Elsevier

Geomorphology

Volume 371, 15 December 2020, 107439
Geomorphology

Impact of drainage integration on basin geomorphology and landform evolution: A case study along the Salt and Verde rivers, Sonoran Desert, USA

https://doi.org/10.1016/j.geomorph.2020.107439Get rights and content

Highlights

  • The Salt and Verde rivers, USA, experienced drainage integration across basins.

  • Drainage integration altered Neogene and Quaternary landform evolution.

  • Complex base-level changes generated incision-related and aggradational landforms.

  • Pediments and alluvial fans evolve as a consequence of drainage integration.

Abstract

The Salt and Verde rivers, Sonoran Desert, USA, integrated multiple endorheic extensional basins near the start of the Quaternary. Integration began via spillover on both rivers. Spillover resulted in headward erosion in upstream basins, leading to basin-wide incision and excavation of large volumes of sediment transported into downstream basins. As a result, the Verde River aggraded to what is now the highest terrace in the lower Verde River valley (LVRV), the Lousley Hills terrace. Evidence suggests deposition of the Lousley Hills terrace fill led to aggradation and backfilling of adjacent pediments. Ancestral Salt River Deposits (ASRD) of the combined Salt and Verde rivers deposited an extensive alluvial fan in the Higley Basin, raising local base level for over 2 million years. Eventually, this led to aggradational piracy of the Salt River (~0.46 Ma) that integrated the Higley and Luke basins. Consequently, this shortened and steepened the Salt River, resulting in ~30 m of aggradation downstream and headward incision upstream. Headward incision abandoned the ASRD and created the Sawik stream terrace. Piedmont pediment and alluvial fan systems that were formerly adjusted to the ASRD incised in response. Since abandonment, the ASRD floodplain has accumulated a sheet of silt and fine sand from aeolian and local fluvial processes. Sedimentary, metamorphic, and granitic pediments that developed in slowly aggrading endorheic basins display evidence of response to base-level adjustments resulting from drainage integration processes. Classic ballena landforms (eroding alluvial fans) began to form in the LVRV only after drainage integration — providing the first known maximum age for the ballena form. Drainage integration of the Salt and Verde rivers clearly demonstrates the impact of base-level fluctuations on basin-scale geomorphology. However, integration led to very different geomorphic responses in different extensional basins, revealing the difficulty of a one-size-fits-all conceptual model of geomorphic response drainage integration.

Introduction

Drainage integration occurs when former hydrologically closed (endorheic) or disconnected drainage basins merge to form a new hydro-geomorphic system (Hilgendorft et al., this issue). Much of drainage integration research has focused on the evolution of main-stem river systems within a drainage basin, resulting in a burgeoning understanding of processes that drive integration (Oberlander, 1965; Meek, 1989; House et al., 2005; Douglass and Schmeeckle, 2007; House et al., 2008; Reheis and Redwine, 2008; Douglass et al., 2009; Gunnell and Harbor, 2010; Lee et al., 2011; Pearthree and House, 2014; García-Castellanos and Larrasoana, 2015; Repasch et al., 2017; Geurts et al., 2018; Geurts et al., this issue; Skotnicki et al., this issue). Despite this, comparatively few studies have investigated the variety and significance of landforms that experienced a basin-scale response to integration processes. Recent studies investigating these basins have begun to illuminate basin-wide, dynamic responses (Geurts et al., 2018; Geurts et al., this issue) of those landscapes — including pediment adjustment (Larson et al., 2010; Larson et al., 2014; Larson et al., 2016) and tributary response (Jungers and Heimsath, 2019). These studies reveal the potential for aiding in the development of conceptual models of basin and landform evolution during and post integration (Menges and Pearthree, 1989) – with significance that goes beyond geomorphology to basin evolution (Roberts et al., 1994), basin sedimentation (Richard et al., 2007), carbon dioxide sequestration (Gootee, 2013), groundwater resource management (Laney and Hahn, 1986; Reynolds and Bartlett, 2002; Skotnicki and DePonty, this issue), and natural hazard mitigation (Jeong et al., 2018).

This paper attempts to shed light on basin-scale adjustment and the landforms resulting from drainage integration. We do this by presenting a variety of landforms, observed and interpreted over >20 yr of field investigation throughout the spatial extent of formerly closed, endorheic basins along the now through-flowing lower Salt and Verde rivers, Arizona, USA (Fig. 1, Fig. 2, Fig. 3).

Section snippets

Study area: the Salt and Verde rivers of central Arizona

Decades of research in central Arizona have led to estimates for the timing and hypothesized potential mechanisms, supported by abundant evidence, of integration of the Salt, Verde, and Gila rivers through the Phoenix metropolitan area (Pope, 1974; Péwé, 1978; Skotnicki, 1996; Skotnicki and Leighty, 1997; Skotnicki and Spencer, 2001; Skotnicki et al., 2003; Block, 2007; Douglass et al., 2009; Larson et al., 2010; Jungers and Heimsath, 2016; Larson et al., 2016; Jungers and Heimsath, 2019; Dorn

Methods

Though much of the contemporary study of geomorphology is tied to quantitative measurement and modeling, the origin of the field of geomorphology in natural history has meant that observation and interpretation have always been a fundamental part of a geomorphologist's research (Rhoads and Thorn, 1996). Indeed, the complexity of geomorphic systems and unique suite of conditions within a given landscape-system fundamentally requires observation and field investigation to understand natural

Landforms as evidence of and response to drainage integration

Basin-scale adjustment to integration processes is largely driven by base-level change, which, itself, is a result of integration. Table 1 summarizes our analysis of how base level changed throughout the late Pliocene and Quaternary in response to drainage integration. In what follows, we first present a variety of landforms tied directly and specifically to basin landscape evolution driven by integration processes along specific reaches of the Salt and Verde rivers. We then highlight classic

Discussion

The location of much of the study area (Fig. 1, Fig. 3) in the Sonoran Desert means that classic desert landforms such as pediments (Kesel, 1977; Péwé, 1978; Parsons and Abrahams, 1984; Pelletier, 2010) and alluvial fans (Melton, 1965; Bull, 1984; Huckleberry, 1994; Melton, 1965; Bull, 1984; Huckleberry, 1994) evolved as a product of drainage integration processes that established through-flowing drainages throughout central Arizona. Our analysis (Table 1) indicates that extensive pediments of

Conclusion

The establishment of a through-flowing river system in a setting formerly occupied only by endorheic drainage can dramatically alter the geomorphology of an integrated basin. The Salt River and Verde River systems of central Arizona cross the Basin and Range extensional tectonic setting and likely established their present course sometime between ca. 2.2–2.8 Ma. A series of drainage integration events occurred that connected the basins through which they now flow. Landforms (e.g., stream

Declaration of competing interest

In regards to the research and findings reported in this paper:

  • 1)

    The authors of this manuscript have no competing financial interests or investments.

  • 2)

    Nor do they have personal relationships or conflicts of interest.

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