The origin of the Silverpit structure, UK North Sea has been contested since its discovery on seismic data in 2002. The Silverpit structure consists of a 3 - 4km central zone of deformation, which includes a conical uplift. This is surrounded by a series of ring faults up to a maximum diameter of 20km. Meteorite impact, evaporite withdrawal, pull-apart basin tectonics and halokinesis tectonics have all been suggested as possible origins. This thesis uses a multi-discipline approach to test these hypotheses and determine with certainty the origin of the Silverpit structure. Seismic interpretation of the Silverpit structure has highlighted that deformation in the central deformation zone and beneath the structure is comparable with other meteorite craters. However, the ring faults are comparable with other structures formed by regional evaporite dissolution and movement. Seismic interpretation on a regional, 3500km2 scale proved that the structure is unique and that salt movement was taking place at the same time as the Silverpit structure was created. Unusual diagenesis in the chalk beneath the Silverpit structure was identified as a result of the presence of both unusual geophysical and geochemical signatures. An anomalous sonic log response is attributed to a significantly decreased porosity at the base of the chalk unit. Anomalously negative stable oxygen isotopes were also found in the chalk beneath the structure. Unusually elevated heat flow is the likely cause of these irregularities. The evidence presented in this thesis leads to the conclusion that the origin of the Silverpit structure is in fact two-phase. Meteorite impact has lead to the formation of the central zone of deformation and conical uplift. It has also influenced the diagenesis of the chalk beneath the crater and created a more brittle chalk unit. Regional salt withdrawal is responsible for the formation of the ring faults, which have only formed in the meteorite impact induced brittle chalk. In simple terms, a meteorite impact formed the 3km crater and then salt withdrawal produced the circular rings during several million years after the impact.

The Onion Creek Diapir is one of many salt domes proximal to the Uncompahgre thrust front of the ancestral rockies in the Paradox Basin. It is comprised of Paradox Formation evaporites and large blocks of Honaker Trail Formation carbonates that were deformed by loading of Permian Cutler Formation progradational alluvial to fluvial fans. The history of salt movement in the Onion Creek Diapir is recorded in the near-salt strata. Large salt bodies and their adjacent mini-basins evolve conforming to a complex relationship between salt withdrawal, creating localized accommodation, and sediment deposition. Migrating mini-basin depo-centers, thinned and folded strata, and spatial facies trends reveal the relative rates of diapirism and sedimentation. The study area outcrop, north of the diapir, is divided by significant stratigraphic horizons that help define depositional periods. Six measured sections in the study area reveal higher preservation rates of fine grained floodplain deposits, typically destroyed in alluvial environments, than at locations correlating to stratigraphic levels high in the outcrop suggesting a low accommodation environment evolving into higher accommodation where stacked channel complexes are preserved. Preserved slump folding at the base of the outcrop reveals that although some salt emergence occurred in the earliest depositional period it was not significant enough to preclude sediment deposition or to divert the Cutler fluvial network and destroy floodplain facies. A 3-D digital outcrop, modeled from photogrammetric data, illustrates the development of localized accommodation, attracting fluvial channel in a near-salt, tight axial syncline during the later depositional period. These evidences suggest a greater emergence of the diapir and likely diversion of the Cutler channel complexes.

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