Coastal subsidence based on speleothem ages: preliminary evidence from Granada coast (Spain)

In karst coastal areas, speleothems preserved in karst caves were widely used to date the seashore emersion, as well as to infer its uplifting rate. Likewise, speleothems would be also used to approach rates of coastal subsidence. Landscape evolution and tectonic driving of Southern Spain is being investigated by relief GIS-analysis, geomorphological indicators, fault analysis and geochronology in the framework of the Spain-funded project titled “Morphomed” (PID2019-107138RB-I00). In the Westernmost Mediterranean Sea, Granada coast shows carbonate cliffs interrupted by bays and inlets filled by delta, alluvial fan and other deposits. Alluvial sediments were deposited on marine terraces located below sea level according to previous gravity and seismic studies. Cliffs barely preserve sediments such as landslides, alluvial fan deposits and karst deposits within fracture caves. Karst deposits comprise speleothems and cave detrital infills, containing fossils of continental gastropods (probably genus Iberus). A total of fifteen speleothems collected in a transect from sea level to 220 m altitude, were dated by the ²³⁸U-²³⁰Th method in Jiaotong University (China). The dating revealed ages older than 650 ka for speleothems located throughout the transect from the cliff bottom to the higher altitude areas. Field observations and datations points out the occurrence of a Chibanian karst in Granada cliff coast, but with a lack of any documented uplifting evidence (e.g., Upper Pleistocene-Holocene speleothems / raised marine deposits). This fact clashes with the occurrence of well-developed marine terraces and clear emerged Quaternary marine deposits reported in nearby shore areas sited to the West (Malaga coast) and to the East (Almeria coast) of the study area. Altogether, preliminary results suggest the relative subsidence of Granada coast since at least the Chibanian, which agrees the occurrence of submerged marine terraces and the tectonic setting defined by previous works.