Sedimentology and sequence stratigraphy of a transfer zone coarse-grained delta, Miocene Suez Rift, Egypt

This study focuses on Miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the Thal Fault segment, Gulf of Suez. The succession generally shoals upwards from offshore mudstone containing pro-delta turbidites, into conglomeratic delta foresets and topsets, with sandstone-dominated shoreface facies coexisting laterally. Despite this upward shoaling, key stratal surfaces marking abrupt changes in relative sea-level allow the succession to be divided into four stratal units. The stacking pattern of the stratal units suggests an initial relative sea-level rise that generated a major marine flooding surface. A relative sea-level fall followed, resulting in widespread exposure and incision. During the ensuing relative sea-level rise a lowstand coarse-grained delta and coeval shoreface succession prograded several kilometres basinward. The stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the Baba-Sidri fault segment, further south. At the transfer zone, low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea-level. In the fault centre location, however, higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas. The results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins.     

Young asteroid mixing revealed in ordinary chondrites: The case of NWA 5764, a polymict LL breccia with L clasts

Polymict chondritic breccias—rocks composed of fragments originating from different chondritic parent bodies—are of particular interest because they give insights into the mixing of asteroids in the main asteroid belt (occurrence, encounter velocity, transfer time). We describe Northwest Africa (NWA) 5764, a brecciated LL6 chondrite that contains a >16 cm³ L4 clast. The L clast was incorporated in the breccia through a nondestructive, low‐velocity impact. Identical cosmic‐ray exposure ages of the L clast and the LL host (36.6 ± 5.8 Myr), suggest a short transfer time of the L meteoroid to the LL parent body of 0.1 ± 8.1 Myr, if that meteoroid was no larger than a few meters. NWA 5764 (together with St. Mesmin, Dimmitt, and Glanerbrug) shows that effective mixing is possible between ordinary chondrite parent bodies. In NWA 5764 this mixing occurred after the peak of thermal metamorphism on the LL parent body, i.e., at least several tens of Myr after the formation of the solar system. The U,Th‐He ages of the L clast and LL host, identical at about 2.9 Ga, might date the final assembly of the breccia, indicating relatively young mixing in the main asteroid belt as previously evidenced in St. Mesmin.     

A process to design a network of marine no-take areas: Lessons from the Great Barrier Reef

In the absence of consensus on the quantity and level of zoning protection required for coral reef and lagoon ecosystems, which process can guide decision makers? The Great Barrier Reef Marine Park Authority (GBRMPA) worked with experts in a collaborative process to develop a set of Biophysical Operational Principles to guide the design of a network of no-take areas. First, 82 expert scientists were asked to provide data and advice on the physical, biological and ecological dimensions of the Great Barrier Reef ecosystem. They recommended that an independent Scientific Steering Committee (the Committee) was set up. How this Committee worked successfully with the GBRMPA staff is detailed here in a manner to enable other resource managers to adopt the process if they are working in data-limited marine environments.     

Large-Eddy Simulation of the Stable Atmospheric Boundary Layer using Dynamic Models with Different Averaging Schemes

Large-eddy simulation (LES) of a stable atmospheric boundary layer is performed using recently developed dynamic subgrid-scale (SGS) models. These models not only calculate the Smagorinsky coefficient and SGS Prandtl number dynamically based on the smallest resolved motions in the flow, they also allow for scale dependence of those coefficients. This dynamic calculation requires statistical averaging for numerical stability. Here, we evaluate three commonly used averaging schemes in stable atmospheric boundary-layer simulations: averaging over horizontal planes, over adjacent grid points, and following fluid particle trajectories. Particular attention is focused on assessing the effect of the different averaging methods on resolved flow statistics and SGS model coefficients. Our results indicate that averaging schemes that allow the coefficients to fluctuate locally give results that are in better agreement with boundary-layer similarity theory and previous LES studies. Even among models that are local, the averaging method is found to affect model coefficient probability density function distributions and turbulent spectra of the resolved velocity and temperature fields. Overall, averaging along fluid pathlines is found to produce the best combination of self consistent model coefficients, first- and second-order flow statistics and insensitivity to grid resolution.     

AD-DICE: an implementation of adaptation in the DICE model

Integrated Assessment Models (IAMS) have helped us over the past decade to understand the interactions between the environment and the economy in the context of climate change. Although it has also long been recognized that adaptation is a powerful and necessary tool to combat the adverse effects of climate change, most IAMS have not explicitly included the option of adaptation in combating climate change. This paper adds to the IAM and climate change literature by explicitly including adaptation in an IAM, thereby making the trade-offs between adaptation and mitigation visible. Specifically, a theoretical framework is created and used to implement adaptation as a decision variable into the DICE model. We use our new AD-DICE model to derive the adaptation cost functions implicit in the DICE model. In our set-up, adaptation and mitigation decisions are separable and AD-DICE can mimic DICE when adaptation is optimal. We find that our specification of the adaptation costs is robust with respect to the mitigation policy scenarios and parameter values. Our numerical results show that adaptation is a powerful option to combat climate change, as it reduces most of the potential costs of climate change in earlier periods, while mitigation does so in later periods.     

Lineated valley fill (LVF) and lobate debris aprons (LDA) in the Deuteronilus Mensae northern dichotomy boundary region, Mars: Constraints on the extent, age and episodicity of Amazonian glacial events

In order to assess the nature, degradational processes and history of the dichotomy boundary on Mars, we conducted a detailed morphological analysis of a 70,000 km² region of its northern portion (north-central Deuteronilus Mensae, south of Lyot, in the vicinity of Sinton Crater). This region is characterized by the distinctive sinuous ∼2 km-high plateau scarp boundary, outlying massifs to the north, and extensive fretted valleys dissecting the plateau to the south. These features represent the first-order modification and retreat of the dichotomy boundary, and are further modified by processes that form lineated valley fill (LVF) in the fretted valleys, and lobate debris aprons (LDA) along the dichotomy scarp and surrounding the outlying massifs. We use new high-resolution image and topography data to examine the nature and origin of LVF and LDA and to investigate the climatic and accompanying degradational history of the escarpment. On the basis of our analysis, we conclude that: (1) LVF and LDA deposits within the study region are comprised of the same material, show integrated flow patterns, and originate as debris-covered valley glaciers; a significant amount of ice (hundreds of meters) is likely to remain today beneath a thin cover of sublimation till. (2) There is depositional evidence to suggest glacial highstands at least 800 m above the present level, implying previous conditions in which the distribution of ice was much more widespread; this is supported by similar deposits within many other areas across the dichotomy boundary. (3) The timing of the most recent large-scale activity of the LDA/LVF in this area is about 100-500 million years ago, similar to ages reported elsewhere along the dichotomy boundary. (4) There is evidence for a secondary, but significantly limited phase of glaciation; the deposits of which are limited to the vicinity of the alcoves; similar later phases have also been reported elsewhere along the dichotomy boundary. (5) Modification of the fretted valleys of the dichotomy boundary has been substantial locally, but we find no evidence that the Amazonian glacial epochs caused retreat of the dichotomy boundary of the scale of tens to hundreds of kilometers. Our findings support the results of an analysis just to the east of the study region and of studies carried out elsewhere along the dichotomy boundary that find further evidence for the remnants of debris-covered glaciers and extensive valley glacial land systems.     

The spatial evolution of stellar structures in the Large Magellanic Cloud

We present an analysis of the spatial distribution of various stellar populations within the Large Magellanic Cloud (LMC). We combine mid-infrared selected young stellar objects, optically selected samples with mean ages between ∼9 and ∼1000 Myr and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC. For the analysis we use Fractured Minimum Spanning Trees, the statistical Q parameter and the two-point correlation function. Restricting our analysis to young massive (OB) stars, we confirm our results obtained for M33, namely that the luminosity function of the groups is well described by a power law with index −2, and that there is no characteristic length-scale of star-forming regions. We find that stars in the LMC are born with a large amount of substructure, consistent with a two-dimensional fractal distribution with dimension     and evolve towards a uniform distribution on a time-scale of ∼175 Myr. This is comparable to the crossing time of the galaxy, and we suggest that stellar structure, regardless of spatial scale, will be eliminated in a crossing time. This may explain the smooth distribution of stars in massive/dense young clusters in the Galaxy, while other, less massive, clusters still display large amounts of structure at similar ages. By comparing the stellar and star cluster distributions and evolving time-scales, we show that infant mortality of clusters (or 'popping clusters') has a negligible influence on the galactic structure. Finally, we quantify the influence of the elongation, differential extinction and contamination of a population on the measured Q value.     

Linking jet emission and X-ray properties in the peculiar neutron star X-ray binary Circinus X-1

We present the results of simultaneous X-ray and radio observations of the peculiar Z-type neutron star X-ray binary Cir X-1, observed with the Rossi X-ray Timing Explorer satellite and the Australia Telescope Compact Array in 2000 October and 2002 December. We identify typical Z-source behaviour in the power density spectra as well as characteristic Z patterns drawn in an X-ray hardness–intensity diagram. Power spectra typical of bright atoll sources have also been identified at orbital phases after the periastron passage, while orbital phases before the periastron passage are characterized by power spectra that are typical neither of Z nor of atoll sources. We investigate the coupling between the X-ray and the radio properties, focusing on three orbital phases when an enhancement of the radio flux density has been detected, to test the link between the inflow (X-ray) and the outflow (radio jet) to/from the compact object. In two out of three cases, we associate the presence of the radio jet to a spectral transition in the X-rays, although the transition does not precede the radio flare, as detected in other Z sources. An analogous behaviour has recently been found in the black hole candidate GX 339-4. In the third case, the radio light curve shows a similar shape to the X-ray light curve. We discuss our results in the context of jet models, considering also black hole candidates.     

Identification of the Bloody Creek structure,a possible impact crater in southwestern Nova Scotia,Canada

Abstract— An approximately 0.4 km diameter elliptical structure formed in Devonian granite in southwestern Nova Scotia, herein named the Bloody Creek structure (BCS), is identified as a possible impact crater. Evidence for an impact origin is based on integrated geomorphic, geophysical, and petrographic data. A near‐continuous geomorphic rim and a 10 m deep crater that is infilled with lacustrine sediments and peat define the BCS. Ground penetrating radar shows that the crater has a depressed inner floor that is sharply ringed by a 1 m high buried scarp. Heterogeneous material under the floor, interpreted as deposits from collapse of the transient cavity walls, is overlain by stratified and faulted lacustrine and wetland sediments. Alteration features found only in rim rocks include common grain comminution, polymict lithic microbreccias, kink‐banded feldspar and biotite, single and multiple sets of closely spaced planar microstructures (PMs) in quartz and feldspar, and quartz mosaicism, rare reduced mineral birefringence, and chlorite showing plastic deformation and flow microtextures. Based on their form and crystallographic orientations, the quartz PMs consist of planar deformation features that document shock‐metamorphic pressures ≤25 GPa. The age of the BCS is not determined. The low depth to diameter ratio of the crater, coupled with anomalously high shock‐metamorphic pressures recorded at its exposed rim, may be a result of significant post‐impact erosion. Alternatively, impact onto glacier ice during the waning stages of Wisconsinian deglaciation (about 12 ka BP) may have resulted in dissipation of much impact energy into the ice, resulting in the present morphology of the BCS.     

Scientific exploration of near‐Earth objects via the Orion Crew Exploration Vehicle

Abstract— A study in late 2006 was sponsored by the Advanced Projects Office within NASA's Constellation Program to examine the feasibility of sending the Orion Crew Exploration Vehicle (CEV) to a near‐Earth object (NEO). The ideal mission profile would involve two or three astronauts on a 90 to 180 day flight, which would include a 7 to 14 day stay for proximity operations at the target NEO. This mission would be the first human expedition to an interplanetary body beyond the Earth‐Moon system and would prove useful for testing technologies required for human missions to Mars and other solar system destinations. Piloted missions to NEOs using the CEV would undoubtedly provide a great deal of technical and engineering data on spacecraft operations for future human space exploration while conducting in‐depth scientific investigations of these primitive objects. The main scientific advantage of sending piloted missions to NEOs would be the flexibility of the crew to perform tasks and to adapt to situations in real time. A crewed vehicle would be able to test several different sample collection techniques and target specific areas of interest via extra‐vehicular activities (EVAs) more efficiently than robotic spacecraft. Such capabilities greatly enhance the scientific return from these missions to NEOs, destinations vital to understanding the evolution and thermal histories of primitive bodies during the formation of the early solar system. Data collected from these missions would help constrain the suite of materials possibly delivered to the early Earth, and would identify potential source regions from which NEOs originate. In addition, the resulting scientific investigations would refine designs for future extraterrestrial resource extraction and utilization, and assist in the development of hazard mitigation techniques for planetary defense.