Controls on fan development — evidence from fan morphometry and sedimentology; Sierra Nevada, SE Spain

Abstract

We have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the Late Pleistocene as a result of the recent uplift of the Sierra Nevada (Betic Cordillera, Spain). Three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans, in connection with a decrease in the volume of fines available in the source areas. The larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment, with the appearance of less elongated fans. In the rest of the system, where subsidence is less, more elongated fans appear, with the development of incised channels and irregular distribution of sediment in depositional lobes. This involves the appearance of markedly asymmetric transverse profiles, as well as lengthy recurrence between the sedimentation events on particular sectors of the fans, where headward-eroding gullies develop. The lithology of the source area, where intensely fractured rocks are found, is responsible for an important sediment supply and a significant degree of clast sorting from the source area. Consequently, a weak longitudinal trend in particle size can be recognised, which influences the predominance of longitudinal constant-slope profiles and anomalous relations between both fan area and fan slope and their drainage areas. Recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments, where mass flows are trapped, and the fans present a subsequently higher proportion of sheet flows. Recent piracy phenomena can be recognised in some of the drainage basins, which indicate rejuvenation of the source area, in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile. Due to the recent nature of the processes, the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area. 0 1997 Elsevier Science B.V.

Subaerial terminoglacial fans III: overview of sedimentary characteristics and depositional model

“…Most of them are interpreted as an effect of lateral shifting of sedimentary subenvironments on the fans, such as channels and overbank areas (Viseras & Fernandez, 1995;Jo et al, 1997), channels and playas (Hubert & Hyde, 1982) or channels and mass-flow areas (Calvache et al, 1997). These cycles can be regarded as records of the the evolution of braided channels and their infillings (the so-called channel cycle of Godin, 1991).…”

A classification scheme for fluvial–aeolian system interaction in desert-margin settings

“…Alluvial fans commonly form extensive bajada where multiple catchments are present in close proximity along mountain fronts in arid settings (e.g., Padul Depression bajada, Spain, Calvache et al, 1997; bajada of northern Oman, Rodgers and Gunatilaka, 2002;Death Valley, Nevada, USA, Harvey, 2011). Similarly, distributive fluvial systems form networks of channels where they pass out onto low relief desert plains (cf.…”

Tectonic and geomorphic controls on the fluvial styles of the Eslida Formation, Middle Triassic, Eastern Spain

“…16 to 2.0 mm/yr, according to the data compiled by Gutierrez et aL (1998), Calvache et al (1997 and Verges et al (1996) depending on the nature of the bedrock and climate. As the basement exposed along the rift shoulders consists of slates and quartzites, indurated but not heavily tectonised, the lower estimates apply to the Eslida Fm period of sedi mentation is about 2-2.5 Ma.…”