Catchment lithology as a major control on alluvial megafan development, Kohrud Mountain range, central Iran

Abstract

The relative importance of tectonics, climate, base level and source lithology as primary factors on alluvial‐fan evolution, fan morphology and sedimentary style remain in question. This study examines the role of catchment lithology on development and evolution of alluvial megafans (>30 km in length), along the flanks of the Kohrud Mountain range, NE Esfahan, central Iran. These fans toe out at axial basin river and playa‐fringe sediments towards the centre of basin and tectonics, climatic change and base‐level fluctuations, were consistent for their development. They formed in a tectonically active basin, under arid to semiarid climate and a long term (Plio‐Pleistocene to Recent) change from wetter to drier conditions. The key differences between two of these fans, Soh and Zefreh fans, along the west and south flanks of this mountain range, is that their catchments are underlain by dissimilar bedrock types. The source‐area lithologies of the Soh and Zefreh fans are in sedimentary and igneous terrains, respectively, and these fans developed their geometry mainly in response to different weathering intensities of their catchment bedrock lithologies. Fan surface mapping (based on 1/50000 topographic maps, satellite images, and fieldwork), reveals that the geomorphic evolution of these fans differs in that the relatively large‐scale incision and through trenching of the Soh fan is absent in the Zefreh fan. Whereas the limited sediment supply of the Soh fan has resulted in a deep incised channel, the Zefreh fan has remained aggradational with little or no trenching into proximal to medial fan surface due to its catchment bedrock geology, composed mainly by physically weathered volcaniclastic lithology and characterized by high sediment supply for delivery during episodic flash floods. Sediment supply, which is mainly a function of climate and source lithology, is a dominant driver behind the development of fan sequences in alluvial megafans. Copyright © 2012 John Wiley & Sons, Ltd.

Controls of basin margin tectonics on the morphology of alluvial fans in the western Ganga foreland basin's piedmont zone, India

“…Whereas the tectonic influence on fan morphology is quite pronounced in piedmonts adjacent to actively rising mountains, the role of source area lithology cannot be undermined in controlling the alluvial fan morphology (e.g., Arzani, ; Stokes & Mather, ). Source area lithology directly controls sediment flux into the basin through its erodibility and thus influences fan aggradation and/or progradation (Arzani, ). In other words, the erodibility of the source area directly correlates with the alluvial fan area.…”

“…As a matter of fact, the FIGURE 7 Source area lithology (based on Karunakaran & Ranga Rao, 1979;Valdiya, 1980), and transverse and longitudinal profiles of the (a), Nandhaur Fan, and (b) Kalaunia Fan [Colour figure can be viewed at wileyonlinelibrary.com] alluvial fan development depends upon two main factors, (a) the characters of the accommodation space in the basin and, (b) sediment supply from the catchment (Goswami, 2016). Sediment supply from the source to sink largely depends upon the tectonics, climate, base level, lithology, geomorphology, and morphometry of the drainage basin (Bull, 1962;Hook, 1968;Calvache, Viseras, & Ferńandez, 1997;Harvey, 2002;Harvey et al, 2005;Blair & McPherson, 2009;Shukla, 2009;Goswami et al, 2009;Arzani, 2012;Bahrami, 2013;Goswami, 2016; and references therein). The characters of the accommodation space on the other hand are closely related to the tectonic activities along the basin-margin and/or in the basin, climate-induced variations in sediment and water influx into the basin and base-level fluctuations (Bahrami, 2013;Clarke, 2015;Goswami et al, 2009;Viseras, Calvache, Soria, & Fernández, 2003;Weissman, Bennett, & Lansdale, 2005;Weissman, Mount, & Fogg, 2002).…”

“…Whereas the tectonic influence on fan morphology is quite pronounced in piedmonts adjacent to actively rising mountains, the role of source area lithology cannot be undermined in controlling the alluvial fan morphology (e.g., Arzani, 2012;Stokes & Mather, 2015).…”

Depositional processes in the distal part of a large alluvial fan's feeder channel in Himalayan foothills, India

“…They form downslope of the pointapex of the fan-where a channel exits the mountainous catchment (Drew, 1873;Bull, 1977). Lecce, 1991;Koss et al, 1994;Whipple and Trayler, 1996;Calvache et al, 1997;Blair and McPherson, 1998;Harvey, 2002;Viseras et al, 2003;Harvey, 2005;Shukla, 2009;Goswami et al, 2009;Salcher et al, 2010;Waters et al, 2010;Storz-Peretz et al, 2011;Arzani, 2012;Bahrami, 2013;Goswami and Mishra, 2013;Fontana et al, 2014, and references therein). Most of these studies have been devoted to understanding the influence of tectonics, climate, lithology and base-level fluctuations on alluvial fan development (e.g.…”

The role of long‐term human impact on avulsion and fan development

“…Fluvial fans are scenes of recurrent avulsions and owe their existence and typical cone‐shaped depositional landform to avulsion activity (Gohain and Prakash, ; Horton and DeCelles, ; Makaske et al , ; Leier et al , ; Assine, ; Walstra et al , , Walker and Fattahi, ; Arzani, ). They are typically located at mountain fronts where rivers are released from their confinement and discharge conditions promote frequent avulsions.…”