The petrology of North Mountain basalts from the wildcat oil well Mobil Gulf Chinampas N-37, Bay of Fundy, Canada

Abstract

Basalts totalling 236 m in thickness were intersected in the wildcat oil well Mobil Gulf Chinampas N-37 in the Bay of Fundy. A 5.5 m section of conventional core retrieved from the middle of the basalt section sampled two fine-grained, phenocryst-poor, amygdaloidal basalt flows. The basalts, though somewhat altered, show concentrations of ferromagnesian elements (e.g., Fe, Mg, Cr, Ni) and immobile elements (e.g., Zr, Nb, Ta, Hf) as well as chondrite-normalized REE patterns typical of high-Ti quartz-normative tholeiites and are identical to more evolved samples of the North Mountain basalts at Digby. These petrographic and geochemical characteristics allow correlation with middle unit flows of the North Mountain basalts. The lower unit of North Mountain basalt may be as thick in the well as in the Digby area (~200 m), but the upper unit is either missing or very thin (< 68 m). A 25 m thick sedimentary section just above the conventional core but within the basalt sequence has not been reported on land and hints at the existence of a basalt unit not present on North Mountain. The conclusion that North Mountain basalts occur in the Chinampas well suggests that the flows underlie most of the Bay of Fundy, originally covered 9400 km2, and had a total volume of 2350 km3.