Hans-Ulrich Schwarz:

Sedimentary structures and facies analysis of shallow marine carbonates

Lower Muschelkalk, middle triassic, southwestern Germany

1975. 100 pages, 35 figures, 1 table, 11 plates, 16x24cm, 280 g
Language: English

(Contributions to Sedimentary Geology, Volume 3)

ISBN 978-3-510-57003-4, paperback, price: 28.00 €

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Synopsis top ↑

Interpretation of the sediments and structures of the Lower Muschelkalk in terms of sedimentation, erosion, deformation, and diagenesis yielded a model for the mode of formation of shallow marine carbonates.

Some uncommon sedimentary structures typical to the sequence under consideration, such as wavy tidal lamination, ‘Kinneyia-ripples’ (= real micro-ripples), shear slab joints (= small-scale intrastratal faulting), and channel-slumping, may indicate an intertidal calcareous environment. Early dolomitization is frequent. In the sandy marginal facies, abundant load structures suggest sudden changes in sedimentation rate. The frequency of deformational structures gave rise to discuss the occurrence of earthquakes.

The evolution of the basin is shown by maps and profiles. Above the terrestrial and near-shore red beds of the Buntsandstein (A) a change from shallow and hypersaline to deeper and normal sea water conditions is shown by the following sequence: red clay and siltstone with evaporites (B)-stromatolitic lagoonal dolomites (C) - barrier-like shell banks (D) - marly shallow-shelf sediments (E) - dark stillwater marls (F). This was followed by a facies development not unidirected and represented by the sequence: bioturbate marls (G) - well bedded marls with cross-bedded carbonates (H) - black stillwater shales (I). The Lower Muschelkalk ends with the reverse of the first-mentioned sequence: marly shelf deposits (K) - tidal flat sediments (L/M) - barrier-like oolitic shell banks (N) - laminated, bituminous marls (O) - stromatolitic, hypersaline dolomites (P) - evaporites with marginal red beds (Q), pointing to a return of evaporitic conditions fully developed later in. the Middle Muschelkalk.

Within this sequence one unit (L) runs unconformable through at least two facies units as a marker layer which is considered as the most reliable isochronous horizon of the Lower Muschelkalk.

Table of Contents top ↑

1. Introduction 2
2. Sedimentary units of the Lower Muschelkalk and facies development
3. Primary composition and texture 4
3.1 Micron-/decimicron-sized carbonate 16
3.2 Oolites and related forms 17
3.3 Skeletal grains 18
3.4 Algal limestones 19
3.5 Ripple marks 22
3.6 Bedding types 25
3.7 Minor facies sequences 29
4. Erosion and lacunae 31
4.1 Tidal creeks 31
4.2 Tidal grooves 32
4.3 Current marks 34
4.4 Intraformational pebbles 35
4.5 Hardgrounds and related forms 36
5. Preconsolidation deformation 39
5.1 Slab joints 39
5.2 Subaqueous slumping and mass flow 47
5.3 Load structures 54
5.4 Ichnofauna and bioturbation 62
6. Diagenesis 66
6.1 Compaction 67
6.2 Cracks and fissures 67
6.3 Stylolites 71.
6.4 Authigenic celestite 71
6.5 Gypsum and residuals 72
6.6 Dolomitization 74
7.Conclusions 77
7.1 General results 77
7.2 Sequence of events 78
7.3 Paleoenvironmental results 79
7.4 Paleogeography 81
7.5 Depositional history 81
8. Acknowledgments 85
9. Appendix: Proposals to field trips 85
10. References 93

Plates 93