Satin Spar Gypsum at Clarke Head

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Crystal veins of satin spar gypsum in fault zone rocks

Clarke Head near Parrsboro in Nova Scotia, Canada, is famous for its melange of fault zone rocks. It lies on the Cobequid Fault Line that runs approximately parallel to the north shore of the Minas Basin, part of the Bay of Fundy. Clarke Head is the most southerly exposure of the fault and the area is characterised by smaller fault strands coming off the main fault, dividing different ages of rocks into adjacent blocks and giving rise to much breccia. Breccia is the deposit that is often generated at fault zones and is comprised mostly of angular broken rock fragments. Some of the breccia has massive stones measuring up to 1.5 meters in diameter and is known as megabreccia. Three main rock types are represented at Clarke Head. These are the Blomidon Formation of Triassic red sandstone and siltstone; the North Mountain Formation basalts of Jurassic age; and light gray Windsor Group limestone of Carboniferous age. However, extensive areas are so affected by faulting action that the constituent rocks are all jumbled up.

The fibrous satin spar gypsum in the images shown here permeated the brecciated areas where it crystallised in deep cracks extending through the deposits in twisted sheet-like form.

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