TY - THES

T1 - Folding versus strike-slip tectonics in the Late Jurassic - Early Cretaceous Leube quarry (Salzburg)

T2 - new insights based on sedimentology and geochemistry

AU - Hirschhuber, Hans

N1 - embargoed until 07-11-2027

PY - 2022

Y1 - 2022

N2 - The Gutratberg area southwest of Salzburg has a long mining tradition and exploitation history within its Late Jurassic to Early Cretaceous sedimentary succession. Due to the excellent outcrop conditions in these normally strongly weathered and therefore covered sedimentary rocks this area experienced a long history of geological studies, resulting in controversial discussions. Nowadays the Leube company mines the predominantly marly silicious limestones (Oberalm and Schrambach Formations) for their cement plant. The open pit mine exposes sedimentary profiles from the Tithonian to the Valanginian with outcrops of the Oberalm, Schrambach and Rossfeld Formations dissected by numerous faults and some strongly folded parts. Multi proxy studies carried out in the past ten years indicate a tectonic setting not in accordance with the presumed folding concept for the quarry interpreting the area as simple anticlinal structure. The aim of this work is to gather new information from a section of the Oberalm Formation on the eastern rim of the pit near the exposed Jurassic/Cretaceous boundary. Still until nowadays the exact position of the Jurassic/Cretaceous boundary is not fixed (GSSP) and all discussed sections worldwide are condensed, in contrast to the Leube quarry section. To avoid a gap in the dataset every bed of the profile was sampled, a thin section prepared and a geochemical XRF analysis performed. Age dating of the profile is based on calpionellid biostratigraphy. The presence of Calpionella alpina along the whole section confirms the Tithonian to Berriasian age. Based on the morphological change of Calpionella alpina to small, globular shapes with an ellipticity below 1, the Jurassic/Cretaceous boundary could be exactly defined, but no other proxies indicate this important system boundary. As almost everywhere the Oberalm formation is build up by macroscopically and microscopically uniform micritic, silicious and in cases marly limestones with intercalated shallow-water turbidites and mass transport deposits throughout the Late Tithonian to Middle Berriasian. Beside some cherty layers no macroscopic specifics were detected and this correlates with the uniform microfacies under the microscope. The limestones and marls can be classified as radiolarian micrites fitting to the high biogenous silica content in the geochemical dataset. To overcome the problems with the microscopic discrimination of this Oberalm limestones, a more detailed study of the geochemical samples was carried out. Beside a closer look on the data distribution and the absolute values of the measured elements, the correlation of the oxides was investigated. Furthermore a principal component analysis was conducted. The outcome of the data analysis combined with the results of the microfacies analysis and biostratigraphic age dating give new insights in the structure and architecture of the whole Leube quarry. In contrast to the folding model (Plöchinger-Antiklinale) in this work a strike-slip regime as dominating tectonic element is the more convincing interpretation, but has to be worked out in a greater scale. The sedimentological difference in the investigated Leube profiles supports the assumption of strike-slip tectonics as well as structural observations during the field work and the geological history of this area. Theses findings imply major changes for the amount of available resources, their quality and distribution in the quarry. The new geological results should also be considered for the future conception of the Leube pit’s geometry.

AB - The Gutratberg area southwest of Salzburg has a long mining tradition and exploitation history within its Late Jurassic to Early Cretaceous sedimentary succession. Due to the excellent outcrop conditions in these normally strongly weathered and therefore covered sedimentary rocks this area experienced a long history of geological studies, resulting in controversial discussions. Nowadays the Leube company mines the predominantly marly silicious limestones (Oberalm and Schrambach Formations) for their cement plant. The open pit mine exposes sedimentary profiles from the Tithonian to the Valanginian with outcrops of the Oberalm, Schrambach and Rossfeld Formations dissected by numerous faults and some strongly folded parts. Multi proxy studies carried out in the past ten years indicate a tectonic setting not in accordance with the presumed folding concept for the quarry interpreting the area as simple anticlinal structure. The aim of this work is to gather new information from a section of the Oberalm Formation on the eastern rim of the pit near the exposed Jurassic/Cretaceous boundary. Still until nowadays the exact position of the Jurassic/Cretaceous boundary is not fixed (GSSP) and all discussed sections worldwide are condensed, in contrast to the Leube quarry section. To avoid a gap in the dataset every bed of the profile was sampled, a thin section prepared and a geochemical XRF analysis performed. Age dating of the profile is based on calpionellid biostratigraphy. The presence of Calpionella alpina along the whole section confirms the Tithonian to Berriasian age. Based on the morphological change of Calpionella alpina to small, globular shapes with an ellipticity below 1, the Jurassic/Cretaceous boundary could be exactly defined, but no other proxies indicate this important system boundary. As almost everywhere the Oberalm formation is build up by macroscopically and microscopically uniform micritic, silicious and in cases marly limestones with intercalated shallow-water turbidites and mass transport deposits throughout the Late Tithonian to Middle Berriasian. Beside some cherty layers no macroscopic specifics were detected and this correlates with the uniform microfacies under the microscope. The limestones and marls can be classified as radiolarian micrites fitting to the high biogenous silica content in the geochemical dataset. To overcome the problems with the microscopic discrimination of this Oberalm limestones, a more detailed study of the geochemical samples was carried out. Beside a closer look on the data distribution and the absolute values of the measured elements, the correlation of the oxides was investigated. Furthermore a principal component analysis was conducted. The outcome of the data analysis combined with the results of the microfacies analysis and biostratigraphic age dating give new insights in the structure and architecture of the whole Leube quarry. In contrast to the folding model (Plöchinger-Antiklinale) in this work a strike-slip regime as dominating tectonic element is the more convincing interpretation, but has to be worked out in a greater scale. The sedimentological difference in the investigated Leube profiles supports the assumption of strike-slip tectonics as well as structural observations during the field work and the geological history of this area. Theses findings imply major changes for the amount of available resources, their quality and distribution in the quarry. The new geological results should also be considered for the future conception of the Leube pit’s geometry.

KW - mining

KW - cement

KW - cement industry

KW - sedimentology

KW - geochemistry

KW - stratigraphy

KW - Bergbau

KW - Zement

KW - Zementindustrie

KW - Sedimentologie

KW - Geochemie

KW - Stratigraphie

M3 - Master's Thesis

ER -