Ask a Geoscientist
Do you have a geoscience question that you want help finding the answer to?
Submit your question to us and we will send it out to our network of Geopark geoscientists, including local geologists living in the Waitaki district and postgraduate geology students at the University of Otago. Responses are sent back within one week and all questions and answers are posted in our archive below.
We especially welcome questions specific to the Waitaki region that cannot be easily answered online, or questions derived from student discussion or activities.
To participate in Ask a Geoscientist, email your earth science question, along with your name, school/community group, and age/year group to: firstname.lastname@example.org
“The important thing is not to stop questioning. Curiosity has its own reason for existing” – Albert Einstein
Q: My family and I were out exploring the Elephant Rocks in the weekend. We saw this marking in one stone, which I feel is the shape of a jaw where some teeth used to be embedded. What do you think?
A: Thanks for sending through a photo of your discovery at Elephant Rocks! You could be right – based on what we can tell from your photo, it looks like someone has used a chisel to remove some of the rock. It looks like someone either chiselled around the circumference of a feature that they wanted to remove in one piece, or like you suggest, chiselled out a horseshoe-shaped feature such as a jaw with teeth. We’ve passed this on to the paleontology group here at the University of Otago and they confirmed that there are no known large sea creatures present in the Elephant Rocks limestone that have rounded jaws with that horseshoe shape. Rather, the penguin, whale and dolphin species known to have occurred in this area have quite narrow, pointy jaw shapes. So it’s unlikely that this shape represents a jaw of any of the species commonly found in the limestone, although there is always a very small chance that there are new species that we have yet to discover!
It's easier to determine features from photos when there is a scale to tell how big things age. Next time you find a cool feature to photograph, put an item in the photo that indicates the scale (i.e. keys, a pencil, your hand).
Q: Over the many years in Otematata we have come across these types of rocks. Can you tell me how they were formed, always interesting.
A: Thanks for the picture of the rock you discovered! It's always exciting to see what people find out in the field. The rock you have photographed is a conglomerate. A conglomerate is a sedimentary rock that is composed of broken pieces of other rock (AKA coarse grained clastic sedimentary rock). They are formed when you get weathering of rock and those fragments are then transported (i.e. by a river) and deposited in a new location with other rock fragments. The space between the clasts consist of finer material or cement (formed through a geological process).
The geology around Otematata is somewhat complex with different Formations abutting each other due to faulting. I would be interested to know exactly where this was found and if it was insitu (in it's original place) or not (i.e. found in a river bed). If I have that information I could narrow down the Formation name for you if you wish, or I could have a look at it when I will be doing site visits later in February.