Facies and depositional environments of the Upper Muschelkalk (Schinznach Formation, Middle Triassic) in northern Switzerland

Abstract

Subsurface sedimentary strata in northern Switzerland, such as the Middle Triassic Upper Muschelkalk, are attracting interest as potential reservoirs for CO 2 sequestration and for geothermal energy production. Characterizing facies in such strata aids prediction of reservoir properties in unexplored areas. Although well studied elsewhere, the Swiss Upper Muschelkalk has received little attention despite containing the southern-most deposits of the Central European Basin. The Upper Muschelkalk represents the deposits of a storm-dominated, homoclinal carbonate ramp, developed during a basinwide 3rd-order transgressive-regressive cycle. Our facies analyses of nine boreholes across northern Switzerland reveal 12 lithofacies, eight lithofacies associations and four types of metre-scale 5th-order cycles corresponding to at least 23 short orbital eccentricity cycles. During the 3rd-order transgression, crinoidal bioherms developed across Switzerland followed by deep-ramp environments. Subsequently, tempestites were deposited up to and after the basin-wide maximum flooding surface. Lateral tempestite correlations indicate that Switzerland lay within an open-marine, mid-ramp environment during almost half of the depositional history. Mid-ramp deposits pass upwards to prograding shelly shoals, which sheltered a back-shoal lagoon containing patchy oolitic shoals. At the top of the Upper Muschelkalk, back-shoal sediments give way to coastal sabkha facies, which were overlain by oolitic shoals during a marine transgression. Shortly thereafter the top of the Upper Muschelkalk was dolomitized by brines from an overlying hypersaline environment that was later removed by a basin-wide erosive event. Overall, the paucity of porous shoal facies, unlike in southern Germany, has resulted in poor primary reservoir properties in the Upper Muschelkalk of Switzerland.

Microfacies analysis of the Palaeocene Lockhart limestone on the eastern margin of the Upper Indus Basin (Pakistan): Implications for the depositional environment and reservoir characteristics

“…The Lockhart Limestone originated on a typical carbonate homoclinal shelf, which develops at low slope angles during times of minimal tectonic activity, resulting in relatively uniform deposition over large regions. Transitional deposition occurs below the wave base from the inner (near shoreline) to the middle shelf (deeper) zones (Adams & Diamond, 2019). Following a basin‐wide unconformity, facies alternations (together with changes in fossil material) between LMF1, LMF2 and LMF3 (Figures 3 and 4) indicate two very short‐term cycles of deepening and shallowing upwards, coinciding with transgression and regression cycles in the area.…”

Microfacies and stable isotope features of the Lower–Middle Jurassic carbonate rocks of Western Saharan Atlas (Aïn Ouarka area, Algeria)

“…Based on the Ramp Microfacies Types (RMF) (Flügel, 2010), these microfacies are interpreted as the deposits of a middle ramp environment. The mid‐ramp facies association is characterized by wackestone, packstone and floastone microfacies, indicate low to moderate energy condition (Adams & Diamond, 2019).…”

3D‐seismic evidence for thick‐skinned tectonics in a ‘classic’ thin skinned tectonics region (external Alpine foreland, Switzerland)

“…The horizons BMa and BTe are taken from Nagra (2019). Mesozoic depositional environment after Adams and Diamond (2019) and Nagra 1989. OMM, Upper Marine Molasse (Obere Meeresmolasse); TER, terrigenous sediments and karst; USM, Lower Freshwater Molasse (Untere Süßwassermolasse).…”

“…The horizons BMa and BTe are taken from Nagra (2019). Mesozoic depositional environment after Adams and Diamond (2019) (Malz et al, 2015;Marchant et al, 2005). Jurassic thickness variations have independently been documented from sedimentological studies showing facies boundaries and thickness maxima to occur in close spatial relationship to Upper Palaeozoic basins (Allenbach, 2001;Wetzel & Allenbach, 2003).…”