Abstract:
The extensive exploration of the ocean floors during the past two decades has gradually led to the recognition of the importance of volcanogenic clastic sediments. Sampling by drilling, piston-coring and dredging from mid-ocean ridges, ocean basins and island arc environments has shown that several distinct lithologic types of volcanogenic sediments occur. They include air-fall ash layers, hyaloclastites, pyroclastic flow deposits and turbidites with an epiclastic, pyroclastic, or hyaloclastic source, to name but a few. The generation of these deposits includes a great variety of processes, such as disruptive vesiculation of magma, spalling and granulation of magma upon quenching, and phreatomagmatic explosions. A review is presented here of the principal processes now recognized in the production, transport and deposition of volcanogenic clastic sediments in ocean basins and at mid-ocean ridges. The recent discovery of numerous hyaloclastite deposits in DSDP holes near mid-ocean ridges, hot spots and within ocean basins emphasizes the important role of basaltic volcanism in the generation of deep-sea volcanogenic sediments. Such hyaloclastites may owe their origin to either in situ granulation and spalling of lava erupted on the deep-sea floor, or they may form at the air-sea interphase on volcanic islands, during granulation, spalling and phreatomagmatic explosions, to be transported and deposited in the deep ocean by slumping, debris flows, and turbidity currents.