MUDDY WATERS: TRIASSIC-JURASSIC SOIL LOSS, EXTINCTION, AND ANOXIA (Invited Presentation)

Soils are a crucial link between the atmosphere, biosphere, and geosphere and 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 and extinction for the end-Triassic mass-extinction event based on proxy data obtained from core material from France, Germany, England, Denmark, and Sweden. Clay mineral and palynological data indicate a strong increase in chemical weathering and mechanical erosion during the latest Rhaetian with the influx of kaolinite and abundantly reworked Palaeozoic organic matter. Based on a new timeline, these changes were coeval with intense volcanic activity in the Central Atlantic Magmatic Province, which released large quantities of volatiles that contributed directly and indirectly to enhanced weathering. Erosion rates likely also rose in response to deforestation, repeated forest fires, and seismic activity related to CAMP emplacement. Using a novel proxy based on biological degradation of fern spore walls, the intensity of biodegradation by fungi and bacteria, a process coupled to organic matter decay in soils, strongly decreased across the T/J boundary. We interpret this as evidence for the widespread removal of soils. Soil loss may also have contributed to turnover in ground beetles, in contrast to flying insects, such as moths and butterflies that show a remarkable diversification. In the marine realm, anoxic to euxinic conditions in shallow seas across the T/J boundary was associated with profound changes in phytoplankton communities. Large scale disturbances in soils likely altered nutrient delivery, increasing ammonium influx, promoting blooms of chlorophyte algae. Taken together, CAMP induced environmental changes led to profound changes in weathering and erosion and removal of soils, while soil resilience during the Hettangian appears to have proceeded hand in hand with recovery in Jurassic seas.