Synsedimentary Tectonics and Mass Wasting Along the Alpine Margin in Liassic Time

Abstract

The transition from Triassic to Jurassic strata along the passive northern margin of the Neotethys elucidates typical drowning successions of huge Triassic carbonate platforms. Drowning goes parallel with synsedimentary block tectonics that was initiated by rifting at the southern margin border. An intriguing case study is exposed along the saw-cut wall sections of quarries around the village of Adnet close to Salzburg. The deeply submerged, inherited relief of a drowned reef mound gave rise to pronounced Liassic facies differentiation, i.e. (1) deposition of grey spiculitic cherty limestone and marl beds in the former shelf basin, and (2) red nodular limestones, and red condensed limestones rich in ammonites and Fe-Mn crusts over the slope and top of the former reef mound. Faulting, tilting and submarine erosion of Hettangian drift deposits at the lower slope was followed by repeated down-slope gliding, shearing and multiple opening of fissures with different generations of sediment infill. Renewed tectonics from Late Pliensbachian to Middle Toarcian created deep reaching vertical fissures and triggered multiple mass flow events. At the upper and middle slope the so-called Adnet Scheck breccia, which is a special debrite deeply eroding and incising into well-bedded condensed hemipelagic limestone strata, was deposited. Further down-slope the Scheck breccia evolves into more matrix-rich nodular breccias. Basin sections reveal intercalations of mudflow deposits and were affected by various magnitudes of sliding and mass flow events forming complex mass transport deposits.