Catastrophic soil loss associated with end-Triassic deforestation

Abstract

Soils are a crucial link between the atmosphere, biosphere, and geosphere. Any disturbance to the health of soils will severely impact plants as well as a multitude of organisms living in or on soils, such as fungi, bacteria, and insects. Catastrophic soil loss is thought to have played a pivotal role during mass-extinction events as a result of major deforestation, but the exact feedbacks remain elusive. Here, we assess the role of soil loss during the end-Triassic mass-extinction event based on proxy data obtained from four sediment sections recovered from France, Germany, and Denmark. Clay mineral and palynological data indicate a strong increase in erosion during the latest Rhaetian with the influx of kaolinite and abundantly reworked Palaeozoic and Neoproterozoic organic matter. Based on a new timeline, these changes were coeval with intense volcanic activity in the Central Atlantic Magmatic Province (CAMP). In addition to vegetation dieback, repeated forest fires, as well as widespread seismic activity related to CAMP emplacement led to landscape destruction triggering removal of soils. The biological degradation of fern spore walls by fungi and bacteria, a process coupled to organic matter decay in soils, strongly decreased across the T/J boundary. We interpret this counter-intuitive result as evidence for rapid and widespread removal of soils. Taken together, CAMP induced environmental changes led to profound changes in erosion and removal of soils, while soil resilience during the Hettangian appears to have proceeded hand in hand with recovery in Jurassic seas.