See more from this Division: Topical Sessions
See more from this Session: From Mud to Mudrock: Use of Modern Depositional Settings as Analogs for the Interpretation of Ancient Mudrocks
Abstract:
A new set of experiments provides critical first hand observations of the processes that shape and propagate mud ripples. These consist of 90 vol. % water, yet their vertical profile is indistinguishable from current ripples formed in sand (clearly developed crest and brink, lee-side slopes approximately 25-30 degrees). A combination of various imaging approaches shows that sediment is transported over the stoss side in the form of diverging boundary layer streaks, the carriers of the bulk of the bedload floccule freight. At the brink line these streaks become point sources of sediment that feed avalanches of floccule-rich sediment lobes. These propagate down the slip face like classical mudflows on a hillside. Lateral shifting of boundary layer streaks averages out sediment deposition across the slip face. Migration rates of floccule ripples vary with flow velocity (example: 25 cm/hour at V=15 cm/sec and 5 cm flow depth). The latter rate is approximately 3 to 4 times slower than comparable sand ripples because of the fundamentally cohesive nature of floccule ripples. Compaction reduces these ripples to sub-mm streaks of clay with internal laminae of a few degrees dip. Nonetheless, it is possible to recognize them in the rock record.
See more from this Division: Topical Sessions
See more from this Session: From Mud to Mudrock: Use of Modern Depositional Settings as Analogs for the Interpretation of Ancient Mudrocks