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Hyperpycnite
You may have heard of turbidites. This type of deposit forms from pulse-like flows, where sediment travels rapidly down a slope because of a gravity contrast with the surrounding fluid. Turbidites typically show an upward decrease in gain size and a vertical succession of structures (massive/planar laminated/ripple cross-laminated) indicative of decreasing energy of the flow. There are, however, some deposits that differ from turbidites by showing a symmetric internal organization, with increasing and then decreasing grainsize, and with structures pointing to increasing and then decreasing energy of the flow. Hyperpycnites are such kind of deposit, forming when a river, laden with sediment during its flooding stage, flows into a basin. The flow typically waxes, reaches peak strength, and then wanes. Therefore, the resulting hyperpycnite reflects the waxing and waning cycle in its internal structure. This picture shows a nice hyperpycnite from the Pennsylvanian Minturn Formation, near McCoy (CO, USA). The bed displays reverse grading in its bottom part and a gradual upward transition from ripple laminated, to planar laminated, to massive (waxing phase). The upper part of the bed shows normal grading and hints of ripple-cross lamination (waning phase).
Sole marks
Sole marks are sedimentary structures found at the base of beds, best seen in surface view. They are typically preserved as casts of incisions/depressions created at the top of the underlying bed and filled with sediment of the overlying bed, often with a grainsize contrast between the beds (sand over mud). Sole marks are common in deposits of sediment gravity flows (like turbidites), where turbulence or bedload transport in an energetic flow can erode or leave marks on the underlying substrate in conjunction with active sedimentation. This picture, showing the base of a bed from the Pennsylvanian Minturn Formation, near McCoy (CO, USA), illustrates several kinds of sole marks: a) Flute casts, elongated scours with a wider round concavity at the upstream end, tapering to a pointed termination down current. Flute casts are formed by turbulent eddies in the flow and are excellent paleocurrent indicators; b) Prod marks, small irregular indentations, caused by particles suspended in the flow that occasionally hit the substrate; c) Groove casts, linear features, parallel to the current direction, formed by particles (like pebbles or sticks) dragged with the bedload and eroding the substrate. Prod marks and groove casts are sometimes called "tool marks," because they form as objects in the flow interact with the substrate. See if you are able to identify the three types of marks in the picture. In which direction do you think the flow was moving, towards the top or the bottom of the image? Lens cap for scale has a diameter of 6 cm.
Bedforms
Bedforms are morphological patterns that form at the interface of flowing fluid and a bed of moving sediment. Typical examples include dunes and ripples. Lateral migration of bedforms can generate sedimentary structures, like ripple cross-lamination or cross-stratification. Geology students often mix up the concept of bedform and sedimentary structure: ripples are bedforms (not sedimentary structures) and ripple cross-lamination is a sedimentary structure (not a bedform). Sometimes, like in this picture of hyperpycnites from the Pennsylvanian Minturn Formation near McCoy (CO, USA), both sedimentary structure and associated bedform are preserved in a bed. The asymmetric profile of unidirectional current ripples (flow towards the left) and foreset laminae dipping to the left are clearly visible at the top of two consecutive sandstone beds, overlain by mudstone beds. Draping of bedforms by finer sediment indicates a decrease in hydrodynamic energy within a rapidly discharged, sediment-laden flow. Pencil for scale.