| A: Seismic section with gamma-ray log|
B, C: Samples from upper part of upper sand
(white arrow in SWC in A)
During the 1812 New Madrid earthquake (southeastern United States), individual bodies of sand as much as 2 m thick appeared patchily over a 4000 km2 area. The sand volume was estimated to be to be 105–107 m3 and there were claims that it was the largest reported extrusive sand (extrudite). There have been no reports of extrusive sands as voluminous as several cubic kilometers. Typically, extrusive sands connect to their parent sandbody or sandbodies in the subsurface via hydraulic fractures.
Using three-dimensional seismic and well data from the northern North Sea, Loseth and colleagues describe a large (10 km3) body of sand and interpret it as extrusive. To their knowledge, this is the world's largest such sandbody. It would bury Manhattan, New York (60 km2), under 160 m of sand, or the whole of London, UK (1579 km2), under 6 m of sand. This sand vented to the seafloor, when it was more than 500 m deep, during the Pleistocene glacial period. The sandbody (1) covers an area of more than 260 km2, (2) is up to 125 m thick, (3) fills low areas around mounds, which formed when underlying sand injectites lifted the overburden, (4) wedges out, away from a central thick zone, (5) is locally absent along irregular ditches, 20 km long and up to 50 m deep, which overlie feeders on the flanks of the mounds, and (6) consists of fine-grained to medium-grained, sub-rounded to rounded grains.
A pretty big sandbox to play in!!