Granulometric study of the Hanaupah Fan, Death Valley, California

Abstract

We applied new granulometric techniques to the various surfaces of the Hanaupah Fan, Death Valley, California, namely the Q1 surface, with an estimated age of 800-490 ka, the younger Q2 (170-105 ka) and Q3 (50-14 ka) surfaces, the <14 ka deposits of the incised channel, and to a (c. 14 ka) Lake Manly shoreline deposit at the northern periphery of the fan. We used these techniques to generate quantitative information on surface clast grain-size distributions, clast sphericity, roundness, and clast orientation to provide a data set that could be used to define fan-segment surfaces, and to help interpret fan genesis. Grain-size analyses were carried out by photo-sieving of 139 surface pictures, by petrographic identification of samples taken in the incised channel, and by identification and measuring of the largest clasts (1452 measurements) on the Q3 surface. The results show that all fan-segment surfaces, regardless of age, have similar size distributions, with a well-defined gravel mode of −2·3 to −3·0 phi, and are poorly to moderately sorted. Samples from the incised channel have distributions that are very similar to each other, regardless of distance from the apex, but display reduced sorting compared to the fan surfaces (which largely lack fines, perhaps from winnowing by secondary overland flow). Only the shoreline deposit is different from the other elements, showing a much narrower, well-defined gravel mode (−3·0 phi), and is moderately well sorted. Sphericity and roundness of clasts on all surfaces show only minor differences, similar to the other sedimentary parameters, indicating a remarkable homogeneity of the surfaces of the sediment body. In addition, measurements of the largest clasts (>100 cm long axis) on the Q3 surface showed no discernible trend either with radial distance or with rock type. These data suggest large depositional episodes that produce extensive sedimentary units without differentiation relative to distance from the source. Of the examined parameters, clast orientation is the best predictor of relative age of fan surfaces. Clast orientation in the main channel is bimodal, i.e. the long axes of clasts are either at right angles or parallel to transport direction. This bimodality disappears with increasing age, and the preferred orientation becomes unimodal (long clast axes normal to transport direction) on the Q1 surface. Although the causes of this change are still in debate, use of this parameter as a relative-age dating tool seems possible.

Depositional processes and particle characteristics on fans in the Southern Alps, New Zealand

“…Particles deposited by debris flows are transitional in size and rounding between avalanche and stream-deposited material because of being cushioned by a matrix of finergrained sediment during transport. They are therefore protected from abrasion to some degree (Ibbeken et al, 1998). A majority of particles on the Hooker Corner fan are angular or very angular (Table 3), in comparison to predominantly subangular to angular material observed on a large debris flow fan by Blair (1999a,c).…”

“…This sampling may also overestimate the average particle size because the finer surface sediment may have been removed through winnowing by rain, overland flow, and wind (Blikra and Nemec, 1998;Ibbeken et al, 1998;Blair, 1999c;Gó mez-Villar and García-Ruiz, 2000). Time constraints also dictated that siltstone as well as sandstone particles were sampled.…”

“…Time constraints also dictated that siltstone as well as sandstone particles were sampled. Although the vast majority of sampled particles are composed of sandstone, this introduces a potential complication to the study because, frequently, particle shape is largely a function of source rock lithology and structure (Gardner, 1971;Sauchyn, 1986;Ibbeken et al, 1998;Blair, 1999a).…”

“…Recent studies on this topic have focussed mainly on arid region fans (e.g., Calvache et al, 1997;Ibbeken et al, 1998;Blair, 1999a,b,c), with less attention paid to fans in humid mountain environments (Sauchyn, 1986;Blikra and Nemec, 1998;Gó mez-Villar and García-Ruiz, 2000). The aim of these investigations has been to shed light on depositional processes on fans, their temporal variability, and the geomorphic dynamics of the basin 0169-555X/$ -see front matter D 2004 Elsevier B.V. All rights reserved.…”

Interactions between a cushion plant (Azorella selago) and surface sediment transport on sub-Antarctic Marion Island

“…As an alternative, photogrammetric techniques have been applied for the quantification of grain size parameters since at least the 1970s, especially in river channel hydraulics (Adams, 1979;Ibbeken and Schleyer, 1986;Whitman et al, 2003;Graham et al, 2005a). Many previous photogrammetric studies of sediment grain sizes have involved manually outlining sediment grains on the digital image (Ibbeken and Schleyer, 1986;Ibbeken et al, 1998;Whitman et al, 2003), although, more recently, the focus of photogrammetric studies has been on automating grain detection and data generation (Butler et al, 2001;Sime and Ferguson, 2003;Graham et al, 2005a). In protected, relatively undisturbed areas, such as Marion Island which has Special Nature Reserve conservation status, it is desirable to use techniques such as these photogrammetric methods as they minimise disturbance to the environment.…”