NEOTETHYAN LATE CRETACEOUS VOLCANIC ARC HYDROTHERMAL VENT FAUNA

Abstract

The barite-polymetallic ore zone of the Late Cretaceous Madneuli volcanogenic massive sulfide (VMS) deposit in the Republic of Georgia contains large tube worm fossils that represent the first ancient hydrothermal vent fauna to be identified from a volcanic arc setting and very likely the shallowest ancient example yet found. The fossil tube walls are formed of an unusual quartz, barite, pyrite, and galena mineral assemblage, rather than only pyrite as in other vent fossils; this probably reflects the low-temperature, high-salinity vent chemistry at the time of preservation, as deduced from fluid inclusion analyses. The Madneuli vent fauna is one of three examples that occurred over a time span of ˜6 m.y. in an area of the Neotethyan Ocean that was as tectonically complex as the present-day west Pacific. The ancient and modern vent faunas appear to occur in a similar range of tectonic settings and bathymetry.