VULCANOGENIC GLASS REMAINS IN TONSTEINS OF THE SAAR-LORRAINE EARLY CARBONIFEROUS - ORIGIN AND EXTENT OF PYROCLASTIC DEPOSITS

Tonsteins in the Carboniferous of the Saar-Lorraine basin are known since about 170 years. Volcanic glass remains, however, have been proven as constituents of the tonstein only recently. They occur in tonsteins of Stephanian A: KTst 0 = 950; Westphalian D: KTst 1 = 700; Westphalian C: KTst 3 = 400, KTst 4a = 330, KTst 4a-beta = 322, KTst 4 = 320, KTst 5 = 300 and KTst 6 = 270. Tonsteins with volcanic glass fragments amount to 18% of the total tonsteins observed in the limnic Saar-Lorraine basin. They are important to applied geology, e.g. for seam identification and correlation, as well as for scientific reasons, namely for the determination of provenance and genesis of tonsteins. The volcanic remains consist of tiny glass splinters, glass fragments, and of fragments with well preserved gasbubble texture. The welded splinter texture is typical of welded pyroclastic ash deposits. Much of the glass has been devitrified to microcrystalline kaolinite. The indisputable evidence of volcanic remains is essential when considering the genesis of tonsteins, as they provide proof that tonsteins are primarily composed of eolian pyroclastic constituents which were altered by chemical weathering and diagenesis. For the 43 horizons of the coal tonsteins found in the Upper Carboniferous of the Saar-Lorraine basin, a pyroclastic eruption quantity of at least 8.2 km3 of solid volume or 20.5 km3 of bulk volume is assumed. The eruptions possibly took place along the nearby deep-seated Metz fault at the southern rim of the Hunsruck. This fault, reaches below the Moho according to reflection seismic.