Alternating diatomaceous and volcaniclastic deposits in Milos Island, Greece. A contribution to the upper Pliocene–lower Pleistocene stratigraphy of the Aegean Sea

Abstract

In the northern part of Milos Island, South Aegean Volcanic Arc, a stratigraphic succession spanning the late Pliocene and early Pleistocene exceeds 300 m in thickness and records an alternation of products from submarine volcanic explosive events and fossiliferous, both siliceous and carbonate marine sedimentary rocks. The accumulation of volcaniclastic deposits took place under subaqueous marine conditions as evidenced by sedimentary features, scarce fossil remains and the local presence of burrow traces. Each major volcanic event was represented by the accumulation of thick-bedded pumice and glassy tuffs, succeeded by the deposition of marine sediments composed mainly of laminated diatomaceous marlstone and sandy limestone. The silica content of the diatomaceous sediments varies from 39% to 70%, mostly in the form of biogenic opal-A. SiO2/Al2O3 ratios ranging from 5 to 21 indicate a varied contribution of reworked volcanic grains. The sequential arrangement of basinal diatomaceous marlstone and shoreface sandy limestone deposits suggests that the depth of water was not great, which is also consistent with features observed in the volcaniclastic deposits. Calcareous nannofossils from the upper part of the succession of northern Milos allow biostratigraphic correlation with nannofossil biozones MNN19a–MNN19b across the Gelasian/Calabrian boundary within the early Pleistocene. A late Pliocene (Piacenzian) age has been estimated for the lower part of the section, where biozone MNN16a has been documented. Diatoms, planktonic foraminifera and calcareous nannofossil assemblages in the diatomaceous beds point to deposition in a partially closed, relatively shallow marine environment. In this setting,warmand stratified water conditions can be concluded for the Piacenzian diatomaceous beds whereas highly productive cool waters are inferred from the Gelasian/Calabrian diatomite.