Volcanic Deposits in the Black Sea – Seismic Recognition Criteria for Differentiating Volcanics from Carbonates

Abstract

Volcanics of various types have been documented in the Black Sea. Complete, intact buried volcanoes as well as partially preserved beheaded volcanoes are observed and sometimes resemble carbonate buildups. Isolated volcanoes as well as volcano clusters comprising volcanic massifs are present. In addition to volcanic edifices, volcanic extrusives also have been observed and documented. Seismic recognition criteria for volcanoes have been developed based on observations from 3D seismic data. Some of these criteria are manifested in section view, while others require a plan view perspective: 1) Volcanic cones with sharp tops and concave-up slopes. Observed volcano flank slopes average 11 degrees grading up to 25 degrees near the tops. 2) Concave-upwards onlapping reflections. 3) Cone-in-cone patterns observable in section view; in plan view the cone-in-cone architecture is expressed as slightly rugose concentric circles. 4) A narrow region of seismic data disruption within the substrate below the volcano immediately beneath the center of the cone. 5) High amplitude, small circular reflections (i.e. mega-amplitude “bursts”) can sometimes be observed within the volcanic cone. 6) volcanic massifs tend to be characterized by internal high-amplitude discontinuous reflections. The implication of intact volcanic cones is that they were formed entirely below wave base. This suggests that the substrate upon which they built must have been at a water depth at least as deep as the relief of the cone. Those volcanoes that have formed subaerially, at least in part, appear beheaded and tend to approach a flat-topped architecture. Where erosion by subaerial and wave processes occurs, resulting volcaniclastics are redistributed in the form of prograding clinoforms. Extrusive volcanics in the form of lava flows have also been observed. These deposits are commonly expressed as high-amplitude reflections that terminate abruptly. In some instances, discrete flow lines with distributive patterns can be observed. Some of these high-amplitude fields appear to be related to fault systems that could have acted as volcanic feeder systems or conduits connecting deeply-buried magma chambers to the surface. Given the context of these extrusives, most of them appear to have been subaqueous.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014