bluuebunny/crossref_metadata_2025 huggingface dataset:
The Cenozoic history of the southern Atacama Desert, Chile
Authors: MORTIMER CEDRIG
Published: December 2007

Four episodes of landscape evolution are recognized, each of which has led to the development of a regional erosion surface. The first phase began upon elevation of northern Chile above sea level in the late Mesozoic, and each subsequent phase commenced with a major incision of drainage into the preceding landscape. Radiometric dating of pyroclastic flows shows that the earliest elements of the present topography already existed in the Lower Eocene, and that most landforms had developed by the Middle-Upper Miocene. Deep canyon formation characterized the latest erosional phase which commenced in the Upper Miocene and is still continuing.

Tectonic elevation of the Cordillera de la Costa in relation to the longitudinal depressions seems to have occurred early in the landscape history, though later remobilization along major structures has since taken place.

Erosional landforms in the high Andes are often blanketed by constructional volcanic features and the migration of eruptive centres since Miocene times has displaced the continental watershed to the east.

Tectonically induced relative sea level changes have caused late Tertiary transgressive deposits in the littoral region to have been terraced during an irregular marine regression. The landscape history which spans the whole of the Tertiary indicates that Andean relief generation has been a prolonged pulsative process.

Supergene enrichment of the copper deposits took place under the older erosion surfaces between the Lower Eocene and the Upper Miocene, and the economic viability of a prospective mine can be largely predicted from the overlying topography.
The state of the
Journal
Authors: Leake Bernard E.
Published: December 2007

As this is the last issue of the present volume some of the progress made with the
Journal
following the magnificent augean task completed by my predecessor, Dr W. W. Bishop, is summarized.

Priority has been given to ensuring that the
Journal
is dispatched regularly on time so that Fellows in the British Isles receive it near to or even before the first day of the nominal month of issue. This has resulted in most Fellows in North America, even those on the west coast, receiving their
Journal
within the month of nominal issue. Many Fellows have noted that their institutional libraries do not receive the
Journal
so promptly and investigations into this reveal that this is mainly because many institutions do not renew their subscriptions until several months after the New Year; a situation that can only be remedied by prompter action by subscribers.

At the same time, great effort has been made within the available limited finance to reduce the backlog of papers awaiting publication. After the May issue of this year all papers have been, and will be, published within a year of receipt of the revised manuscript, except for one paper whose author made changes in the figures two months after submitting the revised version. The last paper
originally
submitted in 1971 appears in this issue; the last paper
originally
submitted in 1972 will appear in the March 1974 issue. Short papers can now be guaranteed publication within six months or even less if urgent and
The origin of the western Mediterranean basin
Authors: AUZENDE JEAN M. , BONNIN JEAN , OLIVET JEAN L.
Published: December 2007

The evolution of the western Mediterranean basin is considered. The Provence basin results from the Oligocene migration of Corsica and Sardinia southeastwards. The North African basin was created by the dislocation of an 'internal zone plate' by the mechanism invoked by Karig. Lower or middle Miocene squeezing of the internal zones against the North African platform caused ejection of the flysch nappes.
The stratigraphy, sedimentary environments and palaeogeography of the Silurian strata of Clare Island, Co. Mayo, Ireland
Authors: PHILLIPS W. E. ADRIAN
Published: December 2007

The Silurian succession of Clare Island, consisting of at least 1700 m of red siltstones, sandstones and conglomerates resting unconformably on Upper Dalradian and older basement, records a cycle of marine transgression and regression within marginal marine and fluviatile sedimentary environments along the northern margin of the Silurian basin of Ireland. Clastic and pyroclastic sediments of probable Wenlock age were derived from a northern land mass formed of high grade metamorphic rocks cut by acid volcanic centres. It is argued that the source area has been removed by large scale strike-slip fault movement along a fracture zone which previously controlled the margin of the Silurian basin
Seismic reflection profiles of the continental margin bordering the Rockall Trough
Authors: BAILEY ROBIN J. , GRZYWACZ JAN M. , BUCKLEY JOHN S.
Published: December 2007

From 25 seismic reflection profiles of the continental margin of the British Isles bordering the Rockall Trough (54° to 57°n Lat.), 15 are selected for description. They reveal a marginal sedimentary succession recording two major phases of subsidence and sedimentation, with an intervening phase of uplift and erosion. Although the Rockall Trough may well date from late Jurassic or early Cretaceous times, a late Cretaceous age of the first phase of subsidence and sedimentation is likely during which a marginal prograding sedimentary series was deposited. The ensuing phase of uplift and erosion is equally tentatively referred to the Palaeocene Epoch. The subsequent transgression and deposition of the overstepping upper sedimentary series is of possible Eocene to Recent date.

There is evidence to suggest that, in addition to these regional phases of subsidence and uplift, the continental margin at 55°20'n Lat. suffered faulting involving major east-west dextral displacement. This occurred prior to the deposition of the older prograding sedimentary series. The sense of movement within the fault zone, and the location and general trend of this zone, are appropriate for correlation with a prolongation or splay of the Great Glen Fault System.
The Daura igneous complex, N Nigeria; a link between the Younger Granite districts of Nigeria and S Niger
Authors: TURNER DAVID C. , WEBB PETER K.
Published: December 2007

The ring complexes of the Nigeria–Niger Younger Granite province occur in three separate districts: Air, the Zinder–é area of S Niger Republic and the Jos Plateau area of Nigeria. Together these form a north-south zone 1300 km long, characterized petrographically by alkaline granites and associated volcanic rocks, and structurally by ring dykes, volcanic cauldrons and high level granite plutons. The three districts are separated by areas of younger sedimentary rocks. Between Air and the S Niger district are Cretaceous rocks, filling the saddle between the sedimentary basins of Iullemmeden and Chad. Between the S Niger and Nigerian districts is an embayment of the Chad basin containing deposits of Pliocene to Pleistocene age (Fig. 1).

The Nigerian district is the best known (

Jacobson
et al.
1958

;

Buchanan
et al.,
1971

). Many of the complexes contain rhyolites within areas of cauldron subsidence. Intrusions into and beneath these rhyolites are mainly granitic but include minor syenites and gabbros. The granites contain such mafic minerals as fayalite, sodic amphibole and pyroxene and biotite. By far the most abundant type is biotite granite, often with tin and niobium mineralization. A Jurassic age of about 160 m.y. has been established for the Nigerian Younger Granites (

Jacobson
et al.,
1963

).

In the S Niger district (
Karpoff 1948
;
Black 1963
) most of the Younger Granite rocks are concentrated in the Mounio massif, which extends for over 100 km south from Gouré Rhyolites occur extensively, and the main intrusive rocks are peralkaline granites and syenites. Traces of cassiterite have
The depths inhabited by Silurian brachiopod communities
Authors: HANCOCK NIGEL J. , HURST JOHN M. , FÜRSICH FRANZ T.
Published: December 2007

The five Llandovery brachiopod communities have equivalents in the Wenlock and Ludlow; in addition the brachiopods spread into deeper environments where a sixth
(Visbyella)
community is described. Size, density and 'biomass' of brachiopods are shown to decrease with depth, while the diversity of the communities increases with depth. Comparison with modern analogues suggests that the deepest Wenlock and Ludlow communities inhabited depths as great as 1000 to 1500 m. In the Wenlock of Wales, the
Visbyella
community extends to the deepest parts of the basin, and there is no clear distinction between shelf and basin areas.
A gravity study of the Sabaloka igneous complex, Sudan
Authors: SADIG ABDELATI A. , ALMOND DAVID C. , QURESHI IFTIKHAR R.
Published: December 2007

The Sabaloka igneous complex of late Precambrian or Cambrian age consists of an elliptical ring dyke of porphyritic microgranite surrounding acid volcanic rocks in the southern half of the area and a basement composed mainly of biotite gneisses in the north. Sandstones of the Nubian formation locally overlie the igneous rocks and the basement. The complex is bisected and displaced by the Jebel Umm Marahik fault.

The igneous rocks have a density of 2.60 g cm
−3
and the biotite gneisses 2.65 g cm
−3
. A gravity low of about 8 mgal in the southern half of the complex indicates a thickness of about 5.5 km of lighter rocks, only 2 km of which can be volcanic, the rest being inferred to be intrusive granitic rocks. A gravity low in the northern half of the ring is indicative of a subsurface granitic intrusion with vertical thickness about 3 km. The ring dyke is intruded into a complicated ring fracture zone, in part a graben up to 2 km wide in which the basement rocks have subsided to a depth of 3 km or more. The outer contact of the ring dyke is steep but has a variable direction of dip—inward, vertical or outward. Gravity evidence for the course and throw of the Jebel Umm Marahik fault is presented and another roughly diametrical fracture trending at 50º to the former is postulated.
A geochronological study of the basement complex of Uganda
Authors: LEGGO PETER J.
Published: December 2007

Geochronological reconnaissance of the Uganda basement suggests that the Watian Granulites of the West Nile are the oldest rocks. These rocks have been closed chemical systems for at least 2880 m.y. although throughout the basement they have also been reactivated at about 2550 m.y. This reactivation is seen as a widespread migmatization event involving a calc-alkaline granitic host magma. Towards the Mozambique Fold Belt in E. Uganda the basement gneisses are involved in a much younger granitic injection phase that dates close to 650 m.y. and is therefore considered to be related to the Mozambique event. The Mirian gneisses of the West Nile, which are unconformable on the older granitic gneisses, contain 950 m.y. zircons. This evidence favours the Mirian event as being the metamorphic equivalent of the 1200 m.y. Karagwe-Ankolean sediments found to the south. A summary of the available ages on the Uganda basement is presented.
The structure and emplacement of the Rio Fortaleza Centred acid complex, Ancash, Peru
Authors: KNOX GORDON J.
Published: December 2007

The Rio Fortaleza centre is one of four known centred complexes of the Coastal Batholith and is a hypabyssal ring-dyke complex. Subterranean cauldron subsidence is represented by a bell-jar pluton, while a later ring-dyke may have produced subaerial pyroclastics associated with a caldera.

Inclusion screens represent the remnants of spalled-off country rock and ring-fault mylo-nites, tuffisites and gas breccias with limited hydrothermal mineralizations are indications of its high-level nature.

The two ring-dykes, some 22 km in diameter, are structurally controlled with polygonal outcrop patterns related to the regional joint pattern. At depth, the intersections of major wrench fractures may have focussed the magmas and delimited the symmetrical disposition of the four centres.

The centred complexes show a close relation between plutonism and vulcanism and prob­ably represent the basal remnants of caldera volcanoes that supplied some of the extrusive envelope of the batholith.
The geological interpretation of a gravity survey of the English Lake District and the Vale of Eden
Authors: BOTT MARTIN H. P.
Published: December 2007

The Lake District is dominated by an east-west belt of relatively low Bouguer anomaly which attains individual minima over the exposed Eskdale, Shap and Skiddaw granites. The negative anomaly is attributed to a composite granite batholith which underlies the central and northern parts of the Lake District, connecting the exposed granites at depth. Interpreting on the basis of surface density measurements, the granites appear to extend to a depth of about 7 to 10 km and the contacts with the country rocks generally slope outwards. There are substantial variations in density within the composite granite body. The roof region of the granite includes a series of shallow granite 'ridges,' one of these connecting the Eskdale and Shap granites, and another connecting the Ennerdale, St. John's, Threl-keld and Skiddaw granites. The Shap granite is probably connected to the Weardale granite by a deep granite ridge.

Present and past uplift of the Lake District may be attributed to the granite mass deficiency, which is estimated to be 1.1 × 10
18
g and is approximately equal to the present elevation of the Lake District above a 270 ft (82 m) datum.

The low gravity values along the Vale of Eden suggest that the Permo-Triassic rocks reach a maximum thickness of at least 1 km northeast of Penrith, and that these rocks formed during contemporaneous subsidence. The detailed gravity interpretation of the structure of the Vale of Eden allows a new assessment to be made of the structural history of the Pennine line which reconciles the Hercynian structures with the occurrence of Whin Sill or dyke pebbles in the Upper Brockram.
The volcanic geology and petrology of Montserrat, West Indies
Authors: REA W. JOHN
Published: December 2007

The island of Montserrat is made of the products of five major and three parasitic volcanoes of Pliocene to Recent age. Apart from South Soufrière Hill where some basalt lava flows and pyroclast falls occur, the volcanoes have erupted only andesites, mostly dome lavas and pyroclast flows. The Montserrat lavas belong to the calc-alkaline series. Major and trace element analyses of rocks and minerals are presented and used in a computer test which shows that fractionation of a basaltic parent could account for the composition of all the Montserrat lavas. Other considerations, notably of field relationships and relative volumes of rock types, suggest that andesites are produced in this way only at South Soufrière Hill. Alternative origins for the Montserrat lavas are considered briefly.
Features of submarine volcanoes shown on long range sonographs
Authors: BELDERSON ROBERT H. , KENYON NEIL H. , STRIDE ARTHUR H.
Published: December 2007

Reconnaissance of the Tyrrhenian Sea by the new method of long range side-scan sonar has provided plan view details of volcanic island slopes and seamounts. Some of the Aeolian Island slopes are notable for submarine cones fashioned into a radial pattern, probably by sliding of ashes and hyaloclastite debris. Other prominent features are NW–SE and NE–SW tectonic trends, a cliff at about 100–200 m below sea level around each island, and a channel system which is tributary to a major canyon. One large central-Tyrrhenian volcanic seamount (Vavilov) has a morphology which suggests construction from a succession of pillow lava flows, while another (Marsili) exhibits strong linear trends, probably mainly tectonic in character.
The structural and metamorphic geology of northern Malawi
Authors: RAY GERALD E.
Published: December 2007

N Malawi includes two main groups of rocks, the Jembia River Granulites to the south and the Misuku Gneisses to the north. The latter are separated into two distinct units, the Chambo and the Songwe Gneisses. The region lies at the junction of the Ubendian, Irumide and Mozambique Orogenic Belts and an insight into the structural history of the area has been gained by mapping and Rb–Sr, K–Ar age determinations.

The Ubendian deformation (pre-1800 m.y.), which was accompanied by granite intrusions, produced the dominant SE structural trend. A subsequent Irumide deformation (
c.
1100 m.y.) resulted in some weak N trending structures. The influence of the Irumide movements is believed to extend into S Tanzania.

The intrusion of the Songwe Syenite Complex (
c.
700 m.y.) occurred during the initial Mozambique deformation. This caused the realignment of many Irumide structures and generated folds whose geometry was controlled by the pre-existing Ubendian structural trend. The Mozambique folding was associated with movement along several shear zones; these include the Mugesse Shear Zone which forms a tectonic junction between the Songwe and the Chambo Gneisses. This shear is a major line of weakness which originated during the Ubendian Orogeny and was reactivated by the Mozambique deformation and recent rift faulting.

A tentative correlation is made between the Misuku Gneisses and rocks of the Ubendian Belt in Tanzania.
A structural cross-section of the Moine and Dalradian rocks of the Kinlochleven area, Scotland
Authors: TREAGUS JACK E.
Published: December 2007

The structure of the Dalradian rocks at the eastern end of Loch Leven has been re-exam­ined. The geometry of the major folds as determined by Bailey (1934) is largely confirmed but a reappraisal of their relative ages, based on the evidence of minor structures, leads to a new interpretation of the overall structure. The new interpretation is extended into the Moine in the Blackwater area. The dominant structural element is the Di Kinlochleven Anticline that faces down to the NW in the west of the area. To the east the lower, inverted, limb of this fold has been deformed by three D3 folds which restore it to an upward-facing attitude at the Moine-Dalradian boundary at Blackwater. A major deflection in strike of the earlier structures is attributed to the D4 Loch Leven Antiform. The relation of these structures to the regional structure is briefly considered.
Mapping of tidal currents near the Skerries Bank
Authors: ACTON JOHN R. , DYER CATHERINE M.
Published: December 2007

During the past five years data on tidal currents have been collected in Start Bay by several cooperating teams using a variety of methods. This paper reduces the data to a standard format, and then uses algebraic interpolation to construct contour maps. These show the variation of the peak current speeds and of the residual tidal currents over the Bay. The maps show that the residual currents are negligible along the spine of the Skerries Bank and it is proposed that this is an important factor in understanding the permanence of the Bank.
Beach stability and particle size distribution, Start Bay
Authors: GLEASON RAY , BLACKLEY MICHAEL W. L. , CARR ALAN P.
Published: December 2007

Monthly sampling showed that the granules and small pebbles of the bay beaches can display pronounced longshore grading from time to time but that the overall picture is complicated by changing beach height and slope, local variations between minor headlands, and sorting parallel with, normal to, and vertically through, the beach, rather than longshore adjustment alone. Particle size is reflected in geological composition.

A short term intensive study of part of the area, designed to show relationships between surface particle size and the wave parameters, only produced significant correlations on Slapton beach. These were between mean phi (
ø
) size and the square root of the significant wave height
(H

3

1/2

)
and, to a lesser extent, between mean ø size and direction of wave approach (θ°)

Thereafter, two tracer experiments using polyurethane-coated shingle were carried out on Slapton beach. Where statistically valid results were obtained it was shown that: there was virtually no correlation between wave parameters and sediment transport; maximum longshore transport corresponded with
smallest
particle size; differing factors (ø weight and frequency, linear parameters, ratios and shape indexes) assumed importance on different occasions and in different beach zones; recoveries at high, mid or low tide levels were often atypical of both the overall recovered population for that tide, and for the injected population.
Apollo and the geology of the Moon
Authors: SCHMITT HARRISON H.
Published: December 2007

The probability is very great that the geology of the decade of Apollo will become one of the fundamental turning points in the history of all science. For the first time the scientists of the Earth have been presented with the opportunity to interpret their home planet through the direct investigations of another. Mankind can be proud and take heart in this fact.

The interpretive evolution of the Moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows:

1. The Beginning—4.6 billion years ago

2. The Melted She11—4.6–4.4 billion years ago

3. The Cratered Highlands—4.4–4.1 billion years ago

4. The Large Basins—4.1–3 9 billion years ago

5. The Light-colored Plains—3.9–3.8 billion years ago

6. The Basaltic Maria—3.8–3.0 (?) billion years ago

7. The Quiet Crust—3.0 (?) billion years ago to the present

The Apollo explorations that permit us to study these stages of evolution each have contributed in progressive and significant ways. Through them we now can look with new insight into the early differentiation of the Earth, the nature of the Earth’s protocrust, the influence of the formation of large impact basins in that crust, the effects of early partial melting of the protomantle and possibly the earliest stages of the breakup of the protocrust into continents and ocean basins.
Sedimentation and tectonism (?Permo-Triassic) on the margin of the North Minch Basin, Lewis
Authors: STEEL RONALD J. , WILSON ALAN C.
Published: December 2007

The (?) Permo-Triassic Stornoway Formation is
c
. 4000 m thick and consists mainly of conglomerates.

The sediments were deposited on alluvial fans as mudflow, streamflood and braided stream deposits, and on floodplains as channel and overbank sediments. In each of the lower, middle and upper units of the Formation there is evidence of two major phases of alluvial fan-building. It is suggested that these phases were tectonically controlled and that within each alluvial fan sequence the time-trend of sedimentation reflects the rate of basin subsidence. Fining-upwards fan sequences suggest basin-margin faulting of gradually decreasing intensity; coarsening-upwards sequences suggest a history of increasing fault intensity. Floodplain deposits, overlying either type of sequence, indicate a cessation of tectonism and a gradual overlap of the old fault lines by fine-grained sediment.

The Stornoway Formation is seen as the sedimentary fill within the deep, western margin of an asymmetrical North Minch (Permo-Triassic) Basin. Palaeogeographic reconstructions through time suggest that this western margin shifted westwards as the locus of faulting and fault-generated sedimentation migrated by 15 km from the Minch Fault.
Rubidium–strontium ages and strontium isotope ratios from the igneous rocks of Leicestershire
Authors: CRIBB S. J.
Published: December 2007

The south Leicestershire diorites and the Charnwood southern diorites give Rb-Sr isochron ages of 546 ± 22 m.y. and 552 ± 58 m.y., respectively, indicating a late Precambrian to Cambrian age of emplacement. Their respective initial
87
Sr/
86
Sr ratios of 0.7056 ± 0.0001 and 0.7061 ± 0.0008 agree with analytical error.

Despite the large error produced by a small spread of Rb/Sr values an age of 311 ± 92 m.y. for the Charnwood northern diorites indicates that the group is younger than previously thought. The initial
87
Sr/
86
Sr ratio is 0.7068 ± 0.0004.

The Mountsorrel Complex gives an age of 433 ± 17 m.y. and an initial
87
Sr/
86
Sr ratio of 0.7070 ± 0.0002. This confirms a late Ordovician to early Silurian age for the intrusion.

An isochron for the Charnwood porphyroids is not presented because of an extremely small spread at Rb/Sr values. However initial
87
Sr/
86
Sr ratios are calculated for the group using likely ages between 500 and 700 m.y. The values obtained, 0.7046–0.7049, are significantly lower than any of the other rock groups studied.

The initial ratios of the porphyroids, diorites and granodiorites rule out melting or partial melting of ancient high level crustal rocks as a source. Values such as those determined could have been produced by the melting or partial melting of lower crustal and mantle rocks.
Cretaceous ammonite distributions and the opening of the South Atlantic
Authors: KENNEDY WILLIAM JAMES , COOPER MICHAEL
Published: December 2007

Analysis of distribution patterns of middle to late Cretaceous ammonites along the line of the opening S. Atlantic suggest that open marine connections, if not actual rifting, developed during early upper Albian times and extended continuously to the close of the Cenomanian. Evidence of early Turonian distributions is equivocal (due largely to an absence of early Turonian marine deposits in Southern Africa), but such evidence as is available also suggests continued connection. Palaeobiogeographic evidence is thus compatible with sea floor spreading and palaeomagnetic data, rather than in conflict, as previously suggested.
Geophysical maps of the eastern Caribbean
Authors: KEAREY PHILIP , PETER GEORGE , WESTBROOK GRAHAM K.
Published: December 2007

The results of marine geophysical surveys by NOAA, Miami and the University of Durham with the Royal Navy in the eastern Caribbean region are presented as maps of the bathymetry, free-air gravity anomaly, Bouguer gravity anomaly and total field magnetic anomaly These maps show in greater detail features which were already known, such as the negative gravity anomaly belt east of the Lesser Antilles, and reveal new features not previously mapped, such as easterly trending anomalies east of the Lesser Antilles and the complicated anomaly pattern of the Aves Ridge. They provide a detailed coverage of the area bounded by latitudes 10°N. and 17°N., and longitudes 57°w. and 65°w.
A radiogeologic study of the granites of SW. England
Authors: TAMMEMAGI H. Y. , SMITH N. L.
Published: December 2007

Sixty-four samples from various sites along the granite batholith of SW. England, from the surrounding country rock, and from Lundy Island have been analyzed for the radiogenic elements potassium, uranium and thorium. An overall picture emerges of a radioactive batholith, uniform along its length, emplaced in a normal and less radioactive country rock. Weathered and kaolinized granites are depleted in U and Th but not K, relative to fresh granite. A proportion of the uranium mineralization found in the region, as well as the many different ages determined for uraninite and coffinite mineralization, are probably caused by the remobilization of the uranium which has been leached from the granites. A traverse across the Dartmoor pluton revealed no marked differences between the megacrystic and poorly megacrystic granites. In contrast, the radiogenic concentrations of the fine grained granites which comprise parts of the Land's End and Carnmenellis plutons are atypical and are possibly rafts of assimilated country rock. Assuming that the radiogenic elements are distributed in exponentially decreasing amounts with depth, then the measured data are consistent with the formation of the batholith near the base. of an originally normal crust with a subsequent high-level emplacement.
Water weakening of quartz, and its application to natural rock deformation
Authors: JONES MERVYN E.
Published: December 2007

New experimental data show that the weakening effect of structure-bound water in the quartz lattice occurs at hydroxyl concentrations lower than those previously considered. This is used, along with analyses of the hydroxyl concentrations of naturally deformed quartz, to show that water weakening can explain low temperature plastic flow in quartz from low grade metamorphic environments.
Devonian lacustrine limestones at the margin of the Orcadian Basin, Scotland
Authors: DONOVAN R. NOWELL
Published: December 2007

A complex overlap of middle Old Red Sandstone occus in N. Caithness and Sutherland. The relief of the underlying surface of Moine metamorphics and intrusions is irregular. The facies variation of the sediments reflects lacustrine transgression and regression within the Orcadian Basin. When the lake level was high and the lake margin coincided with the basin margin, thick (
c.
4m) carbonates were deposited on the unconformity. Carbonate deposition was controlled by photosynthesizing algae. At such sites the depositional environment was oxygen-rich and the carbonates do not contain biotite, organic carbon or pyrite. The offshore facies was deposited in deeper stratified lakes, anoxic at depth, and comprises organically-enriched sediments (with pyrite and biotite). When the lake margin was not coincident with the basin margin alluvial sediments mantled the unconformity as rivers cut to a lower base level. At marginal sites compaction of the lacustrine sediments over the irregular basement during periods of low lake level, when no deposition occurred, produced local unconformities.
Rates of deformation
Authors: PRICE NEVILLE J.
Published: December 2007

Information relating to rates of deformation, that is strain-rates, is rare, partly because of the problems of determining strain, but mainly because of the difficulties encountered in determining the period during which any specific strain is generated. These practical difficulties are discussed and specific examples are presented of strain-rates involved in geological processes. These include slow strain-rates, relating to down warp and uplift, and fast strain-rates associated with meteoritic impact, volcanic activity and faulting. There follows a discussion of strain-rate associated with intrusive events and the rates of deformation which may obtain during folding are inferred from model data.
On the rate of emplacement of batholiths
Authors: PITCHER WALLACE S.
Published: December 2007

Determination of the rate of emplacement of batholiths is complicated by the complexity of a process involving segregation, intrusion and congelation, and by a lack of knowledge of the nature of granite magma. Times of uprise and freezing of individual pulses are of the order of a million years, possibly much longer for segration; rates which are similar to that of sea floor spreading. The construction of a composite batholith takes some 50–70 m.y. and although distinct episodes may be recognized locally it is likely to be, overall, a sensibly continuous process for a single, linear, consanguineous batholith such as that of coastal Peru.
Dredged rocks from Hatton Bank, Rockall Plateau
Authors: WATTS A. B. , SCHREIBER B. C. , HABIB D.
Published: December 2007

Three dredge hauls were obtained in 1973 by R/V Vema from the northern slopes of Hatton Bank. The most common rock types in each haul are arkosic and subarkosic arenite. The arkosic arenite is associated with other sedimentary rocks which include fossiliferous oolitic limestones. The age range of the limestones inferred from palynology is Cretaceous-Palaeogene. We argue that these rocks are of local origin and that they were formed near the margin of a shallow-water basin during the early separation of Rockall Plateau and Greenland.
Magnetic anisotropy and susceptibility of late Precambrian tillites from northwestern Scotland
Authors: ABOUZAKHM A. G. , TARLING D. H.
Published: December 2007

Graded siltstones of late Precambrian age from the Garvellach islands have previously been shown to contain directions of remanence that fall into two groups interpreted as ‘primary’ (acquired during deposition) and ‘Caledonian’ (acquired during low-grade metamorphism). The magnetic anisotropy of both groups is shown to be very low so that the directions of remanence must have been unaffected by any stress fields associated with the Caledonian orogeny. The original interpretation of the shallow inclination of ‘primary’ remanence as representing low palaeolatitudes is therefore unaltered. Changes of the degree of magnetic anisotropy with temperature also confirm that the regional temperature did not exceed 400°C during the Caledonian orogeny.
The Chinamora Batholith: diapiric intrusion or interference fold?
Authors: SNOWDEN P. A. , BICKLE M. J.
Published: December 2007

Mapping of the Chinamora Batholith of Rhodesia has revealed a complex suite of rock types which include old gneisses with infolded green-stone belt relics (metamorphosed to upper am-phibolite and granulite facies), intruded by a series of granitic
(s.l.)
bodies. The youngest of these granites is a distinctive porphyritic adamellite which is shown to have been deformed by two phases of tight folding. It is argued that the intensity of these deformations would effectively obscure any earlier intrusive relationship between the porphyritic adamellite (or older intrusive granites) and the greenstone belt rocks. The granite-greenstone distribution of the Chinamora area is explained as a large scale interference fold and it is suggested that small folds measured in part of the Chinamora Batholith as well as folds apparent on maps of the surrounding greenstone belt rocks can be related to this large scale folding.
The formation of crenulation cleavage
Authors: COSGROVE J. W.
Published: December 2007

Investigation of a theory of buckling of an anisotropic material has enabled the micro-folding of mineral fabrics to be more clearly understood. It is shown that “Crenulations” (microfolds) are associated with a variety of buckling instabilities which develop in stressed mineral fabrics or finely laminated multi-layers. Crenulation cleavage planes are generally formed as a consequence of mineral migration which occurs in response to stress gradients intimately associated with the developing microfolds.
Upper Carboniferous sedimentary cycles produced by river-dominated, elongate deltas
Authors: ELLIOTT T.
Published: December 2007

Coarsening upwards cycles in the upper Carboniferous Bideford Group of north Devon reflect the repeated progradation of riverdominated, elongate deltas. The cycles consist of
progradational sequences
(large-scale, prodelta to mouth bar coarsening upwards sequences, and major distributary channel sandstones),
aggradational sequences
(small-scale beach-spit coarsening upwards sequences and fining upwards crevasse channel sequences), and sporadically developed
abandonment fades
(thin, bioturbated siltstones and a coal horizon). Variations between cycles are governed principally by the location of bar fingers, and axial, lateral and (?) distal bar finger successions are distinguished.
Geochronology of the Channel Islands and adjacent French mainland
Authors: ADAMS C. J. D.
Published: December 2007

Rb-Sr whole-rock dating of igneous and metamorphic rocks of the Channel Islands region has delineated the following major events: 1) Formation of the Pentevrian basement gneisses
c.
2600 Ma ago in the northern Guernsey, Alderney and Cap de la Hague region. 2) Possible isotopic rejuvenation of these gneisses during a second metamorphic episode
c.
1950 Ma ago. 3) Formation of Pentevrian gneisses in the southern, St Malo-St Brieuc region, 1000–1100 Ma ago. 4) Deposition of the Brioverian sedimentary series in the interval 650–1000 Ma. 5) Emplacement of igneous rocks 650–690 Ma ago during initial phases of the Cadomian Orogeny (late Precambrian) followed by 6) a main regional metamorphic event 620–650 Ma ago, and 7) a post-metamorphic igneous phase 560–610 Ma ago. 8) On Jersey a further post-tectonic granite phase, 480–520 Ma, can be recognized

Within this framework, nearly 130 K–Ar and Rb–Sr mineral ages from the area are interpreted as reflecting initiation of cooling and uplift of the Cadomian orogen as a whole in late Precambrian or Cambrian times.

Only a very few, young minor intrusions are connected with Variscan orogenic events.

Some preliminary comparisons can be made with late Precambrian igneous and metamorphic rocks elsewhere in the Massif Armoricain, southern Britain, eastern Canada and U.S.A.
Early Phanerozoic annelid worms and their geological and biological significance
Authors: GLAESSNER M . F.
Published: December 2007

The earliest ‘shellly’ fossils deserve more detailed studies than they have received. Examination of the Cambrian genus
Volborthella
shows that it resembles in significant characters tubes of sabellariid worms, and on this basis the morphology and ecology of the animal can be reconstructed. The Cribricyathida, which include
Cloudina
and range from late Precambrian to lower Cambrian, are not related to Archaeoeyatha but are polychaete worm tubes with some structural characters which resemble those of serpulids. The problematic Angustiochreida
(Anabarites
etc.), of similar age, also show such resemblances. The first appearance in the geological record of mineralized skeletons (‘shelly fossils’), built according to various interrelated modes in annelids and in a different manner in other Metazoa, is not a suitable stratigraphic marker. The early differentiation of annelid worms can now be documented palaeontologically.
Deformation textures in metals
Authors: Dillamore I. L.
Published: December 2007

Compared with geological problems those encountered in understanding deformation texture (fabric) development in metals are fairly simple. The sample history is well documented, the material is usually single phase, any phase transformations have been at constant composition and the material has been 100 % dense throughout. For most technologically important metals the deformation occurs only by glide, for which lattice rotations causing preferred orientation development are readily analysed. The methods involved are given by Chin
et al.
1966.

The most important case for study in metals is that of the texture developed in rolling, which, in its most common form as used to roll sheet and plate, involves plane strain conditions. For this process f.c.c, metals (e.g. Cu and Al) should, according to the analysis (Dillamore & Katoh 1972), develop textures in which the principal feature is a spread of orientations from (110) [1
12
] to an orientation near to (211) [1
11
] (the indices (11, 4, 4) [8,
11
,
11
] are a good description for the actual orientation found), while b.c.c, metals (notably Fe) should develop the principal spread (112) [
1
10]–(8, 11, 11) [
11
, 4, 4]. It will be noted that the f.c.c, and b.c.c, textures are related by simply interchanging the indices denoting the rolling plate with those denoting the rolling direction. This is a direct consequence of the fact that the glide plane in the f.c.c, case is of the form {111} and the glide direction for b.c.c, metals of the form 〈111〉.

These textures are predicted
Fabric development in plastically deformed quartzite masses
Authors: Lister G. S.
Published: December 2007

Dislocation glide is an important mechanism allowing plastic deformation of quartzites. A computer program using the Taylor-Bishop-Hill analysis (
Taylor 1938
,
Bishop & Hill 1951
) has been used to simulate quartz fabrics. This method of analysis requires a knowledge of a) the possible dislocation systems that can operate, b) the critical resolved shear stresses on each system, and c) the deformation path. All of these factors determine the type of lattice rotations in the grains of the rock and hence the types of fabric produced. If basal a glide is the dominant slip system then the c-axes tend to lie near the shortening axis, while if prism c glide operates the reverse applies. If, however, prism a glide operates then it is difficult to predict the e-axis fabric.

It has been found that elements of an orien-pattern tation appear after only 30% shortening in specific angular relations to the kinematic stretching axes. With an increase in strain the patterns become more intense. Hence the fabric of superposed deformations reflect only the orientation of the kinematic stretching axes of the last stage of deformation with early patterns being rapidly obscured.

Through an intensive study of fabric transitions an ordering of deformation environments according to the c-axes pattern developed is possible. Thus it has been possible to predict the orientation patterns found experimentally by
Tullis (1970)
and Tullis
et al.
1973.
Transmission electron microscopy of experimentally and naturally deformed carbonates
Authors: Barber D.J. , Wenk H.R.
Published: December 2007

Studies of dislocation microstructures are being carried out on (I) experimentally deformed calcite crystals, (2) experimentally deformed limestones and (3) carbonates from the Central Alps deformed at different metamorphic grades. The aims of the work are to study deformation mechanisms in carbonates, the calcite/aragonite transformation, and to investigate sub-microscopic features in relationship to metamorphic grade.

Normal twinning (e) generally produces numerous dislocations and twin intersection generates very high local dislocation densities. Twinning in the cleavage plane(r) is also found and gliding on this plane is very disruptive at low temperatures producing small mosaic blocks by microcracking. The results of a limited study of limestones from the Bergell Alps show a good correlation between dislocation structures and supposed metamorphic grade and can be compared with a study of quartzites from the same region (

Liddell
et al.,
1974

).

Differences in the behaviour of dislocations in calcite and dolomite are apparent. Dislocations in recovered dolomite tend to be oriented in crystallographic directions, indicating directions of minimum line energy in the ordered structure. Effects of disorder and non-stoichiometry are seen in some grains, which contain lamellar features and branching arrays of faults, as yet unidentified.
The Whewell–Darwin controversy
Authors: CANNON W. FAYE
Published: December 2007

In formulating his approach to natural history in 1837–8, Darwin combined ideas and techniques from several areas, of which five are identified. But these do not show why he formulated such an all-embracing approach, going from geology to human instincts, morality, and aesthetic responses. The hypothesis presented here is that Darwin was responding to a Romantic view of natural history such as the one held by Willian Whewell. The Romantics challenged the adequacy of reductionist systems which, they said, could not explain the ‘higher’ faculties. Darwin sought a reductionist (‘materialist’) system which would meet the Romantic objections.
Structural style in slump sheets: Ludlow Series, Powys, Wales
Authors: WOODCOCK NIGEL H.
Published: December 2007

The slump deformation in sediments of the Montgomery Trough is described and compared with tectonic deformation. The structures within each slump sheet are systematically oriented with respect to the inferred palaeoslope. The slump folds have lognormal size distributions and their range of styles closely matches that of tectonic folds. Similar folds are rare, and deformed lineations show that buckling was important during slump fold formation. Axial microfold lineations and axial plane cleavages are associated with the slump folds. Also present is a spaced cleavage, thought to have formed in soft sediment.

Structural style cannot discriminate between slump and tectonic structures. The distinction may in many cases rely on subjective and uncommon features of soft-sediment deformation, such as the absence from folds of tension cracks and veins.
The Recent volcanology of Terceira, Azores
Authors: SELF STEPHEN
Published: December 2007

Terceira shows a great diversity of lavas and pyroclastics for an oceanic island and is noteworthy for voluminous production of peralkaline salic magma. Four volcanoes form the island; three are composed of both basic and salic rocks and one has only salic rocks exposed. Since the emergence of the island a compositionally bimodal population of rocks has been represented.

The products of over 100 eruptions in the upper Terceira Group have been recognised. These include ignimbrites, pumice fall deposits, salic lava extrusions, strombolian scoria deposits, basaltic lava flows and littoral (surtseyan) basaltic tuffs. Basaltic activity is concentrated along a fissure zone which bisects the island diagonally from NW to SE and may be the subaerial expression of the Terceira Rift. Volumetric studies show the rate of accumulation of new crust along this small spreading centre; 5.46 km
3
of new material has been erupted on the island in the past 23 000 years, of which over 4 km
3
is of comendite–pantellerite composition.

The pumice fall deposits are of
sub-plinian
type characterised by smaller dispersal areas than plinian deposits, inverse grading of pumice and internal stratification. The pumice deposits were produced by eruptions of lower explosivity than those which occur on other Atlantic islands, which are interpreted as resulting from lower magmatic gas contents.
‘Older’ granites as time-markers in Dalradian evolution
Authors: BRADBURY H. J. , SMITH R. A. , HARRIS A. L.
Published: December 2007

The ‘older’ granites of Perthshire were emplaced in the Dalradian between the second and third deformation episodes of a Caledonian D1–D4 sequence.

Pankhurst & Pidgeon (1976) have furnished a zircon U-Pb and Rb/Sr whole-rock age (514 +6/–7 Ma) for emplacement of the Ben Vuirich granite which provides a minimum age for the D2 event. A somewhat younger Rb/Sr whole-rock isochron age (491 ± 15 Ma) obtained from the Dunfallandy Hill granite may date D3.

Migmatisation which occurred in the D2–D3 interval is, by inference, also dated.

Dl and D2, which deform Arenig rocks of the Southern Highlands Group are pre-514 Ma events implying a pre-514 Ma time base for the Ordovician.
Configuration of the geomagnetic field in early Tertiary times
Authors: HAILWOOD E. A.
Published: December 2007

An analysis of early Tertiary palaeomagnetic data from the Pacific, North America, Greenland and European plates is presented. A correction for discrepancies in palaeomagnetic directions and pole positions of this age resulting from plate motions has been attempted by means of two independent techniques: (i) palaeoequator determinations from Deep Sea Drilling Project Pacific cores, and (ii) identification of the Icelandic hot spot as a fixed reference frame. The corrected palaeomagnetic data from the Pacific and North American plates are inadequate to allow firm conclusions to be drawn, but the data from Greenland and Europe appear to indicate that the time-averaged departures of the geomagnetic field from a centred axial dipole configuration during the past 25 Ma, identified by R. L.
Wilson (1970)
, might in fact have persisted for at least 53 Ma.
Early basic bodies in the type Laxfordian complex, NW Scotland and their bearing on its origin
Authors: DAVIES F. B. , WATSON J. V.
Published: December 2007

Two views on the origin of the Laxfordian gneiss complex have been proposed (1) that it was formed by the repeated modification of gneisses originally produced during early Scourian ( = Badcallian) metamorphism at about 2700 Ma and (2) that it was derived from metamorphism of a post-Badcallian supracrustal series. The paper describes, from the type Laxfordian complex, remnants of metamorphosed layered basic-ultrabasic bodies which can be matched in terms of individual rock-types and of the total rock-assemblage with pre-Badcallian layered intrusives in the adjacent Scourian complex. The wide distribution and structural relationships of these remnants show that much of the Laxfordian complex is derived from pre-Badcallian parent rocks. Field evidence supports the view that the distinctive geochemical features of the Laxfordian complex (high K, Rb, U, Th relative to the depleted granulites of the Scourian complex) were established in pre-Laxfordian times and suggests that differences in the history of granitic intrusion during Scourian events may have been a more important factor in establishing these features than differences in the crustal level at which metamorphism took place.