- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Africa
-
Central Africa
-
Congo (1)
-
-
East Africa
-
Zambia (1)
-
-
North Africa
-
Algeria (1)
-
Morocco (1)
-
-
Southern Africa
-
Botswana (1)
-
South Africa (1)
-
-
-
Asia
-
Central Asia
-
Kazakhstan (1)
-
-
Middle East (1)
-
Siberia (1)
-
-
Australasia
-
Australia
-
Queensland Australia
-
Century Deposit (1)
-
-
Victoria Australia
-
Bendigo Australia (2)
-
-
-
-
Canada
-
Western Canada
-
British Columbia (1)
-
-
-
Commonwealth of Independent States
-
Kazakhstan (1)
-
-
Copperbelt (1)
-
Europe
-
Western Europe
-
United Kingdom
-
Great Britain
-
Wales
-
Powys Wales (1)
-
Welsh Basin (1)
-
-
-
-
-
-
Red Dog Mine (1)
-
South America (1)
-
United States
-
Alaska
-
Brooks Range (1)
-
-
Cincinnati Arch (1)
-
Iowa (1)
-
Kentucky (1)
-
Midcontinent (2)
-
Minnesota (1)
-
Mississippi Valley
-
Upper Mississippi Valley (1)
-
-
Missouri
-
Saint Francois Mountains (1)
-
-
Nevada
-
Carlin Trend (5)
-
Elko County Nevada (1)
-
Lander County Nevada (1)
-
-
Ohio (1)
-
Wisconsin (1)
-
-
-
commodities
-
barite deposits (1)
-
brines (1)
-
metal ores
-
cobalt ores (1)
-
copper ores (4)
-
gold ores (5)
-
iron ores (1)
-
lead ores (5)
-
lead-zinc deposits (2)
-
polymetallic ores (1)
-
rare earth deposits (2)
-
silver ores (3)
-
zinc ores (5)
-
-
mineral deposits, genesis (10)
-
mineral exploration (1)
-
mineral resources (1)
-
phosphate deposits (2)
-
-
elements, isotopes
-
carbon
-
C-13/C-12 (8)
-
-
halogens
-
bromine (1)
-
chlorine (1)
-
-
hydrogen
-
D/H (1)
-
-
isotope ratios (10)
-
isotopes
-
radioactive isotopes
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
-
stable isotopes
-
C-13/C-12 (8)
-
D/H (1)
-
He-4/He-3 (1)
-
Ne-22/Ne-20 (1)
-
O-18/O-16 (4)
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
S-34/S-32 (3)
-
Sr-87/Sr-86 (2)
-
-
-
metals
-
alkali metals
-
potassium (1)
-
sodium (1)
-
-
alkaline earth metals
-
strontium
-
Sr-87/Sr-86 (2)
-
-
-
gold (1)
-
lead
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
-
rare earths (1)
-
titanium (1)
-
zirconium (1)
-
-
noble gases
-
helium
-
He-4/He-3 (1)
-
-
neon
-
Ne-22/Ne-20 (1)
-
-
-
oxygen
-
O-18/O-16 (4)
-
-
sulfur
-
S-34/S-32 (3)
-
-
-
fossils
-
Chordata
-
Vertebrata (1)
-
-
Graptolithina
-
Graptoloidea (1)
-
-
Invertebrata
-
Brachiopoda (1)
-
-
microfossils
-
Chitinozoa (1)
-
Conodonta (3)
-
-
palynomorphs
-
Chitinozoa (1)
-
-
Plantae (1)
-
-
geochronology methods
-
tephrochronology (1)
-
U/Pb (1)
-
U/Th/Pb (1)
-
-
geologic age
-
Cenozoic
-
Tertiary
-
Neogene
-
Pliocene
-
upper Pliocene (1)
-
-
-
-
-
Mesozoic
-
Cretaceous (1)
-
Jurassic
-
Middle Jurassic
-
Aalenian (1)
-
Bajocian (1)
-
-
-
-
Paleozoic
-
Carboniferous
-
Mississippian (1)
-
Pennsylvanian
-
Upper Pennsylvanian (1)
-
-
-
Devonian
-
Middle Devonian (1)
-
Popovich Formation (1)
-
Upper Devonian (3)
-
-
Lisburne Group (1)
-
Ordovician
-
Middle Ordovician
-
Galena Dolomite (1)
-
Platteville Formation (1)
-
-
Upper Ordovician (1)
-
-
Permian (1)
-
Silurian
-
Lower Silurian
-
Llandovery
-
Aeronian (1)
-
Telychian (1)
-
-
Wenlock (2)
-
-
Middle Silurian
-
Roberts Mountains Formation (1)
-
-
Upper Silurian
-
Ludlow (1)
-
-
-
upper Paleozoic (1)
-
-
Precambrian
-
upper Precambrian
-
Proterozoic
-
Mesoproterozoic (2)
-
Neoproterozoic (1)
-
-
-
-
-
metamorphic rocks
-
metamorphic rocks
-
metasedimentary rocks (1)
-
-
-
minerals
-
carbonates
-
calcite (1)
-
dolomite (1)
-
-
native elements (1)
-
oxides
-
hematite (1)
-
iron oxides (1)
-
rutile (1)
-
-
phosphates
-
apatite (1)
-
-
silicates
-
framework silicates
-
silica minerals
-
quartz (3)
-
-
-
-
sulfates
-
barite (2)
-
-
sulfides
-
pyrite (4)
-
sphalerite (1)
-
-
-
Primary terms
-
absolute age (3)
-
Africa
-
Central Africa
-
Congo (1)
-
-
East Africa
-
Zambia (1)
-
-
North Africa
-
Algeria (1)
-
Morocco (1)
-
-
Southern Africa
-
Botswana (1)
-
South Africa (1)
-
-
-
Asia
-
Central Asia
-
Kazakhstan (1)
-
-
Middle East (1)
-
Siberia (1)
-
-
Australasia
-
Australia
-
Queensland Australia
-
Century Deposit (1)
-
-
Victoria Australia
-
Bendigo Australia (2)
-
-
-
-
barite deposits (1)
-
brines (1)
-
Canada
-
Western Canada
-
British Columbia (1)
-
-
-
carbon
-
C-13/C-12 (8)
-
-
Cenozoic
-
Tertiary
-
Neogene
-
Pliocene
-
upper Pliocene (1)
-
-
-
-
-
Chordata
-
Vertebrata (1)
-
-
deformation (1)
-
diagenesis (3)
-
Europe
-
Western Europe
-
United Kingdom
-
Great Britain
-
Wales
-
Powys Wales (1)
-
Welsh Basin (1)
-
-
-
-
-
-
faults (1)
-
foliation (1)
-
geochemistry (2)
-
geochronology (2)
-
geomorphology (1)
-
Graptolithina
-
Graptoloidea (1)
-
-
hydrogen
-
D/H (1)
-
-
inclusions
-
fluid inclusions (4)
-
-
intrusions (1)
-
Invertebrata
-
Brachiopoda (1)
-
-
isotopes
-
radioactive isotopes
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
-
stable isotopes
-
C-13/C-12 (8)
-
D/H (1)
-
He-4/He-3 (1)
-
Ne-22/Ne-20 (1)
-
O-18/O-16 (4)
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
S-34/S-32 (3)
-
Sr-87/Sr-86 (2)
-
-
-
Mesozoic
-
Cretaceous (1)
-
Jurassic
-
Middle Jurassic
-
Aalenian (1)
-
Bajocian (1)
-
-
-
-
metal ores
-
cobalt ores (1)
-
copper ores (4)
-
gold ores (5)
-
iron ores (1)
-
lead ores (5)
-
lead-zinc deposits (2)
-
polymetallic ores (1)
-
rare earth deposits (2)
-
silver ores (3)
-
zinc ores (5)
-
-
metals
-
alkali metals
-
potassium (1)
-
sodium (1)
-
-
alkaline earth metals
-
strontium
-
Sr-87/Sr-86 (2)
-
-
-
gold (1)
-
lead
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (1)
-
-
rare earths (1)
-
titanium (1)
-
zirconium (1)
-
-
metamorphic rocks
-
metasedimentary rocks (1)
-
-
metamorphism (1)
-
metasomatism (1)
-
mineral deposits, genesis (10)
-
mineral exploration (1)
-
mineral resources (1)
-
noble gases
-
helium
-
He-4/He-3 (1)
-
-
neon
-
Ne-22/Ne-20 (1)
-
-
-
orogeny (1)
-
oxygen
-
O-18/O-16 (4)
-
-
paleoecology (1)
-
paleogeography (1)
-
Paleozoic
-
Carboniferous
-
Mississippian (1)
-
Pennsylvanian
-
Upper Pennsylvanian (1)
-
-
-
Devonian
-
Middle Devonian (1)
-
Popovich Formation (1)
-
Upper Devonian (3)
-
-
Lisburne Group (1)
-
Ordovician
-
Middle Ordovician
-
Galena Dolomite (1)
-
Platteville Formation (1)
-
-
Upper Ordovician (1)
-
-
Permian (1)
-
Silurian
-
Lower Silurian
-
Llandovery
-
Aeronian (1)
-
Telychian (1)
-
-
Wenlock (2)
-
-
Middle Silurian
-
Roberts Mountains Formation (1)
-
-
Upper Silurian
-
Ludlow (1)
-
-
-
upper Paleozoic (1)
-
-
palynomorphs
-
Chitinozoa (1)
-
-
paragenesis (5)
-
phosphate deposits (2)
-
Plantae (1)
-
plate tectonics (1)
-
Precambrian
-
upper Precambrian
-
Proterozoic
-
Mesoproterozoic (2)
-
Neoproterozoic (1)
-
-
-
-
reefs (1)
-
sea-level changes (3)
-
sedimentary rocks
-
carbonate rocks (2)
-
chemically precipitated rocks
-
evaporites (1)
-
phosphate rocks (1)
-
-
clastic rocks
-
shale (1)
-
-
-
sedimentary structures
-
secondary structures
-
stylolites (1)
-
-
-
sedimentation (1)
-
sediments
-
clastic sediments
-
clay (1)
-
-
-
South America (1)
-
sulfur
-
S-34/S-32 (3)
-
-
tectonics (3)
-
United States
-
Alaska
-
Brooks Range (1)
-
-
Cincinnati Arch (1)
-
Iowa (1)
-
Kentucky (1)
-
Midcontinent (2)
-
Minnesota (1)
-
Mississippi Valley
-
Upper Mississippi Valley (1)
-
-
Missouri
-
Saint Francois Mountains (1)
-
-
Nevada
-
Carlin Trend (5)
-
Elko County Nevada (1)
-
Lander County Nevada (1)
-
-
Ohio (1)
-
Wisconsin (1)
-
-
-
sedimentary rocks
-
sedimentary rocks
-
carbonate rocks (2)
-
chemically precipitated rocks
-
evaporites (1)
-
phosphate rocks (1)
-
-
clastic rocks
-
shale (1)
-
-
-
-
sedimentary structures
-
sedimentary structures
-
secondary structures
-
stylolites (1)
-
-
-
-
sediments
-
sediments
-
clastic sediments
-
clay (1)
-
-
-
ABSTRACT Pinnacle reef tracts are geomorphic features of carbonate systems that originated in the early Silurian and display an episodic distribution into the Cenozoic. Detailed study of Silurian pinnacle reefs of the United States midcontinent demonstrates repeated motifs, but most enigmatic is the coincidence of carbonate carbon isotope (δ 13 C carb ) excursions and reef pulses. Silurian δ 13 C carb excursions were associated with environmental changes and extinctions, and reefs appear to mark a resurgence of conditions favorable to biomineralizers following those extinction events. Previous workers in the region identified six discrete reef origination events in the United States midcontinent during the Silurian. Our reevaluation of outcrops and cores, conodont collections, and the generation of considerable new chemostratigraphic data across the region are clarifying the age relations of these events and their relationships to perturbations of the global carbon cycle.
Abstract Times of metal-rich brine discharge into ancient ocean basins, associated with the formation of sedimentary-exhalative (sedex) Zn-Pb-Ba ore deposits, coincided with short-duration positive excursions (“spikes”) in the global marine Sr isotope record. While these spikes are unexplained by conventional oceanic models, chronostratigraphic correlations, combined with mass balance evidence and oceanographic modeling, suggest that the flux of radiogenic Sr from sedex brines during ore formation is sufficient to explain these previously enigmatic 87 Sr/ 86 Sr spikes. We review existing 87 Sr/ 86 Sr data and present new data as verification of these global 87 Sr/ 86 Sr spikes and their correlations with the formation of giant sedex ore deposits. Major events include an 1 ×10 −4 (~0.7078–~0.7079) excursion contemporaneous with formation of the Rammelsberg deposit at ~389 Ma; spikes on the order of 1 to 3 × 10 −4 , coeval with formation of the Meggen deposit at ~381 Ma, several ore deposits in the Macmillan Pass district at ~379 to 375 Ma, and the Silvermines deposits at ~352 Ma; and two >6 × 10 −4 spikes coincident with formation of the giant Navan deposit at ~346 Ma and Red Dog deposits at ~337 Ma. Moreover, the timing of peak 87 Sr/ 86 Sr spikes correlates with global δ 13 C and δ 18 O spikes, deposition of metal-rich black shales and ironstones, metal-induced malformation (teratology) of marine organisms, and mass extinctions. The relationships among these features were poorly understood, but our new model explains how the flux of key biolimiting nutrients and metals contained in sedex brines, demonstrably equivalent to or exceeding that of the total modern riverine flux to the ocean, spurred ocean eutrophication, which, ultimately, through a series of positive feedback mechanisms, may have triggered global chemical and biological events. If, as we hypothesize, sedex hydrothermal systems are recorded in the global marine isotopic, geologic, and biological records, our findings define a new approach to the study of and exploration for sedex deposits. We demonstrate that fluid inclusion solute chemistry and isotopic and stratigraphic studies of sedex deposits, coupled with chronostratigraphic correlation and high-resolution 87 Sr/ 86 Sr isotope chemostratigraphy, can be used to answer long-standing questions about geologic processes responsible for formation of these extraordinary deposits. This approach provides evidence for the age, duration, and fluxes of fluids and metals vented into the ocean by these giant hydrothermal systems. Accordingly, the marine 87 Sr/ 86 Sr curve constitutes a global exploration tool that could be applied to assess the mineral potential of sedimentary basins. To illustrate the potential of this tool to identify favorable stratigraphic ages and basins with potential for undiscovered giant sedex deposits, we highlight several spikes, on par with those characteristic of the Red Dog and Navan deposits, which have not been correlated with known metal deposits. Given these strong temporal correlations, mass balance estimates, and results of ocean chemistry modeling, our study suggests that further work is warranted to determine the extent to which periodic venting of hydrothermal basinal brines into the ocean has influenced the evolution of marine chemistry. Ultimately, these global signatures can be applied to the study of and exploration for sedex deposits.
Abstract The Central African Copperbelt is the world’s premier sediment-hosted Cu province. It is contained in the Katangan basin, an intracratonic rift that records onset of growth at ~840 Ma and inversion at ~535 Ma. In the Copperbelt region, the basin has a crudely symmetrical form, with a central depocenter maximum containing ~11 km of strata positioned on the northern side of the border of the Democratic Republic of Congo and Zambia, and marginal condensed sequences <2 km in thickness. This fundamental extensional geometry was preserved through orogenesis, although complex configurations related to halokinesis are prevalent in central and northern parts of the basin, whereas to the south, relatively high-grade metamorphism occurred as a result of basement-involved thrusting and burial. The largest Cu ± Co ores, both stratiform and vein-controlled, are known from the periphery of the basin and transition to U-Ni-Co and Pb-Zn-Cu ores toward the depocenter maximum. Most ore types are positioned within a ~500-m halo to former near-basin-wide salt sheets or associated halokinetic structures, the exception being that located in extreme basin marginal positions, where primary salt was not deposited. Stratiform Cu ± Co ores occur at intrasalt (Congolese-type), subsalt (Zambian-type), and salt-marginal (Kamoa-type) positions. Bulk crush-leach fluid inclusion data from the first two of these deposit types reveal a principal association with residual evaporitic brines. A likely signature of the ore fluids, the brines were generated during deposition of the basin-wide salt-sheets and occupied voluminous sub and intrasalt aquifers from ~800 Ma. Associated intense Mg ± K metasomatism was restricted to these levels, indicating that capping and enclosing salt remained impermeable for prolonged periods of the basin’s history, isolating the deep-seated aquifers from the upper part of the basin fill. From ~765 to 740 Ma, the salt sheets in the Congolese part of the basin were halokinetically modified. Salt was withdrawn laterally to feed diapirs, ultimately leading to localized welding or breaching of the former hydrological seal. At these points, deeper-level residual brines were drawn into the intrasalt stratigraphy to interact with reducing elements and form the stratiform ores. It is probable that salt welding occurred diachronously across the northern and central parts of the basin, depending upon the interplay of original salt thickness, rates and volumes of sediment supply during accumulation of salt overburden, and tectonism. The variable timing of this fundamental change in hydrologic architecture is poorly constrained to the period of halokinetic onset to the earliest stages of orogenesis; however, the geometry of the ores and associated alteration patterns demands that mineralization preceded the characteristically complex fragmentation of the host strata. Thus, while an early orogenic timing is permissible, mineralization during the later stages of extensional basin development was more likely. In situ reducing elements that host Zambian-type stratiform Cu ± Co ores were in continuous hydrological communication with subsalt aquifers, such that ore formation could have commenced from the ~800 Ma brine introduction event. The nonhalokinetic character of the salt in this region allowed the intact seal to have maintained suprahydrostatic pore pressures, facilitating fluid circulation until late stages of basin growth and possibly early stage orogenesis. Leachate data from ores positioned in the depocenter maximum and southern parts of the basin that underwent relatively high grade metamorphism record mixing of residual and halite dissolution-related brines. Salt dissolution was likely triggered by emergence of diapirs or thermally and/or mechanically induced increased permeability of halite. While it is certain that halite dissolution occurred during and after orogenesis, conditions favorable for salt dissolution may have existed locally during extension in the depocenter maximum. The permeability of salt increased to a point where it became the principal aquifer. The salt’s properties as an aquiclude lost, originally deep-seated residual brine mixed with new phases of evaporite dissolution-related brine to produce ores at middle levels of the basin fill. During the final stages of ore formation, recorded by postorogenic Pb-Zn-Cu mineralization in the depocenter maximum, the salinity of fluids was dominantly derived from the dissolution of remnant bodies of salt.
Regional- to Deposit-Scale Geologic Controls on Copper-Silver Mineralization in the Kalahari Copperbelt, Botswana
Abstract The Kalahari Copperbelt in northwestern Botswana is characterized by structurally controlled, stratabound, mineralogically zoned copper-silver deposits hosted along a major redox boundary within a late Mesoproterozoic rift succession. Copper-silver mineralized rocks occur on the limbs and in the hinge positions of regional-scale folds that characterize the Pan-African Ghanzi-Chobe zone fold-and-thrust belt. Regional facies changes along the base of the transgressive marine D’Kar Formation, the host to the majority of mineralized rocks, delineate a series of synsedimentary basin highs and lows. The facies changes were identified through both lithostratigraphic analysis of drill holes and along-strike variations in magnetic lithostratigraphy, a technique that correlates the magnetic fabrics of second vertical derivative aeromagnetic maps with changes in lithostratigraphy. Basin highs controlled the development and distribution of favorable lithostratigraphic and lithogeochemical trap sites for later sulfide precipitation. Major facies changes across the Ghanzi Ridge area straddle a significant crustal structure identified in gravity datasets that appears to have influenced extensional activity during basin development. During basin inversion, the basin highs, cored by rheologically stronger bimodal volcanic rocks, localized strain within mechanically weaker rock types of the Ghanzi Group metasedimentary rocks, leading to the development of locally significant permeability and the formation of structural trap sites for mineralization by hot (250°–300°C), oxidizing, metalliferous Na-Ca-Cl brines. Structural permeability was maintained within trap sites due to silicification and/or feldspar alteration during progressive deformation and associated hydrothermal mineralizing events.
Sequence boundaries and chronostratigraphic gaps in the Llandovery of Ohio and Kentucky: The record of early Silurian paleoceanographic events in east-central North America
Mineral Thermometry and Fluid Inclusion Studies of the Pea Ridge Iron Oxide-Apatite–Rare Earth Element Deposit, Mesoproterozoic St. Francois Mountains Terrane, Southeast Missouri, USA
Abstract Each year an estimated 56,000 metric tons (t) of rare earth elements (REEs), including 23,000 t of heavy REEs (HREEs), are mined, beneficiated, and put into solution, but not recovered, by operations associated with the global phosphate fertilizer industry. Importantly, the REEs in sedimentary phosphorites are nearly 100% extractable, using technologies currently employed to meet global phosphate fertilizer needs. Our evaluation suggests that by-product REE production from these phosphate mines could meet global REE requirements. For example, the calculated REE flux accompanying phosphate production in the United States is approximately 40% of the world’s total and, alone, could supply 65% of global HREEs needs. Moreover, recognition that the tonnages and HREE concentrations of some unmined phosphorite deposits dwarf the world’s richest REE deposits suggests that these deposits might constitute stand-alone REE deposits. The hypothesized genesis of these REE-rich occurrences strongly supports the long-debated suggestion that oceanic REE contents vary in a secular fashion and that associated high-grade REE abundances reflect oceanic redox state transitions during specific time periods. Here, we use this new process-based model, based on observed variations in global-secular REE abundances, to identify phosphorite horizons deposited during periods favorable for highgrade REE accumulation.
Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales
Constraints from Fluid Inclusion Compositions on the Origin of Mississippi Valley-Type Mineralization in the Illinois-Kentucky District
Genesis of the Touissit-Bou Beker Mississippi Valley-Type District (Morocco-Algeria) and Its Relationship to the Africa-Europe Collision
Distal signatures of Late Ordovician oceanic anoxia—New data from a classic epeiric ramp transect
ABSTRACT New data and review of classic sections from the Middle and Upper Ordovician North American Midcontinent in the Upper Mississippi Valley provide a refined picture of the age, stable isotope geochemistry, faunal composition, and—ultimately—origin of this epeiric ramp succession. Sequence stratigraphic analysis reveals a series of unconformity-bounded, genetically related facies packages. Shallowing and deepening trends are sometimes difficult to resolve due to a paucity of hydrodynamic indicators, yet unconformity surfaces are well marked by hardgrounds and confirmed by negative C-isotope spikes. Recent conodont biostratigraphy, new U-Pb radioisotopic ages for K-bentonites, and correlation of C-isotope profiles to global trends suggest that the succession spans the Darriwilian to Hirnantian epochs. Focus on Platteville to lower Galena Group strata (Sandbian to early Katian) provides a temporally high-resolution look at the onset and evolution of a long-term (>2 m.y.) positive carbon-isotope excursion, short-term perturbations in that record, and relationship to the preservation and diversity of the enclosed fauna and strata. Major changes in authigenic mineral suites and organic carbon content throughout the Upper Ordovician Upper Mississippi Valley suggest at least three major redox cycles. The combined evidence for globally recognized, positive carbon-isotope excursions coincident with these redox cycles, as well as high-frequency, sea-level fluctuations and successive faunal turnover events, suggests far-field responses to multiple global oceanic anoxic events.