Lake Ferry Bluffs

The lowest exposed unit is marine mudstone deposited during the Pliocene (5.33 million to 2.58 million years BP). This is overlain by Quaternary (2.58 million years BP to present) conglomerates, lacustrine (lake) siltstone and loess (wind blown silt). An unconformity exists between the mudstone and overlying conglomerate and siltstone sediments (representing missing time). The unconformity formed when a marine bench was incised into the coast during a sea level highstand in the last interglacial at about 84 ka (oxygen isotope stage 5a). The overlying deposits were deposited during colder glacial climates at about 60ka when sea level was lower. The conglomerates in this landscape are fluvial, being rounded in shape and moderately sorted (similar sizes) showing that they have travelled downstream and been shaped by the flowing water. With this information we can interpret these as mid catchment river conglomerates.

The height of the marine bench generally increases from 30 m above sea level in the west to 130 m and more in the east at Cape Palliser due to tilting associated with uplift on various local faults. This bench is one of four benches visible in the Southern Wairarapa along the south coast. The benches form as sea level rose and fell repeatedly by up to 130 m through each glacial-interglacial cycle of the last ice age cutting new benches each time the sea level was high. As the land continued to rise due to tectonics, each marine cut bench was uplifted and preserved above sea level.

When you arrive take a moment to look around Palliser Bay and spot the marine benches and appreciate their extent both to the left and right of the field location. If you decide to scramble up to the bluffs to take a closer look and see if you can find any fragmented shells in the marine mudstone, or spy some silt lenses within the conglomerate. If you climb into the left side of the eroded bluff you will find a fossilised tree stump within lacustrine siltstones. The fossil tree is still upright (in situ) with roots extending into the fine sediment that was once the ground that it grew on.