Neoproterozoic Incised Valleys of the Eastern Great Basin, Utah and IdahoFluvial Response to Changes in Depositional Base Level

1994 ◽  
Author(s):  
Marjorie Levy ◽  
Nicholas Christie-Blick ◽  
Paul Karl Link
Keyword(s):  
Great Basin ◽  
Base Level ◽  
Incised Valleys ◽  
Fluvial Response

The origin of elevated plateaus along passive continental margins

2020 ◽  
Author(s):  
Johan M. Bonow ◽  
Peter Japsen ◽  
Paul F. Green ◽  
James A. Chalmers
Keyword(s):  
Sea Level ◽  
Continental Margins ◽  
East Greenland ◽  
Passive Margins ◽  
Base Level ◽  
Wide Range ◽  
The World ◽  
Incised Valleys ◽  
Break Up ◽  
High Level

<p>Many passive continental margins around the world are characterised by elevated plateaus at 1 to 2 km or more above sea level cut by deeply incised valleys and commonly separated from an adjacent coastal plain by one or more escarpments. Mesozoic–Cenozoic rift systems parallel to the coast are commonly present offshore with a transition from continental to oceanic crust further offshore. These landscapes occur in arctic, temperate and tropical climate and in different geological settings independent of the time span since break-up (e.g. along the Atlantic from south to north).</p><p>The plateaux are typically more than 100 km wide, much larger in some cases, and extend hundreds of kilometres along the margin, cutting across bedrock of different ages and resistances. The key to understanding the formation of regional, low-relief erosion surfaces is the base-level, as this is the level to which fluvial systems grade the landscape. The most likely base level is sea level, particularly for locations along continental margins during the post-rift development of passive margins.</p><p>It is commonly assumed that the characteristic, large-scale morphology of elevated, passive continental margins with  high-level plateaux and deeply incised valleys persisted since rifting and crustal separation Further, it is assumed that the absence of post-rift sediments is evidence of non-deposition, despite continental-stretching theory predicting deposition of a thick post-rift sequence overlying both the rift and its margins.</p><p>However, our studies of the passive continental margins of West and East Greenland, Norway, NE Brazil and southern Africa provide evidence of km-scale, post-rift subsidence and that the plateau surfaces were graded to sea level long after break-up and subsequently lifted to their present elevations. In some of these cases, the presence of post-rift marine sediments at high elevation provide direct proof of this interpretation. Since elevated plateaux cut by deeply incised valleys are a characteristic feature of these and other margins, this similarity suggests that such topography elsewhere in the world may also be unrelated to the processes of rifting and continental separation. We present a wide range of evidence from passive margins around the world in support of this hypothesis,</p><p> </p><p>Bonow et al. 2014: High-level landscapes along the margin of East Greenland – a record of tectonic uplift and incision after breakup in the NE Atlantic. Global and Planetary Change.</p><p>Green et al. 2018: Post-breakup burial and exhumation of passive continental margins: Seven propositions to inform geodynamic models. Gondwana Research.</p><p>Japsen et al. 2019: Elevated passive continental margins: Numerical modeling vs observations. A comment on Braun (2018). Gondwana Research.</p>

scholarly journals Autogenic delta progradation during sea-level rise within incised valleys

Geology ◽  
2020 ◽  
Author(s):  
L. Guerit ◽  
B.Z. Foreman ◽  
C. Chen ◽  
C. Paola ◽  
S. Castelltort
Keyword(s):  
Sediment Supply ◽  
Strong Decrease ◽  
Surface Evolution ◽  
Incised Valley ◽  
Sequence Stratigraphic ◽  
Base Level ◽  
Reservoir Models ◽  
Incised Valleys ◽  
Delta Progradation ◽  
The Trinity

Using a simple conceptual model of incised-valley evolution, we show that the classic sequence stratigraphic phenomenon of bayhead deltaic systems can be generated by purely autogenic progradation during the late stage of valley flooding. This transient “auto-advance” event occurs under conditions of constant base-level rise and sediment supply, and it results from a strong decrease of in-valley accommodation as base level rises toward the valley apex. We present a laboratory experiment to illustrate the plausibility of this mechanism and apply it to the incised valleys of the Trinity and Brazos Rivers (Texas, USA) as field case studies. Auto-advance can produce out-of-sequence regressive bayhead diastems during highstands similar to a transient change in allogenic forcing. Combined with other recent studies, our findings support the idea that mesoscale autogenic patterns are ubiquitous in the fluviodeltaic record and need to be more extensively incorporated into reconstructions of Earth surface evolution and reservoir models.

scholarly journals Management of Landscapes for Established Invasive Species

2021 ◽  
pp. 133-184
Author(s):  
Therese M. Poland ◽  
Jennifer Juzwik ◽  
Allen Rowley ◽  
Cynthia D. Huebner ◽  
John C. Kilgo ◽  
...  
Keyword(s):  
Invasive Species ◽  
Great Basin ◽  
Large Scale ◽  
Invasive Plant ◽  
Management Strategies ◽  
Plant Management ◽  
Management Activity ◽  
Invasive Plant Management ◽  
Base Level ◽  
Hydrologic Unit

AbstractLong-term management strategies are invoked once an invasive species has become established and spread beyond feasible limits for eradication or containment. Although an invasive species may be well-established in small to large geographical areas, prevention of its spread to non-affected areas (e.g., sites, regions, and cross-continent) through early detection and monitoring is an important management activity. The level for management of established invasive species in the United States has increasingly shifted to larger geographical scales in the past several decades. Management of an invasive fish may occur at the watershed level in the western States, with watershed levels defined by their hydrologic unit codes (HUC) ranging from 2 digits at the coarsest level to 8 digits at the finest level (USGS 2018). Invasive plant management within national forests, grasslands, and rangelands can be implemented at the landscape level (e.g., Chambers et al. 2014), although management can still occur at the stand or base level. Landscapes in this chapter refer to areas of land bounded by large-scale physiographic features integrated with natural or man-made features that govern weather and disturbance patterns and limit frequencies of species movement (Urban et al. 1987). These are often at a large physical scale, such as the Great Basin.

scholarly journals Geomorphic signatures of the transient fluvial response to tilting

2019 ◽  
Author(s):  
Helen W. Beeson ◽  
Scott W. McCoy
Keyword(s):  
Sierra Nevada ◽  
Transient Response ◽  
River Network ◽  
Drainage Area ◽  
Spatial Gradient ◽  
Convergent Margins ◽  
Stream Network ◽  
Base Level ◽  
Fluvial Response ◽  
The Relationship

Abstract. Nonuniform rock uplift in the form of tilting has been documented in convergent margins, postorogenic landscapes, and extensional provinces. Despite the prevalence of tilting, the transient fluvial response to tilting has not been quantified such that tectonic histories involving tilt can be extracted from river network forms. We used numerical landscape evolution models to characterize the transient erosional response of a river network initially at equilibrium to a punctuated rigid-block tilting event. Using a model river network composed of linked 1-D river longitudinal profile evolution models, we show that the transient response to punctuated tilting creates characteristic forms or geomorphic signatures in mainstem and tributary profiles that are distinct from those generated by other perturbations such as a step change in uniform rock uplift rate or major truncation of headwater drainage area that push a river network away from equilibrium. These signatures include 1) a knickpoint in the mainstem that separates a downstream profile with uniform steepness (i.e., channel gradient normalized for drainage area) from an upstream profile with nonuniform steepness, with the mainstem above the knickpoint more out of equilibrium than the tributaries following forward tilting towards the outlet, versus the mainstem less out of equilibrium than the tributaries following back tilting towards the headwaters; 2) a pattern of mainstem incision below paleotopography markers that increases linearly up to the mainstem knickpoint, or vice-versa following back tilting; and 3) tributary knickzones with nonuniform steepness that mirrors that of the mainstem upstream of the slope-break knickpoint. Immediately after tilting, knickpoints form at the mainstem outlet and each mainstem-tributary junction. Time since tilting onset is recorded by mainstem knickpoint location relative to base level and by the upstream end of tributary knickzones relative to tributary-mainstem junctions. Tilt magnitude is recorded in the spatial gradient of mainstem incision depth and, in the forward tilting case, by tributary knickzone drop height. Heterogeneous lithology can modulate the transient response to tilting and, post-tilt, knickpoints can form anywhere in a stream network where more erodible rock occurs upstream of less erodible rock. With a full 2-D model, we show that stream segments flowing in the tilt direction have elevated channel gradient during the transient and that the magnitude of tilt can be recovered from the relationship between channel gradient and azimuth, but only shortly after tilting. Tilting is also reflected in network topologic changes via stream capture oriented in the direction of tilt. As an example of how these geomorphic signatures can be used in concert to estimate timing and magnitude of a tilting event, we show a sample of rivers draining the west slope of the Sierra Nevada, California, USA, a range long thought to have been tilted westward towards river outlets in the late Cenozoic.

scholarly journals Geomorphic signatures of the transient fluvial response to tilting

2020 ◽  
Vol 8 (1) ◽  
pp. 123-159
Author(s):  
Helen W. Beeson ◽  
Scott W. McCoy
Keyword(s):  
Sierra Nevada ◽  
Transient Response ◽  
River Network ◽  
Drainage Area ◽  
Spatial Gradient ◽  
Rigid Block ◽  
Stream Network ◽  
Base Level ◽  
Fluvial Response ◽  
Sierra San Pedro Martir

Abstract. Nonuniform rock uplift in the form of tilting has been documented in convergent margins, postorogenic landscapes, and extensional provinces. Despite the prevalence of tilting, the transient fluvial response to tilting has not been quantified such that tectonic histories involving tilt can be extracted from river network forms. We used numerical landscape evolution models to characterize the transient erosional response of a river network initially at equilibrium to rapid tilting. We focus on the case of punctuated rigid-block tilting, though we explore longer-duration tilting events and nonuniform uplift that deviates from perfect rigid-block tilting such as that observed when bending an elastic plate or with more pronounced internal deformation of a fault-bounded block. Using a model river network composed of linked 1-D river longitudinal profile evolution models, we show that the transient response to a punctuated rigid-block tilting event creates a suite of characteristic forms or geomorphic signatures in mainstem and tributary profiles that collectively are distinct from those generated by other perturbations, such as a step change in the uniform rock uplift rate or a major truncation of the headwater drainage area, that push a river network away from equilibrium. These signatures include (1) a knickpoint in the mainstem that separates a downstream profile with uniform steepness (i.e., channel gradient normalized for drainage area) from an upstream profile with nonuniform steepness, with the mainstem above the knickpoint more out of equilibrium than the tributaries following forward tilting toward the outlet, versus the mainstem less out of equilibrium than the tributaries following back tilting toward the headwaters; (2) a pattern of mainstem incision below paleo-topography markers that increases linearly up to the mainstem knickpoint or vice versa following back tilting; and (3) tributary knickzones with nonuniform steepness that mirrors that of the mainstem upstream of the slope-break knickpoint. Immediately after a punctuated tilting event, knickpoints form at the mainstem outlet and each mainstem–tributary junction. Time since the cessation of rapid tilting is recorded by the mainstem knickpoint location relative to base level and by the upstream end of tributary knickzones relative to the mainstem–tributary junction. Tilt magnitude is recorded in the spatial gradient of mainstem incision depth and, in the forward tilting case, also by the spatial gradient in tributary knickzone drop height. Heterogeneous lithology can modulate the transient response to tilting and, post tilt, knickpoints can form anywhere in a stream network where more erodible rock occurs upstream of less erodible rock. With a full 2-D model, we show that stream segments flowing in the tilt direction have elevated channel gradient early in the transient response. Tilting is also reflected in network topologic changes via stream capture oriented in the direction of tilt. As an example of how these geomorphic signatures can be used in concert with each other to estimate the timing and magnitude of a tilting event, we show a sample of rivers from two field sites: the Sierra Nevada, California, USA, and the Sierra San Pedro Mártir, Baja California, Mexico, two ranges thought to have been tilted westward toward river outlets in the late Cenozoic.

Representation of information in SEM by equal signal lines

1978 ◽  
Vol 36 (1) ◽  
pp. 144-145
Author(s):  
E. Rau ◽  
N. Karelin ◽  
V. Dukov ◽  
M. Kolomeytsev ◽  
S. Gavrikov ◽  
...  
Keyword(s):  
Electronic System ◽  
Space Distribution ◽  
Specimen Surface ◽  
Universal Method ◽  
Base Level ◽  
Signal Value ◽  
Information Signal ◽  
Fixed Base ◽  
Scanning Line ◽  
Amplitude Analyzer

There are different methods and devices for the increase of the videosignal information in SEM. For example, with the help of special pure electronic [1] and opto-electronic [2] systems equipotential areas on the specimen surface in SEM were obtained. This report generalizes quantitative universal method for space distribution representation of research specimen parameter by contour equal signal lines. The method is based on principle of comparison of information signal value with the fixed levels.Transformation image system for obtaining equal signal lines maps was developed in two versions:1)In pure electronic system [3] it is necessary to compare signal U (see Fig.1-a), which gives potential distribution on specimen surface along each scanning line with fixed base level signals εifor obtaining quantitative equipotential information on solid state surface. The amplitude analyzer-comparator gives flare sport videopulses at any fixed coordinate and any instant time when initial signal U is equal to one of the base level signals ε.

Estimating the slip rates of normal faults in the Great Basin, USA

2000 ◽  
Vol 12 (3-4) ◽  
pp. 227-240 ◽  
Author(s):  
C. M. dePolo ◽  
J. G. Anderson
Keyword(s):  
Great Basin ◽  
Normal Faults ◽  
Slip Rates
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