The Stratigraphically Preserved Signature of Persistent Backwater Dynamics in a Large Paleodelta System: The Mungaroo Formation, North West Shelf, Australia

Martin, J. M.; Fernandes, Anjali M.; Pickering, Jennifer; Howes, Nick; Mann, Simon; McNeil, Katja

doi:10.2110/jsr.2018.38

Cited by 46 publications

(48 citation statements)

References 86 publications

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“…However, if only focusing on the nonuniform flow zone defined by L bw , the sorting will dominantly increase downstream for Cases 1, 3 and 4. This result is consistent with field observations (Petter, ) and subsurface data (Martin et al, ). This also suggests that (a) it's important to examine sorting beyond backwater length scale to test the modelled trend in grain size distribution, and (b) the presence of a strong peak of standard deviation in median grain size within the backwater zone might indicate base‐level rise (Case 2).…”

Section: Implications For Stratigraphic Recordsupporting

confidence: 92%

“…A higher rate of channel bed aggradation is found upstream of the river mouth in Cases 1–3 and results in an increase, then decrease in the thickness of fluvial stratigraphy from the upstream model boundary to the river mouth (Figure e–h). Similar trends have also been observed in ancient fluvial–deltaic systems considered to be influenced by backwater effects (Martin et al, ). The spatio‐temporal variability in channel bed aggradation reflects the diffusive and advective nature of the sediment transport processes, which is evidenced by the upward concave river profiles (Parker et al, ; Swenson, Paola, Pratson, Voller, & Murray, ; Wright & Parker, ).…”

Section: Discussionsupporting

confidence: 79%

“…They hypothesize that sand‐prone, aggradational ribbon channel elements represent the terminal expression of distributary channels, where hydrodynamic drawdown produces multiple, clustered scour surfaces at the base of channel fills. More recently, based on analysis of subsurface data (seismic and well log), Martin et al () demonstrate downstream decreases of channel belt width and median channel sandstone grain size in the fluvial–deltaic system of the Mungaroo Formation, Carnarvon Basin (Australia) as evidence of the influence of nonuniform flow hydrodynamics. However, recognizing downstream deepening of paleoflow depth based on bar thickness is still challenging with subsurface data (Martin et al, ), and observations of downstream increase in bar thickness within the backwater reach of modern fluvial–deltaic systems (e.g., the Mississippi River, Fernandes, Törnqvist, Straub, & Mohrig, ) still require testing in the rock record.…”

Section: Background: Nonuniform Flow In Sedimentary Dispersal Systemsmentioning

confidence: 99%

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Impacts of backwater hydrodynamics on fluvial–deltaic stratigraphy

Nitterour

2019

Basin Research

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The hydrodynamics of rivers approaching a receiving basin are influenced by the onset of backwater conditions that give rise to decelerating reach-average flow velocity and decreasing boundary shear stress. These changes occur across a spatial gradient over which decreasing sediment transport capacity triggers morphodynamic responses that include sediment deposition at the transition from uniform to nonuniform flow. As a consequence, the channel width-to-depth ratio and bed sediment grain size decrease downstream. While nonuniform flow and associated morphodynamic adjustments have been investigated in modern fluvial-deltaic systems, the impacts to fluvial-deltaic stratigraphy remain relatively unexplored. This represents an important unresolved gap: there are few contributions that link morphodynamic response to nonuniform flow, impacts on sediment deposition and influence on the rock record. This study uses a numerical model to explore how variable channel hydraulics influence long-term (1000s years) patterns of sediment deposition and development of stratigraphy. The model results indicate that: (a) nonuniform flow propagates upstream beyond the backwater transition that is traditionally estimated with a basic backwater length scale relationship. (b) Base-level fluctuations, especially rising, enhance the impact of nonuniform flow. (c) Sediment deposition shows large spatio-temporal variability, which ultimately contributes to unique stacking patterns of fluvial-deltaic stratigraphy. (d) Nonuniform flow imparts spatial variation in flow depth, channel bed slope and sediment grain size over the delta, and these signatures are potentially preserved and recognizable in the rock record.

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Section: Implications For Stratigraphic Recordsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 79%

Section: Background: Nonuniform Flow In Sedimentary Dispersal Systemsmentioning

confidence: 99%

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Impacts of backwater hydrodynamics on fluvial–deltaic stratigraphy

Nitterour

2019

Basin Research

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“…The bend wavelength for an entire channel belt also is typically different than the bend wavelength of the channel (Fig. 3), which can be observed in examples for both modern and ancient systems (e.g., Fernandes et al, 2016;Martin et al, 2018). On Mars, supporting observations for deposit inversion includes ridges at distinct stratigraphic levels and ridges comprised of amalgamated channel deposits (Malin and Edgett, 2003;Moore et al, 2003;Burr et al, 2009Burr et al, , 2010DiBiase et al, 2013;Kite et al, 2013Kite et al, , 2015aCardenas et al, 2017).…”

mentioning

confidence: 92%

Formation of sinuous ridges by inversion of river-channel belts in Utah, USA, with implications for Mars

Hayden

Lamb

Fischer

et al. 2019

Icarus

154

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Sinuous ridges are important landforms on the surface of Mars that show promise for quantifying ancient martian surface hydrology. Morphological similarity of these ridges to river channels in planform led to a hypothesis that ridges are topographically inverted river channels, or "inverted channels", formed due to an erosion-resistant channel-filling material that preserved a snapshot of the channel geometry in inverted relief due to differential erosion. An alternative depositinversion hypothesis proposes that ridges represent exhumed river-channel belts, with geometries that reflect the lateral migration and vertical aggradation of rivers over significant geologic time, rather than the original channel geometry. To investigate these hypotheses we studied sinuous ridges within the Cretaceous Cedar Mountain Formation near Green River, Utah, USA. Ridges in Utah extend for hundreds of meters, are up to 120 meters wide, and stand up to 39 meters above the surrounding plain. Ridges are capped by sandstone bodies 3-10 meters thick that contain dune-and bar-scale inclined stratification, which we interpret as eroded remnants of channel ACCEPTED MANUSCRIPT 2 4/18/2019 12:45 PM belts that record the migration and aggradation of single-thread, sand-bedded rivers, rather than channel fills that can preserve the original channel geometry. Caprocks overlie mudstones and thinner sandstone beds that are interpreted as floodplain deposits, and in cases additional channel-belt sandstones are present lower in the ridge stratigraphy. Apparent networks from branching ridges typically represent discrete sandstone bodies that cross at different stratigraphic levels rather than a coeval river network. Ridge-forming sandstone bodies also have been narrowed during exhumation by cliff retreat and bisected by fluvial erosion. Using a large compilation of channel-belt geometries on Earth and our measurements of ridges in Utah, we propose that caprock thickness is the most reliable indicator of paleo-channel geometry, and can be used to reconstruct river depth and discharge. In contrast, channel lateral migration and caprock erosion during exhumation make ridge breadth an uncertain proxy for channel width. An example in Aeolis Dorsa, Mars, illustrates that river discharge estimates based solely on caprock width may differ significantly from estimates based on caprock thickness. Overall, our study suggests that sinuous ridges are not inverted channel fills, but rather reflect exhumation of a thick stratigraphic package of stacked channel belts and overbank deposits formed from depositional rivers over significant geologic time.

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“…The depth of 1D model captures the change in WSE across the BW transition, which allows the 2D model to capture the sediment flux. The current approaches in geomorphological assessment in the BW zone are mainly limited to either a few years-worth or thousands years of geomorphic changes [29][30][31][32][33][34][35][36][37][38]. In contrast, the presented integrated model builds on the existing body of knowledge in geosciences which can predict geomorphological alterations in the BW zone of the rivers over a short to intermediate time scale applicable to civil engineering applications.…”

Section: Introductionmentioning

confidence: 99%

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Hosseiny

Smith

2019

Water

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Predicting morphological alterations in backwater zones has substantial merit as it potentially influences the life of millions of people by the change in flood dynamics and land topography. While there is no two-dimensional river model available for predicting morphological alterations in backwater zones, there is an absolute need for such models. This study presents an integrated iterative two-dimensional fluvial morphological model to quantify spatio-temporal fluvial morphological alterations in normal flow to backwater conditions. The integrated model works through the following steps iteratively to derive geomorphic change: (1) iRIC model is used to generate a 2D normal water surface; (2) a 1D water surface is developed for the backwater;(3) the normal and backwater surfaces are integrated; (4) an analytical 2D model is established to estimate shear stresses and morphological alterations in the normal, transitional, and backwater zones. The integrated model generates a new digital elevation model based on the estimated erosion and deposition. The resultant topography then serves as the starting point for the next iteration of flow, ultimately modeling geomorphic changes through time. This model was tested on Darby Creek in Metro-Philadelphia, one of the most flood-prone urban areas in the US and the largest freshwater marsh in Pennsylvania.the river increases gradually upstream to form a smooth transition between a quasi-normal flow and standing water, forcing an alteration of the hydraulic conditions. The segment of the river affected by this response-which might exceed hundreds of kilometers in low slope rivers-is called the backwater zone [12].The shift in BW hydraulics causes the water surface slope to decrease independent of the bed slope, resulting in a gradual longitudinal alteration of the flow depth and velocity [13]. The vertical velocity distribution in BW conditions is less divergent compared to the one in a uniform flow [14]. These changes in the hydraulics of the vertical and horizontal flow velocity in BW zones consequently alter the sediment transport processes.Current approaches to BW in morphological studies are primarily based on either measured or estimated hydraulic parameters coupled with the estimated sediment transport [9,11,[15][16][17][18][19][20][21]. The studies of sediment transport in BW conditions are scarce due to the complex dynamics of the sediment transport in BW zones and the lack of field-measured data. The presence of the BW complicates different types of hydrometric measurements including the water surface slope, velocity, and discharge [19]. A lack in measured data is even more severe for transitional areas where the flow state changes from normal to a gradually varied flow [18]. Nittrouer et al. used measured cross sections in the lower Mississippi River to back calculate velocity, shear stress and sediment discharge [22]. They concluded that where the flow transitions to the BW zone, the cross-sectional area increases in the downstream in low-moderate flows, resultin...

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The Stratigraphically Preserved Signature of Persistent Backwater Dynamics in a Large Paleodelta System: The Mungaroo Formation, North West Shelf, Australia

Cited by 46 publications

References 86 publications

Impacts of backwater hydrodynamics on fluvial–deltaic stratigraphy

Impacts of backwater hydrodynamics on fluvial–deltaic stratigraphy

Formation of sinuous ridges by inversion of river-channel belts in Utah, USA, with implications for Mars

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

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