Sedimentary processes in a submarine canyon excavated into a temperate‐carbonate ramp (Granada Basin, southern Spain)

Abstract

During the Late Tortonian, shallow‐water temperate carbonates were deposited in a small bay on a gentle ramp linked to a small island (Alhama de Granada area, Granada Basin, southern Spain). A submarine canyon (the ‘Alhama Submarine Canyon’) developed close to the shoreline, cross‐cutting the temperate‐carbonate ramp. The Alhama Submarine Canyon had an irregular profile and steep slopes (10° to 30°). It was excavated in two phases reflected by two major erosion surfaces, the lowermost of which was incised at least 50 m into the ramp. Wedge‐shaped and trough‐shaped, concave‐up beds of calcareous (terrigenous) deposits overlie these erosional surfaces and filled the canyon. A combination of processes connected to sea‐level changes is proposed to explain the evolution of the Alhama Submarine Canyon. During sea‐level fall, part of the carbonate ramp became exposed and a river valley was excavated. As sea‐level rose, river flows continued along the submerged, former river‐channel, eroding and deepening the valley and creating a submarine canyon. At this stage, only some of the transported conglomerates were deposited locally. As sea‐level continued to rise, the river mouth became detached from the canyon head; littoral sediments, transported by longshore and storm currents, were now captured inside the canyon, generating erosive flows that contributed to its excavation. Most of the canyon infilling took place later, during sea‐level highstand. Longshore‐transported well‐sorted calcarenites/fine‐grained calcirudites derived from longshore‐drift sandwaves poured into and fed the canyon from the south. Coarse‐grained, bioclastic calcirudites derived from a poorly sorted, bioclastic ‘factory facies’ cascaded into the canyon from the north during storms.

Tectonic control on the palaeogeographic evolution of thrust‐top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)

“…Dominance of the Hapalidiales as the major rhodolith‐forming taxa indicates deposition in middle‐outer ramp settings, at some tens of metres of water depth (Braga & Aguirre, 2001, 2004). In different Mediterranean‐ and Atlantic‐linked Betic Neogene basins, similar factory facies accumulated offshore shoal systems (Aguirre & Braga, 2022; Braga et al., 2006; Martín et al., 1996, 2004; Puga‐Bernabéu et al., 2007, 2008).…”

“…Occasionally, fine‐grained matrix‐supported conglomerates reached deeper settings, as erosive bodies interspersed in finer sediments such as silts and fine sandstones (Facies 11; see below). They can represent reworked conglomerates from shallower settings mobilized offshore by high‐energy events, such as storms (Aguirre, 2000; Braga et al., 2006; Puga‐Bernabéu et al., 2008, 2014). Capuano (1991) described similar deposits in the Pliocene conglomerates and coarse sands deposited in the Montecalvo in Foglia piggyback basin, NE Italy.…”

Relationships between high‐magnitude relative sea‐level changes and filling of a coarse‐grained submarine canyon (Pleistocene, Ionian Calabria, Southern Italy)

“…A possibility is that the sea‐level dropped below the shelf edge leading to a first excavation phase as an incised valley, followed by a drowning (e.g. Puga‐Bernabéu et al. , 2008).…”

Evolution of a carbonate delta generated by gateway‐funnelling of episodic currents

“…Turbidity current deposits, on the other hand, comprise a substantial part of some cool‐water carbonate accumulations (Hansen, ; Pomar & Tropeano, ; Pomar et al ., ; Massari & Chiocci, ; Puga‐Bernabéu et al ., ). These deposits are commonly attributed to storm events dismantling the sea floor and delivering vast amounts of skeletal debris to the platform edge, where sediment cascades evolve into turbidity currents due to the excess weight of the sediment–water mixture with respect to the ambient seawater.…”

“…(). An important mechanism for the removal of sediment from cool‐water carbonate platforms are currents associated with the offshore migration of subaqueous dunes, which may generate thick sequences of cross‐bedded deposits on the platform slope (Pomar & Tropeano, ; Pomar et al ., ; Massari & Chiocci, ; Puga‐Bernabéu et al ., , ).…”