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Chapitre D'ouvrage Année : 2018

Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France

Joachim Place
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Yves Géraud
Hemin A Koyi
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Résumé

The Merkwiller-Pechelbronn oil field of the Upper Rhine Graben has been a target for hydrocarbon exploration for over a century. The occurrence of the hydrocarbons is thought to be related to the noticeably high geothermal gradient of the area. Its magnitude peaks at about 100 °C.km −1 a few kilometres east of the oil field, in the vicinity of the Soultz-sous-Forêts horst, which has been the target of geothermal exploration in recent decades (Figure 7.1). Seismic investigations in the 40 km wide Upper Rhine Graben reveal significant details. We have chosen a 5 km time-migrated section of the PHN84J profile that focuses on the eastern flank of the Soultz-sous-Forêts horst to illustrate the complexity of basement-sedimentary cover deformation patterns involving décollements (Figure 7.2). This is a slightly revised version of the original interpretation of Place et al. (2010), where the deformation in the décollement level was more emphasized than in the present interpretation. The section shows a couple of major normal faults bounding a graben within the upper part of the sedimentary cover, rooted in décollements of Triassic anhydrite or clay series (top of Buntsandstein to Middle Muschelkalk, and Keuper). These faults are interpreted to have been active during the Oligocene when the Upper Rhine Graben opened (Roussé, 2006). The seismic profile also reveals the presence of a deeply-located fault-bounded block labelled (1) within the décollement zone. This block, which we call 'inverted horst', has formed in two main stages: Firstly, extension in the basement (along at least one basement fault), decoupled from the cover by décollement level(s), resulted in the formation of a large-scale monocline Figure 7.
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Dates et versions

hal-02959693 , version 1 (07-10-2020)

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  • HAL Id : hal-02959693 , version 1

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Joachim Place, M Diraison, Yves Géraud, Hemin A Koyi. Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France. Atlas of Structural Geological Interpretation from Seismic Images, 2018. ⟨hal-02959693⟩
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