Gravel Bay - calcrete horizon in Moor Cliffs Formation

Freshwater West, Gravel Bay and East Pickard Bay

Moor Cliffs Formation in Gravel Bay.

This photo shows an even closer view of a calcrete soil development in mainly reddened mudstone beds in the Moor Cliffs Formation at the western end of Gravel Bay. The white mottled patches are irregular carbonate patches.

The lens cap is 72 mm in diameter.

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.