Abstract
Detailed characterization of variations in sediment architecture, flux, and transport processes in peri-orogenic basins offers insights into external climatic or tectonic forcings. We tested how four well-known tectonic/erosional events in the Oligocene/Miocene Alpine source area are recorded in the sediment-accumulation rates (SARs) of the deep marine sink in the Northern Alpine Foreland Basin (NAFB): exhumation of the Lepontine Dome (starting at 30 Ma) and the Tauern Window (23-21 Ma), erosion of the Augenstein Formation (~21 Ma), and the visco-elastic relaxation of the European Plate. The Upper Austrian NAFB offers a unique opportunity to investigate external forcings on sedimentary infill due to the large amount of data on the Alpine source and Foreland. Deep-marine sedimentation, forming the Puchkirchen Group and the basal Hall Formation, was controlled by a basin-axial submarine channel (3-5 km wide, >100 km length). Two basin-wide unconformities were recognized in seismic-reflection data: the Northern Slope Unconformity (NSU) and the Base Hall Unconformity (BHU). We combine biostratigraphic and chemostratigraphic analyses of 316 drill-cutting samples from three wells with a large 3D-seismic-reflection data set (3300 km2, >5 km depth) to determine age and duration of the unconformities and to calculate spatially averaged SARs for the submarine channel and its overbanks, separately. Deepening of the basin, recorded by the NSU, occurred between 28.1 and 26.9 Ma. The Puchkirchen Group (26.9–19.6 Ma) is characterized by constant SARs (within standard deviation) in the channel (432–623 (t/m2/Ma)) and on the overbanks (240–340 (t/m2/Ma)). The visco-elastic relaxation of the European Plate results in low SARs on the overbanks (186 (t/m2/Ma)), a decrease in sediment grain size in channel deposits and a decrease in sea level at the BHU (19.6–19.0 Ma). In the upper Hall Formation (19.0–18.1 Ma), clinoforms prograding from the south filled up the basin (1497 (t/m2/Ma)) within 1 Myrs. We conclude that only two of the tectonic signals are recorded in this part of the deep-marine sink, erosion of Augenstein Formation and visco-elastic relaxation of the European Plate; the exhumation of the Tauern Window and Lepontine Dome remain unrecorded.
Highlights
Sediment production, paleotopography, sediment-routing and transport processes control the temporal and spatial infill of peri-orogenic basins
Samples for bio- and chemostratigraphy were collected from three drill sites, one from the northern margin (Well H; Figures 1, 5) and two from the southern margin of the basin (Well W and Well Z, Figures 6, 7)
As nannofossil markers indicative of NP25 or younger are absent, we suggest an age of NP24 which is in agreement with Sachsenhofer et al (2010) and Soliman (2012)
Summary
Paleotopography, sediment-routing and transport processes control the temporal and spatial infill of peri-orogenic basins. The identification of the dominating control processes offers insights into the underlying external environmental forcing mechanisms such as climatic transitions or deep-seated tectonic processes (Clift, 2006; Guillocheau et al, 2012; Gulick et al, 2015). Calculation of spatially averaged sediment-accumulation rates (SARs) allow to investigate these external environmental forcings and intrinsic controls within the sediment-routing system (Romans et al, 2016). The correct interpretation of external environmental forcings from the sedimentary record remains challenging as its signal might be buffered (Clift and Giosan, 2014), shredded (Jerolmack and Paola, 2010), delayed (Schlunegger and Castelltort, 2016), or masked by autogenic processes (Murray et al, 2009). The precise evaluation of all depositional environments of the sedimentary system, both in space and in time, is crucial, as environmental signals may be recorded differently in different depositional environments within a single sedimentary system (e.g., Romans et al, 2016)
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