Early Permian during the Variscan orogen collapse in the equatorial realm: insights from the Cantabrian Mountains (N Iberia) into climatic and environmental changes

We report the results of a multidisciplinary study of the early Permian (Artinskian-Kungurian) Sotres Formation of northern Spain integrating sedimentology, palaeosols, mineralogy, stable isotopes, palynology, ichnology and tectonics. This continental unit was deposited in the near-equatorial Peri-Tethyan Cantabrian Basin. Having developed in the middle of the Variscan fold belt, it is preserved within the present-day Cantabrian Mountains. Three subunits are recognised in the Sotres Formation based on tectono-stratigraphic and sedimentological data: a lower alluvial subunit, a middle carbonate lacustrine subunit, and an upper palustrine subunit. Multidisciplinary results reveal an upward change in climate from humid-subhumid conditions at the base of the formation (Artinskian) to semi-arid and arid conditions at the top of the formation (Kungurian), which may reflect global deglaciation near the end of the Late Paleozoic Ice Age and a probable northward migration of the Intertropical Convergence Zone. This general upward warming/drying climate trend was interrupted by a short-lived interval of monsoon conditions in mid-Kungurian times, which may have coincided with a pulse of global cooling. Our findings are in agreement with the climate trends reported for other central Pangaean basins. Rising CO2 levels may have been a driving factor for climate transition during this time interval. However, in our study area, which lies within the active central Variscan orogenic belt, tectonic conditions must have also played a role in driving climate change.

Automated summary

This multidisciplinary study of the early Permian Sotres Formation in northern Spain reveals a climate transition from humid-subhumid conditions to semi-arid and arid conditions over time, with a brief interval of monsoonal conditions. The findings suggest a possible connection to global deglaciation and a northward migration of the Intertropical Convergence Zone towards the end of the Late Paleozoic Ice Age. Tectonic conditions within the active central Variscan orogenic belt may have also played a role in driving climate change in the study area.