Use of GIS in Optimizing Timber Thinning Strategies in the Eastern Sierra Nevada*

This paper demonstrates the use of a Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective thinning potential were forest health and fire hazard ratings. By eliminating environmentally sensitive, economically unfeasible, or low fire hazard areas from consideration, the use of GIS reduced the area that was considered appropriate for thinning by approximately 58%. GIS offers considerable potential for improving resource management strategies.     

Winds and sand movements in the Namib Sand Sea

Wind regimes in the vicinity of the Namib Sand Sea are high energy unimodal near the coast, becoming bimodal or complex inland. There is an overall decrease in wind energy and sand transport rates from south to north and west to east, such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea. Such a pattern can explain much of the observed spatial variability in dune types, sizes, and sediment characteristics and lends support to a climatic model of sand sea formation in this region. Seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport, most of which is generated by winds of moderate velocity and frequency.     

Dunes on the skeleton coast,Namibia (South West Africa): Geomorphology and grain size relationships

Simple, and locally compound, transverse and barchanoid dunes dominate the 2000 km² Skeleton Coast dunefield in northwestern Namibia/South West Africa. Dune height and spacing are closely correlated (r = 0-89) and decrease across the dunefield from southwest to northeast, with an accompanying change from transverse to barchanoid ridges and ultimately barchans. The dunes are aligned transverse to the dominant strong south and south southwest onshore winds. Alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune-forming winds to swing to the right over the dunes, but resume their original direction beyond. Grain size and sorting vary at three scales: the dune, the dune landscape and through the dunefield. Overall the sands, derived from three localities by deflation from beaches supplied by vigorous longshore drift, become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing. A statistically significant relationship (r = ?0?65) was established between dune spacing and the phi grain size of the coarser fraction of the dune sands, demonstrating the importance of the protective effects of coarse grains, and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand.     

Characterization of halophiles in natural MgSO4 salts and laboratory enrichment samples: Astrobiological implications for Mars

The presence of sulfate salts and limited subsurface water (ice) on Mars suggests that any liquid water on Mars today will occur as (magnesium) sulfate-rich brines in regions containing sources of magnesium and sulfur. The Basque Lakes of British Columbia, Canada, represent a hypersaline terrestrial analogue site, which possesses chemical and physical properties similar to those observed on Mars. The Basque Lakes also contain diverse halophilic organisms representing all three Kingdoms of life, growing in surface and near-subsurface environments. Of interest from an astrobiological perspective, crushed magnesium sulfate samples that were analyzed using a modified Lowry protein assay contained biomass in every crystal inspected, with biomass values from 0.078 to 4.21 mg_biomass/g_salt; average=0.74±0.7 mg_biomass/g_salt. Bacteria and Archaea cells were easily observed even in low-biomass samples using light microscopy, and bacteria trapped within magnesium sulfate crystals were observed using confocal microscopy. Regions within the salt also contained bacterial pigments, e.g., carotenoids, which were separate from the cells, indicating that cell lysis might have occurred during entrapment within the salt matrix. These biosignatures, cells, and any ‘soluble’ organic constituents were primarily found trapped within fluid inclusions or fluid-filled void spaces between intergrown crystals. Diffuse reflectance infrared Fourier transform spectroscopy (reflectance IR) analysis of enrichment cultures, containing cyanobacteria, Archaea, or dissimilatory sulfate-reducing bacteria, highlighted molecular biosignature features between 550-1650 and 2400-3000 cm⁻¹. Spectra from natural salts demonstrated that we can detect biomass within salt crystals using the most sensitive biosignatures, which are the 1530-1570 cm⁻¹, C-N, N-H, -COOH absorptions and the 1030-1050 cm⁻¹ C-OH, C-N, PO₄³⁻ bond features. The lowest detection limit for a biosignature absorption feature using reflectance IR was with a natural sample that possessed 0.78 mg_biomass/g_salt. In a model cell, i.e., a 0.5 by 1 μm bacillus, this biomass value corresponds to approximately 7.8×10⁸ cells/g_salt. Based on its ability to detect biomass entrapped within natural sulfate salts, reflectance IR may make an effective remote-sensing tool for finding enrichments of organic carbon within outcrops and surficial sedimentary deposits on Mars.     

Archean to Recent aeolian sand systems and their sedimentary record: Current understanding and future prospects

The sedimentary record of aeolian sand systems extends from the Archean to the Quaternary, yet current understanding of aeolian sedimentary processes and product remains limited. Most preserved aeolian successions represent inland sand‐sea or dunefield (erg) deposits, whereas coastal systems are primarily known from the Cenozoic. The complexity of aeolian sedimentary processes and facies variability are under‐represented and excessively simplified in current facies models, which are not sufficiently refined to reliably account for the complexity inherent in bedform morphology and migratory behaviour, and therefore cannot be used to consistently account for and predict the nature of the preserved sedimentary record in terms of formative processes. Archean and Neoproterozoic aeolian successions remain poorly constrained. Palaeozoic ergs developed and accumulated in relation to the palaeogeographical location of land masses and desert belts. During the Triassic, widespread desert conditions prevailed across much of Europe. During the Jurassic, extensive ergs developed in North America and gave rise to anomalously thick aeolian successions. Cretaceous aeolian successions are widespread in South America, Africa, Asia, and locally in Europe (Spain) and the USA. Several Eocene to Pliocene successions represent the direct precursors to the present‐day systems. Quaternary systems include major sand seas (ergs) in low‐lattitude and mid‐latitude arid regions, Pleistocene carbonate and Holocene–Modern siliciclastic coastal systems. The sedimentary record of most modern aeolian systems remains largely unknown. The majority of palaeoenvironmental reconstructions of aeolian systems envisage transverse dunes, whereas successions representing linear and star dunes remain under‐recognized. Research questions that remain to be answered include: (i) what factors control the preservation potential of different types of aeolian bedforms and what are the characteristics of the deposits of different bedform types that can be used for effective reconstruction of original bedform morphology; (ii) what specific set of controlling conditions allow for sustained bedform climb versus episodic sequence accumulation and preservation; (iii) can sophisticated four‐dimensional models be developed for complex patterns of spatial and temporal transition between different mechanisms of accumulation and preservation; and (iv) is it reasonable to assume that the deposits of preserved aeolian successions necessarily represent an unbiased record of the conditions that prevailed during episodes of Earth history when large‐scale aeolian systems were active, or has the evidence to support the existence of other major desert basins been lost for many periods throughout Earth history?     

Stardust impact analogs: Resolving pre‐ and postimpact mineralogy in Stardust Al foils

Abstract– The grains returned by NASA’s Stardust mission from comet 81P/Wild 2 represent a valuable sample set that is significantly advancing our understanding of small solar system bodies. However, the grains were captured via impact at ～6.1 km s^?1 and have experienced pressures and temperatures that caused alteration. To ensure correct interpretations of comet 81P/Wild 2 mineralogy, and therefore preaccretional or parent body processes, an understanding of the effects of capture is required. Using a two‐stage light‐gas gun, we recreated Stardust encounter conditions and generated a series of impact analogs for a range of minerals of cometary relevance into flight spare Al foils. Through analyses of both preimpact projectiles and postimpact analogs by transmission electron microscopy, we explore the impact processes occurring during capture and distinguish between those materials inherent to the impactor and those that are the product of capture. We review existing and present additional data on olivine, diopside, pyrrhotite, and pentlandite. We find that surviving crystalline material is observed in most single grain impactor residues. However, none is found in that of a relatively monodisperse aggregate. A variety of impact‐generated components are observed in all samples. Al incorporation into melt‐derived phases allows differentiation between melt and shock‐induced phases. In single grain impactor residues, impact‐generated phases largely retain original (nonvolatile) major element ratios. We conclude that both surviving and impact‐generated phases in residues of single grain impactors provide valuable information regarding the mineralogy of the impacting grain whilst further studies are required to fully understand aggregate impacts and the role of subgrain interactions during impact.     

Tertiary Tsondab Sandstone Formation: preliminary bedform reconstruction and comparison to modern Namib Sand Sea dunes

The Tertiary Tsondab Sandstone Formation, which underlies much of the present Namib Sand Sea, is a key element in understanding the Cenozoic evolution of the Namib Desert. Outcrops of the aeolian facies of the Tsondab Sandstone at Elim and Diep Rivier consist of two sequences of bioturbated cross-strata separated by likely formation-scale surfaces of stabilisation. Cross-strata consist of scalloped sets about 200 m in width and separated by southeast dipping bounding surfaces. Internally, sets contain reactivation surfaces of probable seasonal origin. The north to south-southeast dipping foresets define crescent shapes with a trough axis trending northeast. Although additional data are needed to define the Tsondab bedform, the outcrop data is best satisfied in computer simulations by north trending, east migrating main bedforms, which had relatively large and slow-moving dunes superimposed upon their eastern flanks and migrated to the north. Foresets dipping to the south to south-southwest at Elim suggest that superimposed dunes also occurred on the western flanks of the main bedform and migrated to the south, but that their record was largely lost with net eastward migration of the main bedform. This preliminary Tsondab model shares attributes such as trend, scale of cross-strata, and presence of scalloped sets with reactivation surfaces with computer models of the modern linear dunes in which large-scale sinuosity migrates alongcrest to the north. Differences emerge in the overall set architecture and the orientation of cross-strata and bounding surfaces, as well as the degree of vegetation that must have characterised Tsondab dunes.     

The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes

Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity.