Bed Forms in Submarine Channels: Comparison of Ancient Examples from Greece with Studies of Recent Turbidite Systems

Abstract

ABSTRACT Side-scan sonar observations have shown the presence of gravel waves, flute-like scours, and parallel erosional furrows in modern marine turbidity-current channels. Similar features are not well known from ancient rocks. Two Cenozoic sections of well-exposed turbidite channel fill in western Greece have been studied to determine why such features are difficult to recognize in the ancient geological record and which sedimentary facies are associated with large gravel bed forms. Gravel waves 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 scours a few meters in size, similar to modern flute-like scours, have been mapped on the surface o debris-flow deposits in one ancient channel fill. Large gravel bed forms are difficult to recognize in the ancient geological record because of their scale and lack of distinctive features to aid lateral correlation across minor gaps in outcrop. Analogy with modern deposits and the sediment association suggest that deposition takes place in channels upslope from major sandy depocenters. The erosional features associated with modern gravel bed forms are difficult to recognize in the ancient record because of poor exposure of shales.