Abstract-The Kärdla crater is a 4 km-wide impact structure of Late Ordovician age located on Hiiumaa Island, Estonia. The 455 Ma-old buried crater was formed in shallow seawater in Precambrian crystalline target rocks that were covered with sedimentary rocks. Basement and breccia samples from 13 drill cores were studied mineralogically, petrographically, and geochemically. Geochemical analyses of major and trace elements were performed on 90 samples from allochthonous breccias, sub-crater and surrounding basement rocks. The breccia units do not include any melt rocks or suevites. The remarkably poorly mixed sedimentary and crystalline rocks were deposited separately within the allochthonous breccia suites of the crater. The most intensely shockmetamorphosed allochthonous granitoid crystalline-derived breccia layers contain planar deformation features (PDFs) in quartz, indicating shock pressures of 20-35 GPa. An apparent Kenrichment and Ca-Na-depletion of feldspar-and hornblende-bearing rocks in the allochthonous breccia units and sub-crater basement is interpreted to be the result of early stage alteration in an impact-induced hydrothermal system. The chemical composition of the breccias shows no definite sign of an extraterrestrial contamination. By modeling of the different breccia units with HMXmixing, the indigenous component was determined. From the abundances of the siderophile elements (Cr, Co, Ni, Ir, and Au) in the breccia samples, no unambiguous evidence for the incorporation of a meteoritic component above about 0.1 wt% chondrite-equivalent was found.

The roundness and surface texture of quartz grains were studied in Devonian sediments of 32 drill cores. Roundness was estimated in more than 800 samples and surface textures were examined under scanning electron microscope on 70 grains. The grains were mostly subrounded to subangular. The concentration of rounded grains in some beds of the Pärnu Formation (Fm.), the basal beds of the Leivu Fm., and the upper part of the investigated sequence indicates zones of sediment recycling and reworking. Based on the distribution of roundness degrees of quartz grains, some possible ancient coastlines in Pärnu time were defined.Variations in quartz surface textures were detected at different stratigraphical levels, whereas the texture created by mechanical processes was predominating. Abundant abrasion features like V-shaped pits, and linear and curved grooves usually give evidence of transport in a fluvial medium. On levels with intensive reworking and redeposition (Burtnieki and Gauja formations and on some levels of the Pärnu Fm.) preliminary relief of grains was smoothed and obliterated. The diagenetic dissolution features were more frequent in the Pärnu Fm., Kernave Fm., and lower part of the Aruküla Fm., where intercalation of dolomitic and siliciclastic rocks is common. Possible chemical etching in Devonian soil profiles was observed in the upper part of the section. Data on the roundness of particles and surface textures of quartz grains, and their horizontal and vertical variability help to clarify the history of basin evolution and to distinguish stratigraphical discontinuites.

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Dermal scales of a new chondrichthyan were discovered in four levels in sandstones of the Härma Beds (lower part of the Burtnieki Regional Stage, Middle Devonian) in the Karksi outcrop of South Estonia. The classification of Karksilepis parva gen. et sp. nov. Märss is still uncertain.

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