Geology of the Halifax Group Anticline

By J.A. Colwell & S.A. Ferguson

tl_files/sites/ees/Images/info/ft-halifaxfm.gifLOCATION - Gaspereau Avenue at the Highway 101 overpass, 1100m (3700 feet) south of Main Street.

ROUTE - Go south on Gaspereau Avenue to the Highway 101 overpass.

DESCRIPTION - Outcrops of Cambro-Ordovician Halifax Group slate (about 500 million years old) are on both sides of the road.  The bedding, indicated by thin alternating layers of lighter and darker colours, is nearly horizontal because the exposure is at the crest of an anticlinal fold (which happens to correspond to the top of the ridge). The cleavage, on the other hand, is almost vertical.

The slate began as fine mud, deposited off the west coast of a continent where Africa is now, across the lapetus Ocean, precursor of the Atlantic. Folding and metamorphism of the muds to slate occurred as the lapetus Ocean closed and the continents collided 380 Ma ago.  A series of major folds formed at this time extend through much of southern Nova Scotia, from Yarmouth to Canso. Their long axes parallel the shoreline of Nova Scotia, and anticlinal crests are about 5 km apart

The cleavage formed perpendicular to the direction of movement as the forces of collision abated and stress on the rock was released.  Because its orientation stays constant, cleavage is nearly parallel to bedding on the limbs of folds; and only seen at a distinct angle, as here, in rare outcrops just at the crests of anticlines or troughs of synclines.  No fossils have been reported here but elsewhere the graptolite Dictyonema sp.,  probably-D. websteri, has been identified.

This is an excellent locality to collect a specimen showing the contrast between bedding and cleavage, or to take a photograph.

There are good views of Minas Basin and Cape Blomidon to the north, and, a little farther along the road, of the Gaspereau Valley to the south.

John A. Colwell and Stewart A. Ferguson Department of Geology, Acadia University, Wolfville, Nova Scotia, 1992

Prepared for the Geological Association of Canada and Mineralogical Association of Canada Joint Annual Meeting in Wolfville, Nova Scotia, May 25-27, 1992. Meeting Hosted by the Atlantic Geoscience Society.