Burning shales and exteme acidity in the Smoking Hills, Arcitc Canada
本讲教师：Stephen E. Grasby
报告人简介:Stephen E. Grasby长期从事沉积地球化学、稳定同位素地球化学及地球微生物学等方面的研究，在Nature Geosciencer Geology, Geochimica et Cosmochimica Acta、Geological Society of America Bulletin、Chemical Geology等国际知名地学期刊上发表论文100多篇。 报告摘要: The Smoking Hills, east side of Cape Bathurst, Canadian Arctic, are characterised by emissions ofsmoke composed of water vapour and hot sulphuric acid gases from vent holes (termed bocannes)that are surrounded by variable, but often brightly coloured, mineral deposits. The burning has beenshown to be related to combustion of organic matter and is associated with oxidation of disseminatedpyrite within the shales. Extinct sites that are no longer venting gas are characterised by vividlycoloured brick red to yellow deposits of thermally altered shale known as clinker deposits. Auto combustion of the Smoking Hills Formation is not restricted to sea cliffs of Franklin Bay as thought byearlier workers. We observed that both bocannes and clinker sites occur over a wide area of Cape Bathurst, between F ranklin Bay and the Anderson River, that occur in clear association with outcropsof the bituminous Smoking Hills Formation. Actively burning sites all occurred in areas with evidenceof recent slumping that has ex posed fresh surfaces of the bituminous shale, either by sea or streamerosion of outcrops. Also, bocannes form not only directly below the failure faces, but within debrisflow lobes extending well down-slope of the initial failure. Previous work in this area noted ponds with pH values as low as 3. Workers had suggested that pondswere acidified ina process similar to modern anthropogenic acid rain acidification oflakes, wherebyclouds of acid gas from bocannes blown inland acidify ponds in the downwind direction. This previouswork though did not examine the ponds relative to the bedrock geology. We show that acid ponds are restricted to outcrop of the Smoking Hills Formation. Some ponds show extreme acidity with pH as lowas negative 1.44(-1.44). In contrast, ponds that are being actively fumigated by burning shales, but lieon the Mason Formation, or glacial materials, are near neutral pH, showing that pH is moderated by thestrong buffering capacity of the underlying bedrock. We hypothesize that the occurrence of acid pondsis related to a process more similar to natural acid mine drainage rather than acid rain. We tested thisthrough lab experiments, whereby samples of the Smoking Hills Formation are shown to acidify waterswithin hours of exposure. Along with low pH, these waters have extremely high trace metal content,creating some of the most toxic naturally occurring waters known.