This page describes the fossil forest lying below the surface of Titahi Bay Beach. Titahi Bay is a seaside suburb in Porirua City.
Titahi Bay map showing location of fossil forest.
Light blue ovals indicate approximate areas of the fossil forest where tree stumps are known to lie.
At low tide at Titahi Bay Beach you can see the remains of a 96,000 year old forest which grew here before the sea level rose after the last ice age. The forest was a mix of rimu, totara and kahikatea and most likely nikau palms, tree ferns, sedge, flax and raupo and the size of the stumps indicates the trees grew to a large size (Begg &Mazengarb, 1996). Amazingly the fossilizing process has preserved the normal characteristics of wood. Distinct growth rings are still visible in some of the samples collected.
The forest fossilized in situ, meaning it was not transported there by other means. The trees grew in a swampy environment during the last warm Inter-glacial period (100-125 ka). When the climate warmed and seawater flooded the vegetation and caused sediment to accumulate around the remaining larger vegetation types, promoting preservation. The broken off tree stumps on the beach today may have been buried by many metres of sediment with the sea level rising considerably higher than today.
Sea level rise between 12-6,000 BP has eroded the coastline, and uncovered the fossil beds in the floor of Titahi Bay. The fossil trees sit in old gravelly, silt and peat beds, that are around 10 m deep and are underlain by a deeper greywacke basement - the same rock as in the headlands of the Bay.
Fossil tree stump exposed in the lower foreshore of the Bay.
The tree stumps along the entire beach are only clearly exposed for extended periods about once every ten years. Conserving the fossil forest is important as it provides clues as to what the climate was like and how forests grew 100,000 years ago. The best time to see the fossil forest is at low tide during spring when northwest storm events have scoured sand from the beach.
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