Ionospheric Scintillation and Dynamics of Fresnel-Scale Irregularities in the Inner Region of the Equatorial Ionization Anomaly

This paper reports differences in the occurrence statistics of global positioning system (GPS) L-band scintillations at observational sites located in the inner regions of the northern and southern crests of the equatorial ionization anomaly. Ground-based GPS data acquired at the closed magnetically aligned stations of Manaus (3.1°S; 59.9°W; dip lat. 6.2°N) and Cuiabá (15.5°S; 56.1°W; dip. lat. 6.2°S), Brazil, from December 2001 to February 2007 are used in the analysis. The drift dynamics of Fresnel-scale ionospheric irregularities at the southern station of Cuiabá are also investigated. Only geomagnetically quiet days with the sum of daily Kp < 24 were used in the analysis statistics and in the irregularity drift studies. The results reveal a clear dependence of the scintillation occurrence with the solar activity, but there exists an asymmetry in the percentage of scintillation occurrence between the two stations throughout the period analyzed. The nocturnal occurrence of the scintillations over Cuiabá is predominantly larger than over Manaus, but this scenario seems to change with the decline in the solar activity (mainly during local post-midnight hours). A broad minimum and maximum in the scintillation occurrence appears to occur over both the stations, respectively, during the June solstice (winter) and December solstice (summer) months. The dynamics of the Fresnel-scale irregularities, as investigated from the estimations of the mean zonal drift velocities, reveals that the amplitude of the eastward drifts tends to reduce with the decline in the solar activity. The magnitude of the zonal drift velocities during the December solstice months is larger than during the equinoxes, with the differences being more pronounced at solar maximum years. Other relevant aspects of the observations, with complementary data from a low-latitude ionospheric model, are highlighted and discussed.     

BEACH RIDGES AND PALEOGEOGRAPHY,CENTRAL BAJA CALIFORNIA,MEXICO

Two spatially separated sets of beach ridges were studied in Baja California. Each set contains several well-preserved beach ridges and each is adjacent to an arroyo mouth. Modern beach ridges mark coastal location whereas abandoned paleobeach ridges record coastal change. Paleobeach ridges were dated by absolute and relative techniques for rate-change, chronology, and longshore correlation purposes. With time, shape becomes more planar, foreslope angle is reduced, and there is a progressive tendency for constituent shingle to disintegrate and develop both rinds and surficial roughness. One paleobeach ridge on the lowest emergent terrace was assigned a 1,150 ± 230 yr. B.P. radiocarbon date whereas another beach ridge 18 km farther north has a partially overlapping date. Older but undated beach ridges also exist on the lowest emergent terrace as well as on the highest persistent terrace. Those beach ridges on the highest persistent terrace are highly weathered and Pleistocene in age. All beach ridges have paleogeographic implications and suggest that shoreline orientation has been generally stable although its position has shifted laterally by up to 720m westward in the last 1,150 ± 230 years.     

AGE ESTIMATES OF INLAND DUNES IN EAST-CENTRAL LOWER MICHIGAN USING SOILS DATA

Extensive deposits of eolian sand occur deep (>50 km) within the interior of east-central lower Michigan. These dunes are most common in the Saginaw lowland where they are parabolic, with limbs oriented northwesterly. Their presence on densely forested landscapes indicates that paleoenvironmental conditions differed sufficiently for dune formation to have occurred. In a previous study, Arbogast et al. (1997) illustrated that surface soils in the northwestern part of the Saginaw dune field were morphologically similar, consisting of weakly developed Spodosols (A/E/Bs/C horizonation). Thus, these dunes must have stabilized concurrently following regional mobilization of eolian sand. In this study, we present soils data from dunes in the southeastern part of the Saginaw dune field. Surface soils were analyzed at 19 sites in the Deford State Game Area in Tuscola County. Morphologically, the soils within the Deford area are similar (A/E/Bs/C horizonation), indicating that Deford dunes stabilized concurrently. Statistical (ANOVA, KW, factor analysis) comparison of Deford soils and soils to the northwest, however, reveals that significant developmental differences exist between the two areas, with Deford soils being better developed. Given that variables (climate, soil texture, pH) are more conducive for Spodosol development to the northwest, we conclude that Deford soils are older. Thus, Deford dunes must have stabilized prior to their counterparts to the northwest. [Key words: eolian processes, sand dunes, soils, Spodosols, Michigan.]     

Sedimentological and provenance response to Cambrian closure of the Clymene ocean: The upper Alto Paraguai Group,Paraguay belt,Brazil

Final Gondwana amalgamation was marked by the closure of the Neoproterozoic Clymene ocean between the Amazonia craton and central Gondwana. The events which occurred in the last stage of this closure were recorded in the upper Alto Paraguai Group in the foreland of the Paraguay orogen. Outcrop-based facies analysis of the siliciclastic rocks of upper Alto Paraguai Group, composed of the Sepotuba and Diamantino Formations, was carried out in the Diamantino region, within the eastern part of the Barra dos Bugres basin, Mato Grosso state, central-western Brazil. The Sepotuba Formation is composed of sandy shales with planar to wave lamination interbedded with fine-grained sandstone with climbing ripple cross-lamination, planar lamination, swaley cross-stratification and tangential to sigmoidal cross-bedding with mud drapes, related to marine offshore deposits. The lower Diamantino Formation is composed of a monotonous, laterally continuous for hundreds of metres, interbedded siltstone and fine-grained sandstone succession with regular parallel lamination, climbing ripple cross-lamination and ripple-bedding interpreted as distal turbidites. The upper part of this formation consists of fine to medium-grained sandstones with sigmoidal cross-bedding, planar lamination, climbing ripple cross-lamination, symmetrical to asymmetrical and linguoid ripple marks arranged in lobate sand bodies. These facies are interbedded with thick siltstone in coarsening upward large-scale cycles related to a delta system. The Sepotuba Formation characterises the last transgressive deposits of the Paraguay basin representing the final stage of a marine incursion of the Clymene ocean. The progression of orogenesis in the hinterland resulted in the confinement of the Sepotuba sea as a foredeep sub-basin against the edge of the Amazon craton. Turbidites were generated during the deepening of the basin. The successive filling of the basin was associated with progradation of deltaic lobes from the southeast, in a wide lake or a restricted sea that formed after 541 ± 7 Ma. Southeastern to east dominant Neoproterozoic source regions were confirmed by zircon grains that yielded ages around 600 to 540 Ma, that are interpreted to be from granites in the Paraguay orogen. This overall regressive succession recorded in the Alto Paraguai Group represents the filling up of a foredeep basin after the final amalgamation of western Gondwana in the earliest Phanerozoic.     

Phase transitions and path dependence in urban evolution

There is a long history of recognising and interpreting discontinuous change—phase transitions—in urban systems. In this paper, we use the aggregate retail model as an archetype to explore some new ideas. For example, we argue that the dependence of paths of development on initial conditions has been understudied, and we offer a new graphical analysis that demonstrates explicitly their influence on discrete change. We introduce an order parameter, and we plot this on a ‘results grid’ to facilitate the discovery of possible phase transitions. We illustrate the use of these new developments with an application to London. We show how retail developers can change the ‘initial conditions’ at a point in time and possibly bring about phase transitions by their actions. This also shows that it should be possible to account for the history of urban development as a sequence of initial conditions, illustrating path dependence. Secondly, the model could be deployed in relation to a new shopping zone, and the tools developed here used to calculate the minimum size of a new development in order for it to compete. We explore the ‘minimum size’ idea in relation to a new shopping zone in London.     

High-precision osmium isotopes in enstatite and Rumuruti chondrites

Isotopic heterogeneity within the solar nebula has been a long-standing issue. Studies on primitive chondrites and chondrite components for Ba, Sm, Nd, Mo, Ru, Hf, Ti, and Os yielded conflicting results, with some studies suggesting large-scale heterogeneity. Low-grade enstatite and Rumuruti chondrites represent the most extreme ends of the chondrite meteorites in terms of oxidation state, and might thus also present extremes if there is significant isotopic heterogeneity across the region of chondrite formation. Osmium is an ideal tracer because of its multiple isotopes generated by a combination of p-, r-, and s-process and, as a refractory element; it records the earliest stages of condensation.Some grade 3-4 enstatite and Rumuruti chondrites show similar deficits of s-process components as revealed by high-precision Os isotope studies in some low-grade carbonaceous and ordinary chondrites. Enstatite chondrites of grades 5-6 have Os isotopic composition identical within error to terrestrial and solar composition. This supports the view of digestion-resistant presolar grains, most likely SiC, as the major carrier of these anomalies. Destruction of presolar grains during parent body processing, which all high-grade enstatite chondrites, but also some low-grade chondrites seemingly underwent, makes the isotopically anomalous Os accessible for analysis. The magnitude of the anomalies is consistent with the presence of a few ppm of presolar SiC with a highly unusual isotopic composition, produced in a different stellar environment like asymptotic giant branch stars (AGB) and injected into the solar nebula. The presence of similar Os isotopic anomalies throughout all major chondrite groups implies that carriers of Os isotopic anomalies were homogeneously distributed in the solar nebula, at least across the formation region of chondrites.     

Time series analysis of daily rainfall and streamflow in a volcanic dike-intruded aquifer system, O��ahu, Hawai��i, USA

A conceptual model of groundwater occurrence was developed for a dike-intruded aquifer system in M??kaha valley, O??ahu, Hawai??i, USA, and used to explain the impacts of water resource development on groundwater levels and streamflow. Time-series analyses were applied to two subsets of daily rainfall, total flow, and baseflow??from the third (1946?C1968) and fourth (1968?C1991) periods of development??to evaluate changes in streamflow response. Autocorrelation, cross-correlation, squared coherency and phase functions were used to estimate the decorrelation lag time, and the correlation length, linearity with frequency, and frequency response delay between rainfall and streamflow. The decorrelation lag time for total flow and baseflow declined by 16?C20?days (d). The correlation length between rainfall and streamflow declined 4?C7?d for total flow and 10?C13?d for baseflow. The squared coherency function indicates an overall decline in linearity between rainfall and total flow across most frequencies. The changes in hydrologic response following increased water-resource development is consistent with a model of groundwater depletion resulting in less groundwater discharge and more induced groundwater recharge. Changes in streamflow response are inconsistent with observed changes in rainfall and imply that streamflow decline is more likely to be the result of groundwater pumping.     

Lunar atmospheric H2 detections by the LAMP UV spectrograph on the Lunar Reconnaissance Orbiter

We report on the detection of H₂ as seen in our analysis of twilight observations of the lunar atmosphere observed by the LAMP instrument aboard NASA’s Lunar Reconnaissance Orbiter. Using a large amount of data collected on the lunar atmosphere between September 2009 and March 2013, we have detected and identified, the presence of H₂ in the native lunar atmosphere, for the first time. We derive a surface density for H₂ of 1.2 ± 0.4 × 10³ cm⁻³ at 120 K. This is about 10 times smaller than originally predicted, and several times smaller than previous upper limits from the Apollo era data.     

Gemstone Mineralization in the Palghat-Cauvery Shear Zone System (Karur-Kangayam Belt), Southern India

We summarize here the occurrence of a number of semiprecious stones within a major gemstone belt in the Palghat-Cauvery shear zone system close to the northern margin of the Madurai Granulite Block, southern India. The gem mineralization in this belt includes different varieties of corundum (star ruby, sapphire), cordierite (iolite), feldspar (moonstones and sunstone of various hues), beryl (emerald, aquamarine), chrysoberyl (alexandrite), kornerupine, topaz, spinel, crystal quartz and amethyst, among others. Gem mineralisation has not been directly dated, but is associated with pegmatites that crosscut rocks metamorphosed in late Neoproterozoic/Early Cambrian times. Similar aged gem mineralization occurs south of the Achankovil Shear Zone in southern India, as well as in Sri Lanka and Madagascar and strengthen the view of a broad late Neoproterozoic-early Cambrian gemstone province in central Gondwana. The ruby mineralization within this belt can be correlated with similar occurrences in eastern Madagascar, supporting a correlation between the Malagasy Betsimisaraka suture zone and the Palghat-Cauvery shear zone system in southern India.     

The Oligocene Lund Tuff, Great Basin, USA: a very large volume monotonous intermediate

Unusual monotonous intermediate ignimbrites consist of phenocryst-rich dacite that occurs as very large volume (>1000 km³) deposits that lack systematic compositional zonation, comagmatic rhyolite precursors, and underlying plinian beds. They are distinct from countless, usually smaller volume, zoned rhyolite–dacite–andesite deposits that are conventionally believed to have erupted from magma chambers in which thermal and compositional gradients were established because of sidewall crystallization and associated convective fractionation. Despite their great volume, or because of it, monotonous intermediates have received little attention. Documentation of the stratigraphy, composition, and geologic setting of the Lund Tuff – one of four monotonous intermediate tuffs in the middle-Tertiary Great Basin ignimbrite province – provides insight into its unusual origin and, by implication, the origin of other similar monotonous intermediates.The Lund Tuff is a single cooling unit with normal magnetic polarity whose volume likely exceeded 3000 km³. It was emplaced 29.02±0.04 Ma in and around the coeval White Rock caldera which has an unextended north–south diameter of about 50 km. The tuff is monotonous in that its phenocryst assemblage is virtually uniform throughout the deposit: plagioclase>quartz≈hornblende>biotite>Fe–Ti oxides≈sanidine>titanite, zircon, and apatite. However, ratios of phenocrysts vary by as much as an order of magnitude in a manner consistent with progressive crystallization in the pre-eruption chamber. A significant range in whole-rock chemical composition (e.g., 63–71 wt% SiO₂) is poorly correlated with phenocryst abundance.These compositional attributes cannot have been caused wholly by winnowing of glass from phenocrysts during eruption, as has been suggested for the monotonous intermediate Fish Canyon Tuff. Pumice fragments are also crystal-rich, and chemically and mineralogically indistinguishable from bulk tuff. We postulate that convective mixing in a sill-like magma chamber precluded development of a zoned chamber with a rhyolitic top or of a zoned pyroclastic deposit. Chemical variations in the Lund Tuff are consistent with equilibrium crystallization of a parental dacitic magma followed by eruptive mixing of compositionally diverse crystals and high-silica rhyolite vitroclasts during evacuation and emplacement. This model contrasts with the more systematic withdrawal from a bottle-shaped chamber in which sidewall crystallization creates a marked vertical compositional gradient and a substantial volume of capping-evolved rhyolite magma. Eruption at exceptionally high discharge rates precluded development of an underlying plinian deposit.The generation of the monotonous intermediate Lund magma and others like it in the middle Tertiary of the western USA reflects an unusually high flux of mantle-derived mafic magma into unusually thick and warm crust above a subducting slab of oceanic lithosphere.