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2005-03-22

Silverpit structure

There has been a bit of discussion lately on the interpretation of the "Silverpit" structure in the Southern North Sea.
A couple of years ago a paper was published in Nature about a circular set of faults surrounding a sub-surface depression in the top-Cretaceous reflector. The interpretation was that this was an impact structure. A summary of the paper can be found at the Geological Society website (if you're really interested, I can email you the paper). Well, there have been alternative interpretations published over the last few months, re-interpreting it as a sagging structure caused by withdrawl of Zechstein salt at depth. John Underhill (of Edinburgh University) has presented data orthogonal to the original section (link above), which does put a very different interpretation on the structure.
It still doesn't look right though - the "central peak" structure in the original paper is still a very anomalous structure, and Underhill's interpretation of thickness variations in the overburden to the salt is inconsistent - the Cretaceous thins in one direction and the Jurassic in another, combining to give the appearence of synsedimentary halokinesis. It still looks odd to me.
I am very surprised at a seismologist of Phil Allen's experience not looking out-of-plane though.
(In other comments since I first wrote this, Mr Allen claims he did, but disagrees with Underhill's interpretation.)