资源环境科技发展态势分析平台

The discovery of elevated concentrations of the cosmogenic radionuclide 3He in deepsea sediments from Ocean Drilling Program (ODP) Site 926 (Atlantic Ocean) and ODP Site 757 (Indian Ocean) points toward accretion of extraterrestrial matter, probably as a result of the catastrophic disruption of a large asteroid that produced the Veritas family of asteroids at ca. 8.3 +/- 0.5 Ma, and which may have had important effects on the global climatic and ecologic systems. Here, we investigated the signatures possibly related to the Veritas event by performing a highresolution multiproxy stratigraphic analysis through the late Tortonian-early Messinian Monte dei Corvi section near Ancona, Italy. Closely spaced bulk-rock samples through a 36-m-thick section, approximately spanning from ca. 9.9 Ma to ca. 6.4 Ma, show an similar to 5-fold 3He anomaly starting at ca. 8.5 Ma and returning to background values at ca. 6.9 Ma, confirming the global nature of the event. We then analyzed, at 5 cm intervals, bulk-rock samples for sedimentary and environmental proxies such as magnetic susceptibility, calcium carbonate content, total organic carbon, and bulk carbonate delta O-18 and delta C-13, through a 21-m-thick section encompassing the He-3 anomaly. Available high-resolution sea-surface temperature data (via alkenone analyses) for this site show a temperature decrease starting exactly at the inception of the He-3 anomaly. Cyclostratigraphic fast-Fourier-transform spectral analyses of the proxies indicate an age of 8.47 +/- 0.05 Ma for the inception of the He-3 anomaly. A search for impact ejecta (analogous to what is present in the late Eocene, where both a He-3 anomaly and large-scale impact events are recorded) was not successful. Detailed cyclostratigraphic analyses of our data suggest that the changes in the stable isotope series and environmental proxy series through this late Tortonian time interval had a common forcing agent, and that perturbations of orbitally forced climate cycles are present exactly through the interval with the enhanced influx of extraterrestrial He-3. Thus, the chemostratigraphic evidence for a collisional event that created the Veritas family of asteroids, coinciding with climate perturbations on Earth, suggests yet another form of interaction between Earth and the solar system.