History of the Middle Berriasian transgression on the Jura carbonate platform: revealed by high-resolution sequence- and cyclostratigraphy (Switzerland and France) |
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Authors: | Jonas Tresch André Strasser |
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Institution: | 1. Department of Geosciences, University of Fribourg, Chemin du Musée 6, 1700, Fribourg, Switzerland 2. Dr. M. Kobel?+?Partner AG, Büro für Technische Geologie, Grossfeldstrasse 74, 7320, Sargans, Switzerland
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Abstract: | The Middle Berriasian deposits of the Jura platform in Switzerland and France have already been well studied in terms of high-resolution
sequence stratigraphy and different orders of depositional sequences (large-, medium-, and small-scale) have been defined.
The hierarchical stacking pattern of the sequences and the time span represented by the investigated interval imply that sea-level
fluctuations in the Milankovitch frequency band as well as differential subsidence caused the observed changes of accommodation
on the Jura platform. The present study focuses on three small-scale sequences within the transgressive interval of a large-scale
sequence. The initial flooding of the platform is marked by a facies change from supra- and intertidal (Goldberg Formation)
to shallow-marine subtidal deposits (Pierre Chatel Formation). Detailed logging and facies analysis of 11 sections allow recognizing
small environmental changes that define elementary sequences within the well-established small-scale sequences and distinguishing
between autocyclic and allocyclic processes in sequence formation. It is concluded that the small-scale sequences correspond
to the 100-ka orbital eccentricity cycle, while allocyclic elementary sequences formed in tune with the 20-ka precession cycle.
Based on the correlation of elementary and small-scale sequences it can be shown that the Jura platform has been flooded stepwise
by repeated transgressive pulses. Differential subsidence and pre-existing platform morphology further controlled sediment
accumulation and distribution during the transgression. The combination of high-resolution sequence stratigraphy and cyclostratigraphy
then enables the reconstruction of hypothetical palaeogeographic maps in time increments of a few ten thousand years. |
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