Strontium isotope profile of the early Toarcian (Jurassic) oceanic anoxic event, the duration of ammonite biozones, and belemnite palaeotemperatures

The chronology of multiple landslide deposits and related lake sediments in the eastern Argentine Cordillera suggests that major mass movements cluster in two time periods during the Quaternary: between 35000 and 25000 14C yr BP and after 5000 14C yr BP. The older cluster may correspond to the Minchin wet period (40000 and 25000 14C yr BP) identified in tropical and subtropical South America, suggesting a causal relation between enhanced landslide activity and climate change. The younger cluster predates the Titicaca wet period that began at about 3900 14C yr BP which also affected other regions in the Andes and the Amazon Basin. No landslide and associated lake sediments are documented during the Tauca wet period (between 16000 and 8000 14C yr BP). However, the two clusters correspond to periods where it assumed that the El Ni?o/Southern Oscillation (ENSO) and tropical Atlantic sea surface temperature dipole (TAD) were active. The analysis of the present-day precipitation patterns in NW Argentina indicates significant spatial and temporal differences between the intra-Andean part of the study area and the Andean foreland. Whereas the TAD seems to consistently increase rainfall, the intensity of precipitation during the El Ni?o phase of the ENSO is reduced to only 25% of the mean annual average in the intra-Andean basins, whereas the regions east of the Andes receive more than 125%. Similar results, but with an opposite sign, characterize La Ni?a events. The comparison of this pattern with paleoprecipitation data as inferred from varved lake sediments suggests that increased interannual climate variability and, therefore, increased fluctuations in rainfall and river discharge in narrow valleys may reduce landsliding thresholds.