bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction
Authors: Jones Mervyn E. , Preston R. M. F.
Published: April 2008

In recognition of the increasing interest in the subject of deformation of sediments and sedimentary rocks shown by Earth scientists in recent years, a major international conference with this theme was held at University College London in April 1985. This volume contains the texts of those contributions to the Conference that were submitted for publication. The collection of papers presented is not a complete record of the proceedings, as some contributors chose not to submit a manuscript. However, most important subject areas are represented, and the papers provide both a review of the present state of the art and pointers for future investigation. The articles have been grouped into three main divisions: experimental and theoretical, process orientated, and descriptive of particular areas or localities. Within those groupings there is no particular significance in the order of printing except that articles with aspects in common have been placed near to one another.

Studies of naturally deformed sedimentary rocks repeatedly indicate that much of the observed deformation resulted from processes active before the rock was lithified. An understanding of the origins of these structures cannot be established using the principles of rock mechanics and crystal physics commonly employed in ‘hard-rock’ structural geology (Rutter 1976; White 1976), the principles of the engineering discipline of soil mechanics being more appropriate. Alternatively, the post-lithification deformation of sediments is a typical rock mechanics problem and may involve an understanding of elasticity (Jaeger & Cook 1969), fracturing (Price 1966; Barton 1976), crystal plasticity (Turcotte & Schubert 1982) and diffusion based deformation mechanisms (Rutter 1976, 1983). The student of sediment deformation must therefore be conversant with all aspects of rock and soil deformation. The Conference, with its contributions by structural geologists, sedimentologists, geotechnical engineers and those conversant with specific aspects of rock and soil mechanics, provided a coverage of this very wide subject area. This is reflected in the contents of the volume.
Pressure solution-deposition creep and associated tectonic differentiation in sedimentary rocks
Authors: Gratier J. P.
Published: April 2008

Several models of pressure solution-deposition have been established by using various hypotheses: on the rate-limiting process of the deformation (kinetics of the solid/fluid reaction or rate of mass transfer); on the driving force for mass transfer (difference in normal stress or elastic, plastic or surface energies) and on the mechanism of mass transfer (diffusion or infiltration). These creep relations have been tested experimentally and in nature. In the last case the observations show that the pressure solution-deposition process is always associated with a chemical differentiation of the rocks when these rocks are initially composed of several minerals with various mobilities under stress. The aim of this paper is to discuss the development of this chemical (and mechanical) differentiation. The first part deals with the initiation and the development of the zone of dissolution (relation between stress and dissolution, effect of the initial heterogeneities, etc.) and of the zone of crystallization (effects of the nature of the rocks, processes of deposition, etc.). The second part deals with the development of chemical differentiation during the progressive deformation. The geometry and the equilibrium composition of the differentiated layer are fixed by various factors such as: the size of the dominant heterogeneities (initial or tectonically induced), the possibilities of mass transfer, the state of stress, and the nature of the solid and that of its solution. The wavelength of some stylolites could also be imposed by these various factors.
Soft-sediment deformations from glaciodeltaic, glaciolacustrine and fluviolacustrine sediments in the Kleszczów Graben (central Poland)
Authors: Brodzikowski K. , Gotowała R. , Hałuszczak A. , Krzyszkowski D. , Van Loon A. J.
Published: April 2008

The Kleszczów Graben, situated some 50 km south of Łódź, has a Tertiary and Quaternary infilling of up to 300–400 m. The graben is some 40 km long and a large exposure is formed by an open-cast browncoal mine. The well discernible structural pattern is due to frequent deformations, many of which are related to subsidence of the graben. The sediments within the graben are all unconsolidated and show a large variety of deformational structures with respect to both genesis and geometry. Various stages of more intense deformation can be discerned. The glaciodeltaic, glaciolacustrine and fluviolacustrine sediments in particular show frequent deformations. They are interpreted as being induced by both endogenic and exogenic agents, often during several phases that affected the same sedimentary unit.
Deformation of Scottish Quaternary sediment sequences by strong earthquake motions
Authors: Davenport Colin A. , Ringrose Philip S.
Published: April 2008

Deformed Quaternary sand, silt, clay and peat sequences from four localities in Scotland are interpreted as seismites by the deformation history of liquefied, fluidized, slumped, and faulted units, and by comparison with seismites documented elsewhere. Two of the sequences consist of outwash sands and silts, deposited during the recession of the Devension ice cap in the region of Perth. Other deposits consist of glacial sands and interglacial peats in the Western Highlands, and glacio-lacustrine silts in the Glen Roy area; both probably deposited during the late stages of the Loch Lomond Readvance.

Careful evaluation of internal geometries and deformation sequences reveals an intimate association of ball-and-illow, fluidization, dish, load, flame and ‘fault-grading’ structures which are most satisfactorily explained by prolonged ground shaking produced by shallow earthquakes. In some cases, potential fault sources for the inferred earthquakes have been identified.
Syn-sedimentary and burial related deformation in the Middle Jurassic non-marine formations of the Yorkshire Basin
Authors: Alexander J.
Published: April 2008

The non-marine formations of the middle Jurassic Ravenscar Group consist of channel sandstone bodies set in interbedded mudstones, silts and thin sheet sandstones. These rocks contain syn-sedimentary and burial related deformation structures.

Frequent discharge fluctuations are deduced to have enhanced inherent river bank instability and with occasional tectonic movements produced a wide range of bank collapse structures. These had a low preservation potential and are observed at various stages of erosion.

Several faults associated with channel sandstones can be related neither to tectonic activity nor to bank collapse. They may be explained as compensation structures formed during differential compaction of the sandstones and adjacent mudstones. Differential compaction structures form on a smaller scale around plant material, early diagenetic nodules and sandstone dykes.

Continued sedimentation on the alluvial plain, together with differential compaction, produces a positive topography over channel sandstones. This effect was reduced by variations in deposition rate and facies. Laterally continuous beds deposited on this topography form gentle folds that are exaggerated by differential compaction during burial.

Although most of the deformation seen in the Ravenscar Group is related to alluvial processes or sediment burial, some is connected to syn-sedimentary tectonic activity.
Aspects of veining in the Welsh Lower Palaeozoic Basin
Authors: Fitches Bill
Published: April 2008

In the Welsh Lower Palaeozoic marginal basin, veins of diverse origin are widely distributed in space and time. The veins are categorized as pre-, syn- and post-tectonic with respect to folding and cleavage development; these sub-divisions denoting different types of veining processes. Among the pre-tectonic veins are those described as regional veins which were emplaced diachronously by hydraulic jacking and related processes due to overpressured pore fluids affecting newly lithified rocks while sedimentation continued above. Other pre-tectonic veins are those around Snowdon which were due to processes closely associated with the development of an Ordovician resurgent caldera. Syn-tectonic veins are uncommon. They include the auriferous lodes of Ogofau in south-central Wales. Post-tectonic veins are the most widespread type and are exemplified mainly by those of the Harlech and Plynlimon Domes. These late veins are attributed largely to regional extension and dewatering of the Lower Palaeozoic pile caused by the early Variscan extensional regime.
The petrochemistry of the northern part of the Chilwa alkaline province, Malawi
Authors: Woolley A. R. , Jones G. C.
Published: April 2008

The Chilwa province of alkaline igneous rocks and carbonatites lies at the southern end of the East African rift, and is unique within the rift for its essentially intrusive nature. The province comprises numerous carbonatite centres (some with nepheline syenite and nephelinite), large complexes of nepheline syenite and syenite, and plutons of peralkaline syenite, quartz syenite and granite, together with dykes compositionally equivalent to all the major rock types. 196 rock samples from the northern half of the province have been chemically analysed and the data indicate that three rock series are present: (1) syenite-quartz syenite-granite, (2) nepheline syenite-syenite and (3) nephelinite-carbonatite-nepheline syenite. It has not proved possible to relate these series to a single parental magma, and it is concluded that three parental magmas of trachytic, phonolitic and nephelinitic-carbonatitic composition were involved.

A model is suggested for the generation of these three magmas involving production of a zoned metasomatized lithosphere wedge by lithosphere focussing. Fracturing of the crust above the growing wedge led to pressure release and to the uprise of geotherms and volatiles with consequent partial melting at different levels throughout the metasomatized wedge. The metasomatism may have reached the base of the crust and it was from this region that trachyte magmas were produced by melting of rocks similar to syenitic fenites. Phonolitic magmas were generated directly at intermediate levels, and nephelinites were generated at the base of the metasomatized lithosphere.
Tertiary alkaline magmatism in East Greenland: a review
Authors: Nielsen T. F. D.
Published: April 2008

The Tertiary alkaline magmatism in E Greenland is the result of the processes related to the continental break-up of the N Atlantic in the Lower Tertiary. The alkaline rocks are divided into three groups: A, inland alkaline lavas, dykes and intrusive complexes of nephelinitic parentage; B, mildly-alkaline to nephelinitic mafic lavas and dykes mostly in areas that previously experienced tholeiitic magmatism; C, salic subalkaline to alkaline dykes and intrusive complexes related to group B.

All three groups are exposed over about 1000 km along the E coast of Greenland, and close to 100 intrusions have been identified, excluding the very intense dyke-swarms. The rocks of nephelinitic parentage occur inland about 100 km W of the coastal zone of most intense magmatism and are believed to constitute an alkaline ‘flank’ activity to the tholeiitic magmatism of the spreading ridge. Early tholeiites and the nephelinites are thought to be derived from the same mantle source. Both group B and group C rocks occur along the coast and along what has been called the ‘initial magmatic lineament’, which in some areas evolved to a spreading zone of intense tholeiitic magmatism. The group B rocks may have been generated in the tholeiite feeder system after the end of the tholeiitic magmatism by processes in replenished magma chambers. Interaction between the magmas in the feeder system and the Archaean crust generated the subalkaline to alkaline salic liquids of group C. The occurrences of the alkaline rocks and their relationships with one another, with the preceding tholeiitic magmatism and with the process of continental break-up are described, and petrogenetic models are presented.
Sedimentology of basin plains
Authors: Pilkey Orrin H.
Published: April 2008

The study of 13 basin plains in the Western N Atlantic Ocean, the Caribbean Sea and the Mediterranean Sea has revealed a number of factors that control basin-plain filling. Basin plains are strongly dominated by turbidity currents which enter the basins mostly from canyon mouths. Such turbidity currents are little affected by channelization, and erosion of pre-existing turbidites is of minor importance. In order to maintain a basin plain, occasional ‘giant events’ are required, i.e. turbidity currents which flow across and cover the entire basin. The two main factors that control sand-layer geometry in basin plains are (1) the arrangement of entry points around the edge of the plain and (2) the ratio of the area of the drainage basin to the area of the basin-plain floor.
Mapping of hemipelagic versus turbiditic muds by feeding traces observed in deep-sea photographs
Authors: Huggett Q. J.
Published: April 2008

The Madeira Abyssal Plain is composed mainly of turbiditic sediments derived from the NW African margin. Through this cover project hills covered with draped pelagic sediments. The surface layers of both sediment types are similar with respect to grain size and mineralogy. Similarly, there is no difference in the distribution of pelagic organisms living in the overlying waters. The foraging behaviour of benthic communities on each sediment type is markedly different, however, so that sediment type can be determined from this parameter alone. It is suggested that the potentially richer food supply available at depth within the turbidites has produced the differences observed.
Geochemical characteristics and provenance of late Quaternary sediments from the Madeira Abyssal Plain, N Atlantic
Authors: de Lange Gert J. , Jarvis Ian , Kuijpers Antoon
Published: April 2008

Late Quaternary sediments of the Madeira Abyssal Plain (MAP) consist of alternations of metre-thick distal turbidites and thin (centimetre to decimetre) pelagic clays, marls and oozes. The geochemical characteristics of 29 turbidites are described using major- and trace-element data from more than 350 samples. These were obtained from two representative piston cores located in the NE and W central parts of the MAP. Three separate groups of turbidites are defined by the geochemical data: (a) organic-rich, (b) ‘volcanic’ and (c) calcareous turbidites. ‘Organic’ turbidites contain 0.3–2% organic carbon. Their sediment originated from the lower continental slope of NW Africa N of 20°N, although one turbidite may have been derived from S of this latitude. ‘Volcanic’ turbidites contain a large proportion of volcaniclastic material and are distinguished by their high TiO
2
contents (about 1.5% on a carbonate-free basis). Much of their sediment originated from the oceanic islands of the Canaries and Madeira to the E. Calcareous turbidites are composed predominantly of pelagic carbonate and are defined by high CaCO
3
values (more than 75%). Their sediment was derived from the Great Meteor-Cruiser Seamount Chain, W of the MAP.
Geochemical oxidation fronts in NE Atlantic distal turbidites and their effects in the sedimentary record
Authors: Thomson J. , Colley S. , Higgs N. C. , Hydes D. J. , Wilson T. R. S. , Sørensen J.
Published: April 2008

Overall sediment accumulation on the abyssal plain E of Great Meteor Seamount is dominated by distal turbidite deposition. A colour contrast is seen at the tops of many individual turbidites, so that a single turbidite has two distinct colour tones. Porewater data from the uppermost turbidite are used to demonstrate that these colour contrasts are consequences of an oxidation-front phenomenon. Distributions of organic carbon, uranium, vanadium and copper are proposed as diagnostic solid-phase indicators in both active and fossil types. A generalized description of the features of such turbidites is presented.
Trace-element mobility during early diagenesis in distal turbidites: late Quaternary of the Madeira Abyssal Plain, N Atlantic
Authors: Jarvis Ian , Higgs Nigel
Published: April 2008

Sediments deposited on the Madeira Abyssal Plain (MAP) during the late Quaternary consist of an alternating succession of distal turbidites and pelagites. Individual turbidites may be correlated over most of the northern MAP. The sediment geochemistry of the succession has been investigated in detail using material from a representative 10 m piston core. The turbidites have been divided into organic-rich (at least 0.5% C
org
) and organic-poor groups. At the time of emplacement all turbidites were characterized by homogeneous major- and trace-element distributions, although thicker beds have thin silty bases of different compositions. Organic-rich turbidites, however, have undergone considerable early post-depositional modification as a result of oxidation of labile organic matter by sea-water oxygen diffusing downwards from the sediment-water interface. The progressive advance of oxidation fronts through the turbidites has produced distinctive two-tone colourations with light-brown tops and olive-green bottoms, and has caused significant early diagenetic relocation of iron, manganese, phosphorus, cobalt, copper, nickel, uranium, vanadium and zinc. Iron is marginally enriched in formerly oxic sediments. Manganese oxyhydroxides occur as dark-brown diagenetic laminations in recently oxidized turbidite tops, but have been dissolved by anoxic conditions in older examples. Mn
2+
pore-water profiles have been preserved by the adsorption of manganese by calcite. Phosphorus, cobalt, nickel and some copper were initially complexed by the precipitation of manganese oxyhydroxides and other processes occurring at active redox boundaries. Copper was also concentrated in the reduced sediments at this time. Later migration of these elements as reduced phases has produced thin purple diagenetic laminations in both turbidities and pelagites. Uranium, vanadium and zinc were relocated into reduced sediments during early diagenesis, but were not remobilized later. The diagenetic sequence in MAP sediments contrasts strongly with established ‘steady-state’ models based on hemipelagic and pelagic environments, but may be typical of a significant proportion of recent and ancient sequences.
Geochemical and Petrological Significance of the Archaean-Proterozoic Boundary
Authors: Taylor S. R.
Published: April 2008

A significant change in the nature of igneous activity responsible for continental growth apparently occurred at the Archaean-Proterozoic boundary. The sedimentary record is consistent with an Archaean upper crust dominated by the bimodal basic-felsic suite, with both units derived by melting at mantle depths. In contrast, the Proterozoic (and younger) upper continental crust is dominated by K-rich granites, derived by intracrustal melting. This major episodic event produced an upper crust enriched in incompatible elements (e.g. Rb, U) as attested inter alia by the increase in
87
Sr/
86
Sr in marine carbonates in the early Proterozoic, and the abundance of early Proterozoic uranium deposits. This event seems to have been connected with the widespread initiation of subduction related calcalkaline volcanism, which, since that time, has been the principal contributor to continental growth. Although the change at the Archaean-Proterozoic boundary was the major episodic event in continental growth, minor episodes of cratonization occurred in the early Archaean, and some greenstone belt development lingered into the early Proterozoic. More recent episodes of continental growth (e.g. 1800 Ma event) appear to have been on a smaller scale. The sedimentary record is transparent to them, and they do not represent any fundamental change in the igneous processes responsible for continental growth.
Early Proterozoic Subaerial Volcanism and Its Relationship to Broken Hill-type Mineralization in Central Sweden
Authors: Parr Joanna , Rickard David
Published: April 2008

Broken Hill-type mineralization is characterized by abundant exhalites in a sulphur-poor, felsic volcanic environment. It is typically Proterozoic. The Ljusnarsberg area in central Sweden is a microcosm of this mineralization type. One part of the amphibolite-grade, supracrustal succession is characterized by a thick sequence of subaerial volcaniclastics which grade into diverse chemical sediments interpreted as exhalities containing sulphide, iron oxide and manganese mineralization. The environment is interpreted as terrestrial with frequent lakes which are fed by volcanic exhalations. Evaporites may also have been present. The non-marine environment may not only have helped determine the nature of the mineralization in the area but also affected the chemistry of the volcanic host rocks. Thus, the occurrence of potassic and sodic metavolcanics may be related to the effects on hydrothermal solution chemistry and water-rock ratios of non-marine surface conditions, as well as alteration temperature and primary volcanic chemistry.
U-Pb Geochronology of Accreted Terranes in the Trans-Hudson Orogen, Northern Saskatchewan, Canada
Authors: Lewry J. F. , MacDonald R. , Livesey C. , Meyer M. , Van Schmus R. , Bickford M. E.
Published: April 2008

U-Pb zircon ages from magmatic rocks in predominantly juvenile accreted terranes of the Trans-Hudson Orogen in northern Saskatchewan constrain timing of orogenic events, and enhance understanding of local domain relations and the relation of the Trans-Hudson to other early Proterozoic orogens in North America. Most units yield zircon ages of 1890 to 1835 Ma. Six metarhyolites, from the La Ronge and Glennie Domains and Hanson Lake Block, give ages of 1888 to 1876 Ma. Most plutons, ranging from ‘early synkinematic’ tonalites and granodiorites to less deformed ‘late’ intrusions such as the Wathaman Batholith and other smaller bodies, yield ages between 1870 and 1835 Ma. Some of the youngest ages were obtained from highly deformed plutons, suggesting that regional thermotectonism postdated 1835 Ma, that variation in deformation of the plutons is a function of extreme heterogeneity of regional strain and that degree of deformation is not a reliable field indicator of relative age. Similarity of ages of volcanics and plutons in different domains suggests that domainal distinctions are mainly lithotectonic, rather than temporal.

Zircons from the Sahli ‘granite’, Hanson Lake Block, yield equivocal data. Discordia upper and lower intercepts for this body suggest that
c.
2500 Ma old granitic rocks were subjected to high grade metamorphism
c.
1900 Ma ago, with substantial resetting of zircons: this supports published Rb-Sr isochron data and indicates that the Sahli granite represents reworked Archaean basement.

Most zircon ages are older than reported Rb-Sr isochron ages on the same or similar units, suggesting open-system Rb-Sr behaviour. Zircon ages from this part of Trans-Hudson Orogen are similar to those from igneous units of the Penokean, Wopmay and Svecofennian Orogens, suggesting near-synchroneity of igneous and tectonic events during early Proterozoic continental assembly.
Geochemistry, Tectonic Setting, and Mineralization of High-Potassium Middle Proterozoic Rocks in Central Labrador, Canada
Authors: Ryan A. B. , Baragar W. R. A. , Kontak D. J.
Published: April 2008

The Sylvia Lake Formation of the Bruce River Group is one of several middle Proterozoic volcanic sequences along the northern margin of the Grenville structural province. It comprises a variety of basaltic to rhyolitic lava flows and pyroclastic rocks, of which the majority are felsic welded ash-flow tuff. The Sylvia Lake Formation is a bimodal sequence, in which low silica (basaltic) and esite and rhyolite are the predominant compositions. The rocks are enriched in potassium, and exhibit other characteristics of the high-K calcalkaline and shoshonite association. The volume of rhyolitic ash-flows in relation to the amount of mafic material, the presence of trachyandesites, and the overall chemistry are indicative of substantial influence of continental crust on the development of the volcanic pile. The volcanics are host to numerous base metal and uranium showings, and have potential for precious metal concentrations. The volcanism of the Sylvia Lake Formation represents the last expression of a long-lived middle Proterozoic plutonic episode in this area, but the tectonic framework at the time of generation of these magmas is poorly constrained.
Proterozoic Volcanic Rocks of the Northern Guiana Shield, South America
Authors: Gibbs A. K.
Published: April 2008

Early Proterozoic greenstone belts exposed over approximately 100 000 km
2
in the northern Guiana Shield resemble many late Archaean greenstone belts in lithostratigraphy, styles of deformation and metamorphism, and probably also in mineral resource potential. Basalts dominate the lower sections, overlain by more diverse and porphyritic mafic, intermediate, and felsic volcanics. Tholeiitic and calcalkaline suites are both common. Few rocks have 63–68 wt% silica, making the population bimodal. Tholeiitic basalts have Ni, Cr, and Co contents as high as many Late Archaean basalts. Magnesian basalts and concordant ultramafic schists suggest the presence of komatiites. Minor high-K calcalkaline andesites occur high in the volcanic sections in Guyana, and might belong to a younger sequence. Hundreds of placer and shallow gold deposits have been developed; exploration for deeper gold deposits is warranted. Common evidence of synvolcanic hydrothermal activity suggests that volcanogenic sulphide ore deposits may be found when appropriate exploration methods are applied.

Felsic volcanics were erupted over much of the Amazonian craton following its consolidation in the 2.1–2.0 Ga Trans-Amazonian orogenic cycle. These were accompanied by epizonal granitoid intrusives and mafic dykes and sills. Alkaline mafic volcanics, alkaline complexes, carbonatites, and possibly also kimberlites were erupted in the late Proterozoic.
Fundamental Uniformity in the Trace Element Patterns of the Volcanics of the Kaapvaal Craton from 3000 to 2100 Ma: Evidence for the Lithospheric Origin of These Continental Tholeiites
Authors: Myers R. E. , Cawthorn R. G. , McCarthy T. S. , Anhaeusser C. R.
Published: April 2008

In order to examine the nature of the mantle beneath the Kaapvaal Craton in southern Africa, data from thirteen volcanic sequences ranging in age from 3000 to 2100 Ma have been examined in this study. Variations in Nb, La, Ce, P, Zr, Ti, and Y have been evaluated using a niobium-normalized spidergram which minimizes variations due to fractional crystallization and clearly illustrates mantle source variations. Using this diagram a pattern, showing strong LREE enrichment of source relatively depleted in niobium and titanium, has been identified which remains quantitatively the same throughout this time period, indicating that it is the result of a reproducible equilibrium process. Melting of an incompatible element enriched (modally metasomatized) subcontinental lithosphere in which renewable metasomatic phases, such as diopside, are residual during melting can explain the quantitative uniformity and the time independence of this pattern.
Geochemistry of Proterozoic Volcanics, Mount Isa Inlier, Australia
Authors: Wilson I. H.
Published: April 2008

The Mount Isa Inlier contains four early to middle Proterozoic depositional cycles comprising terrestrial and shallow marine metasediments and intercalated metavolcanics. Several phases of granite and swarms of dolerite dykes (both partly comagmatic with the volcanics) intrude the sequence which is regionally metamorphosed in the greenschist and amphibolite facies. Structure is locally complex.

The oldest cycle (Leichhardt Metamorphics: 1865 Ma) comprises metamorphosed rhyodacite and rhyolite. The second cycle (Magna Lynn Metabasalt and Argylla Formation: 1777 Ma) contains metamorphosed basalt, andesite, dacite, rhyolite, and clastic sediments. The Eastern Creek Volcanics (about 1700 Ma) is the most extensive example of the third cycle which is dominantly metabasalt and metamorphosed clastic sediments. The final cycle (1680–1610 Ma) is characterized by highly potassic (alkaline or altered) volcanics ranging from mafic lavas to felsic tuffs, interbedded with clastic and dolomitic sediments (e.g. at Mount Isa) which show little evidence of metamorphism.

Almost five hundred specimens from twenty volcanic formations have been analysed since 1969, in conjunction with 1:100 000 regional mapping of the Inlier (60 000 km
2
) by the Bureau of Mineral Resources and Geological Survey of Queensland. For most specimens eleven major elements, four volatiles, and fifteen trace elements were determined, but up to thirty eight trace elements (including REE and F) were determined for representative pecimens of each major rock type. The analyses and isotopic dating have been used in characterizing the different volcanic units, petrological studies, tectonic modelling, and studies of alteration and ore genesis. Most of the mafic volcanics have tholeiitic affinities. The older felsic volcanics have calcalkaline affinities consistent with partial melting of a pelitic source. The later volcanics have bimodal characteristics.
Post-Palaeocene evolution of regional groundwater flow systems and their relation to petroleum accumulations, Taber Area, southern Alberta, Canada
Authors: Tóth J. , Corbet T.
Published: April 2008

Three regionally extensive fluid dynamic systems have been mapped in a 23 500 km
2
portion of the Western Canada Sedimentary Basin in south-eastern Alberta. The Modern Land Surface System reaches depths of 300 m and is well adjusted to the modern relief. The subjacent Erosional Rebound System occupies most of the 600 m thick predominantly shale Colorado Aquitard including its often gas-bearing sand members. It is characterized by extensive regions of sub-hydrostatic pressures. Below the Colorado Aquitard is the Cypress Plain System which has strong upward-directed forces and mild but definite lateral components. The lateral components oppose the modern relief and are oriented from the centre of the study area toward its western and eastern boundaries where most of the known oil fields are also located. The three dynamic systems are interpreted to be transient stages of sequentially superimposed gravitational and dilatational force fields. The gravitational fields depend on topography and the dilatational field results from elastic rebound of the Colorado Aquitard in response to erosional removal of 700 m of overburden during Pliocene and Pleistocene times.

The flow pattern that existed during the time of the Cypress Plain was generated after Palaeocene (58 Ma) or Eocene (36 Ma) times by a palaeo-relief dominated by the NE-SW-trending Bow Island Topographic High. It was composed of and maintained as cross-formational gravity-flow systems throughout at least the Miocene (i.e. for more than 30 m.y.). Oil migrated to and was entrapped in the discharge regions of these systems. Subsequently, dilation of the Colorado Aquitard created the hydraulic sink in the Erosional Rebound System and induced gas to exsolve and accumulate in the sands.

Based on a one-dimensional solution of the diffusion equation, periods of 10 m.y. and 0.1 m.y. respectively were calculated to be required for pore pressures below and above the Colorado Aquitard to adjust to changes in the land surface. Compared with inferred ages and durations of palaeo-topographies, these times agree with the hypothesized evolutionary history of flow systems. There was sufficient time for flow in the Cypress Plain System to adjust to the post-Eocene relief but not enough time has yet elapsed for it to re-adjust to the Modern Land Surface which was initiated during middle Pleistocene (1 Ma) times. In contrast, the Modern Land Surface System has had 10 times the 0.1 m.y. required for it to adjust to the modern relief, and thus its apparent steady state is expected.
Fluid flow and diagenesis in the East Midlands Triassic sandstone aquifer
Authors: Bath A. H. , Milodowski A. E. , Strong G. E.
Published: April 2008

The flow system, hydrochemistry and isotope hydrology of the freshwater aquifer in the E Midlands Triassic sandstone are reviewed. Isotopic data suggest a mean flow velocity of around 0.6 m.y. over the last 30 k.y., in contrast with the present-day velocity of around 0.2 m.y. The difference is attributed to changes in hydraulic gradients over this period; fluctuations in recharge and gradients would have influenced meteoric water influx and diagenesis over the last 10
7
years or more. The diagenetic modifications to the arkosic sandstone are described and are divided into those taking place before and during compaction, probably with saline pore water, and those occurring as a result of meteoric water influx following uplift and denudation.

The relation between the kinetics of diagenetic reactions and the groundwater flow velocity is discussed. Relevant experimental data for reaction kinetics are summarized. The hydrochemistry and flow velocity of the present regime are used to deduce mass transfers within and outside the aquifer. These are equivalent to uniform porosity increases of only about 0.17fb3e69cer million years for each of the dolomite and K-feldspar dissolution reactions. Both these dissolution reactions are incongruent, and precipitate calcite and kaolinite respectively. The spatial arrangement of reactant and product minerals in incongruent reactions is expected to reflect interplay between dissolution/precipitation kinetics and water flow rate. Scanning electron micrographs show the proximity of K-feldspar and kaolinite. Constraints can be placed on the flow rates responsible by considering chemical balances for aluminium and silicon and their maximum production rates by feldspar dissolution.

This approach involves many simplifications and assumptions, but with further experimental kinetic data it offers the possibility of deducing information on past flow systems from detailed measurements of diagenetic mineralogy and geochemistry in clastic sediments.
Quaternary landforms, sediments, depositional environments and gastropod isotope ratios at Adrar Bous, Tenere Desert of Niger, south-central Sahara
Authors: Williams M. A. J. , Abell P. I. , Sparks B. W.
Published: April 2008

Sediments deposited in a variety of environments including fluviatile sands and gravels, aeolian sands, lacustrine clays and diatomites, and swamp clays crop out in and around Adrar Bous, an isolated ring-complex in the northern Tenere Desert of Niger. These sediments range from Recent to at least Middle Pleistocene in age, and contain both reworked and primary-context stone artefact assemblages testifying to recurrent prehistoric occupation of the plains around the massif from at least Upper Acheulian times onwards. During the early Holocene a small lake, stable at 710 m a.s.l. supported a community of Epi-Palaeolithic hunter-gatherers who also ate aquatic foods until the lake dried out at around 7500–7000
bp
. Occupation of the piedmont plains resumed during 6000–4000
bp
when Neolithic pastoralists grazed their cattle around a smaller lake stable at 700 m a.s.l. The Holocene mollusc assemblage and the stable isotope ratios obtained for different species of Holocene gastropods are entirely consistent with, and help to refine, the palaeoenvironmental reconstruction based upon stratigraphic and sedimentary analyses supplemented by the use of prehistoric stone tool assemblages as ‘zonal fossils’.
Aeolian abrasion of quartz particles and the production of silt-size fragments: preliminary results
Authors: Whalley W. B. , Smith B. J. , McAlister J. J. , Edwards A. J.
Published: April 2008

Experimental abrasion of quartz sand in an air stream shows that particles with initially high angularity are progressively rounded by the chipping of edges and corners. Grains closely resemble dune sand grains from deserts with respect to rounding and microscopic surface textures after 48 hours of abrasion. Results show an initially high weight loss from the original grains (primarily by edge chipping), compared with subsequent abrasion. High percentages of coarse and medium silt are produced but there is a gradual increase in the percentage of fine silt as rounding increases and the quantity of fines generated declines. Silica extraction from the fines using water shows concentrations of several hundred ppm. Implications for loess production and silcrete formation are suggested.
The mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern Negev, Israel
Authors: Pye K. , Tsoar H.
Published: April 2008

Entrainment, transport and deposition of dust in and around deserts has major geological implications. A consideration of the mechanics of dust transport and deposition shows that ‘desert loess’ can only accumulate in vegetated desert fringe areas which are relatively close to a major source of dust. Dust deposition can also contribute to the stabilization of active sand dunes, and infiltrated dust plays an important role in the early diagenesis of a wide range of desert sediments.
Dune networks
Authors: Warren A. , Kay S.
Published: April 2008

Dune networks are one of the commonest of dune types, and yet the least understood. A nomenclature is developed for describing the components of these systems. It uses the idea of dune memory: dune systems with little sand have little memory, those with more sand ‘remember’ the effect of the most dominant wind throughout the year; some dunes may have ‘mega-memories’, remembering events from the Pleistocene. The nomenclature defines the components of dune networks according to both relative dominance and whether the components are transverse, seif-like or nodal elements. Using this nomenclature, the dynamics of two dune networks in the Wahiba Sands of Oman are described. In one low-memory dune system, where individual dunes are 1 to 2 m high, a plot of 150 by 50 m was surveyed. In a second, higher memory dune system, where individual dunes are 5 to 6 m high, a 200 by 200 m plot was surveyed and an intensive study of sand movement was conducted. Both areas were surveyed in January and March 1986. A further survey was conducted in mid-July. Dune movement is related to topographic parameters such as altitude, slope angle and slope azimuth, slope curvature and proximity to other slopes. An analysis of sand loss or gain at one site is also presented. The dunes were found to be highly mobile. Some crests moved up to 80 cm in 9 hr. Movement was restricted to the upper flanks of ridges. However, adjustment to new wind conditions is very quick.
Late Palaeozoic cold-climate aeolianites, southern Cooper Basin, South Australia
Authors: Williams B. P. J. , Wild E. K. , Suttill R. J.
Published: April 2008

Core facies analysis of the Permo-Carboniferous Gidgealpa Group of the southern Cooper Basin, South Australia has revealed sandstones of aeolian origin within the glacigenic Merrimelia Formation. The aeolianites comprise exclusively porous, poorly cemented, medium- and fine-grained sandstones dominated by parallel lamination. Sharp, planar truncation surfaces divide the suite into units composed mainly of translatent windripple lamination and minor amounts of sandflow bedding with primary depositional dip (post-compaction) varying between 0° and 25°. Distinctive compressional, tensional and dissipation structures are preserved in deformed lee-slope deposits and the inclusion of low-angle cross-strata and wedge-bedded units locally indicate deposition on the basal aprons of dunes or in contiguous sand sheets. Wet interdune sediments with adhesion ripples are also exhibited in the cores. The aeolianites, up to 232 m thick, have been traced subsurface by integrating core facies, wireline logs and seismic reflection analysis. A low-interval transit time on sonic logs is characteristic of the porous aeolianite sand and has facilitated mapping of the dune field using seismic data. The sandstone body trends SE-NW, is 6 to 8 km wide and passes laterally into outwash fan and fluvioglacial, braidplain deposits. Potential hydrocarbon traps may occur at the top of the aeolianites, or within them beneath intraformational seals formed by possible muddy interdune facies. The overall high-latitude, cold-climate nature of the Merrimelia Formation, deposited during the extensive Gondwanaland glaciation, is well known but this discovery not only records the first Gondwanan aeolianite suite but may also detail the first pre-Quaternary example of paraglacial aeolianites.
Discrimination of depositional environments using sedimentary characteristics in the Mega Kalahari, central southern Africa
Authors: Thomas D. S. G.
Published: April 2008

Unconsolidated Kalahari sand covers 2.5 million km
2
of central southern Africa, the ‘Mega Kalahari’, extending far beyond the Kalahari Desert of today. Relic aeolian, lacustrine and fluvial landforms indicate that in the Quaternary the Kalahari sand has been deposited and reworked by a variety of processes. Large areas of the sand have no identifiable landform associations, and because of this, sedimentological studies are necessary for a better interpretation of the palaeoenvironmental history of the Mega Kalahari. To this end, almost 200 Kalahari sand samples, in and not in identifiable landform associations, were collected and analysed in order to: investigate sedimentological characteristics; determine whether different processes have imparted distinct sedimentological characteristics to the sand; and thereby attempt to determine the depositional environments of samples without prior knowledge of the landform associations. Three methods have been used: (1) standard sedimentological techniques of grain size and shape determination; (2) multivariate discriminant analyses, to determine whether depositional environments could be better distinguished by considering grain size and shape parameters in combination; and (3) scanning electron microscope analyses of samples which lie centrally in any group identified by statistical analyses. Results indicate that aeolian processes have dominated the environmental history of the Kalahari sand, with only limited modification by subsequent processes. Multivariate discriminant analysis achieved only limited success in differentiating process environments. SEM investigations best identified the subtle modification of sand characteristics by non-aeolian processes, because individual grain texstures are more readily adjusted than overall sample fabrics, and may therefore be the best technique for elucidating palaeoenvironments from sediment characteristics.
Remote sensing of sediment transfer processes in playa basins
Authors: Millington A. C. , Jones A. R. , Quarmby N. , Townshend J. R. G.
Published: April 2008

Landsat
Thematic Mapper and Multispectral Scanner data have been used to detect changes in the spectral reflectance and absorption of three playas in south-central Tunisia. Change detection images have been used to analyse changes between wet and dry seasons and between different years. Changes in geomorphological phenomena are interpreted from changes in soil and foliar moisture levels, differences in reflectance between different salts and sediments, and the spatial expression of geomorphological features. The intra-annual changes that can be detected from multidate imagery include surface moisture, texture and chemical composition, vegetation cover and the extent of aeolian activity. Detected inter-annual changes are divisible into those restricted to playa margins—sedimentation from sheetwash and alluvial fans, erosion from surface runoff, and cliff retreat—and those found at central playa locations which are related to the redistribution of water, salt and sediment.
Controls on the geometry and distribution of carbonate cements in Jurassic sandstones: Bridport Sands, southern England and Viking Group, Troll Field, Norway
Authors: Kantorowicz J. D. , Bryant I. D. , Dawans J. M.
Published: April 2008

The petrography and diagenesis of calcite cements in the Lower Jurassic, Bridport Sands (southern England) and Upper Jurassic, Viking Group sandstones (Troll Field, offshore Norway) have been investigated in order to assess their geometry and effect on hydrocarbon recovery.

In the Bridport Sands, sediment texture and mineralogy controlled carbonate cementation. Clay-rich fairweather sediments were weakly cemented and are now compacted. Bioclast-rich storm deposits were stabilized mechanically by early fringing cements. During burial bioclasts and fringing cements were replaced or dissolved, and pores were filled by simultaneously precipitated ferroan calcite. Thus, cemented beds are laterally continuous for several kilometres in the Bridport Sands as a consequence of the sheet-like geometry of the storm beds in which they developed.

In the Viking Group sandstones, carbonate cementation was controlled by rate of burial. Fringing cements formed locally during non-deposition or emergence. Cementation continued with non-ferroan calcite incorporating bacterially derived bicarbonate generated during prolonged residence in near surface zones of bacterial activity. Cement geometries will reflect the distribution of emergent surfaces and the longevity of residence near the surface.

These two cases demonstrate the potential for laterally extensive carbonate cements to develop in shelf sandstones. The cements in these examples have different origins but in both cases their distribution is related to the episodic nature of deposition in the shelf environment.
Trace-element source and mobility during limestone burial diagenesis—an example from the Middle Jurassic of eastern England
Authors: Emery D.
Published: April 2008

Two phases of burial calcite from the Lincolnshire Limestone (Bajocian) of central Lincolnshire have been analysed for their trace element (Fe, Mn, Mg, Sr) and strontium isotopic compositions.

The earliest, non-ferroan, brightly luminescent phase has the following mean trace element concentrations: Fe- 919 ppm; Mn- 116 ppm: 3 1778 ppm; Sr- 327 ppm. The later, ferroan, dully luminescent phase has the following mean compositions: Fe- 3580 ppm; Mn- 225 ppm; Mg- 1400 ppm; Sr- 318 ppm. The strontium isotopic composition of the two phases is indistinguishable, with a mean
87
Sr/
86
Sr ratio of 0.70820. This value is considerably more radiogenic than host Bajocian marine carbonate (
87
Sr/
86
Sr = 0.70725).

The Fe and Mn of the burial calcites were sourced by iron and manganese oxyhydroxides associated with shales bounding (and internal to) the Lincolnshire Limestone. The relatively shallow maximum burial depths (550 m) and low temperatures (maximum of 42°C) attained by the formation in the area of study preclude major clay or sandstone diagenetic transformations as potential sources for Fe and Mn. These trace elements moved into the Limestone in solution via compaction driven cross-formational flow from bounding shale aquicludes.

The Sr and Mg trace element components of the burial cements were derived from: (i) remobilized Bajocian marine carbonate, and (ii) remobilized Carboniferous marine carbonate. These sources satisfy the requirements of a linear Sr versus Mg relationship observed for the burial cements, that is, a constant Sr/Mg ratio with time, but highly variable absolute Sr and Mg contents. These sources also satisfy the near constant
87
Sr/
86
Sr composition of the burial calcites.

The burial hydrology required by the trace element budget above is a convective flow system with cross-formational elements as normal bleeder faults connecting the Carboniferous Limestone and the Lincolnshire Limestone. Additional compaction-driven flow occurred from bounding shale formations (chiefly the underlying Grantham Formation and to a lesser extent the Upper Estuarine ‘Series’) to the Lincolnshire Limestone. Up-dip flow within the fully confined Limestone provides an enformational limb to the convective system.