Stratigraphic architecture of a mixed clastic-carbonate succession and ⁸⁷Sr/⁸⁶Sr-based chronostratigraphy along the margin of a synorogenic extensional basin (Hochmoos Formation, upper Santonian, Northern Calcareous Alps)

Abstract The Gosau Group (Turonian to Ypresian) of the Eastern Alps is a synorogenic wedge-top succession that accumulated in active depocenters an oblique-convergent plate tectonic setting. Due high morphological differentiation by tectonism, displays wide range facies as well marked heteropy and thickness variations over short lateral distances. In area locations Russbach, Hochmoos Formation along SE basin margin near Gosauschmied comprises coastal shallow-marine deposits small rudist bioconstructions was investigated way field mapping, profile descriptions, microfacies analysis, isotope measurements assessment fossil content. Strontium ratios ( 87 Sr/ 86 Sr) from 0.707485 (oldest) 0.707549 (youngest) indicate latest Santonian age, with youngest parts possibly extending into Campanian. On west side study area, lithologies content record transgression fan-delta marginal-marine environment (lowstand transgressive systems tract), followed shallow neritic deposition (part tract) and, finally, progradational stacking limestone beds highstand tract, culminating growth thickets inner shelf partially protected ‘lagoonal’ milieu. Eventually, at inception following falling stage input large clasts Dachstein Limestone, quartz chert recurrence subaqueous part fan-delta. east preponderance rudist-clastic limestones few biostromes preserved situ normal-marine punctuated high-energy events, such storms or tsunami. scarcity benthic foraminifera presence only isolated specimens colonial corals underscore habitat calcarenitic substrate frequently shifted currents. Several lines evidence western more proximal relative eastern one. With maximum 68 m, slightly thicker distal than outcrops located nearer farther towards (Schmiedsippl, Katzhofgraben), but significantly thinner nearly 300 m Pass-Gschütt, 170 observed Rigaus-Abtenau West. These are interpreted result extensional syndepositional tectonism. At Gosauschmied, vertical arrangement records cycle sea-level change may have been tectonically enhanced.