Type and structure of sieve deposits in the terminal strip of low relief alluvial fans (Rambla Castellarda, Valencia)

Abstract

This work describes the deposits of the distal terminal fringe of three small alluvial fans located on the Rambla Castellarda, second tributary of the Turia river by its left margin. These fans occupy the space of abandoned gravel extraction areas and are active since the beginning of the present century. They are characterized by having low slopes, ending in waterlogged areas in times of flooding and being formed by sieve bars that reach between 30% and 50% of its surface. The analysis of these deposits reveals three types of sieve bars, of which the lobed ones are the predominant. The internal structure of these bars is that of a porous and permeable deposit with little matrix and structured in small coarsening upwards sequences from silts and sands to pebbles. The arrangement of these sequences is that of a vertical stacking in horizontal position or with cross stratification. These lobes advance frontally on brown silts deposited during the waterlogging of the alluvial valley in avenues, and with which they have a net non-erosive contact.