bluuebunny/crossref_metadata_2025 huggingface dataset:
Preferential pathways in an Eocene clay: hydrogeological and hydrogeochemical evidence
Authors: Walraevens K. , Cardenal J.
Published: April 2008

This study was initiated to test the extent to which the cation exchange capacity of marine clay-rich units, through which fresh water has been recharged, controls the composition of pore waters in an aquifer. The semi-confined Ledo-Paniselian (Eocene) aquifer in Flanders is recharged in elevated regions, where it is covered by Bartonian Clay. These sediments were initially laid down in marine conditions. The effects of recharging fresh CaHCO
3
water by downward flow through the overlying clay within the aquifer were modelled using PHREEQM. In the aquifer, progressively fresh waters are found in an upstream direction, which indicates a reduced influence of the initial marine conditions. Different stages of cation exchange produce a chromatographic sequence of groundwater types. Hydrogeological and hydrogeochemical evidence suggests the existence of preferential, faster flow pathways for recharge groundwater flow through the Bartonian Clay overlying the aquifer. These conclusions are indicated by differences between the observed and predicted features of the aquifer. It is necessary to invoke hydraulic conductivity values of 10
−9
m s
−1
rather than 10
−10
m s
−1
(measured values) for the Bartonian Clay so that the predicted head distributions in the aquifer match the observed heads. Furthermore, the measured exchangeable cations in clay collected from cores in the recharge area show less freshening than is predicted from the model to produce either the observed groundwater type within the aquifer in the recharge area or the overall distribution of groundwater types in the aquifer. Given the discrepancy between the observed and calculated state of freshening it is assumed that the analysed flow line in the core must be part of a slower flow pathway.
Methodologies for multi-well sequence analysis using borehole image and dipmeter data
Authors: Prosser Jeremy , Buck Stuart , Saddler Shaun , Hilton Vince
Published: April 2008

Borehole image logs provide high-resolution directional data sets, in addition to a wealth of information concerning sedimentary fabric and texture. The data derived from these images are typically used for lithofacies characterization, palaeotransport analyses, and fault and unconformity recognition. These data are ideal input variables to the development of correlative models, particularly within a sequence stratigraphical context. However, in field settings characterized by low structural dip (less than 15°), unconformity recognition can be very difficult within shallow marine sediments, which would have had very low depositional or sedimentary dip. In the study described, integration of borehole image data with core sedimentological and ichnofabric analyses has enabled calibration of images for lithofacies recognition, identification of bioturbation fabrics, and the degree of bioturbation present. In particular, comparison of the results of dip trend analyses with the results of ichnofabric analyses has indicated that subtle, though consistent variations in shale bed dip azimuth correspond closely with the locations of sequence boundaries. This has provided increased confidence in unconformity recognition in un-cored well sections, and enabled correlations to be developed. Lessons learned from interpretation and calibration of high sample density borehole image logs (FMI) within cored well sections has enabled interpretive methodologies to be transferred to lower density FMS and SHDT data sets. Similarly, examination of core-photographs as a continuous ‘photographic image log’ in the workstation environment has revealed that when displayed at appropriate scales, even vintage core photographic plates contain a phenomenal amount of data. This is obviously useful for calibration of dipmeter data where, due to climate etc., cores are poorly if at all preserved. Perhaps more surprisingly, comparison of core-photographic data with existing cores has revealed that when displayed on a workstation, core photographs are suitable for detailed ichnofabric analysis. This has allowed reinterpretation of effectively ‘lost’ data within the context of recent advances in sedimentology. The procedures described constitute an innovative approach to the integration of different data types gathered using existing, proven techniques.
Stratigraphic relationships in the upper Rotliegend: interpretations from horizontal and vertical well borehole images, core and logs in the Lancelot area, Southern North Sea, UK
Authors: Went David J. , Fisher William C.
Published: April 2008

Interpretation of data from core and borehole images in horizontal and vertical wells in Lancelot area fields has resulted in a clearer understanding of the stratigraphic relationships in the upper section of the Rotliegend reservoir. The complex stratigraphy of the upper Rotliegend stems from the reworking and marine inundation of an erg margin. Extensive erosion, fluidization and reworking of the erg occurred but a remnant aeolian topography was retained. The remnant aeolian dune sequence (Unit 3) shows a mounded geometry with a relief up to 40 m and an estimated wavelength of 2 km. Sets of aeolian dune cross bedding are heterogeneous with low permeability layers associated with foresets and set boundaries. Cross bed set orientation and sizes affect upscaled permeability. Differences in set size may relate to a mixture of dune and draa slipfaces or variously sized dunes migrating over draa without slipfaces. The reworked sequence (Unit 4) is a variably thick, commonly erosively-based interval of slightly to heavily cemented sandstone. It is commonly structureless but locally contains slumped aeolian dune foreset beds, dewatering structures, deformed bedding, and sequences featuring repeated intervals of marine shale (Kupferschiefer). The distribution of the various subfacies is related to a model of remnant aeolian dune relief which influenced the style of sediment reworking. The geometric attributes and heterogeneity distributions associated with Units 3 and 4 have important implications for successful targetting of horizontal wells, particularly those planned for close to the top of the reservoir (ensuring maximum standoff from the field gas water contact), for volumetric estimates and reservoir simulations.
Use of Resistivity At Bit (RAB) images within an Eocene submarine channel complex, Alba Field, UKCS
Authors: McGarva R. M. , Bell C. , Bedford J.
Published: April 2008

To aid reservoir description a Resistivity At Bit (RAB) tool was run in a series of near-horizontal wells within the Alba Field. The tool characterized lithology types and detailed bed geometry through oriented resistivity images of the borehole. Image quality ranged from good to uninterpretable through zones of image artifact, and image resolution was less than that of conventional resistivity imaging tools. Shale intervals locally display good bedding detail, whereas sandstones display hole spiralling and yield little meaningful information. Shales are conductive, but locally, images show the presence of thin and sharp-based, relatively resistive shale beds that progressively ramp upward into the background shales. These resistivity ramp-defined bedding units may be individual mud-flows, with the resistive beds being possibly coarser grained or cemented. Following correction for structural tilt, bedding surfaces between and within shale successions range from uniform to irregular and possibly indicate some degree of shingling between individual flow units. Tool runs typically encounter long near-uniform sections of sandstones and shales with well defined lithological boundaries. RAB images show that these sandstone-shale transitions are sharp and steep (22°–88°). Such dips imply either steep channel margins, faulted contacts or more likely, the result of borehole bias in horizontal wells drilled into channellized successions. The lateral margins to an individual sandstone body, sampled as entry and exit points along the well path, commonly display discordant strikes, possibly implying lenticular geometries. Sandstone-shale contacts may allow qualitative estimation of the direction of the channel element thickening. Compactional shale drape deformation is often present away from the sandstone masses. Sedimentation is modelled as a two phase system with slope-supplied, mud-dominated gravity-flows temporally disconnected from deposition of shelf-derived turbiditic sandstones. Infrequent depositional events resulted in channels that were infilled with sand from high-density turbidity currents. Fractures and faults are imaged with the RAB tool and indicate a possible topographical control to structural development.
Insights from simultaneous acoustic and resistivity imaging
Authors: Hansen T. , Parkinson D. N.
Published: April 2008

We describe a method of thin-bed petrophysical analysis that exploits the availability of both acoustic and resistivity images of the same rock. In developing our method we have gained a number of insights into the contrasting response of these images to rock properties, which may be of general interest to the imaging community. The case-study we present is from a thin-bedded, deep-water siliciclastic depositional environment. The resistivity image was used to increase the resolution of a conventional resistivity device. Comparison of bedding dips between the two images suggests a resistivity depth of investigation of around three inches. However, the best fit between image and conventional resistivity was obtained using a somewhat deep-reading resistivity measurement. The acoustic image was used to increase the resolution of our porosity measurement. The best fit to acoustic image amplitude was with the neutron porosity log, rather than with density, slowness, or with any combination of two porosity logs. Given high-resolution resistivity and porosity measurements from the images, and the precise information on bed boundaries that images provide, we proceeded with petrophysical analysis at a much higher resolution than obtainable from the conventional logging suite.
Borehole images of the ocean crust: case histories from the Ocean Drilling Program
Authors: Brewer T. S. , Harvey P. K. , Haggas S. , Pezard P. A. , Goldberg D.
Published: April 2008

Downhole logging is an integral part of the Ocean Drilling Program (ODP), although the choice of tool deployment is primarily a function of the scientific objectives of an individual leg. Following the successful deployment of the Formation Microscanner (FMS) during Leg 126, FMS images have been used to constrain a variety of sedimentary, igneous, metamorphic and tectonic questions in the ocean. However, it is only recently, that the full potential of FMS images and other logging data has been employed in the study of volcanology, which provides important constraints on the evolution of the volcanic pile when fully integrated with core based measurements. Furthermore, many of the holes drilled into the volcanics often have incomplete core recovery and here the logging results can be used to constrain the lithological, chemical and mineralogical variations in such intervals. Using the log based stratigraphy from crust created at slow (Hole 395A) and intermediate (Holes 504B and 896A) spreading centres, it is evident that the proportions of volcanic rock types (pillows/flows/breccias) correlate with the spreading rate. This relationship is suggested from submersible observations, but the ODP data provide additional data to test such hypotheses and to also extended and test it within the third dimension.
A reassessment of Manx Group acritarchs, Isle of Man
Authors: Molyneux S. G.
Published: April 2008

The biostratigraphy of acritarch assemblages from the Manx Group, Isle of Man, has been reassessed in the light of evidence from the Skiddaw Group, rocks in the English Lake District that are the Manx Group’s equivalents in terms of both age and lithofacies. Assemblages from the Santon Formation (formerly the Lonan Flags) and the Glen Dhoo Unit (formerly the Glen Dhoo Flags) are considered to be of early Arenig rather than the previously suggested latest Tremadoc age, and indicate that these two formations probably correlate with each other, and with the Hope Beck Formation of the Skiddaw Group. An acritarch assemblage associated with volcanic rocks at Peel is reassessed as being of early Arenig age, rather than late Arenig as previously thought. The age of an assemblage from the Glen Rushen Formation (formerly the Maughold Banded Group) is now considered to be of mid-Arenig age and to indicate correlation with the Loweswater Formation of the Skiddaw Group, while that from the Lady Port Formation is regarded as being an upper Arenig assemblage indicating correlation with the Kirk Stile Formation. An assemblage from Glenfaba Brickworks was previously assigned to the Niarbyl (Flags) Formation, but is now considered to be from undifferentiated Manx Group rocks. It is a poor assemblage that is not younger than early Arenig, but could be as old as Late Cambrian, although its proximity to the Peel locality makes an early Ordovician age more likely.
Macrofauna and ichnofauna of the Manx Group (early Ordovician), Isle of Man
Authors: Orr P. J. , Howe M. P. A.
Published: April 2008

Within the Manx Group, the key elements of the limited macrofauna include a
Rhabdinopora
-like graptoloid from Cronk Sumark and a didymograptid-dichograptid fauna from Baltic Rock. The ichnofaunal assemblage is dominated by fodinichnia (mainly examples of
Phycodes
). This is atypical of Phanerozoic deep-marine environments as a whole, but is a feature of other early Ordovician deep-marine ichnofaunal assemblages, notably that within the Skiddaw Group of the English Lake District.
Dictyodora zimmermani
and
Glockerichnus radiatus
occur within the Manx Group; these ichnotaxa are present in other ichnofaunal assemblages of early Ordovician age which were also emplaced at high southerly palaeolatitudes.
Revised lithostratigraphy of the Manx Group, Isle of Man
Authors: Woodcock N. H. , Morris J. H. , Quirk D. G. , Barnes R. P. , Burnett D. J. , Fitches W. R. , Kennan P. S. , Power G. M.
Published: April 2008

The existing lithostratigraphy of the Manx Group (lower Ordovician) of the Isle of Man is formalized as far as is possible given a paucity of biostratigraphical and structural control. Coherent packages of strata can be recognized within northeast striking structural tracts. Some tract boundaries are faulted but poor exposure leaves doubt about the nature of others. Some structural repetition of successions is likely. However, the long-held equivalence of the sandstone units on either side of the island can no longer be maintained, because the Niarbyl Formation in the west is now known to be of Silurian age. Repetition of Manx Group units across a syncline along the axis of the island is therefore in doubt. Different outcrops of superficially similar units are accordingly named separately on each flank of the island. The stratigraphy of part of the northern Manx Group is left unrevised awaiting further work.

The southeastern, sandstone-dominated units of the Manx Group comprise three tracts divided into the Lonan and Santon (lower Arenig) Formations, the Port Erin and Mull Hill Formations, and the Ny Garvain and Creg Agneash Formations. The Creg Agneash Formation is stratigraphically overlain by the mudstone-dominated Maughold Formation. The next two tracts to the northwest both contain a black mudstone unit, the possibly correlative Barrule and Glen Rushen (middle Arenig) Formations, each structurally overlain by laminated silty mudstone of the Injebreck Formation. A further unit of laminated siltstone and mudstone, the Creggan Mooar Formation, is defined in tract 6, west of which an enigmatic unit contains lowest Arenig fragmental volcanic rocks. In the most northwesterly tract, the Lady Port Formation is a varied assemblage of black mudstone, turbidites, pebbly mudstone and quartz arenite. Lithological correlation of these different Manx Group successions is attempted, but is constrained by only four biostratigraphical control points.

The Manx Group stratigraphy has long been correlated with that of the Skiddaw Group of the Lake District. A tentative correlation of events on this part of the early Ordovician margin of Gondwana can be made assuming some synchroneity of Early Arenig lowstand turbidite fans, of a mid-Arenig transgression, and of a late Arenig mass-wasting event.
Lithofacies of Lower Palaeozoic deep-marine sediments in the Isle of Man: a new map and stratigraphic model of the Manx Group
Authors: Quirk D. G. , Burnett D. J.
Published: April 2008

A classification scheme for lithofacies in the Lower Palaeozoic Manx Group has been designed based on a simple assessment of the sandstone:mudstone ratio, bed thickness and sedimentary structures. The scheme was used to acquire high-resolution, standardized field data over areas of good exposure on the Isle of Man. These data were then correlated in order to produce a lithostratigraphic framework and a simplified geological map. Overall, the succession appears to young northwestwards from early Arenig, sand-rich sediments on the southeast coast to mud-rich sediments of mid-late Arenig age inland and on the northwest coast. A number of alternative structural reconstructions have been made which fit to a greater or lesser degree with limited biostratigraphic data. The favoured model involves a compromise between inferred duplication of stratigraphic units by reverse faults and repetition of similar depositional cycles or sequences within the succession. This model implies that the Manx Group is between 5400 and 9250 m thick and contains within it both a lateral facies change (from proximal to distal character east-west) and an overall fining-upwards stratigraphic signature. The sediments are interpreted to have been rapidly deposited on the west dipping margin of a basin situated between the Isle of Man and southeast Ireland, which forms an embayment on the northwest edge of Eastern Avalonia. The main depositional processes were turbidity currents and debris flows, with evidence of possible current deflection or reworking of the upper parts of turbidites by northwards flowing contour currents. During the Caledonian orogeny, the basin was inverted with the development of northeast-southwest trending thrusts and east-west dextral faults. Tentative evidence also exists for the presence of an older north-northeast-south-southwest normal fault trend, although whether it was active during the Arenig is uncertain. It is recommended that future stratigraphic work should concentrate on testing possible correlations between and within the mixed sand-mud Lonan, Port Erin, Injebreck and Creggan Mooar Formations.
An early Ordovician turbidite system on the Gondwana margin: the southeastern Manx Group, Isle of Man
Authors: Woodcock N. H. , Barnes R. P.
Published: April 2008

The southeastern part of the Manx Group comprises sandstone-rich deep-marine turbidites of Arenig (early Ordovician) age, deposited on the Avalonian segment of the Gondwana margin. The main area comprises a 2 km thick succession from thin-bedded wacke sandstone and mudstone of the Lonan Formation up into medium-bedded wacke and arenite of the Santon Formation. This succession is interpreted as the distal part of a mixed mud-sand ramp overlain by a major distributary channel and lobe system. The Keristal Member is a unit of thick-bedded quartz arenite within the Lonan Formation recording a short-lived incised channel system with small terminal sand lobes.

Flutes and scours in the Lonan and Santon Formations show west-southwest directed transport, contrasting with north-northwest directed estimates from ripple cross-lamination. Constraint by margin topography may have caused the higher concentration components of the flows to run along-margin, whilst flow-stripping of the lower concentration flow-tops allowed them to collapse down the regional north-northwest facing palaeoslope.

The southwestern and northeastern areas contain fault-bounded successions that can be correlated only tentatively with the main area. In the southwest, thin-bedded wackes and mudstones of the Port Erin Formation pass up into the quartzose Mull Hill Formation, which shows the thickening-up motif of a fan lobe. In the northeast, the Creg Agneash Formation resembles the Mull Hill Formation, and probably overlies the quartzose wackes of the Ny Garvain Formation.

The contrast of arenite and wacke sandstones in the Manx Group may have resulted partly from the intrabasinal separation of sand and mud, e.g. by flow stripping. However, the major factor was the availability on the basin margin of both clean and muddy sediment. The quartz arenite sands were probably sourced from the widespread Armorican quartzite facies of Gondwana, constraining the rifting of Avalonia from its parent continent to mid-Arenig time or later.
Debris flows on the Ordovician margin of Avalonia: Lady Port Formation, Manx Group, Isle of Man
Authors: Woodcock N. H. , Morris J. H.
Published: April 2008

The Lady Port Formation (Arenig, Lower Ordovician) occurs in a fault-bounded tract on the northwestern coast of the Isle of Man. It forms part of the Manx Group, deposited on the outboard edge of the Avalonian margin of Gondwana. The formation is dominated by laminated siltstones and mudstones deposited from low-concentration turbidity flows, and rare manganiferous ironstones. This facies is overlain in places by thin-bedded sand-based turbidites with conspicuously bioturbated mud tops. These sands are quartzose wackes and contrast with a third facies of quartzose arenite turbidites that punctuate the laminated mudstones. This arenite facies suggests a discrete inboard source of clean sand which was occasionally diverted into this part of a predominantly mud-prone basin.

The Lady Port Formation also features units of pebbly mudstone and associated intervals of quartz arenite or mudstone showing strongly disrupted bedding. The pebbly mudstones are the products of cohesive debris flows. Clast compositions distinguish debrites derived from the bedded facies with which they are now intercalated from debrites that contain further travelled, but still intrabasinal, clasts. The disrupted facies preserves a spectrum of soft-sediment fragmentation of bedding, culminating in bed fragments being incorporated into the base of pebbly mudstone units. The facies is interpreted as the product either of downslope slumping, the possible precursor to debris flows, or of deformation ahead of and below advancing debris flows.

The local derivation of slumps and debrites implies an actively forming topography in this part of the Manx Group basin. The slumps and debrites of the Lady Port Formation are matched in other, less well-exposed, parts of the northwestern Manx Group. The available biostratigraphic control suggests that the formation is of late Arenig (Fennian) age and contemporaneous with the Buttermere olistostrome and pebbly mudstones in the Kirk Stile Formation of the Skiddaw Group, Lake District. A widespead mass wastage event is indicated on the Gondwana margin, perhaps coeval with the rifting from Gondwana of the Avalonian microcontinent.
The Silurian fauna (graptolite and nautiloid) of the Niarbyl Formation, Isle of Man
Authors: Howe M. P. A.
Published: April 2008

The discovery of a mid-late Wenlock (Silurian) graptolite and orthoconic nautiloid fauna at Traie Dullish Quarry, Peel Hill, in the Niarbyl Formation (Dalby Group) of the Isle of Man, disproves all earlier correlations between the Niarbyl and Lonan Flags on the west and east coasts of the island, respectively. All previous structural hypotheses require re-examination. The graptolites comprise
Cyrtograptus
cf.
lundgreni, Monograptus flemingii
cf.
warreni
and
Monograptus
ex gr.
flemingii
. They suggest, but do not prove, a
lundgreni
Biozone age, thus indicating a possible correlation between the Niarbyl Formation and the Birk Riggs Formation of the English Lake District, and the Denhamstown Formation of the Balbriggan Inlier, Southern Ireland.
Palaeomagnetism of (Palaeozoic) Peel Sandstones and Langness Conglomerate Formation, Isle of Man: implications for the age and regional diagenesis of Manx red beds
Authors: Piper J. D. A. , Crowley S. F.
Published: April 2008

The Peel Sandstones are a sequence of fault-bounded fluvially deposited red beds of uncertain age exposed on the western coast of the Isle of Man. Palaeomagnetic study identifies partial preservation of an A component pre-dating deformation at four of eight sampled sites; the presence of both polarities in this remanence defines a positive class C reversal test. This component adjusted for tilt is
D/I
= 356.9/−47.1° (48 samples, α
95
= 5.6°) and is interpreted to be a post-depositional detrial remanence. The palaeolatitude (29° S) corresponds to the position of Britain during Late Silurian-Early Devonian times and implies that these sediments are correlative with Lower Old Red Sandstone molasse from elsewhere in the British Caledonides; a post-mid-Carboniferous age is excluded. Palaeomagnetic and geological evidence are used to constrain an age of
c.
410–400 Ma for the Peel Sandstones, whilst a declination contrast of 40–50° is interpreted to reflect either: (a) tectonic emplacement of a unit including the Peel Sandstone outcrop; or (b) wider post-Early Devonian and pre-Late Carboniferous counterclockwise rotation between the Isle of Man and the mainland during final shaping of the Caledonides. A post-folding B component of uniform reversed polarity (
D/I
= 195.6/−30.8°, 45 samples, α
95
= 4.8°) is present at all sites and was acquired during diagenesis at
c.
250 Ma.

Red sandstones within the Langness Conglomerate Formation, near the base of the Lower Carboniferous (Chadian-Arundian) succession exposed in the southeast of the Isle of Man, have a uniform reversed magnetization (
D/I
= 209.7/−24.2°, 20 samples, α
95
= 6.8°). Like the B magnetization in the Peel Sandstones, this was acquired by diagenesis in Early Permian times (
c.
250 Ma) and during the Permo-Carboniferous Reversed Superchron. It is temporally related to early extensional tectonism in the Irish Sea region.
Crustal magnetic structure of the Irish Sea region: evidence for a major basement boundary beneath the Isle of Man
Authors: Kimbell G. S. , Quirk D. G.
Published: April 2008

Imaging and modelling of regional aeromagnetic data indicate a significant change in crustal magnetization across a boundary which extends northeast-southwest across the Irish Sea. A concealed magnetic basement is interpreted to underlie the area to the southeast of the boundary at mid-crustal levels, whereas relatively non-magnetic rocks lie at these levels to the northwest. The boundary does not coincide with the Iapetus Suture as defined by seismic evidence in the Irish Sea and palaeontological evidence on the east coast of Ireland. Instead, it appears to extend towards the northern margin of the Precambrian rocks of southeast Ireland. Its orientation swings sharply in the vicinity of the Isle of Man from north-northeast-south-southwest in the south to east-northeast-west-southwest in the northeast. There is an apparent correlation between the magnetic basement structure and an overlying, shallow, anomalous zone along the axis of the island which is revealed by gravity and high-resolution aeromagnetic data. Modelling indicates that shallow and deep structures may be related if both are assumed to dip to the northwest, a dip direction supported by seismic reflection data acquired immediately to the south of the island. The preferred interpretation is that the mid-crustal magnetic block is of Precambrian age and represents the northern part of an Avalonian basement which was assembled in late Precambrian-early Cambrian times. The geometry of the boundary beneath the Isle of Man may have been inherited from the pre-existing Avalonian basement architecture. Planes of weakness could have been reactivated as major, early Palaeozoic extensional structures and subsequently been activeunder a compressional regime during the closure of the Iapetus Ocean and the Acadian Orogeny.
Shallow geophysical and geological evidence for a regional-scale fault duplex in the Lower Palaeozoic of the Isle of Man
Authors: Quirk D. G. , Burnett D. J. , Kimbell G. S. , Murphy C. A. , Varley J. S.
Published: April 2008

A distinctive set of linear anomalies is seen on potential field data crossing the Isle of Man in a northeast-southwest belt, 5–6 km wide. The lineaments occur in an imbricate pattern with three constituent trends: northeast-southwest, east-west (to east-northeast-west-southwest) and north-south. The belt can be traced into the offshore where it ties with a northwest dipping set of anomalous high-amplitude seismic reflections interpreted as fluid-filled fractures or intrusions along fractures. In the field, the lineaments coincide with northeast-southwest reverse faults, east-west dextral strike slip faults and north-south sinistral strike slip faults interpreted to have formed during northwest-southeast compression in the late Caledonian. Several of the strike-slip faults were later sites of mineralization. In addition, there is limited kinematic evidence for an earlier period of sinistral transpression on east-west ductile shear zones. A tentative model is proposed where the Manx Group is located on the eastern side of an inverted Lower Palaeozoic basin (the Manannan Basin) forming an embayment on the northwest margin of Eastern Avalonia. During closure of Iapetus, the direction of maximum principal stress (σ
1
) rotated from north-northeast-south-southwest to northwest-southeast as Eastern Avalonia docked and then locked against Laurentia. The imbricate belt developed as a duplex at the eastern edge of the basin during the later stages of contraction. The implications of the model is that the stratigraphy of the Manx Group is telescoped.
Impact of tephra fall and environmental change: a 1000 year record from Matakana Island, Bay of Plenty, North Island, New Zealand
Authors: Giles Teresa M. , Newnham Rewi M. , Lowe David J. , Munro Adam J.
Published: April 2008

Palynological evidence was used to determine the development of vegetation communities on Matakana Island, North Island, New Zealand, over the last 1000 radiocarbon years. The pollen record indicates that changes occurred in the vegetation immediately following fallout deposition of the Kaharoa Tephra approximately 100 km from source at
c.
665 years BP. Such changes may be a direct response to the impact of tephra fall, although the possibility of anthropogenic disturbance cannot be discounted. As a result of the eruption some taxa (
Leucopogon fasciculatus
and
Tupeia antarctica
) became at least temporarily extinct from the area. Two phases of anthropogenic influence on the environment are recorded in the pollen record: Polynesian, followed by European inhabitation of the island, giving a detailed history of human influence in the area for the millennium.
The role of tephrachronology in recognizing synchronous caldera-forming events at the Quaternary volcanoes Longonot and Suswa, south Kenya Rift
Authors: Scott Stuart C. , Skilling Ian P.
Published: April 2008

The Quaternary volcanoes Longonot and Suswa, located in the south Kenya Rift, each have a caldera formed by incremental collapse accompanied by airfall, pyroclastic flow and pyroclastic surge activity. To constrain the relative ages of caldera formation at these two closely spaced centres, syn-caldera deposits are correlated using tephrachronology.

Volcanic products from Longonot and Suswa display contrasting Nb/Zr ratios which provide a unique signature for each centre. Early syn-caldera pyroclastics at Suswa contain airfall pumice beds which have Longonot Nb/Zr signatures. Variation of FeO(T) and Al
2
O
3
with Zr is particularly effective at discriminating the various Longonot units in two component space, and has been combined with volcanological evidence to identify the equivalent Longonot deposits as either early syn-caldera or late syn-caldera. In both cases, the correlation indicates synchronous initiation of caldera formation. This suggests that caldera formation is a regional rather than local event in the southern part of the rift, highlighting the potential rôle of regional tectonics as a controlling mechanism.

Major alignments of eruptive vents, fissures and the caldera collapse centre at each volcano are parallel to rift faults, suggesting that rift floor tension fractures or normal faults are utilized as conduits for magma transport. Synchronous caldera formation at Longonot and Suswa may, therefore, be linked to lateral magma withdrawal along rift floor fractures and decompression of the shallow-level magma chambers during a period of rift floor extension.
Eruptive and seismic activity at Etna Volcano (Italy) between 1977 and 1991
Authors: Vinciguerra S. , Garozzo S. , Montalto A. , Patanè G.
Published: April 2008

A review of volcanic and seismic activity at Etna (Sicily, Italy) between 1977–1991 is presented with the purpose of looking for possible relations between the main phases of seismic energy release and the principal eruptive episodes. Flank eruptions are normally preceded by both deep and shallow seismic swarms (0 <
h
<20km) which accompany the opening of fracture systems some hours before the eruption onset. Conversely, summit eruptions usually take place without any immediate change in the seismic patterns, even if moderate seismic activity some months before the onset suggests that magma uprises gradually and might rest within shallow reservoirs during ascent. It is worth noting that in some cases (1981, 1983, 1984 and 1986) significant episodes of seismic energy release occurred during the late phases of the eruptions. The analysis of the temporal evolution of the coefficient
b
of the magnitude-frequency relation suggests that the shallow seismicity of the eastern flank reflects the existence of a high level of geodynamic activity, probably associated with both regional tectonic forces and seaward sliding of this unbuttressed sector of the volcano.
An assessment of discriminant function analysis in the identification and correlation of distal Icelandic tephras in the British Isles
Authors: Charman Daniel J. , Grattan John
Published: April 2008

This paper assesses the potential of discriminant function analysis (DFA) for tephrochronology in the UK and Ireland. Current identification and correlation of Holocene tephras relies largely on radiocarbon dating to suggest a likely candidate eruption followed by a geochemical comparison using binary and ternary plots of selected major oxides. As more tephras are discovered, and the patterns of deposition appear increasingly complex, this approach is likely to work less effectively. In addition, the utility of tephra for the establishment of chronozones will be limited by the availability of radiometric dates to constrain the initial candidate eruption. The results of a DFA on some of the limited published geochemical data are presented and it is clear that this statistical technique offers advantages to the application and development of tephrochronology in western Europe. Future work should concentrate on the provision of discriminant functions from a more complete reference dataset, which will enable the identification of unknown tephras with a known probability of misclassification.
Reconstruction of the 1706 Montaña Negra eruption. Emergency procedures for Garachico and El Tanque, Tenerife, Canary Islands
Authors: Solana M. C. , Aparicio A.
Published: April 2008

In May 1706, after several earthquakes, an eruptive fissure opened in the hills of the Garachico district, forming the Montaña Negra Volcano. In < 15 h the village of El Tanque and part of the town of Garachico, including the harbour, were buried under lava flows. A week later, another flow buried the village of San Juan del Reparo and much of the remaining town of Garachico.

Today, over 6700 people live in the immediate vicinity of this former eruption. Although most of the population is concentrated in the main villages, dwellings are located throughout the district and any future eruption will inevitably destroy property. The reconstruction of the 1706 eruption shows that in any future event only a short time will be available to evacuate the population, but it may be possible to try to prevent the effects of the flows.
Evolving models of the Tertiary evolutionary geomorphology of southern England, with special reference to the Chalklands
Authors: Jones David K. C.
Published: April 2008

This paper examines recent advances in understanding of the Tertiary evolutionary geomorphology of the southern England Chalklands, a subject of continuing controversy despite over a century of investigation. It begins by briefly outlining the classic Wooldridge and Linton model and discussing the many lines of criticism. Particular attention is paid to the explanation of discordant drainage and numerous lines of evidence are presented to explain why the ‘superimposition model’ has been rejected in favour of an explanation involving the development of anteconsequents. Attention is then directed to the new models of evolution advanced in the early 1980s which placed heavier emphasis on Palaeogene denudation and pulsed tectonism. These models are compared and contrasted, and attention focused on the growing recognition that the fundamental erosional surface is an etchplanated Summit Surface originating in the Palaeogene rather than a peneplanated surface developed during the Miocene and Pliocene. Significant developments of the last fifteen years are then reviewed — the establishment of inversion tectonics, lithostratigraphical division of the Chalk, apatite fission-track dating of uplift episodes and new information on the extent of the late Pliocene Red Crag incursion — and combined to produce a new evolutionary sequence which differs from previous interpretations in a number of regards. First, the concept of structural compartmentalization into morphotectonic regions removes the need for uniformity of evolution and indicates that uplift could have been variable in time and space, thereby removing the problems caused by continual adherence to the concept of mid-Tertiary tectonism. Second, the growing evidence for Pleistocene differential uplift of at least 200 m is considered. Third, an explanation of the so-called Plio-Pliocene marine bench involving modified etchplanation is advanced. The paper concludes with a discussion of remaining uncertainties.
Chattian and Miocene elements in the modern landscape of western Britain and Ireland
Authors: Walsh Peter , Boulter Michael , Morawiecka Iwona
Published: April 2008

The best preserved denudation surfaces which are benched into the margins of the pre-Permian oldland massifs of western Britain and Ireland are those comparatively close to sea-level. Such surfaces have frequently been regarded as being of late Pliocene or Pleistocene age and of marine origin. Recent discoveries reviewed in this work reinforce a growing view that these low-level planations are much older and may be of terrestrial origin. Evidence from Wales and southwest England suggests that these little-modified planation elements represent landscapes some 15 Ma old. This paper reviews the palaeobotanical, sedimentological and geomorphological evidence for the close association of several bodies of non-marine Chattian and Miocene sediment and saprolite with some of the better known planation features. In these areas, the former vegetation comprised mixed coniferous/deciduous forest, extinct species of modern north temperate genera, well known from contemporaneous deposits in north Europe. Evidently, differential relief in those times was appreciably less than that of the present and it seems probable that much of what is now the western half of the British Isles was then a wide, forested extension of a previous North European Plain, which varied in altitude by no more than a few decametres.
An overview of Pliocene to present-day uplift and denudation rates in the Northern Apennine
Authors: Bartolini Carlo
Published: April 2008

Quaternary, Holocene and present denudation rates in the Northern Adriatic basin and sedimentary supply rates, formerly to the Northern Apennine Foredeep and at present to the Adriatic Sea, are approximately consistent. The Quaternary denudation rate, based on sediment feeding to the foredeep is 0.45 mm a
−1
. This value is congruous with a mean exhumation rate since the Early Pliocene, deduced from apatite fission track dating, of 0.5 mm a
−1
in the Apuan Alps. The Quaternary supply rate to the foredeep (0.047 km
3
a
−1
) is over twice as fast as that of the Pliocene (0.021 km
3
a
−1
), and reflects an increased denudation rate due to higher energy relief and a slightly larger catchment basin. The Pleistocene increase in uplift/denudation rates is emphasized by the onset of fast prograding sedimentation pattern since 1.0 to 0.8 Ma on both the Padan and the Tyrrhenian side of the Apennines. Pleistocene uplift also had a considerable impact on Apennine morphology and drainage pattern evolution.
Landscape evolution and the preservation of tectonic landforms along the northern Yammouneh Fault, Lebanon
Authors: Butler R. W. H. , Spencer S.
Published: April 2008

The Yammouneh Fault is commonly considered to be the principal active strand of the Dead Sea Transform in Lebanon — an inference reached primarily from interpretations of the geomorphological expression of the fault on satellite images. However, new geological field observations show the Yammouneh Fault to be sealed stratigraphically by the Homs Basalt, dated using new K-Ar ages at 5.2–6.5 Ma. Drainage systems which link to the pre-Homs Basalt palaeosurface show evidence of fault disruption. Those valleys incised into the basalt show no evidence for transcurrent offsets. The inferred left-lateral displacement of
c.
45 km on the Dead Sea Transform that post-dates the Homs Basalt is presumed to have bypassed to the west of Mount Lebanon. These linked geological and geomorphological studies indicate that landscape evolution can be exceptionally slow in northern Lebanon. Faceted spurs, poljes and offset drainage along the Yammouneh Fault across Mount Lebanon, evident on satellite images, are interpreted as being of Miocene age and are not indicative of Plio-Quaternary displacements on the fault. Much of the Lebanese tectonic landscape has thus remained stable for many millions of years, although locally incised during large-scale uplift of the Mount Lebanon range. Presumably landscape insensitivity reflects the arid climatic conditions together with inhibited run-off due to the regional karst system.
Influence of crustal movements on landforms, erosion and sediment deposition in the Irangi Hills, central Tanzania
Authors: Eriksson Mats G.
Published: April 2008

The influence of crustal movements on landforms, erosion and sediment deposition has been analysed in the severely eroded Irangi Hills in Kondoa District, central Tanzania. Field observations, in combination with satellite imagery, aerial photographs, and topographical and geological maps have been used. The Irangi Hills, which are uplifted relative to the vast Maasai Plain, consist of several tectonic blocks, with each block being tilted to the west. Frequent earthquakes indicate that relative uplift, faulting and tilting of the Irangi Hills are still taking place. The drainage pattern of the area and the deposition of river sediments are directly influenced by the morphotectonics. Where fault scarps occur, large rivers have cut into the bedrock across the fault scarps and follow antecedent stream courses, while small streams have been dammed, forming swamps or lakes. The denudation rate for a small catchment (33.4km
2
) has been calculated to 2.7mm a
−1
for the years 1836–1992 by using a dated sediment record. This is considered to be an accelerated denudation rate. The soil erosion of the Irangi Hills is a long-term natural stripping of regolith, accelerated by anthropogenic causes, probably in combination with crustal uplift and the tilting of tectonic blocks.
Uplift and landscape stability at Taroko, eastern Taiwan
Authors: Petley David N. , Reid Sharon
Published: April 2008

The Taroko area of Taiwan represents an extremely dynamic environment, of rapid geological and geomorphological change. The location of the area on the collision zone between the continental Eurasian plate and the oceanic Philippine Sea plate leads to a high frequency of seismic activity, intense internal deformation and high rates of tectonic uplift. The rate of uplift, which is believed to be one of the highest measured, is approximately 5.5mm per annum, with higher rates inferred for the last million years. In consequence, the area, which consists predominantly of relatively weak, intensely deformed marble and schist, has a high potential energy providing ideal conditions for rapid landform evolution.

In addition to high rates of uplift, high rates of denudation are also favoured by the extreme climatic conditions. In particular, the area is seasonally affected by tropical cyclones (typhoons); an average of 16 of these occur in the northwest Pacific per annum, about three of which affect Taiwan. The passage of a typhoon is marked by heavy rainfall which may reach intensities of 100mm per hour and 1500mm in 24 hours. The high rainfall intensities generate intense fluvial activity, including extensive overland flow, high peak discharges, the mobilization of debris channels, landslides and rockfalls.

Intense tectonic and geomorphological activity provide the ideal environment for studying the rapid evolution of landscapes. In this paper, uplift data are combined with daily hydrological records from a major river for the last fifteen years. The hydrological records, which include discharge, mean flow rates and sediment volumes, are used to estimate the sediment budget for the river and hence to estimate denudation rates. It is demonstrated that average aerial denudation rates approximately equal uplift rates. These data are then used to generate a simple computer model for the evolution of Taroko Gorge, which demonstrates that current landforms may be created without substantial changes in the rate of uplift.
The landscape evolution of Nemegt Uul: a late Cenozoic transpressional uplift in the Gobi Altai, southern Mongolia
Authors: Owen Lewis A. , Cunningham W. Dickson , Windley Brian F. , Badamgarov J. , Dorjnamjaa D.
Published: April 2008

The geomorphology and structural geology of Nemegt Uul, Southern Mongolia, is examined as an example of a mountain range that has formed within a restraining bend along a major intracontinental strike-slip fault system, the Gobi-Tien Shan fault system. Structural and geomorphological analysis demonstrates that the mountain belt is young and has been differentially tilted and eroded. A geomorphological model is developed showing that uplift and erosion have resulted in the formation of deeply incised mountains, alluvial fans, badlands, desert pavements and dunes.