TY  - JOUR
A1  - Hülscher, Julian
A1  - Sobel, Edward R.
A1  - Kallnik, Niklas
A1  - Hoffmann, J. Elis
A1  - Millar, Ian L.
A1  - Hartmann, Kai
A1  - Bernhardt, Anne
T1  - Apatites record sedimentary provenance change 4-5 myrs before clay in the Oligocene/Miocene Alpine molasse
JF  - Frontiers in Earth Science
N2  - Extracting information about past tectonic or climatic environmental changes from sedimentary records is a key objective of provenance research. Interpreting the imprint of such changes remains challenging as signals might be altered in the sediment-routing system. 
We investigate the sedimentary provenance of the Oligocene/Miocene Upper Austrian Northern Alpine Foreland Basin and its response to the tectonically driven exhumation of the Tauern Window metamorphic dome (28 +/- 1 Ma) in the Eastern European Alps by using the unprecedented combination of Nd isotopic composition of bulk-rock clay-sized samples and partly previously published multi-proxy (Nd isotopic composition, trace-element geochemistry, U-Pb dating) sand-sized apatite single-grain analysis. 

The basin offers an excellent opportunity to investigate environmental signal propagation into the sedimentary record because comprehensive stratigraphic and seismic datasets can be combined with present research results. The bulk-rock clay-sized fraction epsilon Nd values of well-cutting samples from one well on the northern basin slope remained stable at similar to-9.7 from 27 to 19 Ma but increased after 19 Ma to similar to-9.1. In contrast, apatite single-grain distributions, which were extracted from 22 drill-core samples, changed significantly around 23.3 Ma from apatites dominantly from low-grade (<upper amphibolite-facies) metamorphic sources with Permo-Mesozoic and late Variscan U-Pb ages and epsilon Nd values of -4.4 to dominantly high-grade metamorphic apatites with late Variscan U-Pb ages and epsilon Nd values of -2.2. 

The change in apatite single-grain distributions at 23.3 Ma is interpreted to result from the exposure of a new Upper Austroalpine source nappe with less negative epsilon Nd values triggered by the ongoing Tauern Window exhumation. Combining these data with the clay-sized bulk-rock epsilon Nd values reveals that the provenance changed 4-5 Myrs later at 19 Ma in the clay-sized fraction. 
Reasons for the delayed provenance-change recording are rooted in the characteristics of the applied methods. 
Whereas single-grain distributions of orogen-wide sediment-routing systems can be dominated by geographically small areas with high erosion and mineral fertility rates, bulk-rock methods integrate over the entire drainage basin, thus diminishing extreme values. Hence, by combining these two methods, spatial information are uncovered, enabling a previously unattained understanding of the underlying environmental change.
KW  - apatite geochemistry and U-Pb dating
KW  - Nd isotopic composition
KW  - clay
KW  - provenance
KW  - Northern Alpine Foreland Basin
KW  - Eastern Alps
KW  - Tauern Window;
KW  - sediment routing system
Y1  - 2022
U6  - https://doi.org/10.3389/feart.2022.914409
SN  - 2296-6463
VL  - 10
PB  - Frontiers Media
CY  - Lausanne
ER  -