Nugget Point is one of the most iconic landforms on the Otago coast. Located at the northern end of the Catlins coast down the road from Kaka Point, this steep headland has a lighthouse at its tip, surrounded by rocky islets (The Nuggets). The point is home to many seabirds, including penguins, gannets and spoonbills, and a large breeding colony of fur seals.
Stratigraphy
Stratigraphy is the study of stratification - basically the study of rock layers and layering. It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy was essentially invented and first rigorously applied by William Smith in England in the 1790s and early 1800s.
The process of stratification follows a few fundamental laws:
1. Sediments are originally laid down in horizontal beds.
2. In an undisturbed sedimentary sequence (series of layers) each layer is younger than the layer below.
3. Layered rocks are depositied in continuous contact.
Dip & Strike
Over time and due to massive forces, usually volcanic or tectonic in nature, layers can become disrupted and deformed. Where the strata has deformed but remains largely intact, these processes are usually gradual and not sudden in nature.
Two fundamental properties of stratification, that can be easily observed and measured using simple apparatus, in order to measure the deformation of the rock strata, are the dip and strike of the rock strata at a location.
Strike can be described as the line of intersection between the strata, or layer, and an imaginery horizontal plane that cuts through it.
This would be the same as the direction you would take if the layer was exposed and you were to traverse across it, remaining at the same elevation. The strike is usually represented in degrees from true north, expressed as the lower of the two bearings that would describe it.
Dip can be described as the angle of the slope of the strata where the dip direction is exactly perpendicular (90 degrees offset) to the strike direction. If the layer was a slope you were standing on, this would be the angle of the slope pointing directly downhill from you.
Geology
The bedrock of the Catlins was laid down between 190 and 135 million years ago during the Jurassic and Triassic periods. During that time, the area was a shallow sea close to the edge of the Gondwanaland super-continent, of which New Zealand was still a part.
The geology of the Catlins is predominantly sandstone, mudstone and siltstone that was formed by the gradual deposition of sediment from the ocean. These rocks distinguish the Catlins from the schist rock typical of the Otago region further north.
The rocks were initially laid down horizontally and then were subjected to a period of approximately 50 million years of geological uplift, folding and faulting. For the past approximately 80 million years, the area has been relatively geologically stable, and erosion during this period has resulted in the distinctive parallel ridges and valleys that run north-west through the Catlins and disappear into the sea at Nugget Point - evidence of the geological feature known as the Southland or Murihiku Syncline.
Fault lines are visible in the cliffs at Nugget Point and at the Cathedral Caves, further south, where sea erosion has carved out caves and chasms along the faults - evidence of the massive upheaval that occurred within the bedrock. Many fossils from the Jurassic era have been retained in the rocks, with shellfish being the most prevalent.
This Earthcache
This is an earthcache and like any earthcache, the purpose of it is to provide a geological lesson at the site you are visiting. This is not a virtual cache and you must visit the site and answer the questions below in order to claim you have 'found it'.
Before claiming your find, you must submit your answers for the questions below to the owner of this earthcache, by clicking on the link to the owner's profile at the top of the page, and sending the owner an email.
When emailing your answers, don't forget to include the name of this earthcache, and choose the option to include your email address so that we can reply to you. Do not include answers in your log on the cache page.
After you have emailed your answers, you can go ahead and log your find. Any problems with your answers, and we'll get back to you.
1. At the published coordinates, and looking at the rock strata upon which the lighthouse sits, please provide the following:
a. The strike direction (use the compass on your GPS device).
b. The dip angle from horizontal (you can take a photo and measure against the horizon on your computer later).
c. The typical/average thickness of the layers in the rock (use a ruler, or an item of known size or that you can measure later).
2. Proceed to the viewing platform beyond the lighthouse (waypoint 2) and describe the stratigraphy of The Nuggets (the rocky islets in the sea). Are they all the same? Are they different from one another and/or from the rock strata you observed and measured in question 1?
3. Describe the rock colours you observed in the exposed rock faces (near waypoint 3) beside the path that lead down to the lighthouse from the car park.
4. Take a photo of the lighthouse and/or The Nuggets and upload it with your 'found log'. Please include yourself or your GPS unit if you can. Upload this photo with your find log.
Please note, this is an easy earthcache to complete if you visit the site, and we will therefore reserve the right to delete logs if answers are incomplete, wildly incorrect, or not provided at all, or if there is no photo uploaded.
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