Modelling spatially and temporally distributed phenomena: new methods and tools for GRASS GIS

Abstract

The concept of GRASS (Geographic Resources Analysis Support System) as an open system has created a favourable environment for integration of process based modelling and GIS. To support this integration a new generation of tools is being developed in the following areas: (a) interpolation from multidimensional scattered point data, (b) analysis of surfaces and hypersurfaces, (c) modelling of spatial processes and, (d) 3D dynamic visualization. Examples of two applications are given-spatial and temporal modelling of erosion and deposition, and multivariate interpolation and visualization of nitrogen concentrations in the Chesapeake Bay.     

Diagenesis and reservoir quality of the Aldebaran Sandstone, Denison Trough, east-central Queensland, Australia

The Lower Permian Aldebaran Sandstone is the principal hydrocarbon reservoir in the Denison Trough (Bowen Basin), east-central Queensland, Australia. It accumulated in a wide range of fluvio-deltaic and nearshore marine environments. Detailed petrological study of the unit by thin section, X-ray diffraction, scanning electron microscopy, electron microprobe and isotopic analysis reveals a complex diagenetic history which can be directly related to depositional environment, initial composition and burial-temperature history. Early diagenetic effects included the precipitation of pyrite, siderite and illite-smectite rims (δ¹⁸O (SMOW) =+8.9 to + 11.3‰). Deep burial effects included physico-chemical compaction and the formation of quartz overgrowths, siderite (δ¹³C(PDB) =?34.0 to + 11.5‰, δ¹⁸O =?0.7 to +22.7‰), illite/illite-smectite and ankerite (δ¹³C=?9.3 to ?4.9‰) δ¹⁸O=+ 7.6 to + 14.4‰). Involved fluids were in part ‘connate meteoric’ water derived from compaction of the underlying freshwater Reids Dome beds. Important post-maximum burial effects, controlled by deep meteoric influx from the surface, were ankerite and labile grain dissolution and formation of kaolinite (δ¹⁸O=+7.8 to +8.9‰, δD=?115 to ?99‰), calcite (δ¹³C=?9.5 to +0.9‰, δ¹⁸O=+9.0 to +20.0‰) and dawsonite (δ¹³C=?4.0 to +2.3‰, δ¹⁸O=+9.8 to +19.8‰), the formation of dawsonite reflecting eventual stagnation of the aquifer. Entrapment of contained hydrocarbons was a relatively recent event which may be continuing today. Reservoir quality varies from marginal to good in the west to poor in the east, with predictable trends being directly linked to depositional environment and diagenesis.     

The Prinsen af Wales Bjerge Formation Lavas, East Greenland: the Transition from Tholeiitic to Alkalic Magmatism during Palaeogene Continental Break-up

We present elemental and isotopic (Sr–Nd–Pb–Hf–Os–He)data on primitive alkalic lavas from the Prinsen af Wales Bjerge,East Greenland. Stratigraphical, compositional and ⁴⁰Ar–³⁹Ardata indicate that this inland alkalic activity was contemporaneouswith the upper parts of the main tholeiitic plateau basaltsand also post-dated them. The alkalic rocks show a marked crustalinfluence, indicating establishment of new magmatic plumbingsystems distinct from the long-lived coastal systems that fedthe relatively uncontaminated plateau basalts. The least contaminatedlavas have high ³He/⁴He isotope ratios (R/R_A 12·4–18·5),sub-chondritic ¹⁸⁷Os/¹⁸⁸Os_i (0·120–0·126),low     

TENDING CULTURAL LANDSCAPES AND FOOD CITIZENSHIP IN TORONTO'S COMMUNITY GARDENS*

ABSTRACT. Scattered throughout the city of Toronto are more than no community gardens, sites of place‐based politics connected to the community food‐security movement. The gardens, spaces where passions for plants and food are shared, reflect the city's shifting cultural landscape and represent an everyday activity that is imbued with multiple meanings. Toronto's community food‐security movement uses gardens as one strategy to regenerate the local food system and provide access to healthy, affordable food. Three garden case studies expand on the complexities of “food citizenship,” illustrating the importance of that concept to notions of food security. The gardens reveal the role gardeners play in transforming urban spaces, the complex network of organizations working cooperatively and in partnership to implement these projects, and the way in which social and cultural pluralism are shaping the urban landscape.     

The effect of Mn on mineral stability in metapelites

Calculations based on a KMnFMASH petrogenetic grid derived using an internally consistent thermodynamic dataset indicate that the principal effect of the presence of Mn in average subaluminous pelite compositions is to stabilize garnet to higher and lower pressures and temperatures over a wide range of bulk compositions. Garnet-bearing fields expand to lower temperatures and pressures with the addition of Mn, and garnet appears as an extra phase at low pressures. The addition of Mn also increases the number and extent of four AMnFM phase assemblages and stabilizes five AMnFM phases along univariant reactions. The KMnFMASH system predictions for typical subaluminous pelite bulk compositions match the sequence of isograds and assemblages observed in the Barrovian zones. The sequence of assemblages observed in the Stonehaven section can also be predicted if there is variation in bulk composition within the stratigraphic section. Mn appears to be less important in producing the sequence of isograds and garnet-absent assemblages in the low-pressure Buchan zones. The addition of Mn to the calculations does not change the sequence of isograds that are predicted to be stable in a regional metamorphic terrane, but the P – T  position of these isograds does change. In particular, the predicted temperature of the garnet-in isograd is lowered by as much as 100 °C by the addition of Mn to KFMASH. Mn also increases the range of metapelite bulk compositions that develop the assemblages traditionally identified as metapelite isograds.     

Mass spectrometric dating of flowstones from Stump Cross Caverns and Lancaster Hole,Yorkshire: palaeoclimate implications

A terrestrial flowstone sequence 97 cm thick from Stump Cross Caverns, Yorkshire, has been dated by both mass spectrometric and alpha spectrometric ²³⁸U-²³⁴U-²³⁰Th dating, and is demonstrated to have been deposited predominantly during interstadial periods over the last 170 ka, with no growth in periods of glaciation or within the Oxygen Isotope Stage 5 interglacial. Growth also occurs within Oxygen Isotope Stages 4 and 6, the former possibly correlating with interstadials recognised in high-resolution ice and ocean-core records. Comparison with the timing of growth of a mass spectrometrically dated Lancaster Hole flowstone, also from the same region, demonstrates only limited agreement. These differences are due to two factors limiting deposition at Stump Cross: flooding of the cave passage in warm periods, and the development of continuous permafrost or glacier cover in periods of severe climatic deterioration. Deposition at Lancaster Hole was controlled by limitations in ground-water supply rather than flooding of the cave passage. The results presented here demonstrate that in addition to regional palaeoclimate factors, local site conditions may limit speleothem growth. We conclude that in future palaeoclimate studies, the growth record from several coeval speleothem samples must be considered before a regional palaeoclimate interpretation can be made.     

Orbital-scale Asian summer monsoon variations:Paradox and exploration

The Asian summer monsoon(ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM.(1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated ~100 kyr(thousand years) periodicity, while the cave oxygen-isotope(δ18 O) records reveal periodicity in an almost pure precession band(~20 kyr periodicity)—the "Chinese 100 kyr problem".(2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8–10 kyr to Northern Hemisphere summer insolation(NHSI), whereas the Asian cave δ18 O records follow NHSI without a significant lag—a discrepancy termed the "sea-land precession-phase paradox". How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the "Chinese 100 kyr problem" and "sea-land precession-phase paradox".     

Resolving Crustal and Mantle Contributions to Continental Flood Volcanism, Yemen; Constraints from Mineral Oxygen Isotope Data

Oxygen isotope ratios determined by laser fluorination analysison olivine, clinopyroxene and plagioclase separated from 31Oligocene flood basalts and rhyolites from Yemen display smallbut significant variations (5·1–6·2