undifferentiated rock units

Paleontology and geology

In the Ordovician, the pieces of land that make up northern Nova Scotia (the Avalon zone), as well as other parts of eastern North America and Europe, rifted from Gondwana. This rifting generated significant volcanism. Red-orange lava flows and volcanic ash deposits are found on top of black basalts, which form tall, angular columns in some areas. Ancient soils (paleosols) developed on the basalt flows when there was a quiet interval and now appear as purple-red layers between the flows. Igneous rocks from the Ordovician, many of which have since been metamorphosed, are exposed in the highlands.

The land that is now southern Nova Scotia (the Meguma Zone) remained off the coast of Gondwana in the Ordovician, but the area was getting shallower as more sediment was accumulating from the continent. These sandstones and shales, most of which have now been metamorphosed, share some characteristics with rocks in western Africa, suggesting that this is where the rocks came from. Igneous rocks from the Late Ordovician and Early Silurian document additional rifting, as this area began to split from Gondwana. Fossils are rare in Ordovician rocks; however, graptolite fossils have been found in the Halifax slate (metamorphosed shale).

Due to the complex history of Ordovician age rocks, including periods of metamorphism, intrusion, and erosion, some of the rocks may appear as undifferentiated Paleozoic rocks on this and other maps.