Gravel Bay - Moor Cliffs Formation 2

Freshwater West, Gravel Bay and East Pickard Bay

Moor Cliffs Formation in Gravel Bay.

This photo shows a closer view of the wave cut platform in the Moor Cliffs Formation at the western end of Gravel Bay. A light purple sandstone bed with greenish laminae is seen in the centre of the photo with red mudstones below (left) and above (right). The darker perpendicular features in the sandstone are trace-fossil Beaconites burrows. Having previously been tentatively ascribed to worm burrows or lung-fish burrows, they are now thought to have been made by primitive millipede-like animals.

The white mottling in the mudstones indicate extensive calcrete soil horizons. The sequence is dipping to the north (right) at approx. 60°.

The walking stick is about 0.9 m long.

Background:
The Moor Cliffs Formation overlies the Freshwater East conglomerates, seen in previous photos, and spans the boundary between the Silurian and Devonian periods. It consists of red mudstones and siltstones with occasional thin sandstone beds. These were deposited on a low-reflief floodplain at the edge of an arid continental margin, the sandstones being deposited by seasonal braided streams, the muds and silts deposited in ephemeral marginal lakes. When not inundated, the muds and silts developed carbonate-rich calcrete (caliche) soil horizons along dessication cracks, burrows and early plant root systems.