RELAXING ASSUMPTIONS OF PERFECT INFORMATION IN PARK VISITATION MODELS*

Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions.     

Magnetic susceptibility variations of the Edicaran cap carbonates in the Yangtze platform and their implications for paleoclimate

1 INTRODUCTION One of the most intriguing phenomena in the late Neoproterozoic (~750 to 543 Ma) is the globa occurrence of thin carbonates that directly overlie glacial deposits in almost every continent (Kennedy 1996; Hoffman et al., 1998; Hoffman and Schrag 2002; Brasier and Shields, 2000; James et al., 2001 Jiang et al., 2003; Nogueira et al., 2003). These “cap carbonates”, commonly several to tens of meters thick, have attracted enormous interests because o their unusually negati…     

Lateglacial oceanographic conditions off Southwest Iceland inferred from shallow-marine deposits in Reykjavík and Seltjarnarnes Peninsula

New palaeoenvironmental data from the Lateglacial in Southwest Iceland add to the record of climatic events during deglaciation of the region. Recently exposed sediments on the north coast of Seltjarnarnes Peninsula in the Reykjavik area, Southwest Iceland, contain evidence of marine deposition during the Bølling Interstadial. The glaciomarine sediments contain both slightly reworked marine macrofossils and microfossils indicating normal marine salinity and subarctic climate conditions. Previous sedimentological studies and radiocarbon dating of the sporadic sediments covering the lava bedrock in Reykjavik have revealed lateglacial marine units from the Allerød, the Allerød—Younger Dryas transition, the Younger Dryas and from the Preboreal. Until now, the only Bølling evidence has consisted of scattered radiocarbon-dated redeposited shell fragments. From the Bollagardar deposits we report the first faunas dated to the Bølling chronozone preserved in marine sediments in the Reykjavik area. Recently published work in Hvalfjördur and Borgarfjördur, West Iceland, has shown that sea level was relatively high during the Bølling and that deglaciation was rapid. Bølling, Allerød and Younger Dryas deposits in the coastal areas of the Reykjavík region accumulated in a relatively open marine environment in oceanographic conditions similar to the present ones. Combined previous and present results indicate that several episodes of glaciomarine deposition occurred.     

Petrogenesis of andalusite–kyanite–sillimanite veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamadan, Iran

Quartz‐rich veins in metapelitic schists of the Sanandaj‐Sirjan belt, Hamadan region, Iran, commonly contain two Al₂SiO₅ polymorphs, and, more rarely, three coexisting Al₂SiO₅ polymorphs. In most andalusite and sillimanite schists, the types of polymorphs in veins correlate with Al₂SiO₅ polymorph(s) in the host rocks, although vein polymorphs are texturally and compositionally distinct from those in adjacent host rocks; e.g. vein andalusite is enriched in Fe₂O₃ relative to host rock andalusite. Low‐grade rocks contain andalusite + quartz veins, medium‐grade rocks contain andalusite + sillimanite + quartz ± plagioclase veins, and high‐grade rocks contain sillimanite + quartz + plagioclase veins/leucosomes. Although most andalusite and sillimanite‐bearing veins occur in host rocks that also contain Al₂SiO₅, kyanite‐quartz veins crosscut rocks that lack Al₂SiO₅ (e.g. staurolite schist, granite). A quartz vein containing andalusite + kyanite + sillimanite + staurolite + muscovite occurs in andalusite–sillimanite host rocks. Textural relationships in this vein indicate the crystallization sequence andalusite to kyanite to sillimanite. This crystallization sequence conflicts with the observation that kyanite‐quartz veins post‐date andalusite–sillimanite veins and at least one intrusive phase of a granite that produced a low‐pressure–high‐temperature contact aureole; these relationships imply a sequence of andalusite to sillimanite to kyanite. Varying crystallization sequences for rocks in a largely coherent metamorphic belt can be explained by P–T paths of different rocks passing near (slightly above, slightly below) the Al₂SiO₅ triple point, and by overprinting of multiple metamorphic events in a terrane that evolved from a continental arc to a collisional orogen.     

Methods of Hierarchical Control of Water Quality Taking into Account Manipulations of the Center and Countermoves of Enterprises

Methods of hierarchical control including manipulations of a Center and the countermove of enterprises are considered using as an example a dynamic two-level model of river water quality control in the presence of point pollution sources and in the absence of nonpoint sources.     

The importance of oxygen isotope provenance in relation to solute content of bulk meltwaters at Imersuaq Glacier,West Greenland

Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s^?1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ¹⁸O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na⁺, K⁺, Ca²⁺, Mg²⁺), SO₄^2? and δ¹⁸O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl^? is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ¹⁸O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ¹⁸O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd.     

The Preboreal climate reversal and a subsequent solar‐forced climate shift

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Geochronological evidence for late‐Grenvillian magmatic and metamorphic events in central Taimyr,northern Siberia*

U–Th–Pb analyses of zircons from six granites and one metasediment collected in the accretionary Central belt of Taimyr, Arctic Siberia, demonstrate that Neoproterozoic (c. 900 Ma) granites intrude late Mesoproterozoic/early Neoproterozoic amphibolite facies metamorphic rocks. This is the first time in the Mamont–Shrenk region that Neoproterozoic ages have been recognized for these lithologies, previously thought to be Archaean/Palaeoproterozoic in age. The Mamont–Shrenk Terrane (MST) represents a Grenvillian age (micro?) continent intercalated with younger Neoproterozoic ophiolites during thrusting and accreted to the northern margin of the Siberian craton sometime before the late Vendian. Basement to the MST may have been derived from the Grenvillian belt of east Greenland. Viable tectonic reconstructions must allow for an active margin along northern Siberia (modern day coordinates) in the middle Neoproterozoic.