Sequence and systems tract interpretation of the epicontinental Oligocene deposits in the Danish North Sea
Michelsen, O.; Danielsen, M. (1996). Sequence and systems tract interpretation of the epicontinental Oligocene deposits in the Danish North Sea, in: De Batist, M. et al. (Ed.) Geology of siliciclastic shelf seas. pp. 1-13 In: De Batist, M.; Jacobs, P. (Ed.) (1996). Geology of siliciclastic shelf seas. Geological Society Special Publication, 117. The Geological Society (London): London. ISBN 1-897799-67-5. 345 pp., more In: Hartley, A.J. et al. (Ed.) Geological Society Special Publication. Geological Society of London: Oxford; London; Edinburgh; Boston, Mass.; Carlton, Vic.. ISSN 0305-8719; e-ISSN 2041-4927, more |
| Authors | | Top | - Michelsen, O.
- Danielsen, M.
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| Abstract | A sequence stratigraphical scheme has been established for the siliciclastic Cenozoic deposits in the southeastem North Sea Basin. The present paper addresses the problem of recognizing systems tracts by means of logs, using the Oligocene sequences as an example. The Oligocene sequences are characterized by an overall prograding seismic reflection pattem, and systems tracts cannot be interpreted from seismic sections alone. The sequences are dominated by marine clay deposits, and abrupt changes in lithological facies are rarely seen. The gamma-ray log trends indicate retrograding, aggrading and prograding stacking pattems. The lowstand deposits are identified as prograding sedimentary bodies. Coarse-grained sharp-based lowstand deposits are found basinwards of the depositional shoreline break of the preceding sequence, and further basinwards they are more fine-grained. Fan deposits are not recognized. A thin interval of transgressive deposits including upward fining clayey sediments is found at the top of the lowstand deposits and in the landward direction at the top of the older highstand deposits. The maximum flooding surface is identified by a high gamma-ray peak. The overlying highstand deposits thicken in the landward direction, and are here characterized by an upward coarsening trend. They thin in the basinward direction and become a condensed clay interval. Deposition took place during a tectonically quiet period in an epicontinental basin with a gently southwestward dipping sea floor. The lowstand deposits comprise forced regressive deposits and prograding deposits, and a deep ramp model is, therefore, suggested for these deposits. |
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