SHIFTS IN THE WHOLESALE TRADE STATUS OF U.S. METROPOLITAN AREAS*

Considerable instability exists among large U.S. metropolitan areas in their status as wholesale trade centers. Differences in wholesale trade growth rates, changes in national shares, and shifts in rank position reflect not only population growth patterns, but also structural changes in the national economy. In the latter instance, the wholesale product mix of SMSAs is an important factor in explaining their differential fortunes within the wholesaling hierarchy.     

Differential exhumation in response to episodic thrusting along the eastern margin of the Tibetan Plateau

Thermochronological data from the Songpan-Ganze˛Fold Belt and Longmen Mountains Thrust-Nappe Belt, on the eastern margin of the Tibetan Plateau in central China, reveal several phases of differential cooling across major listric thrust faults since Early Cretaceous times. Differential cooling, indicated by distinct breaks in age data across discrete compressional structures, was superimposed upon a regional cooling pattern following the Late Triassic Indosinian Orogeny. ⁴⁰Ar/³⁹Ar data from muscovite from the central and southern Longmen Mountains Thrust-Nappe Belt suggest a phase of differential cooling across the Wenchuan-Maouwen Shear Zone during the Early Cretaceous. The zircon fission track data also indicate differential cooling across a zone of brittle re-activation on the eastern margin of the Wenchuan-Maouwen Shear Zone during the mid-Tertiary, between 38 and 10 Ma. Apatite fission track data from the central and southern Longmen Mountains Thrust-Nappe Belt reveal differential cooling across the Yingxiu-Beichuan and Erwangmiao faults during the Miocene. Forward modelling of apatite fission track data from the northern Longmen Mountains Thrust-Nappe Belt suggests relatively slow regional cooling through the Mesozoic and early Tertiary, followed by accelerated cooling during the Miocene, beginning at ca. 20 Ma, to present day.

Regional cooling is attributed to erosion during exhumation of the evolving Longmen Mountains Thrust-Nappe Belt (LMTNB) following the Indosinian Orogeny. Differential cooling across the Wenchuan-Maouwen Shear Zone and the Yingxiu-Beichuan and Erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults. Thermochronological data from the Longmen Mountains Thrust-Nappe Belt reveal a greater amount of differential exhumation across thrust faults from north to south. This observation is in accord with the prevalence of Proterozoic and Sinian basement in the hanging walls of thrust faults in the central and southern Longmen Mountains. The two most recent phases of reactivation occurred following the initial collision of India with Eurasia, suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the LMTNB.     

Hydrochemical and stable isotope evidence for the extent and nature of the effective Chalk aquifer of north Norfolk, UK

In eastern England the Chalk aquifer is covered by extensive Pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer. In this study, the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions (δ¹⁸O and δ²H) are interpreted to reveal the extent and nature of the effective Chalk aquifer of north Norfolk. It is found that the Chalk aquifer can be divided into an upper region of fresh groundwater, with a Cl concentration of typically less than 100 mg l⁻¹, and a lower region of increasingly saline water. The transition between the two regions is approximately 50 m below sea-level, and results in an effective aquifer thickness of 50–60 m in the west of the area, but less than 25 m where the Eocene London Clay boundary is met in the east of the area. Hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the Chalk. Where the Chalk is confined by low-permeability Chalky Boulder Clay, isotopically depleted groundwater (δ¹⁸O less than −7.5‰) is present, in contrast to those areas of unconfined Chalk where glacial deposits are thin or absent (δ¹⁸O about −7.0‰). The isotopically depleted groundwater is evidence for groundwater recharge during the late Pleistocene under conditions when mean surface air temperatures are estimated to have been 4.5°C cooler than at the present day, and suggests long groundwater residence times in the confined aquifer. Elevated molar Mg:Ca ratios of more than 0.2 resulting from progressive rock-water interaction in the confined aquifer also indicate long residence times. A conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater, occupying areas where confined groundwater dates from the late Pleistocene, is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body.     

Reviews

THE PERMAFROST ENVIRONMENT by S. A. Harris. 23 × 14 cm, viii and 275 pages. Croom Helm: London 1986 (ISBN 0 7099 3713 X) $A57.50 (hard).

ENVIRONMENTAL POLICIES: An International Review edited by C. C. Park. 14 × 22 cm, 315 pages. Croom Helm: London 1986 (ISBN 0 7099 2062 8) $A56.25 (hard).

A MODERN DICTIONARY OF GEOGRAPHY by J. Small and M. Witherick. 15 × 23 cm, vi and 233 pages. Edward Arnold: London 1986 (ISBN 0 7131 6434 4) $A28.95 (soft).

PROGRESS IN POLITICAL GEOGRAPHY edited by M. Pacione. 14 × 22 cm, 275 pages. Croom Helm: London 1985 (ISBN 0 7099 2087 3) $A56.25 (hard).

THE PRICE OF WAR: Urbanization in Vietnam 1954–1985, by N. Thrift and D. Forbes. 14 × 22 cm, xiv and 188 pages. Allen & Unwin: London 1986 (ISBN 0 04 3012108) $A59.95 (hard).

INDUSTRIALISATION AND LABOUR FORCE PROCESSES: A Case Study of Peninsular Malaysia (Research Papers on Development in East Java and West Malaysia No. 1) by T. G. McGee and seven others. 17 × 24 cm, xviii and 244 pages. Research School of Pacific Studies, Australian National University: Canberra 1986 (ISBN 0 86784 991 6) $A15.00 plus postage and packing (soft).

CITIES OF THE WORLD: A Compilation of Current Information on Cultural, Geographical, and Political Conditions in the Countries and Cities of Six Continents. Based on the Department of State's ‘Post Reports’ (second edition) edited by M. W. Young and S. L. Stetler. 16 × 23 cm, 3,056 pages in 4 volumes. Gale Research Company: Detroit 1985 (ISBN 0 8103 2059 2) $US235.00 (hard). Supplement 758 pages. 1986 (ISBN 0 8103 1110 0) $US84.00 (hard).     

Evidence for frost on Rhea's surface

We have observed Rhea (S5) at 1.6 μm and 2.2 μm at Mt. Wilson using the Caltech photometer on the 1.52m and 2.54m telescopes. The infrared spectral reflectances relative to 0.55μm are 0.8 (±0.1 p.e.) at 1.65μm and 0.6 (±0.1 p.e.) at 2.2μm. Such absorption bands in the near infrared are not consistent with spectra of most rocks or minerals; even carbonaceous chondritic materials have nearly flat reflectances over this spectral region. Frosts, however, have strong absorption bands in the 1–3μm region. In particular, the broadband infrared reflectances of Rhea are similar to those of the Galilean satellites Europa (J2) and Ganymede (J3) and also the rings of Saturn (all of which are known from high resolution scans to have water frosts on their surfaces). The broadband photometry does not have sufficient resolution to identify the frost species: but Rhea's low density, high albedo and relatively flat reflectance from 0.3μm to 1.1μm as well as the low infrared reflectances reported here are consistent with the presence of water ice on Rhea's surface.     

Strong hydrographic controls on spatial and seasonal variability of dissolved organic carbon in the Chukchi Sea

A detailed analysis of dissolved organic carbon (DOC) distribution in the Western Arctic Ocean was performed during the spring and summer of 2002 and the summer of 2003. DOC concentrations were compared between the three cruises and with previously reported Arctic work. Concentrations of DOC were highest in the surface water where they also showed the highest degree of variability spatially, seasonally, and annually. Over the Canada Basin, DOC concentrations in the main water masses were: (1) surface layer (71±4 μM, ranging from 50 to 90 μM); (2) Bering Sea winter water (66±2 μM, ranging from 58 to 75 μM); (3) halocline layer (63±3 μM, ranging from 59 to 68 μM), (4) Atlantic layer (53±2 μM, ranging from 48 to 57 μM), and (5) deep Arctic layer (47±1 μM, ranging from 45 to 50 μM). In the upper 200 m, DOC concentrations were correlated with salinity, with higher DOC concentrations present in less-saline waters. This correlation indicates the strong influence that fluvial input from the Mackenzie and Yukon Rivers had on the DOC system in the upper layer of the Chukchi Sea and Bering Strait. Over the deep basin, there appeared to be a relationship between DOC in the upper 10 m and the degree of sea-ice melt water present. We found that sea-ice melt water dilutes the DOC signal in the surface waters, which is contrary to studies conducted in the central Arctic Ocean.