Late Quaternary kinematics of the Pallatanga strike-slip fault (Central Ecuador) from topographic measurements of displaced morphological features

The northeast-trending Pallatanga right-lateral strike-slip fault runs across the Western Cordillera connecting N50E-N70E trending normal faults in the Gulf of Guayaquil with N-S reverse faults in the Interandean Depression. Over most of its length, the fault trace has been partly obscured by erosional processes and can be inferred in the topography only at the large scale. Only the northern fault segment, which follows the upper Rio Pangor valley at elevations above 3600 m, is prominent in the morphology. Valleys and ridges cut and offset by the fault provide an outstanding record of right-lateral cumulative fault displacement. The fault geometry and kinematics of this particular fault segment can be determined from detailed topographic levellings. The fault strikes N30E and dips 75 to the NW. Depending on their size and nature, transverse morphological features such as tributaries of the Rio Pangor and intervening ridges, reveal right-lateral offsets which cluster around 27 ± 11m, 41.5 ± 4 m, 590 ± 65 m and 960 ± 70 m. The slip vector deduced from the short-term offsets shows a slight reverse component with a pitch of about 11.5 SW. The 41.5 ± 4 m displacements are assumed to be coeval with the last glacial termination, yielding a mean Holocene slip-rate of 2.9- 4.6 mm yr⁻¹. Assuming a uniform slip rate on the fault in the long term, the 27 m offset appears to correlate with an identified middle Holocene morphoclimatic event, and the long term offsets of 590 m and 960 m coincide with the glacial terminations at the beginning of the last two interglacial periods.     

A new method for sampling and analyzing volcanic sublimates — application to Merapi volcano, Java

A new method for the sampling of sublimates from high-temperature volcanic gases has been used at Merapi volcano, Java, in 1978. The sublimates were collected on the inner walls of silica tubes introduced into fumarolic vents. Volcanic gases were allowed to move freely through the tubes and as they cooled, a fraction of the volatile components condensed on the inner walls of the tubes along the temperature gradient. The sublimates were then analyzed by a combination of light microscopy, scanning electron microscopy, electron microprobe and X-ray diffraction.Six successive zones of different compositions and mineralogical associations have been identified along the covered range of temperatures (900° to around 400°C). From the high to the low temperatures, these zones are composed of: (1) cristobalite, magnetite, hercynite; (2) molybdenite; (3) acmite; (4) halite, sylvite; (5) sphalerite, pyrite; and (6) galena. Equilibrium calculations show that these crystalline phases are stable for pS₂, pC₁, and pO₂, values typical of magma-buffered gases that have not been contaminated by atmospheric oxygen.The deposits observed in the tubes may be useful in aiding the understanding of the mechanisms acting during the cooling of the gaseous phase on its way to the surface and before its emission into the atmosphere.     

Tar ball frequency data and analytical results from a long-term beach monitoring program

Following the spill of fuel oils from the New Carissa in February 1999, approximately 300 km of beaches on the Pacific coast of North America were surveyed. A long-term observation program focused on the documentation of stranded tar balls in the vicinity of the spill site. Systematic beach surveys which were conducted over the period March 1999 to April 2001 and semi-logarithmic scale, time-series plots proved the most useful format for identifying trends. Beach monitoring continued through to August 2001. by which time 212 tar balls had been analyzed by GC/MS for their chemical characteristics. The samples of tar balls collected between February 1999 and August 2001 were qualitatively compared with New Carissa source oils (NCSO) and 101 (48%) were not consistent with NSCO. The presence of tar balls that are not related to an incident can confound attempts to define cleanup or endpoint criteria and to assess possible injury to natural resources.     

Post-collision neogene volcanism of the Eastern Rif (Morocco): magmatic evolution through time

Neogene volcanism in the Eastern Rif (Morocco) comprises a series of calc-alkaline, potassic calc-alkaline, shoshonitic and alkaline volcanic rocks. According to new stratigraphical, along with new and previous chronological and geochemical data, the orogenic volcanism was successively (1) calc-alkaline (basaltic andesites and andesites: 13.1 to 12.5 Ma, rhyolites: 9.8 Ma), (2) K-calc-alkaline (basaltic andesitic to rhyolitic lavas and granodiorites: 9.0 to 6.6 Ma), and (3) shoshonitic (absarokites, shoshonites, latites, trachytes: 7.0 to 5.4 Ma). The later Pliocene volcanism was basaltic and alkaline (5.6 to 1.5 Ma). The calc-alkaline and K-calc-alkaline series exhibit lower K₂O (0.7–5.3 wt.%), Nb (8–19 ppm) contents and higher ⁸⁷Sr/⁸⁶Sr (0.70773–0.71016) than the shoshonitic series (K₂O: 2.4–7.2 wt.%, Nb: 21–38 ppm, ⁸⁷Sr/⁸⁶Sr: 0.70404–0.70778). Pliocene alkaline basalts have a sodic tendency (Na₂O/K₂O: 1.7–3.5), high Nb content (up to 52 ppm), and low ⁸⁷Sr/⁸⁶Sr ratio (0.70360–0.70413). The variations through time of K₂O, Nb and Sr isotopic ratio reflect different mantle sources: (i) calc-alkaline, potassic calc-alkaline and shoshonitic series are derived from a mantle source modified by older subduction, (ii) alkaline basalts are derived mainly from an enriched mantle source. Through time, incompatible elements such as Nb increased while ⁸⁷Sr/⁸⁶Sr decreased, suggesting a decreasing influence of metasomatized mantle (inherited subduction). Such evolution is related to the post-collision regimes operating in this area, and could be linked to the succession of extensional, compressional and strike-slip fault tectonics.     

The December 4, 1983 to February 18, 1984 eruption of Piton de la Fournaise (La Reunion, Indian Ocean): Description and interpretation

On December 4, 1983 an eruption started at vents located 1.5 km southwest of the summit of Piton de la Fournaise at the base of the central cone. After 31 months of quiescence this was one of the longest repose period in the last fifty years. The eruption had two phases: December 4 to January 18 and January 18 to February 18. Phase 1 produced about 8 × 10⁶ m³ of lava and Phase II about 9 × 10⁶ m³. The erupted lava is an aphyric basalt whose mineralogical and geochemical composition is close to that of other lavas emitted since 1977.The precursors of the December 4 outbreak were limited to two-week shallow (1.5–3 km) seismic crisis of fewer than 50 events. No long-term increase was noted in the local seismicity which is very quiet during repose periods and no long-term ground inflation preceded the eruption. Outbreaks of Phases I and II were preceded by short (2.5 hours and 1.5 hours) seismic swarms corresponding to the rise of magma toward the surface from a shallow reservoir. Large ground deformation explained by the emplacement of the shallow intrusions, was recorded during the seismic swarms. A summit inflation was observed in early January, before the phase II outbreak, while the phase I eruption was still continuing.Piton de la Fournaise volcanological observatory was installed in 1980. Seismic and ground deformation data now available for a period of 4 years including the 1981 and the 1983–1984 eruptions, allow us to describe the physical behavior of the volcano during this period. These observations lead us to propose that the magma transfer from deep levels to the shallow magma reservoir is not a continuous process but a periodic one and that the shallow magma reservoir was not resupplied before the 1981 and 1983–1984 eruptions. Considerations on the eruptive history and the composition of recent lavas indicate that the reservoir was refilled in 1977.     

Cratering and modification of wet‐target craters: Projectile impact experiments and field observations of the Lockne marine‐target crater (Sweden)

Abstract— Marine impacts are one category of crater formation in volatile targets. At target water depths exceeding the diameter of the impactor, the zones of vaporization, melting, and excavation of the standard land‐target cratering model develop partially or entirely in the water column. The part of the crater that has a potential of being preserved (seafloor crater) may to a great extent be formed by material emplacement and excavation processes that are very different from land‐target craters. These processes include a high‐energy, water‐jet‐driven excavation flow. At greater water depths, the difference in strength of the target layers causes a concentric crater to evolve. The crater consists of a wide water cavity with a shallow excavation flow along the seabed surrounding a nested, deeper crater in the basement. The modification of the crater is likewise influenced by the water through its forceful resurge to fill the cavity in the water mass and the seafloor. The resurge flow is strongly erosive and incorporates both ejecta and rip‐up material from the seabed surrounding the excavated crater. A combination of field observations and impact experiments has helped us analyze the processes affecting the zone between the basement crater and the maximum extent of the water cavity. The resurge erosion is facilitated by fragmentation of the upper parts of the solid target caused by a) spallation and b) vibrations from the shallow excavation flow and, subsequently, c) the vertical collapse of the water cavity rim wall. In addition, poorly consolidated and saturated sediments may collapse extensively, possibly aided by a violent expansion of the pore water volume when it turns into a spray during passage of the rarefaction wave. This process may also occur at impacts into water‐saturated targets without an upper layer of seawater present. Our results have implications for impacts on both Earth and Mars, and possibly anywhere in the solar system where volatiles exist/have existed in the upper part of the target.     

The 15 m.y. geomagnetic reversal periodicity: a quantitative test

We have analyzed the three most commonly used geomagnetic polarity time scales that cover the past 100 m.y.. In the three cases, different spectral analyses show a 13–16 m.y. periodicity in the rate of reversal occurrence. To test whether this periodicity is real or simply arises from a random generator we have compared these polarity time scales with a large number of synthetic sequences produced by a random process, characterized by a linear time variation of its mean activity. Geomagnetic and generated sequences were regularly sampled by using sliding windows, anf then the Fourier spectra of the obtained frequency signals were compared. This test shows that the detected periodicity is presumably not a simple statistical fluctuation of an aperiodic generator, and consequently that a long-term periodicity in the geodynamo must be seriously considered.     

Inferring Glacier Mass Balance Using Radarsat: Results From Peyto Glacier, Canada

The capability of RADARSAT synthetic aperture radar (SAR) for the purpose of snow-line/accumulation area mapping for a temperate alpine glacier is examined. In agreement with other orbital C-band SAR studies, RADARSAT can discriminate between firn and bare ice facies. Limited observations are reported with respect to the electromagnetic variability of the ice facies in the ablation area, but they are inconclusive. Operational considerations are discussed with respect to reconciling the uncertainties of late-summer weather and their possible impact on the dielectric and scattering properties of the glacier surface. Vagaries associated with other glacier settings, mass balance states and their associated facies configurations are discussed including the difficulty of using the transient snow-line to define the equilibrium line and the lower extent of the accumulation area for glaciers where superimposed ice may form.
The radar remote-sensing reconnaissance of equilibrium line altitude (ELA) and accumulation area ratio (AAR) for estimating glacier mass balance requires serious consideration in those instances where traditional ground measurements used in the direct glaciological method are absent. However, with respect to the ELA, such estimates can vary depending on the accuracy of the reference digital elevation information. Moreover, for many glacier configurations, where mass balance variations due to altitude are influenced or in some cases completely masked by local balance variations, defining the ELA may be an irreconcilable problem. Using the AAR may be more robust in this regard. It is further determined that the total error inherent in the reconnaissance method would have serious implications for the confident estimation of mass balance normals and climate-related trends if the method were to be utilized over the longer term.     

Tracing of variabilities within a geological barrier by molecular organic geochemistry.: Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)

The Callovo-Oxfordian claystones located at 500 m depth at Bure (Meuse, France) are currently being investigated by Andra (the French National Radioactive Waste Management Agency) for testing the feasibility of long-term and deep geological nuclear waste disposal. In order to evaluate its potential as a geological barrier, it is very important to study, assess and describe its physico-chemical variability. The molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter, the chemistry of the depositional environment, the preservation and diagenesis conditions. It also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series. The abundance of unsaturated biomarkers, the distribution of steroids and hopanoids and CPI values >2 prove the thermal immaturity of the organic matter. The co-occurrence of plankton, bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions. The data also reveal that the organic matter was deposited under oxic and open-sea conditions except for a brief event of photic zone anoxia at the beginning of the Middle Callovian. In the claystones, the geosynthesis of diasterenes is favored to the detriment of the formation of steranes, especially in smectite-rich levels, and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays. On the scale investigated, the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view. Yet, detailed investigation of specific molecular families indicates changes related to major claystone–limestone transitions. The homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub-horizontal paleotopography on which they were deposited. This study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers.     

A new mammalian fauna from the earliest Eocene (Ilerdian) of the Corbières (Southern France): palaeobiogeographical implications

A new mammal fauna from the earliest Eocene of Le Clot (Corbières, Southern France) is described. Some taxa identified there, such as Corbarimys hottingeri and Paschatherium plaziati, allow a correlation with the previously described Corbières fauna of Fordones. Moreover, the presence at Le Clot of Lessnessina praecipuus, which is defined in Palette (Provence, Southern France) allows correlating both localities. All three of these localities are referred to the MP7 reference level, even if a direct correlation with the type locality of MP7 (Dormaal, Belgium) is not ascertained. A Southern Europe biochronological sequence is proposed for the beginning of the Eocene: Silveirinha, Fordones/Palette/Le Clot, Rians/Fournes. The diagnosis of a new species of a neoplagiaulacid multituberculate (?Ectypodus riansensis nov. sp.) is proposed. From a compilation of data concerning the earliest Eocene faunas from both Northern Europe and Southern Europe, we conclude that two faunas corresponding to two distinct palaeobiogeographical provinces existed in Western Europe. This faunal disparity, probably related to climatic differences, makes correlations particularly difficult between the two provinces.