Evidence of Carboniferous Volcanic Ash in Pictou Group (Westphalian D), Sydney Coalfield, Nova Scotia, Canada

LYONS, PAUL C., U.S. Geological Survey, Reston, VA, PETER A. HACQUEBARD, Atlantic Geoscience Centre, Dartmouth, Nova Scotia, Canada, and WILLIAM F. OUTERBRIDGE, U.S. Geological Survey, Reston, VA

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)