Nonlinear Time Series Analysis of Sunspot Data

This article deals with the analysis of sunspot number time series using the Hurst exponent. We use the rescaled range (R/S) analysis to estimate the Hurst exponent for 259-year and 11 360-year sunspot data. The results show a varying degree of persistence over shorter and longer time scales corresponding to distinct values of the Hurst exponent. We explain the presence of these multiple Hurst exponents by their resemblance to the deterministic chaotic attractors having multiple centers of rotation.     

Fe- and Al-Rich metapelites of the Teiskaya Group, Yenisei Range: Geochemistry, protoliths, and the behavior of their material during metamorphism

The Fe- and Al-rich metapelite of the Teiskaya Group in the trans-Angara part of the Yenisei Range are characterized by variable P-T parameters of their metamorphism. Geochemical data on these rocks were used to reproduce the nature and composition of their protolith. The metapelites were determined to be redeposited and metamorphosed Precambrian weathering crusts of the kaolinite type, which were produced by the erosion of Archean rocks of predominantly acid (granitoid) composition in shallow-water continental-margin basins in a humid climate. These results are consistent with the results of the lithological-facies analysis and geodynamic reconstruction of the Precambrian geological evolution of complexes in the Yenisei range. Differences were revealed between the REE patterns in metapelites in various metamorphic zones caused by both the compositional heterogeneity of the protoliths and the prograde (in terms of pressure) mineral reactions of collision metamorphism with the predominant effects of various processes during different evolutionary stages.     

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The temporal variation of the spherical and Cartesian multipoles of the gravity field: the generalized MacCullagh representation

 The Cartesian moments of the mass density of a gravitating body and the spherical harmonic coefficients of its gravitational field are related in a peculiar way. In particular, the products of inertia can be expressed by the spherical harmonic coefficients of the gravitational potential as was derived by MacCullagh for a rigid body. Here the MacCullagh formulae are extended to a deformable body which is restricted to radial symmetry in order to apply the Love–Shida hypothesis. The mass conservation law allows a representation of the incremental mass density by the respective excitation function. A representation of an arbitrary Cartesian monome is always possible by sums of solid spherical harmonics multiplied by powers of the radius. Introducing these representations into the definition of the Cartesian moments, an extension of the MacCullagh formulae is obtained. In particular, for excitation functions with a vanishing harmonic coefficient of degree zero, the (diagonal) incremental moments of inertia also can be represented by the excitation coefficients. Four types of excitation functions are considered, namely: (1) tidal excitation; (2) loading potential; (3) centrifugal potential; and (4) transverse surface stress. One application of the results could be model computation of the length-of-day variations and polar motion, which depend on the moments of inertia. Received: 27 July 1999 / Accepted: 24 May 2000     

Subtropical to temperate facies from a transition zone, mixed carbonate–siliciclastic system, Palaeogene, North Carolina, USA

Palaeogene passive margin sediments on the US mid‐Atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate–siliciclastic shelves. This study utilizes well cuttings, outcrop, core, and seismic data to document temporal and spatial variations in admixed bryozoan‐rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone. This zone was situated between north‐flowing, warm waters of the ancestral Gulf Stream (carbonate dominated settings) and south‐flowing, cold waters of the ancestral Labrador Current (siliciclastic dominated settings). Some degree of mixing of carbonates and siliciclastics occurs in all facies; however, siliciclastic‐prone sediments predominate in nearshore settings, while carbonate‐prone sediments are more common in more open marine settings of the inner shelf break and deep shelf. A distinctive dual‐break shelf depositional profile originated following a major Late Cretaceous to Palaeocene transgression that drowned the earlier shallow platform. This profile was characterized by prominent mid‐shelf break dividing the shallow shelf from the deep shelf and a major continental shelf/slope break. Incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin. Storm wave base also contributed to the preservation of the dual‐break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid‐shelf break. Sediment fines in deep shelf facies were produced in place, transported downdip from the shallow shelf by storm ebb currents and boundary currents, and reworked from adjacent areas of the deep shelf by strike‐parallel boundary currents. Regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf, with warmer waters and more humid climates favouring carbonate deposition and cooler, more arid conditions favouring glaucony and siliciclastic dominated deposition. Continuous wave and current sweeping of the shallow shelf favoured deposition of mud‐lean facies across much of the shallow shelf. Skeletal components in much of the carbonate‐rich strata formed in warm, nutrient‐rich subtropical waters, as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages. These indicators of warm water deposition within the bryozoan‐mollusk‐rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage; such facies generally are associated with cooler water depositional settings.     

Mg-lattice associations in red coralline algae

Recent investigations have shown red coralline algae to record ambient temperature in their calcite skeletons. Temperature recorded by variation in Mg concentrations within algal growth bands has sub-annual resolution and high accuracy. The conversion of Mg concentration to temperature is based on the assumption of Ca replacement by Mg within the algal calcite skeleton at higher temperatures. While Mg-temperature relationships in coralline algae have been calibrated for some species, the location of Mg within the calcite lattice remains unknown. Critically, if Mg is not a lattice component but associated with organic components this could lead to erroneous temperature records. Before coralline algae are used in large scale climate reconstructions it is therefore important to determine the location of Mg. Synchrotron Mg-X-ray absorbance near edge structure (XANES) indicates that Mg is associated with the calcite lattice in Lithothamnion glaciale (contemporary free-living, contemporary encrusting and sub-fossil free-living) and Phymatolithon calcareum (contemporary free-living) coralline algae. Mg is deposited within the calcite lattice in all seasons (L. glaciale & P. calcareum) and thallus areas (P. calcareum). These results suggest L. glaciale and P. calcareum are robust Mg-palaeotemperature proxies. We suggest that similar confirmation be obtained for Mg associations in other species of red coralline algae aiding our understanding of their role in climate reconstruction at large spatial scales.     

Radiating 1.0 Ga Mafic Dyke Swarms of Eastern Brazil and Western Africa: Evidence of Post-Assembly Extension in the Rodinia Supercontinent?

Several mafic dyke swarms of similar composition and age (tholeiite- ca.1.0 Ga) occur on both sides of the Atlantic Ocean in eastern South America and western Africa. When assembled to their pre-drift position in the Mesozoic, the Brazilian coastal dyke province of Bahia, and the African dykes in Cameroun (Ebolowa suite) and Congo (Comba and Sembe-Ouesso provinces) define a giant radiating pattern (1200 km × 800 km) similar to other dyke swarms elsewhere associated with large-scale continental rifting. Magma flow indicators of the Brazilian dykes and branching propagation styles of their African counterparts indicate that the dyke conduits were fed with magmas diverging from a source beneath the long axis of the Meso-Neoproterozoic West-Congolian Basin in Africa. There, MORB-like metabasalts have been described in the La Bikossi Group of the Mayombian Supergroup. Whether the rifting event and intrusion of dyke swarms were triggered or not by a mantle plume beneath part of the Rodinia subcontinental lithosphere remain to be confirmed.     

Microzoning of agates as a reflection of their formation dynamics

Agates are natural hierarchicalal structural assemblies composed largely of silica minerals: chalcedony, quartz, and quartzine. Microstructural heterogeneities, most typical of those of agate-forming minerals, are characterized by variations in periods of helicoidal twisting of chalcedony and by micrometric rhythmic alternation of zones with a low refractive index within the matrix of normal chalcedony, quartz, and quartzine. A study of the degree of crystallization of chalcedony using the Barsanova-Yakovleva method showed that neither helicoidal twisting nor refractive index zoning brought about any significant disturbance in the chalcedony structure. Helicoidal twisting is a result of the stresses caused by substitution of Si⁴⁺ for Al³⁺ asymmetric with respect to chalcedony crystal. It is suggested that layering by the refractive index developed due to accumulation of small portions of gel consisting of high silica polymers at the front of crystal growth.     

Towards the question of the movement of hydrothermal solutions: The case of the Schlema-Alberoda vein deposit

The paths of the movements of hydrothermal solutions are considered in the case of one of the world’s largest uranium vein deposits, the Schlema-Alberoda, which was mined by the Soviet-German corporation Wismut JSC in the second half of the 20th century. Detailed geological exploration to a depth of 2 km was accompanied by specialized research, the results of which have remained practically unpublished due to confidentiality. The data obtained show that the region adjoining the largest fault was draining rather than ore-conducting. This circumstance specifies and supplements the current concept concerning the movement of hydrothermal fluids.     

Temporal variations in the position of the heliospheric equator

It is shown that the centroid of the heliospheric equator undergoes quasi-periodic oscillations. During the minimum of the 11-year cycle, the centroid shifts southwards (the so-called bashful-ballerina effect). The direction of the shift reverses during the solar maximum. The solar quadrupole is responsible for this effect. The shift is compared with the tilt of the heliospheric current sheet.