Fossil Park Rocks! - Limestone Exam
~ ~ ~ WELCOME TO FOSSIL PARK ~ ~ ~
- Nearly 375 million years ago, northwest Ohio was a great sea teeming with life. Fossil Park is rich in fossilized brachiopods, coral, and more than 200 species of prehistoric life. There is another great Earthcache here that teaches you a little bit about a few types of fossils you may find here. This Earthcache will look closer at the bedrock/geology where those fossils have been preserved for millions of years. Also, you will get a chance to examine a few less common fossils not mentioned in the other Earthcache.
Limestone Types:
Large limestone rocks found in this region are principally micritic limestones. They are sub categorized as grainstones, fossiliferous wackestones, and/or fossiliferous packstones.
1. Fossiliferous wackestones -
These rocks are a type of limestone rock composed of carbonate mud that supports more than 10% fossil fragments. They are defined as mud-supported because the lime mud (micrite) acts as the matrix, holding the fossils in place rather than the fossils themselves being in contact. These rocks are found in low-energy, shallow-water marine environments and often contain fossils such as crinoids, bryozoans, and corals.
2. Fossiliferous packstones -
These rocks are a type of limestone containing a high concentration of fossils where the fossil fragments and other grains are the primary support, rather than being mud-supported. Packstone is defined as a grain-supported carbonate rock that contains 1% or more mud-grade fraction.These rocks form in shallow, high-energy marine environments and can be packed with various marine fossils like brachiopods, crinoids, bryozoans, and shells. They are often collected and sold as specimens due to the visible fossils preserved within the rock.
3. Grainstone - A limestone grainstone is a type of limestone composed of carbonate grains that are the main component, with little to no carbonate mud (micrite). These rocks are grain-supported, meaning the grains are in direct contact and support the rock's structure, unlike mud-supported rocks such as mudstones or wackestones. Grainstones are formed by physical and biological processes, such as the accumulation of skeletal fragments, ooids, or other allochems (allochems are transported carbonate grains).
Limestone grain size:
Dunham classification -
1. grain-supported vs. mud-supported
2. mudstone, wackestone, packstone, or grainstone.
Grabau system -
- Calcirudite: Limestones with grains larger than 2 mm (lime-rubble).
- Calcarenite: Limestones composed of sand-sized carbonate grains (0.0625 – 2 mm).
- Calcilutite: Fine-grained limestones with particles less than 0.0625 mm (lime-mud).
Fossils:
Fossils that can be found here are typical Paleozoic shallow marine invertebrates - favositid corals, stromatoporoids, blastoids, bivalves, gastropods, cephalopods, rostroconchs, and tentaculites. Microfossils include conodonts and charophyte oogonia. Other fossils in the Columbus Limestone include vertebrates (fish), land plants (rare), and trace fossils.
Favositid Coral - Favosites is an extinct genus of tabulate coral characterized by polygonal closely packed corallites (giving it the common name honeycomb coral).
Stromatoporoids - They were extinct, bottom-dwelling marine animals, now classified as a type of calcareous sponge, that built layered calcium carbonate skeletons. They were significant reef-builders during the Paleozoic era, particularly in the Silurian and Devonian periods, forming large mounds on the seafloor. These sessile invertebrates are known from the fossil record and are characterized by their layered, mound-like structures, often with bumps and canals on the surface.
Blastoids - Blastoids were an extinct group of marine invertebrates, related to crinoids, that lived during the Paleozoic Era. Also called "sea buds," they were stalked animals that attached to the seafloor and filtered food from the water using brachioles, which were slender, tentacle-like structures. Their bodies were protected by a calcium carbonate shell called a theca, and they are commonly found as fossils, especially in rocks from the Mississippian period.
Bivalves - Bivalve fossils are the preserved shells of aquatic mollusks like clams, mussels, and oysters, which have existed for over 500 million years. They form when the sediment burying the bivalve hardens into rock, and their fossils can be used to determine the age and environment of the rock layers. These fossils show that bivalves have been abundant throughout Earth's history and can be found in both marine and freshwater environments.
Gastropods - Gastropod fossils are the remains of ancient snails, which are a type of mollusk. While some fossils are the original shell, many are replaced by other minerals or are internal/external casts and molds left after the shell has dissolved. These fossils are found in various rock types and geological periods and can show detailed features like the shell's spiral angle and growth lines.
Cephalopods - Cephalopod fossils are the preserved remains of marine animals like modern squids, octopuses, and nautiluses, and they are typically hard external shells from soft-bodied creatures. These fossils can be straight, curved, or coiled and are found from the Cambrian Period to the present day.
Rostroconchs - These fossils are the remains of an extinct class of mollusks that lived from the Cambrian to the Late Permian. These fossils are found in Paleozoic-age rocks and are characterized by their ribbed, calcitic shells, bilateral symmetry, and heart-shaped cross-section.
Tentaculites - Tentaculites are an extinct genus of conical fossils of uncertain affinity, class tentaculita, although it is not the only member of the class. It is known from Lower Ordovician to Upper Devonian deposits both as calcitic shells with a brachiopod-like microstructure and carbonaceous 'linings'. The "tentaculites" (i.e. tentaculita) are also referred to as the styliolinids.
Conodonts - Conodonts were extinct, fish-like animals that are now known only from their fossilized "teeth," called conodont element. These microscopic, mineralized structures are extremely common as fossils, especially in marine sedimentary rocks from the Paleozoic and Triassic eras, and are used as index fossils to date rock layers. While the animal itself was soft-bodied, complete fossils of the feeding apparatus have been found, revealing they had complex head structures and were likely early vertebrates.
Charophytes - A charophyte fossil is the preserved remains of a primitive green algae from the group Charophyta, most commonly the calcified reproductive structures called gyrogonites. These fossils are valuable because charophytes are the closest living relatives to land plants, and their fossil record provides evidence of plant evolution, particularly the transition from water to land.
Questions:
To log this cache, attach required photo(s) to your log entry and email or geocache message me, the answers to the following questions:
1. What type of limestone do you believe makes up this rock slab? (grainstone, packstone or wackestone)
2. What grain classification would you give to this piece of limestone using the Grabau System?
3. What grain classification would you give to this piece of limestone using the Dunham Classification? (grain-supported vs. mud-supported)
4. Do you think the composition of this limestone will hold up to nature's elements and erosion? If yes, why? If no, how many years would you guess until this rock slab turns into a pile of limestone debris? (There is an example of this near the entrance path to fossil park)
5. Task: Find two fossil specimens described in this lesson. Use the reference photos for a more in depth look at each type and the various species they may contain. What two fossils did you discover? Take a photo of your favorite specimen and post with your log..
6. Post a photo of yourself or personal item with the fossil rock (REQUIRED). You MUST be AT the posted coords.
Thanks for visiting my Earthcache!