3D seismic reflection mapping of the Silverpit multi-ringed crater, North Sea

Abstract

The fi rst comprehensive mapping of the Silverpit multi-ringed crater is presented, based on fi ve adjoining 3D seismic surveys that together provide 78% (216 km 2 ) areal coverage of the structure with spatial and depth sampling of ~10 m. The top Cretaceous surface shows an excavated crater 3 km in diameter surrounded by 10-15 concentric ring structures out to a radius of 9.4 km. Seismic sequence stratigraphy and drilled wells indicate the lower age bound is a disconformity spanning 74-54 Ma. The upper bound is Eocene termination of concentric ring fault growth (ca. 45 Ma). The inner rings are extensional faults defi ning rotated fault blocks that would be considered part of the crater in an impact structure interpretation, giving a fi nal impact crater diameter of 8 km. The outer rings show a surprising variation in style, from graben in the west to compressional structures in the east. This may be explained by postcratering gravity spreading on easterly dipping intra-Cretaceous detachments. Within the crater, the top Cretaceous seismic refl ector is disrupted and blocky, but defi nes a central uplift with a slight crestal depression. Below this uplift, the prominent base Cretaceous seismic refl ector shows Jurassic strata rising into a cone 300 m high and 1 km wide, characterized by radial faults. This central uplift within the crater may structurally balance the inner ring fault blocks via a slumping model, but we also identify low seismic velocity in the uplifted Jurassic, so fracturing may have contributed to growth of the central peak. At a radius of 2.5 km, base Cretaceous shows a dish-shaped depression that we interpret as marking either the extent of slumping toward the crater at this structural level or the limit of shockwave-induced porosity collapse. Seismic refl ectors above the top Cretaceous excavated crater show differential com-paction during the Eocene, accommodated by drape structure plus two conical faults that defi ne narrow ring graben and represent the fi nal phase of crater-related tectonics.

Estimates of yet-to-find impact crater population on Earth

“…First, there is a candidate impact crater (the Silverpit structure) imaged on 3D seismic data in the Upper Cretaceous section, buried by 500 m of sediment ( Fig. 1a and b; Stewart & Allen 2005). Second, although several impact craters are predicted, including three in the size range of the Silverpit structure, Silverpit is the only candidate impact structure described to date, suggesting that several more remain to be discovered.…”

“…(a) Seismic reflection cross-section of Silverpit structure, North Sea (Stewart & Allen 2005). (b) Map view of Silverpit structure, North Sea (Stewart & Allen 2005). (c) Seismic reflection 3D cube of Praia Grande structure, Santos Basin, Brazil (Correia et al 2005).…”

“…Vertical exaggerations in range 2-5. (a) Seismic reflection cross-section of Silverpit structure, North Sea (Stewart & Allen 2005). (b) Map view of Silverpit structure, North Sea (Stewart & Allen 2005).…”

Circular geological structures outcropping in the sedimentary basins of Saudi Arabia

“…Within of the ring fault system, the Sharawra and Tawil formations are folded into a gentle ring syncline with minor concentric, spiral and low angle faults (Figures 4,5;Janjou et al, 1997). Faults with spiral trend in planview can occur in ring structures that involve centripetal movement of material, see discussion in Stewart & Allen, (2005). Moving from the synclinal hinge towards the center of the ring, structural dips increase towards the base of the Sharawra Formation, locally reaching 45 degrees at the contact with the Qusaiba Formation and always dipping away from the center of the ring thus defining a dome at top Qusaiba level.…”

In situ seismic measurements in borehole LB‐08A in the Bosumtwi impact structure, Ghana: Preliminary interpretation

“…The structures as delineated by seismic means depend on many variables such as the volume and extent of melt sheets, the amount of brecciation or damage, and the size of the structure. The number of seismological studies of impact structures has grown substantially over the last few years with studies at scales ranging from hundreds of kilometers over large impact structures such as Chicxulub in Mexico (Morgan et al 2000) and Sudbury (Wu et al 1995;Boerner et al 2000) to smaller structures such as the Mjølnir structure, which is 40 km in diameter (Dypvik et al 2004) in the Barents Sea, and the buried (but not yet confirmed to be an impact) Silverpit structure, which is ~10 km in diameter, that was well resolved in 3-D seismic images (Stewart and Allen 2005). The age range for these seismically studied structures extends from the 2.02 Gyr old Vredefort-Witwatersrand structure of South Africa (cf.…”