Clastic dike

Neptunian dikes are filled with sediment former columns of the seabed, which occur mainly in carbonate rocks.

Word origin

The word neptunian comes from English and means under the sea '. It refers to the submarine origin of the columns and their fillings. It is now used mainly for carbonate rocks. First, the combination was used neptunian dike 1896 by Alexis P. Pavlov for the Lower Cretaceous sedimentary transitions that occur as sandstone transitions in clay sediments.

Shape and distribution

Neptunian dikes are mostly perpendicular or oblique to the stratification, but they can also occur in layers parallel.

The width of Neptunian Dikes lies in the centimeter to meter range. They can range in the depth and length can be several kilometers to several meters, in some cases hundreds of meters or more. The walls of the columns are parallel to each other and have a straight to wavy surface. In some cases there is not a column, in other cases there are entire columns droves. The columns often come in solidified surfaces (Hard Grounds ), subject to geological unconformities.

The columns are soon or some time after its formation filled with new sediment. This can be both under water ( mud or similar packing material ) as well as in the open air step (eg sand dunes ). Submarine splits are often bound to carbonate, but they can also be on the continental slope or in basins are created.

Emergence of the columns

The columns that are later filled with sediment, can be divided into four classes: primary columns, synsedimentary columns, epigenetic and tectonic columns. The mechanisms are naturally almost the same as those for column formation in sedimentary dikes.

Primary columns are formed mainly in the vicinity of a coral reef. They correspond to the gaps and cracks between large coral rubble blocks or large reef builders. They are usually filled with the debris that results from the removal of the reef.

Synsedimentary columns are formed during the sedimentation mainly caused by slipping sediment on a slope ( slumping ), often as a result caused by earthquake vibrations. Further columns can arise under a coat or over Basement structures by different reduction of sediment. Another mechanism for the formation of columns is the drying up of shallow marine areas or lakes and the formation of desiccation cracks.

After deposition and solidification epigenetic columns can occur at the earth's surface by karst or solution processes.

Tectonic columns arise mainly from a strain of the substrate, usually as a result of block tilting and faulting during the deposition of sediments. A special form is the injection of sedimentary material due to increased pore water pressure from below by layering or sideways into the space between the layer surfaces.

Filling

Neptunian dikes are filled with sediments such as clay or sand and fossil remains, moreover, different cement generations are usually present.

Sometimes the filling is colored differently than the older flanking rock in which they occur, they are not readily detectible. In other cases, they can hardly be distinguished from the surrounding rock, and it requires investigations of thin sections under the microscope, or a detailed analysis of the fossil content. At high flow rate of water through the column to ripple marks and similar sedimentary structures can develop.

The fillings of undersea and on land resulting columns can be distinguished by characteristic features. Incurred and backfilled On land columns list, for example, no marine fossils found in some cases remnants of soil formation, and the nature of the cement indicates a formation at the free surface.

In most cases, a sedimentary transition does not change after the formation and filling. However, the filling of the columns can develop in rare cases, by re- ripping, so that multiple generations of filling materials occur. However, frequently the change by solution processes and Karst, when the rock is at the surface.

Fossil guide

On the walls of the columns, which consist of solidified sediment or solid rock, sometimes lived sessile aquatic organisms such as brachiopods and algae, which were later buried by mud. In most cases, however, today present in the fossil animals were already flushed dead in the columns.

In some columns lasting deposition of fossils such as ammonites, bivalves and gastropods have formed properly continuous fossil sites by the long time. The fossils are then often without existing outside the column between sediments before that on the basis of fossils assignable sequence is then in a much shorter sequence before ( condensed profile). In the filling of the columns are next to find normally microfossils, who lived at the time of deposition of these filling and often form the only evidence of a younger age of the filling.

Occurrence

Neptunian dykes are widespread. Examples of Neptunian Dykes found, for example in the Dachstein Limestone of the eastern Alps. Other examples are known from Devonian limestones in Australia or from Riffkomplexen in Permian sediments of the U.S. Gulf Coast and in Mexico. A modern example of Neptunian Dykes may have some of the so -called Blue Holes of the Bahamas.

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