Petrographic analysis of eolian detrital sediments in beach-dune systems of La Graciosa Island (Canary Islands)

Abstract

La Graciosa island is formed by volcanic and sedimentary processes since the Middle Pleistocene, features low-lying plains where stand out volcanic cones. Approximately half of its surface is covered by aeolian sands (jables) and muddy sediments occasionally in endorheic basins. Studies were conducted on six beach-dune systems distributed across the northern, eastern, and southern sectors of the island. Only the northern systems (Las Conchas and Lambra beaches) are currently active; the others are semi-active, with no recent marine sand inputs. A total of 21 aeolian and 5 endorheic basin detrital samples were petrographically analyzed to determine the composition and relative abundance of sand grains. The predominant sands are bioclastic (average of 77.5%; σ = 8.6), mainly composed of mollusk remains (55%) and fragments of red coralline algae (22.5%). Terrigenous components (volcanic rock fragments and sedimentary intraclasts) account for 22.5%, with intraclasts being more abundant (14.5%; σ = 5.9) and in lower proportion volcanic terrigenous with 8% (σ = 1). Endorheic basin muddy sands consist almost exclusively of intraclasts (98.5%). Slight variations in abundance percentage occur both among different eolian systems and within them, influenced by sample location and, the geological and geomorphological nearby elements.