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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Asia
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Far East
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China
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Hubei China (1)
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Yangtze Platform (1)
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North America (2)
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United States
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Alabama (1)
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Illinois
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Franklin County Illinois (1)
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Macoupin County Illinois (1)
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Putnam County Illinois (1)
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Richland County Illinois (1)
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Illinois Basin (2)
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Iowa
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Fremont County Iowa (1)
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Midcontinent (3)
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Minnesota
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Goodhue County Minnesota (1)
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Mississippi Valley
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Upper Mississippi Valley (1)
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Tennessee
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Blount County Tennessee (1)
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Virginia (1)
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elements, isotopes
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boron
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B-11/B-10 (1)
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isotope ratios (5)
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isotopes
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radioactive isotopes
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stable isotopes
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O-18/O-16 (3)
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metals
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actinides
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gallium (1)
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oxygen
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fossils
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microfossils
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geochronology methods
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geologic age
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Triassic
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Paleozoic
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metamorphic rocks
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minerals
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apatite (2)
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Primary terms
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Asia
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Far East
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China
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Hubei China (1)
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boron
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climate change (1)
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crystal chemistry (1)
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data processing (2)
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geochemistry (1)
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glacial geology (2)
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isotopes
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radioactive isotopes
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U-238/U-234 (1)
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stable isotopes
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B-11/B-10 (1)
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O-18/O-16 (3)
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Mesozoic
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Triassic
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Lower Triassic
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Permian-Triassic boundary (1)
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metals
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actinides
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uranium
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U-238/U-234 (1)
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gallium (1)
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North America (2)
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oxygen
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O-18/O-16 (3)
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paleoclimatology (6)
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paleoecology (2)
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paleogeography (2)
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Paleozoic
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Carboniferous
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Pennsylvanian
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Middle Pennsylvanian
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Carbondale Formation (1)
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Upper Pennsylvanian
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Missourian (1)
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Chattanooga Shale (1)
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Devonian (1)
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Ordovician
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Middle Ordovician
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Deicke Bentonite Bed (2)
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Platteville Formation (1)
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Trenton Group (1)
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Upper Ordovician
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Katian (1)
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Mohawkian (1)
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Sandbian (1)
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Permian
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Maokou Formation (1)
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Upper Permian
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Permian-Triassic boundary (1)
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Silurian
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Clinch Sandstone (1)
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sea water (2)
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sedimentary rocks
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carbonate rocks
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limestone (2)
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clastic rocks
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black shale (2)
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shale (1)
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sedimentary structures
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planar bedding structures
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cyclothems (2)
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United States
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Alabama (1)
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Illinois
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Franklin County Illinois (1)
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Macoupin County Illinois (1)
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Putnam County Illinois (1)
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Richland County Illinois (1)
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Illinois Basin (2)
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Iowa
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Fremont County Iowa (1)
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Midcontinent (3)
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Minnesota
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Goodhue County Minnesota (1)
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Mississippi Valley
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Upper Mississippi Valley (1)
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Tennessee
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Blount County Tennessee (1)
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Virginia (1)
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sedimentary rocks
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sedimentary rocks
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carbonate rocks
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limestone (2)
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clastic rocks
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black shale (2)
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shale (1)
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sedimentary structures
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sedimentary structures
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planar bedding structures
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cyclothems (2)
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Boron proxies record paleosalinity variation in the North American Midcontinent Sea in response to Carboniferous glacio-eustasy
ABSTRACT A laterally discontinuous sandstone at the south end of the Tellico-Sevier syncline in Blount County, Tennessee, was mapped in 1955 by Robert Neuman and in 1965 by Neuman and Willis Nelson of the U.S. Geological Survey as a “quartzite” that they considered to be the uppermost bed of the Bays Formation (Ordovician). On the basis of new mapping and conodont biostratigraphy, lithostratigraphy, and regional K-bentonite correlations, this sandstone, a distinctive quartz arenite, is reassigned to and correlated with the Clinch Sandstone (Silurian). At the Harrison Branch section (HBRA) in Blount County, in an exposure near the confluence of Harrison Branch and the Little Tennessee River, this sandstone underlies the Devonian Chattanooga Shale, and it overlies ~43 m of gray limestones and shales that are themselves above the red clastic and minor carbonate rocks of the Bays Formation. The limestones and shales between the Bays Formation and this sandstone crop out on a wooded hillside and were apparently not observed by Neuman and Nelson during their mapping of the region. We measured the HBRA section, collected 20 samples from the limestone interval, and processed them for conodonts. These limestones contain a definitive Late Ordovician (Katian) conodont fauna that includes Drepanoistodus suberectus , Plectodina tenuis , Panderodus gracilis , and Phragmodus undatus . On the basis of this fauna, the 40+ m of limestone between the youngest red beds of unequivocal Bays Formation (below) and the quartz arenite (above) can be assigned to the Ordovician P. tenuis zone or younger, making them correlative regionally with limestones of the Trenton Group. Using these new biostratigraphic data combined with existing tephrostratigraphic relations of Ordovician K-bentonites, we identify the overlying sandstone at the HBRA section as an erosional outlier of the Silurian Clinch Sandstone, and we correlate the Ordovician-Silurian-Devonian unconformities at these two localities, which are now better constrained, with unconformities A through F in the Silurian and Devonian of this region, as identified and described in detail at several exposures north and northwest of the Tellico-Sevier syncline, most prominently at outcrops near Wytheville, Seven Mile Ford, and Max Meadows in southwest Virginia, where Devonian strata unconformably overlie Ordovician strata.
An ancient estuarine-circulation nutrient trap: The Late Pennsylvanian Midcontinent Sea of North America
Testing the early Late Ordovician cool-water hypothesis with oxygen isotopes from conodont apatite
Global-ocean redox variation during the middle-late Permian through Early Triassic based on uranium isotope and Th/U trends of marine carbonates
ASSESSING THE PALEOENVIRONMENTAL SIGNIFICANCE OF MIDDLE–LATE PENNSYLVANIAN CONODONT APATITE δ 18 O VALUES IN THE ILLINOIS BASIN
Did intense volcanism trigger the first Late Ordovician icehouse?: COMMENT
DID A VOLCANIC MEGA-ERUPTION CAUSE GLOBAL COOLING DURING THE LATE ORDOVICIAN?
Numerical models of the ocean-climate system indicate that during the early Late Ordovician, water from the higher southern latitudes flowed north toward the equator. The cold-water masses welled up into and penetrated the epicontinental sea of Laurentia. The “cold-water conditions” existed despite high levels of pCO 2 (~15× preindustrial atmospheric levels) and did not necessarily indicate the onset of glaciation during the early Late Ordovician; rather the cold-water conditions may indicate the onset of a cooling event that plunged the Ordovician Earth system toward ice-house conditions that would lead later to the end-Ordovician (Hirnantian) glaciation. Furthermore, the observed distribution of cold-water masses across the southeastern margin of Laurentia is consistent with the interpretation that a cold-water event caused a regional extinction in the Mohawkian of eastern Laurentia.