Dendritic Valley Research Articles

Alpine topography of the Gamburtsev Subglacial Mountains, Antarctica, mapped from ice sheet surface morphology

Abstract. Landscapes buried beneath the Antarctic Ice Sheet preserve information about the geologic and geomorphic evolution of the continent both before and during the wide-scale glaciation that began roughly 34×106 years ago. Since the inception of this ice sheet, some areas have remained cold-based and non-erosive, preserving ancient landscapes remarkably intact. The Gamburtsev Subglacial Mountains in central East Antarctica are one such landscape, maintaining evidence of tectonic, fluvial and glacial controls on their distinctly alpine morphology. The central Gamburtsev Mountains have previously been surveyed using airborne ice-penetrating radar; however, many questions remain as to their evolution and their influence on the East Antarctic Ice Sheet, including where in the region to drill for a 1.5×106 year-long “oldest-ice” core. Here, we derive new maps of the planform geometry of the Gamburtsev Subglacial Mountains from satellite remote sensing datasets of the ice sheet surface, based on the relationship between bed roughness and ice surface morphology. Automated and manual approaches to mapping were tested and validated against existing radar data and elevation models. Manual mapping was more effective than automated approaches at reproducing bed features observed in radar data, but a hybrid approach is suggested for future work. The maps produced here show the detail of mountain ridges and valleys on wavelengths significantly smaller than the spacing of existing radar flightlines, and mapping has extended well beyond the confines of existing radar surveys. Morphometric analysis of the mapped landscape reveals that it constitutes a preserved (>34 Ma) dendritic valley network, with some evidence for modification by topographically confined glaciation prior to ice sheet inception. The planform geometry of the landscape is a significant control on locations of basal melting, subglacial hydrological flows and the stability of the ice sheet over time, so the maps presented here may help to guide decisions about where to search for oldest ice.

Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology

We compare estimates of atmospheric precipitation during the Martian Noachian–Hesperian boundary 3.8Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2–H2O–N2 atmospheres with surface pressures varying from 20mb to 3bar with input solar luminosity reduced to 75% the modern value.Results from the valley network analysis are of the order of a few mmd−1 liquid water precipitation (1.5–10.6mmd−1, with a median of 3.1mmd−1). Atmospheric model results are much lower, from about 0.001–1mmd−1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favor a cold early Mars with episodic snowmelt as a source for runoff.Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity – which affect the atmospheric result – as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.

Wet Mars implications of revised scaling calculations for Evros Vallis

In this paper we report the results of our investigation of Evros Vallis, a martian late Noachian dendritic valley network centered at ∼12°E, 12°S. The study area is located SSW of Schiaparelli and SE relative to Meridiani Planum. After establishment of the valley system, the region underwent extensive erosion and tectonic activity, which partly obliterated and modified Evros Vallis's original features. We used Mars Global Surveyor Mars Orbiter Laser Altimeter, Mars Odyssey Thermal Emission Imaging System, and Mars Express High Resolution Stereo Camera imagery and altimetry data to carry out observations and morphometric analysis of the system, and applied network scaling parameters to our measurements of valley widths, slopes, lengths and drainage areas. We obtained the following results: (a) Hack's law exponent n=1.02; (b) width–area scaling exponent b=0.21; and (c) slope–area scaling exponent θ=0.23. These values are different from those previously derived from analysis of the eastern extent of the valley system. We found that network scaling is not applicable to the investigation of Evros Vallis, a conclusion that may be relevant also to other martian network valleys. The concave-up 790 km-long profile of the main valley suggests that a classic equilibrium status was reached. Our findings are in agreement with models of a warmer and wetter martian climate at the end of the Noachian.

Chaos terrain, storms, and past climate on Mars

Channel networks on the plateau adjacent to Juventae Chasma have the highest drainage densities reported on Mars.We model frozen precipitation on the Juventae plateau,finding that the trigger for forming these channel networks could have been ephemeral lakeshore precipitation,and that they do not require past temperatures higher than today.If short-lived and localized events explain some dendritic channel networks on Mars, this would weaken the link between dendritic valley networks and surface climate conditions that could sustain life. Our analysis uses MRAMS simulations and HiRISE DTMs.We model localized weather systems driven by water vapor release from ephemeral lakes during outflow channel formation.At Juventae Chasma,mean snowfall reaches a maximum of 0.9mm/hr water equivalent on the SW rim of the chasm.Radiative effects of the thick cloud cover raise maximum (minimum, mean) plateau surface temperatures by up to 24K(9K, 17K)locally.The key result is that the area of maximum modeled precipitation shows a striking correspondence to the mapped Juventae plateau channel networks.Three independent methods show this fit is unlikely to be due to chance.We use a snowpack energy balance model to show that if the snow has the albedo of dust(0.28), and for a solar luminosity of 0.8($\equiv$3.0Gya), then if the atmospheric greenhouse effect is unchanged from(6K warmer than)today only 0.4%(21%)of lake-induced precipitation events produce snowpack that undergoes melting.However, warming from associated dense cloud cover would allow melting over a wider range of conditions.In these localized precipitation scenarios, global temperatures need not be higher than today, and the rest of the planet remains dry.

The stratigraphy of the Amenthes region, Mars: Time limits for the formation of fluvial, volcanic and tectonic landforms

We present results of our morphologic and stratigraphic investigations in the Amenthes region for which our observations suggest a complex spatial and temporal interrelation between volcanic and possibly water-related processes. We have produced a series of self-consistent geological maps and a stratigraphic correlation chart that show the spatial and temporal distribution of volcanic, fluvial and tectonic processes. The Amenthes region consists of a broad trough-like topographic depression that has served as a path for the supply of materials from Hesperia Planum to Isidis Planitia. It is most likely that Hesperia Planum and, in particular the area north of Hesperia Planum, including Tinto Vallis, Palos crater and the surrounding dissected highlands have acted as a source region for materials that were transported into the Amenthes trough and farther into the Isidis basin. The Amenthes trough, as well as the graben of Amenthes Fossae were formed after the Isidis impact in the Noachian and represent likely the oldest features in the Amenthes region. Dendritic valley networks, that bear evidence for surface runoff, have dissected the highlands adjacent to Amenthes Planum and within the Tinto Vallis and Palos crater region before ∼3.7 Ga. The ridged volcanic plains located near the Palos crater and Tinto Vallis region, within Amenthes Planum as well as within the Isidis transitional plains were formed between ∼3.5 and 3.2 Ga and represent the volcanic activity which resulted in the flooding of the Amenthes trough. The sinuous channel of Tinto Vallis was formed in the Hesperian (≲3.5 Ga) and shows characteristics, which are consistent with both ground water sapping and igneous processes. The Palos crater outflow channel was formed nearly at the same time as Tinto Vallis, between ∼3.5 Ga and ∼3.2 Ga and postdates the volcanic flooding of the Amenthes trough in the Hesperian. Small valleys (∼3.4–2.8 Ga) incised into the ridged plains of Amenthes Planum appear also within the transitional plains located between the Amenthes plains and the Isidis interior plains. Our model ages show that Tinto Vallis, the Palos crater outflow channel as well as the small valleys are unlikely formed at the same time and by the same processes as the dendritic valley networks and represent an episode that clearly postdates the volcanic activity.

Titan's fluvial valleys: Morphology, distribution, and spectral properties

Titan's fluvial channels have been investigated based on data obtained by the Synthetic Aperture Radar (SAR) instrument and the Visible and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. In this paper, a database of fluvial features is created based on radar-SAR data aiming to unveil the distribution and the morphologic and spectral characteristics of valleys on Titan on a global scale. It will also study the spatial relations between fluvial valleys and Titan's geologic units and spectral surface units which have become accessible thanks to Cassini-VIMS data. Several distinct morphologic types of fluvial valleys can be discerned by SAR-images. Dendritic valley networks appear to have much in common with terrestrial dendritic systems owing to a hierarchical and tree-shaped arrangement of the tributaries which is indicative of an origin from precipitation. Dry valleys constitute another class of valleys resembling terrestrial wadis, an indication of episodic and strong flow events. Other valley types, such as putative canyons, cannot be correlated with rainfall based on their morphology alone, since it cannot be ruled out that they may have originated from volcanic/tectonic action or groundwater sapping. Highly developed and complex fluvial networks with channel lengths of up to 1200km and widths of up to 10km are concentrated only at a few locations whereas single valleys are scattered over all latitudes. Fluvial valleys are frequently found in mountainous areas. Some terrains, such as equatorial dune fields and undifferentiated plains at mid-latitudes, are almost entirely free of valleys. Spectrally, fluvial terrains are often characterized by a high reflectance in each of Titan's atmospheric windows, as most of them are located on Titan's bright ‘continents’. Nevertheless, valleys are spatially associated with a surface unit appearing blue due to its higher reflection at 1.3μm in a VIMS false color RGB composite with R: 1.59/1.27μm, G: 2.03/1.27μm, and B: 1.27/1.08μm; the channels either dissect pure bluish surface units or they are carved into terrain with a mixed spectral signature between bright and bluish surface materials. The global picture of fluvial flows clearly indicates a high diversity of parameters controlling fluvial erosion, such as climatic processes, as well as surface and bedrock types. Recent fluvial activity is very likely in the north polar region in contrast to more arid conditions at lower latitudes and at the south pole of Titan. This divergence is probably an indication of seasonal climatic asymmetries between the hemispheres. However, traces of previous fluvial activity are scattered over all latitudes of Titan, which is indicative of previous climatic conditions with at least episodic rainfall.

Noachian–Hesperian geologic history of the Echus Chasma and Kasei Valles system on Mars: New data and interpretations

New high-resolution datasets have prompted a mapping-based study of the 2500-km-long Echus Chasma and Kasei Valles system that utilizes geomorphic details, stratigraphic relations, and cratering statistics derived from the new datasets. Our results suggest that between the Hesperian and Amazonian Epochs on Mars (3.7 Ga to Recent) the study area was affected by at least 4 episodes of widespread volcanic activity and 4 periods of episodic fluvio-glacial activity. This paper discusses the Noachian to Hesperian (> 2.6 Ga) history of the study area, during which time in the Hesperian three of the volcanic episodes took place along with the first two episodes of fluvio-glacial activity. Highlights of our new findings and refinements from this time period include (1) two ancient western floods sourced from Tharsis that occurred around 3.61 and 3.4 Ga and carved the east-trending path of north Kasei Valles; (2) Uranius Dorsum with 58 aligned cones along its length that was emplaced in north Kasei around 3.6 Ga between these periods of early flooding; (3) possible ash deposits surrounding Echus Chasma, one of which contains narrow dendritic valley systems that may have been carved over a period of about 10,000 yr; and (4) evidence that suggests glaciers and near-surface ice may have contributed to erosion of local units.

Morphologic, stratigraphic and morphometric investigations of valley networks in eastern Libya Montes, Mars: Implications for the Noachian/Hesperian climate change

“Dendritic valley networks” and broad “longitudinal valleys” are widespread within the eastern Libya Montes region. The morphologic characteristics of the studied dendritic valleys, especially their occurrence at local summits, provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater-induced processes. Our crater counts and model ages show, that the dendritic valley networks (average age ∼ 4.0 Ga) formed earlier than the longitudinal valley systems (average age ∼ 3.7 Ga). Both fluvial forms indicate a temporal change of the erosive environment at the Noachian/Hesperian transition at ∼ 3.8 Ga. Our results suggest that the fluvial activity within our investigation area lasted for ∼ 800 My, from ∼ 4.1 Ga to ∼ 3.3 Ga. The dendritic valleys show valley densities between 0.12 km − 1 and 0.57 km − 1 , indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on Mars.

Volcanic processes as alternative mechanisms of landform development at a candidate crater‐lake site near Tyrrhena Patera, Mars

Palos crater, a prominent candidate crater‐lake site in the Hesperia region of Mars, is located at the mouth of a sinuous inlet channel that extends from the northern flanks of Tyrrhena Patera. Previous studies of this site have concluded that channels and basin‐infill units likely formed through aqueous processes that partly involved karst‐like removal of materials in the subsurface by the flow of groundwater. As with many locales on Mars, the aqueous processes hypothesized to have been involved in the formation and evolution of terrain features are compelling. However, the characteristics of this site suggest that an alternative set of mechanisms for landform development should be considered alongside aqueous hypotheses. The main attributes of channels and infill of the central crater include: (1) an association with a very large volcanic rise to the south; (2) the existence of roofed segments of the main inlet channel; and (3) infill of the central crater and outlet channel by materials that have characteristics consistent with those expected of volcanic plains. These general attributes are consistent with formation through or in association with processes that involved the flow of lava. Although a volcanic model may account for the presence and basic nature of landforms previously considered supportive of a paleolake interpretation of the site, an overprint of dendritic valley networks on parts of the inlet system suggests that aqueous processes may have also acted in the evolution of the site. A complex interrelation between past igneous and aqueous processes at this site is possible.

Alba Patera, Mars: Topography, structure, and evolution of a unique late Hesperian–early Amazonian shield volcano

New spacecraft data, especially MOLA topography, reveal important characteristics of Alba Patera that were either unknown or poorly resolved in previous data sets. The major and consistent breaks of slope and the specific pattern of lava flows within a broad region around Alba Patera permit division of this area into two major parts that appear to be related to different episodes of volcanism at Alba Patera: a low‐lying apron of lava flows that broadly surrounds the edifice, a high‐standing main construct, consisting of a central edifice, western and eastern flanking lobes, and a summit area characterized by a summit plateau and a summit dome topped by a caldera complex. Volcanic activity apparently began as massive effusive eruptions that formed the broad apron of lava flows, followed by more focused effusive eruptions that built the central construct. The construct spread gravitationally in a northerly direction to favor E‐W dike propagation, leading to the formation of Tharsis‐Montes‐like flanking lobes. The final stages of volcanic activity at Alba Patera were concentrated in the summit area, forming a summit dome ∼400 km in diameter, a caldera complex, and two small shields near and inside the caldera, which underwent late‐stage tilting and deformation; the load of the newly documented summit dome may have led to the development of Alba Fossae, reactivation of graben within Tantalus Fossae, and tilting of the summit dome to the east. A clear sequence in eruptive style is observed (early massive sheet flows, later tube‐fed flows, and late, shorter‐length and lower‐volume sheet flows). Dendritic valley networks on the northern flanks of Alba Patera have been interpreted to be evidence of easily erodable material of pyroclastic origin, but new data suggest that these friable deposits and the valley networks may have formed instead during Amazonian climate excursion periods. The extensive apron of lava flows, combined with the flanking lava lobes and the Tharsis‐Montes‐scale summit dome, make Alba Patera much more similar to the Tharsis Montes than to the Hesperian‐aged paterae. The Alba Patera lava apron was emplaced on early Hesperian ridged plains largely during the middle to late Hesperian; stratigraphic relationships suggest that effusive eruptions from Alba Patera interacted with ice‐rich deposits in the northern lowlands. Alba Patera flanking lobes and the summit dome were emplaced in the earliest Amazonian, accompanied by late‐stage loading, graben formation, and edifice tilting.

Groundwater‐controlled valley networks and the decline of surface runoff on early Mars

Fluvial erosion on early Mars was dominated by valley networks created through a combination of groundwater processes and surface runoff. A reduced greenhouse effect due to CO2 loss, together with a declining geothermal heat flux, promoted the growth of a cryosphere and a Hesperian hydrologic regime dominated by outflow channel formation. We test the hypothesis that the transition from valley network to outflow channel formation was preceded by a more subtle evolution characterized by a weakening of surface runoff, leaving groundwater processes as the dominant, final source of valley network erosion. Our hypothesis, supported by a terrestrial analog in the Atacama desert of Chile, is related to the groundwater sapping reactivation hypothesis for densely dissecting highland valley networks on Mars suggested by Baker and Partridge in 1986 and focuses on the age analysis of large, sparsely dissecting valley networks such as Nanedi Valles, Nirgal Vallis, valleys in fretted terrain, and tributaries of outflow channels and Valles Marineris chasmata. We find that these features are consistently late Noachian to Hesperian in age, younger than Noachian densely dissecting dendritic valley networks in the southern highlands. In the Tharsis region the observation of dense and sparse valley network morphologies on Hesperian terrain suggests that while surface runoff gave way to groundwater processes consistent with our hypothesis, the transition may have occurred later than elsewhere on the planet. The volcanic nature of Tharsis suggests that geothermal heat and volatile production led to episodically higher volumes of surface runoff in this region during the Hesperian.

Age relations of Martian highland drainage basins

Dendritic valley patterns in the equatorial highlands of Mars show evidence of internal drainage into restricted basins, which are interpreted to be floored with sedimentary fill. Based on crater frequency characteristics of six areas of enclosed basins, the origin of these intercrater plains fill units ranges from middle to late Noachian. In contrast, the age of modification of the same plains units derived from the frequency of fresh craters occupies a relatively narrow range centered on the Noachian/Hesperian boundary. In half the areas studied the timing of highlands and plains crater modification is consistent with a sedimentary origin for basin fill materials. The other plains units most likely consist of interlayered sedimentary and volcanic materials. Relations between the age of stability of these internally drained highland units and their elevation are not as distinct as prior studies suggested; a trend of decreasing age with decreasing elevation for the plains materials is not matched by similarly derived ages of the dissected highlands. Remapping and age dating of the dissected highlands and associated basins suggest that volcanic plains may be more extensive than those used in past models for magma and volatile evolution, and support local volcanism rather than a global‐scale magmatic head model for highlands plains formation.

Sequence Stratigraphy and Onlap Relationships of a Stratigraphic Trap, Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River Basin, Wyoming: ABSTRACT

In Hilight field more than 74 million bbl of oil and 244 bcf of gas have been produced from thin fluvial and shallow marine sandstones of the Lower Cretaceous Muddy Sandstone. In this area the Muddy was deposited during a late Albian sea level rise and onlaps a lowstand subaerial surface of erosion including a dendritic valley system incised into the underlying Skull Creek Shale. Transgressive valley-fill deposits of the Muddy Sandstone in the Hilight field area consist of four regionally correlative, time-bounded, back-stepping, progradational units. The retrogradational nature of these units indicates they belong in a transgressive systems tract rather than a lowstand wedge, as is often implied for valley-fill sequences. Each unit is capped by a regionally extensive marine flooding surface. The contact between units is placed at the surface representing maximum flooding or at the correlative horizon landward of the maximum transgression. Two of these contacts include thin bentonite beds which substantiate the time-stratigraphic interpretation. Petroleum is trapped in each unit by the onlap of reservoir sandstone facies against the lowstand surface of erosion on the impermeable Skull Creek Shale. Top seals are formed by mudstones at the base of overlying units or by the Shell Creekmore » Shale, which overlies the Muddy Sandstone above a regionally extensive marine flooding surface. Reservoir heterogeneity is explained by lateral facies changes within each unit. The lateral and vertical distribution of reservoir-quality sandstone in the Muddy sequence in this area can be used as a model to predict occurrences in similar sequences elsewhere.« less

Sea Level and Paleotectonic Controls on Distribution of Reservoir Sandstone of Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River Basin, Wyoming: ABSTRACT

To date, over 74 million bbl of oil have been produced from stratigraphic traps at Hilight field. Production is primarily from thin but stratigraphically complex fluvial and shallow marine sandstone of the Lower Cretaceous Muddy Sandstone. The deposition and preservation of these reservoirs were controlled by the interplay between sea level and tectonics. The Muddy Sandstone in Hilight field was deposited during a late Albian sea level rise. It onlaps an erosional surface, developed during the preceding sea level drop, including a dendritic valley system cut deeply into the underlying Skull Creek Shale. In this area, the Muddy consists of four members that are bounded by transgressive disconformities. These members were deposited during stillstands in the overall rise of sea level. The lower two members consist of fluvial and fluvial-estuarine deposits which fill the valley system; the upper two members consist of fluvial-deltaic and barrier island deposits. Three northeast-trending lineaments transect Hilight field. These lineaments are interpreted to represent basement faults that experienced recurrent movement during Muddy deposition. Relative structural downdrop controlled the orientation of drainages that cut the Hilight valley system. Recurrent movement provided structural and topographic lows within which relatively thick fluvial-deltaic and barrier island sandstones were depositedmore » and preserved. Thinner sequences were deposited and subsequently eroded on adjacent structural and topographic highs.« less