STEM/AEM evidence for preservation of burial diagenetic fabrics in Devonian shales: Implications for fluid/rock interaction in cratonic basins (U.S.A.)
- Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Geological Sciences
Fabrics, microstructures, and compositions of authigenic illite-rich clays in Devonian intracratonic basin shales were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning transmission electron/analytical electron microscopy (STEM/AEM) methods in order to relate the extent of clay diagenesis to the timing of mudstone-system closure and to reconcile conflicting radiogenic and paleomagnetic ages obtained from these shales and associated limestones and bentonites. Authigenic illite in these Devonian shales is similar to post-transition illite-rich mixed-layer illite/smectite (I/S) in Gulf Coast and other young basin mudstones that have formed through replacement of detrital smectite or smectite-rich I/S without subsequent diagenetic modification. Preservation of burial diagenetic, authigenic, mixed-layer I/S microstructures in these Devonian shales implies that they have remained effectively closed systems following the smectite-to-illite transformation. Later Alleghenian (ca. 300 Ma) tectonic or fluid-flow events recorded by authigenic minerals in bentonites and carbonate lithologies throughout the US. Midcontinent are apparently not recorded in these Devonian shales. Preservation of diagenetic fabrics indicates that radiogenic isotope dating of cratonic basin shales should yield syndepositional to early burial diagenetic ages corresponding to the timing of I/S authigenesis.
- OSTI ID:
- 277598
- Journal Information:
- Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, Vol. 66, Issue 3; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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