Fossils at Putangirua Stream – Amazing Geology in NZ
Overview
The Putangirua Stream is not only known for its impressive rock formations, but also for its geological past, which tells a fascinating story. The sediments of the riverbed contain numerous fossils that lived in a shallow marine area millions of years ago. These fossils are a window into the past and show that today's land was once underwater.
While the Pinnacles are widely known as a geological attraction, the fossil-rich environment of the Putangirua Stream offers an equally exciting but less noticed way to explore the geological development of New Zealand. Here you can search for well-preserved fossils yourself and gain a direct insight into the maritime past of this region.
LOG CONDITIONS
To log this Earthcache, go to the coordinates given in the listing and answer the questions below. Please send your answers directly by email or via the message center.
- Which of the fossils listed above can you find here. (Note: Use the fossil representation of the creatures in the listing) and describe the structure you found? What is the length/width of the largest fossil you found?
- What color is the surrounding rock and what conclusions can you draw from this.
- If you look at image 1: Age determination using fossils, can you then use the fossils you found to determine the age of the fossil?
- Obligatory: Take a photo of yourself or a personal item at the coordinates given, without spoiling any information about the fossils or the questions asked.
Geological formation of the region
About 7-10 million years ago, what is now the Wairarapa region was covered by a shallow sea. In this marine environment, sediments containing numerous fossils were deposited over long periods of time. Tectonic movements, particularly the uplift of New Zealand's land masses along the Pacific-Australian plate boundary, caused the area to gradually rise out of the sea.
The Aorangi mountain range played a key role in this. Its formation can be traced back to the same tectonic processes that shaped the terrain today. As the earth's crust rose, mountain ranges such as the Aorangi Mountains were formed, which had an important influence on the regional climate, erosion and river courses. The Putangirua Stream has worn away the soft sediments over the millennia through the erosive power of water, exposing the Pinnacles and the fossil-rich layers.
Erosion by wind and water has exposed these layers over the millennia, so that today we can see both the Pinnacles and the fossil-rich deposits in the riverbed. The fossils you find here are remnants from this time and prove the region's once marine origin.
How are fossils formed?
When a living thing dies, it is usually eaten by other animals or decomposed by microorganisms such as bacteria and fungi. This causes most traces to disappear and only under certain conditions can a fossil be formed.
If the remains are quickly covered by sediment such as sand, mud or clay, the decomposition process can be slowed or stopped. Conditions are particularly favorable in riverbeds or on the sea floor, as the organic material is shielded from oxygen and thus cannot completely decay. Over long periods of time, these sediments are further compacted and converted into rock. The organic structures are often replaced by minerals - a process known as fossilization. This conversion can lead to the preservation of fine details of the original organisms.
Dating from fossils
Dating rock layers, a technique known as biostratigraphy, uses characteristic fossils to date the layers. Such fossils, which are common worldwide in certain geological periods, are called index fossils.
If identical index fossils are found in different places on Earth, it can be concluded that the rocks in question are approximately the same age. This method enables scientists to make a precise relative age determination of geological layers.
Image 1
Examples of fossil creatures
(Please note that not all of the fossils shown here can be found here in the Putangiruo Valley):
Rudists
Rudists were an extinct group of marine organisms that had mussel-like shells. During the Cretaceous period (about 150 to 66 million years ago) they played an important role as reef builders in warm, shallow seas. Their atypical, often conical or cylindrical shells enabled them to anchor themselves firmly in the sea floor. One of the two halves of the shell was greatly enlarged and served as a base, while the other was smaller and often formed as a lid. Rudists could grow up to two meters tall and lived lying down or upright on the bottom. At the end of the Cretaceous period they disappeared completely.
Image 2: Source: Photomontage from Pixabay and Reddit Source: Geo-Link
Gastropods
Gastropods, better known as snails, are among the most species-rich mollusks. Their characteristic spiral-shaped shell provides protection and stability. Fossil representatives of this group date back to the Cambrian period. They were widespread in both marine and terrestrial habitats. They are characterized by their spiral-shaped, often asymmetrical body structure, with many species having a protective shell.
Image 3: Source: Photomontage from: Pixabay und freepik Source: Geo-Link
Mussels
Mussels (Bivalvia) are bivalve mollusks that occur in salt and fresh water. They have been preserved as fossils since the early Cambrian period and played an important role in marine ecosystems.
Image 4: Source: Photomontage aus Pixabay und freepik Source: Geo-Link
Ammonites
Ammonites were a very diverse group of cephalopods that populated the seas for over 350 million years. Their spiral-shaped shells are characteristic and are often found in fossil deposits. Some species reached diameters of up to 1.80m. In addition to the organs, the shell also contained gas-filled buoyancy chambers. This allowed them to control up and down movements in the water using the gas volume in the buoyancy chambers. They serve as important index fossils for determining the age of rocks.
Image 5: Source: Wikipedia Source: Geo-Link
Belemnites
Belemnites were squid-like sea creatures that were widespread in the Mesozoic era. Their cone-shaped skeletal elements, the rostra, which are also known as "thunderbolts" or "devil's fingers", are mostly preserved in fossils. Due to their widespread distribution in the Mesozoic era, they are often considered index fossils today.
The belemnites looked similar to today's squid. They had 10 tentacles and an ink sac, but did not have suction cups on their tentacles, but rather hooks. Belemnites probably developed from the bactrites like the ammonites.
Image 6: Source: Wikipedia Source: Geo-Link
Sources
Wikipedia
Steinkern.de
simplyscience.ch
Wikipedia.de
steine-und-minerale.de
scinexx.de
Photos of the fossils: Own photos
Photos of the living organisms: Wikipedia, pixabay, Reddit, freepik
Image 1: own creation