Evidence for synsedimentary coseismic hydraulic fracturing in the Middle Devonian Cedar Valley Group, Plum River Fault Zone of Iowa
- Univ. of Iowa, Iowa City, IA (United States)
Correspondence between the Plum River Fault Zone and stratigraphic asymmetry the Middle Devonian Wapsipinicon and Cedar Valley groups in eastern Iowa have long been considered to record probable paleotectonism. Mesoscopic evidence for Devonian paleotectonism is exposed in strata of the Rapid Mbr of the Little Cedar Fm (Givetian) at the Silver Creek Graben, a 150 m-wide fault block within the Plum River Fault zone in southern Jackson county, Iowa. Little Cedar limestones are cut by multiple generations of brittle microstructures including compound sediment/spar-filled veins, tectonic stylolites that cut bedding at high angles, and late calcite veins coupled with stylolites. Internal sediments filling compound veins are preserved as unfossiliferous early gray and late olive-colored inclusion-rich microspars, both with mottled luminescence. Inclusions in the microspars consist of detrital illite and diagenetic microdolomite. Spars enclosing the internal sediments have a constructional oscillatory luminescent-nonluminescent zonation. Internal sediments in compound veins at Silver Creek Graben apparently were drawn downward through 15--30 m of overlying Cedar Valley carbonates to fill dilational fractures opened by coseismic hydraulic fracturing during the late Givetian erosional episode that followed deposition of the Coralville Fm. Preliminary sampling of cements and gray microspars from compound veins have [delta][sup 18]O values ranging from [minus]6 to [minus]5 [per thousand] and [delta][sup 13]C values ranging from [minus]6.5 to [minus]3 [per thousand]. These components are interpreted to record diagenesis in a meteoric phreatic environment.
- OSTI ID:
- 7069795
- Report Number(s):
- CONF-9303210-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:3; Conference: 27. annual Geological Society of America (GSA) North-Central Section meeting, Rolla, MO (United States), 29-30 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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