GLASS VS. GLASS: BEDIASITES AND MELT LITHOLOGIES IN THE EYREVILLE DRILL CORE B; CHESAPEAKE BAY IMPACT STRUCTURE, USA

While the genetic connection of the North American tektites strewn field and the related microtektites in upper Eocene sediments to the Chesapeake Bay impact event 35 m. yrs. ago is undisputed, their precursor materials, and the physical constraints are not understood in detail yet. We focus on geochemical properties of Bediasites, microtektites, and melt lithologies in the USGS-ICDP Eyreville drill core B. Gas analyses on four Bediasites by directly coupled evolved gas analyzing system (DEGAS) up to 1450°C show that this group of tektites is totally dry, i.e., less than 10 ppm H₂O, much less than published by previous authors. The glass foams above 1300°C. At this temperature bubbles/vacuoles release H₂O, fluorine, CO₂ and CO. Chemically, these tektites are quite homogeneous, and differ from glass shards in the suevites mainly by much higher Al₂O₃ (15.5 to 16.6 wt%), and lower CaO (about 0.45 wt%) contents. Trace element and isotope determinations (TIMS, LA-ICP-MS) as well as electron energy loss spectroscopy (EELS) are currently performed in order to identify precursor lithologies and redox conditions during glass formation.