Abstract: Origin of Authigenic Smectite and Zeolite in the Lower Jurassic McCoy Brook Formation, Fundy Basin, Nova Scotia

Lawrence H. Tanner

The McCoy Brook Formation was deposited in the Fundy rift basin during Hettangian-Pliensbachian time as alluvial-fan, fluvial, lacustrine, eolian, sandflat, playa, debris-flow, and talus facies. Authigenic smectite occurs as grain coatings in the fluvial and eolian facies and as void fillings and matrix clay in the debris-flow and talus facies. This smectite is identified as an Fe-rich saponite with a formula of:

[EQUATION]

The calcium zeolites chabazite, heulandite and stilbite occur as pore-filling cements and displacive crystal growths in the eolian, debris-flow and talus facies.

The smectite and zeolites formed by the alteration of basalt associated with these facies under near-surface conditions. Clasts of basalt are incorporated into the eolian, debris-flow and talus facies. These facies were deposited in proximity to paleocliffs of the North Mountain Basalt, which underlies the McCoy Brook Formation. Fluvial sandstones do not contain basalt clasts, but are in fault contact with the North Mountain Basalt. The products of chemical weathering of the basalt were transported by groundwater flow through the permeable sandstones, resulting in neoformation of smectite.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994