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At least 433 records · Page 24Linked to original sources

Tidal-bundle sequences in the Jordan Sandstone (Upper Cambrian), southeastern Minnesota, U.S.A.: Evidence for tides along inboard shorelines of the Sauk Epicontinental Sea

This study documents for the first time tidal bundling in a lower Paleozoic sheet sandstone from the cratonic interior of North America, providing insights into the hydrodynamics of ancient epicontinental seas. The Jordan Sandstone (Upper Cambrian) in the Upper Mississippi Valley contains large-scale planar tabular cross-sets with tidal-bundle sequences, which were analyzed in detail at an exceptional exposure. Tidal-bundle sequences (neap-spring-neap cycles) were delineated by foreset thickening-thinning patterns and composite shale drapes, the latter of which represent accumulations of mud during the neap tides of neap-spring-neap tidal cycles. Fourier analysis of the bundle thickness data from the 26 measurable bundle sequences revealed cycles ranging from 15 to 34 bundles per sequence, which suggests a semidiurnal or mixed tidal system along this part of the Late Cambrian shoreline. We extend the tidal interpretation to widespread occurrences of the same facies in outcrops of lesser quality, where the facies is recognizable but too few bundles are exposed for tidal cycles to be measured. By doing so, this study shows that tidally generated deposits have a significant geographic and temporal extent in Upper Cambrian strata of central mid-continent North America. The deposition and preservation of tidal facies was related to the intermittent development of shoreline embayments during transgressions. The tidally dominated deposits filled ravined topographies that were repeatedly developed on the updip parts of the shoreface. Resulting coastal geomorphologies, accompanied perhaps by larger-scale changes in basinal conditions and/or configuration, led to changes in depositional conditions from wave-dominated to tide-dominated. Outcrops of the Jordan Sandstone tidal facies in the Upper Mississippi Valley represent the farthest inboard recorded transmission of ocean-generated tides in the Laurentian epicontinental seas, demonstrating that tidal currents were significant agents in the transport of sand along the far cratonic interior shorelines of Cambrian North America. The results of this study improve the facies-level understanding of the genesis of sheet sandstones. Furthermore, tidalites documented here occur in a specific position within a sequence stratigraphic architecture for the Jordan Sandstone. This provides a framework to compare these ancient deposits and processes to younger (e.g., Carboniferous) epicontinental systems where stratal and sediment dynamics are better documented.

Illinois, Indiana, Iowa, Michigan, Minnesota, Miss↗

Longitudinal analyses of catch-at-age data for reconstructing year-class strength, with an application to lake trout (Salvelinus namaycush) in the main basin of Lake Huron

We investigated using longitudinal models to reconstruct year-class strength (YCS) from catch-at-age data, with an example application to lake trout ( Salvelinus namaycush ) in the main basin of Lake Huron. The best model structure depended on the age range used for model implementation. The YCS trajectory from the full age range (3–30 years) was similar to the trajectory from a narrow age range that approximated the age of recruitment to the fishing gears (5–7 years), but YCS estimates from the full age range included additional variations due to time-dependent selectivity and mortality. When using ages younger or older than the likely ages of recruitment, YCS estimates did not represent recruitment abundances and were also biased by trends in age-specific selectivity and mortality across years. Longitudinal YCS estimates are likely more robust than single-age recruitment indices, which are often subject to interannual changes in catchability and selectivity. Our findings provide guidance for future applications of the longitudinal YCS reconstruction that in turn may inform and supplement more comprehensive research and management programs for understanding fish recruitment dynamics.

Lake Huron↗

On the survival and habitat use of hatchery-reared cisco (Coregonus artedi) in Lake Erie

Cisco ( Coregonus artedi ) have been extirpated from Lake Erie in North America since the 1960s, but they once supported one of the largest Laurentian Great Lakes fisheries. Numerous potential impediments to rehabilitation have been identified, including summer habitat refugia and predation. We used acoustic telemetry to investigate the thermal habitat use and survival of hatchery-reared adult cisco in Lake Erie. Fish were experimentally released (n = 50 per site) offshore at Dunkirk, New York, in the eastern basin and Huron, Ohio, in the central basin. Cisco in both basins found suitable summer oxythermal habitat in the metalimnion, suggesting that coldwater habitat availability is likely not an impediment for reestablishment. However, track end dates or predation dates were distributed across only four months with the last detection at 155 days. Predation sensors combined with temperature values during digestion indicated different potential predators: lake trout ( Salvelinus namaycush ) for the Dunkirk group and walleye ( Sander vitreus ) for the Huron group. Additionally, digestion temperatures of two tags indicated bird predation was also important, likely underestimated and suggested substantial use of the epilimnion by tagged fish. The results highlight the need for additional studies to address stocking optimization questions in support of future reintroduction experiments and related cisco conservation efforts.

Lake Erie↗

Long-term decline in freshwater mussels (Bivalvia: Unionidae) of the western basin of Lake Erie

Long-term trends in the abundance of unionids in the western basin of Lake Erie were examined from data collected at 17 stations in 1961, 1972, and 1982. The mean number of unionids at these stations declined over this time period, decreasing from 10 m −2 in 1961, to 6 m −2 in 1972, down to 4 m −2 in 1982. This decline in abundance was reflected in the decrease in the number of stations where mussels were found; unionids were found at 16 of the 17 stations in 1961, but at only 6 stations in 1982. Reasons for the decrease in the unionid population are not generally apparent, but are probably related to the decline in water quality and periods of low oxygen levels over the time period of the surveys.

Lake Erie↗

Trade-offs between suppression and eradication of sea lampreys from the Great Lake

Ecosystem managers confronted with newly invasive species may respond with a program of suppression or eradication. Suppression of an invasive species refers to management of a species such that its effect on other biota in the local ecosystem is acceptable. Eradication is the removal of all individuals of a species from a defined region. We examine the cost and benefit trade-offs between suppression and eradication of Laurentian Great Lakes sea lampreys ( Petromyzon marinus ) based on discussions at the 3rd Sea Lamprey International Symposium (held in 2019). Substantial effort has been expended annually since the 1960s to suppress sea lampreys in the Great Lakes basin. Choosing between suppression and eradication is a value judgement, ideally made jointly by scientists, decision-makers, stakeholders, and society. Successful large-scale eradications have been limited to a small number of cases for which the cost to human society justified and supported the long-term commitment necessary for success. The greatest challenge to successful eradication of sea lampreys from the Great Lakes may be a suitable social, political, legal, and institutional environment. Preparations could be made now for a transition in which public pushback on current control methods (pesticide applications and barriers to fish passage) leads to more extensive use of an alternative control method, such as genetic control.

Great Lakes and Saint Lawrence River areas↗

Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis

Seismic reflection data show that the densely populated Puget Lowland of western Washington state is underlain by subhorizontal Paleogene and Neogene sedimentary rocks deformed by west and northwest trending faults and folds. From south to north beneath the Lowland, features seen on the seismic data include: the horizontally-stratified, 3.5 km thick Tacoma sedimentary basin; the Seattle uplift with south dipping (∼20°) strata on its south flank and steeply (50° to 90°) north dipping strata and the west-trending Seattle fault on its north flank; the 7.5 km thick, northward-thinning Seattle sedimentary basin; the antiformal Kingston arch; and the northwest trending, transpressional Southern Whidbey Island fault zone (SWIF). Interpreting the uplifts as fault-bend and fault-propagation folds leads to the hypothesis that the Puget Lowland lies on a north directed thrust sheet. The base of the thrust sheet may lie at 14 to 20 km depth within or at the base of a thick block of basaltic Crescent Formation; its edges may be right-lateral strike-slip faults along the base of the Cascade Range on the east and the Olympic Mountains on the west. Our model suggests that the Seattle fault has a long-term slip rate of about 0.25 mm/year and is large enough to generate a M 7.6 to 7.7 earthquake.

Washington↗

Geochemistry of Florida Bay sediments: Nutrient history at five sites in eastern and central Florida Bay

Recent seagrass dieoff and massive microalgal blooms have focused attention on the health of the Florida Bay ecosystem. Changes in nutrient input and the nutrient dynamics of Florida Bay are hypothesized to be linked to these problems, but crucial baseline information is still lacking. Efforts to restore Florida Bay to its natural condition will require information on the nutrient history of the bay. The purpose of this study was to examine distributions of organic C, total N, and total P in carbonate sediments from sites of continuous and known sedimentation rate (210Pb and 137Cs dated), in eastern and central Florida Bay. These sediments provide a record of historical changes in the C, N, and P load to the eastern and central bay. Analyses were conducted on sediments from cores collected at five sites, and on buried seagrass fragments at two sites. At three of the sites, sediments from seagrass-covered and adjacent barren areas were examined to determine differences in sedimentary geochemistry. Stable isotope analyses (??13C and ??15N) of sedimentary organic C and total N and of buried seagrass fragments were also carried out at two sites to examine possible changes in nutrient sources to the estuary. Results were consistent with recent increases in N and P in eastern Florida Bay, beginning in the early to mid 1980's. The timing of the increase in nutrient load observed in the sediment data directly preceded the first observations of massive microalgal blooms and seagrass dieoff in Florida Bay in 1987. The observed nutrification was greater for P than N, and was most pronounced at the most northeasterly site sampled (Pass Key). Isotope data (??15N) suggested that an increase in algal production accompanied the increase in N load at the Pass Key site. Along record of organic C, total N, and total P distributions from Whipray Basin in central Florida Bay showed historical peaks (mid 1700's and late 1800's) in organic C and total N, but not total P; these enrichments were nearly equivalent to recent inputs to the estuary. Barren areas were observed to have generally lower concentrations of organic C, total N, and total P in near surface sediments compared to seagrass-covered areas, but had generally similar concentrations in deeper sediments. This suggested that barren areas adjacent to seagrass-covered sites were places where relict sediment was physically transported and covered seagrass beds. This dataset provides an historical view of changes in nutrient inputs to Florida Bay, and baseline information needed for nutrient modeling of the bay.

Journal of Coastal Research↗

Structure of the Koyna-Warna Seismic Zone, Maharashtra, India: A possible model for large induced earthquakes elsewhere

The Koyna-Warna area of India is one of the best worldwide examples of reservoir-induced seismicity, with the distinction of having generated the largest known induced earthquake (M6.3 on 10 December 1967) and persistent moderate-magnitude (>M5) events for nearly 50 years. Yet, the fault structure and tectonic setting that has accommodated the induced seismicity is poorly known, in part because the seismic events occur beneath a thick sequence of basalt layers. On the basis of the alignment of earthquake epicenters over an ~50 year period, lateral variations in focal mechanisms, upper-crustal tomographic velocity images, geophysical data (aeromagnetic, gravity, and magnetotelluric), geomorphic data, and correlation with similar structures elsewhere, we suggest that the Koyna-Warna area lies within a right step between northwest trending, right-lateral faults. The sub-basalt basement may form a local structural depression (pull-apart basin) caused by extension within the step-over zone between the right-lateral faults. Our postulated model accounts for the observed pattern of normal faulting in a region that is dominated by north-south directed compression. The right-lateral faults extend well beyond the immediate Koyna-Warna area, possibly suggesting a more extensive zone of seismic hazards for the central India area. Induced seismic events have been observed many places worldwide, but relatively large-magnitude induced events are less common because critically stressed, preexisting structures are a necessary component. We suggest that releasing bends and fault step-overs like those we postulate for the Koyna-Warna area may serve as an ideal tectonic environment for generating moderate- to large- magnitude induced (reservoir, injection, etc.) earthquakes.

Journal of Geophysical Research↗

The Palos Verdes Fault offshore southern California: late Pleistocene to present tectonic geomorphology, seascape evolution and slip rate estimate based on AUV and ROV surveys

The Palos Verdes Fault (PVF) is one of few active faults in Southern California that crosses the shoreline and can be studied using both terrestrial and subaqueous methodologies. To characterize the near-seafloor fault morphology, tectonic influences on continental slope sedimentary processes and late Pleistocene to present slip rate, a grid of high-resolution multibeam bathymetric data, and chirp subbottom profiles were acquired with an autonomous underwater vehicle (AUV) along the main trace of PVF in water depths between 250 and 600 m. Radiocarbon dates were obtained from vibracores collected using a remotely operated vehicle (ROV) and ship-based gravity cores. The PVF is expressed as a well-defined seafloor lineation marked by subtle along-strike bends. Right-stepping transtensional bends exert first-order control on sediment flow dynamics and the spatial distribution of Holocene depocenters; deformed strata within a small pull-apart basin record punctuated growth faulting associated with at least three Holocene surface ruptures. An upper (shallower) landslide scarp, a buried sedimentary mound, and a deeper scarp have been right-laterally offset across the PVF by 55 ± 5, 52 ± 4 , and 39 ± 8 m, respectively. The ages of the upper scarp and buried mound are approximately 31 ka; the age of the deeper scarp is bracketed to 17–24 ka. These three piercing points bracket the late Pleistocene to present slip rate to 1.3–2.8 mm/yr and provide a best estimate of 1.6–1.9 mm/yr. The deformation observed along the PVF is characteristic of strike-slip faulting and accounts for 20–30% of the total right-lateral slip budget accommodated offshore Southern California.

California↗

Florida: A Jurassic transform plate boundary

Magnetic, gravity, seismic, and deep drill hole data integrated with plate tectonic reconstructions substantiate the existence of a transform plate boundary across southern Florida during the Jurassic. On the basis of this integrated suite of data the pre-Cretaceous Florida-Bahamas region can be divided into the pre-Jurassic North American plate, Jurassic marginal rift basins, and a broad Jurassic transform zone including stranded blocks of pre-Mesozoic continental crust. Major tectonic units include the Suwannee basin in northern Florida containing Paleozoic sedimentary rocks, a central Florida basement complex of Paleozoic age crystalline rock, the west Florida platform composed of stranded blocks of continental crust, the south Georgia rift containing Triassic sedimentary rocks which overlie block-faulted Suwannee basin sedimentary rocks, the Late Triassic-Jurassic age Apalachicola rift basin, and the Jurassic age south Florida, Bahamas, and Blake Plateau marginal rift basins. The major tectonic units are bounded by basement hinge zones and fracture zones (FZ). The basement hinge zone represents the block-faulted edge of the North American plate, separating Paleozoic and older crustal rocks from Jurassic rifted crust beneath the marginal basins. Fracture zones separate Mesozoic marginal sedimentary basins and include the Blake Spur FZ, Jacksonville FZ, Bahamas FZ, and Cuba FZ, bounding the Blake Plateau, Bahamas, south Florida, and southeastern Gulf of Mexico basins. The Bahamas FZ is the most important of all these features because its northwest extension coincides with the Gulf basin marginal fault zone, forming the southern edge of the North American plate during the Jurassic. The limited space between the North American and the South American/African plates requires that the Jurassic transform zone, connecting the Central Atlantic and the Gulf of Mexico spreading systems, was located between the Bahamas and Cuba FZ's in the region of southern Florida. Our plate reconstructions combined with chronostratigraphic and lithostratigraphic information for the Gulf of Mexico, southern Florida, and the Bahamas indicate that the gulf was sealed off from the Atlantic waters until Callovian time by an elevated Florida-Bahamas region. Restricted influx of waters started in Callovian as a plate reorganization, and increased plate separation between North America and South America/Africa produced waterways into the Gulf of Mexico from the Pacific and possibly from the Atlantic.

Florida↗

Review: Regional land subsidence accompanying groundwater extraction

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Various ground-based and remotely sensed methods are used to measure and map subsidence. Many areas of subsidence caused by groundwater pumping have been identified and monitored, and corrective measures to slow or halt subsidence have been devised. Two principal means are used to mitigate subsidence caused by groundwater withdrawal—reduction of groundwater withdrawal, and artificial recharge. Analysis and simulation of aquifer-system compaction follow from the basic relations between head, stress, compressibility, and groundwater flow and are addressed primarily using two approaches—one based on conventional groundwater flow theory and one based on linear poroelasticity theory. Research and development to improve the assessment and analysis of aquifer-system compaction, the accompanying subsidence and potential ground ruptures are needed in the topic areas of the hydromechanical behavior of aquitards, the role of horizontal deformation, the application of differential synthetic aperture radar interferometry, and the regional-scale simulation of coupled groundwater flow and aquifer-system deformation to support resource management and hazard mitigation measures.

Hydrogeology Journal↗

Lake-wide annual status of Mysis diluviana population in Lake Michigan in 2015

Mysis diluviana is one of the most abundant zooplankton by biomass in the Laurentian Great Lakes of North America, a predator of other zooplankton and an important prey for fishes. Studies of long-term trends in Lake Michigan have shown 2005–2016 densities to be 50–80% lower than 1990s densities, but these observations have been based on annual monitoring that is either spatially or seasonally limited. We combined Lake Michigan Mysis data from three annual programs and the 2015 Cooperative Science and Monitoring Initiative to achieve broad spatial coverage during spring, summer, and fall of 2015 and broad depth coverage during spring 2016. Lake-wide, annual density and biomass were 82 (SE: 10) Mysis /m 2 and 200 (SE: 36) mg dry mass/m 2 . Density and biomass estimates were highest offshore, generally higher in the north basin, and seasonally highest in summer. Annual lake-wide averages for depths >30 m were better captured by seasonally-extensive annual programs than spatially-extensive annual programs, although spring sampling may bias annual values low. Mysis cohorts grew 0.026 mm/d (age-0) and 0.007 to 0.027 mm/d (age-1). Annual mortality was 81–98%. Reproduction was fall-spring and seasonal lake-wide estimates ranged from 0.6 to 19.1% females brooding, 13–20 embryos/brood, and 3–46 embryos/m 2 . Annual production (423 mg dry mass/m 2 /yr, SE: 31) was lower than all but one previous estimate from lakes Michigan, Huron, and Ontario. While Mysis tend to persist, low Mysis production may be a concern for prey fishes that feed on Mysis .

Lake Michigan↗

Spatial and temporal distributions of Dreissena spp. veligers in Lake Huron: Does calcium limit settling success?

The larval stage of invasive Dreissena spp. mussels (i.e., veligers) are understudied despite their seasonal numerical dominance among plankton. We report the spring and summer veliger densities and size structure across the main basin, North Channel, and Georgian Bay of Lake Huron, and seek to explain spatiotemporal variation. Monthly sampling was conducted at 9 transects and up to 3 sites per transect from spring through summer 2017. Veliger densities peaked in June and July, and we found comparable densities and biomasses of veligers between basins, despite differences in density of juvenile and adult mussels across these regions. Using a generalized additive model to explain variations in veliger density, we found that temperature, chlorophyll a , and nitrates/nitrites were most important. We generated an index of veliger attrition based on size distributions that revealed a higher rate of attrition in the North Channel than the rest of the lake. A logistic model indicated a threshold calcium concentration of around 22 mg/L was necessary for veligers to survive to larger sizes and recruit to their juvenile and benthic adult life stages. Improved understanding of factors that regulate the production and survival of Dreissena veligers could improve the ability of managers to assess future invasion threats as well as explore potential control options.

Lake Huron↗

Hydrodynamic and morphologic response of a back-barrier estuary to an extratropical storm

We investigated the hydrodynamic and morphologic response of Barnegat Bay-Little Egg Harbor, New Jersey, USA to Hurricane Sandy. We implemented a three-dimensional, coupled ocean-wave-sediment transport model of the estuary and explored the role of offshore water levels, offshore waves, local winds and waves by systematically removing forcings from a series of simulations. Offshore water levels had the largest impact on water levels in the bay while waves and local wind forcing created substantial spatial variation along the longitudinal axis of the bay. The shape of the bay and its orientation relative to the storm track influenced the response to winds and restricted the maximum water levels in the northern bay and reduced the maximum volume of surge. Basin-average hydrodynamic residence time was reduced by 40%, though its typical spatial distribution remained during the storm. Wave and current-induced bed shear stress resuspended fine sediment resulting in net erosion from the shoals with ensuing net deposition over fringing low-lying land. The net sediment exchange between the bay and the ocean was several times smaller than the exchange at the peak of the storm resulting in negligible net change in the bay volume. Overall, our results suggest that water level responses are highly sensitive to the specific orientation of storm winds relative to the estuary, thereby limiting the utility of simple inundation models. The sediment transport patterns indicate that storms are an important mechanism for redistributing sediment from shoals to fringing wetlands, while net change to sediment budget can be negligible.

New Jersey↗

Clean coal initiatives in Indiana

Purpose - Indiana is listed among the top ten coal states in the USA and annually mines about 35 million short tons (million tons) of coal from the vast reserves of the US Midwest Illinois Coal Basin. The implementation and commercialization of clean coal technologies is important to the economy of the state and has a significant role in the state's energy plan for increasing the use of the state's natural resources. Coal is a substantial Indiana energy resource and also has stable and relatively low costs, compared with the increasing costs of other major fuels. This indigenous energy source enables the promotion of energy independence. The purpose of this paper is to outline the significance of clean coal projects for achieving this objective. Design/methodology/approach - The paper outlines the clean coal initiatives being taken in Indiana and the research carried out at the Indiana Center for Coal Technology Research. Findings - Clean coal power generation and coal for transportation fuels (coal-to-liquids - CTL) are two major topics being investigated in Indiana. Coking coal, data compilation of the bituminous coal qualities within the Indiana coal beds, reducing dependence on coal imports, and provision of an emissions free environment are important topics to state legislators. Originality/value - Lessons learnt from these projects will be of value to other states and countries.

International Journal of Energy Sector Management↗

Sediment source fingerprinting as an aid to large-scale landscape conservation and restoration: A review for the Mississippi River Basin

Reliable quantitative information on sediment sources to rivers is critical to mitigate contamination and target conservation and restoration actions. However, the determination of the relative importance of sediment sources is complicated at the scale of large river basins by immense variability in erosional processes and sediment sources over space and time, heterogeneity in sediment transport and deposition, and a paucity of sediment monitoring data. Sediment source fingerprinting is an increasingly adopted field-based technique that identifies the nature and relative source contribution of sediment transported in waterways. Notably, sediment source fingerprinting provides information that is independent of other field, modeling, or remotely sensed techniques. However, the diversity in sediment fingerprinting sampling, analytical, and interpretive methods has been recognized as a problem in terms of developing standardized procedures for its application at the scale of large river basins. Accordingly, this review focuses on established sediment source fingerprinting studies conducted within the Mississippi River Basin (MRB), summarizes unique information provided by sediment source fingerprinting that is distinct from traditional monitoring techniques, evaluates consistency and reliability of methodological approaches among MRB studies, and provides prospects for the use of the sediment source fingerprinting technique as an aid to large-scale landscape conservation and restoration under current management frameworks. Most established MRB studies got creditable fingerprinting results and considered near-channel sources as the dominant sediment sources in most cases, while the comparability of their results suffers from a lack of standardization in procedural steps. Findings from MRB studies demonstrate that sediment source fingerprinting is a highly valuable and reliable sediment source assessment approach to assist land and water resource management under current management frameworks, but efforts are still needed to make this technique ready to be used in a more predominant way in large-scale landscape conservation and restoration efforts. We summarized research needs and suggested the best fingerprinting practices for management purposes with the aim of ensuring that this technique is as robust and reliable as it moves forward.

Mississippi River Basin↗

Earthquakes induced by hydraulic fracturing are pervasive in Oklahoma

Wastewater disposal is generally accepted to be the primary cause of the increased seismicity rate in Oklahoma within the past decade, but no statewide analysis has investigated the contribution of hydraulic fracturing (HF) to the observed seismicity or the seismic hazard. Utilizing an enhanced seismicity catalog generated with multi‐station template matching from 2010‐2016 and all available hydraulic fracturing information, we identified 274 HF wells that are spatiotemporally correlated with bursts of seismicity. The majority of HF induced seismicity cases occurred in the SCOOP/STACK plays, but we also identified prominent cases in the Arkoma Basin as well as some more complex potential cases along the edge of the Anadarko Platform. For HF treatments where we have access to injection parameters, modeling suggests poroelastic stresses are likely responsible for seismicity, but we cannot rule out direct pore pressure effects as a contributing factor. In all of the 16 regions we identified, ≥75% of the seismicity correlated with reported HF wells. In some regions, >95% of seismicity correlated with HF wells and >50% of the HF wells correlated with seismicity. Overall, we found ~700 HF induced earthquakes with M ≥ 2.0, including 12 events with M 3.0‐3.5. These findings suggest state regulations implemented in 2018 that require operators in the SCOOP/STACK plays to take action if a M > 2 earthquake occurs could have a significant impact on future operations.

Oklahoma↗

Chryse Basin channels: low-gradients and ponded flows.

Gradients on the floors of the Martian outflow channels that are derived from radar-elevation profiles across Lunae Planum and Chryse Basin have much lower values than those obtained from the U.S. Geological Survey's topographic map. Whereas the gradients of Maja and Ares Valles are similar to those of the catastrophic flood channels in the Scablands of Washington State, the gradients of Simud and Tiu Valles are essentially level, and the movement of fluids to the N poses problems. It is proposed that ponding may have formed lakes in depressions associated with the Valles Marineris grabens, ancient craters in the chaotic terrain area, and possibly even the regional low where most chaotic terrains occur. It is envisaged that lakes eventually overflowed, forming the present channels. When dams broke, floods were released catastrophically, with a final gigantic flood from the Valles Marineris system of troughs, which would have had sufficient head to move fluids across nearly level gradients through the Simud and Tiu channels.

Journal of Geophysical Research↗