Biostratigraphy of the Lower Cretaceous Schrambach Formation on the classical locality of Schrambachgraben (Northern Calcareous Alps, Salzburg Area)

Abstract

Schrambach Formation in the Eastern Alps area is conceived from the lithological and stratigraphical point of view rather non-uniform. Therefore a 200 m thick section in the type locality of the Schrambach Formation, situated south of Salzburg, is documented in this study. The studied sequence in the Schrambachgraben seems to be in the prevailing part of section in simple, monoclinal mode of deposition. The opposite is true. The section studied begins with the Oberalm Formation, passes gradually into the Schrambach Formation and ends with the lower part of the Rossfeld Formation. According to our detail results, deposits of the Schrambach Formation in this type of section occur in a minimum of three tectonic slices. The first tectonic slice is composed of a transitional sequence of the Oberalm Formation to the Schrambach Formation. The uppermost part of the Oberalm Formation is dated as the Middle Berriasian Calpionella Zone (Elliptica Subzone). According to calcareous dinoflagellates, the lower part of the stratal sequence of the Schrambach Formation belongs to the Fusca Acme Zone, which corresponds to the early part of the Late Berriasian. According to the occurrence of the calpionellids Calpionellites uncinata, Cts. darderi and Cts. major, the second slice belongs to the Early Valanginian. With respect to occurrences of ammonites and non-calcareous dinoflagellates findings, the tectonic slice belongs to the higher Late Berriasian Subthurmannia boissieri ammonite Zone. The Early Valanginian age of the uppermost accessible part of the section is indicated by sporadic findings of Calpionellites darderi and Cts. major and ammonite Thurmanniceras pertransiens. A new genus, Schrambachoceras gen. nov., and a new species, Schrambachoceras weidichi sp. nov., were identified. The basal part of the Rossfeld Formation contains ammonites and non-calcareous dinoflagellates of Late Valanginian age (Neocomites peregrinus ammonite Zone).