This thesis investigates the influence of marine currents on sedimentary processes and reef development within the Laurasian Seaway during the Middle Jurassic, with a focus on northern Switzerland. Integrating seismic, core, outcrop, petrographic, mineralogical and biostratigraphic data, the study offers a new perspective on the interplay between oceanographic and geological processes in a shallow epicontinental seaway, where the sedimentology was previously interpreted as predominantly storm- and tectonically driven.
Newly acquired 2D and 3D seismic data reveal a series of mounded, oval to rounded carbonate platforms embedded within a fine-grained basinal succession, including the previously undocumented «Herrenwis Unit». This 40-meter-thick coral-rich body developed atop a low-relief, clay-rich depositional high and displays features indicative of growth under mesophotic conditions, at water depths of 20–30 meters approximatively. Reef architecture, associated moat structures, and surrounding mounded drift geometries suggest a dominant role of marine currents in shaping the sedimentary environment. The reef shows low coral diversity but high abundance, with twelve coral genera identified and a strong dominance of Periseris, Isastrea, Thamnasteria, and Dendraraea. Palynological dating places the reef in the Early Bajocian (Sauzei and Humphriesianum ammonite zones), aligning its development with similar-aged coral buildups in the Eastern Paris Basin.
In addition to the Herrenwis platform, seismic and core data document other carbonate buildups across the region, including the Gisliflue reef, the subsurface structure near Jestetten, and a newly identified platform north of Herrenwis. These features form a spatially aligned pattern across the northern margin of the Tethys, supporting the hypothesis of widespread, current-influenced reef growth during the Bajocian. The identification of contourite features, including moats, elongated mounded drifts, and erosional truncations, within the surrounding mudstone and limestone units further underscores the influence of bottom currents in this shallow seaway. Hardgrounds and condensed sections interbedded within these successions point to repeated phases of non-deposition or erosion, reinforcing a current-dominated depositional model.
The findings presented in this thesis challenge traditional interpretations of Middle Jurassic strata in the region by highlighting the dominant role of marine currents in both reef ecology and sediment distribution. By documenting reef development in low-relief, current-dominated settings, this work contributes to a broader understanding of Jurassic paleoceanography and reef recovery following Early Jurassic biotic crises. The revised depositional model calls for a reassessment of sedimentary dynamics and reef growth potential in epicontinental seaways under varying climatic and oceanographic regimes.
