Stable isotopic chemostratigraphy of the Middle Devonian Cedar Valley Group: Initial data from the uppermost Givetian Lithograph City Formation
Conference
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· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:6949788
- Univ. of Iowa, Iowa City, IA (United States). Dept of Geology
- Iowa Dept of Natural Resources, Iowa City, IA (United States). Geological Survey Bureau
- Illinois State Univ., Normal, IL (United States). Dept. of Geography-Geology
Nonluminescent brachiopods (Hadrorhynchia solon) from pelletal wackestones/packstones of the State Quarry Member of the Lithograph City Formation (norrisi Zone; Metzger, 1993, GSA Abst. w/Prog., 25(6):53) yield a marine calcite value of [delta][sup 18]O = [minus]5.5 [per thousand] and [delta][sup 13]C = 1.5 [per thousand]. This value represents a 1.5 per mil decrease in marine calcite [delta][sup 18]O in relation to the underlying coralville Formation, limiting the range of a Givetian (380--374 Ma) secular increase in marine [delta][sup 18]O from [minus]6.5 [per thousand] to [minus]4.0 [per thousand] that had been detected in the two underlying formations of the Cedar Valley Group of eastern Iowa. Earlier studies of carbonate diagenesis in the Cedar Valley Group have shown that the shallowing-upward depositional history of successive T-R formations is encoded in the carbon and oxygen isotopic compositions of all rock components. Specifically, episodes of subaerial exposure and consequent meteoric diagenesis resulted in pervasive diagenetic overprinting of the upper portions of each T-R cycle. For example, in the Coralville Formation, nonluminescent brachiopods in the upper part of the formation are depleted by up to 3.5 per mil in [delta][sup 18]O and 4.5 per mil in [delta][sup 13]C relative to their counterparts at the base. Accordingly, the basal portions of the T-R formations, which were chemically stabilized in rock-dominated diagenetic systems, best preserve the original marine compositions of Cedar Valley Group carbonates. A meteoric calcite line of [delta][sup 18]O = 7.0 [per thousand] is suggested from preliminary data on calcite cements from the Lithograph City Formation.
- OSTI ID:
- 6949788
- Report Number(s):
- CONF-9404217--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 26:5
- Country of Publication:
- United States
- Language:
- English
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Conference
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Sun Feb 28 23:00:00 EST 1993
· Geological Society of America, Abstracts with Programs; (United States)
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Conference
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Sun Feb 28 23:00:00 EST 1993
· Geological Society of America, Abstracts with Programs; (United States)
·
OSTI ID:7069795
Revised lithostratigraphy and biostratigraphy of the Middle-Upper Devonian strata of central Missouri, southern part of Iowa basin
Conference
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Sun Feb 28 23:00:00 EST 1993
· Geological Society of America, Abstracts with Programs; (United States)
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OSTI ID:5018702