Higher-order neighbor analysis of the Tartarus Colles cone groups, Mars: The application of geographical indices to the understanding of cone pattern evolution     

Mark A. Bishop 《Icarus》2008,197(1):73-83

Cone fields of ambivalent origin exist in the Elysium, Amazonis, Cerberus, Isidis, Acidalia and Cydonia regions of Mars. Considerable interest exists in regard to their location and origin as their occurrence in many instances, is most likely associated with near surface ground ice; the presence of which has consequences for past and present climate, astrobiological activity, and future exploration. This research has outlined an understanding of both spatial and geomorphic processes of cone development for a region within the Tartarus Colles, Mars, as well as the manner in which spatial statistical indices can be affected by modification to the areal unit of study. This study found that cone groups for the region of the Tartarus Colles, are completely spatially random (CSR) across all distances extending to their sixth-order neighbor. However, significant statistical indices of aggregation were found for groups where post-emplacement erosional modification may have occurred by solifluction-like mechanisms or magmatic incursion into or over frozen ground. Such circumstances imply that R-indices reflect both the underlying spatial and geologic processes of cone formation, and also, an overprint of erosional modification of the cone-field within a glacial or periglacial setting, in this instance. The comparison of spatial indices can therefore offer a viewpoint from which geomorphic change can be recognized and quantitatively evaluated for cone fields.  相似文献   

Geomorphological evidence of water level changes in Nepenthes Mensae, Mars     

Miguel Ángel de Pablo  Andrea Pacifici 《Icarus》2008,196(2):667-671

In the western sector of Nepenthes Mensae, Mars, there are some geomorphological features that could be related to a standing water sheet in the area, such as fluvial terraces, deltas and shorelines. A detailed analysis of these features reveals two variations in water level, probably related to tectonic processes, as suggested by the existence of a fissural volcano at this site.  相似文献   

Mojave Mars simulant—Characterization of a new geologic Mars analog     

Gregory H. Peters  Gregory H. Bearman  J. Anthony Smith  Susanne Douglas 《Icarus》2008,197(2):470-479

We have identified and characterized a basaltic Mars simulant that is available as whole rocks, sand and dust. The source rock for the simulant is a basalt mined from the Tertiary Tropico Group in the western Mojave Desert. The Mojave Mars Simulant (MMS) was chosen for its inert hygroscopic characteristics, its availability in a variety of forms, and its physical and chemical characteristics. The MMS dust and MMS sand are produced by mechanically crushing basaltic boulders. This is a process that more closely resembles the weathering/comminution processes on Mars where impact events and aerodynamic interactions provide comminution in the (relative) absence of water and organics. MMS is among the suite of test rocks and soils that was used in the development of the 2007/8 Phoenix Scout and is being used in the 2009 Mars Science Laboratory (MSL) missions. The MMS development team is using the simulant for research that centers on sampling tool interactions in icy soils. Herein we describe the physical properties and chemical composition of this new Mars simulant.  相似文献   

Frosted granular flow: A new hypothesis for mass wasting in martian gullies     

Chris H. Hugenholtz 《Icarus》2008,197(1):65-72

Recent gully deposits on Mars have been attributed to both wet and dry mass wasting processes. In this paper frosted granular flow (FGF) is presented as a new hypothesis for recent mass wasting activity in martian gullies. FGF is a rare type of granular flow observed on a talus slope in the Province of Québec, Canada [Hétu, B., van Steijn, H., Vandelac, P., 1994. Géogr. Phys. Quat. 48, 3-22]. Frost reduces dynamic inter-particle friction, enabling flows to mobilize onto relatively low slope gradients (25-30°) compared to those involving dry granular flow of the same material (35-41°). Resulting erosional and depositional features include straight to sinuous channels, levees and digitate to branching arrangements of terminal deposits. Similar features are commonly found in association with geologically-young gully systems on Mars. Based on terrestrial observations of FGF processes the minimum criteria required for their occurrence on Mars include: (i) readily mobilized, unconsolidated sediment at the surface; (ii) an upper slope gradient at or near the angle of repose; (iii) frost accumulation at the surface; and (iv) triggering by rock fall. All four conditions appear to be met in many areas on present-day Mars though triggering mechanisms may vary. Compared to terrestrial FGFs, which are lubricated by thin liquid films at inter-particle contacts, those occurring on Mars are more likely lubricated by vaporization of CO₂ and small amounts of H₂O frost that becomes incorporated in the translating mass. Some recent mass wasting activity in martian gullies, therefore, could be interpreted as the product of FGF.  相似文献   

Experimental study on the impact fragmentation of core-mantle bodies: Implications for collisional disruption of rocky planetesimals with sintered core covered with porous mantle     

Chisato Okamoto  Masahiko Arakawa 《Icarus》2008,197(2):627-637

Impact experiments of inhomogeneous targets such as layered bodies consisting of a dense core and porous mantle were conducted to clarify the effect of the layered structure on impact strength. The layered structure of small bodies could be the result of the thermal evolution of planetesimals in the solar nebula. So, the impact disruption of thermally evolved bodies with core-mantle structure is important for the origin of small bodies such as asteroids. We investigated the impact strength of rocky-layered bodies with porous mantle-sintered cores, which could be formed at an initial stage of thermal evolution. Spherical targets composed of soda-lime glass or quartz core and porous gypsum mantle were prepared as an analog of small bodies with a core-mantle structure, and the internal structure was changed. A nylon projectile was impacted at the impact velocity from 1 to 5 km/s. The impact strength of the core-mantle targets decreases with the increase of the core/target mass ratio (RCM) in the specific energy range from 1×¹⁰³ to 4×¹⁰⁴ J/kg. We observed two distinct destruction modes characterized by the damage to the core: one shows a damaged core and fractured mantle, and the other shows an intact core and broken mantle. The former mode was usually observed with increasing RCM, and the boundary condition of the core destruction () was experimentally found to be , where is the specific energy required to disrupt a glass core. From this empirical equation, it might be possible to discuss the destruction conditions of a thermally evolved body with a porous mantle-sintered core structure. We speculate that the impact strength of the body could be significantly reduced with the progress of internal evolution at the initial stage of thermal evolution.  相似文献   

Evolution and depositional environments of the Eberswalde fan delta, Mars   总被引：2，自引：0，他引：2  

Monica Pondrelli  Angelo Pio Rossi 《Icarus》2008,197(2):429-451

The Eberswalde crater and its contributing basins have been analyzed in detail in order to reconstruct the geological evolution of the water-related landforms with particular focus on the Eberswalde delta-like feature. Based on a complex strata organization characterized by a topset-foreset-bottomset geometry, typical of delta progradation on Earth, we interpret the Eberswalde feature to be a fan delta associated with a lacustrine system. Depositional sub-environments have been recognized and mapped and the sedimentary processes discussed. A sequence stratigraphy approach has been used to evaluate the system, which we interpret to result from three depositional sequences. These sequences suggest relative water level fluctuations and a longer trend over time towards decreasing water content inside the basin.  相似文献   

黄土坡滑坡形成与变形的地质过程机制   总被引：2，自引：0，他引：2  

陈松  陈国金  徐光黎 《地球科学》2008,33(3):411-415

巴东黄土坡滑坡是三峡库区重大滑坡之一, 规模大, 而且形成与变形地质过程机制复杂.是与三峡库区构造强烈隆升、河流急剧下切、斜坡重力卸荷等各种作用相伴生的地质过程的结果; 其中的Ⅰ号崩滑堆积体在回水条件下深层蠕动变形较明显, 受到多方面的关注.采用地质过程类比分析方法, 通过对滑坡形成、回水前变形破坏、回水条件下变形的地质过程机制分析, 预测了深层蠕动变形使其中部和前部产生较大变形的发展趋势, 目前发现Ⅰ号崩滑堆积体的深层蠕动变形问题, 主要是库水升降的动态过程与降雨效应耦合作用的结果.   相似文献   

Some new random field tools for spatial analysis     

Robert J. Adler 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):809-822

  相似文献   

Relationships between hydrosedimentary processes and occurrence of mercury-resistant bacteria (merA) in estuary mudflats (Seine, France)     

Ramond JB  Berthe T  Lafite R  Deloffre J  Ouddane B  Petit F 《Marine pollution bulletin》2008,56(6):1168-1176

The Seine estuary (France) is one of the world's macrotidal systems that is most contaminated with heavy metals. To study the mercury-resistant bacterial community in such an environment, we have developed a molecular tool, based on competitive PCR, enabling the quantification of Gram-negative merA gene abundance. The occurrence of the Gram-negative merA gene in relation with the topology (erosion/deposit periods) and the mercury contamination of three contrasted mudflats was investigated through a multidisciplinary approach and compared with a non-anthropized site (Authie, France). The higher abundance of the Gram-negative merA gene in the Seine estuary mudflats indicates a relationship between the degree of anthropization and the abundance of the merA gene in the mudflat sediments. In the Seine mudflats, the maxima of abundance are always located in fresh sediment deposits. Therefore, the abundance is closely related with the hydrosedimentary processes, which thus seem to be determining factors in the occurrence of the Gram-negative merA gene in the surface sediments of the Seine's mudflat.  相似文献   

Effect of altered flow regime on bankfull area of the Lower Yellow River,China   总被引：2，自引：0，他引：2  

Baosheng Wu  Junqiang Xia  Xudong Fu  Yuanfeng Zhang  Guangqian Wang 《地球表面变化过程与地形》2008,33(10):1585-1601

The adjustment of the bankfull channel area in the Lower Yellow River has been dramatically affected by altered flow regimes caused by human activities. This paper presents a study on the effects of altered discharge and suspended sediment load on the bankfull area at Gaocun, a representative hydrometric station in the Lower Yellow River. The analysis demonstrates the cumulative effect of previous years' flow and sediment conditions on channel adjustment, a phenomenon commonly occurring in geomorphic systems due to the delayed channel response to flow and sediment conditions. A methodology for the prediction of bankfull area was developed based on the general concept that the rate of adjustment is proportional to the difference between the bankfull area and its equilibrium value. The proposed methodology is not only applicable for the prediction of the bankfull area in response to the changes in flow and sediment conditions in the Lower Yellow River, but can also be extended to other studies where the response times have a key role to play in the assessment of channel adjustment to external changes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献