What status for the Quaternary?

The status of the Quaternary, long regarded as a geological period effectively coincident with the main climatic deterioration of the current Ice Age, has recently been questioned as a formal stratigraphic unit. We argue here that it should be retained as a formal period of geological time. Furthermore, we consider that its beginning should be placed at the Gauss-Matuyama magnetic chron boundary at about 2.6 Ma, rather than at its current position at about 1.8 Ma. The Quaternary would be formally subdivided into the Pleistocene and Holocene epochs. The global chronostratigraphical correlation table proposed is enclosed at the back of this issue.     

Contemporaneous Trachyandesitic and Calc-alkaline Volcanism of the Huerto Andesite, San Juan Volcanic Field, Colorado, USA

Locally, voluminous andesitic volcanism both preceded and followedlarge eruptions of silicic ash-flow tuff from many calderasin the San Juan volcanic field. The most voluminous post-collapselava suite of the central San Juan caldera cluster is the 28Ma Huerto Andesite, a diverse assemblage erupted from at least5–6 volcanic centres that were active around the southernmargins of the La Garita caldera shortly after eruption of theFish Canyon Tuff. These andesitic centres are inferred, in part,to represent eruptions of magma that ponded and differentiatedwithin the crust below the La Garita caldera, thereby providingthe thermal energy necessary for rejuvenation and remobilizationof the Fish Canyon magma body. The multiple Huerto eruptivecentres produced two magmatic series that differ in phenocrystmineralogy (hydrous vs anhydrous assemblages), whole-rock majorand trace element chemistry and isotopic compositions. Hornblende-bearinglavas from three volcanic centres located close to the southeasternmargin of the La Garita caldera (Eagle Mountain–FourmileCreek, West Fork of the San Juan River, Table Mountain) definea high-K calc-alkaline series (57–65 wt % SiO₂) that isoxidized, hydrous and sulphur rich. Trachyandesitic lavas fromwidely separated centres at Baldy Mountain–Red Lake (westernmargin), Sugarloaf Mountain (southern margin) and Ribbon Mesa(20 km east of the La Garita caldera) are mutually indistinguishable(55–61 wt % SiO₂); they are characterized by higher andmore variable concentrations of alkalis and many incompatibletrace elements (e.g. Zr, Nb, heavy rare earth elements), andthey contain anhydrous phenocryst assemblages (including olivine).These mildly alkaline magmas were less water rich and oxidizedthan the hornblende-bearing calc-alkaline suite. The same distinctionscharacterize the voluminous precaldera andesitic lavas of theConejos Formation, indicating that these contrasting suitesare long-term manifestations of San Juan volcanism. The favouredmodel for their origin involves contrasting ascent paths anddifferentiation histories through crustal columns with differentthermal and density gradients. Magmas ascending into the mainfocus of the La Garita caldera were impeded, and they evolvedat greater depths, retaining more of their primary volatileload. This model is supported by systematic differences in isotopiccompositions suggestive of crust–magma interactions withcontrasting lithologies. KEY WORDS: alkaline; calc-alkaline; petrogenesis; episodic magmatism; Fish Canyon system     

Columnar calcites as testimony of diagenetic overprinting at the boundary between Upper Tournaisian dolomites and limestones (Belgium): multiple origins for apparently similar features

In topographic flat areas, sedimentary settings may vary from one outcrop to another. In these settings, calcite precipitates may yield macroscopically similar columnar features, although they are products of different sedimentary or diagenetic processes. Three columnar calcite crystal fabrics, i.e. rosettes, palisade crusts and macro-columnar crystal fans, have been differentiated near and at the contact between Upper Tournaisian dolomites and limestones along the southern margin of the Brabant-Wales Palaeohigh. Their petrographic characteristics, and geochemical and fluid inclusion data provide information on the (dia)genetic processes involved. Rosettes composed of non-luminescent columnar calcite crystal fans (1–5 cm in diameter) developed on top of one another, forming discrete horizons in repetitive sedimentary cycles. The cycles consist of three horizons: (I) a basal horizon with fragments from the underlying horizon, (II) a micrite/microspar horizon with incipient glaebules, (III) an upper horizon consisting of calcite rosettes, with desiccation features. The petrographical features and δ¹⁸O signatures of −10·0 to −5·5‰ and δ¹³C values of −5·5 to −3·2‰ support either evaporative growth, an evaporative pedogenic origin, or overprinting of marine precipitates. Palisade crusts, composed of a few to 10 mm long non-luminescent calcite crystals, coat palaeokarst cavities. Successive palisade growth-stages occur which are separated by thin laminae of micrite or detrital quartz, displaying a geopetal arrangement. Palisade crusts are interpreted as intra-Mississippian speleothems. This interpretation is supported by their petrographic characteristics and isotopic signature (δ¹⁸O = −8·7 to −6·5‰ and δ¹³C = −4·8 to −2·5‰). Macro-columnar crystals, 1–50 cm long, developed mainly perpendicular to cavity walls and dolomite clasts. Crystal growth stages in the macro-columnar crystals are missing. δ¹⁸O values vary between −16·4 and −6·8‰ and δ¹³C values between −5·2 and −0·9‰. These features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification.     

OPERATION IRAQI FREEDOM: A MILITARY GEOGRAPHICAL PERSPECTIVE*

ABSTRACT. The war in Iraq has spanned the full spectrum of military operations: intense combat, stability‐and‐support operations, and peacetime activities. Regardless of their nature and relative intensity, military operations are shaped by the characteristics of the military operating environment. Consequently, the scale, tempo, and complexity of any type of military endeavor are linked to the physical and cultural landscapes of the region in which it is conducted. Military geographers use geographical information, tools, and techniques to examine those links. Iraq's operating environment is studied to identify the relevant components of its physical and human geography. This military geographical examination of Iraq tells us a great deal about how the physical and cultural environment have influenced the war, as well as how the complexity of its human landscape continues to affect the postwar rebuilding of the country.     

Assessing participatory GIS for community-based natural resource management: claiming community forests in Cameroon

This paper critically reviews and analyses participatory GIS (PGIS) and participatory mapping applications within participatory spatial planning for community-based natural resource management in developing countries. There is an often implicit assumption that PGIS use is effective, in that it meets content needs, satisfies underlying local stakeholder interests and therefore is a tool for better governance. The analytical framework looks at participatory spatial planning performance with respect to key dimensions of governance, especially the intensity of community participation and empowerment, equity within communities and between 'governed' and 'governing', respect for indigenous knowledge, rights, ownership, legitimacy, and effectiveness. Specific development focus is given by a case study using participatory mapping and PGIS in community forest legitimization, planning and management in Tinto, Cameroon. 'Good governance' criteria are applied ex-post to the implementation procedures, the geo-information outputs, and the longer-term outcomes of the PGIS processes. Impacts of incorporating PGIS were examined in terms of the types and degrees of participation in the process; access to, and the uses made of, the geographic information; whether the information outputs met stakeholders' requirements; and the overall changes in equity and empowerment in the community. It was found that PGIS/participatory mapping processes contributed – positively, though not comprehensively – to good governance, by improving dialogue, redistributing resource access and control rights – though not always equitably – legitimizing and using local knowledge, exposing local stakeholders to geospatial analysis, and creating some actor empowerment through training. PGIS promoted empowerment by supporting community members' participation in decision-making and actions, and by enabling land use planning decisions beyond community forestry itself.     

Beyond the 'Outer Crescent': the Mackinder century in New Zealand geopolitics

This paper proposes that, although Mackinder never mentions New Zealand in his influential 1904 paper and despite the absence of a formal Kiwi geopolitical tradition, 'The geographical pivot of history' provides a useful framework with which to approach New Zealand geopolitics. The argument uses two Mackinderian ideas to suggest three phases in New Zealand's security relationships during the Mackinder century. First, New Zealand's commitment to Mackinder's 'pivot area' notion of 'imperial defence' and 'collective security' characterized its dependent security phase. Between 1973 and 1990/91 there was a transitional security phase towards Mackinder's second 'global interconnectedness' idea. Third, this shift led to a current interdependent security phase which is characterized by the recognition that New Zealand's security relationships, despite its geographic isolation, are mutually dependent on political, economic, and military events around the world. The impact of 11 September 2001 and the consequent 'war on terror' are also considered. The paper concludes by suggesting that New Zealand's post-conflict reconstruction efforts in Afghanistan and Iraq point to the continuing relevance of Mackinder's 'The geographical pivot of history' to New Zealand geopolitics.     

Towards a framework for learning with GIS: The case of Urban World, a hypermap learning environment based on GIS

Off-the-shelf GIS toolboxes are inadequate for pedagogic purposes. Urban World , an Arc View application, attempts to address this shortcoming by including special features designed to foster student progress towards a better understanding of urban environments. This paper provides context for the Urban World system in an active, authentic learning environment for students of urban geography and planning at junior and senior levels in undergraduate curricula at universities in the United States. The paper describes the rationale for, and implementation of, several components of Urban World : a special graphid user interface; productivity tools for facilitating the acquisition of practical skills of mapping and spatial analysis; tools for accessing, undertaking, and submitting homework assignments in a paper-less class; and various devices for assisting students to undertake spatial reasoning. GIS are Seen as an enabling technology for improving understanding by means of engaging students in empirical analysis. Spatial problem solvers and decision makers reach sound conclusions by employing reasoning skills applied to well-formed databases; scientific research makcs progress with sound reasoning of many types. The effective teaching and learning about the geography of our world requires a strong foundation of spatid reasoning.     

The Invasion of Human Epidemic Diseases into Australia, New Zealand, and the Southwest Pacific: The Geographical Context

Abstract. Changes in the spread of disease-causing viruses into Australia, New Zealand and the Southwest Pacific are examined. Particular reference is made to the impact of reduced travel times between those areas and both Western Europe and Southeast Asia on the transfer of infectious human diseases, notably smallpox, measles, influenza and rubella. The likely consequences of increasing population size and decreasing remoteness on the entry of other infectious diseases are noted.     

Near-surface shrinkage and carbonate replacement processes, Arran Cornstone Formation, Scotland

A 47 m thick succession of conglomerates, sandstones and mudstones, of Late Devonian or Early Carboniferous age, outcrops at Fallen Rocks in northeast Arran (western Scotland). It is defined here as the type section of the Arran Cornstone Formation. At numerous levels in the succession, varieties of fissures and carbonate concretions formed during the accumulation of the Formation. The fissures opened as a result of drying-shrinkage, and were closed again either by filling with different sediment, or by wetting and expansion of the fissure wall sediment. Carbonate concretions form complete beds, discontinuous, bedding-concordant sheets, or bedding-discordant nodules or rods (the rod cornstones). These concretions formed close enough to the surface to be incorporated, after erosion and redeposition, as clasts into overlying beds. The concretions were formed by growth of micrite, mainly by replacement, but shrinkage displacement played an important role in subsequently fracturing and reworking the micrite. The micrite was also locally replaced by microspar and spar, and this involved dissolution and precipitation. No independent evidence of biological influence in any of these processes has been found.     

Replacement of evaporites within the Permian Park City Formation, Bighorn Basin, Wyoming, USA

The Permian Park City Formation consists of cyclically bedded subtidal to supratidal carbonates, cherts and siltstones. Early diagenesis of Park City Formation carbonates occurred under the influence of waters ranging from evaporative brines to dilute meteoric solutions and resulted in evaporite emplacement (syndepositional nodules and cements), as well as dolomitization, silicification and leaching of carbonate grains. Major differences are seen, however, in the diagenetic patterns of subsurface and surface sections of Park City Formation rocks. Subsurface samples are characterized by extensively preserved evaporite crystals and nodules, and preserve evidence of significant silicification (chert, chalcedony and megaquartz) and minor calcitization of evaporites. In outcrop sections, the evaporites are more poorly preserved, and have been replaced by silica and calcite and also leached. The resultant mouldic porosity is filled with widespread, very coarse, blocky calcite spar. These replacements appear to be multistage phenomena. Field and petrographic evidence indicates that silicification involved direct replacement of evaporites and occurred during the early stages of burial prior to hydrocarbon migration. Siliceous sponge spicules provided a major source of silica, and the fluids involved in replacement were probably a mixture of marine and meteoric waters. A second period of replacement and minor calcitization is inferred to have occurred during deep burial (under the influence of thermochemical sulphate reduction), although the presence of hydrocarbons probably retarded most other diagenetic reactions during this time interval. The major period of evaporite diagenesis, however, occurred during late stage uplift. The late stage replacement and pore-filling calcites have δ¹³C values ranging from 0·5 to -25·3%, and δ¹⁸O values of -16·1 to -24·3₀ (PDB), reflecting extensive modification by meteoric water. Vigorous groundwater flow, associated with mid-Tertiary block faulting, led to migration of meteoric fluids through the porous carbonates to depths of several kilometres. These waters reacted with the in situ hydrocarbon-rich pore fluids and evaporite minerals, and precipitated calcite cements. The Tosi Chert appears to have been an even more open system to fluid migration during its burial and has undergone a much more complex diagenetic history, as evidenced by multiple episodes of silicification, calcitization (ferroan and non-ferroan), and hydrocarbon emplacement. The multistage replacement processes described here do not appear to be restricted to the Permian of Wyoming. Similarly complex patterns of alteration have been noted in the Permian of west Texas, New Mexico, Greenland and other areas, as well as in strata of other ages. Thus, multistage evaporite dissolution and replacement may well be the norm rather than the exception in the geological record.