Caversham Sandstone Fossils at Blackhead

Collection site is on Blackhed Road near Quarry

As one drives from the Dunedin to Waldronville via Blackhead Road and before the Blackhead Quarry turnoff large banks of a creamy yellow material can be seen. This material is known as Caversham Sandstone which is more prevalent just south of Dunedin. Along the Coast are massive cliffs of this calcareous sandstone overlain by sandy limestone and calcareous mudstone Stretching from St Clair to Blackhead.

A popular walk from around this area is Tunnel Beach – with its hand carved tunnel down to the beach.

Fossils appear in the roadside bank as part of the weathering process and of course by the hand of man – when roadworks are being carried out.

If collecting from this site –a ladder is a handy thing to have because as you all well know the fossil that you see or want is usually out of reach.

A bit more on the Caversham Sandstone -

This is a thick (>120 m) (early Miocene 35mya) marine unit which crops out along a 40 km coastal strip from near Dunedin to Palmerston, eastern Otago. Despite its thickness and extent, this formation has been discussed only briefly in formal literature.

When the ancient seas began to slowly recede off the Otago penplain , marine conditions became quiet and a thick layer of calcareous sandstone was laid down, known as the Caversham sandstone, which is dramatically exposed in the cliffs north and south of Tunnel beach. The incoming of quartz in these sandstones is an indication of geological change with uplift in Central Otago rejuvenating the river systems, leading to increased erosion in the schist. In a few places north of Karitane and at a couple of spots around Dunedin harbour, limestones were deposited on top of the calcareous sandstones

Parts of Caversham Sandstone yield rich microfaunas (foraminifera, ostracods), but macrofossils are rare. Bryozoans, brachiopods, pectinid and other bivalves, gastropods, echinoderms, and rare cetacean bones have been collected from the Caversham Formation.

The difference in age between the Caversham Sandstone is about 17 million years old and the Dunedin Volcanic Group rocks which are about 14 million years old, is a lot. This means there is about 3 million years that is represented by the palaeosol soil layers and other unconformities.