Flume Experiments with Carbonate Muds and Their Relevance for the Micrite Problem and the Deposition of Ancient Carbonates

Flume experiments on clay deposition have established that clays can be deposited from swift moving suspensions. At flow velocities that transport and deposit sand (20-35 cm/s, 5 cm flow depth) clay suspensions produce deposition-prone floccules that form migrating floccule ripples. Clay beds that form when these ripples accrete have a finely laminated appearance once compacted.

A racetrack flume with paddle-belt drive (to avoid destruction of floccules) was used to repeat these flume experiments with synthetic aragonite and natural carbonate mud in water of 35 ‰ salinity. The same pattern of flocculation, ripple formation, and bed accretion as seen previously in experiments with clays was observed. The carbonate mud beds that form as a consequence of floccule ripple accretion appear parallel laminated at first glance, but reveal internal low angle clinoforms on closer inspection. In plan view, the observed pattern of ripple foresets is identical to rib and furrow structure in sandstones.

Just as previously assumed for terrigenous muds, there has been a long-standing notion that abundant carbonate mud accumulation reflects quiescent conditions of offshore and deeper water environments. The experiments clearly demonstrate that carbonate muds can also accumulate in more energetic settings. In the sedimentary record of carbonate rocks, interbedded grainstones and micrites may thus not necessarily reflect significant shifts in depositional energy (or water depth), but alternatively may imply a shift in supplied sediment type. Likewise, wackestones may reflect energy conditions that are comparable to those of associated grainstones.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California