Optical dating of Holocene sediments from a variety of geomorphic settings using single grains of quartz

This paper presents an improved method for the optical dating of Holocene sediments from a variety of geomorphic settings. We have measured the equivalent dose (D_e) in individual grains of quartz, using green laser light for optical stimulation, and have simulated the D_e distributions for multiple-grain ‘synthetic’ aliquots using the single-grain data. For 12 samples of known (independent) age, we show that application of a ‘minimum age model’ to the single-grain and ‘small’ (10-grain) aliquot D_e data provides the most accurate estimate of the burial dose for nine of the samples examined (3 aeolian, 5 fluvial, and 1 marine). The weighted mean D_e (as obtained using the ‘central age model’) gives rise to burial age overestimates of up to a factor of 10 for these nine samples, whether single grains, small aliquots, or ‘large’ (100-grain) aliquots are used. For the other three samples (two aeolian and one fluvial), application of either the minimum age model or the central age model to the single-grain, small aliquot, and large aliquot D_e data yields burial ages in accord with the independent age control. We infer that these three samples were well bleached at the time of deposition. These results show that heterogeneous bleaching of the optical dating signal is commonplace in nature, and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition. We also show that grains sensitive to infrared (IR) stimulation can give rise to low D_e values, which will result in significant underestimation of the burial dose and, hence, of the age of deposition. We demonstrate that use of a modified single-aliquot regenerative-dose protocol incorporating IR stimulation prior to green light stimulation deals effectively with contamination by IR-sensitive grains. We conclude that application of the modified protocol to single grains or small aliquots of quartz, using the lowest D_e population to estimate the burial dose, is the best means of obtaining reliable ages for Holocene sediments from a wide range of depositional environments.     

Tectonostratigraphic relationships and coalification trends in the Narragansett and Norfolk Basins, New England

Carboniferous basins in southeastern New England provide insight into, and constraints on, models for Alleghanian orogenesis. In particular, the Narragansett and Norfolk basins represent Devonian- to Pennsylvanian-aged, non-marine basins in southeastern Massachusetts and Rhode Island that were variably deformed and metamorphosed during the Alleghanian orogeny, and intruded by Permian granites generated by crustal thickening. As such these basins provide an unusually complete documentation of the Alleghanian orogeny. We summarize their sedimentologic, structural and metamorphic features, with emphasis placed on the Narragansett basin, and provide a comprehensive bibliography of recent work. The Narragansett basin also contains complexly deformed and variably metamorphosed coals that are unlike coal describe from other orogenic terrains. Thus we describe these unusual, high rank coal deposits and their response to orogenesis.     

Structure of the larvikite-lardalite complex,Oslo-region,Norway, and its evolution

Structures not previously described from the southern part of the Permian rift-system in the Oslo-district, Norway, are presented. These indicate that the larvikite massif is a ring complex consisting of numerous individual sections which are roughly circular and repeatedly cut each other in a manner that suggests sequential shifting of centres of igneous activity towards the west. The compositions of these sections vary from quartzbearing varieties in the earliest parts through intermediate types to larvikite and lardalite with excess nepheline in the youngest parts.As this complex covers almost the total width of the Oslo rift-system, it forms an important profile across the graben structure. It suggests unilateral westward migration of centres of igneous activity in this region, viewed either as magma injection or cauldron subsidence and therefore provides additional information regarding the origin and evolution of the Oslo paleo-rift system.

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Zusammenfassung Die Arbeit behandelt bisher nicht beschriebene Strukturen im südlichen Teil des permischen Bruchsenkungsgebietes im Oslogebiet in Norwegen. Sie zeigen, daß das Larvikit-Massiv einen ringförmigen Komplex bildet aus zahlreichen, ungefähr zirkulären und untereinander diskordanten Teilbereichen. Die Lage der Diskordanzen erlaubt die Annahme, einer westlich gerichteten sukzessiven Verlagerung der Zentren magmatischer Aktivität. Mit abnehmendem Alter dieser Teilbereiche verändert sich deren Mineralbestand von quartzführend über intermediär hin zur larvikitischen und lardalitischen Zusammensetzung mit Nephelinüberschuß.Da dieser Komplex fast den gesamten Bereich des Osloer Bruchsenkungsgebietes deckt, stellt er ein wichtiges Profil durch die Grabenstruktur dar. Dieses läßt plausibel erscheinen, daß die Zentren der magmatischen Vorgänge der Gegend einem einheitlich westgerichteten Trend gefolgt sind gleichviel, ob man in ihnen großräumige Vorgänge ringförmiger Magmen-intrusion sieht oder zylindrische Kesselbrüche (Cauldrons). Die in der Arbeit dargelegten Ergebnisse sind somit geeignet, die Frage des Ursprungs und der Entwicklung des Osloer Bruchsenkungsgebietes weiter zu erhellen.

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Résumé Une nouvelle analyse structurale de massif de larvikite au sud du rift permien d'Oslo, Norvège, montre que ce massif forme un complexe annulaire comprenant de nombreuses composantes à peu pres circulaires et discordantes entre elles. Les segments se recoupent successivement indiquant un déplacement des centres d'activité magmatique vers l'ouest. Les larvikites passent de types à composition acide avec quartz dans les premiers segments, à des types intermédiaires puis a des compositions sousatourée avec néphéline en excess dans les segments les plus jeunes.Comme le massif occupe presque toute la largeur du rift d'Oslo il constitue une coupe importante de cette fosse paléozoique. Sa structure suggère une migration continue vers l'ouest des centres d'activité volcanique pour autant qu'on y voie des intrusions annulaires de magma, ou des effondrements successifs de la caldeira. Ce résultat apporte une information nouvelle sur l'origine et l'évolution du rift permien d'Oslo au sud de la Norvège.

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Soil erosion assessment tools from point to regional scales—the role of geomorphologists in land management research and implementation

Geomorphological research has played an important role in the development and implementation of soil erosion assessment tools. Because policy and management approaches include the use of soil erosion assessment tools, soil erosion research directly affects the public in terms of providing information on natural hazards and human impacts, and also as the basis for regulatory policy on land management. For example, soil loss calculations and geomorphological expertise are used to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites.To be useful for decision makers, soil erosion models must have simple data requirements, must consider spatial and temporal variability in hydrological and soil erosion processes, and must be applicable to a variety of regions with minimum calibration. The growing use of erosion models and Geographic Information Systems (GIS) in local to regional scale soil and water conservation raises concerns about how models are used. This has prompted interest in methods to assess how models function at management scales and with the types of data that are commonly available to users. A case study of a GIS-based soil erosion assessment tool using the process-based Water Erosion Prediction Project (WEPP) shows that using commonly available data rather than research grade data can have (predictably) a significant impact on model results. If model results are then used in management decisions, it is critical to assess whether the scale and direction of variation in results will affect management and policy decisions. Geomorphologists provide unique perspectives on soil erosion and can continue to affect policy through soil erosion research. This research should focus on fundamental processes, but equally important is continued development and evaluation of models that are matched to real world data availability, geomorphic settings, and information needs.     

Ascent-driven crystallisation of dacite magmas at Mount St Helens, 1980–1986

We introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system Qz-Ab-Or-H₂O in order to relate variations in volcanic glass chemistry to changing pressure (P) and temperature (T) conditions in the sub-volcanic magma system. By this means an important distinction can be made between ascent-driven and cooling-driven crystallisation under water-saturated or undersaturated conditions. In samples containing feldspar and a silica phase (quartz or tridymite), quantitative P-T estimates of the conditions of last equilibrium between crystals and melt can be made. Formation of highly silicic melts (i.e. >77 wt% SiO₂) is a simple consequence of the contraction of the silica phase volume with decreasing pressure, such that high silica glasses can only form by crystallisation at low pressure. Resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation. Groundmass and inclusion glasses in dacites from the 1980-1986 eruption of Mount St Helens volcano (WA) span a wide range in SiO₂ (68-80 wt%, anhydrous). The compositions of the least evolved (SiO₂-poor) inclusions in amphibole phenocrysts record entrapment of silicic liquids with Е.4 wt% water, corresponding to a water saturation pressure of ~200 MPa at 900 °C. The compositions of more evolved (higher SiO₂) plagioclase-hosted inclusions and groundmass glasses are consistent with extensive ascent-driven fractional crystallisation of plagioclase, oxide and orthopyroxene phenocrysts and microlites to low pressures. During this polybaric crystallisation, plagioclase phenocrysts trapped melts with a wide range of dissolved water contents (3.5-5.7 wt%). Magmas erupted during the Plinian phase of the 18 May 1980 eruption were derived from a large reservoir at depths of ̈́ km. Subsequent magmas ascended to varying depths within the sub-volcanic system prior to extraction. From glass chemistry and groundmass texture two arrest levels have been identified, at depths of 0.5-1 and 2-4 km. A single dome sample from February 1983 contains groundmass plagioclase, tridymite and quartz, testifying to temperatures of at least 885 °C at 11 MPa. These shallow storage conditions are comparable to those in the cryptodome formed during spring 1980. The corresponding thermal gradient, А.2 °C MPa^-1, is consistent with near-adiabatic magma ascent from ~8 km. We argue that the crystallisation history of Mount St Helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation. This challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980-1986 eruption. Because the crystallisation process is both polybaric and fractional, it cannot be simulated directly using isobaric equilibrium crystallisation experiments. However, calculation of the phase proportions in water-saturated 910ᆣ °C experiments by Rutherford et al. (1985) over the pressure range 220-125 MPa reproduces the crystallisation sequence and phenocryst modes of Mount St Helens dacites from 18 May 1980. By allowing for the effects of fractional versus equilibrium crystallisation, entrained residual source material, and small temperature differences between nature and experiment, phase compositions can also be matched to the natural samples. We conclude that decompression of water-saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres.     

Shoreline variability via empirical orthogonal function analysis: Part II relationship to nearshore conditions

The method of empirical orthogonal function (EOF) or principal component analysis (PCA) was used to investigate the spatial and temporal variability of shoreline data sets from Duck, North Carolina, the Gold Coast, Australia, and the United States Pacific Northwest. In the present work, an attempt is made to relate the individual modes of shoreline variability identified by the EOF analyses to select parameterizations of the nearshore environment. The parameters considered include the wave energy (E), the cross-shore and longshore wave energy fluxes (F_x and F_y), the wave steepness (H_o/L_o), the non-dimensional fall velocity parameter (Ω), the profile parameter (P), the surf-similarity parameter (ζ), and a surfzone Froude number (F_r). Correlation analyses were used to evaluate the linear relationship between each of these parameters and the temporal eigenfunctions, c_k(t), associated with individual modes of shoreline change. Typically, strong correlations were observed between longshore uniform modes and the monthly means of several of the nearshore parameters.     

Achieving environmentally relevant organochlorine pesticide concentrations in eggs through maternal exposure in Alligator mississippiensis

Alligator mississippiensis eggs from organochlorine pesticide (OCP) contaminated sites in Florida exhibit high rates of embryonic mortality compared to reference sites (P < 0.05). The objective of the present study was to use captive adult alligators to test the hypotheses that maternal exposure to OCPs results in increased OCP concentrations in eggs, and that increased exposure is associated with increased embryonic mortality. A total of 24 adult alligators (8 males and 16 females) were housed in eight pens. Eight females in four pens were dosed with a mixture of p,p'-DDE, toxaphene, dieldrin, and chlordane at a rate of 0.2+/-0.01 mg/kg/day for 274+/-8 days. Treated females produced eggs containing higher OCP concentrations (12,814+/-813 ng/g yolk) than controls (38+/-4 ng/g yolk). Eggs of treated females exhibited decreased viability (13+/-22%) as compared to controls (45+/-20%). Results indicated that 0.6% of administered OCPs were maternally transferred to the eggs of American alligators, and that maternal exposure is associated with decreased egg/embryo viability in this species.     

Protecting the North-East Atlantic: enhancing synergies by institutional interplay

This article examines the interplay between three different international institutions on marine pollution in the North Sea and the wider North-East Atlantic: the International North Sea Conferences (INSC), the OSPAR-Convention and preceding conventions as well as the European Union (EU). It argues that interplay between these institutions have proved synergetic in two ways. First, the INSC-process has speeded up decision-making within OSPAR and the EU by means of leadership, change in membership and institutional arrangements. Second, OSPAR and the EU have subsequently facilitated domestic implementation of the North Sea Conference Declarations by means of higher authoritativeness and enforcement competence. These three institutions have fulfilled different functions all of which are needed to make international environmental cooperation effective.