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Geology of Georgia

Geologic Time Scale. Source: Geologic Time Scale, Geological Society of America, 1999, from Boggs, 2006.. . Periods in this Chapter. From oldest to youngestLate OrdovicianOrdovician: 490 and 443 million years agoSilurian443 and 417 million years agoEarly DevonianDevonian: 417 and 354 million years ago.

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Geology of Georgia

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    1. Geology of Georgia Paleozoic Deposits of the Late Ordovician, Silurian and Early Devonian Periods by Kimberly Sams May 1, 2006

    3. Periods in this Chapter From oldest to youngest Late Ordovician Ordovician: 490 and 443 million years ago Silurian 443 and 417 million years ago Early Devonian Devonian: 417 and 354 million years ago

    4. Geographic Region

    5. Geologic Map of Georgia

    6. Geologic Map of Georgia

    7. Geologic Map of the Eastern United States Beyond the GA boundaries, these provinces extend from the northeast corner of AL, through N. GA and continue as part of the Appalachian Mountains into Canada. Beyond the GA boundaries, these provinces extend from the northeast corner of AL, through N. GA and continue as part of the Appalachian Mountains into Canada.

    8. Principal Rocks

    9. As I begin the discussion to describe the deposits within my chapter of the Paleozoic Era, I want to draw your attention to the table at the bottom corner of the slide. It is a smaller version of the statrigraphic column on the previous page that will help guide my presentation and hopefully make it easier for you to visualize the cross section. Late Ordovician deposits include the Trenton limestone and the Maysville limestone. TheTrenton limestone overlies the Lowville-Moccasin limestone of the Middle Ordovician that Andrea presented. The Maysville limestone lies above the Trenton limestone. While resources available for the development of this document are limited, analysis of writings by Milici and Wedow, Jr. exhibit evidence that the Maysville and Trenton limestones once were referred to as the Leipers and Inman Formations, respectively (1977). As I begin the discussion to describe the deposits within my chapter of the Paleozoic Era, I want to draw your attention to the table at the bottom corner of the slide. It is a smaller version of the statrigraphic column on the previous page that will help guide my presentation and hopefully make it easier for you to visualize the cross section. Late Ordovician deposits include the Trenton limestone and the Maysville limestone. TheTrenton limestone overlies the Lowville-Moccasin limestone of the Middle Ordovician that Andrea presented. The Maysville limestone lies above the Trenton limestone. While resources available for the development of this document are limited, analysis of writings by Milici and Wedow, Jr. exhibit evidence that the Maysville and Trenton limestones once were referred to as the Leipers and Inman Formations, respectively (1977).

    10. Upper Ordovician The Inman Formation consists of a limestone that is gray-red or green-gray in color. These deposits contain calcisiltites and shales and are generally laminated to thinly bedded. Fine cross-bedding also is evident. Globular bryozoans, brachiopods and carbonized pelecypods are common fossils found in the Inman Formation. The Inman Formation consists of a limestone that is gray-red or green-gray in color. These deposits contain calcisiltites and shales and are generally laminated to thinly bedded. Fine cross-bedding also is evident. Globular bryozoans, brachiopods and carbonized pelecypods are common fossils found in the Inman Formation.

    11. Upper Ordovician The Leipers limestone is medium-gray in color, thick-bedded and contains argillaceous calcilutite or calcisiltite (Milici and Wedow, Jr., 1977). Burrowing organisms and fossils are present in the formation, including large brachiopods.The Leipers limestone is medium-gray in color, thick-bedded and contains argillaceous calcilutite or calcisiltite (Milici and Wedow, Jr., 1977). Burrowing organisms and fossils are present in the formation, including large brachiopods.

    12. Silurian Two levels of the stratigraphic column Sequatchie Formation Red Mountain Formation Primarily iron-rich sandstone, siltstone and shale Silurian Period rocks are contained within two levels of the stratigraphic column. They include the Sequatchie and the Red Mountain Formations and consist primarily of iron-rich sandstone, siltstone and shale. These formations overlie the Upper Ordovician Maysville limestone deposit. Silurian Period rocks are contained within two levels of the stratigraphic column. They include the Sequatchie and the Red Mountain Formations and consist primarily of iron-rich sandstone, siltstone and shale. These formations overlie the Upper Ordovician Maysville limestone deposit.

    13. Silurian Similar to the Murfreesboro limestone, the Sequatchie formation is found in the valleys of the West Chickamauga Creek (Furcron, 1969). The formation lies above the Maysville limestone of the Upper Ordovician and is further divided into three members; the Ringgold, Shellmound and Mannie. Similar to the Murfreesboro limestone, the Sequatchie formation is found in the valleys of the West Chickamauga Creek (Furcron, 1969). The formation lies above the Maysville limestone of the Upper Ordovician and is further divided into three members; the Ringgold, Shellmound and Mannie.

    14. Silurian The Ringgold Member is the lowest positioned Silurian-aged deposit. It consists of red, green and gray siltstones, sandstones and shales (Chowns and OConnor, 1992). It does not exhibit fossils, but Chowns and OConnor report that the member resembles those deposited in a clastic tidal flat (1992). Mud cracks, ripple marks and birdseye structures are just a few that are displayed in the Ringgold member. The Ringgold Member is the lowest positioned Silurian-aged deposit. It consists of red, green and gray siltstones, sandstones and shales (Chowns and OConnor, 1992). It does not exhibit fossils, but Chowns and OConnor report that the member resembles those deposited in a clastic tidal flat (1992). Mud cracks, ripple marks and birdseye structures are just a few that are displayed in the Ringgold member.

    15. Silurian The Shellmound Member lies between the Ringgold and Mannie members. It is a small formation that contains calcarenites and calcareous siltstones with some bioturbation (Chowns and OConnor, 1992). The member is recognizable by the bioturbated siltstones (Chowns and OConnor, 1992). Fossils within this member include brachiopods, bivalves and bryozoans (Chowns and OConnor, 1992). The Shellmound Member lies between the Ringgold and Mannie members. It is a small formation that contains calcarenites and calcareous siltstones with some bioturbation (Chowns and OConnor, 1992). The member is recognizable by the bioturbated siltstones (Chowns and OConnor, 1992). Fossils within this member include brachiopods, bivalves and bryozoans (Chowns and OConnor, 1992).

    16. Silurian The Mannie Member is the upper-most Sequatchee Formation deposit and consists of a shale rich in phosphate, limestones, bioturbated sandy mudstones, muddy sandstones, siltstones and bioclastic wackestones (Chowns and OConnor, 1992). Fossils are present in the Mannie member, which are similar to the Shellmound member (Chowns and OConnor, 1992). They include gastropods, bivalves and bryozoans (Chowns and OConnor, 1992). The Mannie Member is the upper-most Sequatchee Formation deposit and consists of a shale rich in phosphate, limestones, bioturbated sandy mudstones, muddy sandstones, siltstones and bioclastic wackestones (Chowns and OConnor, 1992). Fossils are present in the Mannie member, which are similar to the Shellmound member (Chowns and OConnor, 1992). They include gastropods, bivalves and bryozoans (Chowns and OConnor, 1992).

    17. Silurian While not confirmed by a source referenced by this chapter of the guide, a comparison of a historical geological formation table for Georgia formations (Veatch, 1909) and various recent sources implies that the Red Mountain Formation was once called the Rockwood Formation. In 1909, Veatch states that the Rockwood Formation forms the uppermost division of the Silurian system. Many formations have shifted order over time as geologists have made great scientific advances to properly date rock samples. The description by Veatch of the Rockwood Formation is similar to the Red Mountain Formation (Veatch, 1909, Georgia Conservancy, The, 1999). While not confirmed by a source referenced by this chapter of the guide, a comparison of a historical geological formation table for Georgia formations (Veatch, 1909) and various recent sources implies that the Red Mountain Formation was once called the Rockwood Formation. In 1909, Veatch states that the Rockwood Formation forms the uppermost division of the Silurian system. Many formations have shifted order over time as geologists have made great scientific advances to properly date rock samples. The description by Veatch of the Rockwood Formation is similar to the Red Mountain Formation (Veatch, 1909, Georgia Conservancy, The, 1999).

    18. Silurian The Red Mountain Formation was deposited in Georgia during the interval between the Taconic and Acadian orogenies in the Appalachian Mountain Basin (Chowns, 1972). Outcrops of the iron ore can be found approximately 20 miles north of Rome, Georgia (Georgia Conservancy, The, 1999). Remnants of cephalopods (Figure 6) are the most common fossil preserved in the broken ore samples of the Red Mountain Formation (Georgia Conservancy, The, 1999). Cephalopods are hollow shells divided into chambers by septa that have been vacated by a living creature after outgrowing the shell (Bishop, Woolley, Hamilton, 2005). These cephalopods range in size from five to 15 millimeters long and two to three millimeters in diameter (Georgia Conservancy, The, 1999).The Red Mountain Formation was deposited in Georgia during the interval between the Taconic and Acadian orogenies in the Appalachian Mountain Basin (Chowns, 1972). Outcrops of the iron ore can be found approximately 20 miles north of Rome, Georgia (Georgia Conservancy, The, 1999). Remnants of cephalopods (Figure 6) are the most common fossil preserved in the broken ore samples of the Red Mountain Formation (Georgia Conservancy, The, 1999). Cephalopods are hollow shells divided into chambers by septa that have been vacated by a living creature after outgrowing the shell (Bishop, Woolley, Hamilton, 2005). These cephalopods range in size from five to 15 millimeters long and two to three millimeters in diameter (Georgia Conservancy, The, 1999).

    19. Silurian The Red Mountain Formation in Georgia is further divided into Lower, Middle and Upper Members. The Lower Member contains gray-red interbedded shales and sandstones with parallel laminations and shallowing upwards (Chowns, 1999). This unit is more fossiliferous than the other members, with crossbedded sandstone that coarsens upward with sole marks (Chowns, 1999). The Red Mountain Formation in Georgia is further divided into Lower, Middle and Upper Members. The Lower Member contains gray-red interbedded shales and sandstones with parallel laminations and shallowing upwards (Chowns, 1999). This unit is more fossiliferous than the other members, with crossbedded sandstone that coarsens upward with sole marks (Chowns, 1999).

    20. Silurian The Middle Member contains mostly gray shale, ironstone and some interbedded sandstone and shale (Chowns, 1999). The Middle Member contains mostly gray shale, ironstone and some interbedded sandstone and shale (Chowns, 1999).

    21. Silurian Alternating beds of sandstone and shale are found in the Upper Member. Additionally, there are fossiliferous limestone and ironstone seams. Alternating beds of sandstone and shale are found in the Upper Member. Additionally, there are fossiliferous limestone and ironstone seams.

    22. Lower Devonian Devonian deposits Sandstone, shale, chert One level of the stratigraphic column Chattanooga Shale Armuchee Chert/Frog Mountain Chert (lower) The Devonian deposits include sandstone, shale and chert. There is one formation in the Early Devonion Period; Armuchee chert, or the Frog Mountain chert. It overlies the Red Mountain Formation deposits of the Silurian.The Devonian deposits include sandstone, shale and chert. There is one formation in the Early Devonion Period; Armuchee chert, or the Frog Mountain chert. It overlies the Red Mountain Formation deposits of the Silurian.

    23. Lower Devonian Armuchee Chert (Frog Mountain Chert) Light gray with lenses of medium to coarse grained sandstone and shale Deposited in thin layers Shallow marine shelf environment Accumulations of sponges due to spiculitic appearance of the chert The Armuchee Chert thinly overlies the Red Mountain Formation. It is light gray with lenses of medium to coarse grained sandstone and shale (Nunan, 1972). The Armuchee Chert varies in thickness but primarily is deposited in a thin layer (Nunan, 1972). The depositional environment is proposed to be a shallow marine shelf with thick accumulations of sponges, due to the spiculitic appearance of the chert (Nunan, 1972). The Armuchee Chert thinly overlies the Red Mountain Formation. It is light gray with lenses of medium to coarse grained sandstone and shale (Nunan, 1972). The Armuchee Chert varies in thickness but primarily is deposited in a thin layer (Nunan, 1972). The depositional environment is proposed to be a shallow marine shelf with thick accumulations of sponges, due to the spiculitic appearance of the chert (Nunan, 1972).

    24. Devonian Chattanooga Shale Fissile Shale Black to gray Deposited in layers up to 10 meters thick May be radioactive (Furcron, 1950) Few fossils Organic matter and pyrite in samples Deposited in stagnant, oxygen-deficient sea water The Armuchee Chert thinly overlies the Red Mountain Formation. It is light gray with lenses of medium to coarse grained sandstone and shale (Nunan, 1972). The Armuchee Chert varies in thickness but primarily is deposited in a thin layer (Nunan, 1972). The depositional environment is proposed to be a shallow marine shelf with thick accumulations of sponges, due to the spiculitic appearance of the chert (Nunan, 1972). The Armuchee Chert thinly overlies the Red Mountain Formation. It is light gray with lenses of medium to coarse grained sandstone and shale (Nunan, 1972). The Armuchee Chert varies in thickness but primarily is deposited in a thin layer (Nunan, 1972). The depositional environment is proposed to be a shallow marine shelf with thick accumulations of sponges, due to the spiculitic appearance of the chert (Nunan, 1972).

    25. Next Susan Manfred will discuss the Mississippian

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