Banderas Fossils
Fossils are the preserved remains or traces of animals (also known as zoolites), 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. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon, up to 3.48 billion years old. The observation 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, even single bacterial cells 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. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils. Finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemofossils or biomarkers.
In some cases the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock 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 skull.
From - Fossil on WikiPedia
Lag vs. In-Situ
Fossils are found either exposed on a surface or still buried. Often, physical processes of erosion, be they aeolian, fluvial or tidal (wind action, rain or stream action, or the action of waves), will leave behind items which are resistant to the erosive processes. Fossils are often more resistant than the surrounding rock, known as the matrix. The wind and rain on an exposed outcrop will produce the winnowed fossils. This is called a lag deposit. Buried fossils, still in the original matrix are considered in-situ, or in place.
To confuse the situation even more, lag deposits, either formed at the time of original deposition or at a later date, can be buried and become fossilized as well.
Glen Rose Formation
The Glen Rose Formation is a shallow marine to shoreline formation of the lower Cretaceous period exposed over a large area of Texas. It is composed of hard limestone strata alternating with marl or marly limestone. The outcrop here is an exposure of one of the marl layers on the Glen Rose Formation. The stepped look of the Texas hill country can be attributed to the different layers of the formation units.
The Earth Cache
On the sides of the road here at the earthcache are some outstanding fossil beds. Spend a few minutes looking at the beds. These beds are Cretaceous limestones or chalks. A wide mix of fossils can be found, clams, sea snails, a few oysters and sea urchins, some of them are of a nice size. Sand dollars and and other types of fossils are reported to have been found nearby as well.
Again, look out for snakes as this is prime snake country and be careful of highway traffic.
To fulfill the requirements of this earthcache:
- Spend some time walking over the outcrop and send me a message describing how you think the fossils are distributed on the site. Especially look at the ditch near the road and look how the fossils are distributed.
- Also include an educated guess on how many fossils fall withing the size range of between 1 inch to 1 1/2 inches in the message. Feel free to collect a few for yourself.
Please do not post photographs of the fossils in the log as I will delete the log.