Cool water geyser travertine: Crystal Geyser,Utah, USA

A sloping travertine mound, approximately 85 m across and a few metres thick is actively forming from cool temperature waters issuing out of Crystal Geyser, east‐central Utah, USA. Older travertine deposits exist at the site, the waters having used the Little Grand Wash Fault system as conduits. In contrast, the present Crystal Geyser travertine mound forms from 18°C waters which have been erupting for the last 80 years from an abandoned oil well. The present Crystal Geyser travertine accumulation forms from a ‘man‐made’ cool temperature geyser system; nevertheless, the constituents are an analogue for ancient geyser‐fed carbonate deposits. The travertine primary fabric is composed of couplets of highly porous, thin micritic laminae intercalated with thicker iron oxide rich laminae. Low Mg‐calcite is the dominant mineralogy; however, aragonite is a major constituent in deposits proximal to the vent and decreases in abundance distally. Cements exhibit a variety of fabrics, isopachous being common. Constituents include micro‐stromatolites, clasts, pisoids and the common occurrence of Frutexites‐like iron oxide precipitates. Leptothrix, a common iron‐oxidizing bacterium, is believed to be responsible for the production of the dense iron‐rich laminae. Pisoids litter the ground around the vent and rapidly decrease distally in abundance and size.     

The surface of labradorite feldspar after acid hydrolysis

After reaction with a pH < 4, the surface of labradorite is extensively enriched in Si and H, and depleted in Al, Ca and Na relative to an unreacted crystal. However, the amount of hydrogen measured in the reacted surface is less than that predicted on the basis of exchange of hydrogen (or hydronium) ions for cations in the feldspar. By analogy with studies of silicate glass, this low concentration of hydrogen suggests that some silanol groups in the reacted surface repolymerize subsequent to ion-exchange and depolymerization reactions. The net result is a relatively porous, Si-rich leached layer which is amorphous to electron diffraction, and which allows rapid diffusion of unreactive solutes.

Both the surface area of the reacted feldspar and the porosity increase with acid hydrolysis. Modeling of nitrogen sorption onto the surface suggests that the pores have a nominal radius of 20–80 Å or less. This distribution of pore sizes resembles other acid-reacted silicate materials, such as glass, chrysotile and kaolinite. Although the mineral surface clearly becomes more porous during acid hydrolysis, the increase in powder area also does not coincide with an increase in the flux of dissolved Si from the powder. We thus attribute most of this increase in area to spallation of the silica-rich surface from the feldspar upon drying.     

Patterns in the Turkish reinsurance claim data, 1998–2002: An application of the extreme value theory

The devastating 1999 Marmara and Düzce earthquakes led to a significant increase in the earthquake studies in Turkey in geological, engineering and financial aspects. Extreme Value Theory (EVT) has a range of applications from stock market changes to natural disasters like floods and hurricanes. Here EVT is fitted to the ordinary and earthquake reinsurance claims of Turkey.     

Carbonate biomineralization induced by soil bacterium Bacillus megaterium

Biogenic carbonates spawned from microbial activities are common occurrences in soils. Here, we investigate the carbonate biomineralization mediated by the bacterium Bacillus megaterium, a dominant strain separated from a loess profile in China. Upon completing bacterial cultivation, the ensuring products are centrifuged, and the resultant supernatant and the concentrated bacterial sludge as well as the un-separated culture are added separately into a Ca-CO₃ containing solution for crystallization experiments. Results of XRD and SEM analysis indicate that calcite is the dominant mineral phase formed when the bacteria are present. When the supernatant alone is used, however, a significant portion of vaterite is also precipitated. Experimental results further reveal that the bacteria have a strong tendency to colonize the center area of the calcite {1 0  4} faces. Observed crystal morphology suggests that the bacterial colony may promote the growth normal to each individual {1 0  4} face of calcite when the cell concentration is high, but may retard it or even cause dissolution of the immediate substrate surfaces when the concentration is low. SEM images taken at earlier stages of the crystallization experiments demonstrate the nucleation of calcite on the bacterial cell walls but do not show obvious morphological changes on the nanometer- to submicron-sized nuclei. δ¹³C measurements unveil that the crystals grown in the presence of bacteria are further enriched in the heavy carbon isotope, implying that the bacterial metabolism may not be the carbon sources for the mineralization. Based upon these findings, we propose a mechanism for the B. megaterium mediated calcite mineralization and conclude that the whole process involves epi- and inter-cellular growth in the local microenvironments whose conditions may be controlled by cell sequestration and proton pumping during bacterial respiration.     

Late‐glacial and Holocene history of the dry forest area in the south Colombian Cauca Valley

Two sedimentary cores with pollen, charcoal and radiocarbon data are presented. These records document the Late‐glacial and Holocene dry forest vegetation, fire and environmental history of the southern Cauca Valley in Colombia (1020 m). Core Quilichao‐1 (640 cm; 3° 6′N, 76° 31′W) represents the periods of 13 150–7720 ¹⁴C yr BP and, following a hiatus, from 2880 ¹⁴C yr BP to modern. Core La Teta‐2 (250 cm; 3° 5′N, 76° 32′W) provides a continuous record from 8700 ¹⁴C yr BP to modern. Around 13 150 ¹⁴C yr BP core Quilichao‐1 shows an active Late‐glacial drainage system and presence of dry forest. From 11 465 to 10 520 ¹⁴C yr BP dry forest consists mainly of Crotalaria, Moraceae/Urticaceae, Melastomataceae/Combretaceae, Piper and low stature trees, such as Acalypha, Alchornea, Cecropia and Celtis. At higher elevation Andean forest comprising Alnus, Hedyosmum, Quercus and Myrica was common. After 10 520 ¹⁴C yr BP the floral composition of dry forest changed, with extensive open grass vegetation indicative of dry climatic conditions. This event may coincide with the change to cool and dry conditions in the second part of the El Abra stadial, an equivalent to the Younger Dryas. From 8850 ¹⁴C yr BP the record from La Teta indicates dry climatic conditions relative to the present, these prevailing up to 2880 ¹⁴C yr BP at Quilichao and to 2720 ¹⁴C yr BP at La Teta. Severe dryness reached maxima at 7500 ¹⁴C yr BP and 4300 ¹⁴C yr BP, when dry forest reached maximum expansion. Dry forest was gradually replaced by grassy vegetation, reaching maximum expansion around 2300 ¹⁴C yr BP. After 2300 ¹⁴C yr BP grassy vegetation remains abundant. Presence of crop taxa (a.o. Zea mays), disturbance indicators (Cecropia) and an increase in charcoal point to the presence of pre‐Columbian people since 2300 ¹⁴C yr BP. After 950 ¹⁴C yr BP, expansion of secondary forest taxa may indicate depopulation and abandonment of previously cultivated land. After 400 ¹⁴C yr BP, possibly related to the Spanish conquest, secondary forest expanded and charcoal concentrations increased, possibly indicating further reduction of cultivated land. During the past century, Heliotropium and Didymopanax became abundant in an increasingly degraded landscape. Copyright © 2002 John Wiley & Sons, Ltd.     

Sampling characteristics and biases of enclosure traps for sampling fishes in estuaries

We evaluated the sampling characteristics of enclosure traps in estuaries in southern California, USA. Using enclosure traps that sampled 0.25, 0.5, and 1-m² footprints, we found that enclosure trap size significantly affected estimates of fish density and the precision of these estimates. The highest estimates were produced by the 0.5-m² trap and the lowest by the 0.25-m² trap. Precision of the density estimates improved with increasing trap size, while the proportion of zero values in the data sets decreased and estimates of species richness increased. The largest trap was difficult to use in the field and often did not function properly; thus we concluded that intermediate enclosure trap sizes offered the best compromise between statistical and logistical considerations. By examination of burrows in sediment cores taken in fished out enclosure traps, we found no evidence to support the widely held view that burrow-dwelling fishes evaded capture by hiding in burrows. We also used mark-recapture techniques to estimate recovery efficiency in 0.43-m² enclosure traps. Recovery efficiency averaged 91% and did not differ significantly among estuaries or sampling stations within estuaries. Based on extensive netting within enclosure traps, we determined that in areas with dense fish populations (>90 fish 0.43-m⁻²), netting could be ceased after the first sweep that captured no fish with only a trivial effect on the estimate of density. In more sparsely populated areas, netting had to continue until 2–3 sweeps had captured no fish in order to obtain estimates of density that were within 90% of the actual values present. Overall, we found enclosure traps to be effective tools for sampling small, abundant fishes in shallow estuaries in southern California, but we recommend that care be taken when choosing trap size and sampling (netting) effort within traps in order to optimize their sampling characteristics.     

Premier pôle paléomagnétique,d'âge Moscovien contraint par un test du pli,obtenu dans le bassin d'Illizi (Craton saharien,Algérie)First palaeomagnetic pole,of Moscovian age constrained by a fold test,in the Illizi Basin (Saharan Craton,Algeria)

Palaeomagnetic study, carried out in the Moscovian (～305 Ma) formation in the Edjeleh anticline, shows the existence of three magnetisation components. Two of them are probably Cenozoic and Permian remagnetisations. The third component determined by both well defined ChRMs and remagnetisation circles analysis passes the fold test. Because the folding started before or during the Stephano-Autunian, this third component is the primary magnetisation. Its palaeomagnetic pole (28.3°S, 58.9°E), close to other poles from the Saharan platform obtained from neighbouring periods but without palaeomagnetic tests, confirms the age of these last data. To cite this article: B. Bayou et al., C. R. Geoscience 334 (2002) 81–87.     

Changes in Habitat Availability for Multiple Life Stages of Diamondback Terrapins (<Emphasis Type="Italic">Malaclemys terrapin</Emphasis>) in Chesapeake Bay in Response to Sea Level Rise

Global sea level rise (SLR) will significantly alter coastal landscapes through inundation and erosion of low-lying areas. Animals that display area fidelity and rely on fringing coastal habitats during multiple life stages, such as diamondback terrapins (Malaclemys terrapin Schoepff 1793), are likely to be particularly vulnerable to SLR-induced changes. We used a combination of empirical nest survey data and results from a regional SLR model to explore the long-term availability of known nesting locations and the modeled availability of fringing coastal habitats under multiple SLR scenarios for diamondback terrapin in the MD portion of Chesapeake Bay and the MD coastal bays. All SLR scenarios projected the rapid inundation of historically used nesting locations of diamondback terrapins with 25%–55% loss within the next 10 years and over 80% loss by the end of the century. Model trajectories of habitat losses or gains depended on habitat type and location. A key foraging habitat, brackish marsh, was projected to decline 6%–94%, with projections varying spatially and among scenarios. Despite predicted losses of extant beach habitats, future gains in beach habitat due to erosion and overwash were projected to reach 40%–600%. These results demonstrate the potential vulnerability of diamondback terrapins to SLR in Chesapeake Bay and underscore the possibility of compounding negative effects of SLR on animals whose habitat requirements differ among life stages. More broadly, this study highlights the vulnerability of species dependent on fringing coastal habitats and emphasizes the need for a long-term perspective for coastal development in the face of SLR.