Downslope-migrating sandwaves and platform-margin clinoforms in a current-dominated, distally steepened temperate-carbonate ramp (Guadix Basin, Southern Spain)

Abstract

During the Late Tortonian, platform-margin-prograding clinoforms developed at the south-western margin of the Guadix Basin. Large-scale wedge-shaped deposits here comprise 26 rhythms of mixed carbonate–siliciclastic bedset packages and marl beds. These sediments were deposited on a shallow-water, temperate-carbonate distally steepened ramp. A downslope-migrating sandwave field developed in this ramp, with sandwaves moving progressively down the ramp to the ramp-slope, where they destabilized, folded and occasionally collapsed. Downslope sandwave migration was induced by currents flowing basinwards. During the Late Tortonian, the Guadix Basin was open north to the Atlantic Ocean via the Dehesas de Guadix Strait and connected east to the Mediterranean Sea through the Almanzora Corridor. According to the proposed current circulation model for the Guadix Basin for this time, surface marine currents from the Atlantic entered the basin from the northern seaway. These currents moved counter-clockwise and shifted the sediment on the ramp, forming sandwaves that migrated downslope. The development of platform-margin prograding clinoforms by the basinward sediment-transport mechanisms inferred here is known relatively poorly in the ancient sedimentary record. Moreover, these wedge-shaped geometries are similar to those found in some shelves in the Western Mediterranean Sea and could represent an outcrop analogue to (sub)-recent, platform-margin clinoforms revealed by high-resolution seismic studies.