Abrupt landscape change post–6 Ma on the central Great Plains, USA

Abstract

The principal control on landscape evolution in the central Great Plains of the United States over the past 10 m.y. is a contentious subject. New sedimentary data collected from Late Miocene Ogallala Group and Pliocene Broadwater Formation of the Nebraskan Great Plains demonstrates a twofold increase in the median grain size (from 20 mm to >40 mm) exported from the Rocky Mountains across the Miocene-Pliocene boundary. Paleoslope reconstructions derived from these data support the tilting of the Miocene Ogallala Group after 6 Ma, but demonstrate that the transport slope of the lower part of the unconformably overlying Pliocene succession is identical to the present-day slope. These data allow us to constrain the timing of differential uplift in the Great Plains to between 6 and 3.7 m.y.; the wavelength and short duration of this tilting are best explained by the initiation of localized dynamic topography. Our results also suggest a threefold to fourfold increase in specifi c stream power at this time, meaning that Pliocene rivers draining the central Rockies were considerably more competent than their Miocene predecessors. Incision during this period was not continuous. A signifi cant episode of aggradation from 3.7 to 2.5 Ma is best explained by high rates of sediment supply relating to the warm, wet mid-Pliocene climate optimum. The modern pattern of incision on the Great Plains occurred from 2.5 Ma, and not from the end of the Miocene as is sometimes supposed, refl ecting the onset of major Northern Hemisphere glaciation.

Controls on Pebbles’ Size and Shape in Streams of the Swiss Alps

“…In mountainous streams, the size and shape of gravels bear crucial information about the transport dynamics and flow strengths of these streams (Hjulström 1935;Shields 1936;Blissenbach 1952;Koiter et al 2013), the sources of sediment, the mechanisms of erosion and transport (Whittaker et al 2007;Duller et al 2012;Attal et al 2015), and the controlling conditions, such as uplift and precipitation (e.g., Heller and Paola 1992;Robinson and Slingerland 1998;Foreman et al 2012;Allen et al 2013;Foreman 2014). Likewise, a stream's bedload material also depends on the bedrock's fabric and the petrological properties of the catchments where the sources of the deposits are (Parker 1991;Paola et al 1992a;Attal and Lavé 2006).…”

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

“…6B, the river incised by ~90m into the Ogallala Group before aggradation, during deposition of the Broadwater Formation, back to almost exactly the same level (see Fig. 1(c) of Duller et al, 2012). The local relief thus represents the incision since the MidPliocene climatic optimum and began at ~2.5 Ma according to Duller et al (2012 The total incision (and thus uplift) decreases from ~500 m at Denver to ~150 m in western Nebraska (Fig. 6B) and to a few dozen metres in central Nebraska (Fig.…”

“…McMillan et _ al., 2002;Heller et _ al., 2003;Condon, 2005;Wobus et _ al., 2010). These deposits are inset by younger fluvial deposits, of the Broadwater Formation, which provide a record of fluctuations in climate and palaeo-hydrology in and around the Mid-Pliocene climatic optimum (Duller et al, 2012). In the locality depicted in Fig.…”

Spatial and Temporal Patterns of Ogallala Formation Deposition Revealed by U-Pb Zircon Geochronology

“…Plains, rather than increased deposition of highland-sourced clasts (Leonard, 2002;Galloway et al, 2011;Duller et al, 2012). A middle Miocene global increase in sedimentation that accelerated during the Pliocene (Molnar, 2004), as well as late-Cenozoic conglomerates adjacent to mountain ranges worldwide (Molnar and England, 1990) are attributed to climate change rather than globally-synchronous tectonic upheaval for which there is no evidence (Molnar and England, 1990;Molnar, 2004).…”

“…Mountains (Trimble, 1980;Leonard, 2002;McMillan et al, 2002;McMillan et al, 2006;Riihimaki et al, 2007;Galloway et al, 2011;Duller et al, 2012). However, this welldocumented uplift episode is probably contemporaneous with Pliocene incision in the High…”