Dish structure

A plate structure is a secondary structure sediment caused by liquefaction or fluidization in the unconsolidated sediments.

Disambiguation

The plate structure (so called dish structure ), sometimes referred to as a plate and pillar structure was named after the household level because of their disk-shaped formation.

History of exploration

The plate structure was scientifically described in 1961 for the first time by Crook, who had at that time but still referred to as discontinuous curved lamination ( discontinuous curved storage). The actual term was first used in 1967 by Stauffer and Wentworth. Comprehensive studies of the plate structure go back to Lowe and LoPiccolo in 1974 as well as Lowe in 1975.

Description of the structure

The plate structure more or less horizontally disposed consists of two parts: the plate and its sediment content, the extends to the next higher plate up. The plate marking the boundary layer can take several forms, the design of which can range from very flat over bowl -like to very concave. The barrier layer consists of thin ( about 2 mm), dark, which may be considerably richer in clay, silt, or the organic material as the surrounding sand / silt medium. The individual plates are staggered. The plate width may vary between 2 and 50 centimeters, the vertical distance of the plate varies between less than 1 and 8 centimeters. In the floor plan seen the shape of the plates changes from circular / polygonal according elliptical / oval. The boundary layer stands out sharply and clearly from the surrounding sediment, but in higher areas, the transitions are smooth.

Usually the plates by vertical, massive stretch of sand, the so-called pillars, separated from each other. The pillar structures can be relatively small ( pillar from the A - type ) or quite large and continuously fail ( pillar of the B - type ), then indicate and increased water flow.

Within a single sediment layer can be observed often as the plate rounding increases in the upward direction with a simultaneous reduction in width.

Occurrence

Plate structures can occur in far enduring principles, but they are not the whole, too often and usually formed only indistinctly. My medium is usually coarse silt, but the structures can also occur in all types of sand. In clays and gravels in but they are never encountered. Sediment layers with plate structures are graded normally.

Faziesräume in which plate structures are for educational purposes are primarily the deep sea, especially the lower continental slope. The structures found in coarse-grained turbidites and associated, highly concentrated mass transports (English grain flows, fluidized flows and liquefied flows). But even in shallow marine, fluvial and lacustrine environments occurred plate structures on occasionally, in Delta sediments were also observed. A special feature in the marine environment is deposited volcanic ash layers which either themselves exhibit plate structures, or they can induce in the underlying sediment.

Within the turbidites Teller structures are generally restricted to the situation Bouma C, but can occasionally be seen even in Bouma B.

Good examples of plate structures come from the Jackfork group in Oklahoma, from the Ordovician turbidites in Cardigan in Wales, from deep sea subjects at San Sebastian in Spain and from the Cerro Toro Formation in Chile. Enormously large plate structures are found at Talara in northern Peru.

Formation

Until 1974 plate structures were viewed as the primary sedimentary structures. Their formation has been associated with either mechanical conditions of sediment transport or with the deposition conditions in highly concentrated mass transports. Lowe and LoPiccolo recognized as the first, the secondary nature of sedimentary structures that form immediately after the deposition. The secondary nature of the structures here is based primarily on the drainage of water- saturated and not yet solidified, rapidly deposited sediment layers.

That plate structures after deposition have formed may occasionally to cut or offset primary sedimentary structures ( such as convolute storage) are observed.

The onset due to the excess pressure in the freshly deposited sediment dewatering process is hindered because of the enriched clay fraction of less permeable layers. The normally upwardly mobile pore water flow is consequently forced sideways while dodging until provides a new opportunity for advancement. This laterally directed stream of water causes a gravity separation in the flow-through sediment - small grains such as clays are indeed initially moved, but then stay back and settle (due to their electrostatic properties ) ultimately to the permeability barriers of which eventually form the clay-rich boundary layer of the plate structures. Entweichstellen the pore water to the plate, the edges are bent upwards. Serves the escape of pore water on sudden, forceful manner, so the sand is fluidized and entrained; the registers are broken and there are drainage canals - the pillars. A variation represent (water cylinder) cylindrical columns, which can reach a diameter up to 10 cm and a length of 23 centimeters. In thick sandstone benches turbidites of the pillar length generally increases against the roof end. The Bank then usually lead to convolute storage (English convolute bedding ).

Importance

Plate structures are good indicators of Hangendrichtung of the respective sediment.