Mud volcanoes in the Alboran Sea: evidence from micropaleontological and geophysical data

During the BASACALB-TTR9 cruise of the R/V Professor Logachev (1999), two mud volcanoes (called Marrakech and Granada) were discovered in the southern sector of the mud diapir province in the West Alboran Basin (WAB). This paper presents micropaleontological and geophysical data on these mud volcanoes from gravity core samples, sidescan sonar (OKEAN) images and high-resolution seismic lines. Mud breccia recovered from the Granada mud volcano is matrix-supported with well-consolidated clasts of limestone, marlstone, claystone, siltstone, sandstone and mudstone, whereas mud breccia from the Marrakech mud volcano contains unconsolidated clasts. The mud breccia matrix contains abundant Miocene calcareous nannofossils (CN), together with Pliocene–Pleistocene species and reworked late Cretaceous and Paleocene–Eocene species. CN dating indicates that clasts in the mud breccia derive from late Cretaceous, Paleocene, Eocene, and probable Miocene sediments. These data suggest that the mud diapirs and mud volcanoes in the WAB can be derived from the olistostromes of Unit VI, the basal stratigraphic sequence in the Alboran Sea basin. Unit VI consists of lower Miocene sediments that incorporated late Cretaceous and Paleocene–Eocene materials and basement-derived rock fragments. The mud volcanic deposits are covered by a thin drape of pelagic marls, suggesting that these two volcanoes are currently inactive. Structures determined on high-resolution seismic profiles across mud volcanoes and surrounding diapirs correspond to the late-stage, Pliocene-to-Quaternary diapir development. This stage is thought to have developed during a compressional tectonic setting that produced folding and wrench tectonics throughout the basin. Mud ascent at that time resulted in active diapirism and mud volcanoes on the seafloor.