A GEOGRAPHIC CRITERION FOR IDENTIFYING PROPERTY-TAX ASSESSMENT INEQUITY

Equitable tax assessment requires that houses having the same market value must also have identical assessed values. With a map of dwellings' assessed-value-to-market-value ratios, it is possible to identify neighborhoods that are significantly overassessed or underassessed; this can lead to an understanding of the causes of misassessment. When houses or neighborhoods are demonstrated to be inequitably assessed, corrective action can be taken to eliminate the inequity. This essay is an example of the application of geographic techniques to spatial public-policy formulation.     

Structure and evolution of mass transport deposits in the South Caspian Basin,Azerbaijan

The Quaternary to late Pliocene sedimentary succession along the margin of the South Caspian Basin contains numerous kilometre‐scale submarine slope failures, which were sourced along the basin slope and from the inclined flanks of contemporaneous anticlines. This study uses three‐dimensional (3D) seismic reflection data to visualise the internal structure of 27 mass transport deposits and catalogues the syndepositional structures contained within them. These are used to interpret emplacement processes occurring during submarine slope failure. The deposits consist of three linked structural domains: extensional, translational and compressive, each containing characteristic structures. Novel features are present within the mass transport deposits: (1) a diverging retrogression of the headwall scarp; (2) the absence of a conventional headwall scarp around growth stratal pinch outs; (3) restraining bends in the lateral margin; (4) a downslope increase in the throw of thrust faults. The results of this study shed light on the deformation that occurred during submarine slope failure, and highlight an important geological process in the evolution of the South Caspian Basin margin.     

Late Pleistocene baldcypress (Taxodium distichum) forest deposit on the continental shelf of the northern Gulf of Mexico

Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud-peat (72±8 ka OSL), mud-sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial-marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) ¹⁴C a BP), which is part of a lower shoreface or marine-dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea-level rise occurring ~60 or ~40 ka ago provided opportunities for local flood-plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf.     

RbSr and KAr ages of paleozoic glauconites from Ohio—Indiana and Missouri,U.S.A.

Glauconite pellets from the Lower Silurian Brassfield Formation on both limbs of the Cincinnati Arch in Ohio and Indiana give a RbSr age of 370 ± 11 Ma, which is substantially younger than the stratigraphic age of the formation. The age is concordantcwith conventional KAr ages of 355 ± 6 and 368 ± 5 Ma for two of the same glauconites. Concordant ages were also obtained from the Viburnum Trend in Missouri, where glauconite pellets from the Davis Formation in an ore-zone collapse structure into the underlying Bonneterre Formation give a RbSr age of 387 ± 21 Ma and conventional KAr ages of 368 ± 5 and 369 ± 5 and 369 ± 5 Ma. A third suite of glauconite from the Bonneterre Formation in the Old Lead Belt ～ 10 km from the nearest ore body has given a RbSr age of 423 ± 7 Ma and slightly older conventional KAr ages of 434 ± 6, 445 ± 6 and 441 ± 11 Ma.Because these glauconite-bearing rocks have been buried to depths of less than 1 km, thermal resetting of the RbSr and KAr systematics appears unlikely. The initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the RbSr isochrons are similar to the ratios for vein- and vug-filling dolomite and calcite. This is consistent with resetting of the RbSr and KAr systems during diagenetic changes which included the isotopic equilibration (perhaps by cation exchange) of the Sr in the glauconite with that in the diagenetic and Mississippi Valley-type ore fluids. This interpretation implies that the age of the Mississippi Valley-type mineralization in the Viburnum Trend is Devonian rather than Carboniferous—Permian as has been inferred from paleomagnetic measurements.Cation-exchange experiments with a dilute Sr-bearing solution and an artificial oilfield brine indicate that glauconite adsorbs large amounts of Sr, some of which is sufficiently strongly attached to the glauconite lattice as to resist leaching with ammonium acetate. The introduction of this strongly attached Sr may be the first step in the resetting of the RbSr systematics of glauconite by cation exchange.     

A multidisciplinary approach to evaluating impacts of shellfish aquaculture on benthic communities

The impact of suspended mussel culture (Mytilus edulis, M. trossulus) on the benthos of a small Nova Scotia cove (7 m depth) was assessed using meehods involving both benthic metabolism and community structure. Due to deposition of mussel feces and pseudofeces, sedimentation rate was higher under the mussel culture lines than at an adjacent reference site of similar sediment texture. Porewater profiles of sediment sulfate and sulfide indicated greater anaerobic metabolism at the mussel site than at the reference site, but sulfide was absent from the upper centimeters of sediments under the mussels. Seasonal measures of sediment oxygen demand showed little change between sites, but maximum rates of ammonium release at the mussel site were twice the highest rates measured at the reference site. Abundance of benthic macrofauna was higher at the reference site, but biomass was generally lower. Biomass at the mussel site was dominated by molluscs (Ilyanassa spp. andNucula tenuisulcata), that were attracted to mussels fallen from the culture and/or enriched organic matter due to biodeposition. Species diversity was lower at the reference site due to the dominance of the polychaeteNephtys neotena. Abundance-biomass comparisons (ABC method) of faunal analysis did not indicate any impact of biodeposition at this site: however, disturbance did not result in a typical assemblage of small opportunistic species anticipated with this method. Cluster analysis of macrofauna usually provided a clear separation between the sites. Since the contruction of a causeway (1968), foraminifera species composition showed a temporal response to temperature changes in the cove by shifting toward calcareous species, but assemblages downcore showed little or no relationship to aquaculture impacts. Although there is a shift toward anaerobic metabolism at the mussel lines, the impact of mussels falling to the sediments was more noticeable in benthic community structure than was any impact due to organic sedimentation or hypoxia. In general the impact of aquaculture on the benthos appeared to be minor. Furtyher assesment of these consequences may mandate both taxonomic and energetic approaches to impact assessment.     

Cathodoluminescence petrography of syntectonic quartz fibres

The cathodoluminescence of low grade metamorphic quartz is reported in the literature to be uniformly brown. This study describes an investigation of syntectonic quartz fibres from veins and pressure shadows contained in different carbonate units of the Helvetic Alps, Switzerland, and of Anglesey, U.K., with the Scanning Electron Microscope in the cathodoluminescence mode. The cathodoluminescence spectra measured show systematic variations between older and younger parts of the same fibre, and between fibres from different tectonic units. These variations can be related first to variations in the temperature of formation of the quartz fibres, and second to deformation-induced differences in the microstructure of the earlier formed parts of fibres during later imposed strains.     

The beachwatch pollution monitoring programme: Changing priorities to recognize changed circumstances

Since the commissioning of the three major deepwater outfalls in Sydney, there has been a dramatic improvement in general beach water quality at Sydney's ocean beaches. This has required the NSW Environment Protection Authority's Beachwatch Programme to shift from assessing the impacts of gross sewage pollution due to nearshore outfalls to more diffuse pollution from stormwater and sewer overflows.

The visual indicators of gross sewage pollution originally used by Beachwatch for the daily assessment of bacterial water quality are now of limited value. General linear models (with multiple effects) were constructed to identify the secondary indicators which best describe the levels of bacterial contamination due to stormwater pollution. Data from four representative Sydney beaches were modelled separately due to the site-specific effects of pollution sources and hydrodynamics. Factors which were built into the models and were known on the day of prediction were rain amount, presence of stormwater material, the maximum daily stormwater rating, drain or lagoon flows at the time of sampling, and the drain/lagoon bacterial concentration two days before sampling.

Results indicate that there is a general linear relationship between visual indicators and bacterial density; however, the reliability of the prediction on a daily basis is poor and rainfall alone as a predictor is equivalent to or better than visual assessment alone. The primary source of information for the preparation of Beachwatch daily pollution bulletins now is rainfall reports from a telemetered network of rain gauges along the coast. This is a more cost-effective approach and has allowed the reallocation of resources to address more directly the problem of stormwater pollution at higher risk beaches.