BED FORMS IN SUBMARINE CHANNELS - COMPARISON OF ANCIENT EXAMPLES FROMGREECE WITH STUDIES OF RECENT TURBIDITE SYSTEMS

Side-scan sonar observations have shown the presence of gravel waves, flute-like scours, and parallel erosional furrows in modern marine tur bidity-current channels. Similar features are not well known from anci ent rocks. Two Cenozoic sections of well-exposed turbidite channel fil l in western Greece have been studied to determine why such features a re difficult to recognize in the ancient geological record and which s edimentary facies are associated with large gravel bed forms. Gravel w aves in ancient channel fills form in massive conglomerates with poor grading at the top of beds. They are found with sandstones of the high -density sandy turbidity current association. Series of erosional scou rs a few meters in size, similar to modern flute-like scours, have bee n mapped on the surface of debris-flow deposits in one ancient channel fill. Large gravel bed forms are difficult to recognize in the ancien t geological record because of their scale and lack of distinctive fea tures to aid lateral correlation across minor gaps in outcrop. Analogy with modern deposits and the sediment association suggest that deposi tion takes place in channels upslope from major sandy depocenters. The erosional features associated with modern gravel bed forms are diffic ult to recognize in the ancient record because of poor exposure of sha les.