We present an inventory of alluvial fans and deltas within martian impact craters based on a systematic global survey of Context Camera images. Our database includes 314 fan‐hosting craters, with a ...total of 890 alluvial fans and 114 deltas. Alluvial fans and deltas are more widespread than previously reported (∼40°N to 54°S) and are strongly banded with respect to latitude. Most craters with alluvial fans occur at higher elevations (10°S–30°S) and along the dichotomy boundary (0°–10°N). Deltas occur at lower elevations (0°–40°N) where access to groundwater may have enabled the formation of lakes, and to a lesser extent in the highlands (0°–30°S). Alluvial fans in southern mid‐latitude craters preferentially formed along the northern and southern walls, which may reflect climatic control through solar insolation. The widespread distribution within the observed latitude bands and the similar Hesperian to Amazonian age of alluvial fan‐hosting craters is consistent with late‐stage synoptic precipitation.
Plain Language Summary
Martian alluvial fans and deltas are intriguing features because they provide evidence for surface water and a climate that was very different than the present‐day conditions. This study presents a planet‐wide catalog of craters that host alluvial fans and interpreted deltas to understand where and when they formed. We systematically searched images from the Context Camera because this data set has the necessary resolution and coverage to identify and classify the landforms of interest. Our inventory of 314 craters with 890 alluvial fans and 114 deltas shows that these landforms are more numerous and widespread than previously reported. The similar age and distribution of craters with alluvial fans in the southern mid‐latitudes is consistent with a late occurring, widespread (rather than local) source of water. Craters with deltas are preferentially located at lower elevations where interactions with groundwater may have enabled the formation and persistence of lakes.
Key Points
Craters with alluvial fans and scarp‐fronted fans (putative deltas) are more numerous than previously reported
The widespread distribution of craters with alluvial fans in observed latitude bands is consistent with late synoptic precipitation
Formation of alluvial fans in southern mid‐latitude craters on northern and southern walls may be influenced by solar insolation patterns
Land-surface quantitative analysis based on digital elevation model (DEM) has been applied for improving the geomorphological mapping of piedmont alluvial fans. Indeed, these fans are frequently ...along a mountain front, where a series of coalescing fans may eventually occur. The margins of adjacent fans are rather difficult to map, thus preventing accurate and meaningful quantification of fan morphometric properties such as fan area, length, and slope. These morphometric properties are essential for informing on the influence of climatic conditions and tectonic factors on the fan-building processes. Therefore, in this paper, we propose a quantitative digital mapping approach along a stretch of about 50 km in the southern front of the Anti-Lebanon Mountains. Here, the Geomorphological Map of Syria at 1:1,000,000 scale (1963) reported at least nine piedmont alluvial fans, but these were poorly characterized in terms of geomorphometric characteristics and construction processes. Adopting the 1-arcsec SRTMv3 DEM, we propose a four-step workflow to analyse the feeding catchments morphology and fan morphometry. In this manner, the identification and geomorphological mapping of coalescent piedmont fans as well as the recognition of the main construction process have been improved. The proposed approach can support geomorphological investigations of wide and inaccessible areas—especially where arid and semi-arid climate conditions prevail—as well as where socio-political issues may prevent effective field work.
•Land-surface quantitative analysis is suitable for geomorphological mapping and characterization of piedmont alluvial fans.•Recognition of the construction processes of the alluvial fan is challenging for a remotely-desk study.•Fluvial fans (FFs) are wider, with longer axis, gentle slope, and extended feeding catchment.•Alluvial fans (AFs) are smaller, with shorter axis, steeper slope, and small feeding catchment.
The sedimentary record of fluvial systems is known to preserve important archives of the effects of climate change on the landscape over time and space. While temperate and arid (semi-arid) regions ...are relatively well studied, our understanding of fluvial dynamics in tropical mountainous areas throughout the Quaternary is poorly known. Here, we propose a model of the landscape evolution of the Upper Caquetá River in the Northern Tropical Andes (NTA) over the past 130 ka, based on mapping and optically stimulated luminescence (OSL) dating of the sediments building alluvial fans and fluvial terraces. The OSL ages indicate that the distributary system was active from 130 to 65 ka; from 65 to 31 ka channels carved the deposits, reorganizing the drainage network to a tributary pattern with rivers flowing into incised valleys. Four fluvial terrace levels were mapped in these valleys and OSL ages indicate sediment deposition around 30, 15, 5, and 1 ka. Based on available palaeoenvironmental data, we have interpreted that the shift in the fluvial landscape from distributary to tributary incised system is related to precipitation change in the NTA, driven by the variation in the latitudinal position of the Intertropical Convergence Zone (ITCZ) due to insolation cycles. Our data suggest that the decreased rainfall, caused by the northernmost position of the ITCZ, combined with the expansion of arboreal elements in the Andean Piedmont, favoured alluvial deposition by both the distributary system (Marine Isotopic Stage - MIS 5 and 4) and the tributary (MIS 2 to the present). Our data supports that following an incision phase during MIS 3, the decrease in the amplitude of precession and obliquity signals led to greater stability of the landscape and to the transition of the distributary fluvial pattern in the upper Caquetá River to its present tributary pattern.
•Equivalent doses in quartz grains from Caquetá River are up to 250 Gy.•We demonstrate a drainage rearrangement in the Eastern Cordillera's Piedmont•The alluvial fans complex (130–60 ka) changed to a tributary system (30 ka)•Variations in climate and vegetation drove the evolution of the Caquetá River•Tectonic activity is slower in Putumayo Basin than in Llanos during late Quaternary
ABSTRACT Autogenic feedbacks can produce large‐scale, organized stratigraphic patterns in alluvial fans, but autogenic depositional signatures of specific upstream boundary conditions remain ...challenging to interpret. Here, a combination of theory, experiment and field application is used to explore how autogenic lithofacies changes can be interpreted as stratigraphic indicators of upstream boundary conditions. Six experiments were conducted to test the effects of sediment supply and water discharge rates on autogenic advance and retreat of the lithofacies boundary (grain‐size transition) in an alluvial fan with two dominant grain sizes. Migration of the grain‐size transition caused a short‐term zigzag pattern in the grain‐size transition position in the dip‐directional deposit section. For each experiment, time‐lapse images and laser topographic scans of the fan surface and stratigraphic cross‐sections of the final deposits were used to quantify characteristic timescales of autogenic processes. Timescales for fan‐margin migration, surface wet‐fraction change and grain‐size transition migration generally shorten as sediment supply rate increases and water discharge rate decreases. Increasing the sediment supply rate shortens the duration of the fluvial sediment storage and release cycle, producing higher frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge tends to widen channels and lengthens the duration of the fluvial sediment storage and release cycle, constructing lower frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge also enables more sediment to transport further downstream during release events, leading to higher magnitude zigzags in the grain‐size transition trajectory. These relationships between upstream boundary conditions and the grain‐size transition trajectory demonstrate how autogenic stratigraphic signals could be used as a tool to infer relative changes in boundary conditions.
Desert oases exist around the alluvial fans of inland river basins in arid areas, where the vegetation growth is wholly dependent on groundwater due to scanty rainfall and arid environment. Climate ...change and water resources exploitation may threaten the groundwater-dependent ecosystems (GDEs) in the arid areas; a case study was proposed to evaluate the vegetative growth state with the normalized difference vegetation index (NDVI), hydrometeorological data, and the exploitation of water resources of the Nalenggele alluvial fan in northwest China. Climate change, and increasing temperature and precipitation may be indispensable factors for vegetation growth; however, based on the results of a correlation analysis, it was found that climatic factors shared little direct correlation with the NDVIs of the Nalenggele alluvial fan. Also, the depth to groundwater table (DWT) and distribution of shallow groundwater (DSG) are the direct influencing factors of vegetation growth. DWT and DSG are mainly controlled by the groundwater recharge mechanism and the original water sources from snowmelt, which are directly correlated with climate change. Predictions for DWT and DSG were made considering water resource exploitation and different river discharges amid climate change. The results reveal that the distribution area of shallow groundwater with the ecological water level (DWT < 4 m) in 2020 will decrease to approximately 78–86% of that in the status quo year, which suggests vegetation may be at risk of degradation from the combined influence of climate change and human activities. Therefore, management strategy and legislation for protecting GDEs should be proactively initiated in other similar areas in China.
Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and ...variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic
Be and
Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2-3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered.
The fluvial archive literature is dominated by research on river terraces with appropriate mention of adjacent environments such as lakes. Despite modern sedimentary basins comprising a significant ...(>88%) volume of distributive fluvial systems, of which alluvial fans (>1 km, <30 km in scale) are a significant part, interaction with these environments tends to be neglected and discussed in separate literature. This paper examines the dynamic role of alluvial fans within the fluvial landscape and their interaction with river systems, highlighting the potential value of alluvial fans to the wider fluvial archive community. Published literature is used to examine both thematic and geographical based benefits of alluvial fan research that can assist understanding of Quaternary fluvial archives. 3 regional case studies are presented that illustrate the interaction between alluvial fan and river terrace archives at Quaternary time-scales at 3 different stages of landscape evolution. These are i) continuous mountain front alluvial fans interacting with a non incising but laterally eroding axial fluvial system; ii) alluvial fans which transition into fluvial terraces as sedimentary basins shift from net aggradation to net incision and iii) tributary-junction alluvial fans that develop predominantly within incising river valley systems. A simple conceptual model is proposed to summarise the dynamic role of alluvial fans within this landscape context. The alluvial fans act as potential ‘buffers’ between hillslopes and river terrace records under ‘top down’ climate-driven high sediment supply and alluvial fan aggradation, and ‘couplers’ during periods of less sediment (in relation to water) discharge and alluvial fan incision. These dynamics will change with the addition of ‘bottom up’ controls such as main river incision, which will typically enhance the coupling effect of both systems.
•Provides the first review paper linking alluvial fan research with research into fluvial archives.•Pulls together material from across sub-disciplines.•Fans act as important ‘buffers’ or ‘couplers’ within the fluvial landscape.•Fan/river interactions change in response to top down and bottom up system drivers.•Dynamic relationships described in a conceptual model of alluvial fan/river interactions.
The Curiosity rover's discovery of rocks preserving evidence of past habitable conditions in Gale crater highlights the importance of constraining the timing of responsible depositional settings to ...understand the astrobiological implications for Mars. Crater statistics and mapping reveal the bulk of the alluvial deposits in Gale, including those interrogated by Curiosity, were likely emplaced during the Hesperian, thereby implying that habitable conditions persisted after the Noachian. Crater counting data sets and upper Peace Vallis fan morphology also suggest a possible younger period of fluvial activation that deposited ~10–20 m of sediments on the upper fan after emplacement of the main body of the fan. If validated, water associated with later alluvial activity may have contributed to secondary diagenetic features in Yellowknife Bay.
Key Points
The bulk of alluvial deposits in Gale were likely emplaced during the HesperianHabitable conditions persisted in Gale crater after the NoachianLimited evidence for possible younger fluvial activation on Peace Vallis fan
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