Reworked tsunami deposits by bottom currents: Circumstantial evidences from Late Pleistocene to Early Holocene in the Gulf of Cádiz

Younger Sand layers (YSLs) have been identified in drill cores of a Late Glacial to Early Holocene muddy contourite succession from the Gulf of Cádiz. In this study, we evaluate the grain size characteristics of the YSL, which display bi-gradational grading, with inverse grading (from silt to fine- or medium-grained sand) followed by normal grading (from fine- or medium-grained sand to silt). Radiocarbon dating shows that the YSL formed at three distinct times: 1) the Bølling-Allerød (sites U1387 and U1386); 2) the Younger Dryas (site U1390), and; 3) the beginning of the Boreal (site U1389). Ichnological analyses and radiocarbon dating of cores from drill site U1389C indicate that the YSLs consist of reworked materials deposited at a high sedimentation rate. The results of sedimentological analyses, ichnological treatment, spatial distributions, and radiocarbon dating of the YSLs suggest that the possibility of an origin of the YSLs is tsunami-related but later reworked by bottom current. However, the source areas of the sandy sediments remain unclear, although our results show them to be variable and area dependent. Some sandy deposits are transported by the Mediterranean Outflow Water (MOW) from the proximal sector of the Gulf of Cádiz Contourite Depositional System (CDS), which is close to the Strait of Gibraltar. However, in other cases it is more probable that local gravity flows, which are the result of instability on adjacent margins, provide the sandy material.