Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland

Nigel H. Platt; Albert Matter

doi:10.1186/s00015-023-00436-1

Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland

Nigel H. Platt^* (Corresponding Author)
, Albert Matter

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

4 Citations (Scopus)

Abstract

The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ¹³C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Delémont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.

Original language	English
Article number	11
Number of pages	27
Journal	Swiss Journal of Geosciences
Volume	116
Issue number	1
Early online date	28 Jul 2023
DOIs	https://doi.org/10.1186/s00015-023-00436-1
Publication status	Published - Dec 2023
Externally published	Yes

Bibliographical note

We thank Mr. J.-P. Clément for borehole access and the late Dr. J.-P. Berger for palaeontological determinations. We are grateful to Prof. Stephen Burns for stable isotope analyses and to the late Dr Maria Mange-Rajetzky for heavy mineral analyses. Mr. Andy Werthemann took core photos and Mr Vlado Greco prepared thin sections. We thank Dr. Beat Keller for discussions on the Molasse, Dr. Chelsea Pederson and Dr. Anne Fetrow for helpful review of stable isotope results and Dr. Damien Becker for kindly sharing unpublished regional correlations as shown in Fig. 4. Reviews by Drs. Daniel Kälin and Claudius Pirkenseer improved the manuscript significantly. For convenience we have used the German abbreviations UMM, OMM, and USM, OSM for the Lower and Upper Marine, and Lower and Upper Freshwater Molasse, respectively.

Data Availability Statement

Core samples were stored at the Institut für Geologie of the Universität Bern. Heavy mineral analyses and palaeontological specimens are unfortunately no longer available due to the sad demise of Drs. Mange-Rajetsky and Berger.

Funding

The work was carried out under a Swiss National Science Foundation grant.

Funders
Swiss National Science Foundation

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 6 Clean Water and Sanitation
SDG 14 Life Below Water
SDG 15 Life on Land

Keywords

Groundwater recharge
Jura
Karstic aquifer
Lacustrine/palustrine freshwater carbonates
Miocene
Onlap
Shallow marine clastics
Swiss Molasse Basin
Tidal deposits

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Cite this

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title = "Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland",

abstract = "The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ13C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Del{\'e}mont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.",

keywords = "Groundwater recharge, Jura, Karstic aquifer, Lacustrine/palustrine freshwater carbonates, Miocene, Onlap, Shallow marine clastics, Swiss Molasse Basin, Tidal deposits",

author = "Platt, \{Nigel H.\} and Albert Matter",

note = "We thank Mr. J.-P. Cl{\'e}ment for borehole access and the late Dr. J.-P. Berger for palaeontological determinations. We are grateful to Prof. Stephen Burns for stable isotope analyses and to the late Dr Maria Mange-Rajetzky for heavy mineral analyses. Mr. Andy Werthemann took core photos and Mr Vlado Greco prepared thin sections. We thank Dr. Beat Keller for discussions on the Molasse, Dr. Chelsea Pederson and Dr. Anne Fetrow for helpful review of stable isotope results and Dr. Damien Becker for kindly sharing unpublished regional correlations as shown in Fig. 4. Reviews by Drs. Daniel K{\"a}lin and Claudius Pirkenseer improved the manuscript significantly. For convenience we have used the German abbreviations UMM, OMM, and USM, OSM for the Lower and Upper Marine, and Lower and Upper Freshwater Molasse, respectively.",

year = "2023",

month = dec,

doi = "10.1186/s00015-023-00436-1",

language = "English",

volume = "116",

journal = "Swiss Journal of Geosciences",

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AU - Platt, Nigel H.

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N1 - We thank Mr. J.-P. Clément for borehole access and the late Dr. J.-P. Berger for palaeontological determinations. We are grateful to Prof. Stephen Burns for stable isotope analyses and to the late Dr Maria Mange-Rajetzky for heavy mineral analyses. Mr. Andy Werthemann took core photos and Mr Vlado Greco prepared thin sections. We thank Dr. Beat Keller for discussions on the Molasse, Dr. Chelsea Pederson and Dr. Anne Fetrow for helpful review of stable isotope results and Dr. Damien Becker for kindly sharing unpublished regional correlations as shown in Fig. 4. Reviews by Drs. Daniel Kälin and Claudius Pirkenseer improved the manuscript significantly. For convenience we have used the German abbreviations UMM, OMM, and USM, OSM for the Lower and Upper Marine, and Lower and Upper Freshwater Molasse, respectively.

PY - 2023/12

Y1 - 2023/12

N2 - The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ13C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Delémont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.

AB - The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ13C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Delémont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.

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KW - Onlap

KW - Shallow marine clastics

KW - Swiss Molasse Basin

KW - Tidal deposits

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DO - 10.1186/s00015-023-00436-1

M3 - Article

AN - SCOPUS:85166263038

SN - 1661-8726

VL - 116

JO - Swiss Journal of Geosciences

JF - Swiss Journal of Geosciences

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M1 - 11

ER -

Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland

Abstract

Bibliographical note

Data Availability Statement

Funding

UN SDGs

Keywords

Access to Document

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Cite this