PET-518 Features in Sedimentary Rocks Ripple marks are undulating surfaces on bedding planes caused by waves or currents while the rocks were being deposited. Here are ripple marks on the muddy bottom of Green Bay, formed during a low stand of the Bay.Mud cracks on the bottom of a modern puddle hese large cross beds probably formed in an offshore sandbar Graded Bedding !ayers where coarse material grades into finer material toward the top, usually caused by fast"moving water that slows down. #loods and submarine landslides are common causes. $asts Relatively rare. hese are s%uare or angular impressions left by salt or gypsum crystals as sediment dried out. he small s%uare lumps on the rock at right are salt crystal casts.&ave 'ction his looks like horrible pollution but is actually perfectly natural. (n the !ake Michigan shoreline, wave action washes away light minerals, leaving only black magnetite sand at the high"water mark. &hen wave conditions are right, layers of almost pure magnetite can form, like those seen in this shallow trench.)oft")ediment *eformation he very uniform layers here are varves, alternating thick and thin layers formed in a glacial lake. he contorted +one running across the center is probably due to glacial ice shoving the upper layers of sediment over the lower layers. *eformation that occurs while sediments are partly or wholly unconsolidated is called Soft-Sediment Deformation #lute $asts )ubmarine landslides are common on the edge of the continental shelf. he landslide flows scour flutes in the underlying sediment, then come to rest as graded beds of sand and silt that fill in the sculpted bottom. &e are looking at the underside of a submarine landslide deposit in ,ew Brunswick