Kentucky Landscapes Through Geologic Time Series XII, 2011 Daniel I
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Kentucky Geological Survey James C. Cobb, State Geologist and Director MAP AND CHART 200 UNIVERSITY OF KENTUCKY, LEXINGTON Kentucky Landscapes Through Geologic Time Series XII, 2011 Daniel I. Carey Introduction The Ordovician Period Since Kentucky was covered by shallow The MississippianEarly Carboniferous Period 356 Ma Many types of sharks lived in Kentucky during the Mississippian; some had teeth for crinoid We now unders tand that the earth’s crust is broken up into a number of tropical seas du ring most of the Ordovician capturing swimming animals and others had teeth especially adapted for crushing and During most of the Ordovician, Kentucky was covered by shallow, tropical seas Period (Figs. 6–7), the fossils found in Sea Floor eating shellfish such as brachiopods, clams, crinoids, and cephalopods (Fig. 23). plates, some of continental size, and that these plates have been moving— (Fig. 4). Limestones, dolomites, and shales were formed at this time. The oldest rocks Kentucky's Ordovician rocks are marine (sea- Spreading Ridge Siberia centimeters a year—throughout geologic history, driven by the internal heat exposed at the surface in Kentucky are the hard limestones of the Camp Nelson dwelling) invertebrates. Common Ordovician bryozoan crinoid, Culmicrinus horn PANTHALASSIC OCEAN Ural Mts. Kazakstania of the earth. This movement creates our mountain chains, earthquakes, Limestone (Middle Ordovician age) (Fig. 5), found along the Kentucky River gorge in fossils found in Kentucky include sponges (of North China crinoid, corals crinoid, central Kentucky between Boonesboro and Frankfort. Older rocks are present in the Rhopocrinus geologic faults, and volcanoes. The theory of plate tectonics (from the Greek, the phylum Porifera), corals (phylum Cnidaria), cephalopod, PALEO- South China Rhopocrinus subsurface, but can be seen only in drill cuttings and cores acquired from oil and gas North America tektonikos: pertaining to building) attemp ts to describe the process and helps bryozoans, brachiopods (Fig. 8), trilobites, snails straight TETHYS large drilling and mineral exploration. Later in Ordovician time, the seas became relative ly Equator EURAMERICA OCEAN crinoid (phylum Gastropoda), clams (phylum Pelecy- trilobite shelled explain the geology of Kentucky. shallow, indicated by mud and shale in the sediments. When the waters were clear and stem poda), squid-like animals (phylum Cephalo- Kentucky Appalachian Malaya bryozoan, Archimedes Mts. Variscan Mts. The geologic story of the rocks that form Kentucky’s landscape began a half warm, a profusion of animal life flourished, particularly brachiopods and bryozoa. poda), crinoids (of the class Echinodermata), Arabia billion years ago when the area was covered by water. Deposits of sand, silt, These became the rich fossil beds that have attracted amateur and professional Africa Australia crinoid, and ostracodes and conodonts. Straight-shelled Pulaskicrinus t ec RHEIC OCEAN oj paleontologists to the stream beds, rocky hillsides, and roadcuts of the Bluegrass r India P AP clay, and lime muds in shallow seas, deltas, swamps, and river systems nautiloids (squid-like cephalopods), shown in M O LE PA e, tes crinoid, Region. co brachiopods South America . S Antarctica R C. Figure 9(a), are common fossils in the Bluegrass 00 accumulated over the next 250 million years, layer upon layer. As each layer 20 © Camptocrinus, was covered by another, the sediments were compressed and solidified Region. Some have been found that are nearly Ancient Landmass GONDWANA enrolled assorted Ancient landmass 4 feet long. A fully preserved 450-million-year- Figure 6. Ordovician life. Illustration by Stephen F. Greb, Modern Landmass crinoids (lithified) into the sedimentary rocks that we see today. Clay became PANTHALASSIC OCEAN Kentucky Geological Survey, © 1995. Modern landmass blastoids, Pentremites North China old crinoid is shown in Figure 9(b). Subduction Zone (triangles point in the directionSubduction of subduction) zone (triangles point in the mudstone and shale, loose sands and silt became sandstone and siltstone, direction of subduction) shell fragments and lime oozes became limestone and dolomite, gravels Sea Floor Spreading Ridge 12,084 sq. mi. (29.9%) Australia Figure 19. The Mississippian world, 325 to 360 million years ago. Four-legged vertebrates fenestrate became conglomerates, and peat swamps became coal. The ages of rocks in Kazakstania evolved in swamps near the equator. Modified from Scotese (2003); used with permission. bryozoan each region, together with a synopsis of the development of life during each Equator North America Siberia Antarctica Mississippian rocks are exposed at the surface in the Mississippian Plateaus (Pennyroyal or Figure 21. Mississippian sea life. Illustration by Stephen F. Greb, period, are shown in Figure 1. PALEO-TETHYS Kentucky Laurentia OCEAN Pennyrile) Region and occur below the surface in both of the coal fields. Mississippian rocks are Kentucky Geological Survey, ©1995. Fossil photos by Rick Schrantz, India Kentucky Paleontological Society; used with permission. Million Where Rocks Baltica South absent in the Bluegrass Region. millions rocks at the IAPETUS China Africa South During most of the Mississippian, Kentucky was covered by shallow tropical seas (Fig. 19). Era of OCEAN Years Appearsurface at the South GONDWANA America years America Tornquist Sea Changing depositional environments led to different types of rocks being deposite d throughout the England Figure 9. (a) Nautiloids and (b) Crinoid. Photos by Rick Schrantz, Kentucky Paleontological Society; used with Era Er Life* PerioPeriod Agoago Surfacein Kentucky in Kentucky New England Avalonia Mississippian (Fig. 20). Black shale continued to be deposited briefly during the Early Mississippian and Nova Scotia Sahara Desert permission. (c) Colonies of cyanobacteria formed stromatolites like this one from the Ordovician. Cyanobacteria, modern humans Quaternary 2 Ancient landmass still living today, photosynthesized for billions of years to give us the oxygen-rich atmosphere in which life flourishes. Period, but soon gave way to a great influx of muds, silts, and sands brought in by rivers and streams Modern landmass Neogene 23 Photo by Brandon Nuttall, Kentucky Geological Survey. from uplands many miles to the northeast that were deposited as a great delta. Peculiar markings on abundant mammals Subduction zone (triangles point in the Paleogene direction of subduction) some slabs of siltstone are indications of water currents and sea-bottom life. (Age of Seafloor spreading ridge 7,399 sq. mi. (18.3%) When seas cleared during the middle part of the Mississippian, great thicknesses of limestone Mammals) dinosaur extinction 65 Cenozoic Figure 4. The Ordovician world, 440 to 500 million years ago. The end of the Ordovician were deposited in the warm, shallow waters. Many caves have developed in these limestones during Figure 23. Mississippian shark teeth, 330 million years old. oldest flowering plants was one of the coldest times in earth history. Modified from Scotese (2003); used with the past 5 million years. This area is now known as one of the world’s most famous karst (cave- Cretaceous Photos by Rick Schrantz, Kentucky Paleontological Society; abundant dinosaurs permission. bearing) regions and is home to the world’s longest cave system, Mammoth Cave. used with permission. 140 Periodically, during the latter part of the Mississippian, tidal deltas and low coastal plains covered large parts of Kentucky. Coastal environments alternated with periods when the sea inundated the Figure 22. A Mississippian embolomere, (Age of oldest birds Jurassic an early amphibian. Illustration by Dinosaurs) region. abundant dinosaurs Mesozoic Most of the Mississippian rocks found in Kentucky are marine, so many of the fossils in them are Stephen F. Greb, Kentucky Geological Kentucky missing in Survey, ©1995. oldest dinosaurs and mammals 210 marine invertebrates (Fig. 21). Common Mississippian fossils found in Kentucky include corals, Triassic bryozoans, brac hiopods, trilobites, snails, clams, cephalopods, crinoids and blastoids, fish teeth, and extinctions of trilobites and ostracodes and conodonts. other marine animals 250 Permian When there was dry land in the form of low coastal plains, land plants and animals lived. Land Figure 20. Interbedded siltstone, sail-backed, mammel-like reptiles limestone, and shale of the 350- 290 Figure 8. A 440-million-year-old brachiopod plants such as seed ferns, true ferns, scale trees, and calamite trees grew in these coastal areas. Insects coal swamps, abundant and arthropods were probably numerous on land. Amphibians lived in estuarie s and ox-bow lakes, million-year-old Fort Payne Forma- Pennsylvanian fossil found in Bath County. The brachiopod is tion along Ky. 61 in Cumberland insects; first reptiles the Kentucky state fossil. Photo by Rick Schrantz, 325 but only one amphibian fossil has been found in Kentucky (in 1995). Called an embolomere (Fig. 22), County. The depositional environ- Kentucky Paleontological Society; used with per- it was about 5 feet long, had a long, streamlined body, and probably lived most of the time in water ment changed throughout the Mississippian mission. crinoids Figure 7. A cephalopod chases trilobites in the Ordovician sea. and ate fish and other small amphibians and reptiles. It was found in Mississippian sandstones on the Mississippian, producing a variety 360 Figure 5. The 450-million-year-old Camp Nelson Limestone along the Kentucky River