Silverpit crater
The 20 km (12 mi) crater-like form,[1][2] named after the Silver Pit—a nearby sea-floor valley recognized by generations of fishermen—was discovered during the routine analysis of seismic data collected during exploration for gas in the Southern North Sea Sedimentary Basin.
An alternative origin was proposed in which the feature was created by withdrawal of rock support by salt mobility,[4] which was overwhelmingly judged to be more plausible in a 2009 debate held by the Geological Society of London.
Analyzing seismic data for a region 130 km (81 mi) off the Humber estuary, Allen noticed an unusual set of concentric rings.
Thinking they resembled a meteor-strike but lacking experience in impact structures, he hung an image of them on the wall of his office, hoping someone else might be able to shed light on the mystery.
[6] The origin of the crater is debated by the geoscience community with alternate theories of salt withdrawal and pull-apart basin[7] proposed, raising doubts as to Silverpit's categorization as an impact structure.
This result was presented at the April 2007 annual meeting of the American Association of Petroleum Geologists[9] Underhill then focused his research attention upon understanding why the salt moves where it does when it does and why the so-called crater took the form that it did.
This led him to publish a peer-review article in the journal, Petroleum Geoscience[10] in August 2009 in which he outlined the evidence for an intrusion-related salt withdrawal cause for the feature's formation.
A thin layer of mobile material beneath a solid crust is easy to understand in the context of icy moons, but is not a common occurrence on the rocky bodies of the solar system.
In their discovery paper, Allen and Stewart stated that Silverpit was formed in Cretaceous chalk and Jurassic shale, but is covered by an undisturbed layer of Paleogene sediment.
[1] The Cretaceous Period ended about 66 million years ago, but, on the evidence of nearby boreholes, the lowermost Paleogene sediments appear to be absent.
However, after a more detailed appraisal of the seismic data, Allen and Stewart gave a more cautious estimate of the age as between 74 and 45 million years (Late Cretaceous – Eocene).
[4] Assuming an impact origin, other possible ways of dating the event include looking for evidence of ejecta material such as tektites, and deposits from the hypothesised tsunami, which might be found anywhere around the North Sea basin.
Two nearby oil exploration wells penetrate the ring system, yet cutting samples from these fail to provide any independent support for the meteor theory, thus weakening the case for it being due to an extraterrestrial body.
