Biostratigraphic control of Neogene volcanism in Sierra de Gata (south-east Spain)

Abstract

The chronology of the magmatic activity in Sierra de Gata is established on the basis of the study of planktonic foraminifera in sediments related to volcanites. Data were obtained from intercalated sediments, from fillings of fissures and holes in the volcanites, as well as from deposits in nearby basins, which were weakly affected by the volcanic activity. Volcanic activity began (stage A) with small submarine flows (Ao phase) intercalated in pelagic marls containing Globigerinoides bisphericus but without Praeorbulina glomerosa, which can be located at around the boundary between the N.7 and N.8 zones of Blow (uppermost Burdigalian). More significant eruptions are observed in association with sediments containing Praeorbulina glomerosa (N.8 zone, Lower Langhian) and others deposited around the FAD of Globorotalia praemenardii, which is used as marker for the Langhian-Serravallian boundary (phases A1 and A2 respectively). As regards the most important period of generalized volcanic activity in the region (stage B), sediments are found containing the Neogloboquadrina siakensis group, Globorotalia menardii and Globigerina nepenthes (N.14 zone, Upper Serravallian) and the dextral-coiling Neogloboquadrina acostaensis group (N.16 zone, Lower Tortonian and lower part of the Upper Tortonian). New volcanic emissions took place during the Late Tortonian and the earliest Messinian, but they only affect local areas of Sierra de Gata: the group of Coastal Volcanoes arose in the littoral area during the early and/or middle part of the Late Tortonian; the Rodalquilar Group developed in the central sector within the Late Tortonian-earliest Messinian interval; finally, the Carboneras lJpper Volcanites were emitted in the northern area and also in the Serrata de Níjar shortly after the Globorotalia mediterranea FAD (Early Messinian). The biostratigraphic results are compared with the radiometric ages of the volcanites, and agree well for stages A and B, and for the Coastal Volcanoes, but there is a considerable disagreement between them for the Rodalquilar Group. Radiometric datings of the Carboneras Upper Volcanoes are not available.