Table of Contents
Where are flute casts found?
Flute-Casts. Sole marks are sedimentary structures found on the bases of certain strata that indicate small-scale (centimeter-scale) grooves or irregularities. This usually occurs at the interface of two differing lithologies.
How are groove marks formed?
Groove or striation marks result from the continuous contact with the muddy bed. Skip or prod marks come from objects that bounce along the surface of the muddy bed. And roll marks result from objects rolling along the muddy bed.
How are load casts formed?
Load casts form on the underside of the overlying denser layer (sands, coarse sands, or gravels), which is superimposed on a less-dense hydroplastic layer (muds, silts or finer sands). The casts take on the form of slight bulges, swellings, deep or rounded sacks, knobby excrescences or highly irregular protuberances.
How are sole marks formed?
Sole marks are features that are preserved when a coarse sand or silt layer deposits onto mud. Typically during deposition of the sand/silt the flow of the water erodes pits and scars into the mud layer and then these depressions are later in-filled with the more coarse material.
How are flute marks formed?
Typically, flute marks are bilaterally symmetrical heel-shaped hollows eroded into mud beds by debris-laden currents, acting either on prior defects on or within the bed, or on self-created defects, if the mud is insufficiently strong.
How do gutter casts form?
The gutter casts form by eroding currents. Several models have been proposed (Myrow 1992), but the most appropriate appears to be helical flow vortices. Gutter casts characterise sedimentation in the bypass zone, and develop during storms when strong currents transport sediment to the outer shelf (Perez-Lopez 2001).
How do dish structures form?
A dish structure is a type of sedimentary structure formed by liquefaction and fluidization of water-charged soft sediment either during or immediately following deposition. Dish structures are most commonly found in turbidites and other types of clastic deposits that result from subaqueous sediment gravity flows.
How are ball and pillow structures formed?
“Ball & pillow” is a type of soft sediment deformation, when fresh sand is deposited atop soft, squishy mud. The density inversion triggers a load/sag phenomenon, and the sand pooches downward while the mud squooches up alongside, folding the sand into a shape much like an up-side-down mushroom cap.
What are slump structures?
Slump structures are mainly found in sandy shales and mudstones, but may also be in limestones, sandstones, and evaporites. They are a result of the displacement and movement of unconsolidated sediments, and are found in areas with steep slopes and fast sedimentation rates. These structures often are faulted.
How is mud cracks formed?
Mudcracks form in very fine clay material that has dried out. As the moisture is removed, the surface will split into cracks that extend a short way down into the mud. These cracks form polygons on the surface of the mud.
How are desiccation cracks formed?
Desiccation structures originate as shrinkage cracks formed by the evaporation of water from the surface of clay-rich sediment. Previously called mud cracks, they are of subaerial origin, and are caused by the slow drying-out of muddy sediments which have been exposed to the action of sun and wind.
How are mud cracks formed?
How do pillow structures form?
A sedimentary structure occurring on the base of some sandstones which are interbedded with mudstones, and characterized by globular protrusions and isolated pillows of sandstone found in the underlying mudstone. These structures form by the differential settling of the unconsolidated sand into less dense mud below.
What are pillow structures?
A structure, observed in certain extrusive igneous rocks, that is characterized by discontinuous pillow-shaped masses ranging in size from a few centimeters to a meter or more in greatest dimension (commonly between 30 cm and 60 cm).
Where do slumps occur?
Slump is common where clay-rich materials are exposed along a steep slope. Such oversteepend slopes naturally occur on the outside of meanders along the Red River. Slump is typically identified as the downward movement of a block of earth material along some curved surface of failure.