Evolution of the Late Jurassic carbonate platform in the NCA

The objective of the proposed project (planned for three years) is to clarify the Late Jurassic to Early Cretaceous geodynamic evolution in time and space of the central Northern Calcareous Alps on the basis of the analysis of shallow water platform carbonates and their resediments in the basinal facies. In general, the Late Jurassic - Lower Cretaceous evolution of these carbonate platforms was interpreted as a time of tectonic quiescence after the formation of basins and rises during late Middle and early Late Jurassic times. Our new investigations show, that the sedimentation of the carbonate platforms and the adjacent basin areas was controlled by strong tectonic activity and sea level changes. We cannot confirm by our investigations of the Late Jurassic carbonate platforms two distinct tectonic pulses 1) late Middle to early Late Jurassic (Callovian to Kimmeridgian) and 2) Hauterivian to Aptian. Our investigations of a multistratigraphic approach carried out showed good accordance between radiolarian biostratigraphy of the cherty basin sediments and the dating of resedimented shallow water platform derived material. This becomes also important since we have first data about the existence of a carbonate platform south of the NCA, evidenced by shallow water debris in mass-flow deposits of the Lower Kimmeridgian to Tithonian Sillenkopf Formation, completely different in facies from the outcrops in the NCA as known at the moment. So the main aims of the proposed project are: 1. To distinguish the southern and northern shallow water carbonate areals and to reconstruct their evolution by facies and stratigraphic data. Dating of the shallow water materials and the matrix (cherty sediments) and the underlying cherty sediments of the shallow water carbonates in the NCA (both by radiolarians) is necessary. 2. By facies and stratigraphic mapping to determine areas and times with increasing subsidence and to get information about the geometry of the areas with increasing subsidence. 3. To investigate the areas of the onset of the shallow water carbonate platform in the NCA. Today the most common models prefer an onset on slides (Hallstatt type), but we can show, that there is no evidence for this. The onset of the shallow water carbonates is bound on thrusts (e.g. Trattberg Rise) and not on the Hallstatt slides. 4. By correlation with radiolarians (underlying sediments and matrix of the mass-flow deposits) to get a better stratigraphic control with evidence for the whole western Tethys realm. 5. To get a better understanding about the late Jurassic tectonic processes discussed controversially at the moment. The Late Jurassic sedimentation was generally interpreted as a period of tectonic quiecence, but we can show, the existence of areas with rapid subsidence, that were filled up by enormous carbonate debris. By ways of this reconstruction, new results about controlling processes of sedimentation in connection with tectonic events are expected, which are very important not only for the tectonic development of the Northern Calcareous Alps and the western Tethys domain but also for our general understanding of sedimentation processes in basins of orogenic belts and the co-existence of newly formed areas with shallow water carbonates. By this, the project is to finish our work since more than 10 years.

The objective of the proposed project (planned for three years) is to clarify the Late Jurassic to Early Cretaceous geodynamic evolution in time and space of the central Northern Calcareous Alps on the basis of the analysis of shallow water platform carbonates and their resediments in the basinal facies. In general, the Late Jurassic - Lower Cretaceous evolution of these carbonate platforms was interpreted as a time of tectonic quiescence after the formation of basins and rises during late Middle and early Late Jurassic times. Our new investigations show, that the sedimentation of the carbonate platforms and the adjacent basin areas was controlled by strong tectonic activity and sea level changes. We cannot confirm by our investigations of the Late Jurassic carbonate platforms two distinct tectonic pulses 1) late Middle to early Late Jurassic (Callovian to Kimmeridgian) and 2) Hauterivian to Aptian. Our investigations of a multistratigraphic approach carried out showed good accordance between radiolarian biostratigraphy of the cherty basin sediments and the dating of resedimented shallow water platform derived material. This becomes also important since we have first data about the existence of a carbonate platform south of the NCA, evidenced by shallow water debris in mass-flow deposits of the Lower Kimmeridgian to Tithonian Sillenkopf Formation, completely different in facies from the outcrops in the NCA as known at the moment. So the main aims of the proposed project are: 1. To distinguish the southern and northern shallow water carbonate areals and to reconstruct their evolution by facies and stratigraphic data. Dating of the shallow water materials and the matrix (cherty sediments) and the underlying cherty sediments of the shallow water carbonates in the NCA (both by radiolarians) is necessary. 2. By facies and stratigraphic mapping to determine areas and times with increasing subsidence and to get information about the geometry of the areas with increasing subsidence. 3. To investigate the areas of the onset of the shallow water carbonate platform in the NCA. Today the most common models prefer an onset on slides (Hallstatt type), but we can show, that there is no evidence for this. The onset of the shallow water carbonates is bound on thrusts (e.g. Trattberg Rise) and not on the Hallstatt slides. 4. By correlation with radiolarians (underlying sediments and matrix of the mass-flow deposits) to get a better stratigraphic control with evidence for the whole western Tethys realm. 5. To get a better understanding about the late Jurassic tectonic processes discussed controversially at the moment. The Late Jurassic sedimentation was generally interpreted as a period of tectonic quiecence, but we can show, the existence of areas with rapid subsidence, that were filled up by enormous carbonate debris. By ways of this reconstruction, new results about controlling processes of sedimentation in connection with tectonic events are expected, which are very important not only for the tectonic development of the Northern Calcareous Alps and the western Tethys domain but also for our general understanding of sedimentation processes in basins of orogenic belts and the co-existence of newly formed areas with shallow water carbonates. By this, the project is to finish our work since more than 10 years.