Age and environment of the Caversham Sandstone

Arthur, Kristina

The Caversham Sandstone is an extensive unit, covering an area from Palmerston, 40 kilometres north of Dunedin, to Black Head 10 kilometres to the south. The unit forms prominent sea cliffs and bluffs. Variation between the base and close to the top of the unit is in the form of the mineralogy, such as the presence or absence of glaucony. Micropaleontology provided ages for the base of the Caversham Sandstone and an outcrop representing the top, with further analysis providing information about the depositional depth of the unit. Key foraminifera identified gave an age of 21 – 19 million years for the base of the unit and 17.5 million years for the top, giving an age range of 1.5 – 3.5 million years in which the sandstone could have been deposited. Analysis of the benthic foraminifera proved the depth of deposition to be 200 – 600 metres depth, or out on the mid to outer continental shelf. The echinoderm fossils present within the Caversham Sandstone all have close relatives inhabiting depths which include the 200 – 600 metre depth range given by the foraminifera. Extant relatives of the different fossil species also suggest the warmer waters similar to those around northern New Zealand extended around the Otago region in the Early Miocene, inferring a warmer climate for that time period.

2007Arthur