Guidebook—Geology of South-central Kansas

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color photo of people spread out across sloping face of outcrop looking for fossils

Field trip participants look for fossils at Round Mound.

Stop 4—Round Mound

The rocks that crop out in the roadcut at Round Mound are in the Kanwaka Shale. The type locality of the Kanwaka Shale is just west of the community of Kanwaka, which is a little west of Lawrence. Numerous fossils of invertebrate marine animals have weathered out of the shale and thin limestones and can be collected here.

Fossils are the ancient remains or evidence of once-living plants and animals, and invertebrates are animals without backbones. In Kansas, invertebrate fossils are much more common than vertebrate fossils. Even so, these fossils represent only a tiny sampling of the animals that once inhabited this part of the earth, most of which lived and died leaving no visible trace. The fossils here give an idea of the variety of animals that lived in the Pennsylvanian seas, roughly 300 million years ago. Among the fossils found at this site are bryozoans, brachiopods, bivalves (oysters, clams, scallops), corals, and trilobites.

Bryozoans are some of the most abundant fossils found in sedimentary rocks, and they are also widespread today, both in marine and freshwater environments. Bryozoans are small animals (just large enough to be seen with the naked eye) that live exclusively in colonies. Bryozoans are sometimes called moss animals--the name comes from two Greek words, bryon (moss) and zoon (animal)--because some colonies resemble mosses. Bryozoans are sometimes confused with corals, another colonial group of animals. Like corals, most bryozoans secrete external skeletons made of calcium carbonate, which form the framework of the colony. Bryozoans, however, are more complex organisms than corals and generally don't build reefs. Fossil bryozoan colonies come in a variety of shapes. Some bryozoans built colonies that grew from the seafloor in branching structures; these fossils look like something like twigs. Other species erected netlike frameworks, while still other spread like a crust on shells, rocks, plants, and even other bryozoan colonies. Learn more about fossil bryozoans in Kansas.

drawing of netlike structure drawing of 2 sticklike forms

Fenestella (left) and Rhombopora (right) are two bryozoans found in Kansas rocks. These enlarged views show Fenestella's netlike structure and the upright, branching stems of Rhombopora (drawings by Al Kamb, KU Natural History Museum, Invertebrate Paleontology).

Brachiopods have a shell consisting of two parts called valves. Their fossils are common in the Pennsylvanian and Permian limestones of eastern Kansas. Brachiopods have an extensive fossil record. They first appear in rocks dating back to the early part of the Cambrian Period, about 545 million years ago, and were extremely abundant until the end of the Permian Period, about 250 million years ago, when they were decimated in the mass extinction that killed more than 90 percent of all living species and was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous that killed off the dinosaurs). A distinctive feature of all brachiopods is that their valves are bilaterally symmetrical--that is, the right half is a mirror image of the left half. (Humans are also bilaterally symmetrical.) The bilateral symmetry of the individual valves differentiates brachiopods from clams and other bivalved mollusks, with which they are sometimes confused. Unlike brachiopods, clam valves are not bilaterally symmetrical; instead, the right and left valves are mirror images of each other. Brachiopod shells come in a variety of shapes and sizes. The outer surface of the valves may be marked by concentric wrinkles or radial ribs. Some brachiopods have prominent spines, but these are generally broken off and incorporated separately in the sediment. Learn more about fossil brachiopods in Kansas.

photo of seven brachiopod fossils on black background

Fossil brachiopods common in Kansas rocks.

Clams and other bivalves are generally easy to recognize because they look a lot like the shells scattered along modern seashores. Clams and their relatives (oysters, scallops, mussels) are often called bivalves (or bivalved mollusks) because their shell is composed of two parts called valves. Like their living relatives, fossil bivalves come in many different shapes and sizes. Typically, the right and left valves are symmetrical, in contrast to the bilateral symmetry of individual brachiopod valves. Some bivalves, however, such as oysters, have valves that are not symmetrical. In western Kansas, fossil clams found in younger rocks from the Cretaceous Period are even more common. Some of these are huge; the inoceramid clams from western Kansas are as much as 6 feet in diameter. Learn more about fossil clams and other bivalves in Kansas.

drawing of two halves of clam, with blue rectangle inserted between them to illustrate plane of symmetry

Symmetry in clams.

Corals are close relatives of sea anemones and jellyfish and are the main reef builders in modern oceans. Corals can be either colonial or solitary. As fossils, corals are found worldwide in sedimentary rocks; the oldest are from rocks deposited during the Middle Cambrian, over 525 million years ago. Corals are among the simplest multicellular animals and are characterized by their radial symmetry and lack of well-developed organs. Corals live attached to the seafloor and feed by trapping small animals with their tentacles. They reproduce both sexually and asexually. Budding, a kind of asexual reproduction, occurs when the parent polyp splits off new polyps. Evidence of budding can be seen in fossil corals. Two groups of corals were important inhabitants of the Pennsylvanian and Permian seas--tabulate and rugose corals.

drawing of chunk of coral colony with veinlike tubes running up outside and circular pores on top surface drawing of cornucopia-shaped coral

The colonial tabulate coral Syringopora (on the left) shows the structure of the hard parts thta protected the polyps and formed the framework of the colony. Note the pores on the surface of the colony, from which the polyps extended their tentacles to feed. The solitary rugose coral Caninia (on the right) is common in eastern Kansas (drawings by Al Kamb, KU Natural History Museum, Invertebrate Paleontology).

Tabulate corals were exclusively colonial and produced calcium carbonate skeletons in a variety of shapes (moundlike, sheetlike, chainlike, or branching). Tabulate corals get their name from horizontal internal partitions known as tabulae. Some tabulate corals were probably reef builders (but not in Kansas). A common characteristic of rugose corals, from which they get their name, is the wrinkled appearance of their outer surface. (The word rugose comes from the Latin word for wrinkled.) Rugose corals may be either solitary or colonial. Because solitary rugose corals are commonly shaped like a horn, these fossils are sometimes called horn corals. Both tabulate and rugose corals died out in the major extinction that occurred at the end of the Permian Period, roughly 250 million years ago. This extinction marked the end of the Paleozoic Era.

The corals that inhabited the post-Paleozoic seas differ significantly from the earlier corals. Because of this, many specialists argue that these later corals may not be closely related to the Paleozoic corals. Learn more about fossil corals in Kansas.

Trilobites are an extinct group of arthropods, relatives of insects, spiders, ticks, crabs, shrimp, lobsters, and numerous other organisms. They were exclusively marine organisms. Trilobites first appear in the fossil record in rocks deposited during the Early Cambrian, about 540 million years ago. Although they were extremely abundant during their first 100 million years or so, by the Pennsylvanian and Permian Periods (when the surface rocks in eastern Kansas were deposited), trilobites were much less dominant. They became extinct, along with many other species, at the end of the Permian. The bodies of trilobites, like insects, have three parts: the head (or cephalon), the thorax, and the tail (or pygidium). Leg-like appendages attached to all three parts, but these are rarely preserved. Because of this, and the fact that trilobites have no living counterpart, paleontologists are hesitant to speculate about how trilobites lived. Trilobite pygidia are sometimes found in eastern Kansas. Learn more about fossil trilobites in Kansas.

This tail, or pygidium, of the trilobite Ameura, came from the Pennsylvanian Drum Limestone, near Independence, Kansas. Most Kansas trilobites belong to the genus Ameura or Ditomopyge.

Stop 4 to El Dorado

As we leave Round Mound, we'll travel west and north along the major gravel road 3 miles to the town of Neal and U.S. Highway 54, which will take us back to El Dorado, about 43 miles to the west. The Kansas Oil Museum, located next to our rendezvous point in East Park, will be open when we return. It is considered the best oil museum in the state and has exhibits that explain the various means of petroleum exploration and production and the ways they've changed over the years. In addition, the museum has exhibits that show what life was like in El Dorado and the company towns that sprang up during the oil boom that followed the discovery of the El Dorado field.

Sources

Tarbuck, Edward J., and Lutgens, Frederick K., 2000, Earth Science (9th Edition): Upper Saddle River, New Jersey, Prentice Hall, 672 p.

Wicander, R., and Monroe, J. S., 1989, Historical Geology--Evolution of the Earth and Life through Time: St. Paul, Minnesota, West Publishing Company, 578 p.

Zeller, Doris, ed., 1968, The Stratigraphic Succession in Kansas: Kansas Geological Survey, Bulletin 189, 81 p.

This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2001-41, from KGS Publications Sales office, 785-864-3965.

Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Jim McCauley, Liz Brosius, Rex Buchanan, and Bob Sawin, Kansas Geological Survey.

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