ALBERT

Description: Organic-rich sediments were deposited in the deeper sectors of the Neuquen Basin during the latest Jurassic and the Early Cretaceous. This paper presents the results of a detailed examination of these deposits in the northern-most extension of the basin, in the Mendoza Province, and explores their wider significance for palaeo-oxygenation studies. The Tithonian--Berriasian Vaca Muerta Formation, the primary source rock for the Neuquen Basin, comprises bituminous shales and interbedded limestones deposited during a major transgression. In the Valanginian, the beginning of a regressive phase enabled the development of shallow-marine carbonates to form the base of the Chachao Formation, which eventually led to extensive biohermal carbonates of the uppermost Chachao Formation. Along the length of the narrow N-S-trending Mendoza Shelf of the Neuquen Basin both units are well exposed, permitting detailed study of the stratigraphy, sedimentology, ichnology and palaeoecology. The analysis of the Tithonian--Valanginian succession in the Salado river valley shows that carbonate production increased up-section. Faunal associations are mostly limited to poorly diverse epibenthos and pseudoplankton in the lower part of the section (Vaca Muerta Formation), with increased diversity in the lower Chachao section, including shallow and deeper infaunal bivalves. A background level of laminated shales to Chondrites bioturbation is typical of anoxic--suboxic conditions. Micritic limestones and carbonate sandstones throughout the section commonly show the development of Thalassinoides suevicus. Relative oxygenation curves based on trace fossils and body fossils were developed and compared. There was a primary substrate control on trace fossil diversity and occurrence, with a primary oxygenation signal provided by body fossil evidence. Interpretation of the palaeo-oxygenation on the basis of trace fossil taxa alone, however, would lead to inaccurate results. This study, therefore, demonstrates the importance of integrated trace and body fossil analysis in the fuller understanding of black shales.

Description: Structural geometries, faults and their movement histories, together with the petrophysical properties of flow units, are some of the major controls on hydrocarbon migration pathways within sedimentary basins. Currently, structural restoration, fault-seal analysis and hydrocarbon migration are treated as separate approaches to investigating basin geohistory and petroleum systems. Each of these separate modelling approaches in their own fields is advanced and sophisticated but they are not compatible with each other. Lack of integration produces incorrect palaeogeometries in basin models and inaccurate migration pathways. A combined structural restoration and fault-seal analysis technique, integrated with fast hydrocarbon migration pathway modelling code based on invasion percolation (IP) methods, is described. These modelling methods are used to develop a 4D basin modelling workflow in which evolving basin geohistories and geometries form an integral part of the analysis of hydrocarbon migration and trapping. By combining structural restoration and 3D fault-seal analysis it is possible to investigate the evolution of structurally complex traps through time. Integration of these techniques with a numerically fast migration pathway modelling technique allows hydrocarbon migration pathways and accumulations to be modelled through the evolution of the basin with time. Additionally, the effects of uncertainties in structural geometry, fault seal or any of the model input parameters can be explored using a risk-driven approach to modelling. These methods are demonstrated using synthetic, computer generated, 3D models and a well-constrained model of the Moab Fault, Utah, USA. Comparison of modelled structural geometries, fault-seal properties and predicted trapped hydrocarbons with outcrop data is used to validate the integrated modelling approach. The validated techniques are then applied to a seismically derived, 3D model from the southern North Sea, UK, to demonstrate how an integrated, risk-driven approach to modelling allows the effects of uncertainties in the distribution of hydrocarbon accumulations to be investigated.

Description: This article examines local myth and folklore related to earthquakes, landslides, and tsunamis in oral traditions from Cascadia (part of the northern Pacific coast of North America) and in written traditions from Japan, particularly in the Edo (present-day Tokyo) region. Local folklore corresponds closely to geological evidence and geological events in at least some cases, and the symbolic language of myth and folklore can be a useful supplement to conventional geological evidence for constructing an accurate historical record of geological activity. At a deep, archetypical level, Japan, Cascadia, and many of the world's cultures appear to share similar themes in their conception of earthquakes. Although folklore from Cascadia is fragmentary, and the written record short, the evolution of Japanese earthquake folklore has been well documented over a long period of history and illustrates the interaction of folklore with dynamic social conditions.

Description: The basal Ediacaran global boundary stratotype section and point (GSSP) horizon beneath Nuccaleena Formation cap dolostone in South Australia's central Flinders Ranges South Australia coincides with an interpreted unconformity preceding deglacial transgression. Detailed lithostratigraphy of three sections across the base of the Ediacaran System at its type area reveals contrasting character of the Elatina FormationNuccaleena Formation transition across c. 9 km of exposure, changing the interpretive context of the GSSP. We suggest that a locally pervasive, incisive flaser-bedded sandstone exposed between Elatina diamictites and Nuccaleena cap dolostone lies above an unconformity that correlates with the defined base of Wilpena Group, reflecting onset of terminal Elatina Snowball Earth' deglaciation and dynamic interplay between eustatic sea level change and isostatic rebound. Nuccaleena cap dolostone is sedimentologically mixed and conformable with underlying siliciclastics at Elatina Creek; hence the recently defined Ediacaran GSSP horizon, at the base of solid cap carbonate at Enorama Creek, lies in continuous section and not at an unconformity. Nuccaleena Formation cap dolostone contains pervasive terrigenous debris, including apparently detrital hematite. While magnetite and/or maghemite is produced in abundance upon heating of the cap carbonate above c. 400{degrees}C, and we cannot exclude secondary origin of any Nuccaleena magnetite, Nuccaleena Formation cap dolostone should preserve primary magnetization.

Description: The Dumfries Basin aquifer supports groundwater abstraction for public supply, agriculture and industry. Abstraction is concentrated in the western part of the basin, where falling groundwater levels and deteriorating water quality both reflect the effects of intense pumping. There are two bedrock units: a predominantly breccia-coarse sandstone sequence in the west, interfingering with a predominantly sandstone sequence in the NE and east. The basin is bounded by weakly permeable Lower Palaeozoic rocks, and is largely concealed by variable superficial deposits. Surface water flows onto the basin from the surrounding catchment via the Nith and the Lochar Water and their respective tributaries. Direct rainfall recharge occurs via superficial sands and gravels, especially in the north, and discharge is predominantly to the rivers in the central area rather than the sea. A picture is developing of two main aquifer types within the basin: the high-transmissivity western sector underlain by a fracture-flow system with younger water and active recharge and a high nitrate content, compared with the east where groundwater residence times are longer and the storage capacity is higher.

Description: The Pan-African Damara orogenic system records Gondwana amalgamation involving serial suturing of the CongoSao Francisco and Rio de la Plata cratons (North Gondwana) from 580 to 550 Ma, before amalgamation with the KalahariAntarctic cratons (South Gondwana) as part of the 530 Ma KuungaDamara orogeny. Closure of the Adamastor Ocean was diachronous from the Aracuai Belt southwards, with peak sinistral transpressional deformation followed by craton overthrusting and foreland basin development at 580550 Ma in the Kaoko Belt and at 545530 Ma in the Gariep Belt. Peak deformation/metamorphism in the Damara Belt was at 530500 Ma, with thrusting onto the Kalahari Craton from 495 Ma through to 480 Ma. Coupling of the Congo and Rio de la Plata cratons occurred before final closure of the Mozambique and Khomas (Damara Belt) oceans with the consequence that the Kuunga suture extends into Africa as the Damara Belt, and the Lufilian Arc and Zambezi Belt of Zambia. Palaeomagnetic data indicate that the Gondwana cratonic components were in close proximity by c. 550 Ma, so the last stages of the DamaraKuunga orogeny were intracratonic, and led to eventual out-stepping of deformation/metamorphism to the RossDelamerian orogen (c. 520500 Ma) along the leading edge of the Gondwana supercontinental margin.

Description: The West Antarctic Ice Sheet (WAIS) flows through the volcanically active, late Cenozoic West Antarctic rift system. Active subglacial volcanism and a vast (〉 106 km3) extent of subglacial volcanic structures have been interpreted from aerogeophysical surveys over central West Antarctica in the past decade, combined with results from 1960s and 1970s aeromagnetic profiles over the WAIS. Modelling of magnetic anomalies constrained by radar ice sounding shows volcanic sources at the base of the ice throughout large areas, whose subglacially erupted hyaloclastite edifices have been eroded by moving ice, as in Iceland. The 1800 m-high divide of the WAIS is underlain by the 400 km-long volcanic Sinuous Ridge, which rises above sea level; most hyaloclastite edifices there have also been glacially removed, indicating migration of the ice divide through time. Northeast of the divide of the WAIS there is a 400-nT positive magnetic anomaly over the shallowest, most rugged bedrock topography (elevation +380m above sea level), probably comprising subaerially erupted flows erupted when the Sinuous Ridge area was deglaciated. Uplift of the Sinuous Ridge may have forced the advance of the WAIS. Other aspects of the subglacial volcanism in Antarctica can be observed in Iceland and have a direct bearing on our understanding of the subglacial conditions of the WAIS and its dynamics.

Description: Concepts of differential geometry are reviewed, and it is demonstrated through examples that the main joint surface, rib marks and hackle of a joint may be described using parametric representations such that the first and second fundamental forms fully characterize these surfaces. Other useful quantities are the unit normal vector, the principal normal curvatures, and the Gaussian and the mean curvature. Sufficiently close to any point on a surface the shape is planar, parabolic, elliptical or hyperbolic. The surface of a joint in chert and another in siltstone were scanned and the resulting data analysed. Although the main joint surface of the chert sample is approximately planar, it is composed of low-amplitude undulations with elliptical and hyperbolic forms. The unit normal vector does not vary by more than about 3.4{degrees} over this surface, which is consistent with the threshold angle for the initiation of hackle based on laboratory experiments. An individual hackle is found to be approximately helicoidal in shape, but only in the breakdown zone. Rib marks on the siltstone sample have distinct and similar morphologies, with a concave base and convex peak. Field and laboratory campaigns designed to test hypothese about the geometry of joints should use the principles and tools of differential geometry.

Description: Basement inliers of high-grade metamorphic rocks within the eastern Colombian Andes record a Grenvillian history. Among them, the Garzon Complex and the Dibulla, Bucaramanga and Jojoncito gneisses were studied using different geochronological methods to produce better correlations in the context of the reconstruction of the Grenville belt and of the supercontinent of Rodinia. The dynamic evolution of all of these units includes a final collisional event with exhumation of high-grade rocks. Such a tectonic history bears strong similarities with the Grenville Province in Canada and seems to confirm that these domains took part in the aggregation of Rodinia. Mesoproterozoic U-Pb zircon ages indicate heritage from magmatic protoliths, and the Sm-Nd model ages, as well as the {varepsilon}Nd values, suggest derivation from an evolved continental domain, such as the Amazonian craton, with some mixing with juvenile Neoproterozoic material. When these continental fragments are correlated with similar terrains in Mexico and the Central Andes, a large crustal fragment is implied; very probably it made up the southern portion of the Grenville belt within Rodinia, which was disrupted when Laurentia separated from Gondwana forming the Iapetus Ocean, leaving behind cratonic fragments that were later accreted to the South American Platform.

Description: We demonstrate a non-contact approach to whole-core and split-core resistivity measurements, imaging a 15 mm-thick, dipping, conductive layer, producing a continuous log of the whole core and enabling the development of a framework to allow representative plugs to be taken, for example. Applications include mapping subtle changes in grain fabric (e.g. grain shape) caused by variable sedimentation rates, for example, as well as the well-known dependencies on porosity and water saturation. The method operates at relatively low frequencies (i.e. low induction numbers), needing highly sensitive coil pairs to provide resistivity measurements at the desired resolution. A four-coil arrangement of two pairs of transmitter and receiver coils is used to stabilize the measurement. One coil pair' acts as a control, enabling the effects of local environmental variations, which can be considerable, to be removed from the measurement at source. Comparing our non-contact approach and independent traditional galvanic' resistivity measurements indicates that the non-contact measurements are directly proportional to the reciprocal of the sample resistivity (i.e. conductivity). The depth of investigation is discussed in terms of both theory and practical measurements, and the response of the technique to a variety of synthetic structures' is presented. We demonstrate the potential of the technique for rapid electrical imaging of core and present a whole-core image of a dipping layer with azimuthal discrimination at a resolution of the order of 10 mm. Consequently, the technique could be used to investigate different depths within the core, in agreement with theoretical predictions.