Notes on late Cenomanian and Turonianammonites from Touraine,Western France

Recent collecting in the type area of the Turonian stage and adjacent parts of Touraine in western France provides new geographic and stratigraphic records as well as additional systematic information on species of the ammonite genera Puzosia, Watinoceras, Metoicoceras, Mammites, Prohauericeras, Collignoniceras, Lecointriceras, Subprionocyclus and Sciponoceras.     

A new interpretation of measured ionic diffusion coefficient in compacted bentonite-based materials

Previous model based on free-water properties to interpret the measured diffusion coefficient in compacted bentonite-based materials is demonstrated to be inadequate. A model considering ionic diffusion in clay surface (bound) and interstitial (free) water is presented to interpret the measured diffusion coefficients and to explain the possible reasons for the discrepancies in the data. The measured diffusion coefficient is determined by the predominant diffusion pathway, which depends on the charge of diffusing species, soil fabric, diffusion time and by the starting concentration condition of the method used.     

Evaluation of Methods for Determining Crack Initiation in Compression Tests on Low-Porosity Rocks

Laboratory testing of rocks is traditionally carried out to determine the peak strength using the ISRM Suggested Methods or other suitable standards. However, it is well known that in low-porosity crystalline rocks there are at least three distinct stages of compressive loading that can be readily identified if the stress–strain response is monitored during the loading process: (1) crack initiation, (2) unstable crack growth, i.e., crack coalescence and (3) peak strength. Crack initiation is noted as the first stage of stress-induced damage in low-porosity rocks, yet the suggested guidelines of the ISRM for compression tests make no mention of crack initiation. In addition, recent research suggests that crack initiation can be used as an estimate for the in situ spalling strength, commonly observed around underground excavations in massive to moderately jointed brittle rocks. Various methods have been proposed for identifying crack initiation in laboratory tests. These methods are evaluated using ten samples of ?sp? Diorite and the results are compared with a simplified method, lateral strain response. Statistically, all methods give acceptable crack-initiation values. It is proposed that the ISRM Suggested Methods be revised to include procedures suitable for establishing the crack-initiation stress.     

Feasibility of geoelectrical monitoring and multiphase modeling for process understanding of gaseous CO2 injection into a shallow aquifer

Potential pathways in the subsurface may allow upwardly migrating gaseous CO₂ from deep geological storage formations to be released into near surface aquifers. Consequently, the availability of adequate methods for monitoring potential CO₂ releases in both deep geological formations and the shallow subsurface is a prerequisite for the deployment of Carbon Capture and Storage technology. Geoelectrical surveys are carried out for monitoring a small-scale and temporally limited CO₂ injection experiment in a pristine shallow aquifer system. Additionally, the feasibility of multiphase modeling was tested in order to describe both complex non-linear multiphase flow processes and the electrical behavior of partially saturated heterogeneous porous media. The suitability of geoelectrical methods for monitoring injected CO₂ and geochemically altered groundwater was proven. At the test site, geoelectrical measurements reveal significant variations in electrical conductivity in the order of 15?C30?%. However, site-specific conditions (e.g., geological settings, groundwater composition) significantly influence variations in subsurface electrical conductivity and consequently, the feasibility of geoelectrical monitoring. The monitoring results provided initial information concerning gaseous CO₂ migration and accumulation processes. Geoelectrical monitoring, in combination with multiphase modeling, was identified as a useful tool for understanding gas phase migration and mass transfer processes that occur due to CO₂ intrusions in shallow aquifer systems.     

New data on the paleogeography of Southern Tuscany (Italy) since Late Miocene time

In order to add new data to the knowledge of the paleogeography of Southern Tuscany and the Tuscan shelf, a multidisciplinary study on the petrology and distribution of magmatic clasts of the widely exposed Messinian, Pliocene, and Quaternary sediments in Southern Tuscany was carried out. The magmatic clasts consist of porphyric aplites and subordinate granite porphyries, which derive from eroded subvolcanic acidic bodies. The porphyric aplite clasts were analyzed in detail to define their textural, petrographic, and chemical (major and trace elements, Sr and Nd isotopic composition) features. The porphyric aplite clasts show strong affinities with the 8.4–7.9 Ma old Capo Bianco aplite, whereas the granite porphyry clasts have affinities with the Portoferraio porphyry (ca. 8 Ma) which intruded the Cretaceous and Paleogene Flysch Units and the Ophiolitic Unit in central-western Elba Island (Northern Tyrrhenian Sea). The present outcrops of the Capo Bianco aplite in central Elba Island cannot be considered as the source rock for the Late Messinian gravels, because at that time such Capo Bianco aplite (located at the lower portion of the laccolitic stack) was there buried at several kilometers depth. However, other Capo Bianco-like aplitic bodies outcropped during the latest Miocene in the host rocks above and also around the 6.8 Ma M. Capanne Pluton in the western Elba areas. The exposure of such bodies was made possible by the activation of the central Elba detachment fault (=CEF), due to the uplift of the M. Capanne pluton. This uplift displaced a significant portion of the cover (including the upper portion of the laccolithic stack) of the granitoid body at about 6, 7 Ma, thus allowing the erosion of the lower part of the laccolith complex made up of the Capo Bianco aplite and of the Portoferraio porphyry and leaving still buried the M. Capanne pluton. The paleogeographic picture of Southern Tuscany arising from the collected evidences is the following: during Late Messinian, the clasts were dispersed by a SSW/NNE-trending complex fluvial system in the Colline Metallifere area. The Early Pliocene extensional tectonics cut off the detrital inputs from the Messinian source areas, because of the onset of the Piombino Channel and of the Campiglia–Gavorrano Ridge. During the Pliocene, the clasts were cannibalized from the previous sedimentary units and reached the easternmost areas due the eastward progressive uplift of the Colline Metallifere, likely connected with the coeval magmatic intrusions. Finally, the Quaternary regional uplift allowed a drainage reversal and a backward displacement of the aplitic clasts toward the Tyrrhenian coast. These data point to a rapidly evolving drainage pattern in Southern Tuscany during the considered time interval, which was mostly driven by the intrusion and uplift of the Messinian to Quaternary plutons. The morpho-tectonic evolution is well framed also within the models since long accepted for the Northern Apennine geodynamics, characterized by an overall eastward shift of the orogenic front.     

Landslide risk assessment and management: an overview

Landslides can result in enormous casualties and huge economic losses in mountainous regions. In order to mitigate landslide hazard effectively, new methodologies are required to develop a better understanding of landslide hazard and to make rational decisions on the allocation of funds for management of landslide risk. Recent advances in risk analysis and risk assessment are beginning to provide systematic and rigorous processes to enhance slope management. In recent years, risk analysis and assessment has become an important tool in addressing uncertainty inherent in landslide hazards.This article reviews recent advances in landslide risk assessment and management, and discusses the applicability of a variety of approaches to assessing landslide risk. Firstly, a framework for landslide risk assessment and management by which landslide risk can be reduced is proposed. This is followed by a critical review of the current state of research on assessing the probability of landsliding, runout behavior, and vulnerability. Effective management strategies for reducing economic and social losses due to landslides are described. Problems in landslide risk assessment and management are also examined.     

Well log interpretation and seismic character of the cenozoic sequence in the northern Alboran Sea

Seismic stratigraphic and main lithological features of the sedimentary cover overlying the basement of the Alboran Sea were established via the analysis of commercial multichannel seismic surveys, geophysical well logs, and well data. Six seismic stratigraphics units (VI to I), bounded by unconformities, form the marine sediments that range in age from early Miocene to Quaternary. They are dated by extrapolation of commercial drilling results from the northern Alboran Sea. Volcanic activity is recorded within sedimentary sequences of units V to II. Undercompaction features are detected in the two basal units.     

Synchronous peak Barrovian metamorphism driven by syn-orogenic magmatism and fluid flow in southern Connecticut, USA

Recent work in Barrovian metamorphic terranes has found that rocks experience peak metamorphic temperatures across several grades at similar times. This result is inconsistent with most geodynamic models of crustal over‐thickening and conductive heating, wherein rocks which reach different metamorphic grades generally reach peak temperatures at different times. Instead, the presence of additional sources of heat and/or focusing mechanisms for heat transport, such as magmatic intrusions and/or advection by metamorphic fluids, may have contributed to the contemporaneous development of several different metamorphic zones. Here, we test the hypothesis of temporally focussed heating for the Wepawaug Schist, a Barrovian terrane in Connecticut, USA, using Sm–Nd ages of prograde garnet growth and U–Pb zircon crystallization ages of associated igneous rocks. Peak temperature in the biotite–garnet zone was dated (via Sm–Nd on garnet) at 378.9 ± 1.6 Ma (2σ), whereas peak temperature in the highest grade staurolite–kyanite zone was dated (via Sm–Nd on garnet rims) at 379.9 ± 6.8 Ma (2σ). These garnet ages suggest that peak metamorphism was pene‐contemporaneous (within error) across these metamorphic grades. Ion microprobe U–Pb ages for zircon from igneous rocks hosted by the metapelites also indicate a period of syn‐metamorphic peak igneous activity at 380.6 ± 4.7 Ma (2σ), indistinguishable from the peak ages recorded by garnet. A 388.6 ± 2.1 Ma (2σ) garnet core age from the staurolite–kyanite zone indicates an earlier episode of growth (coincident with ages from texturally early zircon and a previously published monazite age) along the prograde regional metamorphic T–t path. The timing of peak metamorphism and igneous activity, as well as the occurrence of extensive syn‐metamorphic quartz vein systems and pegmatites, best supports the hypothesis that advective heating driven by magmas and fluids focussed major mineral growth into two distinct episodes: the first at c. 389 Ma, and the second, corresponding to the regionally synchronous peak metamorphism, at c. 380 Ma.     

The glacial and interstadial sediments at the Burn of Benholm,Kincardineshire: evidence for onshore pre‐Devensian ice movement in northeast Scotland

Pebbly clays and diamictons containing marine shell fragments and peat lenses exposed beneath subglacially deposited Late Devensian till at the Burn of Benholm provide new insights into the glacial history of Quaternary sequences in eastern Scotland. The peat yielded pollen of interstadial affinity (including Bruckenthalia spiculifolia) and non‐finite radiocarbon dates. Comparisons with other pre‐Late Devensian pollen records in northern Scotland suggest that the peat lenses are remnants of an Early Devensian interstadial deposit, of Oxygen Isotope Substage 5c or 5a age. Reworked faunal assemblages in the shelly sediments include Quaternary marine molluscs of low boreal aspect, as well as Mesozoic and Palaeozoic microfossils. Amino acid ratios from fragments of Arctica islandica suggest that the shells are of Oxygen Isotope Stage 9 age or older. The fabric and composition of the shelly sediments are consistent with their emplacement as deformation till during the onshore movement of glacially transported rafts of marine sediment. Folded and sheared contacts between the shelly deposits, peat lenses and the overlying Late Devensian till indicate that the fossiliferous sediments were glacitectonised during the main Late Devensian glaciation, when ice moved from Strathmore and overrode the site from the southwest. British Geological Survey. © NERC 2000.     

Natural and anthropogenic hydrocarbons in the Antarctic marine environment

The Antarctic marine environment contains a range of hydrocarbons at low concentrations, which are generally biogenic in origin. All major classes of hydrocarbons have been found in the Antarctic ecosystem. At present, anthropogenic input is very low and difficult to resolve from background levels. Pollution in the Antarctic is limited to only a few sources and although contamination can be locally chronic it is very restricted in extent. To date there have been few studies of hydrocarbon pollution and those available have been patchy in spatial coverage and generally lack time-series data. The low levels of natural hydrocarbons and restricted human activity make the Antarctic ecosystem suitable as an indicator of global hydrocarbon pollution.