Source-to-sink studies help improve the understanding of material pathways within sedimentary basins. This information is of interest to address problems of sediment distribution patterns and mountain range morphological evolution. The Tremp-Graus-Ainsa basin (Southern Pyrenees, Spain) was filled by clastic and carbonate sediments deposited in an active tectonic system of piggyback foreland basin during Late Cretaceous to Oligocene times. The sedimentary infill provides a record of uplift, thrusts motion, weathering and erosion of the active mountain range. Thanks to excellent outcrop continuity and stratigraphic constraints this basin provides an ideal natural example to study sediment pathways and provenance reconstruction in a tectonically active environment and during a period of important climate change (early Eocene climatic optimum). So far, previous studies have focused separately on sandstone petrography in the fluvial-alluvial environment of the Tremp-Graus sub-basin, or on the deep-marine turbiditic environment of the Ainsa sub-basin, without considering the whole source-to-sink relationship between them. Here, automated petrographic characterization of sandstones using QEMSCAN (Quantitative Evaluation of Materials by Scanning Electron Microscopy) is employed on polished thin sections from 6 different locations, combined with optical mineralogy to better constrain the diagenetic overprint on these rocks, and also X-ray diffraction to accurately identify the different clay species. Final quantitative petrographic information is used to reconstruct sediment provenance with modal mineralogy data and heavy mineral ratios. The preliminary results show significant differences in the compositions of sands deposited in the submarine fan systems compared to the fluvial sandstones that are supposedly feeding them. To address this further, QEMSCAN and optical petrography on basement rocks from the surrounding Pyrenean Axial Zone and the Catalan Coastal Ranges was performed to identify possible sediment sources thanks to heavy mineral ratios present in these igneous and metamorphic rocks. The possible mineralogical changes due to diagenetic influence and low-grade metamorphism overprint during burial were also constrained. Finally, clay analysis allows to evaluate the influence of climatic variations between lowstand deposition of sediments in submarine fan systems and sedimentation in continental environment during trangressions and sea level highstands.