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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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Popigay Structure (1)
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Atlantic Ocean
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North Atlantic (1)
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Canada
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Eastern Canada
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Ontario (1)
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Chesapeake Bay impact structure (1)
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Commonwealth of Independent States
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Russian Federation
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Popigay Structure (1)
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Southern Ocean
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Weddell Sea (1)
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United States
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Virginia (1)
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elements, isotopes
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isotope ratios (2)
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isotopes
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stable isotopes
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Os-188/Os-187 (2)
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metals
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platinum group
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osmium
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Os-188/Os-187 (2)
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geologic age
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Cenozoic
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Tertiary
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Paleogene
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Eocene
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upper Eocene (1)
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Mesozoic
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Cretaceous
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Lower Cretaceous
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Valanginian (1)
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igneous rocks
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igneous rocks
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volcanic rocks
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basalts (1)
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metamorphic rocks
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metamorphic rocks
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impactites
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impact breccia (1)
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meteorites
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meteorites
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stony meteorites
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achondrites (1)
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chondrites
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ordinary chondrites (1)
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Primary terms
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Asia
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Popigay Structure (1)
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asteroids (1)
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Atlantic Ocean
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North Atlantic (1)
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Canada
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Eastern Canada
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Ontario (1)
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-
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Cenozoic
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Tertiary
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Paleogene
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Eocene
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upper Eocene (1)
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-
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Deep Sea Drilling Project
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IPOD
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DSDP Site 603 (1)
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-
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igneous rocks
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volcanic rocks
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basalts (1)
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-
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isotopes
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stable isotopes
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Os-188/Os-187 (2)
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-
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Mesozoic
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Cretaceous
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Lower Cretaceous
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Valanginian (1)
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-
-
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metals
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platinum group
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osmium
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Os-188/Os-187 (2)
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-
-
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metamorphic rocks
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impactites
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impact breccia (1)
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-
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meteorites
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stony meteorites
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achondrites (1)
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chondrites
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ordinary chondrites (1)
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-
-
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Ocean Drilling Program
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Leg 113
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ODP Site 692 (1)
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-
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Southern Ocean
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Weddell Sea (1)
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United States
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Virginia (1)
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Valanginian climate cooling and environmental change driven by Paraná-Etendeka basalt erosion
Fifteen impactites from various intervals within the Eyreville cores of the Chesapeake Bay impact structure were sampled to measure siderophile element concentrations. The sampled intervals include basement-derived rocks with veins, polymict impact breccias and associated rocks, and crater-fill sediments. The platinum group element (PGE) concentrations obtained are generally low (e.g., iridium concentrations less than 0.1 ng/g) and are fractionated relative to chondrites. There is no clear distinction in concentration between the different impactite units. So far in the Chesapeake Bay material, only the impact melt rocks from the 823-m-deep Cape Charles test hole, drilled over the central uplift of the structure, have generated a bulk chondritic signature of 0.01–0.1 wt% meteoritic contribution based on a mixing model of 187 Os/ 188 Os isotopic ratios and Os concentrations. However, none of the samples studied shows PGE abundances that enable identification of the type of projectile responsible for the formation of the structure. Hence, it is at present not possible to link the Chesapeake Bay impact to the proposed ordinary chondrite falls by projectiles recorded for other late Eocene craters, namely the 100-km-diameter Popigai impact structure in Siberia and 7.5-km-diameter Wanapitei structure in Canada. The absence of a clear projectile signature hinders further discussions on the existence and the nature of the late Eocene shower event (asteroid versus comet).