A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale.

摘要: The geologic time scale for the Cenozoic Era has been notably improved over last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, middle Eocene remains a weak link. so-called “Eocene gap” reflects scarcity suitable study sections clear astronomically-forced variations in carbonate content, primarily because large parts oceans were starved during greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored carbonate-rich sedimentary sequence age Mentelle Basin (Site U1514, offshore southwest Australia). consists nannofossil chalk exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows extraction an astronomical signal construction astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. XRF-derived ratio between calcium iron (Ca/Fe) tracks lithologic variability serves as basis our astrochronology. We present 16 million-year-long (40-56 Ma) nearly continuous history sedimentation paced eccentricity obliquity. supplement XRF data low-resolution bulk carbon oxygen isotopes, recording long-term cooling trend from Paleocene-Eocene Thermal Maximum (PETM – ca. 56 into (ca. 40 Ma). Our early astrochronology corroborates existing chronologies based on deep-sea sites Italian land sections. For Eocene, sedimentological record at provides single-site geochemical backbone thus offers further step towards fully orbital resolution.