The Tumblagooda Sandstone is a geological formation deposited during the Silurian or Ordovician periods, between four and five hundred million years ago, and is now exposed on the west coast of Australia in river and coastal gorges near the tourist town of Kalbarri, Kalbarri National Park and the Murchison River gorge,[1] straddling the boundary of the Carnarvon and Perth basins.

[4] The base of the formation is not exposed, but geophysical data (primarily magnetic) indicate the sandstone unconformably overlies a Proterozoic basement.

[2][5] The lowest facies association in the unit is dominated by trough cross-stratification, deposited by broad, high-energy braided rivers, which formed the outwash plain of an alluvial system.

FA2 also contains a dense, varied trace fossil assemblage, taken by some[2][5] as indicative of a tidal, marine-influenced setting, given the Tumblagooda Sandstone clearly predates the widespread development of land plants.

Current and wave ripple marks are also widespread, which may have formed on tidal flats as water depths varied,[2] or perhaps in shallow streams, with flooded hollows hosting the creators of the trace fossils.

The upper units are strongly bioturbated, with an abundance of vertical burrow such as Skolithos[2][5] - a fossil typically found in marine environments.

[3] It has been interpreted as an inter-distributary bay,[2] or alternatively as a sandy coastline featuring wave-generated bars, perhaps with tidal influence; braided fluvial streams often reworked the sediments.

Since the Tumblagooda Sandstone comprises a sedimentary succession with no volcanic layers (which could be dated radiometrically) and with virtually no body fossils, its age is very difficult to constrain.

[11] This was apparently confirmed by the identification in the overlying beds of a conodont fauna with a recognizably Silurian character,[12] but when the palæomagnetism of the area was studied, an early Ordovician age was deduced.

Only one body fossil, Kalbarria (an early euthycarcinoidic arthropod) has been found in the Tumblagooda, mainly due to the large clast size and the abundance of predatory and burrowing organisms.

[15] (This meant that oxygen could penetrate to good depths in the sediment, permitting decomposing organisms to decay anything that burrowing animals had not eaten too rapidly for fossils to form.)

[3] Behaviour can be inferred from these traces; in places, they parallel features which modern observation notes forming at the edge of a wind-blown pond, just on the landward side of the shore.