Clastic sediments associated with radiolarites (Tauglboden—Schichten, Upper Jurassic, Eastern Alps)

During the early Upper Jurassic, widespread deep-sea radiolarites were deposited in most parts of the Northern Limestone Alps. In the formation described (Tauglboden-Schichten), these pelagic sediments interfinger with local-source clastic material. Depending on the topography and the kind of material, either slides and slumps, mudflows, grain flows or turbidity currents operated and formed slump-folded beds, mud-flow breccias, fluxoturbidites or turbidites. A breccia had been traced over an area of 20 km². Its variation is described in terms of lithological columns, bed thicknesses, maximum grain sizes and grain orientations. It forms a tongue-shaped body, which was probably a part of a submarine fan. The fluxoturbidites of the proximal area grade distally on three sides into turbidites within 3–5 km. The clastic material consists of marls and limestones of Rhaetian and Jurassic age. It was probably derived from a tectonically uplifted palaeo-high by an interplay of tectonics and gravity. The clastics were deposited on submarine fans bordering this high. In its lithology the formation closely resembles certain marginal facies of flysch troughs.     

The relationship between basin and margin thermal evolution assessed by fission track thermochronology: an application to offshore southern Norway

Abstract We use a quantitative model of apatite fission track (AFT) annealing to constrain the thermal evolution of a sedimentary basin and its margin. Apatites deposited in a basin contain several types of information. Provided temperatures remained below ?70°C, they retain much of their provenance thermal signatures and mainly record the thermal evolution of their source area. Above 70°C, the fission tracks in apatite rapidly fade, reflecting the thermal evolution of the basin. Therefore, downhole AFT dates in a well section can in principle be used to assess both the provenance detail (from shallow/cool samples) and the subsequent thermal history in the basin (from the deeper samples). We apply this concept to the south Norwegian offshore and onshore using AFT and ZFT (zircon fission track) data; the latter constrain maximum palaeotemperatures and provide additional provenance information. AFT and ZFT data from three offshore wells in the northern North Sea are shown to contain a record of palaeogeographical and tectonic evolution, closely associated with the Norwegian basement. ZFT data from Middle Triassic sediments suggest a Permian volcanic source. Modelling of AFT data from Jurassic sediments presently residing at temperatures below 70°C indicate rapid cooling during the Late Triassic to Early Jurassic, similar to onshore AFT data. During the Cretaceous minor sediment supply was derived from the Norwegian basement, as evidenced by ZFT ages that do not correlate to the onshore, suggesting that parts of southern Norway were covered with sediments at this time. At the end of the Palaeogene and during the Neogene, the south Norwegian basement again became a major source of elastics. AFT and ZFT data indicate that all wells are presently at maximum temperatures. No significant (> 500 m) erosion events are indicated in the three wells since the Jurassic. AFT data have not yet effectively equilibrated to present-day temperatures as nonzero fission track ages are maintained in sediments currently at temperatures of > 120°C. This implies that the present-day thermal regime has only recently been installed. Probable causes include rapid subsidence and an increase in the geothermal gradient during the last 5 Myr.     

RURAL REGIONAL GOVERNANCE IN THE UNITED STATES: THE CASE OF THE RESOURCE CONSERVATION AND DEVELOPMENT PROGRAM*

Rural governance has drawn considerable attention from both local government officials and scholars in the United States since the early 1990s. It is touted as a way to mitigate the limitations of the traditional government unit‐based approaches to problem solving and decision making and to foster partnerships across both jurisdictional boundaries and sectors (public, private, and nonprofit). Established in 1962, the Resource Conservation and Development (rc&d ) program of the U.S. Department of Agriculture provides a unique model of rural regional governance. Acting as a coalition of governments, private businesses, individuals, and interest groups, the rc&d program provides the flexibility needed to deal with issues at the appropriate spatial scale. It incorporates aspects of both grassroots and governmental organizations and can bring together local interests and expertise with governmental policy and support in service provision, problem solving, and economic development. The approach does not necessarily entail loss of power on the part of the state, but it does provide a mechanism for local people to exercise their agency, to tackle their problems, and to decide which elements of their lives they want to sustain.     

Melting of Amphibole-bearing Wehrlites: an Experimental Study on the Origin of Ultra-calcic Nepheline-normative Melts

Olivine + clinopyroxene ± amphibole cumulates have beenwidely documented in island arc settings and may constitutea significant portion of the lowermost arc crust. Because ofthe low melting temperature of amphibole (1100°C), suchcumulates could melt during intrusion of primary mantle magmas.We have experimentally (piston-cylinder, 0·5–1·0GPa, 1200–1350°C, Pt–graphite capsules) investigatedthe melting behaviour of a model amphibole–olivine–clinopyroxenerock, to assess the possible role of such cumulates in islandarc magma genesis. Initial melts are controlled by pargasiticamphibole breakdown, are strongly nepheline-normative and areAl₂O₃-rich. With increasing melt fraction (T > 1190°Cat 1·0 GPa), the melts become ultra-calcic while remainingstrongly nepheline-normative, and are saturated with olivineand clinopyroxene. The experimental melts have strong compositionalsimilarities to natural nepheline-normative ultra-calcic meltinclusions and lavas exclusively found in arc settings. Theexperimentally derived phase relations show that such naturalmelt compositions originate by melting according to the reactionamphibole + clinopyroxene = melt + olivine in the arc crust.Pargasitic amphibole is the key phase in this process, as itlowers melting temperatures and imposes the nepheline-normativesignature. Ultra-calcic nepheline-normative melt inclusionsare tracers of magma–rock interaction (assimilative recycling)in the arc crust. KEY WORDS: experimental melting; subduction zone; ultra-calcic melts; wehrlite     

Amalgamated accumulations resulting from climatic and eustatic changes, Akchar Erg, Mauritania

The Akchar Erg of the Sahara of western Mauritania shows a morphology and stratigraphy that can be recognized as the amalgamation of late Pleistocene and Holocene deposits that reflect eustatic and climatic events. Mapping, trenching, and dating by ¹⁴C methods and artefacts show that the prominent complex linear dunes (draas) of the Akchar Erg are actually composite features showing at least three constructional and two destructional phases. The constructional phases are represented by three convex-up layers: (i) a modern veneer moulded into superimposed crescentic dunes, which partially mantle the larger linear bedforms; (ii) a middle, partly root-turbated sand deposited sometime during the last 4000 years; and (iii) a core of linear dune sand formed during the last glacial period (13 000–20 000 yr BP), which today shows relict relief, intense root-turbation, and pedogenesis. These constructional phases are separated by super bounding surfaces that coincide with erg destructional phases. Surface 2 bounds the middle aeolian sand, and is marked by a lag surface of small granules. Surface 1 is a very prominent surface with an abundance of Neolithic artefacts, and represents stabilization of the linear dunes during the humid, interglacial period (4000–11 000 yr BP). Interdraa deposits originated during the interglacial period, and consist of continental lacustrine limestones and sandstones, humic sands deposited in marshes, and sabkhas on the coast. The sabkhas originated during interglacial highstand of sea-level when interdraa areas were marine embayments, and subsequently dried during regression. The draa and interdraa sequences, therefore, in spite of being adjacent facies, actually represent different events and were not formed simultaneously. The upwind sand-sheet margin of the Akchar Erg shows exposures of the middle and core aeolian sands (which were previously protected from deflation by vegetation) being progressively cannibilized in the current phase of erg construction, and revealing a crystalline basement rock. In this proximal area, conditions are not favourable for the incorporation of these aeolian accumulations into the stratigraphic record.     

Ultra-calcic Magmas Generated from Ca-depleted Mantle: an Experimental Study on the Origin of Ankaramites

Ultra-calcic ankaramitic magmas or melt inclusions are ubiquitousin arc, ocean-island and mid-ocean ridge settings. They areprimitive in character (X_Mg > 0·65) and have highCaO contents (>14 wt %) and CaO/Al₂O₃ (>1·1). Experimentson an ankaramite from Epi, Vanuatu arc, demonstrate that itsliquidus surface has only clinopyroxene at pressures of 15 and20 kbar, with X_CO2 in the volatile component from 0 to 0·86.The parental Epi ankaramite is thus not an unfractionated magma.However, forcing the ankaramite experimentally into saturationwith olivine, orthopyroxene and spinel results in more magnesian,ultra-calcic melts with CaO/Al₂O₃ of 1·21–1·58.The experimental melts are not extremely Ca-rich but high inCaO/Al₂O₃ and in MgO (up to 18.5 wt %), and would evolve tohigh-CaO melts through olivine fractionation. Fractionationmodels show that the Epi parent magma can be derived from suchultra-calcic experimental melts through mainly olivine fractionation.We show that the experimental ultra-calcic melts could formthrough low-degree melting of somewhat refractory mantle. Thelatter would have been depleted by previous melt extraction,which increases the CaO/Al₂O₃ in the residue as long as someclinopyroxene remains residual. This finding corrects the commonassumption that ultra-calcic magmas must come from a Ca-richpyroxenite-type source. The temperatures necessary for the generationof ultra-calcic magmas are     

Why not SQL!

Abstract

The application of traditional database query languages, primarily the Structured Query Language SQL, for geographical information systems (GIS) and other non–standard database applications has been tried unsuccessfully; therefore, several extensions to the relational database query language SQL have been proposed to serve as a spatial query language. It is argued that the SQL framework is inappropriate for an interactive query language for a GIS and an extended SQL is at best a short term solution. Any spatial SQL dialect has a number of serious deficiencies, particularly the patches to incorporate the necessary spatial concepts into SQL.     

AD HOC REGIONALISM IN RURAL DEVELOPMENT*

Government units such as counties and cities have long been the basis for economic development, service delivery, and problem solving in rural America, but they are increasingly inappropriate, because many of them are too small to reach the critical mass and because rural issues often transcend arbitrarily set political boundaries. To overcome the resultant adverse effects, many rural communities have been rethinking their development strategies and actively forging regional partnerships. Ad hoc regionalism is a politically feasible and effective way for rural communities to collaborate in these initiatives. The exact issues that spark such collaboration may vary from place to place, but they are all grassroots, voluntary regional governance frameworks or innovations. They allow rural communities to pool their resources and reach the critical mass necessary to tackle a variety of regional issues and take advantage of new economic development opportunities without replacing or threatening existing government units. The two case studies discussed in this article—the western Kansas Rural Economic Development Alliance and the San Juan Forum in the Four Corners region of the southwestern United States—show that ad hoc regionalism offers several advantages over rural communities working independently but that challenges in implementing it exist.     

The Subsolidus History of the Artfj?llet Gabbro: a TEM Study of Olivine, Augite and Orthopyroxene

A transmission electron microscope study of the microstructuresof olivine, augite and ortho-pyroxene in the Artfj?llet gabbroshows that the gabbro has been affected by two phases of deformation,exsolution and alteration. During the first phase, deformationand annealing of olivine led to the formation of elongated subgrains,with (100) subgrain boundaries consisting of regularly spacededge dislocations with [100] Burgers vectors. Localized strongerdeformation resulted in the development of mosaic subgrainswith (100) and (001) boundaries. Exsolution produced blebs and(100) lamellae of orthopyroxene in augite. Two types of blebsoccur, referred to as symplectitic augite and blebby augite.Symplectitic augite formed through discontinuous precipitation.The blebs in blebby augite are considered to have nucleatedat subgrain boundaries or dislocations in the augite. Blebs,melon pips and (100) lamellae of augite formed in orthopyroxene.These blebs and melon pips are thought to be due to nucleationat dislocations or to thickening of (100) lamellae at dislocations.Brown hornblende formed as blebs in augite and to a lesser extentorthopyroxene. This first event took place while the gabbrowas at a temperature of c. 900-1000 ?C and is thought to berelated to D_2b, a regional flattening and thrusting event. Renewed exsolution in the pyroxenes occurred later, probablybefore the second subsolidus phase, -but its timing is poorlyconstrained. "100" lamellae of low-Ca clinopyroxene formed inaugite at an estimated temperature of c. 600 ?C. Thin (100)lamellae and Guinier-Preston zones were developed in orthopyroxene. During the second phase, deformation resulted mainly in cracks,along which hydrous fluids entered the gabbro, causing a variabledegree of metamorphism at a temperature of c. 500-550 ?C. Inolivine irregular dislocations of mixed edge-screw characterformed. Cr-spinel with an unknown phase, or magnetite with diopsideprecipitated in the olivine. Oxide minerals formed in the pyroxenesand brown hornblende: Cr-spinel in Cr-rich augite; rutile andilmenite in other augite, orthopyroxene and brown hornblende.The formation of these oxide minerals is thought to be due toexsolution of cations such as Ti and Cr, which these mineralsdo not tolerate in their structures at low temperatures, combinedwith oxidation in the case of magnetite in olivine. Alterationresulted in thin amphibole lamellae parallel to (010) in augite.This second subsolidus phase is correlated with the D₃ regionaldeformation phase and the concomitant retrograde metamorphism.