Ground-penetrating radar stratigraphy and dynamics of megaflood gravel dunes by Paul A Carling, Charles S. Bristow, and Alexey S. Litvinov Journal of the Geological Society Volume 173(3):550-559 May 3, 2016 © 2016 The Author(s)‏

Location of the Kuray Basin (K) and the Chuja Basin (C) in the Altai mountains of southern Siberia. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Detail of the location of the Kuray dunefield in the Kuray Basin. Detail of the location of the Kuray dunefield in the Kuray Basin. The main dunefield was formed by reworking of gravel fan deposits of the Tetyo River. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Soviet (undated) vertical aerial photograph of the Kuray dunefield (50 Soviet (undated) vertical aerial photograph of the Kuray dunefield (50.169124°N, 87.921584°E). Soviet (undated) vertical aerial photograph of the Kuray dunefield (50.169124°N, 87.921584°E). The largest dunes occur in the NW corner, to the east of the valley of the Tetyo River. The boxed area shows the approximate area of GPR investigations (see Fig. 5). Palaeoflow left to right. Scale c. 1:30 000; field of view c. 3 km. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) View along the crest of Dune 5 towards the south. (a) View along the crest of Dune 5 towards the south. (b) View to the SW across the dunefield. Black arrow points to the crest of the largest dune (Dune 1) with the pine forest of the Tetyo River immediately behind (see Fig. 3). Photographs were taken from near the confluence of the Chuja and Tetyo Rivers (see Fig. 2). Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Location of GPR and topographic survey-lines in 2010 and 2012 at the western extremity of the Kuray dunefield. Location of GPR and topographic survey-lines in 2010 and 2012 at the western extremity of the Kuray dunefield. Palaeoflow approximately left to right (west to east). Image source: Google Earth, 2015. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Radar stratigraphy for the box-section (see Fig Radar stratigraphy for the box-section (see Fig. 5 for location) (a) without and (b) with migration correction. Radar stratigraphy for the box-section (see Fig. 5 for location) (a) without and (b) with migration correction. The labelled cubes show relative GPR profile location and orientation. The subhorizontal reflections on the north–south profiles 2 and 4 are consistent with strike sections perpendicular to flow and depositional dip confirming that the east–west dip sections are parallel to flow and depositional dip. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Interpretation of five flow-parallel radar profiles (10 m apart) obtained in 2010 for Dune 1. Interpretation of five flow-parallel radar profiles (10 m apart) obtained in 2010 for Dune 1. As well as well-defined cross-sets the radar stratigraphy shows reactivation surfaces and the unconformable interface with the underlying gravel deposits. Palaeoflow right to left. At right are shown representative examples of radar facies: radar facies 1, basal subhorizontal discontinuous discordant reflections; radar facies 2, poorly defined discordant reflections within the stoss toes; radar facies 3, planar inclined reflections dipping steeply (20–30°) downstream; radar facies 4, sigmoid inclined reflections dipping downstream; radar facies 6, low-angle inclined reflections with high attenuation. Radar facies 5 is not present in this image. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) 2012 radar reflections for Dune 1; (b) interpretation of the 2012 radar facies for Dune 1. (a) 2012 radar reflections for Dune 1; (b) interpretation of the 2012 radar facies for Dune 1. As well as well-defined cross-sets the radar stratigraphy shows bounding surfaces and the unconformable interface with the underlying gravel deposits. Palaeoflow right to left. See online version for colour. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) 2012 radar reflections for Dune 2; (b) interpretation of the 2012 radar facies for Dune 2. (a) 2012 radar reflections for Dune 2; (b) interpretation of the 2012 radar facies for Dune 2. The well-defined cross-sets are of low angle. The radar stratigraphy shows bounding surfaces and the unconformable interface with the underlying gravel deposits. Palaeoflow right to left. See online version for colour. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) 2012 radar reflections for Dune 3; (b) interpretation of the 2012 radar facies for Dune 3. (a) 2012 radar reflections for Dune 3; (b) interpretation of the 2012 radar facies for Dune 3. The well-defined cross-sets are relatively steep in contrast to Dune 2. The radar stratigraphy shows bounding surfaces and the unconformable interface with the underlying gravel deposits. Later fill in the lee-side trough has subdued the modern topography. Palaeoflow right to left. See online version for colour. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) 2012 radar reflections for Dune 4; (b) interpretation of the 2012 radar facies for Dune 4. (a) 2012 radar reflections for Dune 4; (b) interpretation of the 2012 radar facies for Dune 4. The well-defined cross-sets are relatively steep. The radar stratigraphy shows bounding surfaces and the unconformable interface with the underlying gravel deposits. Later fill in the dune troughs has subdued the modern topography. Palaeoflow right to left. See online version for colour. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

(a) 2012 radar reflections for Dune 5; (b) interpretation of the 2012 radar facies for Dune 5. (a) 2012 radar reflections for Dune 5; (b) interpretation of the 2012 radar facies for Dune 5. The well-defined cross-sets are of variable steepness. The radar stratigraphy shows bounding surfaces and the unconformable interface with the underlying gravel deposits. Later fill in the stoss-side trough has subdued the modern topography. The air wave is due to the tree visible at the end of the GPR profile in Figure 5. Palaeoflow right to left. See online version for colour. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏

Schematic interpretation of four packages (1–4) of cross-strata separated by bounding reactivation surfaces above a basal unconformity; downlap and truncation of reflections are represented by small arrows. Schematic interpretation of four packages (1–4) of cross-strata separated by bounding reactivation surfaces above a basal unconformity; downlap and truncation of reflections are represented by small arrows. Package 1 consists of irregular stratification, in the upflow position, deposited as an incipient bedform against which steep cross-sets were deposited once steady flow and the bedform were established. Activation surface (AS) represents the bounding surface between radar facies 2 and radar facies 3 and activation of the dune slipface. RS1 is a reactivation surface associated with a subsequent event that represents cutting of the lee side of package 1. Reactivation surface 2 (RS2) represents cutting of the lee side of package 2. Packages 2, 3 and 4 represents renewed deposition of cross-sets in the lee of the bedform stranded after three repeated floods to give a history owing to four floods in total. Paul A Carling et al. Journal of the Geological Society 2016;173:550-559 © 2016 The Author(s)‏