1/320 f/6.3 85.0 mm ISO 100

Canon EOS 600D

EF-S15-85mm f/3.5-5.6 IS USM


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Geology Geology



Keywords

rocks
Pembrokeshire
Wales
geology
coast
sandstone
burrow
trace fossil
Gravel Bay
Moor Cliffs Formation
Beaconites


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Gravel Bay - millipede-like burrows in Moor Cliffs Formation sandstone

Gravel Bay - millipede-like burrows in Moor Cliffs Formation sandstone
Freshwater West, Gravel Bay and East Pickard Bay

Moor Cliffs Formation in Gravel Bay.

This photo shows a close-up view of the light purple sandstone bed with greenish laminae seen in the previous photo. 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 bed is approx. 50 cm thick (top to bottom) in this photo.

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.

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