Fluvial Landscapes and Stratigraphy in a Flume

Abstract

We use data from an experiment conducted in the Experimental EarthScape (XES) facility, National Center for Earth-surface Dynamics (NCED), St.Anthony Falls Laboratory (SAFL), University of Minnesota, to demonstrate why incised valleys preserved in the stratigraphic record probably bear little resemblance to the actual valleys as they appeared in the paleolandscape. In an experiment designed to study fluvial response to changes in sea level, we find that preserved incised-valley structures are typically broader and have more gentle side slopes, than the topographic features from which they develop. Also, because of widening driven by valley wall erosion during both relative sea-level rise and fall, there is virtually no remnant of terraces formed during falling relative sea level preserved in the stratigraphic record.The process of filling an incised valley due to rising relative sea level is not a passive depositional process that simply buries and preserves the original shape of the valley; rather, it includes an energetic erosional component that substantially reshapes the original valley form. INCISED VALLEY EVOLUTION AND PRESERVATIONThe geological community has long recognized the significance of identifying incised valleys in the stratigraphic record as well as understanding the relationships between the filling of incised-valleys and their geomorphologic evolution. Incised valley geometries and fill are often used to infer the record and effects of sea level change on coastal environments, both as a tool in petroleum exploration (e.g. Van Wagoner et al. 1988, 1990Posamentier and Allen 1999) and to better understand the environmental consequences of sea level change (Warrick et al. 1993; Nicholls and Leatherman 1994). Furthermore, incised valleys typically comprise basin scale erosional unconformities that can be identified in seismic sections, well logs, and outcrops, and thus are used to correlate stratigraphic facies and time (e.g., Van Wagoner et al. 1990).Previous work on both modern and preserved incised valleys has illustrated the complexity of incised valley fill. A common interpretation of the stratigraphic record in such fills is that detailed layering reflects discrete external (allogenic) forcing mechanisms, including high frequency climate change, (low amplitude) high frequency tectonic movement, eustatic sea level and lake level fluctuations, and local faulting (Kraus and Middleton 1987;Bromely 1991; LopezGomez and Arche 1993;Blum and Tornqvist 2000). The question of whether there are other mechanisms that could potentially produce the same geomorphic and stratigraphic signatures as these external factors is difficult to address from field data alone. Here we use experimental data to illustrate the role of autogenic (internal) processes in producing this complexity. EXPERIMENTAL FACILITIESThe experimental data presented in this paper come from an experiment conducted in the Experimental EarthScape (XES) facility, National Center for Earth-surface Dynamics, St. Anthony Falls Laboratory,...

Geological controls on the geometry of incised‐valley fills: Insights from a global dataset of late‐Quaternary examples

“…Incised‐valley widening is partly driven by the lateral migration of fluvial channel belts (Martin et al., ). Previous work based on experiments, numerical modelling and field studies (Strong & Paola, , ; Martin et al., ; Blum et al., ) have shown that lateral channel migration and channel‐belt deposition are closely concomitant with valley incision unless the valley sidewalls are resistant to erosion or the system is starved of sediments, implying that valley widening generally follows valley incision temporally during relative sea‐level fall. The examples associated with active margins studied here are all incised into unconsolidated sand‐rich coastal or shelf deposits, such that valley‐fill width is expected to be scaled with valley‐fill thickness.…”

Upstream Channel Changes Following Dam Construction and Removal Using a GIS/Remote Sensing Approach1

“…, 1998), mathematical models (e.g., Paola, 2000), and detailed flume studies (e.g., Heller et al. , 2001; Strong and Paola, 2006) to reproduce the stratal patterns observed in seismic lines of fluvial systems upstream of the delta and coastline, in response to base level changes and other long‐term, large‐scale geological processes not relevant to this discussion (such as paleoclimate change and tectonic subsidence).…”

Lithological heterogeneity in a back-barrier sand island: Implications for modelling hydrogeological frameworks

“…The northern interfluve represents the eroded outer meander (cut bank) of the palaeovalley and, therefore, has a steeper profile. It should be noted, however, that modification of the channel cross-sectional profile takes place during transgression and asymmetry may also result from tidal inlet development (Strong and Paola, 2006). The facies association model also shows that the fluvial gravels in the palaeovalley are not connected to the shallow gravel deposits in the north of the island.…”

“…Reshaping of the valley crosssectional profile may also have taken place due to transgressive erosion, but evidence of transgressive ravinement is equivocal. The palaeovalley is considered to have been broadened in a similar manner to that shown by the experimental model of Strong and Paola (2006). This resulted in a valley depression with a very low aspect ratio, which promoted the deposition of gently dipping tabular sedimentary units within the already partially filled valley.…”