Epiclastic sedimentation during the Upper Miocene-Lower Pliocene volcanic hiatus of Gran Canaria: Evidence from Sites 953 and 954

Abstract

The geologic history of a volcanic oceanic island is recorded in the sediments deposited in its volcanic apron, including noneruptive periods that are typically poorly represented or missing from subaerial outcrops. In this study, the history of Gran Canaria during the Gran Canaria 'volcanic hiatus,' a period of volcanic quiescence from 8.3 to 4.3 Ma, is examined in detail using multiple lines of evidence from lithology, grain-size analysis, mineralogy, and micropaleontology of turbidites. Examined are Sites 953 and 954 on the north flank of the Gran Canaria apron. Sediments deposited during the late Miocene/early Pliocene noneruptive period on Gran Canaria bear a number of qualities that reflect the environment of their source. They were deposited slowly (~22 m/m.y.), because there was no active volcanism adding fresh volcaniclastic debris to island reservoirs as at other times during island development and because the surface area of the island was probably small. Turbidite structures and textures indicate transport by low-density turbidity currents, rather than high density types observed in intervals affected by active eruption. Benthic foraminifer assemblages indicate that the volcaniclastics were stored on the upper slope prior to turbidite transport to the apron, and show little influence from a shelf reservoir as do faunas from the late Pliocene and Quaternary. The composition of the clastic particles indicates that erosion dissected volcanic formations older than the volcanic hiatus, mainly the lava flows and ignimbrites of the Fataga Group and the basaltic shield of Gran Canaria. We infer the rapid formation of deep barrancos during the geomorphological evolution of the island when volcanic activity was absent. Active volcanism returned during the latest part of the 'volcanic hiatus' at ~5.5 Ma in the form of submarine hydroclastic basaltic activity (pre-Roque Nublo volcanic phase), marked by the presence of hydroclastic particles and by a change in the composition of the clinopyroxenes of the sand fraction.