A COMPUTER PROGRAM FOR GRAIN-SIZE DATA1

The computer program presented here seeks to improve estimation of statistical parameters for grain-size data by use of interpolated values. Interpolation is made by fitting a series of overlapping parabolas to the data, and follows the method of Snyder (1961). The values are used in moment formulas to compute standard statistical measures. Skewness and kurtosis are reduced by the interpolation data, and extreme positive values of kurtosis tend to be greatly reduced. The program also picks major modes, the median, and sediment type.     

Authigenic pyrite and gypsum in South West African continental slope sediments

An unusual association of authigenic pyrite and authigenic gypsum has been found in silty clays recovered from the South West African continental slope. Nannofossil content suggests that the sediments are Upper Miocene-Lower Pliocene in age. Pyrite occurs as (1) granular masses, (2) ‘worm’tubes, (3) foraminiferal infillings, and (4) framboids. Gypsum occurs as euhedral single or twinned crystals of selenite. ‘Worm’tubes and foraminiferal infillings of pyrite are partially or completely enclosed in some gypsum crystals. Electron microprobe analyses show a relatively high concentration of manganese in both the granular masses and tubes. Present-day waters off this coast are dominated by the upwelling of cold, nutrient-enriched waters (the Benguela Current). These rich waters support an enormous population of plankton. Death and decomposition of these plankton consume oxygen, thereby creating a belt of anaerobic sediments close to shore. An Upper Miocene-Lower Pliocene regression (Dingle & Scrutton, 1974) lowered sea level and shifted an older analogue of this upwelling zone seaward, eventually establishing an anaerobic environment in places on the present continental slope. Anaerobic bacteria thrived in these conditions. They reduced SO₄ dissolved in sea water, initiating the formation of H₂S. The H₂S reacted with iron minerals present in the sediment to form FeS. Addition of elemental sulphur produced pyrite. This strongly reducing, low pH, environment became saturated with calcium obtained by the dissolution of planktonic calcareous organisms. Gypsum was precipitated once the product of the concentrations of dissolved calcium and SO₄ exceeded the gypsum solubility product.     

Petrology of recent caliche pisolites, spherulites, and speleothem deposits from central Texas

Recent caliche, including nodules, pisolites, crusts, internal sediment, speleothem deposits, and spherulites, has formed within the dolomitic Cretaceous Edwards Formation of central Texas. As weathering altered the host strata, rhombic crystals of calcite were precipitated concomitantly with dissolution of the dolomite, thereby forming nodules. The highly altered dolomite (i.e. pulverulite) was then removed and spar, internal sediment, and travertine accumulated in the internodular voids. Nodular masses of calcite and dolomite are the most prominent constituent of the caliche. Some of the nodules have a well developed concentric structure as well as other characteristics similar to hypersaline pisolites. Features which appear to be useful in distinguishing caliche from hypersaline pisolites are: regional geological setting, association with other caliche and palaeosoil deposits, types of fossils present, and the presence of rhombic calcite and/or bladed sparry calcite with triangular shaped cross-section. A brick-like calcite texture and relict aragonite rays characterize hypersaline pisolites. Incipient neomorphism of the nodules and pisolites has resulted in the development of a radial pattern of spar within these structures. Geopetal deposits of internal sediment, including terra rossa soil, inhibited spar growth in the upward direction; consequently, spar is much better developed on the undersides of pisolites. Crusts and travertine flowstone (speleothem) deposits are intimately associated with the nodular masses and internal sediment. The brecciated thin crusts and travertine flowstone are end products of the same processes. The crusts formed during times of periodic desiccation of the growing surface while the flowstone formed when water was relatively abundant. Spherulitic bodies within the caliche, commonly 1–2 mm in diameter, display a radial texture and yet are composed of single crystals of calcite. The structures are the product of neomorphosed Microcodium or Microcodium-like globular bodies.     

波浪操纵说

(一)通论谈天气学者,挽近可分三派:曰挪威派创自皮叶克纳司(V.Bjrk-ncs),其说以为天气之变化,其主因仅限于对流层内,是为极面学说(Polarfront-Theorie)。曰弗朗克孚(Frankfurt a.M.)派,以为天气之变化,其主因并不在于对流层,而在平流层中。此说导源于费干(H.v.Ficker)及德芳(A.Defant),但发挥而光大之,则为弗朗克孚大学已故教授司徒沸(G.ve)及其助手米盖(R.Mügge),是为平流层操纵说(Stratosphrische Steuerung)。曰来布齐(Leipzig)派,创自魏克孟(L.Weickmann),以为天气之演变,由于大气中波浪之起伏,此种波浪,既可导源于平流层,亦可导源于对流层,是为波浪操纵说(Wcllen-     

THE LAST ICE SHEET IN NORTH-WEST SCOTLAND: RECONSTRUCTION AND IMPLICATIONS

Recent models of the last Scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation. This proposition has been investigated on 140 mountains over an area of 10,000 km² in NW Scotland. Outside the limits of the later Loch Lomond Readvance in this area there is evidence for a single high-level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris. This limit occurs at altitudes ranging from 425 to 450 m in the Outer Hebrides to >950 m on the mainland, and is best developed on lithologies that resisted breakdown after ice-sheet downwastage. Interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by: (1) joint-depth and Schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit; (2) a much greater representation of gibbsite (a pre-Late Devensian weathering product) in the clay fraction of soils above the limit; (3) cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit; (4) the sharpness of the limit at some sites and its regular decline along former ice flowlines; and (5) shear stress calculations based on the inferred altitude and gradient of the former ice surface. Reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from >900 m to ca. 550 m at the north coast. Independent dispersion centres fed broad ice streams that occupied major troughs. On Skye an ice dome >800 m deflected the northwestwards movement of mainland ice, but the mountains of Rum were over-ridden by mainland ice up to an altitude of ca. 700 m. The Outer Hebrides supported an independent ice cap that was confluent with mainland ice in the Minches. Extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative, and suggests that low-gradient ice streams extended across the Hebridean Shelf offshore. Wider implications of this research are: (1) that blockfields and other periglacial weathering covers are not all of the same age or significance, depending on the resistance of different lithologies to frost weathering; (2) that the contrasting degree of glacial modification in the Western and Eastern Highlands of Scotland may reflect a former cover of predominantly warm-based ice in the former and predominantly cold-based ice in the latter; and (3) that the approach and techniques developed in this study have potential application for constraining ice-sheet models, not only in areas peripheral to the main centres of ice accumulation in Britain and Ireland, but also in other mountain areas where nunataks protruded through warm-based Late Pleistocene ice masses.     

Holocene denudation of the northwest sector of Iceland as determined from accumulation of sediments on the continental margin

Radiocarbon-dated marine cores, measurements of sediment density and seismic surveys were used to estimate the sediment and mass accumulation rates (m/kyr and kg/m²/kyr) in the troughs from the southwest to north-central Iceland shelf (i.e. northwest sector of Iceland). The 3.5-kHz seismic survey showed varying thicknesses of acoustically transparent sediment in the troughs, whereas the inter-trough banks were largely devoid of sediment. The survey showed a pervasive reflector 1 to ≥60 m below the sea floor, which turned out to be Saksunarvatn tephra, dated at 10 180±60 cal. yr BP. The 3.5-kHz analogue data were digitized at 1-min intervals and provided 1645 estimates of maximum sediment thickness and 979 estimates of sediment accumulation over the last 10 200 cal. yr BP. Maximum sediment accumulation occurred in the mid-troughs and not, as expected, in the fjords. The median sediment accumulation rate (SAR) based on the core data was 0.23 m/kyr, but was 0.77 m/kyr based on the seismic data: the difference is attributed to coring limitations. Based on the volume of offshore sediment and the contributing terrestrial drainage area, the Holocene denudation of northern Iceland (c. 50 000 km²) is calculated to have been between 0.02 to 0.05 m/kyr, substantially lower that the 1-3 m/kyr derived from the suspended sediment load of rivers from southern Iceland but in agreement with the rate of accumulation of Holocene glacial lacustrine sediments in central Iceland.     

Peat multi-proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia

Sillasoo, Ü., Mauquoy, D., Blundell, A., Charman, D., Blaauw, M., Daniell, J. R. G., Toms, P., Newberry, J., Chambers, F M. & Karofeld, E. 2007 (January): Peat multi‐proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia. Boreas, Vol. 36, pp. 20–37. Oslo. ISSN 0300–9483. As part of a wider project on European climate change over the past 4500 years, a 4.5‐m peat core was taken from a lawn microform on Männikjärve bog, Estonia. Several methods were used to yield proxy‐climate data: (i) a quadrat and leaf‐count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water‐table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100,3010–2990,2300, 1750–1610, 1510, 1410, 1110, 540 and 310 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP, the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Mannikjarve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog micro‐depressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.     

Marginal formations of the last Kara and Barents ice sheets in northern European Russia

Glacial landforms in northern Russia, from the Timan Ridge in the west to the east of the Urals, have been mapped by aerial photographs and satellite images supported by field observations. An east-west trending belt of fresh hummock-and-lake glaciokarst landscapes has been traced to the north of 67°N. The southern boundary of these landscapes is called the Markhida Line, which is interpreted as a nearly synchronous limit of the last ice sheet that affected this region. The hummocky landscapes are subdivided into three types according to the stage of postglacial modification: Markhida, Harbei and Halmer. The Halmer landscape on the Uralian piedmont in the east is the freshest, whereas the westernmost Markhida landscape is more eroded. The west-east gradient in morphology is considered to be a result of the time-transgressive melting of stagnant glacier ice and of the underlying permafrost. The pattern of ice-pushed ridges and other directional features reflects a dominant ice flow direction from the Kara Sea shelf. Traces of ice movement from the central Barents Sea are only discernible in the Pechora River left bank area west of 50°E. In the Polar Urals the horseshoe-shaped end moraines at altitudes of up to 560 m a.s.l. reflect ice movement up-valley from the Kara Ice Sheet, indicating the absence of a contemporaneous ice dome in the mountains. The Markhida moraines, superimposed onto the Eemian strata, represent the maximum ice sheet extent in the western part of the Pechora Basin during the Weichselian. The Markhida Line truncates the huge arcs of the Laya-Adzva and Rogovaya ice-pushed ridges protruding to the south. The latter moraines therefore reflect an older ice advance, probably also of Weichselian age. Still farther south, fluvially dissected morainic plateaus without lakes are of pre-Eemian age, because they plunge northwards under marine Eemian sediments. Shorelines of the large ice-dammed Lake Komi, identified between 90 and 110 m a.s.l. in the areas south of the Markhida Line, are radiocarbon dated to be older than 45 ka. The shorelines, incised into the Laya-Adzva moraines, morphologically interfinger with the Markhida moraines, indicating that the last ice advance onto the Russian mainland reached the Markhida Line during the Middle or Early Weichselian, before 45 ka ago.     

WHAT'S IN A NAME? LINGUISTICS,GEOGRAPHY, AND TOPONYMS*

In differing ways, linguistics and geography each observes that a name's significance is connected to a society. According to lexical theory, a word is arbitrary: Its sound and meaning have no intrinsic link; its function is grammatical. Names are, however, special words. We bestow names based on how they sound or on what they may already have come to represent; names are not arbitrary. In turn, toponyms are special names, and as example we discuss a specific one, “New Orleans.” Far from an arbitrary pairing of form and meaning, this toponym reveals that names reflect the experience of the people who use them.     

THE CHANGING LOCATION OF TRADE AND SERVICES IN GUADALAJARA,MEXICO, 1994–2004*

The location of trade and services in Guadalajara, Mexico, is in flux as suburban commercial centers compete with the traditional downtown for new businesses and employment. Since the mid‐1990s a factor driving the change has been the introduction of American‐style big‐box retailers, corporate franchise supermarkets, and large suburban shopping malls. In this article I analyze the changing patterns of commercial and service businesses and employment from 1994 to 2004 in order to compare suburban and urban growth. My analysis includes comparative measures of change in neighborhoods immediately surrounding Walmart stores and by disaggregated types of commercial districts. Results indicate that a complementary relationship has developed: Suburbs are increasingly strong in the services, but the downtown remains a commercial hub. Moreover, some traditional small vendors in close proximity to Walmart may suffer, but growth in employment and in the service sector near Walmarts is high.