Silverpit crater

54.2333333333331.85Koordinaten: 54 ° 14 '0 " N, 1 ° 51' 0" E

The Silverpit crater is near the coast of Great Britain in the North Sea lying crater. It was discovered in 2001 during an analysis of seismic data collected during the search for oil wells. Initially, he was thought to be an impact crater, but also alternative origins have since been proposed. The Silverpit crater is estimated at an age of about 55-65 million years ago.

• 4.1 Age
• 4.2 part of several strikes?

Discovery

During a search for unknown sources of oil in 2001 seismic data in a region 130 kilometers distance to the estuary of the River Humber were collected. The geologist Simon Stewart ( BP ) and Phillip Allen (Production Geoscience Ltd.). Encountered when analyzing these data on an unlisted anomaly. Allen noticed a series of concentric rings, but just could not interpret and hung a picture of the measurements in his office. Stewart, for other reasons to visit at Production Geoscience, saw this card and suggested as a possible origin before an impact crater. The discovery as well as the preliminary hypothesis on the origin of the crater were published in the journal Nature in 2002. (Lit.: Stewart and Allen, 2002)

The name of the crater was against the - chosen name for the crater enclosing lowering of the seabed - emanating from local fishermen. It is believed that this reduction is an old river bed of the ice age.

Only three years before the Silverpit crater was discovered statistical calculations showed that, given their size and the number of crater formations with high probability is an impact crater in the North Sea.

The crater lies under a up to 1500 meters thick sediment layer, which forms the bottom of the North Sea at a depth of about 40 meters. Studies suggest that the area at the time of crater formation was 50 to 300 feet below the water surface.

Origin

Formation by a meteorite impact

Allen and Stewart came to the investigation of the crater to the conclusion that the impact of a meteorite represents the best explanation for the origin. They tested immediately after the discovery of the crater alternative mechanisms, but rejected it again. Volcanism was excluded because the crater does not have the typical volcanic eruptions magnetic anomalies. The erosion of salt deposits - a known mechanism for the formation of crater-like structures - was excluded, as the layers of Triassic and Permian had below the crater no signs of erosion. As strong evidence for a meteorite impact of the central peak is seen inside the crater, which may be without a start can hardly be formed.

Mineralogical and geochemical studies of drill cores from the central region of the crater were investigated for evidence of a meteorite hit back. Signs of change of minerals by a strike outgoing shock waves (shock metamorphism ) were able to be found as little as traces of the offending meteorites. (Lit.: Koeberl and Reimold, 2004)

A weft forming into a sea meteorite of this size would also generate large tsunamis. The deposits formed in this way in other places would constitute a definitive proof of an impact, however, could not be detected until 2004. ( Ref: Smith, 2004)

Alternative theories

Professor John Underhill, a geologist at the University of Edinburgh claimed, however, after analysis of older, created on a larger scale, seismic data, the depth of the crater erosion explain better. (Lit.: Underhill, 2004) Underhill found that all strata are folded to Perm synclinal ( with an age of about 250 million years ago) - that represent a concave indentation. Sediments of this era are thinned out around the crater, indicating crater formation during deposition of Permian sediments.

The central mountain is by Underhill nothing more than an artifact of the image processing. Subsequent seismic studies confirm the existence of this survey, however. (Lit.: Stewart and Allen, 2005)

Also Ken Thomson of the University of Birmingham in mid-2004 showed that accumulate salts in the southern North Sea in large, linear deposits whose leaching could well have produced the concentric structures. (Lit.: Thomson, 2004)

Structure of the crater

The Silverpit crater has a diameter of about 2.4 kilometers. Around the crater spread concentric rings in a distance up to 10 kilometers from. These terrestrial craters quite rare appearance leaves the Silverpit structure the Valhalla crater on the ice-covered moon of Jupiter and Callisto some craters in the icy crust of Jupiter 's moon Europa may seem similar. (Lit.: Allen and Stewart, 2003) Under normal circumstances, such " ringed " crater but are far greater than the Silverpit what the origin of ring structures can appear questionable under the assumption of the impact hypothesis. Is further complicated by the finding, especially since nearly all known impact craters on land and are therefore the effects of impacts are studied far worse in water. The investigated probably best maritime Crater is the Chesapeake Bay crater.

One possibility is that initially the impact threw out a bowl- shaped depression, then slipped softer material in the direction of the crater, while leaving the concentric rings. It is assumed that the layer soft material such purpose be quite thin and further, brittle material would have to decide. Unlike ice-covered moons a thin layer of moving material under a solid crust on the rocky bodies of the solar system is only rarely encountered. A conjecture states that under high pressure limestone could have acted under the surface as a soft, movable material. (Lit.: Collins, Turtle and Melosh, 2003)

The impact

From the size of the crater and assumptions about the speed of an impacting object, the size of the meteorite can be estimated. Such objects are moving in the Earth's orbit usually at speeds between 20 and 50 kilometers per second. To create a crater the size of Silverpit, an asteroid would have a diameter of approximately 120 meters and a mass of 2 million tons have, during a comet due to the lower density would still be slightly larger.

As a comparison: The diameter of the object, which threw out the Chicxulub crater is estimated to be about 10 kilometers. At his impact around 500,000 times more energy is released than would have been free by impact in the development of Silverpit crater.

Age

The stratigraphy, ie the position of the crater within the rock and sediment layers on the ocean floor, can be used to estimate its age: sediments that covered the sea floor before the formation of the crater were whirled in contrast to later sediments. Allen and Stewart discovered that the Silverpit was formed in the Cretaceous limestone and shale from the Jurassic and was covered by a continuous layer of sediment from the Tertiary. The Cretaceous period ended about 65 million years, but nearby research boreholes suggest that the lowermost Tertiary strata are missing in the sedimentary layering. Accordingly, the Silverpit crater between 55 and 65 million years old. The Chicxulub whose formation is probably responsible for the extinction of the dinosaurs, was born at the end of the Cretaceous period, 65 million years ago.

This stratigraphic age determination is coarse and is provided by Underhill's hypothesis in question. Other ways of dating are the study of ejecta - tektites about Impaktgläsern or - or deposits of tsunamis triggered. The latter should be possible to find at an impact across the North Sea basin, but could have been repeatedly affected by glaciation. In addition to a precise dating radimetrischen these studies could also strengthen the impact hypothesis. However, so far could not be assigned to the Silverpit crater ejection materials and no deposits of tsunamis found, shall be collected and examined.

Part of several strikes?

The estimated age of the crater Silverpit inevitably leads to speculation as to whether there is a link to the much larger Chicxulub crater and the extinction of the dinosaurs. Also have more crater about the same age - all between latitudes 20 ° N and 70 ° N - discovered which could indicate that the Chicxulub impact was only one of several strikes at the end of the Cretaceous: In addition to Chicxulub and Silverpit is also likely to Boltysh crater in Ukraine (24 km diameter, age 65.2 ± 0.6 million years) have occurred at the K / T boundary, and possibly also the still insufficiently studied crater Eagle Butte ( Canada) and Vista Alegre (Brazil ) with diameters of around 10 km.

The collision of the comet Shoemaker- Levy 9 with Jupiter in 1994 showed that a comet be broken by tidal forces into several parts and thus distributed over several days at different locations set up on a planet can. Comets are exposed to such forces, especially in the vicinity of a gas giant, so that fragmentation with high probability had already taken place some time before the impact. In the absence of more precise dating can only speculate about whether there has actually been a multiple impact on Earth at the end of the Cretaceous period, but researchers are currently.