bluuebunny/crossref_metadata_2025_split huggingface dataset:
Devonian marine incursions into the Orcadian Basin, Scotland
Authors: MARSHALL J. E. A. , ROGERS D. A. , WHITELEY M. J. 
Published: December 2007

BP/Chevron well 14/6–1 drilled in the East Orkney Basin has penetrated Devonian sedimentary rocks which can be dated palynologically as within the latest Givetian to early Frasnian interval. This microflora contains the first substantiated record in Western Europe of
Archaeoperisaccus,
a spore hitherto regarded as restricted to northern Laurasia. Three grey-green intervals within the well contain marine microfossils which provide the first direct evidence for the movement of marine waters into the northern part of the Old Red Sandstone continent.

Onshore an Eday Marls section in the Bay of Berstane, Orkney contains a marine microfauna which demonstrates the presence of a marine incursion of mid––late Givetian age. This is the first record of a Devonian marine incursion in Scotland.
Combination of this palaeontological data with sedimentological studies of the Eday Marls and Upper Old Red Sandstone suggests that a wide flat sabkha plain extended eastwards from the onshore Orcadian Basin during the later stages of its infill, and was subjected to episodic marine incursions. These incursions are tentatively linked with marine transgressions into the Argyll area of the Central North Sea.
Two orders of cyclicity occur within the dated Devonian interval of 14/6–1, and are interpreted as resulting from orbital cyclicity (at periodicities of 39.5 and 413.9 ky). This indicates that the control on the Devonian sea level maxima may have been orbital cyclicity. These marine incursions are speculatively correlated to high-stands on the Devonian sea-level curve. The Bay of Berstane marine incursion representing the Taghanic Onlap whilst those in 14/6–1 are the Rhinestreet, Middlesex and Genundewa transgressions. Reconsideration of the palaeogeography of the northern margin to the marine Devonian indicates that the sea entered the Orcadian Basin from the east along the Tornquist Zone at the margin of the Fenno-Scandian High.
Evolution of landscapes in northern South Australia in relation to the distribution and formation of silcretes
Authors: SIMON-COINÇON R. , MILNES A. R. , THIRY M. , WRIGHT M. J. 
Published: December 2007

Geomorphological features on the southwestern margins of the Lake Eyre Basin provide a basis for interpreting the evolution of old landscapes containing pedogenic and groundwater silcretes. and thick bleached and weathered profiles. Recurrent sequences of cut-and-fill and duricrust formation have been identified and related to major sea level changes and tectonic movements in the Lake Eyre Basin.
An extensive high pediment had formed around a basement inlier by the late Eocene. An armour of pedogenic silcrete developed on this pediment under alternating dry and wet climates during the late Eocene and Oligocene. The characteristic kaolinite + opal + alunite + gypsum assemblage of the bleached profiles formed in acid saline groundwaters during the Miocene at a time of regional low water table and arid climate. Groundwater silcretes formed in the bleached profile in response to dissection of the high pediment. They are related to a period of high groundwater tables. humid climate. and gradual sinking of the Lake Eyre basin. In the meantime, widespread low pediments (glacis) formed in Lake Eyre catchment, possibly in the early Pliocene.
There is a good correspondence between a geomorphic approach, taking in to account the relationship between weathering features and palaeolandscapes, and the information provided from stratigraphic studies in the region.
Late Archaean to early Proterozoic granitoid magmatism and high-grade metamorphism in the central Limpopo belt, South Africa
Authors: JAECKEL P. , KRÖNER A. , KAMO S. L. , BRANDL G. , WENDT J. I. 
Published: December 2007

The Central Zone of the Limpopo belt in southern Africa has previously been interpreted as a segment of Archaean crust which experienced its main deformation and metamorphism around 2.7 Ga ago. We report new single zircon U/Pb and Pb/Pb ages for granitoid gneisses, supracrustal rocks and anatectically derived granitic melt patches in the area around Messina, South Africa. The Sand River Gneiss is a composite suite of tonalitic to trondhjemitic rocks with protolith ages between 2.6 and 3.2 Ga.
The Singelele gneiss, a heterogeneous granodioritic to quartz monzonitic rock, has protolith ages between 2.55 and 2.58 Ga. Since both the Sand River and Singelele gneisses experienced polyphase high-strain ductile deformation this must have occurred later than 2.55 Ga ago.

Granulite-facies pelitic gneisses of the Beit Bridge Complex contain abundant spherical, multifacetted zircons which reflect new zircon growth near or at the peak of metamorphism. These zircons provide ages with a mean at 2026.5 ± 6.3 Ma which is interpreted as reflecting a high
P
–
T
event (>10 kbar, 825 ± 25°C).

Granitic melt patches in the metapelites as well as in the Sand River Gneiss and anatectic granites are probably related to rapid near-isothermal decompression to below 3–5 kbar and 600–750°C. These rocks contain new magmatic zircons which yielded a mean age of 2005.6 ± 4.4 Ma and probably reflect a crustal melting event resulting from rehydration of the granulitic assemblage.

Our zircon data support previous suggestions for only one single granulite-facies event in the Central Zone, and we suggest that this event occurred
c.
2027Ma ago. Since most of the deformation seen in the gneisses of the Messina area must have occurred later than 2.55 Ga ago, it is likely that the ‘Limpopo Orogeny’, at least in the Central Zone, is not an Archaean event but took place in the early Proterozoic.
The Woolhope and Usk Basins: Silurian rift basins revealed by subsurface mapping of the southern Welsh Borderland
Authors: BUTLER A. J. , WOODCOCK N. H. , STEWART D. M. 
Published: December 2007

Subsurface mapping of the southern Welsh Borderland has utilized over 600 km of seismic data and three exploration boreholes to investigate the subsurface of this classic geological area. The survey reveals two Silurian basins, each about 400 km
2
in area, in the western part of the Midland Platform.

The Woolhope Basin underlies the Silurian inlier of the Woolhope Anticline. The basin fill is bounded to the northwest by faults of the Neath Disturbance, and was also influenced by WNW-striking extensional growth faults. The fill thins eastward towards the Malvern Line. Lower Silurian sequences thin southward before thickening again, particularly across WNW-striking faults. The resulting Usk Basin, underlying the Usk Inlier, has ill-defined margins, but some additional N-S fault control.
The Fownhope-1 and Usk-1 wells indicate that rapid subsidence occurred in both basins during Rhuddanian and Aeronian (Early to Mid-Llandovery) time. Modelling of this subsidence, assuming the finite duration lithospheric extension model, yields stretching factors of between 1.3 and 1.6. The later part of the fill to both basins is marine, but red conglomerates, sandstones and mudstones in their Early Llandovery intervals suggest continental fluvial environments in the initial stages of basin development.
The Woolhope and Usk Basins show that the western sector of the Midland Platform rifted during Early to Mid-Llandovery time, perhaps during regional dextral transtension. The rifting is synchronous with, and perhaps genetically related to, an episode of mafic volcanism in the southwest part of the platform. However, this rifting apparently predates the Late Llandovery (Telychian) fault-controlled subsidence seen in the Welsh Basin to the northwest.
Australia-Banda Are collision as an analogue for early stages in Iapetus closure
Authors: SNYDER D. B. , BARBER A. J. 
Published: December 2007

A comparison of structures formed since the Pliocene during Australia-Banda Are collision with structures hi the central British Isles provides insights into early tectonic events and later structures formed along the Laurentian margin of the Iapetus Ocean between Ordovician and Devonian tunes. In particular, the timing of ophiolite emplacement, incorporation of a volcanic are into a continental margin and early stages hi nappe formation can be recognized by comparing seismic reflectors and mapped geological structures hi both regions. In this comparison the Midland Valley of Scotland is interpreted as a compressed and composite volcanic are, formed hi two stages as the result of are reversal and becoming more mafic than adjacent blocks which were formed from accretionary prisms.

Uniformitarian principles are used to interpret geochemical processes and tectonic events throughout the Phanerozoic and have also been used to interpret events in the Proterozoic and Archaean (e.g. Taylor & McLennan 1995). The Tonga-Kermadec, Aleutian, Andean and Banda-Sunda ares are often cited as present-day analogues of ancient convergent plate boundaries. Similar logic motivated BIRPS to acquire two deep seismic reflection profiles across the currently active Australia-Banda are collision zone to the east of Timor (Figs 1 & 2a) in order to provide a better understanding of the tectonic events represented by structures that formed along the margin of Laurentia during the closure of the Iapetus Ocean c. 450 Ma (Fig. 2) and that are observed in the crust of the British Isles today.
The Banda Arcs mark the site of subduction of
The application of sequence stratigraphy to Upper Carboniferous fluvio-deltaic strata of the onshore UK and Ireland: implications for the southern North Sea
Authors: HAMPSON GARY J. , ELLIOTT TREVOR , DAVIES SARAH J. 
Published: December 2007

Stratigraphical correlations and fades interpretations of Upper Carboniferous fluvio-deltaic strata have been based traditionally on cyclothems bound by marine flooding surfaces (marine bands). The recent recognition of major, regionally extensive erosional unconformities (Exxon-style sequence boundaries) within selected cyclothems questions their validity as units of genetically related strata. U sing examples from the Carboniferous of the onshore UK and Ireland, we present sedimentological criteria for the recognition of sequence boundaries, placing particular emphasis on the regional context of these surfaces. Sequence boundaries comprise widespread, deeply eroded surfaces at the base of major fluvial sandstone complexes, and laterally equivalent palaeosols developed on interfluves at the margins of the fluvial complexes. These sequence boundaries define units of genetically related strata (sequences) which contain other key surfaces of time-stratigraphic significance, including marine bands and regionally extensive coals. The recognition of key surfaces enables the construction of a high resolution stratigraphic framework within which coeval facies relationships can be interpreted.
Sequence boundaries can be correlated between individual basins in the onshore UK, by reference to their position in relation to a particular marine band. For example, the sequence boundary at the base of the Farewell Rock in the South Wales Basin can be correlated with that at the base of the Rough Rock in the Pennine Basin, northern England, since both these sandstone bodies are directly overlain by the Subcrenatum Marine Band. Interbasinal correlations of this nature imply that potential fluvial sandstone reservoirs within major incised valley fills in the Upper Carboniferous strata of the southern North Sea can be predicted by correlation with the onshore UK. The stratigraphical framework can be extended and tested using core and well-log data, particularly spectral gamma-ray data, which are able to identify key sequence stratigraphic surfaces.
Upper Pleistocene loess stratigraphy in the southern Yenisei Siberia area
Authors: FRECHEN MANFRED , YAMSKIKH ANATOLY F. 
Published: December 2007

The loess-like sediments along the river Yenisei provide a detailed palaeoclimatic archive of the last interglacial/glacial cycle for the southern part of Central Siberia. The loess-like sediments were formed by aeolian, alluvial, lacustrine–alluvial, slope wash and flood processes. Chernozem or chernozem-like palaeosols formed during the interglacial and interstadials. The loess-like sediments and palaeosols at the sections of Tatysh and Cholnokovo near Krasnoyarsk and Berezov were investigated with thermolumi-nescence and infrared optically stimulated luminescence dating methods. Luminescence dating suggests that the oldest sediments below the lowermost chernozem formed during the penultimate glaciation. It is likely that the lowermost chernozem at the Tatysh, Cholnokovo and Berezov sections formed during oxygen isotope stage 5. A large hiatus occurs above and below this lowermost chernozem, indicating that most of the last interglacial and early glacial record is missing in the sections investigated.The intercalated duplicate chernozem-like palaeosols in the upper part of the section formed during an interstadial within oxygen isotope stage 3, indicating forest-steppe climatic conditions between 25 and 35 ka BP. The youngest loess-like sediments, overlying the duplicate palaeosol horizon, apparently have a very high sediment-accumulation rate.
Lake-level changes, sedimentation and faunas in a Middle Devonian basin-margin fish bed
Authors: TREWIN N. H. , DAVIDSON R. G. 
Published: December 2007

The classic Devonian fossil fish site at Tynet Burn, Fochabers, NE Scotland has been investigated following recent excavations. The fish assemblage consists of placoderms, acanthodians, an actinopterygian, porolepiforms, osteolepiforms and a dipnoan. The assemblage is typical of the 'Achanarras Fauna' of Eifelian age which is widespread in the Orcadian basin, representing a time of generally high lake levels. The most diverse fauna occurs in the Upper Nodule Bed which can be divided into top and bottom levels, where fish are mainly preserved in calcareous nodules, and a middle level with fish in laminated limestone.
Three fluvial to lacustrine cycles are exposed in the Tynet Burn in 27 m of strata. Fish are abundant in the Upper Nodule Bed, and are also sparsely represented in lacustrine strata both above and below this level. The lacustrine laminites of the Upper Nodule Bed were deposited following a rapid rise in lake level. Subsequent fall in lake level resulted in deposition of a thin shallow water massive limestone, prior to exposure and desiccation of the lake floor. Disruption of laminites by sediment sliding and sand intrusion was followed by compaction and concretion formation. Chemotrophic bacteria later invaded open cracks and porosity and partially oxidized the fish remains; the bacterial oxidation event being responsible for the characteristic pink, red and purple colours of fossil fish from Tynet Burn. Subsequent lake level rise resulted in deposition of shales with abundant diagenetic concretions, rarely containing fish. With increasing clastic input alluvial sands prograded over the area from the south.
The rapid deepening event associated with the base of the Upper Nodule Bed at Tynet is considered to be synchronous with similar events represented in other Achanarras-equivalent fish beds. However, elements of the Achanarras fish assemblage can be encountered in less persistent lacustrine intervals both above and below this level.
Minor cyclicity, superimposed on the main Achanarras event, resulted in repetition of fluvial to lacustrine transitions. The main control on cyclicity is considered to have been climatic, but subsidence and sediment supply rates were also a significant influence.
Structural evolution of shale diapirs from reactive rise to mud volcanism: 3D seismic data from the Baram delta, offshore Brunei Darussalam
Authors: VAN RENSBERGEN P. , MORLEY C. K. , ANG D. W. , HOAN T. Q. , LAM N. T. 
Published: December 2007

Two areas of shale diapirism in a deltaic setting were examined using 3D seismic data from offshore Brunei to determine the origin, evolution and geometry of shale diapirs. The study areas cover parts of the Egret and Ampa fields within the Baram Delta province. The Ampa diapir consists of a small bulge of the mobile Setap shale around which lies a zone of chaotically disrupted country-rock reflections. At the crest of this chaotic zone, vertical, cylindrical shale pipes arise that end in a wider head. The diapir heads wear halos of high amplitude reflections, probably due to the presence of methane gas. The Egret data show the same features, except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden. The bulging of the Setap shale on the Ampa data is interpreted as modified reactive diapirism in response to differential loading. The initial reactive diapir shape was modified by lateral or oblique upward migration of fluidized shales into the hanging wall of the fault controlling the reactive diapir. This probably occurred as a network of dykes and sills. The presence of some preserved bedding is indicated by weak but coherent reflectivity from the area initially defined as chaotic shale.
The spreading of overpressure and the injection of shale into the overburden is thought to be a late phenomenon, possibly Late Pliocene or Early Pleistocene and the mobility of the shale is attributed to overpressure increase due to gas generation within the Setap shale and maybe the lower part of the overburden. Gas migration, perhaps ahead of the diapir intrusion, probably facilitated the mud injection. The Ampa and Egret diapirs formed in two diapiric phases, an early reactive diapirism and a later active diapirism. But the phases have little in common; they are seperated by about 9 million years of inactivity and differ in process and probably differ in degree of overpressure, in overpressure generating mechanism, and in properties of the diapiric mud.
Unravelling tectonic and climatic signals in sedimentary successions
Authors: PEDLEY H. M. , FROSTICK L. 
Published: December 2007

During the past two decades scientists and governments have progressively been drawn towards a search for a fuller understanding of the mechanisms of climatic change. In recent times attention of the public has been drawn to an apparent increase in adverse weather conditions leading to such processes as increasing mean world sea levels and accelerated desertification. The leading question was and still is 'how much of this is small oscillations on a longer term climatic trend'. Equally importantly, 'how much is related directly to man's activities'.
Less easy to speculate upon are tectonic signals. Many, such as the Mount St Helens eruption, leave a legacy of atmospheric repercussions felt for many years, yet these are effectively instantaneous in a geological context. In contrast, longer term plate and polar wanderings, and mountain-building episodes, are insignificant when measured in a human life span.
The mainly observational data set upon which scientists base all predictions for future change spans little more than a few centuries. Only by accurately interpreting the sedimentary record will it be possible to extend the 'data set', thereby providing the spring-board upon which to base forward projections. There is, therefore, a pressing fundamental requirement to establish a set of tools which will tease out the tectonic and climatic strands from the depositional record.
A two day meeting was held at Burlington House jointly by the British Sedimentological Research Group and the Geological Society (26–27 June 1997) specifically to address some of these problems by examining a range of
The role of sediment supply in controlling alluvial architecture: an example from the Spanish Pyrenees
Authors: VINCENT STEPHEN J. 
Published: December 2007

This study isolates the controls on the alluvial architecture of two interfingering late Lutetian fluvial systems preserved at the northern margin of the Tremp-Graus Basin, in the south central Pyrenees. One of these, a northerly, mountain-belt-derived, high-gradient, bedload-dominated gravelly system, displays marked variations in its alluvial architecture, with systematic changes in the width, depth, internal facies arrangement and stacking pattern of its channel bodies. The other, an easterly, basin-axis-derived, lower gradient, poorly drained alluvial system, displays no discernible systematic variations in alluvial architecture.
A common control that would similarly affect both of the interfingering fluvial systems cannot be responsible for their contrasting architectural patterns. Variations in base level, despite the contemporaneous shoreline being only 18 km downstream, climate, or the tectonic rotation of the study area are therefore discounted. Fluctuations in sediment supply to the northerly derived system resulting from the episodic uplift of its drainage basin are instead proposed, although intrinsic controls cannot be totally discounted. Similar sediment flux variations in the headwaters of the easterly derived system are envisaged, but its longer, lower-gradient transport path was effective in dampening out these fluctuations upstream of the study area.
The late Miocene climate of northeastern Africa: unravelling the signals in the sedimentary succession
Authors: GRIFFIN DAVID L. 
Published: December 2007

Examination of the depositional profile of the Miocene/Plio-Pleistocene succession at two locations in the Gulf of Suez and seven locations in the Red Sea leads to the conclusion that the Messinian (Zeit Formation and equivalent) sedimentary rocks were deposited at a rate greater than other units of the Miocene/Plio-Pleistocene in these areas. The Zeit Formation contains a significantly higher clastic content than the underlying South Gharib Formation. These two aspects of the stratigraphy are taken to indicate that the Messinian was a time of high rainfall and high sediment yield rates. This period, named the Zeit Wet Phase, stands in marked contrast to the arid conditions of the preceding Tortonian Stage. The latter stage is represented in the Gulf of Suez and Red Sea area by the halite-bearing South Gharib Formation and its equivalents.
Physical evidence for a humid Messinian is provided by five lines of evidence involving four sites around the Red Sea and two sites offshore. It is suggested that the Zeit Wet Phase was marked by high monsoonal activity as demonstrated by drilling sites of the Ocean Drilling Program. It is probable that the wet phase peaked in the late Messinian at the time of the low-stand of the Mediterranean during the Messinian Salinity Crisis.