摘要 :
Lobate debris aprons (LDA) and lineated valley fill (LVF) have been broadly recognized in the mid latitudes of Mars and their subsequent analyses using data from the SHAllow RADar (SHARAD) instrument has suggested evidence for con...
展开
Lobate debris aprons (LDA) and lineated valley fill (LVF) have been broadly recognized in the mid latitudes of Mars and their subsequent analyses using data from the SHAllow RADar (SHARAD) instrument has suggested evidence for contemporary ice preserved beneath these features. In this study, we conduct detailed characterization of newly identified LDA flow units within the Tanaica Montes region (39.55 degrees N, 269.17 degrees E) of Mars to assess and understand the similarities in their emplacement with respect to LDA flow units mapped in other regions of Mars. We utilize the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images and SHAllow RADar (SHARAD) datasets for geomorphic and subsurface analysis and Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) point tracks for topographic analysis. Geomorphic observation of LDA flow units surrounding the montes flanks and massif walls reveal integrated pattern of convergence and divergence and evidence of bending and deflection within the flow lines that resulted in concentric, loop-like flow patterns in the downslope. Brain-terrain texture and craters with varying morphological characteristics (ring-mold type) is suggestive that LDAs may be similar to ice-rich, debris -covered glaciers. MOLA point track based convex-up topographic profiles of LDAs suggest that their thickness vary in the range of similar to 100-200 m in both the northwestern and southeastern portions of study region. Further, the slope values of mapped LDA surfaces within the study region are within similar to 0.1 degrees-4 degrees. The extent of mapped LDAs within the study region is such that some of the low elevation (similar to 0.8-1.3 km) portions of montes flanks are surrounded by relatively less extent (up to similar to 0.5-0.8 km) of LDA flow units. Geomorphic and topographic evidence for flow units that appear to be superposed on the main LDA body collectively suggest the possibility of episodic glacial activity in the region. Furthermore, based on the alignment of subsurface reflectors with the surrounding plains when a permittivity of ice (3.2) is assumed and the radargram is depth-corrected, we infer that some of the portions of LDA flow units have preserved ice in their subsurface up to 300-500 m depth. Crater size frequency distribution of craters counted on LDA surface indicates that the best-fit age is similar to 110 Ma. In addition, the LDA surfaces exhibit different best-fit ages for different types of crater morphologies (bowl shaped, ring-mold and infilled craters) included in the crater count statistics. Together, these observations and the interpretations suggest that most, if not all, of the LDAs in the study region are like classical LDAs mapped in other regions of Mars (e.g. along the mid-latitude dichotomy boundary and eastern Hellas region). These results indicate that a widespread accumulation and preservation of ice has occurred during the Late Amazonian as suggested in previous studies. (C) 2017 Elsevier Inc. All rights reserved.
收起
摘要 :
Morphologic characteristics of ice-rich landforms in the martian mid-latitudes record evidence for significant modification of the landscape in response to spin-axis/orbital parameter-driven shifts in the Late Amazonian climate. T...
展开
Morphologic characteristics of ice-rich landforms in the martian mid-latitudes record evidence for significant modification of the landscape in response to spin-axis/orbital parameter-driven shifts in the Late Amazonian climate. These landforms are spatially distributed across the mid-latitudes and their co-existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while Mars was undergoing major-moderate-minor shifts in its Late Amazonian climate. We have therefore carried out an in-depth investigation of Moreux crater (similar to 135 km, centered at 41.66 degrees N, 44.44 degrees E in the Protonilus Mensae region) for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater. Evidence for extensive modification of the surfaces over crater rim/wall and around central peak by emplacement of multiple scales of ice-rich landforms that represents large history of glacial activities was found. From our results we document phases of major-moderate-minor glacial activities within the crater as: (1) piedmont lobes/lobate debris aprons/linear valley fills (similar to 1 Ga-100 Ma), (2) viscous flow features (similar to 30-0.1 Ma) and (3) gullies/thermal contraction crack polygons (similar to 2.1-0.4 Ma). The form and distribution of the random valleys observed within Moreux suggests their formation by pressure-induced melting and flow occurring beneath an extensive layer of ice. We also suggest that central peak of Moreux probably acted as the locus for accumulation of ice/snow and the diversity of glacial/periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice/snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes. Taken together, these ice-rich deposits within Moreux suggest that sequential modification of the crater surfaces over the rim/wall and around central peak has occurred over the last tens of millions of years of martian history. This new evidence thus adds another well-documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of Mars in recent martian history. (C) 2014 Elsevier Inc. All rights reserved.
收起
摘要 :
Lobate debris apron (LDA) in the Mars' mid-latitudes substantiate extensive glaciation during the Late Amazonian. Detailed investigation of these landforms is imperative because different areas distributed at different latitudes, ...
展开
Lobate debris apron (LDA) in the Mars' mid-latitudes substantiate extensive glaciation during the Late Amazonian. Detailed investigation of these landforms is imperative because different areas distributed at different latitudes, distinct geologic settings and varied regional topography may have responded to climate in different ways. In this study, mapping of LDA deposits in Erebus Montes region in the flat, low-lying plains of the northern mid-latitudes has been undertaken and examined at a detail previously not attempted to infer new insights on the history of extensive glaciation. LDA deposits show convex-up, steep terminus profiles consistent with typical down-gradient flow characteristics, and integrated flow patterns akin to the glacial landforms reported along the dichotomy boundary. Evidence for a broad piedmont-like lobe, down-gradient flow within a possible oblique-impact crater, and infilled craters, suggest focused localized flow and glaciation. Lobate flows emanating from small alcoves and superposed on the main LDA are not observed, which likely suggests that there is a lack of multi-stage glaciation facilitated by the alcove microclimatic conditions in the region. Linear-curvilinear ridges on the LDA deposits could be the remnant of the internal flow lineations, and are most likely produced by the sublimation of debris-rich ice. Brain-terrain textures, polygonal cracks and ring-mold craters are ubiquitous on the upper surface of LDA deposits, which provides the morphological evidence for the past accumulation of LDM in the region. Hitherto, radar-based investigations do not provide substantial evidence for the presence of extant water ice beneath LDA deposits. We find that the LDA deposits examined here are more consistent with the cold-based glacial behavior - morphological observations supports existence of the sublimation process in the region. We suggest that the derived best-fit age of similar to 30 Ma for the LDA deposits indicates age of the debris apron that has been mantled and the mapped LDA deposits in our study should be better represented by a broad age range of similar to 10-100 Ma. Together, our findings add another well-documented case to support the rapidly accumulating evidences for widespread extensive debris-covered glacial landsystems in the northern mid-latitudes of Mars in the Late Amazonian geological history.
收起
摘要 :
Evidence for mid-high latitude glacial episodes existing within the Late Amazonian history of Mars has been reported from analysis of variety of glacial/periglacial landforms and their statigraphic relationships. In this study, us...
展开
Evidence for mid-high latitude glacial episodes existing within the Late Amazonian history of Mars has been reported from analysis of variety of glacial/periglacial landforms and their statigraphic relationships. In this study, using the Context Camera (CTX) images, we have surveyed the interior of craters within the Alba Mons region of Mars (30 degrees-60 degrees N; 80 degrees-140 degrees W) to decipher the presence of ice-related flow features. The primary goals of this study are to (1) suggest from observations that the flow features identified in the interior of Alba Mons craters have flow characteristic possibly different from concentric crater fill (CCF) landforms and (2) interpret the extent of glacial activity that led to formation of flow features with respect to previously described mid-latitude ice-related landforms. Our geomorphic investigation revealed evidence for the presence of tongue-like or lobate shaped ice-related flow feature from the interior of similar to 346 craters in the study region. The. presence of ring-mold crater morphologies and brain-terrain texture preserved on the surface of flow features suggests that they are possibly formed of near-surface ice-rich bodies. We found that these flow features tend to form inside both the smaller (<5 km) and larger (>5 km) diameter craters emplaced at a wide range of elevation (from similar to -3.3 km to 6.1 km). The measurement of overall length and flow direction of flow features is suggestive that they are similar to pole-facing small-scale lobate debris apron (LDA) formed inside craters. Crater size-frequency distribution of these small-scale LDAs reveals a model age of similar to 10-100 Ma. Together with topographic and geomorphic observations, orientation measurements, and distribution within the study region, we suggest that the flow features (identified as pole-facing smallscale LDAs in the interior of craters) have flow characteristic possibly different from CCF landforms. Our observations and findings support the results of previous analyses that suggests Mars to have preserved records of multiple debris-covered glacial episodes occurred in the Late Amazonian.
收起
摘要 :
Long-term monitoring of dune/non-dune gullies has substantiated extensive and diversified morphological changes whose timing correlates with the time of removal of CO2 frost, thereby implying seasonal control on the active process...
展开
Long-term monitoring of dune/non-dune gullies has substantiated extensive and diversified morphological changes whose timing correlates with the time of removal of CO2 frost, thereby implying seasonal control on the active processes. We present evidence for present-day changes in sand-filled gully channels consistent with ripples. These channels are ubiquitous in the mid-latitudes and found in gullies formed over a variety of substrates on crater walls. We investigated 1483 gullied craters having coverage of at least two High Resolution Imaging Science Experiment (HiRISE) images between 30 degrees S and 75 degrees S and identified 98 craters (6.6% of the total) with sand-filled gully channels. Among these 98 craters, sand-filled gully channels in 25 craters (25.5% of the total) exhibit morphological changes indicative of avulsion, narrow channel incision, formation of channels with potential terminal pits, channel widening and extension, downslope flow of mobilized sand inside channels, dark flows and rapid boulder movement inside channels, and local sand rearranging and erasing of channels. Investigation of the sequence of events revealed CO2 frost inside the sand-filled gully channels in the image acquired during winter and prior to the image in which recent changes have been observed. This suggests a connection with the sublimating frost inside the channels and a seasonal control that subsequently produces extensive changes in the sand-filled gully channels during defrosting seasons in approximately a Mars year. Comparison of changes on both sand-filled gully channels and dune gully channels substantiates that the currently active processes have similar effects on the loose, unconsolidated substrate in both the gully types. For example, CO2 frost processes are able to erode both sand-filled gully channels and dune gully channels to form linear channels with terminal pits. In contrast, we have not found similar evidence of linear channels with terminal pits on bedrock and/or LDM substrate on the crater wall suggesting that the bedrock and LDM substrate may not be able to be eroded by CO2 frost processes in a manner similar to the loose, unconsolidated substrate in sand-filled gully channels investigated in this study. Together, the results signify that the sand-filled gully channels represent a significant component of present-day modification of gully channels on Mars.
收起
摘要 :
A wide range of methods for detection of glacial lakes and their expansions using multi-temporal remote sensing images have been employed in the past. This paper presents a framework for semiautomatic detection of glacial lakes an...
展开
A wide range of methods for detection of glacial lakes and their expansions using multi-temporal remote sensing images have been employed in the past. This paper presents a framework for semiautomatic detection of glacial lakes and estimation of its expansion in Chamkhar Chu Basin, Hindukush Himalaya, Bhutan, with the help of ASTER multispectral image classifications. Lakes in the glacierized area tend to have a varying spectral response ranging from light blue or green to almost black which makes them difficult to be differentiated from shadows in the region. Detection of glacial lakes has been performed using NDWI technique and support vector machine image classification approach and results were compared. An integrated thermal-optical dataset was generated for applying SVM technique, and results showed that the lakes under cast shadow were accurately detected. Water spread extent of the lake has been estimated and it was observed that the present expansion rate of glacial lake has increased by twofolds from its previous rate in the last decade. The formations, deformations around glacial lake and related geomorphological variations occurring around lake were employed in defining the expansion mechanism of the lake. This study also demonstrates that ASTER data provide the possibility of accurate detections and estimation of water spread of glacial lake without simultaneous field observations.
收起
摘要 :
Space exploration missions of planetary bodies in our solar system have provided new insights to understand their formation and evolutionary processes that such bodies have undergone leading to their current geological state. Remo...
展开
Space exploration missions of planetary bodies in our solar system have provided new insights to understand their formation and evolutionary processes that such bodies have undergone leading to their current geological state. Remote sensing from orbiter mission has helped in identifying surface features, delineating surface topography, mapping surface composition and deriving reliable age estimates of different planetary surfaces. In particular, high spatial and spectral resolution spacecraft observations have significantly contributed to our current understanding of the geological, physical and chemical processes that resulted in divergent evolutionary paths undertaken by different planetary objects such as inner and outer planets, dwarf planets, the moons and small solar system bodies (asteroids and comets). Hyperspectral remote sensing has been an emerging field of space-based reflectance spectroscopy and in recent years many imaging spectroscopy instruments have flown on different planetary missions, e.g. Moon Mineralogy Mapper on-board Chandrayaan-1, VIMS on Cassini mission, CRISM on Mars Reconnaissance Orbiter (MRO) mission, etc. This article provides a review on imaging reflectance spectroscopy for understanding the surface composition through mineralogy for different planetary bodies.
收起
原文获取