Dropstone

A Drop Stone ( engl. of to drop: drop and stone: stone) is an isolated rock fragment of pebble - to block size that has come within fine-grained sediments to be deposited. Characterized by the deposition manner is not normal transport along the sea floor or lake bottom, but by a vertical fall through the water body.

Background

Evidence of a deposition of a rock fragment as Dropstone are its isolated occurrence in fine-grained sediments, together with an incurred by the impact of depression on the underside as well as signs of ejected material at the edges of the fragment. Subsequently deposited sediment material covers the stone and its crater without interference. These signs can be seen most clearly in feingeschichtetem sediment.

Pathogenesis of

Glaciers and icebergs

Glaciers take on the flow rocks from the ground and are often showered with debris. When they get to the coast, glaciers begin to calve, and icebergs calve from her forehead. This can drive for long periods where they melt slowly or shift, so that debris sinks into the water and falls into the mud at the bottom.

In contrast to attachments that are commonly used in Till ( boulder clay ), the deposition of glacial dropstones always happens in the water, either in the sea (marine ) or in lakes ( lakustrisch ). Typical of such Dropstones which is often very fine-grained sediment in which they occur, and which indicates a very little energy deposition environment. Examples of such glacial dropstones are, for example, from the sea off Greenland known.

Volcanoes

In volcanic eruptions rock blocks can be thrown as volcanic bombs by the force of the eruption several miles through the air. If this incident in a lake or in the ocean, they sink to the bottom and are included as dropstones in the sediment.

Dropstones thus generated are relatively rare, because most of the ejected rocks landing on land or near the coast, where it is unlikely that they are preserved. Only at larger eruptions flying rocks far enough to land in fine-grained sediment and to be recognizable as dropstones.

Turbidites

Dropstones can be produced by the effects of strong turbidity currents on the sea floor, leading to the formation of turbidites.

Man Large blocks were found in geologically young, finely stratified deposits from the Eocene near Jamaica, which was not covered by glaciers since its creation. Although turbidity currents are considered to cause the deposition of these blocks, no other deposits were found in the vicinity which were caused by the turbidity currents.

Drift wood and other biological causes

Stones can travel long distances as components of driving wood and plant materials that have been transported into the sea at about flooding of rivers. Dissolves the vegetable raft on, as well as the stones sink to the bottom. In the vicinity of such drop Stones are usually found plant remains, which fell to the stone floor. Dropstones may eventually come from the stomach contents of larger marine life.