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Fossilisation
Fossils (from Latin fossus, literally "having been dug up") are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record. The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years ago.
Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon several billion years old. The observations that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.
Like extant organisms, fossils vary in size from microscopic, such as single bacterial cells only one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Preservation of soft tissues is rare in the fossil record.
Fossilisation occurs in a number of different ways:
Permineralization - Permineralization occurs after burial, as the empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater and the minerals precipitate from the groundwater, thus occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decaying process.
Casts and molds - In some cases the original remains of the organism have been completely dissolved or otherwise destroyed. When all that is left is an organism-shaped hole in the rock, it is called an external mold. If this hole is later filled with other minerals, it is a cast. An endocast or internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a cranium.
Replacement and recrystallization - Replacement occurs when the shell, bone or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material.
Compression fossils - Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state. Often what remains is a carbonaceous film. This chemical change is an expression of diagenesis.
Bioimmuration - Bioimmuration is a type of preservation in which a skeletal organism overgrows or otherwise subsumes another organism, preserving the latter, or an impression of it, within the skeleton. Usually it is a sessile skeletal organism, such as a bryozoan or an oyster, which grows along a substrate, covering other sessile encrusters.
Earthquakes Whale Fossil Site (published coordinates)
It was originally thought that the slumped and creviced ground here formed during a powerful earthquake. In reality, however, the broken formations you will see at this location were created during a major landslide thousands of years ago.
Large blocks of Otekaike Limestone here have broken and fallen as the ground underneath slumped - a huge block nearest the road has moved northwards perhaps on a weaker underlying layer while the southern block has remained in place at the top of the hill.
Visible in the cliff face, visitors to this location can clearly see the upper Otekaike Limestone layer (approximately 10m thick) and the lower and thinner Kokoamu Greensand layer, termed greensand because of the presence of grains containing the green mineral glauconite. Both of these layers were formed in shallow seas in the late Oligocene period, around 23 to 28 million years ago.
At this location it is in a large fallen block of basal Otekaike Limestone, where a significant fossil of a baleen whale has been discovered and partially excavated.
The partially exposed fossil bones are those of an ancient baleen whale, distantly related to the large filter-feeding whales of our modern oceans, like the Minke whale of the Antarctic Oceans. The fossil whale is identified by remains of the lower jaws - the fragments of which being toothless and oval in cross-section, similar to baleen whales living today.
Present here are the broken parts of the skull, both lower jaws, many vertebrae and ribs of one whale. The fossil was discovered when the broken oval ends of both the lower jaws were spotted on the rock face. No other parts were visible so the excavation was largely a 'voyage of discovery'.
When viewing the fossil, the head is facing out towards the visitor while the skeleton curves back and to the right. More bones probably lie unexposed within the rock.
This full skeleton fossil is uncommon in the Waitaki region where almost all fossilised whales and dolphins occur as just a few bones from the same animal. After death, this whale sank to the bottom of the sea, at a depth of 75-100m, where its bones were moved perhaps only a little by currents and scavengers, and it was relatively quickly covered and buried by gently moving sand.
Anatini Whale Fossil Site (additional waypoint)
The name Anatini means 'many caves' and refers to the interesting limestone formations at this site. Like numerous sites in the local area, exposed Otekaike Limestone that formed in shallow seas during the late Oligocene period (23 to 28 million years ago) has eroded into strange and beautiful formations, including a large natural arch.
The whale fossil located at this site is preserved in Otekaike Limestone, this layer of which was formed between 24 and 26 million years ago when this area was a broad shallow seaway opening to the south. The yellow/white rock formed when limey sand, mainly comprising tiny fossil fragments, settled in quiet waters about 75-100m deep. At the time, New Zealand consisted of a series of small islands and shoals.
The sediments were buried and hardened into Otekaike Limestone. Uplift of the land over the last few million years has brought the limestone to the surface where it has weathered and eroded, exposing the bones once again.
Like the whale fossil found at the Earthquakes site, this fossil is that of an ancient baleen whale, distantly related to the large filter-feeding whales of our modern day oceans. The oval and toothless lower jaw is once again the key to this identification.
The length of this whale when it was alive can be estimated from the size of the jawbone fragment found at the site. The fragment suggests a jawbone of between 1.5 and 1.8m in length, and hence a skull 1.7 to 2.0m long. Many living whales have a body about 5 times the length of the skull, so this whale was probably 8 to 10m in length.
Most of the fossil whales and dolphins found in the limestones of the Waitaki district occur as a few bones from one animal, and this fossil is a typical occurence with just a few bones from the front of the whale being present here.
It is rare to find an entire skeleton fossilised in life position, as currents and scavengers tend to break bodies apart. It is likely that other bones from this whale dropped elsewhere as the carcass floated in the water, or were washed away by ocean currents. For a skeleton to be preserved completely, the dead animal must sink to the bottom and be buried rapidly without disturbence.
This Earthcache
In order to log this earthcache, you will need to visit the published coordinates and the additional waypoint and perform the tasks listed below. Answers are to be emailed to the cache owner, and NOT included in your online log.
These whale fossil sites are located on private property, but public foot access to view the fossils is permitted by the owners. Please respect that these areas are working farms and go quietly if animals are present. No samples whatsoever may be collected from either of these sites.
At all times during this earthcache, at both sites, please be aware that this limestone is still eroding and these sites can be dangerous. Be aware what is above and below you at all times - if it looks unsafe then it probably is. Particularly at the Earthquakes site, stick to the trail as crevasses may be hidden by grass. NO samples may be taken from either site.
1. At the Earthquakes site (published coordinates) perform the following tasks:
a. Count the number of bones visible in the partially exposed whale fossil.
b. How big was this whale when it was alive?
c. Within what year range did this whale die? (Age of the block of rock in which the fossil was discovered - give a 1 million year range only)
d. Which type of fossilisation process has occured here resulting in the whale fossil at this site? (Choose from the 5 types of fossilisation listed above)
e. Take a photo showing the cliffs and/or rocks in the background and including your GPS near the published coordinates. Do NOT include the whale fossil. Please post this photo with your online log.
2. At the Anatini site (additional waypoint), perform the following tasks:
a. Name the five types of bones present in this fossil.
b. Which type of fossilisation process has occured here resulting in this whale fossil? (Choose from the 5 types of fossilisation listed above)
c. On the way down the path to this waypoint, you passed a natural arch. Estimate the internal height of this interesting feature.
d. Take a photo showing the cliffs, rocks and/or natural arch in the background and including your GPS near the waypoint coordinates. Do NOT include the whale fossil. Please post this photo with your online log.
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
Happy earthcaching!
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