
39
Ar constraints on obduction of the Seram ultramafic complex: consequences for the evolution of the southern Banda Sea
Authors: Linthout Kees , Helmers Henk , Wijbrans Jan R. , Van Wees Jan Diederik A. M.
Published: April 2008

On Kaibobo (W Seram), obduction of hot oceanic lithosphere produced high-grade metamorphism and granite in overthrust continental crust.
40
Ar/
39
Ar plateau ages of 5.65–6.0 Ma and 5.4 Ma of muscovite and biotite from the sole, among the youngest so far measured on single crystals, indicate complete resetting of the Ar-isotope system. Chloritized biotite crystals gave disturbed spectra and younger ages. Single fusion on biotite from the granite gave an age of 5.5 Ma. Time limits for the obduction-exhumation history of the Kaibobo complex and sole are approximated by simple 1D forward P-T-t modelling, constrained by PT data and
40
Ar/
39
Ar thermochronology (
c.
400°C at 6 Ma;
c.
320°C at 5.5 Ma). Best fit results indicate that the decelerating post-emplacement exhumation of ophiolite and sole began ≤ 8 Ma ago. The rate during the first 1 Ma of this uplift exceeded 7.5 mm a
−1
. Undoing 8 Ma of migration in the SW Pacific and Australian regimes of motion back-tracks Kaibobo to the site where obduction-emplacement ended: near the southeastern corner of the Banda Sea plate. Similar compositions and time-settings of the Kaibobo and N Timor ophiolites lead us to postulate that, during the Early Miocene, slow-rate spreading occurred in the oceanic lithosphere of the southern Banda Sea, south of the current volcanic arc.
The geology and tectonic evolution of the Bacan region, east Indonesia
Authors: Malaihollo Jeffrey F. A. , Hall Robert
Published: April 2008

Bacan is located in the zone of convergence between the Eurasian, Philippine Sea and Australian plates. The oldest rocks in Bacan belong to the Sibela Continental Suite and are probably of Precambrian age. The complex includes continental phyllites, schists and gneisses of upper amphibolite facies. Isotopic dating yielded extremely young ages due to interaction with hydrothermal fluids. Juxtaposed against the continental rocks is the mostly unmetamorphosed, arc-related Sibela ophiolite, probably derived from the Philippine Sea plate. Isotopic dating yielded a Cretaceous age with an Oligocene-Miocene overprint. In north Bacan, the oldest formation is the Upper Eocene Bacan Formation which comprises interbedded arc volcanic and turbiditic volcaniclastic rocks, metamorphosed under conditions between the prehnite-pumpellyite and greenschist facies. A similar Lower Miocene sequence, assigned to the same formation, is exposed in south Bacan. The Oligocene Tawali Formation on Kasiruta, NW of Bacan, consists of arc basalts and volcaniclastic turbidites, metamorphosed to zeolite facies. The Bacan and Tawali Formations represent different parts of an arc, active from Late Eocene until Early Miocene, resulting from northward subduction of the Australian plate under the Philippine Sea plate. There is a major Lower Miocene unconformity, representing collision of the Australian continent with the Philippine Sea plate, above which shallow marine limestones of the Lower-Middle Miocene Ruta Formation were deposited. This deposition was interrupted by sudden influxes of volcaniclastic sands, forming the Amasing Formation. The Upper Miocene-Pleistocene Kaputusan Formation, rests locally unconformably on older rocks, and includes three members. The Goro-goro Member consists of arc andesites, originating from four eruption centres, which erupted from Late Miocene to Pleistocene, with the oldest in south and the youngest in north Bacan. The Pacitak Member consists of shallow marine pyroclastic rocks. The Mandioli Member formed fringing coastal reef limestones. The volcanic rocks of this formation were produced by eastward subduction of the Molucca Sea plate. Quaternary basalts are related to movement along the Sorong fault. It is concluded that most of the Bacan region has been part of the Philippine Sea plate since the Cretaceous; volcanic rocks of different ages all have an arc character and chemistry, and lithological variations reflect different positions within the volcanic arc; and there is evidence for continental crust of Australian origin in the Bacan area by the Early Miocene.
Gondwana origin of the Baoshan and Tengchong terranes of west Yunnan
Authors: Wopfner Helmut
Published: April 2008

Upper Palaeozoic glaciomarine deposits combined with the presence of cold-water faunas andGlossopterisindicate a Gondwana provenance of the Baoshan and Tengchong Blocks in western Yunnan. The glacial origin of these Permo-Carboniferous deposits is verified by a three-fold subdivision of the basal sequence comprising, in ascending order: diamictites with faceted and striated clasts, laminites with dropstones, and a black anaerobic de-glaciation facies. The succeeding carbonates of the upper Permian and Lower Triassic originated during a post-glacial phase of a much warmer climate. Although the two blocks are adjacent to each other their Upper Palaeozoic sequences show significant differences. The glacigene successions of the Baoshan Block are comparatively thin and are overlain by thick basalts and red beds. On the Tengchong Block the glacigene marine deposits exceed 1000 m and are followed by thick reefal limestones of Lower Permian age. An active volcanic rift setting is suggested for the Baoshan Block and a proximal passive margin environment at a somewhat lower latitude for the Tengchong Block. The succession of the latter is comparable with Permo-Carboniferous sections in NW Australia, especially that of the Bonaparte Gulf basin, and it is assigned to the Sibumasu tectono-stratigraphic unit. The Baoshan sequence shows similarities to sequences of Tibet and NE India and is therefore assigned to the Tibetan realm. Both terranes separated from Gondwana in the late Early Permian. Docking commenced in the Late Triassic concomitant with the closure of the Changning-Menglian Belt. Lateral displacements in the course of the Himalayan orogeny moved the Tengchong Block north, bringing it into juxtaposition with the western margin of the Baoshan Block. This tectonic contact is now the Nujiang Line.
Early Mesozoic orogeny in Fujian, southeast China
Authors: Zhou Zuyi , Lao Qiuyuan , Chen Huanjiang , Ding Sijiang , Liao Zhongting
Published: April 2008

The Mesozoic sedimentary successions of west Fujian evolved from Lower Triassic deep marine fine turbidites to Upper Triassic and Jurassic coal-bearing molasse deposits, and represent a typical foreland basin sedimentary sequence. This foreland basin was generated by an early Mesozoic continental collision to the south, between the South China block and the South China Sea block. This collision led to the formation of Permo-Triassic S-type granites, and a first stage of thrusting in a NNW-SSE direction. Post-collisional convergence resulted in the accumulation of thick molasse deposits. Two main unconformities, within the molasse and separating the molasse from the underlying flysch, necessitate a re-evaluation of the traditional concepts of ‘Indosinian’ and ‘Yanshanian’ movements in SE China. The tectonic and stratigraphic evolution of the west Fujian foreland basin, together with the structural features in the basin, show that the Early Mesozoic orogeny in the region was a mild and continuous process.
Metal-organic interactions in the Dinantian Solway Basin, UK: inferences for oil migration studies
Authors: Veale C. , Parnell J.
Published: April 2008

Carboniferous basins within the British Isles show a variety of metal-organic fluid interactions, including the precipitation of thoriferous bitumen nodules. These represent the interaction between a thorium-rich fluid, such as groundwater, and migrating hydrocarbons. They are found in the Dinantian of the Northwest Irish Basin and the Solway Basin. In the latter case, nodules are found in coarse-grained clastics laid down in a variety of depositional environments. The source of the thorium was the nearby Caledonian Criffel-Dalbeattie Granite. Studies of sedimentological parameters of both nodule-bearing and barren beds, and the structure of the basin, show that factors controlling the distribution of nodules include the maturity and porosity of the host rock, with an enhanced maturity and high porosity preferable, as well as the depositional environment. In the case of the Dinantian of the Solway Basin, distal shallow-marine sediments and channelized deposits host the nodules. Chemical age dating of the thoriferous inclusions within the nodules points to the possible use of these nodules in assessing the timing as well as spatial distribution of hydrocarbon migration within sedimentary basins. Results indicate a correlation with previous models of Mesozoic hydrocarbon migration.
Biotic gradients on a homoclinal ramp: the Alamogordo Member of the Lake Valley Formation, Lower Mississippian, New Mexico, USA
Authors: Jeffery David L. , Stanton Robert J.
Published: April 2008

The Lower Mississippian Alamogordo Member of the Lake Valley Formation in south-central New Mexico represents a well exposed carbonate-dominated homoclinal ramp with little evidence of sediment transport. Biotic components present and evident in thin section have distinct distributions in the level-bottom facies in relation to their shoreward and basinward ramp positions. Assemblages (I–IV) are established along the depth gradient from shallow to deep water, and are useful in palaeobathymetric interpretation; they are similar in composition to the depth-related phases recognized in Dinantian mounds by Lees & Miller (1985). The biotic assemblages shift laterally in successive beds of the Alamogordo Member, indicating variations in sea level during deposition. As a result, deepening and successive shallowing during a transgressive-regressive cycle can be tracked within the Alamogordo Member. The ramp slope is interpreted to have been of the order of 0.5°, based on the maximum depths for green and red algae having been 110m and 250m respectively. The systematic positions of several problematical taxa (
Asphaltinella, Sphaerinvia
, stacheiins and salebrids) are discussed.
Late Viséan buildups at Kingscourt, Ireland: possible precursors for Upper Carboniferous bioherms
Authors: Somerville Ian D. , Strogen Peter , Jones Gareth LL. , Somerville H. E. Anne
Published: April 2008

Two late Viséan (Asbian-early Brigantian) buildup complexes occur in the Kingscourt Outlier in Ireland, near the top of the Mullaghfin Formation, a shallow-water, grainstone unit. These massive buildups at Ardagh and Cregg accumulated on the margins of a carbonate platform bordering a deep-water basin. Both have a buildup facies of fine-grained, peloid-rich, algal lime mudstones and wackestones, interbedded with coarser grained intraclastic, skeletal packstones and grainstones (interbuildup facies). Microbial structures are well developed in the buildup facies, principally domal stromatolites, thrombolites and oncoidal fabrics of cyanophytes (
Ortonella
and
Girvanella
) with encrusting formainifers (
Aphralysia
and
Textrataxis
). Algal structures include rhodoliths (
Solenopora
) and fragments of
Ungdarella
and stacheiids, with less abundant chlorophytes (
Koninckopora
); in the interbuildup facies,
Koninckopora
is more abundant.

Near the top of the Ardagh buildup is an unusual development of phylloid algal boundstone composed of the possible ancestral coralline red alga
Archaeolithophyllum
. This boundstone also contains encrusting bryozoans and foraminifers, and directly overlies abundant Brigantian
in situ
fasciculate rugose corals. This upper unit appears to be associated with a rapid shallowing event, which stimulated the development of a wave-resistant rigid framework.

Laterally, bedded intraclastic skeletal packstones and grainstones, with thin interbedded clays and shales, pass into the lower part of the massive Ardagh buildup, but appear to onlap and drape the upper part of the buildup. Buildup clasts occur within the interbuildup facies and proximal flank facies, indicating synsedimentary cementation.

Late Viséan buildups of the Ardagh type highlight an important period of diversification of colonial rugose corals and calcareous algae associated with the development of widespread shallow-water carbonate platforms worldwide. This allowed the emergence of new algal groups, particularly the red algae (
Archaeolithophyllum
and
Ungdarella
) and the palaeoberesellid green algae (
Kamaenella
), which subsequently dominated Upper Carboniferous wave-resistant bioherms.
Evidence for catastrophism at the Famennian-Dinantian boundary in the Iberian Pyrite Belt
Authors: Moreno Carmen , Sierra Sonia , Sáez Reinaldo
Published: April 2008

Terrigenous shelf sedimentation during the Devonian created a homogeneous basin in the Iberian Pyrite Belt. This shallow south-Iberic basin changed into a mosaic of horsts and graben at the Famennian-Dinantian boundary and subsequent evolutionary history can be explained in terms of locally increased rates of subsidence. Deposits commonly related to highly energetic processes characterize this change (fan-deltas, sediment gravity flows, rapid basin-shallowing). These resulted from convulsive/catastrophic events related to the Bretonic phase of the Hercynian Orogeny.
The stratigraphy and cyclicity of the late Dinantian platform carbonates in parts of southern and western Ireland
Authors: Gallagher Stephen J.
Published: April 2008

The late Dinantian platform carbonate successions of the Burren, Buttevant and Callan areas in Ireland have been correlated using detailed litho- and biostratigraphy. Several subdivisions or lithofacies associations (LA) of the Asbian to Brigantian part of the succession have been recognized in each area (lithofacies associations 1–5). Holkerian(?) to early Asbian ramp carbonates of LA 1 underlie the late Asbian successions in both the Burren and Buttevant areas. The influx of the bilaminar palaeotextulariid
Cribrostomum lecomptei
coincides with the onset of late Asbian shallow-marine cyclic platform sedimentation (LA 2) in all areas. The sediments of LA 2 have abundant
Kamaenella
and foraminifera, and are characterized by palaeokarstic surfaces and shales that cap a minimum of nine shallowing-upward minor cycles in the Burren and Buttevant areas. Two new biostratigraphic subdivisions (Cf6γ1 and Cf6γ2) of the late Asbian/Cf6γ subzone are described for the first time in this part of the succession. Brigantian sedimentation (LA 3) is typified by amalgamated beds of crinoidal limestone and abundant Asteroarchaediscidae. Thin peloidal limestones with coral thickets cap shallowing-upward cycles within this succession. These cycles, which are thinner and less numerous than those of the underlying late Asbian, rarely terminated in emergence, but most reached shallow subtidal depths prior to the next transgression. The change in cyclicity style across the Asbian/Brigantian boundary may be related to the sedimentation rates of the crinoidal limestones, due to increases in cyclic oscillation in the Brigantian. Brigantian LA 4 is characterized by deep subtidal cherty limestones, with abundant algal-coated wackestone intraclasts.
Fasciella
and
Howchinia bradyana
are typical microfossils. No cyclicity is observed, probably owing to the deep subtidal nature of this unit. LA 4 is overlain by another unit of cyclic crinoidal limestones (LA 5) in the Burren, which has no correlatives in the other areas studied. The succession in all areas is unconformably overlain by Namurian siliciclastic rocks. The nature and number of minor cycles in the late Dinantian of Ireland is similar to those of platform successions of the same age elsewhere in the British Isles, suggesting that eustatic changes were one of the major controls on cyclicity during the late Dinantian.
Controls on ramp, platform and basinal sedimentation in the Dinantian of the Dublin Basin and Shannon Trough, Ireland
Authors: Strogen P. , Somerville I. D. , Pickard N. A. H. , Jones G. LL. , Fleming M.
Published: April 2008

In the Dublin Basin a Courceyan ramp phase of sedimentation was followed in the Chadian by tectonic break-up of the basin into distinct shallow-water platforms, on which production of carbonate sediments continued in considerable volume, and ‘deep’ basinal areas in which it ceased. Progradation of the platforms across these basinal areas was limited, and mainly confined to the dip-slope of hanging wall blocks; progradation across fault scarps was rare. In the Shannon Trough basement-fault control was evident in the distribution and migration patterns of volcanic centres in the Chadian to Arundian, but despite this, ramp sedimentation occurred throughout the Dinantian, evolving into a purely constructional large platform by late Dinantian time. There was no break-up of the basin as in the case of the Dublin Basin.

The reason for the contrasting behaviour of the two basins is related to the rate of upwards movement of extensional faults relative to sedimentation rates. In the Dublin Basin these faults penetrated to the palaeosurface to form scarps by the late Chadian, and this topography survived into the Brigantian. In the Shannon Trough these faults failed to surface, but deep basement structures controlled the distribution of Dinantian volcanic centres which lie on a series of ENE-trending lineaments. These lineaments, which parallel the axis of the Shannon Trough, almost certainly mark the traces of active down-to-basin faults that controlled its half-graben structure.

The basement rocks of the two basins are clearly of a different nature; the Dublin Basin is floored by basement of a much more heterogeneous nature than the Shannon Trough, the former lying south and the latter north of the putative Iapetus Suture line.
Siliceous rocks of the Culm Basin, Germany
Authors: Gursky Hans-Jürgen
Published: April 2008

The classic Dinantian cherts of the Rhenish Massif and Harz Mountains, Germany, were analysed for their petrography and sedimentology. They occur in five lithostratigraphic units: the Lower Alum Shale Formation, the Black Chert Formation, the Pale Chert Formation, the Siliceous Limestone Formation, and the Siliceous Transitional Formation (upper Hastarian to Asbian, CuII to CuIIIα of the German cephalopod zonation). Mafic volcanic rocks are locally associated with these strata. Four regional facies zones have been defined.

Radiolarian chert, spiculitic chert, homogeneous chert, and silicified quartz-trachytic tephra and tuffite are the main chert types. These mostly form current-laminated grey, black, greenish or reddish beds rhythmically alternating with layers of siliceous mudstone and, in places, variably intercalated with grey and black mudstones and siltstones, phosphorites, metabentonites, limestone turbidites, greywackes and quartz arenites. The siliceous rocks were deposited in a moderately deep (upper bathyal) strait of an equatorial sea that was part of palaeo-Tethys. Westward-driven nutrient-rich currents from the palaeo-Pacific Ocean favoured high radiolarian fertility. Relatively pure biosiliceous ooze was deposited under temporarily anoxic conditions when, due to dry climate and high sea-level, detrital input decreased.

Deposition of the siliceous facies ended with increased detrital input and breakdown of the ocean-current system due to the collision of Laurasia and Gondwana during the Variscan Orogeny.
Reconstruction of a lost carbonate platform on the shelf of Fennosarmatia: evidence from Viséan polymictic debrites, Holy Cross Mountains, Poland
Authors: Belka Zdzislaw , Skompski Stanislaw , Sobon-Podgorska Janina
Published: April 2008

The sedimentary sequence of a totally eroded carbonate platform on the shelf of Fennosarmatia in Poland has been reconstructed based on the analysis of detrital material derived from the platform and deposited in an adjacent basin. The database was taken from a polymictic debrite unit intercalated in the Viséan basinal succession exposed in the southwestern Holy Cross Mountains. The unit represents a gravity-flow deposit and contains carbonate clasts ranging from Frasnian to Viséan in age. They provide evidence for a Frasnian carbonate platform located south of the Holy Cross area that drowned during Famennian and Tournaisian times but subsequently, during the early Viséan, started to recover. This reversed trend is interpreted to have resulted from the combined effect of eustatic sea level fall and tectonic uplift. The geographical extent of the inferred carbonate platform system, named here as the Nida Platform, cannot be precisely outlined, but most probably corresponded with the Jedrzejow High, an elevated fragment of Precambrian basement.
Cyclic stratigraphy, facies and fauna of the Lower Carboniferous (Dinantian) of the Moscow Syneclise and Voronezh Anteclise
Authors: Makhlina Mariya KH.
Published: April 2008

On the basis of sedimentological investigation of rocks, together with bed-by-bed studies of foraminifers, conodonts and spores, rhythmic sedimentation has been demonstrated in the Lower Carboniferous of the Moscow Syneclise and Voronezh Anteclise. Cycles of different order have been established using the methods of rhythmic stratigraphy elaborated by Tikhomirov. Four transgressive-regressive cycles of the sixth order have been recognized in the Dinantian of the Russian Platform. The latter are time-stratigraphic equivalents of the newly proposed stages of the Khaninian and Shurinovkian in the Tournaisian, and Kozhimian and Okian Stages in the Viséan. Each of these cycles includes two or three smaller cycles which represent the initial and maximum transgressive units and a regressive unit.
Sequence biostratigraphy of the Tournaisian-Lower Viséan rocks of the Russian Platform
Authors: Rukina G. A.
Published: April 2008

A statistical analysis of foraminiferal communities was used to study Tournaisian to lowermost Viséan rocks of the Moscow Syneclise, Voronezh Anteclise, Volga-Urals region and the northern part of the Pre-Caspian Depression. Eleven levels of foraminiferal community reorganizations were recognized and traced over the Russian Platform. These levels correspond to changes in foraminiferal dominance which often coincide with changes in lithology and thus reflect an environmental sequence. An understanding of regional events affecting the sedimentary basin, including foraminiferal reorganizations, leads to more precise correlation of depositional sequences from one area to another.
Evaluation of volcano flank instability triggered by dyke intrusion
Authors: Elsworth Derek , Voight Barry
Published: April 2008

Instability of volcano flanks may result from the mechanically and thermally generated pore fluid pressures that accompany dyke intrusion. These complementary methods of pore pressure generation act on potential basal failure planes, decreasing effective stresses and consequently decreasing frictional resistance to failure. The twin agents of pore pressure generation provide a rational and quantifiable means of initiating and sustaining flank instability, even as the driving forces provided by magma pressurization ultimately drop as flank displacement is initiated, Pore pressures developed by mechanical and thermal effects are readily evaluated using simple, but mechanistically rigorous, models. Mechanically induced pore fluid pressures are evaluated through an analogy with a moving line dislocation within a saturated porous-elastic medium. Thermally induced pore fluid pressures are evaluated from a one-dimensional advective-diffusive solution for low Peclet transport, representing behaviour around a plane feeder dyke of infinite extent. Induced pore pressure magnitudes condition stability through the parameters representing the geometry and dimensions of the flank and failing flank block, together with the parameters modulating volumetric magma intrusion rate and heat supply. Where appropriate parameter magnitudes are selected, the resulting mechanical and thermal pore fluid pressures are sufficient to initiate failure. Where the pervasive influence of thermally induced pore pressures is included, or where shear collapse of the saturated pore structure occurs, the disturbance is sufficient to sustain failure. This presents the possibility for long runout instabilities of extremely large volume.
Mutual influence of dyking and collapses at Stromboli volcano, Italy
Authors: Tibaldi Alessandro
Published: April 2008

The island of Stromboli represents the emergent part of a 2.6 km high composite volcano. The evolution of this summit zone is characterized by a complex dyke pattern and repeated collapses. Three summit collapses and one southeastward minor lateral collapse occurred between 85 and 21 ka
bp
. From 13 ka to a few thousand years ago, three large lateral collapses occurred northwestwards. During the last 100 ka of volcanic history, which is reconstructed on the basis of data derived from the emergent part of the cone, the majority of dykes have been injected along a NE-SW zone of weakness which cuts the summit of the volcano. In the southern part of the island a N-S dyke zone connected, for a short period, the main Stromboli conduit to an off-shore crater. Another dyke zone developed after 13 ka
bp
along the walls of the earliest lateral collapse which occurred towards the NW at around this time. Dykes are vertical, especially along the NE-trending weak zone, whereas the other more external dykes tend to parallel the cone slopes and the collapse depression. Cumulative dyke thicknesses have a NW-SE horizontal maximum. Dyking along the NE-SW weak zone may have exerted a geometric control and provided a trigger for the NW-SE lateral collapse event. In turn the more external dyking was extremely sensitive to the local σ3 induced by debuttressing, in the case of injection planes parallel to the lateral collapse escarpments, and by the gross volcano morphology, in the case of dykes which parallel the cone slopes.
The influence of regional stresses on the mechanical stability of volcanoes: Stromboli (Italy)
Authors: Russo Guido , Giberti Grazia , Sartoris Giovanni
Published: April 2008

An elastic model was developed to study the mechanical stability of a volcanic system that includes a volcanic edifice and a magmatic feeding system (conduits and reservoirs) with axial symmetry around a vertical axis. Stability depends critically on the horizontal regional stress which comes into the problem as a boundary condition imposed at large horizontal distance. We considered three types of boundary conditions: (1) zero horizontal displacement (NHD); (2) lithostatic regional stress (LITH); (3) non-axisymmetrical regional stress corresponding to a strike-slip regime (NAS). For the third case (NAS), we used a 3-D model. The stress distributions were calculated by a numerical finite element method. The development of tensile tangential stress in the elements adjacent to the walls of conduits and reservoirs is assumed to be a sufficient condition for the instability of the plumbing system. In compression, we have adopted the Navier-Coulomb criterion for failure. We apply this model to Stromboli volcano, which is characterized by a steep volcanic edifice and open conduits filled with magma. There is geochemical evidence for a deep reservoir (
c.
10 km depth) of unknown size and indirect evidence of a shallower reservoir (at the base of the edifice) with volume of the order of 1 km
3
. The persistent explosive activity has been steady for the last 2000 years: this implies that the feeding system is mechanically stable. It is found that the deep reservoir has no influence on the stability of the edifice. With NHD boundary condition, implying that the horizontal regional stress is one-third of the vertical component, Stromboli’s volcanic system is unstable. In general, any volcanic system with an open and magma-filled plumbing system, with NHD boundary conditions, is mechanically unstable. With lithostatic regional stresses (LITH), the magmatic feeding system is mechanically stable and the slopes of the subaerial edifice are unstable, being subject to landslides. Both NHD and LITH conditions imply that the regional horizontal stress is isotropic which is not appropriate for the Southern Tyrrhenian Sea. With the NAS boundary condition, the stability of the plumbing system of Stromboli volcano allows us to place an upper limit on the maximum shear stress Δ
0
= (|σ

h

|

max

− |σ

h

|

min

)/2 For Δ
0
= 10 MPa, the magmatic feeding system is at the limit of mechanical instability. The subaerial edifice has steep slopes and it is at the limit of gravitative instability independent of the boundary conditions.
Hydrothermal pore fluid pressure and the stability of porous, permeable volcanoes
Authors: Day S. J.
Published: April 2008

Lateral collapses of large volcanoes are commonly associated with phreatic explosions and other evidence for the presence of pressurized hydrothermal pore fluids within the volcanoes prior to collapse. Furthermore, hydrothermal alteration of volcanic edifices is a major factor in increasing susceptibility to collapse. This is generally held to be because of a reduction in effective friction coefficient μ through alteration. However, this is inconsistent with an analysis of the factors affecting the strength of fluid-saturated rocks and volcanic debris in terms of the Rubey & Hubbert equations for shear failure of such materials. Instead, this analysis indicates that reductions in the strength of volcanic materials are mainly due to the effect of high pore pressure relative to confining pressure, expressed as the ratio λ of the two. Consideration of field and seismic evidence, together with simple calculations, indicates that high values of, and large increases in, λ are produced by a variety of mechanisms: heating of confined pore water by intrusions; degassing of intrusions; discharges of highly pressurized fluids from depth through clastic dykes; and by deformation associated with faulting. The sensitivity of pore fluid pressures to perturbation by these mechanisms is however highly dependent upon the permeability of their host rocks, which may itself be subject to rapid changes by fracturing, faulting and other processes. The rapidity of temperature changes and other mechanisms for pressurization in volcanic edifices means that the resultant pore pressure changes are large even in quite highly permeable rocks, but the effects are unpredictable. Detection of the development and spreading of high pore pressures within active volcanoes may however be possible by careful monitoring of patterns of seismicity.
The role of basement in volcano deformation
Authors: Vries Benjamin Van Wyk De , Borgia Andrea
Published: April 2008

Growing volcanoes load their basements, causing isostatic flexure, compaction and brittle and ductile deformation. Deformation of basement in turn exerts stress onto the edifice, which also responds by deforming. This deformation will be gradual or catastrophic, depending on the nature of the cone, and the properties of the underlying rocks. The physical properties of substratum, most especially the viscosity, can vary greatly. Thus a substratum of lava will support a volcano to a greater extent than fine clastic rocks. Compaction, crustal flexure, and sagging (a result of viscous flow of substratum) create a depression below the volcano. In the cone this induces compression, which increases with increasing sagging. However over long time spans, or in low viscosity substratum, sagging generates volcano spreading, where elastic compression is relaxed. The role of basement in volcano stability at four Nicaraguan stratocones 1.5–2 km high, constructed of similar materials on three types of basement has been studied. San Cristobal volcano has a volcanic basement of lava and ignimbrite, which has sagged by small amounts. Mombacho volcano has a basement of volcanic and marine strata. Sagging occurs, but spreading is slow. Compressive stresses have been released in the cone by thrust faulting. These structures have probably been exploited by three sector collapses. Concepción and Maderas volcanoes rest on sedimentary strata of weak mudstones, and large amounts of sagging and spreading have occurred. The study shows that spreading promotes gradual deformation in the volcano, because slopes are reduced and stresses relaxed. Catastrophic failure is favoured when compression is dominant, because stresses are large enough to fracture rock and produce decollements. Fracturing also promotes hydrothermal circulation, which further weakens the construct.
Coastal elevation changes in eastern Sicily: implications for volcano instability at Mount Etna
Authors: Firth C. , Stewart I. , McGuire W. J. , Kershaw S. , Vita-Finzi C.
Published: April 2008

The eastern flank of Mount Etna, Sicily has been recognized as being unstable, and three contrasting models have been proposed to account for this phenomenon, these being deep-seated spreading, shallow sliding and tectonic block movements. These models are examined by making reference to the rates and patterns of crustal movement along the eastern coastline of Sicily as determined from palaeoshoreline data. The south-eastern coastline of Sicily (Portopalo to Catania) provides no evidence of Holocene emergence. In contrast the volcanic coastline (Catania to Capo Schiso) and the northeastern shoreline (Taormina to Milazzo) display widespread evidence of coastal emergence. Radiocarbon dated remains indicate that both the volcano and northeastern Sicily have been uplifted at a rate exceeding 1.5 mm a
−1
during Holocene times, although more recent rates of uplift may have been greater. The pattern of uplift suggests that the northeastern coastline of Sicily, including the volcanic edifice, is apparently uplifting as a coherent unit, with superficial flank movements being superimposed on a regionally uplifting sub-volcanic basement.