Resumé
Shingled sandstone bodies constitute part of a lower shoreface unit, deposited on the margin of a Lower Cretaceous rift basin in West Greenland. Excellent outcrops have enabled a detailed study of the sand body geometry and sedimentary structures.
The sandstone bodies are 0.5 to 4 m thick with lateral extensions from a few meters to more than 30 m paralleling depositional strike. Laterally they grade into thin sand sheets which continue for at least 130 meters along the entire outcrop or swell within a distance of 20-30 meters to form another sandstone body. The lower boundaries are sharp with local erosional reliefs up to 1 m. Quasi-planar lamination, hummocky cross-stratification and low angle cross-stratification compose the sandstone bodies. Internal bounding surfaces are characterized by symmetrical wave ripples. Interbedded are 10-60 cm thick laminated mudstone beds.
The sedimentary structures are produced by unidirectional and oscillatory currents and the observed interbedding demonstrate a close genetic relationship. Results from recent flow experiments by other workers suggest that only minor changes in the proportions between oscillatory and unidirectional currents in a combined flow determines whether 2 or 3 dimensional bedforms or a plane bed develops. In the present study sediment transport was predominantly obliquely offshore as indicated by the orientation of wave ripple crests, parting lineations and foresets in cross-stratified beds. The evidence for co-existence of differently oriented oscillatory and unidirectional currents strongly suggests deposition by geostrophic flows on the lower shoreface during major storms.
The sandstone bodies are 0.5 to 4 m thick with lateral extensions from a few meters to more than 30 m paralleling depositional strike. Laterally they grade into thin sand sheets which continue for at least 130 meters along the entire outcrop or swell within a distance of 20-30 meters to form another sandstone body. The lower boundaries are sharp with local erosional reliefs up to 1 m. Quasi-planar lamination, hummocky cross-stratification and low angle cross-stratification compose the sandstone bodies. Internal bounding surfaces are characterized by symmetrical wave ripples. Interbedded are 10-60 cm thick laminated mudstone beds.
The sedimentary structures are produced by unidirectional and oscillatory currents and the observed interbedding demonstrate a close genetic relationship. Results from recent flow experiments by other workers suggest that only minor changes in the proportions between oscillatory and unidirectional currents in a combined flow determines whether 2 or 3 dimensional bedforms or a plane bed develops. In the present study sediment transport was predominantly obliquely offshore as indicated by the orientation of wave ripple crests, parting lineations and foresets in cross-stratified beds. The evidence for co-existence of differently oriented oscillatory and unidirectional currents strongly suggests deposition by geostrophic flows on the lower shoreface during major storms.
| Bidragets oversatte titel | Facies arkitektur af sandstenslegemer: Evidens for geostrofisk strømning |
|---|---|
| Originalsprog | Engelsk |
| Status | Udgivet - 1994 |
| Udgivet eksternt | Ja |
| Begivenhed | AAPG Annual Convention 1994 - Denver, USA Varighed: 12 jun. 1994 → 15 jun. 1994 |
Konference
| Konference | AAPG Annual Convention 1994 |
|---|---|
| Land/Område | USA |
| By | Denver |
| Periode | 12/06/94 → 15/06/94 |
Programområde
- Programområde 3: Energiressourcer