Using Small Craters to Determine the Erosion Rates of Martian Sedimentary Rock

Mars sedimentary rock erosion rates constrained using crater counts, with applications to organic matter preservation and to the global dust cycle

Authors:

Kite et al

Abstract:

Small-crater counts on Mars light-toned sedimentary rock are often inconsistent with any isochron; these data are usually plotted then ignored. We show (using an 18-HiRISE-image, >10^4 crater dataset) that these non-isochron crater counts are often well-fit by a model where crater production is balanced by crater obliteration via steady exhumation. For these regions, we fit erosion rates. We infer that Mars light-toned sedimentary rocks typically erode at ~10^2 nm/yr, when averaged over 10 km^2 scales and 10^7-10^8 yr timescales. Crater-based erosion-rate determination is consistent with independent techniques, but can be applied to nearly all light-toned sedimentary rocks on Mars. Erosion is swift enough that radiolysis cannot destroy complex organic matter at some locations (e.g. paleolake deposits at SW Melas), but radiolysis is a severe problem at other locations (e.g. Oxia Planum). The data suggest that the relief of the Valles Marineris mounds is currently being reduced by wind erosion, and that dust production on Mars older than 3 Gya greatly exceeds the modern reservoir of mobile dust.

The Strontium Cycle of the NeoProterozoic was Driven by Seemingly Unique Paleogeography

Paleogeographic forcing of the strontium isotopic cycle in the Neoproterozoic

Authors:

Goddéris et al

Abstract:

The period spanning from 825 to 540 Ma is characterized by major changes in the surficial Earth system. This extraordinary interval starts with the breakup of the Rodinia supercontinent and eruption of a series of large igneous provinces and ends with the assembly of Gondwana, giving rise to the Pan-African orogenies. This paleogeographic reorganization is accompanied by a global climatic cooling, including the paroxysmal Cryogenian “snowball” glacial events. The 87Sr/86Sr of seawater displays a major long-term rise over this interval that is punctuated by episodic, smaller declines and inflections. We use a coupled deep time climate-carbon numerical model to explore the complex role of tectonics and climate on this distinct evolution in seawater 87Sr/86Sr. We show that the modulation of the weathering of the erupted large igneous provinces by continental drift explains the changes in seawater 87Sr/86Sr from 800 to 635 Ma. The subsequent sharp rise in seawater 87Sr/86Sr from 635 to 580 Ma is the result of erosion of radiogenic crust exposed in the Pan-African orogens. Coeval evolution of atmospheric CO2 displays a decrease from about 80 times the pre-industrial level around 800 Ma to 5 times just before the beginning of the Phanerozoic.

Were Titan's Channels Carved by Ethane & Ammonia?

Formation mechanisms of channels on Titan through dissolution by ammonium sulfate and erosion by liquid ammonia and ethane

Authors:

Gilliam et al

Abstract:

Data obtained from the Cassini Visual and Infrared Mapping Spectrometer (VIMS), Imaging Science Subsystem (ISS), and Synthetic Aperture Radar (SAR) instruments have revealed an array of fluvial channels on Titan's surface, often several hundreds of kilometers in length. The paucity of impact craters on Titan's surface suggests a formation by fluvial erosion into the water-ice bedrock. Additionally, at the landing site, the Huygens Probe Descent Imager and Spectral Radiometer (DISR) imaged Earth-like rounded cobbles 0.3–15 cm in diameter composed of water ice, reminiscent of rounded stream clasts on Earth. In this paper we examine different fluvial features on Titan, identified by the Cassini spacecraft, and evaluate the possibilities of channel formation by dissolution of ice by a concentrated solution of ammonium sulfate, and by mechanical erosion by flow of liquid ammonia and liquid ethane. We find that chemical erosion of Titan's channels could be completed in 280 to 1100 years (all units of time in this paper are Terrestrial, not Titanian), much shorter than the period of about 84,000 years that a concentrated (NH4)2SO4-H2O solution could exist as a liquid on the Titan surface. Mechanical erosion of Titan's channels is generally a much slower process, on the order of 102 to 105 years to completion, and is also slower than mechanical erosion of a model river on Earth, averaging 103 to 104 years. The erosional sequence of the channels on Titan may have started after the formation of water-ice on the surface by the process of chemical dissolution by (NH4)2SO4-H2O, overlapping, or followed by, a period of mechanical erosion by liquid NH3. A final stage on the cooling surface of Titan might have been characterized by liquid C2H6 as an agent of mechanical erosion.

A Classification of Martian Gullies

A Classification of Martian Gullies from HiRISE Imagery

Authors:

Auld et al

Abstract:

Due to the large and varied population of gullies observed in Mars High Resolution Imaging Science Experiment (HiRISE) imagery that exhibit diverse characteristics, this paper develops a classification of martian gullies based on their morphological characteristics. This provides a firmer foundation for future investigation of the genesis of different gully morphologies. The Mars Reconnaissance Orbiter (MRO) image catalog on the HiRISE website was examined and 869 images, chosen from the first 25,000 orbits, show a wide variety of gully morphologies. The images were analyzed using ENVI 4.4 and ENVI Zoom and the gullies were cataloged and divided into groups based on the presence and character of the dominant morphological components of alcove, channel, and apron associated with each gully. 7519 gullies were identified in the images and the length and width of the components were measured in ENVI to facilitate classification. Seven classes were developed based on morphology.

Present-day formation and seasonal evolution of linear dune gullies on Mars

Present-day formation and seasonal evolution of linear dune gullies on Mars

Authors:

Pasquon et al

Abstract:

Linear dune gullies are a sub-type of martian gullies. As their name suggests they only occur on sandy substrates and comprise very long (compared to their width) straight or sinuous channels, with relatively small source areas and almost non-existent visible deposits. Linear dune gullies have never been observed on terrestrial dunes and their formation process on Mars is unclear. Here, we present the results of the first systematic survey of these features in Mars’ southern hemisphere and an in-depth study of six dunefields where repeat-imaging allows us to monitor the changes in these gullies over time. This study was undertaken with HiRISE images at 25–30 cm/pix and 1 m/pix elevation data derived from HiRISE stereo images. We find the latitudinal distribution and orientation of linear dune gullies broadly consistent with the general population of martian gullies. They occur predominantly between 36.3°S and 54.3°S, and occasionally between 64.6°S and 70.4°S. They are generally oriented toward SSW (at bearings between 150° and 260°). We find that these gullies are extremely active over the most recent 5 Martian years of images. Activity comprises: (1) appearance of new channels, (2) lengthening of existing channels, (3) complete or partial reactivation, and (4) disappearance of gullies. We find that gully channels lengthen by ∼100 m per year. The intense activity and the progressive disappearance of linear dune gullies argues against the hypothesis that these are remnant morphologies left over from previous periods of high obliquity millions of years ago. The activity of linear dune gullies reoccurs every year between the end of winter and the beginning of spring (Ls 167.4°–216.6°), and coincides with the final stages of the sublimation of annual CO₂ ice deposit. This activity often coincides spatially and temporally with the appearance of recurrent diffusing flows (RDFs)—digitate-shaped, dark patches with low relative albedo (up to 48% lower than the adjacent dune) that encompass the active site. South- and SSW-facing dune slopes are those which preferentially host CO2 frost deposits, however, it is only those with angles of ∼20° just below the crest which possess linear dune gullies, suggesting a slope-limited formation process. These observations provide a wealth of temporal and morphometric data that can be used to undertake numerical modeling, to direct future image monitoring and guide laboratory experiments that can be used to better constrain the formation process of these features.

Fluvial erosion as a mechanism for crater modification on Titan

Fluvial erosion as a mechanism for crater modification on Titan

Authors:

Neish et al

Abstract:

There are few identifiable impact craters on Titan, especially in the polar regions. One explanation for this observation is that the craters are being destroyed through fluvial processes, such as weathering, mass wasting, fluvial incision and deposition. In this work, we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on Titan. We find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as Cassini, given enough time and a large enough erosion rate. A difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in Titan’s crater population. Fluvial erosion also removes central peaks and fills in central pits, possibly explaining their infrequent occurrence in Titan craters. Although many craters on Titan appear to be modified by aeolian infilling, fluvial modification is necessary to explain the observed impact crater morphologies. Thus, it is an important secondary modification process even in Titan’s drier equatorial regions.

Geomorphological map of the Afekan Crater region, Titan

Geomorphological map of the Afekan Crater region, Titan: Terrain relationships in the equatorial and mid-latitude regions

Authors:

Malaska et al

Abstract:

We carried out geomorphological mapping in a mid-latitude area surrounding the Afekan Crater region on Titan. We used Cassini RADAR (Synthetic Aperture Radar mode) data as the basemap, supplemented by Cassini RADAR microwave emissivity, Imaging Science Subsystem (ISS) infrared data, Visual and Infrared Mapping Spectrometer (VIMS) spectral images, and topography derived from Synthetic Aperture Radar (SAR). Mapping was done at a spatial scale of 300 m/pixel, which corresponds to a map scale of 1:800,000. We describe multiple terrain units and their spatial relations. We describe five broad classes of units that are in agreement with previous mapping efforts: crater, labyrinth, hummocky/mountainous, plains, and dune terrain classes. We subdivide these into seven crater units, four hummocky/mountainous units, six plains units, and three dunes units. Our results show that plains are the dominant class of terrain unit in Titan’s mid latitudes. Of the plains units, the undifferentiated plains are the largest by total areal extent in the mapped region, accounting for over 45% of the mapped area. We developed a stratigraphic sequence that has the hummocky/mountainous and labyrinth terrains as the oldest units. The observed properties of the hummocky/mountainous terrain are consistent with fractured water ice materials, while the labyrinth terrains are consistent with organic materials. The youngest units are the dune units and streak-like plains units, with the undifferentiated plains units being of intermediate age. The microwave emissivity of the undifferentiated plains and dune units are consistent with organic materials. Given their properties and stratigraphic placement, we conclude that the hummocky/mountainous terrains are most consistent with the presumed crustal materials of Titan. The plains materials are consistent with deposits resulting from the transport and emplacement of organic-rich materials predominantly by aeolian mechanisms. Our geomorphological mapping results are consistent with the equatorial and mid-latitudes of Titan being dominated by organic materials that have been deposited and emplaced by aeolian activity.

Formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on Titan and Mars

Formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on Titan and Mars

Authors:

Howard et al

Abstract:

In many terrestrial channels the gravel bed is only transported during rare floods (threshold channels), and rates of erosion are very slow. In this paper we explore how coarse debris delivered to channels on Mars and Titan from erosion may inhibit further erosion once a coarse gravel channel bed develops. Portions of the equatorial region of Titan are fluvially eroded into banded (crenulated) terrain, some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment. No mechanism that can chemically or physically break down ice (likely the most important component of Titans crust) has been unambiguously identified. This paper examines a scenario in which fluvial erosion on Titan has largely involved erosion into an impact-generated megaregolith that contains a modest component of gravel-sized debris. As the megaregolith is eroded, coarse gravel gradually accumulates as a lag pavement on channel beds, limiting further erosion and creating a dissected, but largely inactive, or senescent, landscape. Similar development of gravel pavements occur in ancient mountain belts on Earth, and partially explain the persistence of appreciable relief after hundreds of millions of years. Likewise, coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on Mars, particularly if weathering were largely due to physical, rather than chemical weathering processes in a relatively cold and/or arid environment.

The Race Between Orogeny and Glacial Erosion in the St Elias Mountains, Alaska During the Pleistocene Quaternary

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

Authors:

Gulick et al

Abstract:

Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

Evidence of Enhanced Erosion During Amazonian Eon Glaciations on Mars

Enhanced erosion rates on Mars during Amazonian glaciation

Authors:

Levy et al

Abstract:

Observations of Mars from the surface and from orbit suggest that erosion rates over the last ∼3 Gyr (the Amazonian) have been as slow as 10−5 m/Myr and have been dominated by aeolian processes, while ancient (Noachian) erosion rates may have been orders of magnitude higher due to impact bombardment and fluvial activity. Amazonian-aged glacial deposits are widespread on Mars, but rates of erosion responsible for contributing debris to these remnant glacial deposits have not been constrained. Here, we calculate erosion rates during Amazonian glaciations using a catalog of mid-latitude glacial landforms coupled with observational and theoretical constraints on the duration of glaciation. These calculations suggest that erosion rates for scarps that contributed debris to glacial landforms are 4–7 orders of magnitude higher than average Amazonian rates in non-glaciated, low-slope regions. These erosion rates are similar to terrestrial cold-based glacier erosion and entrainment rates, consistent with cold-based glacier modification of parts of Mars.

How Formation of Gullies on Martian Craters

Quantitative analysis of the morphology of martian gullies and insights into their formation

Authors:

Yue et al

Abstract:

The process of formation of observed geologically recent gully features on Mars has remained a topic of intense debate since their discovery. In this study, we performed quantitative morphological analysis on certain parameters of gullies from different settings, such as crater walls, terraces, and sand dunes, on the martian surface in addition to the Meteor and Xiuyan craters on the Earth. The morphometric parameters were measured for cross profiles, which were extracted along each gully at certain intervals. Some interesting relationships among the parameters were determined, which could provide us a comprehensive understanding of the morphologies of the gullies’. The results show that strong correlations exist among those parameters, and the gullies are morphometrically similar, except for a scale difference in different geologic settings. The morphometric similarity implies that they were probably formed by some common processes. On the other hand, the morphometric differences indicate that the processes may have played different roles in the formation of the gullies. The formation of gullies on the Earth crater walls was heavily affected by surface flow and slippage, and pre-existing fractures and faults were also very influential in their formation. We propose that gullies in martian crater walls and terraces should have a similar formation mechanism, and they can probably account for most of gullies appearing on crater walls. The morphometric differences between the gullies in sand dunes and other gully types are probably a result of the disparity in lithological settings, which have significant influence on erosion ability even for the same agents.

Gondwana's Ediacaran NeoProterozoic Afro-Brazilian "Himalayas" Found

Scientists have found evidence for a huge mountain range that sustained an explosion of life on Earth 600 million years ago.

The mountain range was similar in scale to the Himalayas and spanned at least 2,500 kilometres of modern west Africa and northeast Brazil, which at that time were part of the supercontinent Gondwana.

"Just like the Himalayas, this range was eroded intensely because it was so huge. As the sediments washed into the oceans they provided the perfect nutrients for life to flourish," said Professor Daniela Rubatto of the Research School of Earth Sciences at The Australian National University (ANU).

"Scientists have speculated that such a large mountain range must have been feeding the oceans because of the way life thrived and ocean chemistry changed at this time, and finally we have found it."

The discovery is earliest evidence of Himalayan-scale mountains on Earth.

"Although the mountains have long since washed away, rocks from their roots told the story of the ancient mountain range's grandeur," said co-researcher Professor Joerg Hermann.

"The range was formed by two continents colliding. During this collision, rocks from the crust were pushed around 100 kilometres deep into the mantle, where the high temperatures and pressures formed new minerals."

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Landslides in the Gale Crater on Mars Hint at Rapid Erosion

Erosion rate and previous extent of interior layered deposits on Mars revealed by obstructed landslides

Authors:

Grindrod et al

Abstract:

We describe interior layered deposits on Mars that have obstructed landslides before undergoing retreat by as much as 2 km. These landslides differ from typical Martian examples in that their toe height increases by as much as 500 m in a distinctive frontal scarp that mimics the shape of the layered deposits. By using crater statistics to constrain the formation ages of the individual landslides to between ca. 200 and 400 Ma, we conclude that the retreat of the interior layered deposits was rapid, requiring erosion rates of between 1200 and 2300 nm yr–1. We suggest that the interior layered deposits are either extremely friable, if eroded strictly by wind, or composed of a material whose degradation has been enhanced by ice sublimation. These erosion rates also confirm that the interior layered deposits have been in a state of net degradation over the past 400 m.y., suggesting that the process that caused net deposition in the past has ceased or slowed substantially on Mars relative to erosion. Our results imply that interior layered deposits with a similar morphology across Mars, including the mound in Gale Crater, have probably undergone similar rapid erosion and retreat, suggesting that their total modern volume underrepresents the depositional record and thus sedimentary history of Mars.

Warming of Permafrost on Siberian Coast is Greatly Increasing Erosion

This photo illustration shows the erosion of the east-Siberian island Muostakh. The blue line marks ist coastal line in the year 1951, the red line presents its status in the year 2012. In the upper right corner one can see an aerial picture of the island's northern tip, taken in the year 2012. At its narrowest point the island is shrinking more than four meters per year.

The high cliffs of Eastern Siberia – which mainly consist of permafrost – continue to erode at an ever quickening pace. This is the conclusion which scientists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research have reached after their evaluation of data and aerial photographs of the coastal regions for the last 40 years. According to the researchers, the reasons for this increasing erosion are rising summer temperatures in the Russian permafrost regions as well the retreat of the Arctic sea ice. This coastal protection recedes more and more on an annual basis. As a result, waves undermine the shores. At the same time, the land surface begins to sink. The small island of Muostakh east of the Lena Delta is especially affected by these changes. Experts fear that it might even disappear altogether should the loss of land continue.

The interconnectedness is clear and unambiguous: The warmer the east Siberian permafrost regions become, the quicker the coast erodes. "If the average temperature rises by 1 degree Celsius in the summer, erosion accelerates by 1.2 meters annually," says AWI geographer Frank Günther, who investigates the causes of the coastal breakdown in Eastern Siberia together with German and Russian colleagues, and who has published his findings in two scientific articles.

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