Evidence of Carboniferous Volcanic Ash in Pictou Group (Westphalian D), Sydney Coalfield, Nova Scotia, Canada
Until now, Carboniferous-altered volcanic ash in North America was known only from the Middle Pennsylvanian (upper Westphalian A to lower Westphalian D) of the Appalachian basin. Now, however, mineralogical analysis of thin claystones (8-24 mm thick) in mineable bituminous coal (Hub and Harbour seams) form the P-boreholes in the Donkin submarine areas of the Sydney coalfield, Nova Scotia, indicates the presence of trace amounts of minerals probably derived from a volcanic ash fall of late Westphalian D age. Water-clear to cloudy quartz splinters and euhedral zircon with sharp crystal faces and edges, and length-to-width ratios up to 6:1--which are typical of Appalachian altered acidic volcanic ash deposits (tonsteins)--were identified in three samples. The volcanic ash grains were adm xed with a dominantly detrital (fluvial?) mineral suite. Fifty to 90% waterlaid silt- to sand-size detrital grains of quartz, tourmaline(?), zircon, white mica, and other minerals are found in the HF residum after the removal of the dominant components: clay minerals, pyrite, and coal particles (spores, secretinite, etc.). The fine size of the volcanic minerals and their low concentration indicate a very distant volcanic ash source, perhaps western Europe, where volcanic activity extended into the Stephanian.
AAPG Search and Discovery Article #91005 © 1991 Eastern Section Meeting, Pittsburgh, Pennsylvania, September 8-10, 1991 (2009)