Swiss National Science Foundation, projects 2.107-0.86 and 20-26218.89.
Sea-Level Changes and Extensional Tectonics in the Lower Jurassic (Northern Helvetic Realm, Western Switzerland)†
- L. E. Frostick2 and
- R. J. Steel3
Published Online: 16 APR 2009
Copyright © 1993 The International Association of Sedimentologists
Tectonic Controls and Signatures in Sedimentary Successions
How to Cite
Loup, B. (1994) Sea-Level Changes and Extensional Tectonics in the Lower Jurassic (Northern Helvetic Realm, Western Switzerland), in Tectonic Controls and Signatures in Sedimentary Successions (eds L. E. Frostick and R. J. Steel), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304053.ch8
- Published Online: 16 APR 2009
- Published Print: 28 FEB 1994
Print ISBN: 9780632037452
Online ISBN: 9781444304053
- sea-level changes and extensional tectonics in lower Jurassic;
- the Fedenrothorn section;
- sea-level changes and tectonics, Switzerland;
- cyclic sedimentation controls;
- depositional water depth;
- stretching models
Located at the hinge between the stable European continental platform and the northern Alpine Tethys, the Lower Jurassic basin of the northern Helvetic realm (western Switzerland) can be subdivided into several elongate symmetrical WSW–ENE sub-basins. Lateral thickness changes are gradual, and areas of non-deposition act as a major control on facies: Helvetic sandy facies near exposed zones and Dauphiné shaley facies in more distal zones.
The sediments were deposited in shallow marine offshore and foreshore zones. However, due to Alpine tectonics, preservation of sedimentary structures and fossils is poor. The sections studied display systematic events which can be interpreted as transgressive surfaces, sequence boundaries, condensed sections and shallowing-up sequences. The Lower Jurassic sedimentary record can be subdivided into genetically related strata recording relative base-level changes. Sedimentary structures or facies assemblages related to episodic palaeofault activity are absent. At least two orders of cyclicity (2nd and 3rd) have been recognized, and the same 3rd-order sequences are found in different sub-basins and in the two main facies types. The mechanisms controlling sedimentary sequences are therefore either regional (main- basin scale) or global. However, correlation with global events is recognized only in some situations, and eustasy is therefore not the only control on cyclic sedimentation.
In order to investigate the regional processes, the subsidence history has been analysed. The tectonic subsidence curves, with corrections for depositional water depth, compaction, tectonic deformation, erosion, eustasy and Airy compensation, have been compared using three stretching models: uniform extension of the entire lithosphere, crustal and subcrustal extension (both non-uniform or depth-dependent discontinuous stretching models). For the study area, the most suitable model is subcrustal stretching, with more extension in the lower lithosphere than in the crust. As predicted using the model, the ratio of initial fault-controlled to thermal subsidence is low and the studied basin is mainly thermally controlled.
The results from sequence and geohistory analyses are integrated. A possible process controlling sequences, and compatible with a mainly thermally controlled basin, is in-plane stress change. This mechanism can explain all observed features, including the asymmetric sedimentary cycles. The stratigraphical record may therefore result from the superposition of both eustasy and in-plane stress changes.
The northern Helvetic Lower Jurassic basin was an intracratonic sag-basin and not, at that time, a constituent part of the more fault-controlled North Tethyan margin.