Orcadian Basin - Palaeogeography

Palaeogeography

The landscape consisted of rounded hills formed of older metamorphic and igneous rock. The lakes varied in depth and extent from time to time, sometimes lapping against the side of the hills and sometimes retreating so that river flood plains were able to form. Stromatolites can be found at Stromness, indicating that the lake was sometimes saline. Locally scolecodonts (marine microfossils) have been found in the Eday Marl suggesting at least a temporary connection to the sea. The hills were bare of vegetation. The land was not colonised by large plants as it is today, so erosion would therefore be rather rapid and probably seasonal, as would be lake productivity. This is reflected in the deep lake carbonates, which show very fine laminations, interpreted as varves.