The history of ideas on boudinage is outlined, and observations in Perthshire are described. Some implications of the “necking hypothesis” are examined.

Several recent plate reconstructions of the Iapetus Ocean describe the margins of Baltica as passive until Silurian collision with Laurentia. Yet there is a variety of evidence to suggest that the accretion of the Scandinavian Caledonides began by latest Cambrian—early Ordovician subduction and imbrication of the passive continental margin. One such evidence is provided by eclogites occurring in the Seve Nappe Complex. Previous work by others dated the high-pressure metamorphism at 503±14 Ma (Sm—Nd garnet-omphacite age), and the uplift through the c. 500°C isotherm at 491±8 Ma (40Ar/39 Ar hornblende plateau ages). The protolith dolerites of the eclogites have been correlated with Iapetan rift-facies dolerites of the Baltoscandian margin. If valid, such a correlation implies early Caledonian destruction of the margin, and thus modification of those plate reconstructions which require passive margins around Baltica in latest Cambrian-early Ordovician time. This paper provides a substantially improved basis for the concept that the protoliths of eclogites and their host rocks derived from Baltoscandian rift basins. The chemical similarity between coronitic dolerites and dolerites of the rift basins pertains not only to element concentrations and variations but also to the specific T-MORB signature shared by the two groups. The variation of psammitic and pelitic schists, graphitic schists, calc-silicate gneisses and marbles of the eclogite host rocks equates with sequences of sandstones, siltstones, shales, black shale, quartzite, dolomite and limestones of Baltoscandian palaeobasins.

At the same time, the paper calls attention to the remarkable preservation of structural and metamorphic contrasts within the eclogite-bearing thrust sheets of the Seve Nappe Complex. Such disequilibrium is generally ascribed to the kinetics of localized deformation and fluid infiltration into dry crust. This paper presents evidence that disequilibrium is found also within inferred subducted sedimentary complexes, which are generally assumed to be pervasively flushed by fluids. Preservation of sedimentary, volcanic and magmatic structures and fabrics, and of both undeformed dolerite dykes and eclogitized dykes demonstrates that neither deformation nor high-pressure metamorphism were pervasive.

Pleistocene deposits near Homa were first visited by Dr. F. Oswald (1914), who described the exposures at Kanjera. Dr. L. S. B. Leakey and his colleagues of the 1931–2 East African Archaeological Expedition located human remains while collecting the fauna of the beds, and the importance of this discovery led to resumption of work on the area by the 1934–5 expedition to which the writer acted as geologist, and to a special study of the geology of the area and provenance of the human remains, for which Professor P. G. H. Boswell joined the expedition at Dr. Leakey's invitation, his visit being facilitated by the Royal Society. Mr. E. J. Wayland, of the Uganda Geological Survey, also spent a short period with the expedition before Professor BoswelPs return. It was a sad disappointment to ali concerned that the early date of the human remains could not be established with certainty (Boswell, 1935), but in tne present note it is proposed to describe the geology of the deposits, which is itself of considerable interest.

The historical background of correlations between various Dalradian successions is examined, and on the basis of recent mapping and observations it is suggested that the Ballachulish succession is the downward extension of the standard Perthshire sequence.

Lower Cretaceous pedogenic carbonates exposed in SE China have been dated by U–Pb isotope measurements on single zircons taken from intercalated volcanic rocks, and the ages integrated with existing stratigraphy. δ13C values of calcretes range from –7.0‰ to –3.0‰ and can be grouped into five episodes of increasing–decreasing values. The carbon isotope proxy derived from these palaeosol carbonates suggests pCO2 mostly in the range 1000–2000 parts per million by volume (ppmV) at S(z) (CO2 contributed by soil respiration) = 2500 ppmV and 25°C during the Hauterivian–Albian interval (c. 30 Ma duration). Such atmospheric CO2 levels are 4–8 times pre-industrial values, almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants. Rapid rises in pCO2 are identified for early Hauterivian, middle Barremian, late Aptian, early Albian and middle Albian time, and rapid falls for intervening periods. These episodic cyclic changes in pCO2 are not attributed to local tectonism and volcanism but rather to global changes. The relationship between reconstructed pCO2 and the development of large igneous provinces (LIPs) remains unclear, although large-scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas. Suggested levels of relatively low pCO2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope (δ13C) excursions characteristic of the oceanic anoxic events OAE1a (Selli Event), Kilian and Paquier events (constituting part of the OAE 1b cluster) and OAE1d. Short-term episodes of high pCO2 coincide with negligible carbon isotope excursions associated with the Faraoni Event and the Jacob Event. Given that episodes of regional organic carbon burial would draw down CO2 and negative δ13C excursions indicate the addition of isotopically light carbon to the ocean–atmosphere system, controls on the carbon cycle in controlling pCO2 during Early Cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity.

Detrital zircon U-Pb ages for 30 Late Jurassic and Cretaceous sandstones from the Eastern Province of eastern New Zealand, combined with previously-published geochronological and palaeontological data, constrain the time of deposition in the Pahau and Waioeka terranes of the Cretaceous accretionary margin of Zealandia, and their adjacent cover strata. The zircon age patterns also constrain possible sediment source areas and mid-Cretaceous geodynamic models of the transition from basement accretionary wedge to passive-margin cover successions. Pahau Terrane deposition was mainly Barremian to Aptian but continued locally through to late Albian time, with major source areas in the adjacent Kaweka and Waipapa terranes and minor inputs from the inboard Median Batholith. Waioeka Terrane deposition was mainly Albian, with distinctive and exclusive sediment sources, principally from the Median Batholith but with minor inputs from the Western Province. Alternative tectonic models to deliver such exclusive Median Batholith and Western Province-derived sediment to the mid-Cretaceous Zealandia continental margin are: (1) the creation of a rift depression across Zealandia or (2) sinistral displacement of South Zealandia with respect to North Zealandia, to expose Western Province rocks directly at the Zealandia margin. Detrital zircon age patterns of Cretaceous cover successions of the Eastern Province of eastern New Zealand demonstrate purely local sources in the adjacent Kaweka and Waipapa terranes. Cretaceous zircon components show a decline in successions of late Early Cretaceous age and disappear by late Late Cretaceous time, suggesting the abandonment or loss of access to both the Median Batholith and Western Province as sediment sources.

The Tremadoc to early Llanvirn is the time interval in the Ordovician for which a global acritarch distribution pattern can be proposed. It is possible to differentiate a high latitude, cold- to temperate-water realm and a low latitude, warm-water realm. The cold-water assemblages, recorded from numerous localities at the northern border of Gondwana in the southern hemisphere, include some diagnostic morphotypes, such as Arbusculidium filamentosum, Arkonia, Aureotesta, Coryphidium-Vavrdovella, Dicrodiacrodium, Frankea and Striatotheca. Assemblages related to warm-water areas are described from Canada, the United States, northern China, Australia, and Baltica. Although a distinction of separate provinces within the cold-water and warm-water realms is difficult, the differentiation between these two units appears evident and a distinction of the assemblages from peri-Gondwana and the microfloras from Baltica is possible. This enables a recognition of the Trans-European Suture Zone in the early to middle Ordovician.

The Chinese Altai is renowned for its rich rare-element resources. Nine representative rare-element (REL) pegmatites were dated using LA-ICP-MS and 40Ar–39Ar methods. The columbite grains yield a weighted mean 206Pb/238U age of 239.6±3.8 Ma for the Dakalasu (Be-Nb-Ta) pegmatite and concordia U–Pb ages of 258.1±3.1 Ma and 262.3±2.5 Ma for the Xiaokalasu (Li-Nb-Ta) pegmatite. The zircons display a weighted mean 206Pb/238U age of 198.5±2.5 Ma for the Husite (Be) pegmatite and concordia U–Pb ages of 194.3±1.6 Ma and 248.2±2.2 Ma for the Qunkuer (Be) and Taerlang (barren) pegmatites. The muscovite 40Ar–39Ar dating gives plateau ages of 286.4±1.6 Ma, 297.0±2.6 Ma, 265.2±1.5 Ma, 178.8±1.0 Ma, 162.2±0.9 Ma, 237.7±1.3 Ma, 237.4±1.2 Ma and 231.9±1.2 Ma for the Talate (Li-Be-Nb-Ta), Baicheng (Nb-Ta), Kangmunagong (barren), Husite (Be), Qunkuer (Be-Nb-Ta), Xiaokalasu (Li-Nb-Ta), Weizigou (Be) and Taerlang (barren) pegmatites, respectively. These new ages coupled with previous geochronological work suggest that the REL pegmatites in the Chinese Altai formed during early Permain – Late Jurassic time. The REL pegmatites located in the Central Altaishan terrane are younger than those in the Qiongkuer–Abagong terrane, showing a correlation with the coeval and adjacent granites. The formation of the REL pegmatites and these granites indicates frequent and strong magmatic activity in the post-orogenic and anorogenic setting. The spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the SE (of age early–middle Permian), to the NW (middle Permian – Middle Triassic) and finally to the central part (Middle Triassic – Jurassic) of the Chinese Altai.

The Desert de les Palmes area, in the southeast Iberian Chain, belongs to a Mesozoic NE–SW high which separated the early Cretaceous basins of the Maestrat and Aliaga-Penyagolosa from the little Orpesa basin. Its structure is characterized by the development of a system of NE–SW to ENE–WSW extensional listric faults detached in a shallow upper crustal level (1.7–2.2 km), mostly affecting the pre-Upper Cretaceous rocks. These faults record two well-differentiated rifting periods: (1) a first late Triassic–early Jurassic rifting period that divided the Desert de les Palmes high in several blocks; (2) a second early Cretaceous rifting period, only developed in the eastern margin of the Desert de les Palmes high, which was related to the opening of the Maestrat, Aliaga-Penyagolosa and Orpesa basins. Based on the comparison of the main features of this Mesozoic structure with an analysis of the structural and subsidence data already known in the neighbouring Mesozoic basins (Maestrat, Aliaga-Penyagolosa and Columbrets), a geodynamic scenario for the crustal evolution of the eastern Iberian Chain is also suggested. This involves four evolutionary stages: (1) Triassic rift (late Permian–Hettangian); (2) early and middle Jurassic postrift (Sinemurian–Oxfordian); (3) late Jurassic and early Cretaceous rift (Kimmeridgian–middle Albian), which includes a short Hauterivian postrift period; and (4) late Cretaceous postrift (late Albian–Maastrichtian).

In order to obtain further evidence for the tectonic environment of generation of the basaltic rocks of the Ballantrae igneous complex, specimens of pillow lavas, dolerites, glaucophane schists and amphibolites were analysed for Ti, Zr, Y and Nb. Using Ti–Zr–Y, Ti–Zr and Y/Nb diagrams, three different genetic groups have been distinguished – (i) hot-spot basalts round Downan Point, round Bennane Head as far N as Balcreuchan Port, and also within serpentinite around Lendalfoot, (ii) island arc low-potassium tholeiites between Balcreuchan Port and Gamesloup, and (iii) possible ocean floor basalts at Knockormal and Knocklaugh. The interrelationships of these groups are in doubt. The hot-spot basalts may have been erupted through oceanic crust, but they could have formed prior to, or subsequent to, the island arc activity. More likely, the hot-spot basalts formed (possibly on oceanic crust) at a considerable distance from the island arc, and the two were later brought together tectonically, probably at the subduction zone associated with the arc.

The tectonic setting of the southern Menderes Massif, part of the western Anatolide belt in western Turkey, is characterized by the exhumation of deeper crustal levels onto the upper crust during the Eocene. The lowermost tectonic units of the Menderes Massif are exposed in the Çine Massif, where Proterozoic basement orthogneisses of the Çine nappe are in tectonic contact with Palaeozoic metasedimentary rocks of the Selimiye nappe. In the southern Çine Massif, orthogneiss and metasedimentary rocks are separated by the southerly dipping Selimiye shear zone, preserving top-to-the-S shearing under greenschist facies conditions. In contrast, in the western Çine Massif, the orthogneiss is deformed and mylonitic near the contact with the metasedimentary rocks. The geometry of the mylonite zone and the observed shear directions change from north to southwest. In the north, the mylonite zone dips shallowly to the north, with top-to-the-N shear sense indicators showing northward thrusting of the orthogneiss over the metasedimentary rocks. In the southwest, the mylonite zone resembles a steep N–S striking strike-slip shear zone associated with top-to-the-SSW sense of shear. Overall, the geometry of the mylonite shear zone is consistent with northward movement of the orthogneiss relative to the metasedimentary rocks. Different shear senses are attributed to strain partitioning.

AFM diagrams and P–T pseudosections with mineral parageneses of metasedimentary rocks of the Selimiye nappe and metasedimentary enclaves within the orthogneiss of the Çine nappe indicate a single Barrovian-type metamorphism. An earlier higher pressure phase is evident from staurolite–chloritoid inclusions in garnets of the Çine nappe, suggesting a clockwise P–T path. A similar path is inferred for the Selimiye nappe. Index minerals and the sequence of mineral parageneses point to a single amphibolite facies metamorphic event affecting metasedimentary rocks of both nappes, which predates Eocene emplacement of the high pressure–low temperature Lycian and Cycladic blueschist nappes. Northward thrusting of the orthogneiss onto the metasedimentary rocks of the Selimiye nappe is coeval with amphibolite facies metamorphism. Recently postulated polymetamorphism cannot be supported by this study. Petrological data provide no evidence for burial of the lower units of the Menderes Massif to depth greater than 30 km during closure of the Neo-Tethys. A major pre-Eocene tectonic event associated with top-to-the-N thrusting and Barrovian-type metamorphism could lend support to the idea of a Neo-Tethys (sensu stricto) suture south of the Menderes Massif and below the Lycian nappes.

Rapakivi granites and several small leucogabbroic and gabbroic bodies are located in the Rangnim Massif, North Korea. The largest batholith in the Myohyang Mountains covers an area of 300 km2 and was intruded into Precambrian metamorphosed rocks. It has a SHRIMP U–Pb zircon weighted mean 207Pb/206Pb age of 1861 ± 7 Ma. The country rocks of rapakivi granites are Neoarchaean orthogneisses and Palaeo-Mesoproterozoic graphite-bearing metasedimentary rocks of granulite facies, and they are similar to those of the rapakivi granites and anorthosites exposed in South Korea and in the North China Craton. We conclude that the three massifs in the Korean Peninsula commonly record an identical Palaeo-Mesoproterozoic anorogenic magmatic event, indicating that they have a common Precambrian basement with the North China Craton.

Conodont faunas from the Eoplacognathus pseudoplanus Zone in five main areas of Middle Ordovician rocks in Sweden are described and discussed and compared with faunas of comparable age from neighbouring areas. The investigation is based on 118 samples which together yielded 175 114 conodont elements. The Swedish conodont faunas are intermediate between shallower-water faunas from the eastern part of Baltica and deeper-water faunas towards the west. Correlation with the Yangtze platform of south-central China is fairly easy, and the occurrence of key taxa, such as Histiodella, makes it also possible to correlate some levels with Laurentia. Although faunal lists for the Swedish localities are almost identical, the conodont taxa have their relative abundance maxima in separate areas: species of Protopanderodus and Periodon are most common in deeper-water settings, Eoplacognathus, Baltoniodus and Microzarkodina characterize intermediate areas, and Semiacontiodus is typical of shallow subtidal environments

New material of dsungaripterid pterosaurs from the Early Cretaceous of Tatal, western Mongolia, allows the diagnoses of Dsungaripteridae and Noripterus to be amended. All pterosaurs found at Tatal belong to Dsungaripteridae (either Dsungaripterus or Noripterus). The name Phobetor is a junior synonym of Noripterus. The differing shapes of the anterior tips of skulls, differing tooth morphologies and the coexistence of both Dsungaripterus and Noripterus may imply that they occupied distinct ecological niches.

Simple trace fossils are reported from three localities in central Spain within a monotonous succession of shale and greywacke and classical turbidites attributed to the Neoproterozoic (Riphean) Lower Alcudian megaunit. The Lower Alcudian strata are believed to have a complex tectonic history including deformation during the Pan-African Orogeny. Chronostratigraphic control is not available for this structurally complex succession and fossil evidence is sparse. Here we report on a low-diversity ichnofossil association including the ichnospecies (isp.) Gordia marina Emmons, 1844, Gordia isp., G. aff. arcuata Książkiewicz, 1977. The stratigraphically inferred Proterozoic age of the rocks, added to the present ichnofossil association, suggests that colonization of deeper waters started before the early Cambrian. We further consider that the plausible oxygen requirements of marine invertebrate(s) which produced the present ichnofossil taxa may well have exceeded the oxygen levels in a largely dysaerobic environment. A circulation model proposed by one of us (Palacios, 1989), implying the presence of extensive upwelling and descending oxygen-rich waters, helps to explain the continuous colonization of deep-water settings in Lower and Upper Alcudian strata. We argue that the ichnofaunal record of strata older than 650 Ma is both rare and inconclusive. Moreover, the present ichnofauna, being similar to ichnofaunal associations in environmentally comparable Upper Alcudian strata, is largely documented from Neoproterozoic (Vendian) and early Palaeozoic associations elsewhere. We conclude that the new ichnofossil evidence is consistent with a Vendian or younger age for the Lower Alcudian megaunit. This view is also consistent with a recently published maximum deposition age of 565 Ma inferred from U–Pb datings of detrital zircons from the supposedly much older (Middle Riphean) Tentudia Group or ‘Serie Negra’, that appears roughly time-equivalent with Lower Alcudian strata. It thus may appear that basin formation and flysch deposition in central Iberia encompass a minor segment of Neoproterozoic time, being probably limited to the Vendian. By default, formerly postulated Pan-African deformation of Neoproterozoic Lower Alcudian strata appears implausible. We further conclude that the complex pre-Phanerozoic structural history of Alcudian strata is probably restricted to Cadomian and younger deformation. Former structural models need substantial revision.

Potassium–argon ages of a variety of rocks and minerals from the Cheviot Hills, northern England, lie in the range 390 m.y. to 370 m.y. The Cheviot granite, dated at 380 m.y., has an age similar to that of many of the younger members of the British late Caledonian granites.

Fingerprints of the opening of the Western Black Sea Basin and collision of Pontides and Sakarya Continent along the Intra-Pontide suture can be traced in the area between Cide (Kastamonu) and Kurucaşile (Bartin) in northern Turkey, along the southern coast of the Black Sea. The Western Black Sea Basin is an oceanic basin opened as a back-arc basin of the northward-subducting Intra-Pontide Ocean. Basement units related to this opening are represented by Lower Cretaceous and older units. The first arc magmatism related to this subduction began during Turonian times. Coeval with this magmatism, back-arc extension affected the region and caused development of horst-graben topography. This extensional period resulted in the break-up of continental crust and the oceanic spreading in the Western Black Sea Basin during Late Santonian times. During the Late Campanian–Early Maastrichtian period, the Sakarya Continent and Pontides collided and arc magmatism on the Pontides ended. After this collision, the Western Pontides thickened, imbricated and developed a mainly N-vergent foreland fold and thrust belt character since Late Eocene–Oligocene times. The palaeostress directions calculated from thrust faults of this foreland fold and thrust belt are 4.6°/156.6° for σ1, 6.4°/66.1° for σ2, and 83.2°/261.9° for σ3. The nature of the imbrication indicates that it was a northward prograding foreland system connected to a floor thrust (detachment) fault at the bottom. Field observations on curved slickenfibres support the theory that the thrust faults of this imbricated structure have transformed to oblique thrusts and strike-slip faults over time.

Isotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The δ13C values of these carbonates are distinctly negative ( −5 to −3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive δ13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excursion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Namibia, and exceeds the magnitude of any post-Varanger δ13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post-Sturtian successions in western North America and elsewhere.

Study of arenite—rudite bodies within the traditional Welsh basin reveals two contrasted modes of situation, here termed concordant and discordant It is inferred that the former represent submarine fans developed on relatively level topography and the latter represent submarine channels adjacent to (and incising) major breaks in palaeoslope. The size and disposition of these palaeoslopes makes their control by deep fractures very probable.

Morphological features of brittle fracture in glass, ceramics and rocks include fracture origin, mirror plane, mist, hackle, radial striations and concentric undulations. The plume structure which characterizes many joint surfaces is analogous to striations or ‘grainy steps’ developed on fracture surfaces of ceramics. Joint surfaces with plumose structures result essentially from tensile failure, but may also be affected by shear stresses. The ellipticity of the plumose structure commonly observed reflects a region of secondary tensional strain parallel to bedding developed due to anisotropic elastic properties of the rock as a result of formational loading. Striations and hackles may have similar orientations. A distinction between them is important since hackles on a joint surface indicate a rapid fracture whereas striations can result from a slow fracture. Intense undulations without hackling may indicate a slow fracture. A smooth mirror plane on a joint surface indicates that while the fracture had been formed, stresses had reached a certain maximum and then subsided. On the other hand, a joint surface that shows a mirror plane with hackle around its boundaries indicates that no decrease of stresses occurred during fracture, and fracture was possibly produced under a constant stress. Since AH is a material property, the fracture stress σfresponsible for a rapid fracture may be calculated following a determination of the mirror constant AH of the rock by σfrH½=AH