Km In Extent Research Articles

Risk and low-density dispersed urbanism

Settlements operate across a wide range of densities and do so for every socio- economic mode of life from those based on hunter-gatherer economies to those which are based on industrial production. Human beings also live across a range of residential densities from very high to very low. Why they do so is a function of many factors, especially differing socio-cultural ways of managing interaction and communication and the associated social and political practices of the communities. Settlement forms are seen as a derivative of many factors because they are. But they are not thereby an epiphenomenon - especially as they become larger, more durable, and bulkier. That gives them inertia and, as a consequence, they become an agency in their own right which produces outcomes with consequences for the communities, which inhabit them. They are not a neutral background. Instead, their materiality, their sizes, and their densities have an impact on the viability of social life. This paper considers the outcomes generated by the regional networks of low-density, urban settlements larger than 100 sq km in extent. The implications of what happened to agrarian-based low-density urban settlements, like Greater Angkor and the Classic Maya settlements, such as Caracol, are of consequence for the risk faced by the regional networks of present-day, low-density urban giants – the megalopoleis and desa-kota. A further perspective is provided by placing these great cities of the past and the present in the larger context of the trajectories and outcomes of smaller low-density settlements over the previous six millennia. The concern is the implications for the viability of low-density urbanism in contexts of the rapid, extreme climate change we are now beginning to experience. The implications are ominous, yet the past also indicates that social and cultural systems are robust, that human beings can survive, and that they retain and continue to remake their social traditions as they adjust to seriously changing circumstances.

Marine bird mass mortality events as an indicator of the impacts of ocean warming

The frequency and severity of marine heatwaves (MHWs), an emergent property of global warming, has led to large-scale disruptions to marine ecosystems. As upper trophic species, marine birds reflect shifts in trophic structure and stability; therefore, a sharp increase in marine bird mortality is a clear signal of ecosystem impact. In this study, we analyzed 29 yr (1993-2021) of beached bird monitoring data (~90000 surveys) to identify marine bird mortality events throughout the Northeast Pacific and Alaska, USA, and examined linkages to ocean-climate variability. Mortality events were documented throughout the study period, but massive events (>500 km in extent, >10 carcasses km-1) occurred infrequently (n = 5), with an unprecedented sequence from 2014-2019. Event characteristics, including encounter rate (carcasses km-1), duration, and spatial extent, were positively related to prior-year averaged sea surface temperature anomaly, with event magnitude (product of encounter rate, extent, and duration) displaying a step-like transition, increasing 5-fold between +0°C and +1°C above baseline (1981-2010) temperatures. Mortality events occurred more frequently following MHWs, and a common sequence of mortality events (at 1-6 and 10-16 mo after heatwave onset) was observed in the California Current large marine ecosystem following 3 prolonged MHW events. Following the second wave of mortality at 10-16 mo after MHW onset, a consistent 16 mo period of depressed carcass encounter rates ensued. Given continued global warming, our results point to more frequent large-scale mortality events and the potential for a new lower carrying capacity for marine birds in the Northeast Pacific.

The Lateral Continuity and Vertical Arrangement of Dust Layers in the Martian North Polar Cap From SHARAD Multiband Data.

Interpretation of radar sounder reflections to infer the structure and composition of the martian polar caps depends on whether bright returns correspond to single packed dust layers or a more finely layered structure. Reflections from multiple layers can create strong resonant scattering (interference) effects that impact analyses of radargram reflectors and inference of dielectric contrast. We identify resonant behavior for an areally extensive reflector in the north polar layered deposits from Shallow Radar data processed in two frequency bands. Echo strength varies by ∼2 dB between subband reflections across a region ∼400 km in extent, with the stronger echo shifting abruptly from the high‐ to low‐frequency band outside the central region of Gemina Lingula. This behavior can arise from resonant scattering between two layers of dust (0.3–0.6 m thick) separated by 0.5–3 m of ice. Such layering requires there be little postdepositional aeolian activity to preserve layer thickness and spacing.

On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study

Abstract. A climatology of the occurrence of strong wind shear in the upper troposphere–lower stratosphere (UTLS) is presented, which gives rise to defining a tropopause shear layer (TSL). Strong wind shear in the tropopause region is of interest because it can generate turbulence, which can lead to cross-tropopause mixing. The analysis is based on 10 years of daily northern hemispheric ECMWF ERA5 reanalysis data. The vertical extent of the region analyzed is limited to the altitudes from 1.5 km above the surface up to 25 km, to exclude the planetary boundary layer as well as strong wind shear in higher atmospheric layers like the mesosphere–lower thermosphere. A threshold value of St2=4×10-4s-2 of the squared vertical shear of the horizontal wind is applied, which marks the top end of the distribution of atmospheric wind shear to focus on situations which cannot be sustained by the mean static stability in the troposphere according to linear theory. This subset of the vertical wind shear spectrum is analyzed for its vertical, geographical, and seasonal occurrence frequency distribution. A set of metrics is defined to narrow down the relation to planetary circulation features, as well as indicators for momentum-gradient-sharpening mechanisms. The vertical distribution reveals that strong vertical wind shear above the threshold occurs almost exclusively at tropopause altitudes, within a vertically confined layer of about 1–2 km in extent directly above the local lapse rate tropopause. The TSL emerges as a distinct feature in the tropopause-based 10-year temporal and zonal mean climatology, spanning from the tropics to latitudes around 70∘ N, with average occurrence frequencies on the order of 1 %–10 %. The horizontal distribution of the strong vertical wind shear near the tropopause exhibits distinctly separated regions of occurrence, which are generally associated with jet streams and their seasonality. At midlatitudes, strong wind shear values occur most frequently in regions with an elevated tropopause and at latitudes around 50∘ N, associated with jet streaks within northward-reaching ridges of baroclinic waves. At lower latitudes in the region of the subtropical jet stream, which is mainly apparent over the east Asian continent, the occurrence frequency of strong wind shear near the tropopause reaches maximum values of about 30 % during winter and is tightly linked to the jet stream seasonality. The interannual variability of the occurrence frequency for strong wind shear might furthermore be linked to the variability of the zonal location and strength of the jet. The east-equatorial region features a bi-annual seasonality in the occurrence frequencies of strong vertical wind shear near the tropopause. During the summer months, large areas of the tropopause region over the Indian Ocean are up to 70 % of the time exposed to strong wind shear, which can be attributed to the emergence of the tropical easterly jet. During winter, this occurrence frequency maximum shifts eastward over the maritime continent, where it is exceptionally pronounced during the DJF 2010/11 La Niña phase, as well as quite weak during the El Niño phases of 2009/10, 2014/15, and 2015/16. This agrees with the atmospheric response of the Pacific Walker circulation cell in the El Niño–Southern Oscillation (ENSO) ocean–atmosphere coupling.

Trajectories to Low-Density Settlements Past and Present: Paradox and Outcomes

The conventional history of urban growth defines agrarian-based cities prior to the 19th century CE as densely inhabited and commonly bounded by defenses such as walls. By contrast industrial-based cities are viewed as more spread out and without marked boundaries. Since the 1960s a trajectory towards extensive, low-density urbanism with sprawling, scattered suburbs surrounding a denser core has been formally recognised and given various names such as megalopolis in the West and desakota in southern and eastern Asia. These sprawling industrial cities have been regarded as a unique derivative of modern phenomena such as mechanized transport and the commercial property market. However, this set of premises are not valid. The agrarian-based world also contained dispersed, low-density urbanism - on its grandest scale, the vast circa 1000 sq km urban complex of Greater Angkor and the famous Maya cities of lowland Central America with maximum areas of about 200 sq km. The Maya only used pedestrian and riverine transport so the conventional transport explanation for industrial dispersed urbanism is at best partial. There was another trajectory to extensive, low-density settlement forms for places which were generally less than 15-20 sq km in extent but could on rare occasions reach areas as large as 40 to 90 sq km. Famous examples are Great Zimbabwe, Chaco Canyon and the European oppida of the late 1st millennium BCE. No-formally agreed term is available to refer to them. I will refer to them by default as “Giants”. The three trajectories to low-density settlement form redefine the history of settlement growth and the meanings of the term “urban”. Worryingly, none of the successive low-density settlements derive from any of the low-density cases of the preceding trajectory. Neither Angkor nor the Classic Maya cities have any connection to the industrial low-density cities. By contrast compact cities, the epitome of the obsolete definition of cities display continuity to succeeding urban forms over several thousand years. The implications for modern, giant, low-density cities are ominous.

Localized geomagnetic field anomalies in an underground gas storage

To investigate possible piezomagnetic effects associated with imposed tectonic stresses, repeated measurements of total magnetic field in an array (∼120 km × 90 km in extent) were performed across the Hutubi underground gas storage (HUGS). Forty repeated measurement stations were established in the HUGS and its surrounding areas. Proton precession magnetometers with a sensitivity of 0.15 nT @ 1 Hz were used to measure the total magnetic field at each repeated station. We conducted two field measurement surveys, one with a minimum pressure during April 2017 and the other with a maximum pressure during November 2017 in the HUGS. The local magnetic field (LMF) of the HUGS and its surrounding areas was obtained after data processing, which included diurnal variation reduction (DVR), secular variation reduction (SVR) and LMF acquisition. The average of the mean standard deviations (σ) of the geomagnetic DVR values were 0.038 nT and 0.045 nT for the first and second field surveys respectively. The amplitude of the LMF varied between about 10 nT and 90 nT in the local area. Negative anomalies with a maximum amplitude of −2.1 nT was observed over a seven-month period (April 2017–November 2017) during the loading process with a constantly increasing pressure in the HUGS. The wide range of negative LMF anomalies shows a negative correlation with the increasing pressure in the HUGS. This result constitutes powerful field observational evidence for the existence of piezomagnetic effects under middle-scale experimental conditions.

Late Quaternary Eruption Record and Probability of Future Volcanic Eruptions in the Long Valley Volcanic Region (CA, USA)

AbstractThe Long Valley volcanic region, eastern California, has been characterized by recurrent and generally explosive eruptions in the past 180,000 years, originating from a N/S elongated area ~50 km in extent, including the Mammoth Mountain lava dome complex, the Mono‐Inyo volcanic chain, and their peripheries. Several temporal clusters of activity have been observed in a relatively well‐preserved time‐stratigraphic record, which is nevertheless affected by uncertainties. This study has two main objectives: (1) to fully describe the past eruption record by using a stochastic model capable of combining radiometric ages and stratigraphic constraints and, (2) based on the uncertainty assessment, to develop a doubly stochastic, long‐term temporal model based on the current situation. Multiple approaches are described and compared, and multimodel forecasts are also presented. Our findings provide fundamental information for hazard assessment and forecasting of the next eruption in the Long Valley volcanic region, of which the mean probability of occurrence is estimated to be ~2.5% in the next 10 years and ~22.5% in the next 100 years.

Growth rate variability of larval European eels (Anguilla anguilla) across the extensive eel spawning area in the southern Sargasso Sea

AbstractThe European eel (Anguilla anguilla) spawns in the Sargasso Sea, and the leptocephalus larvae are distributed in the Subtropical Convergence Zone (STCZ), covering an area approximately 500 × 2,000 km in extent. The STCZ is hydrographically diverse and highly dynamic, which is likely to impact growth and survival opportunities of the larvae. Here we investigate the temporal and spatial growth rate variability of larvae collected along seven sampling transects across the STCZ during March–April 2014. Scanning electron microscopic analyses of otolith ring‐formations were used to estimate larval age‐at‐length, initial growth and growth trajectories. Analyzed larvae averaged 14 mm in length and 30 days of age. Age estimation indicated that the larvae were spawned during one continuous period, extending from mid‐February to late‐March, and that spawning had peaked during the new moon of 4 March. Growth estimates (average: 0.38 mm/day, ~6% weight increase/day) showed substantial variability among individuals. There were no apparent spatial trends in this variability, and no linkage to measures of temperature and salinity, while earlier‐spawned leptocephali showed slightly higher growth rates than later‐spawned larvae. The variability in growth rates at single sampling sites was as great as variability across the entire area of distribution. This indicates that individual growth opportunities are strongly impacted by variable conditions in the immediate environment while average conditions for larval growth and survival are basically the same throughout the immense area of larval distribution.

In situ U-Pb geochronology and geochemistry of a 1.13 Ga mafic dyke suite at Bunger Hills, East Antarctica: The end of the Albany-Fraser Orogeny

Antarctica contains continental fragments of Australian, Indian and African affinities, and is one of the key elements in the reconstruction of Nuna, Rodinia and Gondwana. The Bunger Hills region in East Antarctica is widely interpreted as a remnant of the Mesoproterozoic Albany–Fraser Orogen, which formed during collision between the West Australian and Mawson cratons and is linked with the assembly of Rodinia. Previous studies have suggested that several generations of mafic dyke suites are present at Bunger Hills but an understanding of their origin and tectonic context is limited by the lack of precise age constraints. New in situ SHRIMP U-Pb zircon and baddeleyite dates of, respectively, 1134 ± 9 Ma and 1131 ± 16 Ma confirm an earlier Rb-Sr whole-rock age estimate of ca. 1140 Ma for emplacement of a major mafic dyke suite in the area. Existing and new geochemical data suggest that the source of the dyke involved an EMORB-like source reservoir that was contaminated by a lower crust-like component. The new age constraint indicates that the dykes post-date the last known phase of plutonism at Bunger Hills by ca. 20 million years and were emplaced at the end of Stage 2 of the Albany-Fraser Orogeny. In current models, post-orogenic uplift and progressive tectonic thinning of the lithosphere were associated with melting and reworking of lower and middle crust that produced abundant plutonic rocks at Bunger Hills. A major episode of mafic dyke emplacement following uplift, cooling, and plutonic activity with increasing mantle input, suggests that the dykes mark the end of a prolonged interval of thermal weakening of the lithosphere that may have been associated with continued mafic underplating during orogenic collapse. If the undated olivine gabbro dykes with similar trend, geochemistry and petrology at Windmill Islands are coeval with the ca. 1134 Ma dyke at Bunger Hills, this would suggest the presence of a major dyke swarm at least 400 km in extent. In such case, the dykes could have been emplaced laterally from a much more distant mantle source, possibly a plume, and interacted with the locally heterogeneous and variably metasomatised lithosphere.

InSAR constraints on soil moisture evolution after the March 2015 extreme precipitation event in Chile

AbstarctConstraints on soil moisture can guide agricultural practices, act as input into weather, flooding and climate models and inform water resource policies. Space-based interferometric synthetic aperture radar (InSAR) observations provide near-global coverage, even in the presence of clouds, of proxies for soil moisture derived from the amplitude and phase content of radar imagery. We describe results from a 1.5 year-long InSAR time series spanning the March, 2015 extreme precipitation event in the hyperarid Atacama desert of Chile, constraining the immediate increase in soil moisture and drying out over the following months, as well as the response to a later, smaller precipitation event. The inferred temporal evolution of soil moisture is remarkably consistent between independent, overlapping SAR tracks covering a region ~100 km in extent. The unusually large rain event, combined with the extensive spatial and temporal coverage of the SAR dataset, present an unprecedented opportunity to image the time-evolution of soil characteristics over different surface types. Constraints on the timescale of shallow water storage after precipitation events are increasingly valuable as global water resources continue to be stretched to their limits and communities continue to develop in flood-prone areas.

Ramp sedimentation across a middle Albian, Arctic embayment: Influence of subsidence, eustasy and sediment supply on stratal architecture and facies distribution, Lower Cretaceous, Western Canada Foreland Basin

AbstractRegional mapping of Middle Albian, shallow‐marine clastic strata over ca 100 000 km2 of the Western Canada Foreland Basin was undertaken to investigate the relationship between large‐scale stratal architecture and lithology. Results suggest that, over ca 5 Myr, stratal geometry and facies were dynamically linked to tectonic activity in the adjacent Cordillera. Higher frequency modulation of accommodation is most reasonably ascribed to eustasy. The Harmon and Cadotte alloformations were deposited at the southern end of an embayment of the Arctic Ocean. The Harmon alloformation, forming the lower part of the succession, constitutes a wedge of marine mudstone that thickens westward over 400 km from <5 m near the forebulge to >150 m in the foredeep. Constituent allomembers are also wedge‐shaped but lack distinct clinothems, a rollover point or downlapping geometry. Ubiquitous wave ripples indicate that the sea floor lay above storm wave base. Deposition took place on an extremely low‐gradient ramp, where accommodation was limited by effective wave base. Lobate, river‐dominated deltas fringed the southern margin of the basin. The largest deltas are stacked in the same area, suggesting protracted stability of the feeder river. A buried palaeo‐valley on the underlying sub‐Cretaceous unconformity may have influenced compaction and controlled river location for ca 3 Myr. Adjacent to the western Cordillera, a predominantly mudstone succession is interbedded with abundant storm beds of very fine‐grained sandstone and siltstone that reflect supply from the adjacent orogen. Bioturbation indices in the Harmon alloformation range from zero to six which reflects the influence of stressors related to river‐mouth proximity. Harmon alloformation mudstone grades abruptly upward into marine sandstone and conglomerate of the overlying Cadotte alloformation. The Cadotte is composed of three allomembers ‘CA’ to ‘CC’, that represent the deposits of prograding strandplains 200 × 300 km in extent. Allomembers ‘CA’ and ‘CB’ are strongly sandstone‐dominated, whereas allomember ‘CC’ contains abundant conglomerate in the west. The dominantly aggradational wedge of Harmon alloformation mudstone records flexural subsidence driven by active thickening in the adjacent orogen: the high accommodation rate trapped coarser clastic detritus close to the basin margin. In contrast, the tabular, highly progradational sandstone and conglomerate bodies of the Cadotte alloformation record a low subsidence rate, implying tectonic quiescence in the adjacent orogen. Erosional unloading of the orogen through Cadotte time steepened rivers to the extent that they delivered gravel to the shore. These observations support an ‘anti‐tectonic’ model of gravel supply proposed previously for the United States portion of the Cretaceous foreland basin. Because Cadotte allomembers do not thicken appreciably into the foredeep, accommodation changes that controlled these transgressive–regressive successions were probably of eustatic origin.

Low-sulfide PGE ore in the Volchetundra gabbro-anorthosite pluton, Kola Peninsula, Russia

The internal structure of the Volchetundra gabbro-anorthosite massif is considered, including localization of low-sulfide PGE mineralization and its mineralogy. The Volchetundra massif 24 km long and 0.5–4.0 km wide occupies the middle part of the Main Range complex, which extends for 75 km in the nearly meridional direction. The main and marginal zones are distinguished in the massif. The marginal zone 20–400 m wide extends along the entire eastern contact of the massif and is primarily composed of mediumgrained meso- and leucocratic norite, gabbronorite, plagioclasite, and less fequent orthopyroxenite. The main zone consists of coarse-grained leucogabbro and gabbronorite with an anorthosite zone in the axial part of the massif. The PGE mineralization of the Volchetundra massif is distinctly subdivided into two types substantially differing in localization, mineralogy, geochemistry, and economic importance. Mineralization of the first type is localized in the marginal zone and characterized by the highest resource potential. Mineralization hosted in the main zone belongs to the second type. The PGE ore of marginal zone is spatially and genetically related to the pyrite-pentlandite-chalcopyrite-pyrrhotite sulfide mineralization (1–5%) in the form of fine inequigranular interstitial disseminations, and less frequent larger grains and pockets localized within two ore zones each up to 2 km in extent. The thickness of separate mineralized layers varies from 0.5 to 3.0 m and up to 45 m in bulges. The average Pt + Pd grade is 1.37 gpt at Pd/Pt = 3.1. The mineralization of the second type has been penetrated by boreholes. Separate intersections do not correlate with one another and are limited in extent both along the strike and down the dip. The PGE mineralization is related to finely dispersed pentlandite-pyrite-pyrrhotite-chalcopyrite sulfides, sulfide emulsions, and less abundant stringer-disseminated sulfide ore. The orebodies vary from 2 to 7 m in thickness. The average Pt + Pd grade is 1.61 gpt; Pd/Pt = 1.3. The PGE mineralization includes 22 mineral species. PGE sulfides (cooperite-braggite-vysotskite; laurite and erlichmanite in insignificant amounts) are predominant. Bismuthotellurides (moncheite-kotulskite-merenskyite) and arsenides (sperrylite, palladoarsenite, arsenopalladinite, atheneite) are subordinate in abundance. In addition, sulfoarsenides (platarsite, hollingworthite), tellurides (telargpalite, sopcheite, keithconnite, melonite, hessite), paolovite, and Pt-Fe alloy have been identified. An admixture of native gold and electrum occur constantly.

Sub-surface small-scale eddy dynamics from multi-sensor observations and modeling

The study of mesoscale and submesoscale [hereafter (sub)mesoscale] hydrodynamic features is essential for understanding thermal and biogeochemical exchanges between coastal areas and the open ocean. In this context, a glider mission was conducted in August 2008, closely co-located and almost simultaneously launched with a JASON 2 altimetric pass, to fully characterize the currents associated with regional (sub)mesoscale processes regularly observed to the north of Mallorca (Mediterranean Sea). A synoptic view from satellite remote-sensing fields, before and during the glider mission, provided a descriptive picture of the main surface dynamics at the Balearic Basin scale. To quantify the absolute surface geostrophic currents, the coastal altimetry-derived current computation was improved and cross-compared with its equivalent derived from glider measurements. Model simulations were then validated both qualitatively and statistically with the multi-sensor observations. The combined use of modeling and multi-sensor observational data reveals the baroclinic structure of the Balearic Current and the Northern Current and a small-scale anticyclonic eddy observed northeast of the Mallorca coast (current∼15cm/s, <30km in extent and >180m deep). This mesoscale structure, partially intercepted by the glider and along-track altimetric measurements, is marked by relatively strong salinity gradients and not, as is more typical, temperature gradients. Finally, the use of the validated model simulation also shows that the geostrophic component of this small-scale eddy is controlled by sub-surface salinity gradients. We hypothesize that this structure contains recently modified Atlantic water arriving from the strait of Ibiza due to a northerly wind, which strengthens the northward geostrophic circulation.

Ore geochemistry, zircon mineralogy, and genesis of the Sakharjok Y-Zr deposit, Kola Peninsula, Russia

The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion ∼7 km in extent and 4–5 km2 in area of its exposed part is composed of Neoarchean (2.68–2.61 Ma) alkali and nepheline syenites, which cut through the Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones 200–1350 m in extent and 3–30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents (1000–5000 ppm Zr, 200–600 ppm Nb, 100–500 ppm Y, 0.1–0.3 wt % REE, 400–900 ppm Rb), REE pattern, Th/U, Y/Nb, and Yb/Ta ratios), nepheline syenite was derived from an enriched mantle source similar to that of contemporary OIB and was formed as an evolved product of long-term fractional crystallization of primary alkali basaltic melt. The ore concentrations are caused by unique composition of nepheline syenite magma (high Zr, Y, REE, Nb contents), which underwent subsequent intrachamber fractionation. Mineralogical features of zircon-the main ore mineral—demonstrate its long multistage crystallization. The inner zones of prismatic crystals with high ZrO2/HfO2 ratio (90, on average) grew during early magmatic stage at a temperature of 900–850°C. The inner zones of dipyramidal crystals with average ZrO2/HfO2 = 63 formed during late magmatic stage at a temperature of ∼500°C. The zircon pertaining to the postmagmatic hydrothermal stage is distinguished by the lowest ZrO2/HfO2 ratio (29, on average), porous fabric, abundant inclusions, and crystallization temperature below 500°C. The progressive decrease in ZrO2/HfO2 ratio was caused by evolution of melt and postmagmatic solution. The metamorphic zircon rims relics of earlier crystals and occurs as individual rhythmically zoned grains with an averaged ZrO2/HfO2 ratio (45, on average) similar to that of the bulk ore composition. The metamorphic zircon is depleted in uranium in comparison with magmatic zircon, owing to selective removal of U by aqueous metamorphic solutions. Zircon from the Sakharjok deposit is characterized by low concentrations of detrimental impurities, in particular, contains only 10–90 ppm U and 10–80 ppm Th, and thus can be used in various fields of application.

Shallow-water anomuran and brachyuran crabs (Crustacea: Decapoda) from southern Bahia, Brazil

The objective of this study was to determine the taxonomic composition and ecological aspects of decapod crustacean species belonging to the infraorders Anomura and Brachyura in shallow marine and estuarine waters from southern Bahia, a coastline about 640 km in extent, corresponding to approximately 7% of the Brazilian coast. Sixteen species of the infraorder Anomura and 68 of the infraorder Brachyura are reported for the study area. The most important families in terms of number of species were the Panopeidae with 11 species, and the Ocypodidae and Portunidae with 9. Among the Brachyura, the southern distribution of the species Austinixa leptodactyla Coelho, 1997 (Pinnotheridae), endemic to Brazil, is extended from the coast of Sergipe to Bahia (Prado, Cumuruxatiba Beach, 17°06'18.6"S, 39°10'50.4"W). The ocypodid Uca (Leptuca) cumulanta Crane, 1943 and also the pinnotherids Austinixa aidae (Righi, 1967) and Fabia byssomiae (Say, 1818) are reported for the first time from the Bahia coast. The specimen of F. byssomiae examined was collected in the mantle cavity of the clam Macoma constricta (Bruchière, 1792) (Bivalvia: Tellinidae), a new host record for the species.

Tectonic and stratigraphic evolution of the Cambrian basin of northern Northwest Territories

Abstract The Cambrian basin of the mainland Northwest Territories has been of considerable economic interest since gas was first discovered in Mount Clark Formation sandstones in 1974. A recently completed assessment by the Geological Survey of Canada has estimated that the Cambrian Clastics play contains almost a billion barrels of oil and 10.7 TCF of gas. The play’s reservoirs, seals and source rocks are all of Cambrian age, making the understanding of the basin’s evolution and contents critical to any exploration effort. The basin is a semi-enclosed, epicontinental marine basin, bordered by positive elements and open to a subsiding continental shelf and margin, and represents the eastern portion of a much larger deposystem that developed after the breakup of Laurentia. A multi-disciplinary study of a large regional reflection seismic grid, supported by borehole and potential field data, shows the basin to have evolved in three stages: 1) Early Cambrian pre-rift regional subsidence of the area lying inland of the Mahony and Bulmer arches, and a newly identified high that pre-dated the Mackenzie Trough. It was during this period that the Mount Clark Formation was deposited; 2) A middle Cambrian rift phase during which a graben system, about 50 km wide and over 400 km long, developed in the basin’s core. The grabens are deepest in south Mackenzie Trough where rifting began, and are progressively shallower and younger to the north and northeast. Mount Cap was deposited during this phase and it is expected that the grabens received finer-grained clastics than did the shallower areas on their flanks; 3) A post-rift subsidence phase that began with deposition of the Saline River Formation during the Late Cambrian and continued, with interruptions, until the middle of the Devonian. Throughout Cambrian time, sediment onlapped the basin’s flanks and its internal arches, each layer advancing further than its predecessor. It was not until the latest Cambrian that the internal arches were completely covered by beds of the lower Franklin Mountain Formation. A previously undocumented Cambrian age graben (herein named McConnell Graben) lies in the hanging wall of the unnamed Laramide thrust fault that emerges from the east flank of the McConnell Range. The fault began as a Cambrian normal fault that separated the Bulmer and Mahony arches on the east from McConnell Graben on the west. The present day ‘St. Charles’ range developed in a similar manner. A preliminary exploration risk analysis, based on the predicted distribution of reservoir, seal and source rocks, reveals two attractive areas for exploration. The larger one, centred on Lac des Bois, is about 150 km wide and extends on a NW-SE trend for about 300 km across the Aubry and Good Hope depocentres. The smaller area (less than 50 × 100 km in extent) lies within Mackenzie Plain depocentre.

Geodynamic settings and formation conditions of crystalline complexes in the south Altai and south Gobi metamorphic belts

The Hercynian mobile belts in Central Asia comprise the Hercynian proper and the Late Hercynian (Indosinian) belts separated by the South Gobi microcontinent, the origin of which is related to the evolution of the South Mongolian and Inner Mongolian basins with the oceanic crust. Crystalline complexes within these belts occur as tectonic sheets of a variety of sizes. At the early stages, the metamorphic grade of these complexes reached conditions of high-temperature subfacies of amphibolite and locally developed granulite facies. In tectonic terms, the Hercynian belt of metamorphic rocks is situated at the margin of the North Asian Caledonian continent and extends from the southeast to the northwest along the southern slope of the Gobi, Mongolian, and Chinese Altai to East Kazakhstan, where metamorphic rocks are localized in the Irtysh Shear Zone. All these rocks are combined into the South Altai metamorphic belt of more than 1500 km in extent. Another belt of isolated outcrops of crystalline rocks conventionally combined into the Indosinian South Gobi metamorphic belt is traced along the junction of the Hercynides with the South Gobi microcontinent. The high-grade metamorphic rocks within both belts are not fragments of an ensialic Caledonian or older basement. These rocks were formed 390–360 and 230–220 Ma ago as a result of the closure of the Tethian South Mongolian and Inner Mongolian oceanic basins (Paleotethys I and Paleotethys II). The spatial position of the South Altai and South Gobi metamorphic belts is caused by the asymmetric structure of the Tethian basins, where active continental margins are expressed most distinctly along their northern parts, while passive margins extend along the southern parts (in present-day coordinates).

Long-term Monitoring of Two Subpopulations of the Federally Threatened Aeschynomene virginica (Sensitive Joint-vetch) in Maryland

Abstract The largest Maryland population of the federally threatened tidal freshwater wetlands legume, Aeschynomene virginica (Sensitive Joint-vetch), is comprised of two subpopulations in the Manokin River watershed. To provide baseline data fundamental to understanding annual fluctuations and long-term trends, annual censuses began in 1991 and 1994 for Taylor Branch and Manokin River subpopulations, respectively, and continued through 2009. In addition, distributional limits, phenology, average plant height, associated plant species, and muskrat activity were recorded to better understand plant and habitat characteristics. Large annual fluctuations in size were common to both subpopulations. The Manokin River subpopulation (2 km in extent) averaged 1,867 ± 268 plants (n = 16), ranged from 715–4,394 plants, and inhabited marshes (56%) and banks (44%). Subpopulation size increased significantly during the survey period. June rainfall may have contributed to a tripling in subpopulation size from 2005 to ...

Manifa field causeway, Saudi Arabia

This paper reviews the design criteria and design development from option study to detailed design, and construction of an offshore island and causeway development off the Eastern Province of Saudi Arabia. The Manifa project, which is currently under construction, consists of 21 km of main causeways and 21 km of lateral causeways connecting to the 27 drilling and water injection islands and will support oil production of 900 000 barrels/day. The islands are each 9 ha (about the size of 13 football pitches). The works require the dredging and land reclamation of approximately 37 Mm3, and the rock armour revetments are approximately 120 km in extent and require the quarrying and placement of 10 Mt of rock. To fulfil environmental requirements, openings have been introduced to the causeway which are bridged by 4 km of bridges including one of 2·4 km.

Documenting channel features associated with gas hydrates in the Krishna–Godavari Basin, offshore India

During the India National Gas Hydrate Program (NGHP) Expedition 01 in 2006 significant sand and gas hydrate were recovered at Site NGHP-01-15 within the Krishna–Godavari Basin, East Coast off India. At the drill site NGHP-01-15, a 5–8m thick interval was found that is characterized by higher sand content than anywhere else at the site and within the KG Basin. Gas hydrate concentrations were determined to be 20–40% of the pore volume using wire-line electrical resistivity data as well as core-derived pore-fluid freshening trends. The gas hydrate-bearing interval was linked to a prominent seismic reflection observed in the 3D seismic data. This reflection event, mapped for about 1km2 south of the drill site, is bound by a fault at its northern limit that may act as migration conduit for free gas to enter the gas hydrate stability zone (GHSZ) and subsequently charge the sand-rich layer. On 3D and additional regional 2D seismic data a prominent channel system was imaged mainly by using the seismic instantaneous amplitude attribute. The channel can be clearly identified by changes in the seismic character of the channel fill (sand-rich) and pronounced levees (less sand content than in the fill, but higher than in surrounding mud-dominated sediments). The entire channel sequence (channel fill and levees) has been subsequently covered and back-filled with a more mud-prone sediment sequence. Where the levees intersect the base of the GHSZ, their reflection strengths are significantly increased to 5- to 6-times the surrounding reflection amplitudes. Using the 3D seismic data these high-amplitude reflection edges where linked to the gas hydrate-bearing layer at Site NGHP-01-15. Further south along the channel the same reflection elements representing the levees do not show similarly large reflection amplitudes. However, the channel system is still characterized by several high-amplitude reflection events (a few hundred meters wide and up to ~1km in extent) interpreted as gas hydrate-bearing sand intervals along the length of the channel.